Abstract:

The effects of temperature, reducing sugar/amino acid molar ratio and pH value on the formation of isovaleraldehyde in Maillard reactions between leucine and four reducing sugars such as glucose, fructose, xylose and ribose were investigated by an orthogonal array design involving 9 experiments of three variables at three levels. The yield of isovaleraldehyde increased when the reaction temperature rose from 100 to 140 ℃. For the Maillard reactions consisting of glucose and ribose, respectively, the yield of isovaleraldehyde increased with the molar ratio of sugar to leucine increasing. The reactions carried out under a slightly acidic or basic condition usually gave isovaleraldehyde in higher yields than those reactions under a neutral condition. Of the four sugars under investigation, glucose and fructose reacted with leucine to give isovaleraldehyde with fewer impurities in much higher yields than xylose and ribose. When a large excess of xylose or ribose reacted with leucine at a relative high temperature, furfural was formed as a major byproduct. Under optimized reaction conditions, the yield of isovaleraldehyde obtained from the reaction of glucose with leucine was about 32%, and fructose gave isovaleraldehyde in about 21% yield.

Key words: leucine, reducing sugar, isovalealdehyde, Maillard reaction, Strecker degradation