Estimation of nutritional composition of kitchen wastes and comparison of the effect of different drying methods on bioactive compounds in the wastes

The study aimed to estimate the nutritional compositions of five most common household kitchen wastes and also analyze some specific bioactive compounds in different drying methods to compare their stability. The stalks of red amaranth have the highest moisture content (91.03%). The largest percentages of ash (11.47%) and fiber (12.43%) are found in banana peel. The most protein (22.58%) and fat (20.53%) content were found in watermelon seeds. Highest amount of Iron was found in watermelon seeds (24.7 mg/100 g), Calcium in cauliflower stalks (226.56 mg/100 g), Phosphorus in watermelon seeds (753.26 mg/100 g). Total antioxidant activity was found profoundly in orange peel and red amaranth stalks as 2.52 g and 2.37 g of Ascorbic acid/100 g sample respectively. Total phenolic content was notably found maximum in banana peel and red amaranth stalks, as 763.67 mg and 317.78 mg of GAE/100 g respectively. Banana peel and orange peel both have extremely high total flavonoid contents, with 624.33 mg and 506 mg of QE/100 g sample, respectively. Tannin content in Red amaranth stalks was found to be extremely high at 511.51 mg of Tannic acid/100 g of sample. More alkaloids were identified in orange peel and red amaranth stalks than other waste items, 53.25% and 55.25%, respectively. According to vitamins, banana peel has 293.2 mg of beta-carotene per 100 g of sample, which is a very high quantity. Cauliflower stalks possess a rich content of Vitamin-C (813.0 mg/100 g sample). The results reveal that different drying methods have different levels of effects on the bioactive compounds. Both sun drying and cabinet drying led to significant reduction (p ≤ 0.05) in these compounds. Freeze drying did not have much effect on the levels of the bioactive compounds. Bioactive compounds are sensitive and are affected by the method of drying employed.