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Antioxidant effects of Maillard reaction products (MRPs) derived from glucose-casein model systems
The Maillard reaction (MR) involves the condensation reaction between amino acids or proteins with reducing sugars, which occurs commonly in food processing and storage. Maillard reaction products (MRPs) were prepared from glucose-casein model system at pH 8, heated at 60, 75 and 90°C for 6, 12 and 24 h, respectively. Browning intensity (BI) of MRPs, as monitored by absorbance at 420 nm increased with an increase in reaction temperature. The reducing power (RP) of MRPs increased (p < 0.05) as the reaction time increased at 60 and 75°C, while at 90°C an increase in RP was observed from 6 to 12 h and thereafter a slight decrease was observed up to 24 h. The 2,2-Azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging activity (ABTS-RS) and Peroxyl radical scavenging (PRS) activity of glucose-casein MRPs produced at 90°C decreased as the reaction time increased. In this study, the ferrous chelation activity of MRPs was higher than that of tert-butylhydroquinone (TBHQ) (0.02%) and Trolox (1 mM), respectively. Moreover, the 1, 1-diphenyl-2-picryl-hydrazil radical scavenging (DPPH-RS) of MRPs increased (p < 0.05) as the reaction time increased irrespective of the heating temperature. The primary and secondary lipid oxidation products were measured using the Peroxide value (PV) and Thiobarbituric acid reactive substance (TBARs) assay in sunflower oil-in-water emulsion, respectively. MRPs derived at 90°C for 12 h had the lowest peroxide value, while the TBARs inhibitory by MRPs ranged from 39.05 – 88.66%. Glucose-casein MRPs displayed superior antioxidant activity than TBHQ (0.02%) and Trolox (1 mM), respectively, as measured by the TBARs assay. The differential scanning calorimetry (DSC) and Rancimat techniques set at 110°C were used to evaluate the oxidative stability the lipid-rich media containing MRPs. At the same temperature program, DSC gave significantly lower reduction times than the Rancimat. Furosine (N-ε-Fructosyl-lysine) and Pyrraline (2-amino-6-(2-formyl-5-hydroxymethyl-1-pyrrolyl)-hexanoic acid) were determined using high pressure liquid chromatography to evaluate the extent of the MR. Furosine concentration of glucose-casein MRPs ranged between 0.44 – 1.075 mg.L-1 in MRPs derived at 60°C, while at 75°C an increase as function of time was observed. MRPs derived at 60 and 75°C exhibited a varied concentration of pyrraline as the reaction time increased with higher temperatures resulted in higher concentrations (0.39 mg.L-1). The results of this study clearly indicated that MRPs possess antioxidant activity and can be used as natural antioxidants in the food industry.