Effect of Roasting on the Formation of Maillard Reaction Products in Sesames

Abstract

Sesame seed is highly susceptible to chemical changes because of consisting especially high lipid content and various amino acids. Among these chemical reactions, Maillard reaction is of great importance during roasting of sesame seeds. The Maillard reaction induces desirable changes in color, flavor and texture properties in the processing of sesame seeds, but also leads to nutritional losses and formation of heat-induced compounds. The new compounds could have both antioxidant activity and potentially toxic properties. The aim of this MSc thesis is the investigation of Maillard reaction products and the changes in their concentrations in sesame seeds under different roasting conditions. For this purpose, 5-hydroxymethylfurfural, acrylamide, furan and dicarbonyl compounds (1-deoxyglucosone, 3-deoxyglucosone, methylglyoxal and diacetyl) together with glycation products namely furosine, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine, were monitored as a result of roasting. After that, two different multiresponse kinetic models were asserted, in this way, major and less significant reaction steps of Maillard reaction and caramelization occurring during roasting of sesame seeds were uncovered. Firstly, some of Maillard reaction and caramelization products were analyzed mentioned above. According to the results, roasting induced the formation of 5-hydroxymethylfurfural, acrylamide, furan and dicarbonyl compounds significantly. From the dicarbonyl compounds, 3-deoxyglucosone was the highest and the rest was in the following order; methylglyoxal > 1-deoxyglucosone > diacetyl. Expectedly, 5-hydroxymethylfurfural concentration increased with the thermal load applied. Since the amount of asparagine was the limiting precursor for the acrylamide formation, acrylamide concentration was correlated with the changes in asparagine level. Furosine concentration reached to the highest at 5 min of roasting at 150°C, then it decreased with the roasting temperature increased. The reason for the decreasing furosine might be the formation of N-ε-carboxymethyllysine, N-ε-carboxyethyllysine by degradation or oxidation of furosine under those conditions.

Secondly, two different multiresponse kinetic models of Maillard reaction and caramelization occurring during roasting of sesame seeds were asserted. The reaction steps were sucrose degradation into glucose and fructofuranosyl cation, formation of Amadori and Heyns products from sucrose degradation products, formation of α-dicarbonyl compounds pathways, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine formation through Amadori/Heyns product or dicarbonyl compounds were included to the first model and the reaction steps were sucrose degradation into glucose and fructofuranosyl cation, formation of 3-deoxyglucosone from glucose or Heyns product, 5-hydroxymethylfurfural formation through fructofuranosyl cation, acrylamide formation through the reaction of asparagine with 5-hydroxymethylfurfural or glucose, degradation products of these compounds were added to second model. The goodness of fit and estimation of reaction rate constant was evaluated via model discrimination. It was found that methylglyoxal-lysine was the dominant pathway in N-ε-carboxymethyllysine formation in the initial of roasting, while Heyns product became predominant at the end of roasting. 5-hydroxymethylfurfural formation was promoted by the pathway via fructofuranosyl cation, not 3-deoxyglucosone. It was concluded that 5-hydroxymethylfurfural acted as a potent carbonyl source in acrylamide formation during sesame roasting. Hence, it was enabled to understand how Maillard reaction and caramelization progressed in the course of roasting.