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 around Nairobi city were evaluated.•The fresh, in use and discarded oils were analyzed for degradation.•They were evaluated for PV, color change, FFA, TBARS, TPC, P-AV and TOTOX.•Some of the fresh oil and all the in-use and discarded oil was highly degraded.•Some of this oil is resold for further use by other vendors.