Mechanism of Maillard reactions in Lactose-hydrolyzed UHT milk and Strategy of Inhibition by Galacto-oligosaccharides

Research output: Book/ReportPh.D. thesisResearch

  • Wei Zhang
Lactose intolerance is widespread in regions such as Asia, the Middle East, Southern Europe and Africa, due to a congenital lactase deficiency. Lactose-hydrolyzed UHT milk is common alternatives to conventional dairy products for the people intolerant to lactose. However, it has been reported that lactose-hydrolyzed UHT milk is prone to Maillard reactions. This PhD project aims to investigate the mechanism of Maillard products in lactosehydrolyzed UHT and then explore their inhibition strategies. In the first part, a comprehensive quantitative characterization of Maillard reactions products were carried out for conventional (CON) and lactose-hydrolyzed (LH) UHT milk during storage at ambient temperatures (20 °C, 30 °C and 40 °C) for up to one year. Analyses included quantification of: -dicarbonyls (3-deoxyglucosone (3- DG), 3-deoxygalactosone (3-DGal)), 5-hydroxymethyl furfural (HMF), and sixteen different Lys-, Arg-, and Cys-derived advanced glycation end products (AGEs): N-ε-carboxyethyllysine (CEL), N-ε-carboxymethyllysine (CML), pyrraline, glyoxal-lysine dimer (GOLD), methylglyoxal-lysine dimer (MOLD), glyoxal-lysine-amide (GOLA), glycolic acid-lysine-amide (GALA), pentosidine, methylglyoxal-hydroimidazolone isomers (MG-H1, MG-H2, MG-H3), glyoxal-hydroimidazolone isomers (G-H1, G-H2, G-H3), argpyrimidine, and S- (carboxymethyl)cysteine (CMC). A model for analysing five major AGEs including CEL, CML, MG-H1, G-H1 and G-H2 was proposed in milk. Significantly higher level of C6--dicarbonyls and AGEs (CEL, MG-H1) wer e found in LH compared to CON milk. Rapid formation of -dicarbonyls from monosaccharide, especially galactose, are responsible for Maillard reactions in LH. Most of Maillard products are temperature-dependence except glyoxal hydroimidazolones. In the second part, a hypothesis was proposed that conversion of lactose into galacto-oligosaccharides (GOS) by transgalactosylating β-galactosidases rather than of hydrolysis to monosaccharides thereof will limit the formation of galactose, thereby inhibiting Maillard reactions in low lactose milk products. The role of GOS in Maillard reactions was thoroughly investigated comparing with lactose, galactose, and combination of glucose and galactose. GOS-containing caseinate models exhibited lower degree of Maillard reactions during incubation (as evaluated by loss of amines and formation of furosine, CEL, MG-H, MOLD, and GOLD) compared to monosaccharide-containing models, suggesting that incorporating galactose units into GOS by usage of commercial β-galactosidases rather than conventional hydrolysis to monosaccharides could potentially inhibit Maillard reactions during storage of UHT milk. GOS did however also result in much higher concentrations ofC6--dicarbonyls [3-deoxyglucosone (3-DG)], but not for short chain dicarbonyls (glyoxal and methylglyoxal),which suggests that GOS is more susceptible to vinylogous β-elimination during sugar degradation. Consistent with the results of 3-DG, a significant increase in the concentration of HMF and pyrraline (at low level) was also observed in GOS model but did not contributed to total AGEs. Characteristics of Maillard products as well as their formation mechanisms have been drawn in the PhD thesis. The lactose-reduced, GOS-increased milk by transgalactosylating β-galactosidases might be regarded as a replacement of conventional lactose-hydrolyzed milk for the lactose-intolerance people with lower Maillard reactions. The present thesis systematically investigates the extent of Maillard reactions in GOS model for the first time. However, the formation of C6--dicarbonyls, especially 3-DG in GOS, must be investigated further, since GOS as a major additive in infant formula milk.
Original languageEnglish
PublisherDepartment of Food Science, Faculty of Science, University of Copenhagen
Publication statusPublished - 2019

ID: 223824974