Investigation of the effect of different heat treatments on the formation of Maillard reaction products in onion

Maillard and caramelization reactions are considered to be the most common side reactions during the processing of foods in various ways. Compounds such as 5-hydroxymethylfurfural (HMF), acrylamide, which appear in the course of those reactions have negative effects on health, are recognized as heat treatment indicators. Within the scope of this thesis, microwave heating (3, 5, 7 min), baking (20, 30, 40 min) and frying (3, 7, 9 min) processes were applied to yellow, purple and white onion bulp samples and The formation of HMF, 2-acetylfuran (2-AF), 2-furoic acid (2-FC), 5-methylfurfural (5-MF), furfural, acrylamide and furosine was studied. The changes in the quercetin (Q), quercetin 3,4'-diglycoside (QDG), quercetin 4'-glycoside (QMG), sugar and free amino acid contents of the samples were also determined. As the heat treatment time increased, the sugar and amino acid content decreased in all samples. HMF and acrylamide were detected in almost all heat treated samples and the content of these compounds was increased with increase in the intensity of the heat treatment. Furfural was detected in all intensely heat-treated samples, while 5-MF was detected just in some of those samples. On the other hand 2-AF and 2-FC could not be detected in any of the samples. Although the furosine content generally increased as the heat treatment time increased, it was observed that it decreased during advance stages of the heat treatments. It was observed that the Q, QDG and QMG contents of onion samples increased as the heat treatment intensity increased, while the contents decreased with further heat treatment. As a result, with this study it was observed that significant amount of thermal process contaminant could be formed during onion bulb cooking. The type of the heat process and time along with onion cultivar are all effective in the presence and concentration of those compounds.