Thermal stability of blending soybean oil with coconut oil during continuous deep-frying of banana chips

Soybean oil is susceptible to thermal deterioration due to its high polyunsaturated fatty acid content. Blending oil is the simplest way to enhance the nutritional profile and stability of frying oil. In particular, coconut oil is resistant to oxidation; adding it to other vegetable oils that are prone to oxidation makes the mixes more stable. This study investigated the thermal stability of soybean oil by blending it with coconut oil and evaluating the blend's physicochemical changes during the continuous deep-frying of banana chips. Refined soybean oil was blended with refined coconut oil at different volume ratios (% v/v), including 100:00 (A), 80:20 (B), 70:30 (C), and 60:40 (D). All blended oils were operated under a deep-frying practice at a constant temperature of 180°C. Banana chips were fried for 1 min at 5 min intervals in nine batches. The results showed significant changes in the physicochemical properties of each frying oil with frying duration (p<0.05). The alteration in free fatty acid and peroxide values was the lowest in treatment C, followed by D, B, and A. Conversely, the highest increment in TOTOX value was found in treatment A, followed by B, C, and D in the ninth batch of frying. The lightness of oil obtained the highest value in the last frying cycle in treatments B and C, followed by D and A, while the color of the fried banana chips achieved the maximum value in treatment D, followed by C. In addition, the lipid content in the fried banana chips was observed in the lowest amount in treatment D, followed by treatment C, in the first batch and in the ninth batch. Blending highly unsaturated soybean oil with coconut oil could enhance its thermal stability. Consequentially, a 70:30 (% v/v) ratio of soybean oil blended with coconut oil exhibited good thermal stability during deep-frying.