Research Article
Nutritional Profile and Physicochemical Properties of Improved Apple (Malus Domestica L.) Varieties in Ethiopia
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Because of its significant advantage for many households including youth different areas like job creation, medicinal property, nutritional worth, income generate, conservation of soil and the environment, apple appears to be one of the potential and strategic fruit crops in the highlands of the country. This research was, therefore, conducted to test nutritional profile and selected physicochemical properties of different apple varieties in Ethiopia. The experiment was carried out at Holeta agricultural research of the EIAR using 13 improved apple varieties planted in the field. The results showed that fruits of improved apple varieties had greater amount of ash (1.645%), protein (2.049%), fat (0.407%) and fiber (6.136%) than the standard reference (0.366, 0.443, 0.223, and 2.786%, respectively) but, lower carbohydrate content and energy value (89.757, and 370.90% respectively). They also exhibited higher mineral content (K (0.444%), Mg (0.024%), Fe (62.964%) and Zn (4.081%)) than the standard reference (0.120, 0.005, 1.600, and 0.447%, respectively), except for Ca (0.015%) while the fruit quality result revealed low moisture content and high titrable acidity (TA) (1.177%) and total soluble solid (TSS) content(13.333%). Nevertheless, variations among the thirteen apple varieties were significant for proximate composition and mineral content as well as for moisture content, total soluble solid and titrable acidity. The study also showed that the improved apple varieties fit the WHO standard nutritional quality of proximate and mineral values, but not for carbohydrate and calcium contents.
Keywords: Apple varieties, Mineral, Nutrient content, Physicochemical
INTRODUCTION
Nutritional and functional characteristics of fruits are closely related to their quality and are usually influenced by genotype and ripening stage, as well as by environmental conditions and orchard management practices [1]. Apple (Malus domestica L.), is an exogenous crop to Ethiopia since it’s a temperate region. It has phosphorus and sodium minerals, important in human nutrition which has a role in bone and teeth formation and other important body functions [2]. It also a good source of soluble carbohydrates such as starches, sugars and a fiber pectin, which helps to reduce cholesterol levels in humans by lowering the secretion of insulin [3,4]. Despite this nutritional advantage, previously apple production was restricted to some pocket areas of southwestern Ethiopia [5]. Subsequently, its production has been expanded in several highland areas of Gamo Gofa, Sidama, Gedeo and Guraghe zones of South nation nationality population (SNNP) region, North Shewa, Arsi and Addis Ababa Zuria of Oromia region, North Shewa, North and South Wello, North and South Gondar and West and East Gojam zones of Amhara region [6], through the support of government and nongovernment institutions, and private growers including smallholder farmers [7].
Growing apple, therefore, is becoming an important horticulture activity in the highlands of Ethiopia which helps farmers to balance their diets, serve as cash crops to generate incomes, diversify production, conserve soil and environment and create employment opportunities for many households including youths and women [8]. Although apple growing is new for the Ethiopian farming community, it has been found as it is highly promising and financially feasible both in terms of fruits and seedlings production and becoming an interesting business for both rural and urban smallholders [9,10].
The rise in demand for apple is mainly due to the transition to a wide urban middle-income class and lifestyle change of consumers in Ethiopia. Ethiopian fruit import in general, apple import, in particular, increased from 350 tons in 2007 to 50,000 tons in 2016 excluding fruit syrup imports [11,12].
Apple varieties are a source of vitamin C, potassium, dietary fiber, and folic acid. They also contain calcium, iron and have a high protein quality, ratio of mg amino acid/gram protein, low in sodium and fat content. Apples are also cholesterol-free and provide dietary fiber, vitamin C, vitamin B6, potassium, and other key nutrients.
So far about 13 apple varieties have been improved and adopted through research from Ethiopian Institute of Agricultural Research, Holeta agriculture research center, and these varieties were demonstrated to consumers and they are being used for house consumption and local markets. However, information on their nutritional profile and quality parameters are scanty [13]. The present study was therefore, conducted to determine the nutritional quality and physicochemical properties of thirteen improved and released apple varieties in Ethiopia.
MATERIALS & METHODS
Experimental set up
The experiment was conducted using samples collected from the existing field that at Holeta agriculture research center (HARC) in the 2018 off season (January-May) at soil and nutrition laboratory. The center is found in the Ethiopian highlands, 34 km away from Addis Ababa in the west direction, located at 9°4'N latitude and 38°30’ E longitudes and at an altitude of 2391 meter above sea level. The mean maximum and minimum temperatures in the center is 22°C and 6°C, respectively. The center receives mean total annual rain fall of 1144 mm with erratic distribution. The soils are Nitosol and Vertisol and the soil texture class is mainly Clay to clay loam with pH of 3.8-6.2 [14]. Standard reference was from national nutrient data base for standard reference apple fruits released by USDA American food distribution program [15].
Sample collection
For quality analysis fruit of 13 apple varieties Anna, Princisa, Dorset Golden, Gala Must, Granny Smith, Ariwa, Royal Gala, Jona Gold, Yataka Crispin, Elaster, Red Delicous, Jona Gored and Winer Banana were collected from experimental plots and cured in the store. Finally, the cured apples fruits were sampled and then unnecessary plant impurities as gravels and others were removed. Depending up on the purpose of analysis, two types of sample preparations methods were followed. In the first method, the samples were ground into fine powder by using automatic gridding machine, sunlight dried and ready ready for physicochemical (Ash, Crude protein, Crude fat, and Crude fiber) analysis. The powdered samples were stored in an airtight bottle at room temperature until further analysis. In the second methods, cleaned fruit samples were ground by grinding machine and filtered and the aliquot liquid or juice was and immediately analyzed for physicochemical analysis (TSS, TA, pH, Color, Juice volume and juice weight) within less than 8 h [16].
Determination of physical parameters
Total soluble solid was determined by using refractometer Index drop of apple juice while titer gridding able acidity was determined by titrating certain juice volume using NaOH as a titrant and phenolphthalein indicator until the pH has come to 8.1, and pH determined by using potentiometric after pH meter calibrated using buffer solution 4, 7 and 9.2 [17]. 80 g of fresh fruity was weighed and prepared the juice. Measure the prepared juice volume (JV) was measured using cylinder and juice weight (JW) was determined by weighing the certain mass using analytical balance. The result was calculated as follows [17]:
JW (%) = (Juice Weight ) / (Weight of original sample) x 100 (w/w)
JV (%) = (Juice Volume)/(Weight of original sample) x 100 (v/w)
Determination of proximate composition of apple varieties
Determination of moisture content: The moisture content of the powdered apple sample was determined in an oven through the drying method (at 105°C) according to the procedure described in AACC (2000). The moisture content in the sample was determined as follows [18]:
Moisture Content (%) = (Weight of original sample - Weight of dried sample) / (Weight of original sample) x 100
Determination of ash content: Ash is an inorganic residue remaining after the material has completely burnt at a temperature of 550°C in a muffle furnace. It is the aggregate of all non-volatile inorganic elements. About 3 g of finely ground dried sample was weighed into a porcelain crucible and incinerated at 550°C for 6 h in an ashing muffle furnace until we got ash. Then the ash was cooled in desiccators and reweighed [17]. We calculated ash content in the apple sample as:
Ash (%) = (Weight of ash) / (Weight of original sample) x 100
Determination of crude proteins: The powdered apple sample was tested for crude protein content according to the Kjeldahl’s method as described in AOAC, which involved protein digestion and distillation and titration. The % nitrogen was calculated using the formula:
Determination of crude proteins: The powdered apple sample was tested for crude protein content according to the Kjeldahl’s method as described in AOAC, which involved protein digestion and distillation and titration. The % nitrogen was calculated using the formula:
% Nitrogen = ((Vs-Vb) x Macid x 0.01401) / (Weight of original sample) x 100
Where, Vs=Volume (ml) of acid required to titrate sample; VB=Volume (ml) of acid required to titrate the blank; M acid=Molarity of acid; W=Weight of sample:
Then, the percentage of crude protein in the sample was calculated from:
Where as, F (the conversion factor) is equivalent to 6.25 [17].
Determination of crude fat: Crude fat was determined using digital SoxtecTM 8000 through the steps of boiling, rinsing, recovery, and auto-shutdown and finally using the gravimetric method [19]. The fat content in the sample was calculated using the formula:
Fat (%) = (Weight of fat) / (Weight of original sample) x 100
Determination of crude fiber: About 2 g of a fat-free sample of powdered apple was taken into a fiber flask and 100 ml of 0.255 N H2SO4 was added. Then the mixture was heated under reflux with a heating mantle for 1 h. We filtered the hot mixture through a fiber sieve cloth. The residue returned into the flask to which 100 ml of 0.313 M NaOH was added and heated under reflux for another one hour. We filtered the mixture through a fiber sieve cloth, and we added 10 ml of acetone to dissolve any organic constituent. The residue was washed with 50 ml of hot water twice on the sieve cloth before. We finally transferred in the pre-weighed crucible. The crucible with residue was oven-dried at 105°C overnight to drive off moisture. The oven-dried crucible containing the residue was cooled in a desiccator and later weighted (W1) for ashing at 550°C for 4 h. The crucible containing white and grey ash (free of carbonaceous material) was cooled in desiccators and weighted to get W2. The crude fiber in the sample was calculated as follows [19].
Fiber (%) = (W_1-W_2) / (Weight of sample) x 100
Fiber (%) = (W_1-W_2) / (Weight of sample) x 100
Determination of Total Carbohydrate: The difference method determined the total percentage of the carbohydrate content in the apple sample. This method involved adding the total values of crude protein, lipid, crude fiber, moisture and ash constituents of the sample and subtracting it from 100. The value obtained is the percentage of carbohydrate constituent of the sample [17]. Thus:
% Carbohydrate =100- (% Moisture + % Crude fiber + % Protein + % Lipid + % Ash)
% Carbohydrate =100- (% Moisture + % Crude fiber + % Protein + % Lipid + % Ash)
Determination of Energy Value: The energy value of the samples was determined by multiplying the protein content by 4, carbohydrate content by 4 and fat content by 9 [3].
Energy Value = (Crude protein x 4) + (Total carbohydrate x 4) + (Crude fat x 9)
Determination of Vitamin C: Redox titration determined vitamin C using Iodine solution of juice sample and finally determine the titrate required for standard [20].
Determination of Mineral content
About 1 g of finely ground powder sample was weighed into a porcelain crucible and incinerated at 550°C for 3 h in an ashing muffle furnace until ash was obtained. The ash was cooled in desiccators and soaked by 2 mL of 37%HCl and 3 dops of distilled water. The soaked sample was extracted in 50 ml volumetric flask using filter paper and funnel and the aliquot was used to determine macro and micro minerals determined using atomic absorption spectrophotometer (AAS) after calibrated using standard solution for each element [21].
Macro and micronutrient were calculated as follows:
Macronutrient Content (%) = ((R-B) * Tv * Df) / (Weight of sample)
Micronutrient (mg/Kg) = ((R-B) * Tv * Df)/(Wt *10,000)
Whereas, R: Sample Reading; B: Blank reading; Tv: Total volume of aliquot extracted (50 mL); Df: Dilution factor when sample concentration above the calibration carve the sample concentration diluted by distilled water.
Statistical analysis
The results were subjected to analysis of variance (ANOVA) technique by statics 10.0 using completely randomized design (CRD) method, and all pair-wise comparison tests were used for mean comparison, whereas the least significant difference test was used for mean separation technique at P ≤ 0:05 [22].
RESULTS & DISCUSSION
Physicochemical properties among apple varieties
Moisture content of fresh apple fruits of different varieties was higher than the WHO standard and showed significance difference among the varieties (Table 1). However, the difference among variety Winter banana, Elester, Jona gold and Anna, and between Crispin, Red delicious and Ariwa was not significant. Similarly, there was no significant difference between variety Dorset golden and Granny smith, and between Princisa and Royal gala but significant difference was observed among Crispin, Red delicious and Ariwa for moisture content.
Regarding juice volume and juice weight no significant difference among varieties in JW but significant difference in JV between Ariwa and Crispin and between Princisa and Jona Gold and also among Anna, Dorset Gold, and Jona Gored but the significant difference among Gala Must, Grannymith, Royal Gala, Yataka, and Red Delicious at p≤0.05. Titrable acidity showed no significant difference among variety Gala must, Gray smith, Royal gala and Red delicious, and between variety Anna, Elester and Crispin, but it was significantly difference for the remaining seven varieties (Table 1).
The total soluble solid (TSS) content was statically similar for variety Yataka and Jona gored, and for Princisa and Ariwa. The difference among variety Anna, Dorset, Royal gala, Elester and Winter banana was not significant, but it was significant between variety Crispin and Red delicious for TSS (Table 1) [23]. Vitamin C result shows no significant difference between Princisa and Ariwa, between Dorset Golden and Jona Gored, and between Red Delicious and Granny Smith and also no significant difference among gala must, Elaster and among Yataka, Crispin and Winter Bananat p≤0.05 (Table 1).
Proximate nutritive value
Moisture content of apple fruits showed no significant difference among all varieties except for Jona Gored at p≤0.05. The result of ash content of apple fruits showed that all varieties had higher values than the WHO standard which fit WHO. Nevertheless, there was different varietal difference for ash content, though difference among variety Princisa, Ariwa and Winter banana, and variety Gala must, Dorset golden, Gray smith, Jona gold, Yataka, Elester and Jona gold where not significant (Table 2).
All varieties showed higher values than the standard reference for protein content. However, there was not significant difference among variety Granny smith, Dorset, Ariwa, Red delicious and Winter banana, and between gala must, Jona gored among Jona gold, Royal gala and the standard (Table 2). Fat content of apple varieties was higher than the standard reference USDA (2018) [21] and there was no significant difference between variety Anna and Granny smith, and Crispin and Winter banana, as well as between variety Yataka and the standard. Similarly, the difference among variety Princisa, Gala must, Jona gold, and between Royal gala, Elester and Jona gored was not significant, but variety Dorset and Ariwa significantly different from others and from each other for fat content (Table 2).
There was significant difference (p≤0.05) among apple varieties for crude fiber content of fruits. However, the difference among varieties Ariwa, Royal gala, Gala must and Jona gold, and between varieties Anna, Jona gored and Winter banana as well as between variety Princisa, Dorset and Yataka and between Elester and Red delicious was not significant. On the other hands, significant difference was observed between variety Crispin and the standard for crude fiber content (Table 2).
Although, they showed no result significant difference between variety Gala must and Winter banana, Ariwa and Jona gold, and among Princisa, Dorset golden and Red delicious varietal response was generally significant for fruit carbohydrate content (Table 2). Similarly, energy value showed no significant difference among variety Royal gala, Dorset, Yataka and Crispin, and among variety Anna, Princisa and Jona gored, and between Grany smith, Jona gold and Winter banana. But significant difference was observed between variety Elester and Red delicious, and between Ariwa and Gala must for energy value (P ≤0.05) (Table 2) [23].
There was no significant difference between variety Dorset and Gala must, and between Red delicious and Jona gored as well as between Royal gala, Elester and Crispin, though other varieties showed significant difference for K content (Table 3).
Similarly, fruits Ca content showed no significant difference between variety Anna and Ariwa, Red delicious and Jona gored and among Gala must, Gray smith, Yataka and Elester, as well as between variety Dorset golden, Jona gold and Winter banana, but there was significant difference between the other varieties (Table 3). In general, fruit content both K and Ca in apple varieties was in agreement with the finding of researcher and higher than the standard reference. The result of Mg content in apple fruits showed no significant difference between variety Gala must and Red delicious, Princisa, Dorset and Ariwa and Anna among variety Royal gala, Yataka, Crispin, Elester and Jona gored (Table 3). The results obtained phosphorus and sulfur lower but higher than standard reference, and we observed significant differences among varieties at P≤0.05.
Micronutrient content among apple varieties
In this studied fruit Cu, Mn, Fe and Zn content of apple varieties were higher than the standard reference and in agreement with the finding of researcher. It was observed that there was no significant difference between variety Winter Banana and Red Delicious, and Royal Gal and Yataka as well as between Granny smith and Jona Gored for Fe content (Table 4). Similarly, fruit Zn content showed no significant difference between variety Princisa and Ariwa, Gala Must and Granny Smith, and between Royal Gala and Yataka but the difference among other varieties was significant difference (Table 4).
The result of Cu in apple varieties were showed no significant difference between variety Princisa and Ariwa, and among variety Gala Must, Grany Smith and Winter Banana and also among variety Royal Gala, Crispin, Elaster and Jona Gored but no significant difference among Anna, Dorset Golden, Yataka and Winter Banana at P≤0.05. It was observed that the result of Mn in apple varieties showed no significant difference between variety Granny Smith and Ariwa, between variety Gala Must and Princisa, between variety Dorset Golden and Jona Gold and also among variety Anna, Jona Gored and Elaster but, significant difference among Royal Gala, Yataka, Red Delicious and Winter Banana at p≤0.05 (Table 4).
CONCLUSION
The result of mean proximate composition showed that improved apple varieties have greater amount of ash, protein, fat and fiber than the standard reference but lower in carbohydrate content and energy value. In addition, these varieties were characterized by being firmer and more showed the highest amount of fiber, protein, and minerals such as Ca and P. Significant differences were observed among the apple varieties for proximate composition and mineral content. The study also showed that the improved apples varieties full fill the WHO quality standards in proximate composition and mineral content and over all nutritive value, except for carbohydrate and Calcium. However, further studies are required for sensorial, bioactive and antibiotic compounds to cosine up with a more comprehensive conclusion.
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