Antioxidant and inhibitory effect of Maillard reaction products (MRPs) against enzymatic browning of Granny smith apples

Abstract

Maillard reaction products (MRPs) were prepared from glucose-casein (1:2 w/w) model systems at pH 8 heated at 60 and 75 °C for 6, 12 and 24 h. Browning intensity (BI) and pH reduction were monitored throughout the reaction. The antioxidant activity (AA) of resulting MRPs was evaluated through metal chelation (MC), reducing power (RP) and 1,1-Diphenyl-2-picryl-hydrazyl radical scavenging (DPPH-RS). Inhibition of enzymatic browning was evaluated through colour change on the CIELab system and the polyphenolase assay. The pH of MRPs decreased (p < 0.05) as the reaction temperature and times increased, which in turn coincided with an increase (p < 0.05) in BI and RP. DPPH-RS of MRPs increased as the temperature increased from 60 to 75°C, although a sudden decrease (p < 0.05) was observed at 75°C for 12 and 24h. The loss in AA was attributed to the formation of high molecular weight melanoidins known to exhibit lower AA. MRPs which resulted in a pH drop below 5 were effective in inhibiting polyphenolase activity. This enzyme has an optimum pH in the range of 5-7. Most MRPs produced after 6 h did not show a pH reduction of less than 5, however, these were able to inhibit the polyphenolase activity. This inhibition was attributed to MC properties of MRPs on the active site of the enzyme for all model systems.