Effects of Continuous Deep-fat Frying on the Physicochemical Properties of Assorted Brands of Edible Cooking Oils Sold in Greater Metropolitan Kampala

Aims: To investigate the effects of continuous deep fat frying of white (Irish) potatoes on the physical and chemical attributes of ten brands of edible cooking oils: Fortune Butto, Roki, Tamu, Best Fry, Mukwano, Golden Fry (hard oils); Sunseed, Sunny, Sunvita and Sunlite (soft oils) sold in Kampala, Uganda.

Place and Duration of the Study: Oil samples of approximate manufacturing dates were obtained from Mega Standard supermarket in Greater Metropolitan Kampala, Uganda. Oil samples were also obtained from local Irish potato fryers in Makindye division of Kampala during ten deep frying cycles. Irish potatoes was procured from Nakasero market, Kampala. Physicochemical analyses were performed at the Quality Control Laboratory of Mukwano Industries Limited, Kampala Industrial area, Kampala. The research was conducted between May 2018 to December 2018.

Methodology: 400g of Irish potato slices (1cm × 1cm × 3cm) were submersed in 1500mL of oil maintained at 140°C for 6 minutes in an Electric Deep Fryer with a frying time of 10 minutes.The color value (CV) and the acidification of the oils as free fatty acid (FFA), peroxide value (POV), paraanisidine value (AnV), iodine adsorption value (IV) and total oxidation (TOTOX) value before and between ten successive frying cycles were determined using ISO and AOCS official methods.The maximum number of reuses of an oil was estimated from the frying round before its POV or AnV surpassed the maximum permissible statutory or Codex Alimentarius limit for edible oils.

Results: For fresh oils, the statistical physicochemical parameter ranges were: CV (0.4R 3.4Y-7.7R 70Y), FFA (0.0430±0.30-0.1508±0.30), POV (0.5951±0.03-6.6134±0.23 meqO2/Kg), AnV (0.90±0.01-4.30±0.19) and IV (57.62±0.17-128.35±0.02gI2/100g). By the 10th fry, the ranges were CV (3.0R 23Y-20.4R 70Y), FFA (0.2286±0.01-0.4817±0.01), POV (11.1138±0.01-15.7525±0.01meqO2/Kg), AnV (10.31±0.03-22.16±0.01) and IV (53.66±0.01-126.03±0.02gI2/100g). Considering oxidizability as TOTOX values, frying stability of the selected brands of cooking oils during the frying cycles followed the order: Roki > Fortune Butto > Sunvita > Sunny > Sunlite > Mukwano > Tamu > Best Fry > Golden Fry > Sunseed.

Conclusion: Reuse of the oils for continuous frying of Irish potatoes on the same day can be done only up to 7 times on average for hard oils and 6 times for soft oils with the oils still regarded as safe for human consumption. Hard oils should be preferred to soft oils for deep frying of Irish potato chips.Further research should elucidate the variation of physicochemical properties of other oil brands on the Ugandan market such as Nile, Fortune, Kimbo, Star Fry, Cow boy and Ufuta and should use other food samples such as fish, cassava, chicken, sweet plantain, dough, meat and edible grasshoppers.