Acerola nectar sweetened with different sweeteners: ideal and equivalent sweetness

Abstract

The study of sweeteners for replacing sucrose is increasingly important for the food industry. The ideal sweetness as sucrose and the equivalent sweetness of acerola nectar with different sweeteners (neotame, sucralose, stevia with 40%, 60%, 80% and 95% rebaudioside A) were measured. The ideal sweetness of the samples sweetened with sucrose at 50 g/L, 75 g/L, 100 g/L, 125 g/L and 150 g/L was assessed by means of a test with 50 consumers using a just-about-right scale. The magnitude estimation method for determining the equivalent sweetness was carried out with 20 assessors. The concentration of sucrose ideal in acerola nectar was 80 g/L, with equivalent concentrations of sweeteners of 0.017 g/L neotame, 0.16 g/L sucralose, 1 g/L stevia with 40 % rebaudioside A, 0.99 g/L stevia with 60 % rebaudioside A, 1 g/L stevia with 80 % rebaudioside A and 1 g/L stevia with 95 % rebaudioside A.

El estudio de edulcorantes que puedan reemplazar a la sacarosa se ha vuelto cada vez más importante para la industria alimentaria. En el presente estudio, se midieron la dulzura ideal de sacarosa y la dulzura equivalente del néctar de acerola en distintos edulcorantes (neotame, sucralosa, stevia con 40%, 60%, 80% y 95% de rebaudiósido A). A través de una prueba aplicada a 50 consumidores utilizando una escala ‘está casi bien’, se evaluó la dulzura ideal de las muestras endulzadas con sacarosa a 50 g/L, a 75 g/L, a 100 g/L, a 125 g/L y a 150 g/L. Con 20 evaluadores se aplicó el método de estimación de magnitud para determinar la dulzura equivalente. La concentración ideal de sacarosa en el néctar de acerola fue 80 g/L, con las concentraciones equivalentes de dulzura de 0,017 g/L neotame, 0,16 g/L sucralosa, 1 g/L stevia con 40% de rebaudiósido A, 0,99 g/L stevia con 60% de rebaudiósido A, 1 g/L stevia con 80% de rebaudiósido A y1 g/L stevia con 95% de rebaudiósido A.

Keywords:

• sensory analysis
• tropical fruit
• food additives
• sucralose
• neotame
• Stevia rebaudiana

Palabras claves:

• análisis sensorial
• fruta tropical
• aditivos alimentarios
• sucralosa
• neotame
• Stevia rebaudiana

Introduction

Acerola, also known as cherry-of-Antilles (Malpighia emarginata DC), is a red dish fruit originating in the Antilles, northern South America and Central America (Neves & Lima, 2009). Acerola is primarily known for its high content of vitamin C, one of the most important natural sources of this vitamin. Moreover, it presents juicy and refreshing pulp with a fruity and sweet taste (Mezadri, Villaño, Fernandez-Pacho, García-Parrilla, & Troncoso, 2008). Although it is consumed fresh, acerola is widely used in the production of nectar, frozen pulp, bottled and pasteurized juice and jelly. Therefore, the cultivation of acerola becomes highly promising, with good prospects for the fruit grower (Maciel, Mélo, Lima, Souza, & Silva, 2010).

The increased consumption of fruit drinks has been promoted by health concern, which has increased the demand for beverages with nutritional characteristics, important for the prevention and control of diseases (Matta, Moretti, & Cabral, 2004). Besides the juice, nectar is another option of acerola-based beverage. By owning the lowest price than whole juices, both juice and nectar have been gaining ground among consumers. The acerola nectar is potentially attractive to this market due to its high content of vitamin C (Figueira et al., 2010).

The population is increasingly concerned with health, which implies increasing demand for reduced-calorie products, especially those that use sweeteners as sucrose substitutes (Moraes & Bolini, 2010). Low-calorie products were known for its high prices. Currently, this category has become widely available, with affordable prices and sensory characteristics similar to conventional products (Cardoso & Bolini, 2007).

Food safety has been a growing consumer concern, especially about food additives. Sweeteners are among the food additives that create more discussion, for its use in products that are widely consumed such as soft drinks, juices and tabletop sweeteners (Mortensen, 2006). The use of these sucrose substitutes in food production is a way to provide the sweet taste without increasing caloric value. High intensity sweeteners are many times sweeter than sucrose, which is why the quantities needed to achieve the same level of sweetness are much lower than those required for sucrose (Zygler, Wasik, Kot-Wasik, & Namiesnik, 2012).

Sucralose is one of the most promising candidates as non-nutritive sweetener, being highly soluble in water and stable at high temperatures, which allows it to be used in thermally processed and acidic food products without loss of sweetness during storage (Basu, Shivhare, & Singh, 2013; Viberg & Fredriksson, 2011). Sensory studies show that sucralose has no bitter taste attributed to other non-caloric sweeteners and it is approximately 600 times sweeter than sucrose (Brusick, Grotz, Slesinski, Kruger, & Hayes, 2010).

Neotame is an artificial sweetener launched recently in the market. Derivative of aspartame, it has essentially the same qualities of aspartame, as sweetness profile close to sucrose without bitter or metallic aftertaste and sweetening power about 5000 times that of sucrose. The discovery of neotame by French researchers was the result of a long research program of The NutraSweet Co., whose objective was the development of new sweeteners with high intensity sweetness and desirable flavor characteristics (Prakash, Corliss, Ponakala, & Ishikawa, 2002).

Stevia rebaudiana (Bertoni) is native to Paraguay, where it has been used to sweeten beverages for over a century, having been called as Caá-êHê in Guarani, meaning sweet herb. This plant has a class of compounds known as steviol glycosides, which are produced by the plant at high concentrations. These intensely sweet components can be purified from the leaf, resulting in a sweetener of natural origin, which is approximately 200 times sweeter than sucrose (Boileau, Fry, & Murray, 2012). The distribution of steviol glycosides in Stevia rebaudiana differs between the parts of the plant, and the leaves have the most abundant concentration of these compounds. The most important glycosides from Stevia rebaudiana are stevioside, rebaudioside A, rebaudioside C and dulcoside A, and the stevioside and rebaudioside A are present in higher concentrations (Gardana, Scaglianti, & Simonetti, 2010; Pól, Hohnová, & Hyotylainen, 2007). The rebaudioside A is more sweeter and stable and less bitter than stevioside (Goyal, Samsher, & Goyal, 2010).

Among the existing methods to evaluate the optimal amount of a compound to be added to a food, the ideal scale is the more effective method, due to both reliability and validity of its results, as well as its simplicity (Cardoso & Bolini, 2007). To successfully substitute sucrose for sweeteners in food formulations, preliminary studies must be carried out to determine the concentrations of sweeteners to be used and its equivalent sweetness as compared to sucrose (Souza et al., 2011). For that, the magnitude estimation method is used among others methodologies (Cardoso & Bolini, 2007). For each food, the equivalent sweetness is unique, once the sweetness potencies depend on the dispersion matrix in which they are inserted (Cadena & Bolini, 2012).

There are few studies on equivalent sweetness in fruit nectars, especially concerning the neotame and comparing stevia extracts with different levels of rebaudioside A. The aim of this study was to evaluate the optimal concentration of sucrose in acerola nectar and determine the sweetness equivalence of different sweeteners to promote a sweetness equivalent to the ideal.

Materials and methods

Acerola nectar samples were prepared by diluting one part of the pulp (Mais Fruta®- Jarinu, São Paulo) to two parts of mineral water according to the manufacturer’s instructions. The samples were sweetened with the following substances: extracts of the leaves of Stevia with 40%, 60%, 80% and 95% rebaudioside A (Steviafarma Brazil® – Maringá, Brazil); sucralose (Sweetmix® – Sorocaba, Brazil); neotame (Sweetmix® – Sorocaba, Brazil); and sucrose (União® – São Paulo, Brazil).

One day before the analysis, the samples were processed in an industrial blender (Sire® – Brusque, Brazil) for one minute, maintained at 6 ± 2 °C and served at 10 ± 2 °C. The sensory evaluations were conducted in individual booths and the samples served in plastic cups coded with three-digit numbers.

The optimum sucrose concentration (%) to be added to the acerola nectar was determined by an acceptance test using a just-about-right scale, from ‘not nearly sweet enough’ = −4.5, to ‘much too sweet’ at the other extreme = +4.5 and ‘just right’ in the middle, corresponding to zero (Meilgaard, Civille, & Carr, 2004). The samples were sweetened with sucrose at 50 g/L, 75 g/L, 100 g/L, 125 g/L and 150 g/L. Then, 30 ml of each nectar was served to the consumer in a monadic order. Fifty consumers of acerola nectar, 36 women and 14 men with mean age of 28 years old and recruited on the Universidade Estadual de Campinas, Brazil, participated in the test. The results were analyzed by linear regression between hedonic values ​​ and sucrose concentration.

Pre-selection of assessors

The pre-selection of assessors was performed by triangular tests using the sequential method (Amerine, Pangborn, & Roessler, 1965). Two samples of acerola nectar were sweetened with sucrose at 50 g/L and 35 g/L, once these concentrations presented significant differences between the values at 1% level. To establish this difference, a paired comparison test was performed with 30 panelists.

To the sequential analysis, the following values ​​were used: p0 = 0.45 (maximum incapability acceptable); p1 = 0.70 (minimum acceptable skill); and the risks α = 0.05 (probability of accepting a candidate without sensory acuity) and β = 0.05 (probability of rejecting a candidate with sensory acuity). Twenty assessors were selected for the determination of equivalent sweetness of different sweeteners in acerola nectar and trained to use the sensory magnitude scale with samples of different sweetness intensities.

Determination of equivalent sweetness

The sweetness equivalency test was carried out in accordance with the methodology proposed by Stone and Oliver (1969) and performed by previously selected assessors. The samples were presented in a balanced complete block design (Macfie, 1989) with a reference sample sweetened with the optimum concentration of sucrose (8.0%), which was designated with a intensity of 100, followed by a series of random samples with sweetness intensities of both lower and higher than the reference sample.

The assessor had to estimate the sweetness intensity of unknown samples relative to the reference. For example, if the sample was twice as sweet as the reference, it should receive an intensity of 200, whereas if the sample was half as sweet, the intensity should be 50, and so on. The assessors were instructed not to evaluate the sweetness intensity as zero.

The concentrations of sweeteners used in these determinations are shown in Table 1, according to others works about equi-sweetness (Cadena & Bolini, 2012; Cardoso & Bolini, 2007; Marcellini, Chainho, & Bolini, 2005). Values ​​were normalized and set to a logarithmic scale. The curves of concentration versus sensory response for each sweetener corresponded to a power function with the following characteristics: S = aCⁿ, where S is the sensation perceived, C is the concentration of the stimulus, a is the antilog of the y value in the intercept and n is the slope obtained (Moskowitz, 1974). The statistical analyses were performed with the help of the statistical program SAS (Statistical Analysis System, 2012–version 8.2, Raleigh, United States of America), licensed to the State University of Campinas.

Table 1. Concentrations of sucrose, sucralose, neotame and stevia extracts utilized for the equi-sweet determination.

Tabla 1. Concentraciones de sacarosa, sucralosa, neotame y extractos de stevia utilizados en la determinación de equi-dulzura.

Sweetener	Concentrations (g/L) for an equi-sweet determination to 80  g/L of sucrose
Sucrose	31.25	50.00	80.00	128.00	204.80
Sucralose	0.063	0.100	0.160	0.256	0.410
Neotame	0.007	0.010	0.017	0.027	0.043
Stevia 40% Reb. A	0.391	0.625	1.000	1.600	2.560
Stevia 60% Reb. A	0.391	0.625	1.000	1.600	2.560
Stevia 80% Reb. A	0.391	0.625	1.000	1.600	2.560
Stevia 95% Reb. A	0.391	0.625	1.000	1.600	2.560

Results and discussion

The evaluation of consumers by just-about-right scale was transformed into numerical data (–4.5 to +4.5), and the ideal sweetness corresponded to the value of 0. From the straight line equation (Figure 1), we obtained a value of 79.8 g/L sucrose as the optimal concentration to be added to acerola nectar. To facilitate subsequent experiments, the value was rounded to 80 g/L as the optimum sucrose concentration.

Figure 1. Sucrose ideal concentration in acerola nectar.

Figura 1. Concentracion ideal de sacarosa en nectar de acerola.

The result found for the optimum sucrose concentration was lower than that found for peach nectar, 100 g/L (Cardoso & Bolini, 2007), guava nectar, 96 g/L (Brito, Câmara, & Bolini, 2007), and concentrated and reconstituted pineapple juice, 85 g/L (Marcellini et al., 2005). A lower value ​​than that of the present study was found for mango nectar, 70 g/L (Cadena & Bolini, 2012). Based on these results, it can be concluded that the optimal sucrose concentration varies with the type of product being evaluated.

Table 2 shows the results for the angular coefficient, Y-intercepts, linear correlation coefficients and the power functions of each sweetener, and Figure 2 shows the relationship between the sweetness intensity and the concentration of the sweeteners represented on a logarithmic scale.

Table 2. Parameters to determine sweetness equivalence of each sweetener.

Tabla 2. Parámetros para determinar las equivalencias de cada edulcorante.

Sweetener	Angular coefficient	Y-intercept	R	Power function
Sucrose	0.9978	−0.9011	0.9966	S = 0.12557.C^0.9978
Sucralose	0.9044	1.6248	0.9975	S = 42.1525.C^0.9044
Neotame	0.8875	2.4601	0.9927	S = 288.4834.C^0.8875
Stevia 40% Reb. A	0.7354	0.7353	0.9951	S = 5.4369.C^0.7354
Stevia 60% Reb. A	0.9038	0.9073	0.9818	S = 8.0792.C^0.9038
Stevia 80% Reb. A	0.8245	0.8244	0.9864	S = 6.6746.C ^0.8245
Stevia 95% Reb. A	0.7757	0.7757	0.9859	S = 5.967439.C^0.7757

Regarding the determination of equivalent sweetness, Table 2 shows values ​​of R higher than 0.9 for all the sweeteners evaluated. However, the values ​​obtained for stevia leaf extracts with 60%, 80% and 95% rebaudioside A were lower than the rest. This fact may be related to the characteristic bitter taste, especially at high concentrations, presented by stevia extracts that may have influenced the perceived sweetness of the product. Cardoso and Bolini (2007) observed that the lowest R value for the sweeteners in peach nectar equivalent to 100 g/L of sucrose was found to Stevia, which the authors attributed to the bitterness present in the samples sweetened with this sweetener.

The position of the curves presented in Figure 2 indicates the sweetness power of each sweetener. The sucrose curve is distant from the others, indicating that for the same sweetness perception a much higher concentration of sucrose is required. The sweetener that requires a lower concentration to induce the same sweetness perception was neotame, followed by sucralose. There is an overlap between the curves of stevia extracts with different rebaudioside A levels, indicating very close results of equivalent sweetness to these sweeteners. According to the literature, the rebaudioside compounds are sweeter than stevioside, and then it was expected lower concentrations of stevia extracts with higher rebaudioside A content to reach the same sweetness perception in acerola nectar. Probably the acidity of the product was a factor that interfered with the sweetness perception of the sweeteners derived from stevia leaf extract, by masking the sweetness. Reis et al. (2011) reported that the acidity interfered with the sweetness perception in a study on equivalent sweetness in strawberry yoghurt.

Figure 2. Relationship between the sweetness intensities and the sweeteners’ concentrations corresponding to the 80 g/L sucrose concentration.

Figura 2. Relación entre las intensidades de dulzura y las concentraciones edulcorantes correspondientes a la concentración de sacarosa 80 g/L.

The concentration of each sweetener was calculated in equivalence of the ideal sweetness of sucrose in acerola nectar (80 g/L) and the sweetness power was defined as the number of times a compound is sweeter than sucrose. These results are shown in Table 3.

Table 3. Equi-sweet concentration and potency of the sweeteners.

Tabla 3. Concentración equivalente y Poder de dulzor.

Sweetener	Concentration equivalent to sucrose 80 g/L	Sweetener potency at 80 g/L sucrose
Sucralose	0.16 g/L	500
Neotame	0.017 g/L	4733
Stevia 40% Reb. A	1.00 g/L	80
Stevia 60% Reb. A	0.99 g/L	81
Stevia 80% Reb. A	1.00 g/L	80
Stevia 95% Reb. A	1.00 g/L	80

According to Table 3, neotame presented the highest sweetness power, being 4733 times sweeter than sucrose, specifically in the case of acerola nectar with 80 g/L sucrose, once 0.017 g/L neotame was required to substitute that sugar. Superior result was found by Cadena and Bolini (2012), who found sweetness power 6026 times higher than sucrose in mango nectar.

Sucralose presented a sweetness power of 500 in acerola nectar (Table 3). A similar result was reported by Marcellini et al. (2005) in concentrated and reconstituted pineapple juice where sucralose presented a sweetness power of 492. Cardoso and Bolini (2007) found a value of 627 for this sweetener in peach nectar, while Moraes and Bolini (2010) found a sweetness power for sucralose of 636 and 599 in instant coffee and ground roasted coffee, respectively.

Regarding the samples sweetened with stevia leaf extracts, the results of sweetness power were very close, ranging from 80 to 81, where the highest sweetness power was observed for the sample with 60% rebaudioside A, as shown in Table 3. The sweetness perception of the samples sweetened with stevia leaf extracts with higher contents of rebaudioside A may have been affected by the high acidity of acerola. Stampanoni (1993) reported a decrease in perceived sweetness in orange and lemon noncarbonated beverages due to the addition of citric acid.

When stevia with 97% rebaudioside A was evaluated in mango nectar, Cadena and Bolini (2012) found a sweetness power of 134, and the authors reported that this high value is related to the high content of rebaudioside in the stevia extract. Higher values were also found by Cardoso and Bolini (2007) and Moraes and Bolini (2010) in peach nectar (101) and in instant coffee (100), respectively. On the other hand, lower values of sweetness power for stevia were found by Moraes and Bolini (2010) and Marcellini et al. (2005) in ground roasted coffee (75) and concentrated and reconstituted pineapple juice (63), respectively.

The equivalent sweetness of neotame and sucralose are within the limits established by current Brazilian legislation (Anvisa, 2008). However, the concentrations found for the stevia extracts with different levels of rebaudioside A were higher than the maximum limits, which may be related to the strong bitterness present in stevia extracts that may have influenced the perception of sweetness. Marcellini et al. (2005) and Cardoso and Bolini (2007) also found higher results than those allowed by law in concentrated and reconstituted pineapple juice and peach nectar, respectively.

Conclusions

The optimum sucrose concentration in the acerola nectar was 80 g/L. Neotame had the highest sweetness power, followed by sucralose. The extracts of stevia leaves with different levels of rebaudioside A showed very similar sweetness power, and the stevia with 60% rebaudioside A showed the highest sweetness power. This study reinforces the importance of determining the sweetness equivalence of sweeteners in the processes of reduced-sugar foods and beverages.