Effect of Processing Methods on Nutrient Contents of Sweet Potato (Ipomoea Batatas L. Lam.) Varieties Grown in Ethiopia

Keywords

Minerals; Proximate Composition; Sweet Potato; Vitamin C.

Introduction

Sweet potato [Ipomoea batatas (L.) Lam.] is a key crop in most eastern and southern African countries, including Uganda, Rwanda, Kenya, Tanzania, Ethiopia, Zambia, Mozambique, and South Africa [7]. Sweet potatoes are the world's seventh most important food crop and the world's second-largest tuber crop, behind Irish potatoes. It produces 124 million tons per year. It trails only Irish potato and cassava in terms of acreage (9.1 million ha) among root and root crops. Sweet potato is Africa's second-largest root crop after cassava, with production concentrated in East Africa [10].

For at least 20 million Ethiopians, sweet potatoes are one of the most essential crops. In terms of sweet potato production, Ethiopia is ranked fifteenth [14]. In 2010, Ethiopia produced 736,000 MT of sweet potatoes, the highest year in FAOSTAT records and the ninth most among African countries. The majority of sweet potatoes are grown in Ethiopia's southern and eastern areas. White-fleshed sweet potatoes are a staple diet for the Southern Regional State's 13 million residents. All of Ethiopia's sweet potato roots are consumed in the domestic food supply, according to the FAOSTAT study [5].

In the context of African cropping systems, sweet potato has several advantages: I it produces food in a relatively short period of time, ii) it yields reliably in sub-optimal growth conditions, iii) it requires lower labor inputs (suitable for vulnerable households), v) it serves as an alternative food source for urban populations facing rising cereal prices, and v) it provides a potential option to reduce vitamin A deficiency [17].

Antioxidants, fiber, zinc, potassium, sodium, manganese, calcium, magnesium, iron, vitamin C, and -carotene are all found in sweet potatoes [8, 11].

Vitamin A insufficiency is a public health issue in Ethiopia, as it is in other countries of Sub-Saharan Africa. Vitamin A insufficiency can cause child and mother deaths, as well as a compromised immune system and blindness. Depending on the variety, 100g of sweet potato can give anywhere from 0 to 100% of the daily vitamin A requirement, which is at least 350 g for newborns and 400 g for early children (1-6 years) [6]. Sweet potato, despite its high carbohydrate content, has a low glycemic index due to the starch's limited digestion, making it good for diabetics and persons who are overweight [3, 4].

Sweet potatoes are commonly consumed in Ethiopia by boiling, steaming, roasting, or frying them [5]. It is vital to obtain knowledge about the loss of nutrients in various processing processes in order to make effective use of nutrients from sweet potatoes. As a result, the goal of this research is to find out how nutrients vary between cultivars and how different processing methods affect nutrient loss.

Materials And Methods

Collection and preparation of samples

A total of four varieties of fresh sweet potato, namely Kulfo (yellow), Tulla (yellow), H-83 (white) and H-09 (white) were collected from the Hawassa Agricultural Research Center. The collected samples of fresh sweet potato varieties were washed with clean tap water and rinsed with distilled water. The peeled and unpeeled sweet potatoes were cut into pieces and cooked using the following methods:

Raw (control): Samples were peeled using a kitchen knife, cut into cubes of about 2.5 cm, washed using distilled water, and then ground using a mortar and pestle, ready for crude protein, crude fat, crude fiber, moisture, ash, and mineral content analyses. Boiling (moist heat): 600 g of unpeeled fresh sweet potato was rinsed in distilled water, immersed in 750 mL water, and cooked for 45-55 minutes in a covered saucepan.

Roasting: Unpeeled sweet potatoes were roasted for 20-22 minutes on hot charcoal, with the sample being moved frequently to ensure equal roasting.

Steaming: Wrapped in banana leaves, unpeeled sweet potatoes were cooked for 55-60 minutes.

Frying: Manual peeling with a kitchen knife was used, as was mechanical chipping with a chipping machine and deep oil frying with vegetable oil at 140 to 150°C for 10 to 12 minutes.

Proximate analysis

The proximate analysis of both fresh (raw) and processed sweet potato variety samples was performed in triplicate using the AOAC 2005 protocol.

Determination of moisture content: Using a 202-1B drying oven at 105°C for 1 hour, the moisture content of maize cultivars was evaluated using the AOAC (2005) 925.10 technique. 2 g of pulverized maize sample was placed in a crucible and dried for one hour at 130°C, then chilled in a desiccator at room temperature before being weighed.

% Moisture content = (Weight loss of maize/ Weight of the orginal maize) × 100

Determination of ash content: Ash content was determined by the method of AOAC (2005) 923.03 using box-type resistance (SX2-4-1 OGJ) muffle furnace at 550oC for overnight.

%Ash content = (Weight of ash/ Weight of the orginal maize) × 100

Determination of fat content: Using a soxtecTM 8000 extraction device, the AOAC 920.39 technique was used to determine the crude fat content. To prevent sample loss, three grams of ground sample were weighed into the soxtec extraction thimble, and cotton was utilized as a stopper. The aluminum cups with thimbles were placed in the Soxtec extraction machine, which was then filled with 50 mL of petroleum ether. The fume hood's water temperature, water flow rate, and flow rate were all set correctly.

For boiling, rising, and recovery time, the soxtec extraction time was modified to 15 minutes, 30 minutes, and 10 minutes, respectively. The extracted and residual solvents were then weighed after being dried in an oven and chilled in desiccators.

% Crude fat content = (Extracted fat of maize/ weight of maize sample) × 100

Determination of crude protein: The Kjeldahl technique was used to evaluate the crude protein content of maize variety samples (FOSS Analytical AB 2003). 0.5 g of ground sample was weighed in a Kjeldahl digestion tube, and 2 Kjeltabs CT 3.5 (or 7 g K2SO4 + 0.210 g CuSO4 x 5H2O + 0.210 g TiO2) were added, followed by 15 mL of concentrated H2SO4. The combination was carefully heated for 60 minutes inside the fume hood, then cooled for 15 minutes. After distillation, the crude protein value was calculated automatically using the Kjeldahl technique.

Determination of crude fiber: The crude fiber of maize varieties was determined using the FibertecTM 8000 auto-fibre analysis system, and the percentage of crude fiber was calculated as follows.

% Crude fiber = (W2 - (W3+C)/W1) × 100

Where, W1 is weight of sample, W2 is weight of (crucible + residue), W3 is weight of (crucible + ash residue) and C is blank.

Determination of carbohydrate content: Carbohydrate content was determined by difference, that means 100% other proximate chemical compositions, using the following formula: Carbohydrate

content (%CHO) = 100 (% crude protein +% fat +% ash +% moisture content +% fiber).

Vitamin C analysis

The analysis was carried out using [2]. The four sweet potato kinds were sliced and frozen, as were processed sweet potatoes (boiled, roasted, fried, and steamed). For further investigation, the frozen samples were freeze-dried and crushed into fine powder before being stored in a freezer at -20°C. Each of the 0.25 g freeze-dried samples was extracted with 10 mL of 3% (w/v) metaphosphoric acid and 30 minutes of shaking at 300 rpm and the extract was centrifuged for 10 minutes at 4000 rpm. The supernatant was taken and used for further investigation. In 3 percent (w/v) metaphosphoric acid, a standard curve comprising a series of known ascorbic acid solutions was produced. 1 mL of either sample extract or standard substance was added to 3 mL of 0.2 mM DCPIP and measured using UV-Vis at a 515 nm wavelength after 15 seconds of mixing. The data are given in milligrams of ascorbic acid per 100 grams of dry weight (mg/100 g DW).

Retention

The apparent retention rate was used to calculate retention. The ratio of the nutrient content in the cooked food to the nutritional content in the raw food, given on a dry weight basis, is known as apparent retention [12].

% Apparent retention = (Nutrient content per g of cooked food(dry basis)/Nutrient content per g of raw food (dry basis)) × 100

Analysis of mineral content

After dry ashing, the mineral contents (Fe, Zn, Ca, and K) of each sample were measured by Atomic Absorption Spectrometry (AAS). 5 mL concentrated HNO3 and 5 mL concentrated HCl acid solutions were used to digest 0.5 g of each ash sample. The solution was gently stirred and cooked on a hot plate until yellow fumes were expelled and it turned clear. After that, a Millipore filter (0.4) was used to filter the solution and the volume was leveled to 50 mL with deionized water [1, 15].

Results And Discussion

The effects of processing on the proximate compositions of sweet potato varieties are shown in Table 1. The moisture content (how much water in the product) was measured in each of the processed and raw samples of sweet potato varieties. Kulfo (raw) and kulfo (steamed) had the highest moisture content (10.48%) and 10.42%, respectively. The minimum amount of moisture content is 5.5% H-09 (raw) and 4.69% H-09 (fried), respectively. Ash refers to the remaining or residual parts, mainly inorganic substances, after the total incineration of organic matter. The ash content is determined from the loss of weight, which occurs from the complete oxidation of the sample at a high temperature of 550°C ± 3°C. The ash content for raw and processed sweet potato varieties ranged from 2.18 to 5.98%.

Fat is an extractable matter from extraction with a specific solvent like n-Hexane. Crude fat is a mixture of crude fat and soluble material in the sample that provides energy in the body. The value of crude fat in sweet potato varieties in raw and processing found to be from 0.24 to 35.15%. Proteins are made up of many building blocks, known as amino acids and second ranked proximate composition next to carbohydrate [16]. The amount of crude protein in sweet potato varieties ranged from 1.95 to 8.31%. Fiber (roughage) is the part of plant-based food such as grains, fruits, vegetables, nuts and beans that the body cannot break down. The amount of crude fiber found in sweet potato varieties ranged from 1.91 to 2.51%. In general, the proximate composition of processing sweet potato varieties are in good agreement with [9].

The effect of processing on the value of vitamin C in sweet potato varieties is also represented inTable 2. The mineral contents such as Fe, Zn, Ca and K in mg/100g are resented in Table 3. Potassium (K (mg/100g)) was found to be highest than others in sweet potato varieties and zinc (Zn (mg/100)) was found to be lowest the others. [13]Have reported the values of iron, zinc, calcium and potassium in sweet potato varieties were found to be in the range of 0.25 to 0.73, 0.11 to 0.27, 24.00 to 29.97 and 300 to 326.67 mg/100g, respectively, which is in good agreements in the present study. Generally, these sweet potato varieties have good nutritional compositions.

The result of vitamin C in sweet potato varieties and processed are presented in Table 2. The vitamin C in mg/100g of Hawassa 83 and Hawassa 09were found to be 56.16 and 56.60, respectively. There is no significant difference in the value of vitamin C on different processing methods, but there is a significant difference between roasting and other methods.

Dry matter

Tulla, kulfo, Hawassa 83, and Hawassa 09 sweet potatoes were studied for dry matter content. Tulla, kulfo, Hawassa 83, and Hawassa 09 sweet potato types have dry matter content of 20.00, 19.45, 31.67, and 24.52, respectively. Hawassa 83 had the highest dry matter value, whereas Kulfo had the lowest.

Statistical Analysis

The data was analyzed using the Statistical Package for Social Sciences (SPSS) version 20.0. The descriptive statistics mean and standard deviation (SD) were calculated, and the data was reported as mean ± SD. Duncan's new multiple range and twoway ANOVA were used to compare the means statistically. At a p<0.05 level, differences in means will be considered significant.

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Table 1:

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Table 1. Effect of processing on the proximate compositions of sweet potato varieties (%).

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Table 2:

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Table 2. The effect of processing on the value of vitamin C in sweet potato varieties.

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Table 3:

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Table 3. Some mineral contents in (mg/100g) of sweet potato varieties and is product processing.

Conclusion

This study compares the nutritional composition of sweet potato cultivars before and after various processing methods (boiling (immersed in water and boiled), roasting (roasted over hot charcoal), steaming (wrapped in banana leaves and boiled), and frying (wrapped in banana leaves and fried) (deep oil frying with vegetable oil). The calcium and potassium content of the types differed significantly (p<0.05) between them, according to the findings of this study. Boiling, steaming, roasting, and frying sweet potato cultivars had no significant (p>0.05) effect on ash and crude fiber content. Within the variations, there is a large variability in calcium and potassium levels. On the other hand, there was a significant difference in vitamin C value (p<0.05) between roasting and other processing methods, and the frying procedure also altered crude fat content. In addition, it was shown that the nutritional makeup of sweet potato cultivars retains better after processing.

Acknowledgments

The Ethiopian Institute of Agricultural Research's directorate of food science and nutrition research has provided financial assistance for this project. The author wishes to convey their heartfelt gratitude for their assistance and contribution to the effective completion of this article.

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