Absorption of Lysine and Deoxyketosyllysine in an Early-Maillard Browned Casein by the Growing Pig

The aim was to determine the small intestinal uptake in the pig of unaltered (unreacted) lysine in a heat-damaged glucose/casein mixture, containing high concentrations of the early-Maillard compound, deoxyfructosyllysine. Diets containing a heated glucose/casein mixture, where approximately one-third of the original lysine was in the form of deoxyfructosyllysine, and an unheated glucose/casein mixture were each fed to four 10 kg live weight pigs. Chromic oxide was used as an indigestible marker, and digesta were sampled at slaughter, from the terminal ileum. The apparent ileal digestibility of unaltered lysine in the heated glucose/casein was less than unity (59 ± 2.3%, mean ± SE). Gel chromatography of digesta (heated glucose/casein) showed a 430 Da, deoxyfructosyllysine-containing peak, suggesting the presence of deoxyfructosyllysine-containing limit peptides. The FDNB reactive lysine method does not allow accurate assessment of lysine availability in heated proteins, due to incomplete digestion and absorption. Nor does the conventional ileal lysine digestibility assay provide accurate estimates due to the partial reversion of early-Maillard compounds to lysine during acid hydrolysis. Keywords: Maillard; lysine