D-Psicose, an epimer of D-fructose isomerized at C-3 position, is a rare ketohexose that is thought to be beneficial for obese people and diabetic patients as a noncaloric sweetener. In the present study, model Maillard reaction products were obtained from D-psicose (or D-fructose) and L-lysine heating at 120 °C up to 8 h with the initial pH 9.0. The changes in pH, UV-vis absorbance, and free amino groups during the reaction were detected. Moreover, the antioxidant potential of the Maillard reaction products at different intervals was investigated. Although there was almost no difference in the oxygen radical absorbance capacity, the Maillard reaction products from psicose performed better than that from fructose in the radical-scavenging activity of 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 1, 1,-diphenyl-2-picryl-hydrazyl. The reducing power of the Maillard reaction products from psicose was also stronger than that from fructose. These results indicated that psicose played an effective role in the Maillard reaction and its Maillard reaction products could act as potential antioxidants in food industry.
The Maillard reaction always occurs during the thermal processing of dairy products, which significantly influences their quality. In the present study, the initial stages of a glucose-proline model system were investigated in water and different types of buffer solutions. Results showed that phosphate buffer accelerated the reversible degradation of the initial stages of the reaction. The proposed catalysis mechanism was that hydrogenous and dihydric phosphate radical anions simultaneously accepted and donated protons for the conversion of the intermediates into N-glycosylamine. The catalysis mechanism was confirmed via testing and no reducing of hydrogenous and dihydric phosphate radical anions was observed during the reaction. Moreover, both N-(1-deoxy-D-fructos-1-yl)proline and its degradation compounds were analyzed. Results showed that degradation of N-(1-deoxy-D-fructos-1-yl)proline to form 5-hydroxymethyl-2-furaldehyde and formic acid was also accelerated by phosphate buffer. An interesting phenomenon was that citrate decreased 5-hydroxymethyl-2-furaldehyde formation, which might be because Strecker-type degradation occurred more easily than 1,2-enolization reaction in citrate buffer solution. However, this hypothesis has not been confirmed, and element label experiments should be carried out in the future.
Summary
Enzymatic hydrolysates from tuna backbone were prepared, and the subsequent Maillard reaction with rare sugars (d‐psicose, d‐sorbose and d‐tagatose) was investigated. The hydrolysates were found to contain a large number of short peptides under 1000 Da and were good sources of essential amino acids. In assays of free radical scavenging activity and reducing power, the Maillard reaction products from rare sugars, especially d‐tagatose, performed better than that from d‐fructose. After heating at 55 °C for 48 h, the scavenging capacity of the hydrolysates for 1,1‐diphenyl‐2‐picryl‐hydrazyl radicals improved by 8.9‐ and 16‐fold in the presence of d‐fructose and d‐tagatose. Hence, hydrolysates with high nutrient contents could be prepared from fish by‐products via proteolysis, and the Maillard reaction of rare sugars may greatly promote the antioxidant activity of the hydrolysates.
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