NUTRITIONAL, ANTINUTRITIONAL AND FOOD VALUE OF ONION SKIN WASTE

Abstract

In this study, the skin of the red onion specie commonly sold and eaten in Eastern Nigeria were analysed to enable the researcher know, as well as compare its food value with existing standards. It was analysed for nutritional, antinutritional, mineral composition and its calorific value calculated to ascertain the balance between nutrients and antinutrients factors which determines food quality. The results from proximate analysis showed moisture content 8.28   0.16%, ash, 6.20  0.03%, fibre, 7.26  0.02%, protein, 4.85  0.01% and carbohydrate content by difference as 72.68  0.02%. The  proximate analysis results indicated that onion skin is a potential source of food nutrients and could meet the recommended daily intake and Acceptable Macronutrient Distribution Range if augumented with other food. Carbohydrate is the major contributor to its calorific value of about 317.65kg as compared with 8500kg or 2000calorie per day. Antinutritional analysis results showed that among the antinutrients analysed, saponin is 5.78   0.02% > trypsin inhibitor 1.30   0.02% > tannic acid 0.66   0.02% > phytic acid 0.24   0.01%. The levels were below reported toxic levels, indicating that onion skin is a good source of plant chemicals and can ameliorate certain deadly diseases. Essential mineral analysis showed that Na (37.43   0.02mg/l > Mg (21.96   0.06mg/l) > Ca (6.88   0.02mg/l) hence good source of macrominerals, but must be consumed with other food source to meet RDI of 500 – 2400mg, 375 – 420mg and 800 – 1300mg respectively. Toxic elements were also found present with Hg (2.33   0.01mg/l) > Pb (0.51 + 0.2mg/l). The result for Hg was above the permissible limit of 0.5mg as given by WHO for food substances. The one-way Anova results showed that the food nutrients, antinutrients and mineral, all differ significantly (p < 0.05). The results similarly showed that onion skin has great food value, suggesting the incorporation of onion skin as part of our diet, rather than a waste. This will not only promote green chemistry but as well maximise the nutritional value of our pots and provide optimum intake of nutrient. Keyword: RDI (Recommended Daily Intake), AMDR (Acceptable Macronutrient Distribution Range), OSW (Onion Skin Waste).