Impact of frying practices and frying conditions on the quality and safety of frying oils used by street vendors and restaurants in Nairobi, Kenya

Frying practices of 11 commercial vendors (6 street kitchens and 5 restaurants) in Nairobi town (Kenya) and its environs were investigated and the quality of their fresh, in-use and discarded oils were evaluated for peroxide value (PV), color, free fatty acid profile (FFA), thiobarbituric acid reactive substances (TBARS), total polar compounds (TPC), p-anisidine value (p-AV) and the total oxidation value (TOTOX). The fresh oil samples showed degradation (with TPCs > 35%; PV > 80%) and this could be an indicator of adulteration of fresh oil and thus measurement of TPCs could be more accurate in evaluating the safety of fresh oil. In-use and discarded oil were highly degraded. Also, the qualitative data indicated that there is widespread practice of reselling the used oil. This oil is highly degraded, and any further use puts into question the toxicological safety of foods prepared with such oils. Most of the street kitchens used shortening and fried their food over firewood while the restaurants used liquid oil and fried their food over charcoal. Highest correlations were found to be between total polar compounds and peroxide value, while lowest were between free fatty acids and TBARS value.