Effect of a modified deep‐fat fryer on chemical and physical characteristics of frying oil

We designed a modified deep‐fat fryer (MDF) to have a smaller oil area (A) relative to depth or height (H) such that H/√A=0.93. The modification was intended to retard the thermal degradation of the frying oil and the production of waste oil. Frozen croquettes were fried in vegetable oil using the MDF (H/√A=0.93) and three conventional deep‐fat fryers (CDF1, H/√A=0.25; CDF2, H/√A=0.20; CDF3, H/√A=0.30) at 180°C for 72 h at 8 h/d. Frying oils were periodically collected, and their chemical and physical characteristics were examined. The acid value (AV) of frying oils used for 72 h in the MDF was lower than that for oils used in the CDF, although the AV was similar in all fryers until 32 h. The oil deep‐fried with MDF had a higher degree of color than that with CDF until 48 h. Polymerized materials and the carbonyl value of frying oil after heating 72h with MDF were lower than those with CDF. The residual tocopherol content of frying oil with MDF was 83% of the content in fresh oil, whereas with CDF the tocopherol contents were less than 63%. The oil consumption by MDF was less than that by CDF, although the turnover rate was higher in MDF than in CDF. These results suggest that during deep‐fat frying the MDF may retard the thermal deterioration of vegetable oils and generate less waste oil.