Effect of variety and agro-ecology on physio-chemical and organoleptic quality of avocado fruit grown in Ethiopia

Abstract

Avocado is the most important fruit with high nutritional value in the tropics and subtropics. It is a widely grown cash crop in Ethiopia’s south, southwest, and east. However, the fruit quality of different varieties has not been studied at various locations. Therefore, the aim of this study was to evaluate the effect of variety and agroecology on the physio-chemical and sensory qualities of avocado fruit. This study used six varieties of avocados (Hass, Fuerte, Nabal, Bacon, Ettinger, and Pinkerton) and three avocado growing locations. The highest maximum values of total soluble solids, pH, and titratable acidity were found in varieties of Bacon at Wondo Genet (10.97%), Nabal at Debre Zeit (7.4), and Pinkerton at Wondo Genet (8.36%). All the study locations showed significant differences in total soluble solids, pH, and titratable acidity values (P > 0.05). Instrumental color measurement revealed statistical variations in the values of L*, a*, b*, chroma (C*), and hue angle among varieties and variety*location interaction (h^o). At Wondo Genet, Nabal (81.38%), Pinkerton (5.76%), Pinkerton (5.73%), and Hass (62.23%) had the highest moisture, ash, protein, and fat content, respectively. The grand mean values of color, appearance, aroma, taste, and overall acceptability for six different avocado varieties at three different locations were 3.72, 3.65, 3.72, 3.75, and 3.68, respectively. The results revealed that physio-chemical and sensory parameters vary with variety and agroecology. Therefore, it is recommended that avocados be grown with proper sensory and physicochemical properties included into the production system for both domestic and industry for various purposes.

Keywords:

• interaction
• location
• proximate, quality
• sensory

PUBLIC INTEREST STATEMENT

Avocado is a nutrient-dense fruit abundant in protein, minerals, and unsaturated fatty acids. Its oil plays significant roles in the pharmaceutical and cosmetics industries for a variety of applications. Avocado production has considerable potential in Ethiopia, where it is mostly cultivated and concentrated in the southern, southwest, and eastern areas. Avocados cultivated in those areas vary in size, color, taste, proximate composition, and other quality characteristics. It is frequently consumed fresh (as juice) or utilized in mixed with cooked split beans or fried egg. In Ethiopia, there is currently a tremendous chance for avocado processing for a wide range of commercial uses. Therefore, this research finding would help to select appropriate avocado varieties having better physicochemical and sensorial quality attributes that can be used in avocado processing in industries for different purposes based on avocado growing agro-ecologies that could compete both domestic and international markets.

1. Introduction

Avocado (Persea Americana Mill.) belongs to the Lauraceae family (Krumreich et al., 2018) and is one of the most important crops in the tropical and subtropical countries of the world (Indriyani et al., 2016; Ojewole et al., 2007). It is a climacteric fruit, which matures but ripens off the tree (Orhevba & Jinadu, 2011). The fruit makes up 65% of the pulp, 20% of the seed, and the skin is 15% (Özdemir et al., 2009). Persea Americana is a well-known plant in West Africa and while the fruit is edible, the bark; leaves, stem, and roots are used in local medicine (Maitera et al., 2014). Avocados have a high-fat content (between 71 and 88%) which is about 20 times higher than the average for other fruits. High consumption of P. Americana has been shown to have a beneficial effect on blood serum cholesterol levels (Onwuka, 2005). It is also a rich source of vitamins, such as vitamins C, E, K, B1, B2, B6, B9, and minerals such as phosphorus, sodium, magnesium, potassium, iron, and zinc (Maitera et al., 2014; Orhevba & Jinadu, 2011; Surukite et al., 2013). The fruit has high-fiber content compared to other fruits with 75% insoluble and 25% soluble fiber. Studies had shown that avocado fruit is rich in monounsaturated fatty acids (MUFA) and phytochemicals. This property of the fruit enables the population to use it as a therapeutic as well as healthy fruit (Nair et al., 2016). It also contains dietary fiber and essential nutrients (Fulgoni et al., 2013). Avocado has a major market share worldwide, for its use in the cosmetics, edible oil, and food processing industries (Indriyani et al., 2016). Compared to other sources of vegetable oil, the major fatty acids of avocado oil are oleic and linoleic acid and they are believed to have incredible health benefits as they help increase levels of HDL-cholesterol (the good cholesterol) and decrease levels of LDL-cholesterol (the bad cholesterol), both of which significantly reduce the risk of cardiovascular diseases (Lunn & Theobald, 2006). Avocado is also rich in unsaponifiable compounds, such as sterols, mainly b-sitosterol, vitamins, carotenoids, and tocopherols, and its phenolic compounds are of significant interest, for their antioxidant and anti-inflammatory properties (Kosińska et al., 2012; Zhang et al., 2013). In addition to its high content of good fats, avocado pulp also contains several hundred phytochemical molecules that may play a role in cancer prevention (Lu et al., 2005). Avocado is one of the most promising fruit crops in Ethiopia with the highest potential for production expansion. The volume of its production has quadrupled during the last five years and about 17% of the total acreage of fruit crops is covered with avocados (Hengsdijk et al., 2021) Avocados grow well in different regions of Ethiopia, the southwestern is the major production belt in this regard. The main crop season is from May to October and major avocado varieties grown in the country include Hass, Pinkerton, Fuerte, Bacon, Ettinger, and Nabal (Faris, 2016). These cultivars have different phytochemical compositions, physicochemical properties, and ripening times (Abebe et al., 2022). Barrett et al. (2010) have determined that some simple instrumental measurements of color (hue, chroma, the L value, and the whiteness index), soluble solids, changes in weight or juice leakage, and ascorbate content (as an indicator of nutritional value) may be used as indices of quality changes in fresh-cut fruits and vegetables. Besides, stages of maturity at harvest as well as storage time and origin of the plant material also influence most of the physical, biochemical, and proximate composition parameters of avocado. In quality terms, physicochemical variables serve as inspection parameters, as total soluble solids (TSS) and pH have been reported as quality indicators (Ferreira da Vinha et al., 2013; Özdemir et al., 2009). Therefore, the aim of this work was to evaluate the effect of variety and agroecology on the physio-chemical and sensory quality of avocado fruit collected from different locations.

2. Material and methods

2.1. Description of the study areas

This study was conducted on six released avocado cultivars grown in three agro-ecologies in Ethiopia. These sites include Melkassa, Debre Zeit, and Wondo Genet.

Melkassa is located at 8°24’N 39,021‘E, approximately 17 km from Adama city and 117 km east of Addis Ababa at an altitude of 1550 m.a.s.l. The site is located in the Upper Awash River Basin, the central rift valley of the country. It is characterized by low and erratic rainfall, with an average annual rainfall of 681.51 mm, peaking in July and August. The predominant soil type is the Andosol of volcanic with a pH between 7 and 8.2. The average annual temperature is 20.58°C with a minimum temperature of 12.46°C and a maximum temperature of 30.06°C (Table 1 and Figure 2). Debre Zeit is located 45 km southeast of Addis Ababa, the capital of Ethiopia, at latitude 8°44’N, longitude 38°58 E, 1900 meters above the sea level, and the average annual rainfall is 847.41 mm. The soil type is black (Vertosol) with a pH value of 6.0 to 7.5. Annual rainfall occurs during the long rainy season from June to September. The annual average maximum and minimum temperatures are 26.30 °C and 17.56 °C respectively (Table 1 and Figure 2). On other hand, Wondo Genet is located at 7°13’N latitude, 38°37 E longitude, about 273 km south of Addis Ababa, at an altitude of 1876 m.a.s.l. Sandy loam (nitisol) with an average pH of 6.4 is the predominant soil in Wondo Genet. The average annual rainfall in this region is 1525.71 mm, with a bimodal distribution in the two rainy seasons; the rainy season is short from February to April and long from July to September. The average annual temperature is 15.42°C with a minimum of 7.70°C and a maximum of 23.00°C. The detailed description of rainfall, temperature coordinates, and other agro-ecological features of the testing sites is presented in Table 1, Figures 1, and 2.

Figure 1. Mean monthly precipitation distribution at Debre Zeit, Melkassa, and Wondo Genet (1981–2021).

Source: NASA (2021).

Figure 2. (a) Mean, maximum and minimum monthly temperatures at Debre Zeit (1981–2021). (b) Mean, maximum and minimum monthly temperatures at Melkassa (1981–2021). (c) Mean, maximum and minimum monthly temperatures at Wondo Genet (1981–2021).

Source: NASA (2021).

Table 1. Summary of site descriptions for three studying locations in Ethiopia

Testing locations	Latitude	Longitude	Soil PH	Soil type	Rainfall (mm)	Altitude (m.a.s.l)	Annual average temperature (^oC)
							Minimum	Maximum	Average
Melkassa	8°24’N	39°21E	7 to 8.2	Andosol of volcanic origin	681.51	1550	12.46	30.06	20.58
Wondo Genet	7°13‘N	38°37‘E	6.4	Sandy clay loam (Nitosol)	1525.73	1876	7.70	23.00	15.42
Debre Zeit	8°44‘N	38°58‘E	6.0 to 7.5	Black heavy clay (Vertisol)	847.41	1900	9.05	26.30	17.56

Source: Melkassa Agricultural Research Center (MARC), Debre Zeit Agricultural Research Center (DARC), and Wendo genet Agricultural Research Center (WARC), meteorological stations’ data. m.a.s.l = meters above sea level, T° = Temperature. NASA power access Data; https://power.larc.nasa.gov/

2.2. Sample collection and preparation

Six avocado varieties (Hass, Pinkerton, Fuerte, Bacon, Ettinger, and Nabal) were harvested at the mature green stage (i.e., mature green unripe at which fruit is hard and tends not to bruise upon impact or fully mature (i.e., is the final stage of maturity at which avocado has a rough green skin with traces of yellow)). They were collected from three locations with similar ages of avocado trees from each site in 2019. Each variety has been established in different stands at MARC (Melkassa Agricultural Research Center), WARC (Wondo Genet Agricultural Research Center), and DARC (Debre Zeit Agricultural Research Center). The collected fruits were packed in a hard paper box and transported to Melkassa Food Science and Nutrition Research laboratory. On arrival at the laboratory, the fruits were stored at 24.05 ± 1.56°C at controlled room temperature with a relative humidity of 38.11 ± 4.03% for about a week and ripened. The uniformity of ripening of the fruits was maintained by ensuring that the fruit did not overlap or cross over (i.e., each fruit was separated from one another by space until ripened). This was applied to six avocado varieties. Ripe avocado fruit was used for all quality assessments. The ripened avocado fruits were well cleaned to remove any dust, washed with distilled water, dried, and weighed. Each ripened fruit was dissected, and the seed and skin were carefully removed from the pulp and weighed. The avocado pulp was sorted and dried in an oven at 45°C. The dried pulp was subjected to physio-chemical and proximate analysis. The ripened and fresh avocado pulp from each variety was prepared and subjected to sensory evaluation.

2.3. Experimental design

A Completely Randomized Design (CRD) comprising two factors (variety and location) was used, with six avocado fruits from each variety considered as replications.

2.4. Physico-chemical parameters

The pulp pH was measured by taking a sufficient quantity of avocado juice in a clean beaker with a 50 ml capacity and then immersing the electrode of the pH meter into the juice (Iroka et al., 2016). Total soluble solids (TSS in % 1:3 dilution) of the avocado flesh juice were determined using a Digital refractometer (Dhatt & Mahajan, 2007). Avocado pulp solution with distilled water was prepared in a 1:3 dilution, which was centrifuged (PLC-025 universal centrifuge, Gemmy Industrial Corp., Taipei, Taiwan) at 3000 rpm for 15 min, and the measurement was made by placing the drop of the supernatant at the digital refractometer. TSS reading was taken directly from the digital scale at 20°C ± 1, and results were expressed in percentage (1°Brix = 1% of sugar concentration when measured @ 20°C). Titratable acidity (TA in %) was determined by titration against 0.1N NaOH soluble using a few drops of phenolphthalein indicator, and values were calculated through the standard method (Visessanguan et al., 2005).

The color on the pulped flesh was determined using a colorimeter (Hunter Lab ARS00073, Virginia, USA) in terms of L* (lightness, darkness), a* (redness, greenness), and b* (yellowness, blueness) values. The system was standardized using the white and black tiles supplied by Hunter Lab for this instrument before starting color measurements on samples. The measurements were taken in triplicate, where L* represents lightness to darkness (0–100), a* represents redness (positive) and greenness (negative), and b* represents yellowness (positive) and blueness (negative) (Francis, 1998). Then, chroma (C*) = (a*²+b*²)^1/2 describes color intensity (vivid (red) versus dull (green)) and hue angle (h*) = tan⁻¹(b*/a*) which describes the position in color space was calculated.

2.5. Proximate composition

The proximate composition (moisture, fat, crude protein, and crude ash contents) of the avocado pulp was determined following the official standard method (AOAC, 2005). Moisture content was determined by drying the samples in an oven at 100°C to a constant weight according to (Method No. 930.15) (AOAC, 2005). The dried avocado pulp was subjected to other chemical analyses. Crude protein content (N × 6.25) was determined in accordance with the Kjeldahl method (Method No. 978.04) (AOAC, 2005). Crude fat was determined in accordance with the Soxhlet extraction method used (Method No. 930.09) (AOAC, 2005). Ash content was assayed by incinerating the samples in a muffle furnace at 550°C (Method No. 930.05) (AOAC, 2005).

2.6. Sensory evaluation

Fresh ripe avocado pulps were prepared and subjected to sensory evaluation. Twenty semi-trained panelists participated in the evaluation. The evaluation was carried out based on color, appearance, aroma, taste, and overall acceptability using a five-point hedonic scale, where 1 = dislike extremely, 2 = dislike moderately, 3 = neither like nor dislike, 4 = like moderately, and 5 = like extremely (Lim, 2011).

2.7. Data analysis

The collected data were subjected to analysis of variance (ANOVA) using statistix 10. The level of significance for all hypotheses was determined by a post hoc test, using a Fisher’s Least Significance Difference (LSD) test at the 5% significant level.

3. Results and discussions

3.1. Physio-chemical parameters

The main factors and interaction effects (variety and location) on physio-chemical properties such as total soluble solid (TSS in % 1:3 dilution), pH, and titratable acidity (TA in %) of avocado varieties are discussed as follows and indicated in Table 2 and Figure 3, respectively. Significant differences were observed regarding the value of total soluble solids (TSS in % 1:3 dilution) for variety Hass (7.95% 1:3 dilution), Pinkerton (7.04% 1:3 dilution), and Fuerte (5.65% 1:3 dilution) (p ≤ 0.05). The pH value (6.76) was maximum for variety Nabal and minimum (5.53) for variety Ettinger. There were significant differences in the value of pH for variety Nabal (6.76), variety Pinkerton (6.56), variety Hass (6.23), and variety Fuerte (5.94). Significant differences were observed among all values of pH, total soluble solids (TSS in % 1:3 dilution), and titratable acidity (TA in %) across all three locations (Melkassa, Debre Zeit, and Wondo Genet).

Figure 3. (a) Interaction effect of variety and location on the physio-chemical characteristics of avocado varieties at Melkassa. (b) Interaction effect of variety and location on the physio-chemical characteristics of avocado varieties at Debre Zeit. (c) Interaction effect of variety and location on the physio-chemical characteristics of avocado varieties at Wondo Genet.

Table 2. Effect of main factors (variety and location) on the physicochemical characteristics of avocado varieties

Variety	TSS (%) 1: 3 dilution	pH	TA (%)
Ettinger	5.66^C	5.53^E	5.11^CD
Fuerte	5.65^C	5.94^D	5.89^A
Hass	7.95^A	6.23^C	5.14^CD
Pinkerton	7.04^B	6.56^B	5.29^BC
Bacon	7.30^AB	5.98^D	5.49^B
Nabal	5.79^C	6.76^A	4.90^D
GM (%)	6.56	6.17	5.30
LSD (0.05)	0.31	0.04	0.13
CV (%)	32.67	15.37	39.60
Location
Debre Zeit	6.21^B	6.45^B	4.86^B
Melkassa	4.70^C	5.12^C	3.23^C
Wondo Genet	8.78^A	6.95^A	7.82^A
GM (%)	6.56	6.17	5.30
LSD (0.05)	0.24	0.03	0.09
CV (%)	34.64	15.16	38.77

Means followed by different letters in the same column are significantly different (P<0.05) according to Fisher’s Least Significance Difference (LSD) test. G.M= grand mean, CV=coefficient of variance, TSS=Total Soluble Solids, TA= Titratable Acidity.

The interaction effects of variety and location on the physicochemical characteristics such as TSS, pH, and TA analysis results are presented in Figure 3. Maximum values of total soluble solids (TSS in % 1:3 dilution) recorded were 10.97, 10.87, and 10.53 for variety Bacon, Hass, and Pinkerton at Wondo Genet, respectively, and the minimum was recorded for variety Ettinger (3.71) at Melkassa (Figure 3(a-c)). Liu et al. (2002) have reported that as the avocado fruit grew in size, the flesh tissue accumulated proportionally higher levels of total soluble solids corresponding to the increase in dry matter.

The suggestion to utilize total soluble solids as an indication of fruit ripeness, quality, and sweetness sprang from a desire for an accessible and quick analytical approach for measuring sugar concentration. Ferreira da Vinha et al. (2013) reported that consumers preferred when the TSS value of Hass avocado of Portuguese origin was 6.68°Brix.

Özdemir et al. (2009) have also reported that in Fuerte avocados, total soluble solid (TSS) content was 8.00% on the 80th day after full bloom and it increased to 10.07% on the 155^th day after full bloom. Then, it decreased and became 7.20% on the 245th day after full bloom. Then, it became 7.67% on the 275^th day after full bloom. This showed that the increase in total soluble solids (TSS) from one harvest time to another harvesting time was not consistent. Buelvas Salgado et al. (2012) have reported increases in °Brix during maturation. The lower amount of water and higher concentration of sugar result from transpiration processes and respiration phenomena, which originated from the climacteric behavior of the avocado, respectively. Maximum minimum values of pH were recorded for the variety Nabal (7.41) and Ettinger (3.86) at Melkassa, respectively. Statistical differences were observed among pH values for varieties Pinkerton (5.37), Fuerte (5.63), Bacon (4.20), and Ettinger (3.86) at Melkassa, varieties Pinkerton (6.97) and Bacon (6.35) at Debre Zeit and variety Ettinger (6.72) at Wondo Genet (Table 3). Soliva-Fortuny et al. (2004) have reported that pH values lie in the range of 6 to 6.5. Buelvas Salgado et al. (2012) have also reported and indicated that pH increases in the fruit maturity stage until approaching neutrality since most of the maximum values were equal or close to that point. In the literature, TSS (^oBrix) and pH have been reported as quality indicators (Ferreira da Vinha et al., 2013; Özdemir et al., 2009).

Table 3. Effect of main factors (variety and location) on the pulp color of avocado varieties

Variety	L *	a *	b *	C* (chroma)	h* (hue angle)
Ettinger	54.52^B	−3.40^B	34.39^D	34.71^D	82.46^AB
Fuerte	58.38^AB	−7.75^D	37.15^C	37.49^C	82.24^AB
Hass	46.05^C	−5.06^C	39.56^B	40.12^B	80.71^A
Pinkerton	49.87^C	−4.07^BC	40.08^B	40.37^CD	83.25^B
Bacon	54.53^B	−3.59^B	36.05^CD	36.37^CD	82.73^B
Nabal	58.83^A	−0.55^A	44.07^A	44.09^A	88.32^C
GM (%)	53.70	3.89	38.55	38.86	83.28
LSD (0.05)	1.92	0.49	0.84	1.70	1.95
CV (%)	11.76	−20.08	5.54	3.60	1.93
Location
Debre Zeit	50.99±8.35^B	−4.03±1.47^A	38.94±2.32^A	37.77^A	81.93^A
Melkassa	50.39±7.63^B	−3.76±0.25^A	39.46±2.63^A	39.20^A	84.101^B
Wondo Genet	59.70±6.66^A	−3.88±2.69^A	37.25±2.60^B	37.66^B	81.93^A
GM (%)	53.70	3.89	38.55	38.21	82.65
LSD (0.05)	1.36	0.35	0.60	1.20	1.38
CV (%)	14.11	−45.71	6.55	9.37	7.76

The data are expressed as means. Values followed by different letters in the same column are significantly different (P<0.05) according to Fisher’s Least Significance Difference (LSD) test. G.M= grand mean, CV=coefficient of variance, L *= difference in lightness and darkness (+ = lighter, – = darker), a *= difference in red and green (+ = redder, – = greener), b *= difference in yellow and blue (+ = yellower, – = bluer).

Al-Galil Rozan et al. (2021) found that six avocado cultivars (Ettinger, Fuerte, Hass, Marma, Pinkerton, and Reed) grown in Egypt had a pH of 6.4. This result makes avocado pulp a good choice for use in sweet and savory dishes because of its low acidity (Krumreich et al., 2018).

The titratable acidity value for the variety Ettinger (2.60%) at Melkassa was the lowest and for the variety Pinkerton (8.36%) at Wondo Genet was the highest (Table 3). Buelvas Salgado et al. (2012) have reported that titratable acidity tends to decrease during fruit storage and maturation. Titratable acidity (TA) decreases due to the consumption of organic acids in different metabolic cycles of the fruit, including tartaric acid, which predominates in avocado; Moreover, acids and carbohydrates are used to provide the energy that the fruit requires during the ripening process according to a research report by Taiti et al. (2015). Acidity is a typical quality feature of the fruit. Pedreschi et al. (2019) reported that tartaric acid is the most abundant acid in avocados. The organic acids in avocados do not significantly affect their quality or taste. This results in a high oil content that greatly improves the quality and flavor of the fruit, unlike other fruits that contain organic acids such as malic, citric, tartaric, and Others (Ahmed et al., 2010; Pedreschi et al., 2019).

Color is one of the important quality traits in food products and is formed by the chemical, biochemical, microbial, and physical changes which occur during growth, maturation, postharvest handling, and processing. Instrumental color measurement of food products is simpler and faster, and correlates well with other physicochemical properties and is also used as an indirect measure of other quality attributes such as flavor and contents of pigments. The L*, a*, and b* units in color measurement (objective means) are often used in food research studies to determine the uniform distribution of colors that are very close to human perception (subjective means) of color according to research reported by Sahin et al. (2011).

Color has a strong impact on consumer perceptions of quality, ranks prominently in food acceptability, and can be a predictor of non-sensory attributes such as moisture content, over-processing, and pigment content (Hutchings, 2006); Moyano et al., 2008). It can also be used as a direct quality estimate for fruits, beverages, oils, and even non-dairy emulsions (Granato & Masson, 2010); Moyano et al., 2008). For both industry and consumers, the color of the avocado’s skin serves as a key indicator of the fruit’s ripening stage (Cox et al., 2004; Villa-Rodríguez et al., 2011). The main factors and interaction effects (variety and location) on the pulp color of avocado varieties are presented in Tables 3 and 4, respectively. All maximum values of L*, a*, and b* were recorded for variety Nabal (58.83), (0.55), and (44.07), respectively, whereas the minimum value of L*, a*, and b* were found to be 46.05 for variety Hass, −7.75 for variety Fuerte, and 34.39 for variety Ettinger, respectively. Significant differences were not observed between the value of L* for location Debre Zeit (50.99) and Melkassa (50.39), the value of a* for location Debre Zeit (−4.03), Melkassa (−3.76) and Wondo Genet (−3.88), and value of b* for location Debre Zeit (38.94) and Melkassa (39.46) (P < 0.05) (Table 3). Most of the L* mean values of avocado pulp color were found to be more than 50, which indicated that the color was light (Table 4). Significant differences were observed among mean values of L* for variety Fuerte (67.25) and Nabal (50.37) at Wondo Genet, variety Fuerte (54.41) at Melkassa, and variety Hass (44.13) at Debre Zeit (P < 0.05) while no significant differences were observed for variety Nabal (52.24), Pinkerton (51.78) and Bacon (51.66) at Melkassa, variety bacon (51.66) at Debre Seit, variety Pinkerton (51.85) and Hass (50.37) at Wondo Genet (P < 0.05) (Table 4). The positive (redness) minimum and negative (greenness) mean a* values were recorded for variety Nabal (1.44) at Melkassa and variety Ettinger at Wondo Genet (−3.15). The positive maximum a* value was recorded for variety Ettinger (3.53) at Debre Zeit, and a negative maximum a* value was recorded for variety Hass (−7.92) at Wondo Genet. Prabha et al. (1980) have reported that the green color is due to chlorophyll presence and some varieties turn purple or black color due to anthocyanin presence. Significant differences were not observed among b values for variety Bacon (36.43) and Ettinger (36.59) at Melkassa, variety Bacon (36.43) and Ettinger (36.59) at Debre Seit. There were no significant differences among b* values for variety Nabal (44.38) at Melkassa, for variety Nabal (43.92) at Debre Zeit, and for variety Nabal (43.92) Wondo Genet (P < 0.05) (Table 4). The chroma (c*) (color maturation or intensity; degree of departure from gray toward pure chromatic color) and hue angle (h^o) (position in color space) are influenced by the coordinate values of a* and b* while measurement of the color. Hue angle can be interpreted as follows: 0° = red-purple; 90°= yellow; 180° = bluish-green; and 270° = blue (McGuire, 1992). The lowest vivid green-yellow color intensity (chroma=C*) was obtained for the variety Ettinger at Wondo Genet and the highest vivid green-yellow color intensity for the variety Nabal at Melkassa. On the other side, most of the values of hue angle (h^o) of varieties at each location were almost approaching 90° which indicated the yellow in color. The statistical significances were not observed among the hue angle (h^o) of Nabal at Melkassa (88.13°), Debre Zeit (88.42°), and Wondo Genet (88.42°) which were the highest values obtained (P < 0.05).

Table 4. Interaction effect of variety and location on the pulp color of avocado varieties

Location	Variety	L *	a *	b *	C* (chroma)	H^0 (hue angle)
Melkassa	Fuerte	54.41^BC	−4.72^BC	38.81^CDE	39.09^CDE	83.07^CDE
Melkassa	Nabal	52.24^CD	1.44^A	44.38^A	44.41^A	88.13^F
Melkassa	Pinkerton	51.78^CD	−4.23^BC	40.39^CD	40.870^CD	81.23^ABCD
Melkassa	Bacon	51.66 ^CD	−3.58^B	36.43^EFG	36.61^EFG	84.39^DE
Melkassa	Ettinger	48.62^CDE	−3.53^B	36.59^EFG	36.76^EFG	84.49^DE
Melkassa	Hass	43.66^E	−7.92^E	40.14^CD	40.57^CD	81.62^ABCD
Debre Zeit	Fuerte	53.48^BC	−5.81^CD	38.23^C-^F	38.67^CDEF	81.35^ABCD
Debre Zeit	Nabal	62.13^A	0.11^A	43.92^AB	43.94^AB	88.42^F
Debre Zeit	Pinkerton	45.97^E	3.48^B	40.87^BC	41.02^BCD	85.13^EF
Debre Zeit	Bacon	51.66^CDE	−3.58^B	36.43^EFG	36.61^EFG	84.39^DE
Debre Zeit	Ettinger	48.62^CDE	3.53^B	36.59^EFG	36.76^EFG	84.49^DE
Debre Zeit	Hass	44.13^E	−7.86^E	37.62^DEF	38.21^DEF	80.84^ABC
Wondo Genet	Fuerte	67.25^A	−4.66^BC	34.41^G	34.72^G	82.29^BCDE
Wondo Genet	Nabal	62.13^A	0.11^A	43.92^AB	43.94^AB	88.42^F
Wondo Genet	Pinkerton	51.85^CD	−4.50^BC	38.97^CDE	39.23^CDE	83.39^CDE
Wondo Genet	Bacon	60.28^AB	−3.60^B	35.29^FG	35.90^FG	79.41^AB
Wondo Genet	Ettinger	66.34^A	−3.15^B	30.00^H	30.62^H	78.42^A
Wondo Genet	Hass	50.37^CDE	−7.46^DE	40.91^BC	41.59^ABC	79.66^AB
GM		53.70	3.89	38.55	38.86	83.38
LSD (0.05)		3.32	0.85	1.46	3.37	1.93
CV		6.19	14.53	3.78	3.60	2.92

The data are expressed as means. Values followed by different letters in the same column are significantly different (P<0.05) according to Fisher’s Least Significance Difference (LSD) test. G.M= grand mean, CV=coefficient of variance, L *= difference in lightness and darkness (+ = lighter, – = darker), a *= difference in red and green (+ = redder, – = greener), b *= difference in yellow and blue (+ = yellower, – = bluer).

Earlier research revealed that alterations in weather conditions (precipitation, temperature, and elevation) might cause variations in the physicochemical characteristics of “Hass” and “Fuerte” avocados (Donetti & Terry, 2014; Landahl et al., 2009; Salameh et al., 2022). There were significant differences in the value of total soluble solids (TSS), titratable acidity (TA), and pH among different types of fruits from different locations and elevations (Dorey et al., 2016; Salameh et al., 2022; Uçkun & Aksoy, 2020). The most acidic fruits (like avocados and olives) were found to be from low-altitude locations, while the lower acidic fruits were mainly from high-altitude locations (Uçkun & Aksoy, 2020). The opposite trends were seen in the cases of different citrus fruits, with the most acidic fruit being harvested from high-altitude locations (Rokaya et al., 2016). The decrease in TA of ripened fruit may be due to the consumption of organic acids during respiration, which causes a decrease in the TA content.

3.2. Proximate composition

The effects of main factors (variety and location) on the proximate composition results are indicated in Table 5. The results showed that the average values of moisture content (wet basis) were found to be 77.27%, 71.43%, 74.04%, 67.75%, 69.36%, and 71.72% for variety Etttinger, Fuerte, Hass, Pinkerton, Bacon, and Nabal, respectively. The highest ash content was obtained from the variety Nabal (4.89%) and the lowest value (2.49%) for the variety Bacon. In this study, the average value of protein content was the highest for the variety Pinkerton (4.82%) and the lowest for the variety Bacon (2.61%). Significant differences were obtained among values of protein content for a variety of Pinkerton, Nabal, Hass, and Bacon. The crude fat content of the Hass variety was the highest (54.02%) and the lowest for the Nabal variety (35.49%) (Table 5). Nair and AC (2018) found that the protein content of four avocado cultivars ranged from 1.15 g/100 to 1.27 g/100. Similarly, Al-Galil Rozan et al. (2021) also reported the total protein content for six avocado cultivars which ranged between 1.87 ± 0.16% and 2.33 ± 0.21%. The nutritional value and quality of dietary protein are among the key factors affecting amino acid composition. Amino acids and their derivatives have been reported to affect the taste and quality of fruit (Ardö, 2006).

Table 5. Effect of main factors (variety and location) on the proximate composition of avocado varieties

Variety	Moisture (Wet basis) (%)	Ash (%)	Protein (%)	Fat (%)
Ettinger	77.27^A	2.92^C	2.90^D	43.10^E
Fuerte	71.43^C	2.69^CD	2.83^D	53.33^B
Hass	74.04^B	3.29^B	3.32^C	54.02^A
Pinkerton	67.75^D	5.09^A	4.82^A	52.59^C
Bacon	69.36^D	2.49^D	2.61^D	51.14^D
Nabal	71.72^C	4.89^A	4.51^B	35.49^F
GM (%)	71.93	3.56	3.50	48.30
LSD (0.05)	0.80	0.14	0.15	0.34
CV (%)	7.07	21.31	21.76	12.81
Location
Debre Zeit	69.82^C	2.70^B	3.45^B	43.94^C
Melkassa	73.89^A	3.96^A	3.04^C	49.89^B
Wondo Genet	72.08^B	4.02^A	4.01^A	51.01^A
GM (%)	71.93	3.56	3.50	48.30
LSD (0.05)	0.57	0.10	0.11	0.24
CV (%)	7.80	5.48	30.87	17.87

The data are expressed as means. Values followed by different letters in the same column are significantly different (P<0.05) according to Fisher’s Least Significance Difference (LSD) test. G.M= grand mean, CV=coefficient of variance.

The interaction effects of variety and location on the proximate composition such as Moisture, Ash, Protein, and fat content are indicated in Figure 4(a-c). Moisture content for variety Nabal (81.38%) at Wondo Genet was found to be the highest and variety Pinkerton (61.92%) at Debre Zeit was the lowest (Figure 4(a-c)). Nnaji and Okereke (2016) and Tango et al. (2004) reported that the highest moisture content explains the fact that it had the lowest oil yield. Nair and AC (2018) reported the moisture content of four avocado cultivars: Pollock (86%), Kallar Round (86.75%), and Purple Hybrid (77.25%) grown in Kerala, India. The moisture content of a fruit determines its shelf-life quality (i.e., fruits with high moisture content deteriorates easily).

Figure 4. (a) Interaction effect of variety and location on the proximate composition of avocado varieties at Melkassa. (b) Interaction effect of variety and location on the proximate composition of avocado varieties at Debre Zeit. (c) Interaction effect of variety and location on the proximate composition of avocado varieties at Wondo Genet.

There were no significant differences among ash content (%) for variety Ettinger (3.31%) and Fuerte (3.13%) at Melkassa and variety Hass (3.20%) at Wondo Genet. Maximum ash content was recorded for variety Pinkerton (5.76%) at Wondo Genet and minimum for variety Fuerte (1.52%) at Debre Zeit. Ash content determines the total minerals found in the food sample. Al-Galil Rozan et al. (2021) opined that the ash content of six avocado cultivars ranges between 1.16 ± 0.11 % and 1.73 ± 0.11% on a wet basis. Similarly, there were no significant differences among protein content (%) for variety Nabal (3.38%), Pinkerton (3.31%) and Ettinger (3.50%) at Melkassa, variety Hass (3.52%) at Debre Zeit, and variety Fuerte (3.35%), Hass (3.45%) and Bacon (3.21%) at Wondo Genet. The highest crude protein content was recorded for variety Pinkerton (5.73%) at Wondo Genet, whereas the lowest was for variety Bacon (2.00%) at Melkassa. Crude fat content ranged between for variety Nabal (33.40%) at Wondo Genet and variety Fuerte (62.23%) at Melkassa and variety Hass (62.23%) at Wondo Genet. Significant differences were observed in most of the crude fat content avocado varieties (P < 0.05) (Figure 4(a-c)). Nasri et al. (2021) have reported that the fat content was 44.69, 55.71, 56.25, and 72.54 for Fuerte, Hass, Reed, and Ettinger, respectively. The lipid (saturated) content of the avocado is a very low significant amount of cholesterol, which lowers harmful triglycerides without raising the low-density lipoprotein (LDL) (bad cholesterol) level of the body by 22%, and it also increases the high-density lipoprotein (HDL) (healthy or good cholesterol) level by 11%, because it contains a high content of both monounsaturated (MUFAs) (oleic and palmitoleic fatty acid) and polyunsaturated (PUFAs) (linoleic fatty acid) fats, which play a great role in controlling the risk of cardiovascular-related diseases (Carvajal-Zarrabal et al., 2014; Jakobsen et al., 2009; Nasri et al., 2021; Sacks et al., 2017; Wang et al., 2015; Wardlaw & Kessel, 2002). The variation in avocado flesh compositions differs depending on the cultivars, stage of maturity, and the geographical area where the plant was grown (Mooz et al., 2012). Negative correlations were observed between moisture and lipid content. It is shown that these two components account for the majority of the fruit pulp, except for the butter pear kind, which exhibited greater quantities of carbohydrates compared to lipids (Mooz et al., 2012; Tango et al., 2004). Climatic characteristics (rainfall/precipitation, temperature, altitude, and other variables), soil properties, and agronomic practices (pruning, use of fertilizer, and others) greatly influence the overall nutritional composition (macro and micro-nutrient) of fruits and vegetables (Aguirre-Arcos et al., 2022; Bhattacharjee et al., 2022; Fischer et al., 2022; United Nations, 2003).

3.3. Sensory evaluation

The effects of the main factors (variety and location) on the sensory evaluation of avocado varieties are presented in Table 6. Sensory evaluation was assessed for color, aroma, taste, appearance, and overall acceptability with 20 semi-trained panelists used in assessing the sensory attributes of avocado fresh pulp. Significant differences were observed between the value of the color for variety Hass (4.05) and for variety Nabal (3.57). The highest aroma value was recorded for variety Hass (3.90) and the lowest for variety Fuerte (3.52). Results of the sensory analysis show that there was no significant difference (P < 0.05) in the taste value of all the avocado varieties. The range of overall acceptability result falls between 3.52 and 3.95. There were no significant differences between values of color, appearance, aroma, taste, and overall acceptability at Debre Zeit and Melkassa, respectively (P < 0.05) (Table 6).

Table 6. Effect of main factors (variety and location) on the sensory evaluation of avocado varieties

Variety	Color	Appearance	Aroma	Taste	Overall acceptability
Ettinger	3.52^B	3.48^B	3.62^AB	3.81^A	3.76^AB
Fuerte	3.67^AB	3.48^B	3.52^B	3.57^A	3.48^B
Hass	4.05^A	3.86^A	3.90^A	3.86^A	3.95^A
Pinkerton	4.00^A	3.86^A	3.76^AB	3.81^A	3.86^A
Bacon	3.52^B	3.48^B	3.62^AB	3.76^A	3.52^B
Nabal	3.57^B	3.43^B	3.48^B	3.71^A	3.52^B
GM (%)	3.72	3.60	3.65	3.75	3.68
LSD (0.05)	0.20	0.19	0.18	0.20	0.17
CV (%)	18.63	18.05	19.36	18.00	16.61
Location
Debre Zeit	3.64^B	3.45^B	3.40^B	3.57^B	3.48^B
Melkassa	3.55^B	3.45^B	3.43^B	3.62^B	3.57^B
Wondo Genet	3.98^A	3.88^A	4.12^A	4.07^A	4.00^A
GM (%)	3.72	3.65	3.72	3.75	3.68
LSD (0.05)	0.14	0.13	0.13	0.14	0.12
CV (%)	18.61	17.59	16.90	16.81	16.01

The data are expressed as means. Values followed by different letters in the same column are significantly different (P<0.05) according to Fisher’s Least Significance Difference (LSD) test. G.M= grand mean, CV=coefficient of variance.

Color values for variety Hass (4.29) at Melkassa were the highest and variety Fuerte (3.14) at Melkassa and variety Ettinger (3.14) at Debre Zeit were the lowest value. Significant differences were not observed among the values of appearance for variety Fuerte (3.14) and Ettinger (3.14) at Melkassa and for variety Nabal (3.14). The aroma values for variety Fuerte (4.43) and for variety Pinkerton (4.43) at Wondo Genet were the highest and variety Fuerte (3.00) at Debre Zeit were the lowest (Figure 5(a-c)). The taste values for variety Hass (4.14) at Melkassa and variety Nabal at Wondo Genet (4.14) were found to be the highest and the lowest taste value (3.29) for variety Fuerte at Melkassa. The hedonic score during avocado maturation is associated with the fruit becoming creamier and less watery in texture with a flavor that is richer with less grassiness (higher grassiness rating) according to research reported by Obenland et al. (2012). The overall acceptability value for variety Fuerte at Melkassa and Debre Zeit was the lowest (3.14) and the highest for the variety Hass at Melkassa with a value of 4.29. Sensory evaluation is generally the most important test of consumer perception of soft-textured processed foods such as mayonnaise, spreads, ketchup, and yogurt (Sharoba et al., 2005). In addition to being used in the preparation of other dishes, avocado is consumed in a variety of ways in Mexico and the northern South of the United States, including in puree salads and as a pro with salt, pepper, vinegar, and other condiments (Koller, 1992). In Brazil, ripe fruit is more popular along with sugar, honey, and liqueurs. The sensory and nutritional qualities of the fruit have a significant impact on consumption (Luíz et al., 2007).

Figure 5. (a) Interaction effect of variety and location on the sensory evaluation of avocado varieties at Melkassa. (b) Interaction effect of variety and location on the sensory evaluation of avocado varieties at Debre Zeit. (c) Interaction effect of variety and location on the sensory evaluation of avocado varieties at Wondo Genet.

4. Conclusions

Avocados are highly nutritious fruits that are locally abundant but have a small local market, especially lacking value addition of this fruit in Ethiopia. All quality parameters analyzed in this study have their own impact on avocado quality and acceptability. Based on the agroecological and variety/cultivar considerations, organoleptic quality characteristics such as color, appearance, aroma, and taste are very important to improve the use and acceptance of avocados not only by consumers but also by the food and pharmaceutical industries. Other quality characteristics, including pH (acidity or basicity indicator), TSS (i.e., attributed to carbohydrates conversion), TA, crude protein content, ash (total minerals) content, and moisture content, have a significant impact on the quality and quantity of lipid or oil content obtained from avocado, which is used in industry for a variety of purposes. An alternative to oil extraction that has significant commercial potential is a variety with high lipid content in the pulp. Total Soluble Solids (TSS), titratable acidity (TA) (i.e., is linked with both sweet and sour tastes), acidity level (pH) and moisture or water content (shelf-life determinant) are some maturity indicators of the fruits that determine the appropriate harvesting time or peak, which is one of the strategies to minimize the post-harvest losses of the horticultural crops. All those statements stated above are crucial ideas and methods of value addition on avocado fruit in terms of its increased utilization, reduced post-harvest loss, and overall acceptability not only on the domestic market but also on the international market too.

In general, the Hass variety that grows in Wondo Genet has the highest pH value, TSS, TA, fat content, and sensorial acceptability compared to varieties that grow in Debre Zeit and Melkassa locations. The highest fat content and L* (white) value of pulp color were recorded in the Fuerte variety in Melkassa and Wondo Genet locations, respectively. Color results of pulped avocado fruits obtained from the instrumental reading revealed that cumulative chroma (C*) and hue angle (h^o) results were influenced by the values of a* (negative = greenness) and b* (positive = yellowness). The differences among the avocado pulp compositions regarding physicochemical, proximate, and hedonic tests vary with cultivars and geographic location of plant growth. From these findings, the results revealed that there are variations in physio-chemical and sensory characteristics due to variety and agroecology. Therefore, it is recommended to cultivate avocados by taking into consideration and associating physicochemical and sensory quality characteristics into the productive system for domestic as well as industrial potentials for various purposes and further research studies should be conducted on amino acid profile avocado varieties at different locations.

Author contributions

D.A.K. conceived and performed the experiments, analyzed data, interpreted the results and wrote the paper. M.Z. supervised the experimental work, and A.Y. performed the experiment and reviewed the paper.

References

Acknowledgment

The authors are indebted to Fruit Breeding team of Melkassa, Debre Zeit, and Wondo Gent Agricultural Research Centers for supplying avocado varieties.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research work described in this paper was supported and funded by the Ethiopian Institute of Agricultural Research, Food Science and Nutrition Research Directorate.

Notes on contributors

Demirew Abera

Demirew Abera. I graduated from Adama Science and Technology University in master’s degree in Synthetic Organic Chemistry. For the past 8 years, I have worked as a Food Science and Nutrition researcher at the Ethiopian Institute of Agricultural Research in Melkassa Agricultural Researcher Center, Ethiopia. My current research interests are in horticulture (fruits and vegetables), legumes, and cereals, as well as value addition to those crops in terms of food quality, nutrition, processing, utilization, and food safety. I am currently pursuing my PhD in Food Science and Technology at Jimma University in Ethiopia