The effects of degraded oil and pre-frying treatments on the quality of tortilla chips

Abstract

Refined soybean oils were degraded at 190C for 60 hours. It was observed that degradation time correlated well with free fatty acid contents, total polar materials, convective heat transfer coefficient, color, specific gravity, viscosity, and surface tension. The off-flavor and foaming developed during frying suggested that the soybean oil should have been discarded after 25 hours of use when the amount of total polar materials reached 27%. The abused soybean oil (degraded for 60 hr) showed a different temperature profile during frying as compared with the fresh oil. The levels of oil degradation did not pose any significant effects on oil content, moisture content, and fracturability. Tortillas were prepared under different pre-frying conditions, i.e., oven-baked in an air forced oven at 190C for 3.5 min (OBL), oven-baked in a 3-tiered gas-fired oven at 343'C, 190C, and 190C for the top, middle, and bottom,, respectively, for 71 sec (OBH), raw, and freezing OBH at-12 C for 24 hours (FT). These tortillas were fried in fresh soybean oil for 60 sec at 190'C and quality of the final products were analyzed. The initial moisture content of the tortilla affected the final oil content of the chip, significantly. The pre-frying treatments affected the final oil and moisture contents of tortilla chips. Environmental scanning electron microscopy (ESEM) pictures demonstrated that the starch/protein matrix and the size of the pores throughout the chip were the most important factors affecting the force needed to break through the tortilla chips.