Influence of storage condition and added vitamin E on oxidation stability of edible sunflower and nigger seed oils produced and sold around Bahir Dar city, Ethiopia

Abstract

In human nutrition, fats are physiologically important food constituents but also the components most liable to oxidative degradation. This study was carried out in order to probe the extent of oxidative alterations in Sunflower Oil (SFO) and Nigger Oil (NO), subjected to daylight and dark storage conditions with, and without added vitamin E, over a period of 5 weeks storage. The magnitude of oxidative changes was monitored by the periodical measurement of acid value, peroxide value, and induction time throughout storage time. The acid value of sunflower oil increased from initial value 4.5 mg KOH/g to (24.7, 19.64, 16.83, and 12.34) mg KOH/g, and of nigger oil from 6.2 mg KOH/g to (21.3, 17.95, 16.83 and 11.22) mg KOH/g for oil samples kept in daylight, dark, daylight+vitamin E, dark+vitamin E for 5 weeks. Like the acid value, the peroxide value of sunflower oil increased from 2.2 meq O2/kg to (27.2, 16.6, 13.2, and 7.2) meq O2/kg, and of nigger oil from 2.0 meq O2/kg to (17.2, 13.2, 8.8 and 4.6) meq O2/kg for oil samples kept in the same conditions with that mentioned in acid value. Unlike the acid value, the induction time of sunflower oil decreased from 1.97 h to 1.51 h, 1.65 h, 1.77 h, and 1.85 h, and of nigger, oil decreased from 2.05 h to 1.60 h, 1.73 h, 1.81h, and 1.92 h for oil samples stored in daylight, dark, daylight+vitamin E, dark+vitamin E for 5 weeks. However, the induction time of fresh sunflower and nigger oils containing added vitamin E increased to 2.11 h and 2. 13 h. Changes in acid value, peroxide value and induction time obtained shows that the oxidative deterioration levels of oils were different between storage conditions. The results of the present study show that light acts as a major catalyst in accelerating the development of rancidity in oils. Also, the addition of vitamin E to oil can increase the oxidation stability of oils during storage. In conclusion, this study has been able to show storage in the light can affect oil stability and minimizes the potency of vitamin E in oils, fats or fat-containing products. Therefore, storing in dark (packaging with material protect light) and supporting with antioxidants is the best way to maintain the quality of oils during storage and domestic uses.