Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2012
Publication Date: 5/2/2012
Publication URL: http://handle.nal.usda.gov/10113/60520
Citation: Qi, P.X., Nunez, A., Wickham, E.D. 2012. Reactions between beta-lactoglobulin and genipin: kinetics and characterization of the products. Journal of Agricultural and Food Chemistry. 60:4327-4335.
Interpretive Summary: Despite its many demonstrated nutritional values and functional properties, just over 50% of whey, a by-product of the cheese-making process, is utilized to manufacture high –value whey ingredients for foods. The rest is used as animal feed or simply disposed after processing to reduce its significant environmental impact. In order to increase the value and use of whey proteins in the food and biomedical industries, beta-lactoglobulin (beta-LG), the predominant protein of whey, representing 50% of those and about 12% of total milk proteins, has been identified as a whey protein of importance, and with some modification, would become highly valuable to the food and biomedical industries. In this study, a naturally occurring cross-linking reagent, genipin, extracted from the fruits of Gardenia jasminoides, a traditional Chinese medicine, was reacted with beta-LG to produce a new class of modified molecules. These new beta-LG molecules have different properties than a single beta-LG molecule and may have applications in improving the nutrition and functional properties of food or in controlled drug release products.
Technical Abstract: In this paper, we present the first detailed report of the reaction kinetics studies and the characterization of the products from the endothermic reactions between beta-lactoglobulin and genipin. The effects of concentration, temperature, and pH were examined. In the temperature range studied, the reaction was approximately pseudo first-order with respect to genipin and independent of pH, but 0.22-order and -0.24-order with respect to beta-lactoglobulin at pH of 6.75 and pH of 10.5, respectively. The activation energy (Ea) was estimated to be 66.2 +/- 3.8 kJ/mol and 9.40 +/- 0.36 kJ/mol for each pH condition. SDS-PAGE studies showed the presence of oligomeric, i.e. dimeric, trimeric, quadrimeric and pentameric, forms of crosslinked beta-lactoglobulin by genipin only at neutral pH; however, an extensive crosslinked network was not observed by AFM. Both temperature and the concentration of genipin, but not that of beta-lactoglobulin, positively affected the extent of the crosslinking reactions.