The effect of pre-formed lipid hydroperoxides, breading, and battering ingredients on pigment formation and thermo-oxidative degradation of oil during institutional frying was evaluated. The food ingredients were fried intermittently in canola oil heated for 8 h daily over 4 consecutive days at 185 ± 5°C. Color component formation, total polar components (TPC), and tocopherols were measured. Glycine-enriched whey protein fried in 1% oxidized canola oil contributed most significantly to oil darkening with a rate ten times that of the control sample. Using whey protein as a base for battering caused the most significant color changes and thermo-oxidative deterioration. Glucose and glycine are two minor ingredients that also contribute to color formation in oil. Breading materials were prone to cause a more significant amount of oil deterioration when compared to battering ingredients most likely due to excess loose breading particles falling into the oil during frying.
Practical applications: The present study evaluated the effect of some components of food coatings on the stability and pigment formation of the frying oil. The results suggest the need to optimize the protein component of coating materials and ensure that the amounts of loose particles on breaded products are adequately minimized. This information will assist institutional frying operators and other relevant industries in product development and food preparation with the view of optimizing performance of the frying oil.