Browning mechanism of sorbitol-glycine system in the presence of glycerol: Regulating conversion of sorbitol to reducing sugars and water status

Abstract

Unexpected browning was observed in sorbitol and amino acid system under high-temperature process and long-term storage. The effect of glycerol on the browning reaction of sorbitol-glycine model system under different heat treatment time was explored. The results confirmed that partial sorbitol was converted to glucose and fructose, which underwent a Maillard reaction with glycine to produce the melanoidins. Glycerol concentration and the heating time were positively correlated with the course of the reaction, which reflected in the increase of browning index, the rise of uncolored intermediate products and fluorescent substance accumulation. Compared with the system without glycerol, the browning index increased by about 100 times and the accumulation of uncolored intermediate products increased by 65 times with the presence of 4 mol/L glycerol. Furthermore, the content of α-dicarbonyl compounds (glyoxal, methylglyoxal and 2, 3-butanedione) in the system was changed by glycerol, which showed a trend of first increasing and then decreasing with the accumulation of melanoidins, and reached a peak value of 190.6 mg/L after heating for 2 h. The glycerol-dependent browning was related to the water activity of the system at a high level (>0.80) and the migration rate of free water to immobilized water ranging from 0.60% to 8.59%. It indicated that glycerol could promote the reaction by influencing the substrate concentration, weakening the inhibition of product and promoting the conversion of sorbitol to reducing sugar.