From food waste to functional component: Cashew apple pomace

Abstract

Globally, large numbers of people suffer from undernourishment and food insecurity, while a third of food produced is lost or wasted. The widely cultivated cashew nut produces large quantities of waste in early processing. It grows on an edible peduncle called the cashew apple which contains many essential nutrients. An estimated 36.9 million tons of cashew apples are produced annually, but only small amounts are used to make juice. The remainder is considered production waste. This review presents the potential of cashew apple pomace as a food ingredient and examines the effects of incorporation on chemical composition, physical properties and sensory evaluation. Inclusion in optimized amounts into food products is a strategy proven to produce palatable results with high acceptability. Transforming this manufacturing by-product into a functional food component will have economic benefits, improve resource-utilization, promote sustainability and potentially increase the nutritional value of foods.

Keywords:

• by-products
• circular economy
• functional food
• sustainability
• upcycling
• valorization

Introduction

To feed the world, the food industry faces a global challenge of creating a system that has a lower impact on the environment, while still feeding the growing population. Successfully meeting this challenge will assure a sustainable food future. If solutions are not found, there will be disastrous results regarding food security, the climate, and humanity (Flanagan, Robertson, and Hanson 2019). Currently, 1 in 9 people in the world suffer from undernourishment, and 2 billion have micronutrient deficiencies (Yadav and Maurya 2022). Innovation and planning are needed, as the population is expected to rise, requiring more than a 50% increase in food production in order to feed close to 10 billion people in 2050 (Searchinger et al. 2019).

Part of the answer may lie in reducing food waste. It is estimated that 1/3 of all food produced is lost or wasted. Thirty percent of this happens at the production stage, with fruit and vegetables having the highest losses (Moshtaghian, Bolton, and Rousta 2021). Though there are several definitions of food loss and waste, commonly it is considered “food that is intended for human consumption but that leaves the food supply chain somewhere between being ready for harvest or slaughter and being consumed” (Flanagan, Robertson, and Hanson 2019). Some definitions include what is termed inedible parts, like pits and bones, recognizing that what is considered inedible by some, is regarded as food by others. This can also be influenced by technology and availability (Okayama, Watanabe, and Yamakawa 2021).

The common cashew (Anacardium occidentale) is the third most produced edible nut in the world and is a major cash crop (Kolliesuah et al. 2020). In 2020 4.1 million tons of cashew nuts were produced in 38 countries around the world, mostly in developing areas (FAO STAT 2021a). Currently, leading producers include Côte d’Ivoire, India, Vietnam, Burundi and the Philippines (Apeda Agrixchange 2020).

The edible portion is divided into two parts: the cashew nut (the kernel and the true fruit), and the cashew apple (CA), an enlarged peduncle, also called a pseudo fruit (Figure 1). The cashew apple makes up approximately 90% of the weight of the cashew fruit (Akyereko et al. 2022), translating into production of around 36.9 million tons of cashew apples. This pseudo fruit is greatly underutilized, in most cases considered a waste product (Tamiello-Rosa et al. 2019). Only 1.3 million tons is being used in commercial production (FAO STAT 2021b) which translates into a mere 3.5% of the available product. When consumed, the peduncle is largely used for juice/beverage production, as has been observed in Brazil (Pinho et al. 2011).

Figure 1. Cashew nut inside shell (A) and Cashew Apple (B) (Sucupira et al. 2020- reprinted with permission).

Cashew apple (CA) is known to have a unique nutritional profile with a vitamin C content up to six times higher than orange juice, as well as other phytochemicals (primarily carotenoids, flavonoids, anacardic acid and tannins), vitamins, minerals and dietary fibers (Das and Arora 2017). The nutrient composition underscores the potential to be developed as a functional food, adding economic value and reducing waste (Prakoso and Mubarok 2021). To meet the definition of a functional food, regular consumption of the cashew apple, or products made from CA, must be part of a diverse diet at efficacious levels. Additionally, positive effects on health beyond basic nutrition must be established (Granato et al. 2020). Several studies indicate that cashew apple products and extracts impact the microbiome (Menezes et al. 2021), improve metabolic parameters (Carvalho et al. 2019; Dionísio et al. 2015; e Silva et al. 2020) and provide gastro-protective effects (da Silva et al. 2021). Despite promising data from animal studies and small clinical trials, currently, there is insufficient evidence to categorize CA or CA products as a functional ingredient for humans.

Some field studies have reported that farmers eat cashew apples in the orchards, as a hunger and thirst quencher, but this is limited to consumption during farming activities (Dimoso, Makule, and Kassim 2020). Clearly, CA is suitable for eating, but only a negligible portion is utilized in this manner, leaving the majority of the apples to rot (Lawal et al. 2011). Wasting of this potential food source is attributed to numerous factors such as inadequate knowledge (Nwosu, Adejumo, and Udoha 2016) accompanied by lack of processing skills and post-harvest technology (Dimoso et al. 2021). High perishability, astringent properties and the seasonal availability further reduce use of this product (Prakoso and Mubarok 2021). To overcome these challenges, chemical, physical and/or biological processing can be done (Reina et al. 2022). Several methods have been applied to preserve the product and reduce astringency, like steaming, use of clarifying agents and microfiltration (Das and Arora 2017). Drying is also a good way to increase shelf-life and is convenient for storage and transport. Dehydration has the potential of being carried out on a small scale locally, or at industrial levels (Dimoso, Makule, and Kassim 2020; Lima et al. 2014).

A minor amount of CA is processed into juice, and from the juice extraction, up to 20% pomace/bagasse/pulp/residual fibers are left. In some cases, this by-product is used as animal feed, but is often discarded and handled as garbage, having a negative environmental impact (Esparza et al. 2020; Sucupira et al. 2020). Limited shelf-life and lack of information regarding alternative usage has led to significant food waste (Guedes-Oliveira et al. 2016).

One can argue that if food is used for animals or to enrich the soil it should not be considered a loss or waste. However, this represents a reduced food supply, which means that more food needs to be grown, demanding additional resources. Food loss and waste calculated as a country, would be the third biggest greenhouse gas emitter in the world. The size of the agricultural area required to grow the food that is wasted would be the size of China (Flanagan, Robertson, and Hanson 2019). The inefficient use of produce has an estimated cost of $1 trillion per year (Searchinger et al. 2019). Increasing focus has been placed on preventing food waste, which can play a critical role in reaching the sustainable development goals set by the United Nations (United Nations 2022). This includes responsible consumption and reducing food loss (Jacob-John et al. 2021). A Food Waste Hierarchy was developed by the European Union that illustrates the most preferred to the least preferred solutions for solving the challenge of food waste (EUR-Lex 2018). "Source prevention" is considered the best way to reduce waste. The next best method is to engage in "Food recovery" which focuses on redistribution via food banks and similar networks. This is followed by "Repurposing", incorporating “waste” into other products. There is a wide range of studies looking at the utilization of fruit- and vegetable by-products in food production (Gómez and Martinez 2018; Quiles et al. 2018; Santos, da Silva, and Pintado 2022), this includes repurposing of pomace/peel etc. into a flour that can be incorporated into other food products. This is seen as a promising technology, as it can be used in numerous applications, increase the economic value of the material, promote sustainability, and be used as a functional food ingredient (Amaral et al. 2021). However, the inclusion of these new ingredients can alter the properties of the product, biochemically, and technologically with impact on organoleptic properties. Therefore, studies are needed to assess each material, and evaluate new product acceptability (Muniz et al. 2020).

To the best of our knowledge, there is no review article that summarizes the findings of the utilization of cashew apple pomace as a food ingredient. Given the large amount of material that is produced, and for economic, environmental and ethical reasons, this review aims to evaluate cashew apple pomace (CAP) as a potential functional food ingredient. It will discuss how the incorporation of cashew apple pomace influences the chemical, physical and sensorial evaluation of food products.

Studies were identified by searching the electronic databases PubMed and Google Scholar and scanning reference lists of included articles. The key words used were: “cashew apple pomace”, “cashew apple bagasse”, “cashew apple fiber”, “cashew apple fibers”, “cashew pomace”, “cashew fiber”, “cashew apple powder”, and additionally “cashew apple” in PubMed. No limits to study design or time were imposed. Studies had to be conducted on the cashew apple from Anacardium occidentale L. (the common, commercial cashew tree), use cashew apple pomace as a food ingredient, and include a sensory analysis. Studies that utilized extracts made from the CAP, or including other complex biotechnological methods, making implementation more difficult in a low-resource setting, were excluded.

The search across databases generated a total of 1958 studies, out of which 26 studies met the specified inclusion criteria (Figure 2).

Figure 2. Review flow chart

Cashew apple composition

In order to valorize the cashew apple, the chemical composition should first be established (Kouassi et al. 2018). Numerous analyses in different laboratories have been carried out and the overall composition of 100 grams of the whole cashew apple (CA), the pomace (CAP) and dried powder are presented with citations in Table 1. As with most fruits, the whole cashew apple is predominately water (81.3–85%), with approximately 1% protein, negligible amounts of lipid (<0.7%), and between 8.4 and 10.6 g/100 g of sugar. Fiber content was measured to be 3.6%, with ash at 1%. The pH was between 3.8 and 5.1, with significant amounts of ascorbic acid (101.6–330 mg/100 g) but only small quantities of Vitamin A and carotenoids. The fruit is a rich source of phenolic compounds (815.3 mg GAE/100 g) and tannins (376.4-1387.8 mg/100 g), and with different amounts of minerals. As expected, analyses of the wet CAP that remained following juice extraction reflected reduced moisture content (67–78.8%) with higher concentrations of most other components. Protein content was increased (1.8%–4.9%) along with total carbohydrates (13.9–19%) and a significant amount of dietary fiber (11.8–12.5 g). Converting the CAP to a dry powder (CAPP) lowered moisture to 3.5–9.3% with marked increases in all macronutrients, most notably carbohydrates. The powder was made up of 44.5–77.5% carbohydrates including reports of 35–79% dietary fiber. Ascorbic Acid ranged from ∼ 6 to 900 mg and phenolic composition, including tannins, remained high during the drying process.

Table 1. Overview of the chemical composition of whole cashew apple and wet and dried apple pomace.

	Whole cashew apple	Cashew apple pomace (wet)	Cashew apple pomace powder (dry)	References
Moisture (%)	81.3-85	67-78.8	3.5-9.3	(Dimoso, Makule, and Kassim 2020; Guedes-Oliveira et al. 2016; Matias et al. 2005; Patra, Abdullah, and Pradhan 2021; Santos, et al. 2007)
Protein (%)	0.7-1.1	1.8-4.9	3.3-13.8	(Lima et al. 2017; Maciel 2022; Matias et al. 2005; Ogunjobi and Ogunwolu 2010; Santos, et al. 2007; Singh et al. 2019)
Lipids (%)	0.66	0.24-0.70	0.86-4.85	(Amaral et al. 2021; Lima et al. 2017; Ogunjobi and Ogunwolu 2010; Portela 2022; Singh et al. 2019)
Carbohydrates (%)		13.9-19	44.5-77.5	(Akubor, Egbekun, and Obiegbuna 2014; de Medeiros et al. 2019; Lima et al. 2017; Nurerk and Junden 2021)
Total sugars (g/100 g)	8.4-10.6	2.5-7.7	2.2-30.6	(Guedes-Oliveira et al. 2016; Matias et al. 2005; Portela 2022; Santos, et al. 2007; Singh et al. 2019; Uchoa et al. 2009)
Reducing sugars (mg/100 g)			13.3-36	(Adegunwa et al. 2020; Matias et al. 2005)
Total dietary fiber (g/100 g)	3.6	11.8-12.5	35-79	(Batista et al. 2018; Guedes-Oliveira et al. 2016; Maciel 2022; Nurerk and Junden 2021; Portela 2022; Singh et al. 2019)
Insoluble dietary fiber (%)		0.96-12.4	27-39	(Batista et al. 2018; Muniz et al. 2020; Nurerk and Junden 2021; Portela 2022)
Soluble dietary fiber (%)		0.04-0.09	7.4-8	(de Medeiros et al. 2019; Duarte et al. 2017; Maciel 2022; Nurerk and Junden 2021; Portela 2022)
Ash (%)	1.08	0.17-2	0.7-2.7	(Guedes-Oliveira et al. 2016; Lima et al. 2017; Nurerk and Junden 2021; Ogunjobi and Ogunwolu 2010; Singh et al. 2019)
pH	3.8-5.1	4-4.3	3.4-4.7	(de Araújo et al. 2021; Dimoso, Makule, and Kassim 2020; Matias et al. 2005; Msoka et al. 2017; Ogunjobi and Ogunwolu 2010; Patra, Abdullah, and Pradhan 2021)
Ascorbic acid (mg/100 g)	101.6-330		6.61-901.2	(Msoka et al. 2017; Portela 2022; Prakoso and Mubarok 2021; Sucupira et al. 2020)
Vitamin A (IU)	10.8			(Santos, et al. 2007)
Carotenoids (µg/100 g)	7.8-12.7		1.7-5.3	(Msoka et al. 2017; Reina et al. 2022)
	Whole cashew apple	Cashew apple pomace (wet)	Cashew apple pomace powder (dry)	References
Total phenolics (mg GAE/100 g)	815.3		49.8-1037.6	(de Medeiros et al. 2019; Dimoso, Makule, and Kassim 2020; Sucupira et al. 2020)
Tannins (mg/100 g)	376.4-1387.8		299	(Msoka et al. 2017; Reina et al. 2022; de Medeiros et al. 2019; Dimoso, Makule, and Kassim 2020; Sucupira et al. 2020)
Calcium (mg/g)	1.45-10.23	0.99	7.4-26.1	(de Medeiros et al. 2019; Msoka et al. 2017; Patra, Abdullah, and Pradhan 2021; Preethi et al. 2021; Santos, et al. 2007) (Msoka et al. 2017; Reina et al. 2022;
Iron (mg/g)	0.0035-0.0041	0.31	0.7-18	de Medeiros et al. 2019; Msoka et al. 2017; Patra, Abdullah, and Pradhan 2021; Preethi et al. 2021; Santos, et al. 2007)
Zinc (mg/g)		0.07	0.1-9.9	(de Medeiros et al. 2019; Patra, Abdullah, and Pradhan 2021; Reina et al. 2022)
Potassium (mg/g)	0.0708	1.450.07	15.6-83.5	(de Medeiros et al. 2019; Msoka et al. 2017; Patra, Abdullah, and Pradhan 2021; Preethi et al. 2021)
Phosphorus (mg/g)	0.6-3.30	1.45	2.7-15.3	(de Medeiros et al. 2019; Msoka et al. 2017; Preethi et al. 2021; Santos, et al. 2007)
Magnesium (mg/g)	0.0348		2.5-4.5	(de Medeiros et al. 2019; Msoka et al. 2017; Preethi et al. 2021)
Sodium (mg/g)		0.54		(Patra, Abdullah, and Pradhan 2021)
Copper (mg/g)			0.3-42	(de Medeiros et al. 2019; Preethi et al. 2021)
Titratable acidity (%)	0.2-0.4	1.7	1.5-2.7	(Amaral et al. 2021; Matias et al. 2005; Msoka et al. 2017; Patra, Abdullah, and Pradhan 2021; Singh et al. 2019)

The high moisture content of the whole apple allows for juice extraction and as seen in the composition data; the cashew apple pomace produced following juice extraction is a good source of bioactive compounds (Sucupira et al. 2020). Variability in composition results from location of cultivation, variety of CA, soil content, method used for analysis etc. (Reina et al. 2022). The techniques used in processing also influence the content. For example, in some studies, the pomace was washed and steamed before drying. In other studies, it was dried directly. This influences sugar content, pH, vitamin levels, and acidity.

One study assessed the difference between commercial CAP, from a juice factory, and “artisanal” CAP produced manually. Significant differences were found for vitamin C (20.3 mg/100 g and 901.2 mg/100 g), total phenolics (49.80 mg GAE/100 g and 97.44 mg GAE/100 g) and antioxidant activity (TAA DPPH 31.92 μM Trolox/g and 109.76 μM Trolox/g). It was stated that the freshness of the industrial pomace was uncertain. Cashew apple is known to have a high content of ascorbic acid, but as seen, the processing conditions greatly affect the content. It is well known that compounds like vitamin C, are susceptible to degradation when exposed to heat, light and oxygen (Sucupira et al. 2020). Still, when looking at the content found in most studies, where several used commercial CAP, Vitamin C content was higher than that found in lemons, mandarins, oranges and peppers (Kapur et al. 2012). This indicates that cashew apple pomace is a good source of vitamin C.

The protein content of the CAPP (up to 13.8%) was found to be higher than what is commonly reported for flours made from fruit peels (3-6%). Protein content is usually higher for seeds, but amounts are variable (e.g., mango kernel with 8% and 28.6% in papaya seed flour) (Larrosa and Otero 2021). The lipid content for CAPP varied (0.86-4.85%) but was overall relatively low and is comparable to what is normally found in fruit peel (2%).

The dietary fiber content reported in the dried CAP varied greatly (34.99-79%) but was higher than that of several other similar products such as dried peach pomace (30.7%) and apple pomace (35.5%) (Matias et al. 2005; Quiles et al. 2018). Levels of soluble dietary fiber found in CAPP (8%) were higher than those found in watermelon peel powder (3.17%) (Garcia-Amezquita et al. 2018) and lemon pomace (6.83%) (Quiles et al. 2018), but depending on the study, data was lower than for carrots (22.7%), apples (20.27%) and orange pomace (13.42%) (Santos, da Silva, and Pintado 2022).

Identified studies

Twenty-six articles were found where cashew apple pomace (CAP) was used as a food ingredient and included sensory analysis. An overview of the studies is presented in Table 2. Ten were published between 2020 and 2022, showing the increasing interest in these products. The studies were from Brazil (n = 18), Nigeria (n = 5), India (n = 2) and Thailand (n = 1). The large number of studies from Brazil is not surprising, as it is one of the few countries that utilizes cashew apple for juice production, leaving the pomace as a waste material (Santos, et al. 2007).

Table 2. Overview of studies that utilize wet cashew apple pomace (CAP) or dried powder (CAPP) as a food ingredient.

BURGERS AND MEAT SUBSTITUTES
Food product	Process	Amount of CAP or CAPP	Sensory test	Biochemical/functional results	Sensory results	Reference
Cashew burger	Apples homogenized and sieved to obtain CAP	CAP added at 89%, compared to 4 commercial burgers (beef, soy, vegetable and vegetable with chicken flavor	50 untrained judges. 9-point hedonic scale	Protein (5.75%) and fat content of cashew burger (7.9%) was lower than ¾ of commercial burgers. Moisture (49.47%), ash (2.89%) and pH (4.75) lower than all controls. Carbohydrates higher than all controls	Sensory score for CAP burger (5.9) lower than commercial products (6.5)	(Lima 2008) Brazil
Hamburger	Apples depulped, ground, residue washed, sanitized, dried and milled	CAPP substituting meat at 0, 7.13, 10.7 and 14.37%	60 high school students. 9-point hedonic scale. 5-point purchase intention scale	Increasing CAPP increased total carbohydrates, and dietary fiber. Moisture, pH, lipids, protein, ash and calories decreased As CAPP increased yield increased (from 70.23% to 75.73% with 7.13% CAPP, and less shrinkage (from 23.65% to 14.42%) Increasing shear force (from 3.88 kgf to 4.43 kgf), then decreasing for highest amount of CAPP (3.36 kgf)	Decreasing scores with increasing CAPP. Flavor with 10.7% not significantly different from control. Global impression control scale: 6.3 for control and 5.2 for 7.13% CAPP	(Pinho et al. 2011) Brazil
Hamburger	Apples, washed, sanitized, blended, sieved, fibers pressed	CAP added at 20, 30 and 50% of total ingredients, commercial hamburger as control	Pre-test with 10 trained panelists. Tested with 48 untrained panelists. 9-point hedonic scale.	As CAP increased, moisture content, ash, carbohydrates and vitamin C increased. Lipids decreased. Calcium, copper, magnesium, sodium and manganese increased with CAP Phosphorus, iron, potassium and zinc decreased with CAP	30% CAP best acceptance, close to 8. 44% found it better than commercial control	(Barros et al. 2012) Brazil
Chicken patties	Apples pulped, ground, filtered, bleached, washed, dried, milled	CAPP replaced vegetable fat at levels of 60, 70, 80 and 90% (3, 3.5, 4 and 4.5% of total ingredient content)	60 untrained judges. 9-point hedonic scale. Purchase intention with binomial scale and then 5-point scale	With 4.5% CAPP, lipids reduced from 7.62% to 4.40%. Energy value from 5.49 kcal/g to 4.95. Carbohydrates from 6.61% to 9.92% Cooking yield increased from 84.89% to 88.39%. Shear force and shortening values were not affected	Replacement of 60% of vegetable fat with washed CAPP (8) scored higher than control (7.9 points) Samples were not significantly different from each other, with substitution up to 90% was accepted (7.9 points) 78% would purchase control, and 79% would purchase 60% replacement of vegetable oil with washed CAPP	(Guedes-Oliveira et al. 2016) Brazil
Vegan burger	Commercial CAP washed and pressed 5x Other treatment: using enzymes	27% CAP of total ingredients from the two different treatments	48 judges. 9-point hedonic scale and 5-point purchase intention	Enzyme treated CAP had lower moisture (70.04%), ash (2.21%), proteins (5.77%), lipids (1.01%) and carbohydrates (20.97%), than not enzymatically treated. During storage at −18⁰C ascorbic acid, pH and adhesiveness reduced. Increased acidity, hardness and cohesiveness	Enzyme treated CAP did not differ sensorially. Sensory acceptance 7.6 and purchase intention 3.9 No changes in acceptability and purchase of intent during frozen storage	(Lima et al. 2017) Brazil
Fish burger	CA sanitized, washed, pressed	CAP added at 0, 5.88, 11.76 and 17.64% partially replacing mechanically separated fish	Pre-tested to determine formulation with 28 judges, sorting samples from most to least preferred 118 untrained judges tested 11.76% CAP compared with control by using 9-point hedonic scale and 5-point purchase intention scale.	Moisture increased from 61.83% to 63.22%. Ash from 0.15% to 0.24% and carbohydrates from 6.34% to 9.93%. Lipids decreased from 10.36% to 8.40%, and proteins from 21.32% to 18.21% pH of control (6.48) higher than with CAP (6.05) Total volatile bases (TVBN) and trimethylamine (TMA) was higher in control – indicating that the CAP helped preserve the experimental formulation. CAP “burger” had higher carotenoid and antioxidant activity.	Global impression score for control 6.93 and 7.81 with the CAP. Purchase intention for control 4.25 and 4.56 for CAP-based one	(da Silva Marques 2018) Brazil
Vegetarian burger with CAP and cowpea	Commercial CAP washed and pressed 5x	First ranking test with different proportions CAP/cowpea (60/40, 50/50, 40/60) 50/50 CAP/cowpea ratio selected	48 judges for ratio determination. 8 professionals from gastronomy in focus group 50 judges. 9-point hedonic scale and 5-point purchase intent	Compared to (Lima 2008) where burgers were made with only CAP, ash, protein and carbohydrate content increased, lipids decreased Lipids (1.19%) and energy value (113 kcal/100 g) lower than traditional meat burgers During frozen storage (-18⁰C) acidity increased and pH decreased. Burgers were microbiologically safe and shelf-stable for 6 months of frozen storage	Sensory score of 7.8. 86% of judges would buy it/would certainly buy it	(Lima et al. 2018) Brazil
Hamburger	Apples washed, sanitized and pressed	Hamburgers made with 15% CA juice or 9.5% CAP	48 untrained judges using 9-point hedonic scale and 5-point purchase of intention	No analysis done	CA juice hamburger scored 6.97 for taste; CAP scored 6.87. Texture with the CAP 6.56 and 6.35 for juice. The global impression scores similar for products with 6.85 for CA juice, and 6.81 with the CAP 66.66% would probably or certainly buy the burger with CA juice, 60.42% would buy with CAP	(de Oliveira Rosa and Lobato 2020) Brazil
Vegan burger	Commercial CAP washed and pressed 5x, then freeze-dried	5 different burgers, two commercial controls, with and without CAPP. Other burgers with 20% CAPP and pea/chickpea/lentil	Pre-test with 14 participants to decide formulation. 60-80 judges using 9-point hedonic scale and 5-point purchase intention	Protein content lower than commercial control (14.5% down to 4.4%) Lipids in commercial control 12.1%, while with CAPP + chickpea it was at 0.8% Ash decreased from 2.7% to 1.9% Carbohydrates up from 11.3% in commercial control to 26.1% in CAPP + chickpea. Caloric value reduced from 212.8 to 129.8 kcal.	Appearance scores better for CAPP containing products than commercial control (highest 6.8 with chickpea and CAPP) Global impression for commercial control and CAPP + pea/chickpea 5.9, while it was 6.1 with CAPP + lentils and 6.7 for commercial CAPP product. This product also had better texture (7.4) than commercial control without CAPP (6.2) 63.75% would probably or certainly buy the commercial CAPP burger	(Maciel 2022) Brazil
BAKED GOODS
Food product	Process	Amount of CAP or CAPP	Sensory test	Biochemical/functional results	Sensory results	Reference
Cake	Juice extracted, pressed, dried pomace, milled. Then submerged fermentation for 4 days, dried and milled	Fermented CAPP substituted 0, 10, 30, 50, 70, 90 and 100% wheat flour	10 judges. 9-point hedonic scale	Ash, protein, fiber, lipids, moisture and pH increased with the CAP that was fermented. Carbohydrate content decreased compared to unfermented CAPP. Crude fiber in control 1.5%, while 7.5% with 10% CAPP. Protein from 5.2% to 11.5%. Ash from 1.5% to 3.5%. Ether extract from 14% to 19% Water retention increased with fermented sample (from 4 ml/g in fresh CAPP to 6.9 ml/g), and color changed from broken white to deep cream Weight of cake lower for 10 and 100% CAPP. Volume lower with CAPP. Moisture loss higher, except for 50, 70 and 90% substitution	General acceptability decreased with increasing substitution levels. Control scored 7.2 and with 10% CAPP 6.7. Appearance score for control 5 and with 50% CAPP 5.9 Texture for 10% CAPP (5.7) was higher than for control (5.4)	(Aderiye, Igbedioh, and Caurie 1992) Nigeria
Cookies	Commercial CAP dried	CAPP added at 0, 5, 10 and 15% of total weight	28 untrained judges. 9-point hedonic scale	Pomace dark yellow, astringent and fibrous	Taste and odor with 10% CAPP same as control. Color and texture scores lower than for control.	(Matias et al. 2005) Brazil
Cookies	Commercial CAP washed, cut into pieces, dried and milled	CAPP substituted 0, 5, 10, 15 and 20% of wheat flour content	Tested 4 days after production. 102 untrained judges. 9-point hedonic scale	As CAPP increased, pH decreased, and total dietary fiber increased. Color darkened with the CAP addition	15% CAPP was found to be better than control. With increasing amounts, scores decreased	(Uchoa et al. 2009) Brazil
Cake	CA washed, juice extracted, pomace sliced, blanched with sodium metabisulphite, drained, dried and milled	Mixture of CAPP (30%) and SBF (70%) substituted for 5, 10, 15, 20, 25 and 30% of WF	20 trained panelists. 5-point hedonic scale	Compared to WF, CAPP had higher ash and fiber content, and lower protein and fat content CAPP had lower bulk density, least gelation concentration, emulsion capacity, emulsion and foam stability than WF. Higher WAI, OAI and foaming capacity With substitution of WF, diameter and width stayed the same, but weight and height decreased with increasing amounts of CAPP/SBF blend	No difference on overall acceptability with 0, 5 and 10% substitution (4.5). Color and texture scores decreased, while flavor increased. Higher levels of substitution showed decreasing scores	(Akubor, Egbekun, and Obiegbuna 2014) Nigeria
Chocolate and cake	Apples cleaned, in salt solution, washed, in potassium metabisulphite, washed, sliced, blanched, drained, dried, milled	Different formulations tested with varying amounts of butter, ghee, sugar and maida.	10 judges. 5-point hedonic scale	18% CAPP in CA chocolate and 6,1% in CA cake showed good acceptance The chocolate had vitamin C content of 58 mg/100 g, and 0,42% tannins. Microbiologically stable storage for 6 months The cake could be stored for 1 month without microbial spoilage	The CA chocolate received score of 3.21. The CA cake got a sensory score of 4.80	(Sobhana et al. 2015) India
Buns (hamburger), sweet bun and cake	CAP dried in solar dryer and milled	CAPP substituted for wheat flour at levels of 5, 10 and 20% for buns 10% for cake	30 untrained judges. Ranking test for the buns, and 9-point hedonic scale for cake	Fermentation/yeast interfered with increasing CAPP. Higher temperature and baking time needed with higher levels of CAPP	No significant difference for flavor of buns with 5 and 10% CAPP. Acceptance of cake not changed by CAPP addition. For the cake, a score of 7.6 was given	(Moura, da Silva, and da Silva 2015) Brazil
Cookies	CA soaked at 80 degrees for 20 minutes, rinsed in cold water, pressed, washed, dried and milled	CAPP substituted wheat flour at 0, 5, 10, 15 and 20%	20 untrained panelists with 9-point hedonic scale	Fat content increased from 18.1% in control to 19.4% with 20% CAPP. Protein content decreased from 11.8% to 9.3% Ash increased from 1.4% to 2.5% and fiber from 6.9% to 9.4% Samples with 20% CAPP had a higher weight (3.31 g) compared to control (2.75 g). Diameter reduced from 3.13 cm to 3.02 cm, while height increased from 0.42 cm to 0.5 cm	Overall acceptability for control 8.3. Not significantly different for 20% CAP with 7.8	(Ebere, Emelike, and Kiin-Kabari 2015) Nigeria
Biscuits	Juice extracted, blanched, drained, dried, milled	CAPP substituted for wheat flour at levels of 0, 5, 10, 20, 30, 40, 50 and 100%	20 trained panelists. 5-point hedonic scale	Biscuits with 10% CAPP had lower protein (4.5%) and moisture, but higher ash (1.7%), fiber (3.2%) and carbohydrate content (67.6%) than control Weight, height and spread ratio reduced with CAPP substitution. Length of biscuits with 10-50% CAPP reduced. Volume increased for 5 and 10% CAPP. Density with CAPP lower than control. Darkening with CAPP. Increasing level of CAPP negatively affected texture, with less cohesiveness and crumblier	Sensory scores decreased with increasing CAPP in biscuits. No significant difference in scores up to 10% substitution. With score of 4.3 for control, and 4 for 10% CAPP	(Akubor 2016) Nigeria
Cupcakes	Apples sanitized, washed, juice extracted, CAP dried, milled	CAPP substituted for WF at 0, 5 and 12%	70 untrained panelists. 9-point hedonic scale and 5-point purchase intention	With increasing CAPP moisture and sucrose decreased. Reducing sugar, fiber and calories increased with increasing CAPP	Sensory scores showed no significant difference in global impression between formulation. 0%: 8 5%: 7.66 10%: 7.69 Appearance scores decreased with increasing CAPP amount due to the darker color	(de Morais et al. 2018) Brazil
Cookies	Commercial cashew apple pomace dried and milled	CAPP substituted for wheat flour at levels of 0, 10 and 15%	100 untrained judges. 9-point hedonic scale	Acidity, moisture, ash, fibers, protein and lipid content increased with increasing amount. Carbohydrates and pH decreased with increasing CAPP content Microbiological analysis showed acceptable results	Sensory score for experimental cookies received better scores than control (6.17), with 10% being highest (6.8). Texture (7.2) and aroma (7.08) scores increased with the CAPP	(de Araújo et al. 2021) Brazil
Cake	CA washed, juice extracted, 15 min. hot water treatment, filtered, dried, milled	CAPP substituted for wheat flour at 0, 5, 10, 15, 20, 25 and 30%	50 semi-trained panelists. 9-point hedonic scale	Titratable acidity and total soluble tannins in the flours increased with increasing CAPP. pH decreased Calcium, magnesium, phosphorus, zinc and iron content significantly increased. Sodium and potassium decreased Oil absorption capacity and bulk density of flours decreased, but water absorption capacity and rehydration index significantly increased with increasing CAPP Viscosity (peak, trough, breakdown, setback and final viscosity) and peak time decreased. Pasting temperature increased as CAPP levels increased Equilibrium moisture content of flour increased with increasing levels of CAPP With increasing CAPP, the yellowness and redness increased, while lightness decreased	Decreasing acceptance with increasing levels of CAPP. 5% CAPP (7.33) was not significantly different from control on overall acceptability (8.0), but texture was (from 8.2 to 7.27)	(Adegunwa et al. 2020) Nigeria
OTHER FOOD PRODUCTS
Food product	Process	Amount of CAP or CAPP	Sensory test	Biochemical/functional results	Sensory results	Reference
Cereal bar	Apples cleaned, sanitized, juice extracted, filtered, dried and milled. Sterilized, fermented 9 hours, dried and ground	Fermented cashew apple pomace (FCAPP) replaced oat at varying levels: 0%, 66% and 39% (with 39% fermented guava peels, FGP)	40 judges. 9-point hedonic scale and 5-point purchase intent	Compared to control, moisture and protein content increased. Lipids increased for only FCAPP and decreased for FCAPP + FGP. Ash decreased for only FCAPP but increased for FCAPP + FGP. Carbohydrate and dietary fiber content decreased, as well as lightness of product and caloric values Hardness, cohesiveness and gumminess decreased with substitution Good stability during 28 days storage, with increased hardness, cohesiveness and gumminess	Sensory score for FCAPP (7.15) and FCAPP + FGP (7). Purchase intent 4.0 for all samples	(Muniz et al. 2020) Brazil
Cashew apple paçoca* (Brazilian savory dish) and cashew apple “meat” ball	Commercial CAP and artisanal CAP (produced manually). Apples sanitized, juice extracted, pomace pressed	49.2% CAP used for cashew apple paçoca 30.1% CAP used for cashew apple ball 4 treatments for CAP products: boiled, steamed, fried and in oven	Tested 2 hours after making with 60 untrained panelists. 9-point hedonic scale. 5-point purchase intent	Ascorbic acid content in artisanal fiber significantly different than industrial CAP (901.2 mg/100 g and 20.3 mg/100 g). Difference in phenolic content with artisanal (97.4 mg GA/100 g) and industrial CAP (49.8 mg GA/100 g) Treatments with frying and cooking in oven better retained bioactive compounds	Sensory analysis score for cashew apple paçocas 6.86. Purchase intent 3.80. For cashew apple “meat” ball 6.86 and 3.65	(Sucupira et al. 2020) Brazil
Jam	Commercial CAP washed, filtered and steamed. Plus concentrated CA juice	Jam made using CAP, 0, 5, 10 and 15% CA juice, and water, sugar, pectin and salt	30 untrained panelists. 9-point hedonic scale	Jam color darkened with the addition of CA juice pH of jam within regulations, with 2.8, and Aw 0.65	Best score for CAP jam with 5% CA juice, with 7.60, compared to 6.47 for control	(Nurerk and Junden 2021) Thailand
Cereal based extrudates	Juice extracted from CA and dried	CAPP substituted for rice flour at 0, 5, 10, 15, 20 and 25%	30 panelists. 9-point hedonic scale	CAPP significantly higher in ash than RC and CF. CAPP rich source of starch, protein, ascorbic acid, phenols, flavonoids and total antioxidant activity CAPP high mineral content: potassium, phosphorus, iron, manganese, zinc, copper and boron – compared to CF and RC. Extrudates showed increasing values of these as CAPP levels increased CAPP darker than CF and RC. WAI, WSI and OAI higher for CAPP than CF and RC Extrudates: expansion ratio, bulk density and lightness decreased. Specific length, firmness, moisture content, WSI and OAI increased	All CAPP samples, except 25% CAPP, higher scores than control (6.03), with 15% CAPP scoring highest (6.65)	(Preethi et al. 2021) India
Plant-based vatapá** (Afro-Brazilian savory dish)	Commercial CAP washed and pressed 3x, then freeze-dried. CAPP soaked in water and drained before cooking	Vatapá with 10, 15 and 20% CAPP (reduced amount of other ingredients, like cashew nut, tomato, coconut oil etc.)	Preliminary focus group with 8 people for product formulation Then 57 untrained panelists. 9-point hedonic scale and 5-point purchase intention. Check all and rate all questionnaires	With washing, pH increased, and acidity and soluble solids decreased. WAI and OAI increased with washing Lipids, ash, protein, carbohydrate, pH and energy value decreased with increasing CAPP. Moisture content increased Terms used to describe formulations: Fibrous texture, yellow, brown color, bitter taste	No significant difference between 10 and 15% CAP, with scores of 7.14 and 7.07. Purchase intention of 3.88 for both. 20% had lower scores, 6.63, and 3.28 for purchase intention	(Portela 2022) Brazil
Croquette-type plant-based product	Commercial CAP, washed with water and expeller pressed 3x	CAP added at 30, 40 and 50%, partially replacing soy protein	Pretests for the processing conditions. 60 untrained panelists. 9-point hedonic scale and 5-point purchase intention	Lipid content decreased from 1.8% with 30% CAP to 1.2% with 50% CAP. Proteins also decreased from 9.61% to 7.2%, while carbohydrates increased from 31.6 to 36.5% Freeze dried CAP was lighter in color, had higher amounts of phenols and vitamin C, as well as higher oil and water binding capacity than the CAP that was dried with air dryer and belt dryer.	All scores given on global impression, external and internal appearance, texture and taste were rated at 7.6 or higher. No significant difference in scores between the formulations. Global impression with 40% CAP scored 8.0, and 90% would probably or certainly buy the product	(Saldanha 2022) Brazil

CAP = cashew apple pomace, CAPP = cashew apple pomace powder, SDF = soluble dietary fibers, IDF = insoluble dietary fibers, FCAPP = fermented cashew apple pomace powder, FGP = fermented guava peels, RF = rice flour, CF = corn flour, WAI = water absorption index/capacity, WSI = water solubility index, OAI = oil absorption index/capacity, SBF = soybean flour, WF = wheat flour.

* Ingredients: CAP, cassava flour, purple onion, ghee, garlic, broth and spices.

** Ingredients: CAP, water, coconut milk, cashew nuts, French bread, tomato extract, oil and spices.

Food products that were used to incorporate the CAP included nine varieties of burgers and meat substitutes; eleven types of baked goods (cakes, cookies, biscuits), local Brazilian dishes, jam, croquettes, and a cereal based extrudate. The pomace in 16 of the studies was dried and used as a cashew apple pomace powder (CAPP), while in ten of the studies, the cashew apple pomace was used without drying. The wet CAP was most often chosen (7 out of 9) for burger or meat substitute formulation including vegetarian and fish options. Ten of the studies used commercially manufactured pomace, while others started with apples that were sanitized and washed, followed by juice extraction. A smaller number of the studies directly dried the CAP, while others had varied approaches for processing the pomace. Blanching, hot water treatment and the use of a salt-solution were all strategies used before incorporation into new products. Several studies washed the fibers numerous times, potentially removing water soluble tannins, reducing acidity, astringency (Lima et al. 2017; Lima et al. 2018; Maciel 2022; Portela 2022; Saldanha 2022) and also modifying sugar content (do Nascimento et al. 2021), which impacts taste and acceptability.

A wide range of concentrations of CAP(P) were used in producing different foods. Control foods contained no pomace and the majority of formulations used no more than 20% in the food product. Some of the studies focused on substituting a percentage of wheat flour, rice flour, meat or vegetable fat, while others added CAP in varying amounts for new product development.

Composition of new formulations

The addition, replacement or partial substitution of ingredients with CAP(P) impacted the chemical composition of the final food product (Table 2). The differences in chemical composition of foods seen with the addition of CAP(P) were directly correlated with the composition of the CA but was also influenced by the make-up of the component of the food product it was replacing or substituting.

Moisture or water content decreased in some products where the cashew apple pomace had a lower moisture content than the ingredient it was replacing (Akubor 2016; de Morais et al. 2018; Lima 2008; Pinho et al. 2011). For example, in a study where 14.27% of meat was replaced with CAPP (dried powder) in hamburger, the moisture content decreased from 71.1% to 63.38% (Pinho et al. 2011).

The opposite was observed when CAP (wet) was incorporated into vegetarian “burgers”, where a commercial control had 59.2% moisture, while the experimental formulation with lentils and 20% CAP had 67.02% water (Maciel 2022).

Similarly, when CAP was used to replace meat and vegetable fat, a reduction in the lipid content was reported (Barros et al. 2012; Guedes-Oliveira et al. 2016; Pinho et al. 2011). This is clearly due to the fact that CAP has a low lipid content. Washed CAP was used as a fat replacer in meat products and different amounts were tested. Using just 4.5% CAP in chicken patties decreased the lipid content from 7.62% to 4.40% (Guedes-Oliveira et al. 2016). However, the lipid content increased in three other products by 0.37% (cake), 2.46% (cookies) and 5% (cereal bar) (Aderiye, Igbedioh, and Caurie 1992; de Araújo et al. 2021; Muniz et al. 2020), when partially replacing wheat flour and oats. Two of these studies fermented the CAPP, but the overall trend was a reduction of fats in food products. Commonly, energy value was also reduced in cases where it was measured. For example, in a study conducted by Maciel (2022), in a vegan burger, lipid content decreased from 12.1% to 0.8% with 20% CAP and the caloric value was reduced from 213 to 130 kcal/100 g.

In general, lower protein concentrations were measured in the newly formulated products. This was improved by either supplementation and substitution with higher protein products like soy or cowpea or with fermentation (Akubor, Egbekun, and Obiegbuna 2014; Lima et al. 2017; Lima et al. 2018). Fermentation is an example of how the processing of the CAP(P) can influence the chemical composition and can be utilized to improve nutritional content. A microorganism, like yeast, utilizes carbohydrates, and as the microorganisms proliferate, the relative amount of protein increases. Protein content of the CAPP was eleven times higher after 9 hours of fermentation (Muniz et al. 2020), and went from 5.2% to 11.5% after 96 hours of fermentation. The ether extract went from 14 to 19%, while carbohydrates decreased from 43.2 to 19.2% (Aderiye, Igbedioh, and Caurie 1992).

In the majority of studies, the amount of ash and carbohydrates was reported to increase with the addition of CAP(P). This is most likely attributable to the increase in soluble and insoluble dietary fibers. Pinho et al. (2011) found that the carbohydrate content increased from 0.39% to 10.96% when 14.27% of the meat (high protein food) was replaced with CAPP, and the total dietary fiber increased from 0% to 7.66%. In contrast, de Araújo et al. (2021) found that the carbohydrate in cookies went from 71.56% in control to 48.83% with 15% CAPP when replacing wheat flour. However, dietary fiber content went from 5.7% to 22.6%.

CA was found to be a rich source of minerals, and in one study, it was substituted for rice flour in increasing amounts. As rice flour does not have a high mineral content, the utilization of CA was very beneficial, increasing the content from 0.76% to 0.87% when using 25% CAPP (Preethi et al. 2021).

Fruit and vegetables are known to be a source of minerals, but there are only a limited number of studies looking at the mineral content in fruit and vegetable by-products (Santos, da Silva, and Pintado 2022). An indication of the mineral content is often determined by the percentage of ash (Adegunwa et al. 2020). The ash found in CAPP was 0.74-2.70%, but the lowest quantity was found in a study where the CAP was washed (Guedes-Oliveira et al. 2016). This can be explained by the fact that minerals are water-soluble (Callahan, Leonard, and Powell 2020). When comparing the ash content to other materials, one study found that cassava flour had 1.60% (Ogunjobi and Ogunwolu 2010), while soybean flour had 3.20%, wheat flour 0.9% (Akubor, Egbekun, and Obiegbuna 2014), rice flour 0.52%, corn flour 0.20% (Preethi et al. 2021), acerola 3.08% and guava 3.56% (Batista et al. 2018). Thus, cashew apple pomace is thought to be a relatively good source of minerals, especially compared to that found in cereals. A few studies analyzed mineral content of the new formulations and overall, addition of CAP(P) enhanced levels. Specifically, one study found, calcium went from 9.30 to 24.90 mg/g, copper from 21.27 to 37.31 mg/g, manganese from 1.14 to 2.14 mg/g, magnesium from 0.82 to 1.86 mg/g, phosphorus from 12.83 to 17.17 mg/g, zinc from 1.54 to 2.95 mg/g, iron from 9.07 to 15.28 mg/g, boron from 0.94 to 1.16 mg/g and potassium from 1.7 to 14.4 mg/g when comparing to control (Preethi et al. 2021).

Cashew apple is naturally acidic, with different organic acids like anacardic acid, tartaric acid and ascorbic acid (Reina et al. 2022). This decreased the pH in many of the newly formulated products. Adegunwa et al. (2020) found that the pH of the control cake was 5.62, while the pH after the addition of 30% CAP was 3.59.

This effect has also been documented with the incorporation of other fruit and vegetable flours into foods. For example, addition of cabbage (Pop, Suharoschi, and Pop 2021), peach and orange fibers can impact pH, but is largely dependent on the pH of the original food ingredients (Mehta et al. 2013).

In the studies that analyzed vitamin C, phenolic compounds, flavonoids and antioxidant activity, addition of CAP(P) increased content, coinciding with increased titratable acidity. Preethi et al. (2021) found that the ascorbic acid content increased from 0 to 8.83 mg/100 g, phenols from 0,25 mg GAE/g to 2.03, flavonoids from 0.03 mg CTE/g to 0.18 and total antioxidant activity from 0.39 mg AAE/g to 2.88. when using 15% CAPP. One study in fish burgers suggested that the lower pH, as well as the increased content of carotenoid and antioxidant activity that was found using 11.76% CAP helped preserve the product during 120 days of frozen storage, as the control had higher levels of total volatile bases (TVBN) and trimethylamine (TMA) – indicators of degradation (Maciel 2022).

Processing conditions can influence the product composition, for example washing the pomace. This increased pH from 3.30 to 5.62, decreased acidity from 0.65% to 0.18% and soluble solids from 10.15 to 0.10 Brix. (Portela 2022). Similarly, Saldanha (2022) increased the pH from 3.3 to 5.6 with 3 washings in a 1:2 ratio of CAP and water which reduced total soluble solids from 10.3 to 0.5. This was noted to be important for conservation/shelf life, as it reduces the growth of microorganisms. It must be taken into consideration that washing affects all water-soluble bio-compounds, including vitamins. These compounds tend to be sensitive to heat, oxygen and light and are also affected by processing and storage conditions (Sucupira et al. 2020).

Changes in physical properties of new products

Color

Consistently, with the utilization of the CAP(P) in food formulations, darkening of the product occurred, as well as increased yellowness and redness. This was not surprising as in 12 out of 26 studies, where CAPP was used to partially replace wheat flour, oats or rice flour the natural darker color of CAPP was evident (Adegunwa et al. 2020; Muniz et al. 2020; Preethi et al. 2021). In addition, the phytochemicals in the CAP(P) can influence color and impact pigment degradation which will also lead to color changes. A negative effect on color was also been reported in studies where fruit and vegetable material was used in bakery products (Gómez and Martinez 2018). In a few cases, the change in color was considered positive, such as the addition of 10-15% mango peel in tortilla chips (Pop, Suharoschi, and Pop 2021). In the studies using CAP(P) reviewed here, the sensory evaluation sometimes had its own category for color, and in other cases for appearance. Though the color and appearance in most cases was negatively affected by the addition of CAP(P), there were five studies where it had a positive influence when added in low concentrations (Aderiye, Igbedioh, and Caurie 1992; da Silva Marques 2018; Guedes-Oliveira et al. 2016; Muniz et al. 2020; Preethi et al. 2021). Improved color was found when CAPP was incorporated into cereal-based extrudates, cereal bars, chicken patties, fish burgers and one variety of cake. For most of these categories, the expectations of product appearance tended to be more variable, in comparison to traditionally light-colored cakes and biscuits.

Additional functional changes

The water absorption index/capacity (WAI/WAC) was seen to increase in all of the studies where tested, with the exception of one study. Oil absorption capacity (OAC) also was increased (Adegunwa et al. 2020). Wheat flour was found to have 75% WAC; in comparison the CAPP had 164%. This can most likely be attributed to the fiber content of CAP which contains polar and hydrophobic constituents that can impact absorption and binding capacity. An increase in the water retention/absorption was also found in a study where the CAP was fermented (Aderiye, Igbedioh, and Caurie 1992). The same increase in water absorption, as well as oil absorption has been observed following washing of the pomace, where the OAC of the CAPP went from 130.82% to 213.4% and the WAC went from 152.20% to 252.50% with three rounds of washing (Portela 2022).

The high water absorption capacity is beneficial in many food applications that require hydration (Adegunwa et al. 2020). The same effect has been reported for other fruit and vegetable products used in studies with food applications (Gómez and Martinez 2018), where citrus is known to have a high water binding capacity (Pop, Suharoschi, and Pop 2021). Additionally, the water absorption capacity can contribute to a greater cooking yield, a result seen in chicken patties where only 4.5% CAPP improved the yield from 84.89% to 88.39% (Guedes-Oliveira et al. 2016). Pinho et al. (2011) used 14.27% CAPP in hamburgers replacing meat, and the yield improved from 70.23% to 88.52% Increased yields have been found with other fiber sources, for example using apple pomace powder in chicken nuggets (Yadav et al. 2016).

Foaming capacity, water solubility index and rehydration index, when measured, were positively affected. However, when compared to wheat flour, the addition of CAPP lowered emulsion capacity, and reduced gelation concentration, emulsion- and foam stability (Akubor, Egbekun, and Obiegbuna 2014). The viscosity of products also decreased with increasing levels of CAPP. In the studies where bulk density was tested, this property was lower for the CAPP containing products than for wheat flour and rice flour (Adegunwa et al. 2020; Preethi et al. 2021). One study found that CAPP had a bulk density of 0.69 g/cm³, while wheat flour had 0.72 g/cm³, and soybean flour 0.38 g/cm³ (Akubor, Egbekun, and Obiegbuna 2014). The bulk density is dependent on the particle mass, size, initial moisture content of flours (Chandra, Singh, and Kumari 2015), and the geometry of the particle (Akubor 2016). When addition of pineapple peel fibers were added to bread it was observed that coarser particles resulted in a higher volume and lower hardness in comparison to fine particles (Gómez and Martinez 2018). The effect of the various methods of processing, as well as the physical properties of the powder/flour from the products, such as drying temperature and particle size, are often not evaluated, but are important for product optimization.

Some of the studies using the CAPP in cake and biscuits also assessed the impact on weight, height and volume following the addition of CAPP. These parameters were often reduced (Aderiye, Igbedioh, and Caurie 1992; Akubor 2016; Akubor, Egbekun, and Obiegbuna 2014). A control biscuit weighed 22.41 g, and with the substitution of 5% CAPP this was reduced to 18.17 g, but by adding 50% CAPP weight was slightly improved (19.1 g). The product volume increased with the addition of CAPP up to 10% (23 cm³ compared to 19 cm³) but decreased with higher concentrations (Akubor 2016). One study did not specifically measure these properties, but said that with increasing CAPP concentrations, yeast fermentation was inhibited in buns (Moura, da Silva, and da Silva 2015). A marked decrease in expansion of doughs resulting a reduced volume of baked goods is a common effect following the addition of dietary fiber from fruit and vegetable powders (Gómez and Martinez 2018). Gluten is a component of wheat flour that is important for holding gas during fermentation and baking, and with less gluten, the height and volume is expected to decrease (Adegunwa et al. 2020). Proteins in gluten are also important for the cohesiveness and structure of baked products, and with a dilution of gluten, and competition for water, these characteristics were affected in the final product (Akubor 2016). One way to overcome this issue is to incorporate the material into products where gluten plays little or no functional role. Meat products or flat breads fit into this category of foods (Gómez and Martinez 2018). The reduction in peak and final viscosity of baked goods incorporating CAPP was most likely related to a lower level of gluten in preparation (Adegunwa et al. 2020).

Several studies reported a negative effect on the texture of food products following the addition of CAP(P). Specifically, cohesiveness can be decreased (from 0.7 in control to 0.3 in the cereal bar with CAPP) (Akubor 2016; Muniz et al. 2020). Firmness was found to decrease in cereal based extrudates from 43.84 N to 36.48 N (Preethi et al. 2021). Results vary dependent on food product and in hamburgers where the shearing force in control was 3.88 kgf,with 7.13% CAPP this increased to 4.43 kgf, before it decreased to 3.36 kgf with 14.27% CAPP (Pinho et al. 2011). This demonstrates that the different changes do not always occur in a dose response manner, and optimization is critical to achieve the best quality end-product when adding CAP(P). Interestingly, some studies found that the CAP(P) had a positive impact on texture based on sensorial evaluation (Aderiye, Igbedioh, and Caurie 1992; da Silva Marques 2018; de Araújo et al. 2021).

Two studies mentioned an effect on cooking time, with one report of higher temperature and longer baking time being needed with higher levels of CAPP in baked goods (Moura, da Silva, and da Silva 2015). In contrast, a second study in a cake product found a reduction in cooking time, but an increase in the pasting temperature, the temperature needed for the starch granules in the product to swell (Adegunwa et al. 2020).

A few studies evaluated microbiological aspects and found satisfactory results, as well as maintenance of product acceptability during 6 months of frozen storage (-18⁰) (Lima et al. 2017; Lima et al. 2018). However, there was an increase in acidity from 0.29% to 0.34% and pH from 5.77 to 5.30 during storage. Storage also affected a cereal bar with added CAPP. Initially, the addition of CAPP resulted in decreased hardness, cohesiveness and gumminess compared to control. These factors increased following 28 days of storage (Muniz et al. 2020).

Sensory evaluation of new products

All the studies discussed in this paper included sensory evaluation. No matter how beneficial the nutritional and environmental aspects of using a certain material might be, it is of no use if consumers do not find it tasty and do not buy it. Therefore, the sensory evaluations and purchase intention are considered critical for determining the marketing potential of new products (Atta et al. 2021), which must meet consumer expectations (Portela 2022).

To carry out sensory evaluations, panelists (n = 10-118) were recruited. Trained, semi-trained and untrained judges were used. Twenty-two of the studies used a 9-point hedonic scale for the evaluation of the food product, with the remaining four studies using a 5-point hedonic scale. Fifteen of the studies included questions regarding purchase intention of the panelists commonly using a 5-point ranking.

The sensory scores where a 9-point scale was used ranged from 5.2-8, and for the studies using the 5-point hedonic scale, the scores ranged from 3.21-4.80. The highest scores were found in a recent publication introducing a croquette-type plant-based product, where the global impression score with 40% CAP was 8, and where 90% of panelists saying they would probably or certainly buy the product (Saldanha 2022).

The majority of studies found a reduction in the sensory evaluation with increasing amounts of CAP(P). In all of the studies using a control, with one exception, it was found that there was no significant alteration in organoleptic qualities in comparison to the control at low levels of substitution. In some cases, scores were even improved with the addition of CAP(P). Sensory evaluation scores were higher for new formulations in five studies, where the overall acceptance score went from 7.9 to 8 with 3% CAPP in chicken patties (Guedes-Oliveira et al. 2016), from 6.03 to 6.65 with 15% CAPP in cereal based extrudates (Preethi et al. 2021), from 6.17 to 6.8 with 10% CAPP in cookies (de Araújo et al. 2021) and from 6.93 to 7.81 with 20% CAP in fish burgers (da Silva Marques 2018). Significantly lower scores in sensory evaluation, 5.9, were observed in a “burger” made with 89% CAP that was compared to four commercial burgers (Lima 2008). It should be noted that in this study, the majority of the product was composed of CAP, which may have limited palatability. The best results in terms of taste, smell and texture seemed to be achieved with a substitution of up to 10% CAP(P).

Six of the studies described pretests that were done with smaller focus groups to determine the ratio and formulation (Barros et al. 2012; da Silva Marques 2018; Lima et al. 2018; Maciel 2022; Portela 2022; Saldanha 2022). One of the studies used professionals from gastronomy to optimize the product and received one of the highest purchase intention scores, 86% (Lima et al. 2018). Taking additional steps, focusing on palatability and acceptability, had a positive effect that led to enhanced optimization of the new formulations.

To avoid negatively modifying the taste of a food, appropriate processing of the raw material, using strong seasonings to mask the bitterness or the addition of lipids/sugar or other ingredients may be helpful (Gómez and Martinez 2018). Undoubtedly, from the articles presented here, that all include sensory evaluations, highly palatable, nutritious products can be developed incorporating the cashew apple pomace as an ingredient.

Overall, it appeared that the studies that treated the CAP either with washing or with a hot water treatment received better sensory scores than the studies where the pomace was directly dried. This could be because the tannins, phenolic compounds known to cause astringency, can be reduced with these processes (Prommajak, Leksawasdi, and Rattanapanone 2020). Phenolic compounds in fruit and vegetables are known to impart a bitter and astringent taste (Gómez and Martinez 2018). This was observed when grape pomace was incorporated into chocolate and attributed to the presence of polyphenols (Pop, Suharoschi, and Pop 2021).

The results from this review indicate that there is a critical concentration of CAP(P) that when surpassed, sensory scores begin to decline. This has also been observed with the addition of other fruit and vegetable flours (Gómez and Martinez 2018). Clearly, at optimal concentrations, the addition of CAP(P) has no negative impact, and can sometimes positively impact organoleptic qualities in comparison to control foods.

Several limitations were identified while preparing an integrated evaluation of the studies included in this review. The variety of cashew (Anacardium occidentale) was identical throughout, but no standard processing of the pomace was used and methods varied from study to study. Treatments ranged from use of wet pomace without any processing, to extensive washing and drying of the CAP. Furthermore, limitations existed regarding the sensory evaluations carried out on the newly developed CAP(P) containing foods. Ten studies did not include a control product for comparison. A few studies did not report scores for all products evaluated or displayed results as a graph making it difficult to determine the exact sensory score. In addition, eight of the studies had 30 judges or less. A limited number of panelists has been noted as a restriction when discussing the topic of utilization of fruit and vegetable flour in food products (Gómez and Martinez 2018). Most of the studies used untrained panelists, which can introduce error. For example, the central tendency error, where untrained judges more frequently give scores in the middle of the scale, in comparison to evaluations made by a trained judge (Sharif et al. 2017). In contrast, it has been suggested that acceptability studies should be conducted with untrained judges (Gómez and Martinez 2018).

There is a clear case for promoting utilization of CAP as a food ingredient, but it is currently not possible to definitively categorize CAP as a functional food. Despite high concentrations of known beneficial components, in order to establish CAP’s contribution to health beyond basic nutrition there is a need for well-designed clinical trials with adequate sample size, along with unequivocal evidence of safety.

Conclusion

There are numerous studies looking at the utilization of fruit and vegetables in food products, but limited attention has been given to the cashew apple. Worldwide, it is produced in large quantities and repurposing would be a meaningful step toward decreasing food waste. The cashew apple is rich in nutritional compounds and has the potential to be categorized as a functional ingredient. These advantages are important tools for facing the nutritional challenges in the world today. Similarly, other studies have pointed out the nutritional and environmental advantages of using fruit and vegetable by-products in new formulations. Increased phytochemical content and reduced caloric density also reflect an overall, improved nutritional value (Gómez and Martinez 2018; Pop, Suharoschi, and Pop 2021).

In order to valorize more of this material, there are several challenges that need to be overcome. First, there is inadequate knowledge regarding the potential use of CAP(P) in the food industry. Additionally, there is a need to find ways to extend the shelf-life of the fresh fruit and develop methodologies for processing that are cost-effective and simple. The breeding of cashew apples with desired traits, for example reduced acidity and increased firmness (Germano et al. 2022) is a longer-term strategy that could also be valuable. To date, product development with appropriate organoleptic testing using professionals has been limited, therefore investing resources in this area may also be advantageous. Products with high nutritional value that help to utilize food waste may also be an attractive marketing approach which involves developing the necessary infrastructure and strategies by food manufacturers to increase awareness and sales. Cashew apple is underutilized and therefore meets the criteria for transformation from food waste to functional ingredient. As this review showed, choosing appropriate food products and optimizing formulation is critical for success. The positive sensory evaluations reported here support the incorporation of cashew apple pomace in a variety of different products. This presents an innovative, sustainable strategy from every perspective: nutritional, environmental and economic.

Acknowledgements

The authors would like to thank Eckbos legat for financial support of NVW during her studies at the Hebrew University of Jerusalem.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.