Recycled cooking oils used for street foods in Kampala, Uganda: Quality and recycling frequency

Abstract

Deep-fried foods are generally popular world over. To cut production costs, the oil used is often recycled. This is concerning because deep-frying is done aerobically at 160–190 °C leading to oil degradation and formation of hazardous compounds. This study evaluated the quality of cooking oil used to deep-fry potato chips (n = 35) and fish (n = 35) by street food-vendors in Kampala, Uganda. Additionally, a safe oil recycling frequency was determined by separately deep-frying several batches of fish and potato chips. After each frying cycle, the quality of oil was analyzed. Over 94 % of oils used to deep-fry chips and fish obtained from food vendors surpassed the recommended specification for peroxide value (10 mEq O2/Kg). Their mean peroxide values were about four times higher than the recommendation. Moreover, none of these oils met the Thiobarbituric acid specification of <2 mg DA/Kg. Oil samples used by vendors to deep-fry fish (100 %) and chips (60 %) had acid values beyond the quality specification of 0.6 mg KOH/g. Their moisture contents and oil densities were almost twice the recommendations. In contrast, their iodine value and color intensities were below the quality specifications. The recycling experiments showed that peroxide values remained consistent while other parameters exceeded quality specifications after the second deep-frying cycle. Therefore, recycled oils used by street-food vendors in Kampala are unsuitable for human consumption. The practice of cooking oil recycling should be discouraged, though it has financial implications especially for commercial food establishments.