Color formation in oils during frying is one o f the most noticeable degradation
reactions that occur in the frying oil. Degradation reactions cause formation o f products that
positively and negatively impact the nutritional and sensory qualities o f both the food being
fried and the frying oil. The origins of these pigment forming reactions in the oil and the
factors affecting these reactions are not well understood. Assessments o f the mechanisms,
the components involved and external conditions affecting oil darkening were conducted.
The effect of basic food ingredients, commercially sold and laboratory formulated
breading and battering, preformed lipid hydroperoxides and phospholipids on color
formation and oil degradation of the frying oil were investigated.
Protein products, specifically whey protein, caused both the fastest darkening and
thermo-oxidative deterioration of the frying oil. This breakdown was aided further through
the addition o f minor food materials such as glucose and amino acids as well as lipid
hydroperoxides in concentrations greater than 5 % of the frying oil. Nonenzymatic browning
is the main reaction causing color formation in the frying oil and utilizes carbonyls from the
food product such as starches, sugars and lipid oxidation products as starting materials
alongside amino groups from proteins and amino acids. Breading ingredients contributed to
oil color formation due to particles from the food crust breaking off into the frying oil to
further accelerate browning reactions.
Increasing the temperature o f the frying oil provided additional stimulus for color
forming and thermo-oxidative reactions to progress at a faster rate.