Formation of α-Dicarbonyls from Dairy Related Carbohydrates with and without Nα-Acetyl-l-Lysine during Incubation at 40 and 50 °C

Abstract

α-Dicarbonyls are reactive intermediates formed during Maillard reactions and carbohydrate degradation. The formation of seven α-dicarbonyls was characterized in solutions containing dairy related carbohydrates (galactose, glucose, lactose, and galacto-oligosaccharides (GOS)) during incubations at 40 and 50 °C with and without Nα-acetyl-L-lysine at pH 6.8 for up to 2 months. The concentrations of α-dicarbonyls in samples of monosaccharides with Nα-acetyl-L-lysine were found to be 3-deoxyglucosone (3-DG) > 3-deoxygalactosone (3-DGal) > glyoxal > glucosone, galactosone > methylglyoxal > diacetyl. The presence of Nα-acetyl-L-lysine resulted in up to 100-fold higher concentrations of C6 α-dicarbonyls but lesser formation of glyoxal in the monosaccharide-containing models compared to what was observed in the absence of Nα-acetyl-L-lysine. Galactose incubated with Nα-acetyl-L-lysine generated the highest concentrations of 3-DGal (up to 130 μM), glyoxal (up to 100 μM), and methylglyoxal (up to 9 μM) compared to the other carbohydrates during incubation. Surprisingly, 3-DG (1500 μM) and 3-DGal (80 μM) were formed at levels of 2 orders of magnitude higher in solutions of GOS in the absence of Nα-acetyl-Llysine as compared to the other carbohydrates at 40 °C, while GOS generated the lowest levels of glyoxal. GOS are widely used as an ingredient in various types of foods products, and it is therefore of importance to consider the risk of generating high levels of the reactive C6 α-dicarbonyl, 3-DG, in these types of products. This study contributes to the understanding of major αdicarbonyl formation as affected by the presence of primary amines in GOS-, lactose-, and galactose-containing solutions under moderate heating in liquid foods.

Limitation of Maillard Reactions in Lactose-Reduced UHT Milk via Enzymatic Conversion of Lactose into Galactooligosaccharides during Production

“…α-Dicarbonyls are reactive intermediates formed during Maillard reactions . Eight α-dicarbonylsgalactosone, glucosone, 3-deoxypentosulose, diacetyl, 3-DG, 3-DGal, glyoxal, and methylglyoxalwere included in the analysis of the three milk types, but only 3-DG and 3-DGal were detected (Figure A,B).…”

“…It is, however, known that α-dicarbonyls, particularly short-chain α-dicarbonyls, glyoxal and methylglyoxal, will rapidly react with other components in milk, such as Lys, Arg, and Cys residues to form AGEs . We have previously found that 3-DG was formed in high concentrations in aqueous solutions of commercial GOS within 24 h of incubation at 40 °C compared to that of lactose or monosaccharides. , It was, therefore, of interest to examine whether 3-DG would be formed to a similar extent in GOS milk compared to a model aqueous solution of commercial GOS. As shown in Figure A, 330 ± 6 μM 3-DG was detected in GOS milk, which is ca.…”

“…Eight α-dicarbonyls, including galactosone, glucosone, 3-deoxypentosulose, diacetyl, 3-DG, 3-deoxygalactosone (3-DGal), glyoxal, and methylglyoxal, were included in the analysis of milk samples. Further details, including peak identification and validation of the method, have been provided previously. , Free HMF was analyzed in the milk samples according to a previously described method. , …”

“…Our previous work in model systems has shown that galactose is more prone to Maillard reactions and the formation of AGEs than lactose and galactooligosaccharides (GOSs) and forms higher levels of reactive α-dicarbonyls (methylglyoxal and glyoxal) that are precursors of AGEs. These studies were performed with a commercially available GOS ingredient combined with sodium caseinate or N -α-acetyl- l -lysine .…”

“…Our previous work in model systems has shown that galactose is more prone to Maillard reactions and the formation of AGEs than lactose and galactooligosaccharides (GOSs) and forms higher levels of reactive α-dicarbonyls (methylglyoxal and glyoxal) that are precursors of AGEs. These studies were performed with a commercially available GOS ingredient combined with sodium caseinate or N -α-acetyl- l -lysine . Commercially available β- d -galactosidases with a transgalactosylating activity can directly convert lactose into GOS in milk, but it is unknown how this conversion affects Maillard reactions in UHT processed milk.…”