Establishment of Indicator during Thermal Treatment of Dairy Products Based on Maillard Reaction

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 17580112
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Food science
• Research Institution: Kochi University
• Principal Investigator: UKEDA Hiroyuki Kochi University, Dept. of Bioresources Sci., Professor, 農学部, 教授 (60184991)
• Co-Investigator(Kenkyū-buntansha): KIM Chul-Sa Kochi University, Dept. of Bioresources Sci., Professor, 農学部, 教授 (30234339)
• Project Period (FY): 2005 – 2006
• Keywords: Maillard reaction / aminoreductone / milk / lactose / XTT / heat treatment / DNP

Research Abstract

Maillard reaction with lactose, a characteristic reducing sugar, occurs in dairy products such as milk during thermal process. The present investigators developed the XTT method for estimating the severity of the heat treatment of milk based on the detection of aminoreductone (AR) formed. Although the present method is feasible and practical, the principle of the method has not yet proven in the practical milk sample. In the present research, we tried to develop a novel derivatization method using dinitrophenylhydrazine (DNP) in order to directly identify the presence of AR in milk.
As the strategy, we tried to add Cu^<2+> into sample solution in order to simultaneously carry out the oxidation and liberation of AR from the protein. Firstly, the effect of Cu^<2+> addition into the model solution was examined with monitoring an appearance of a characteristic peak (OAR-DNP) in the HPLC. We separated the characteristic peak which increased with increasing the Cu^<2+> concentration and analy zed it with NMR. Consequently the structure in which two molecules of DNP were bound to the skeleton of AR was clearly identified. When the present derivatization method was applied to lactose-lactalbumin model solution, the same peak was observed in the chromatogram. These results suggest that the present derivatiozation method was applicable to liberate and identify the AR structure on the protein. Next, the method was applied to a commercial milk sample. The analysis of the derivative by the normal phase HPLC resulted in the appearance of the same peak as OAR-DNP. In order to confirm that the peak was identical with the above structure, the peak was again separated. The NMR analysis clearly showed that the structure was identical to the above identified one. This result clarified that AR formed during the Maillard reaction in practical milk. Additionally, we succeeded to prove that the XTT assay for detecting the heat severity of dairy products without any special pretreatment is based on the formation of AR in the early stage of the Maillard reaction.