Concentrations of Maillard reaction products and advanced glycation end-products in commercially available extruded dry, retorted wet, and mildly cooked (fresh) cat foods from the United Kingdom and United States.

Maillard reaction products (MRP), including advanced glycation end-products (AGE), form during food processing, particularly under high temperatures, and vary across feline diet formats. Increased AGE consumption has been associated with adverse health effects in humans and rodent models. The health implications of AGE intake in cats remain unclear, and limited data on MRP levels in feline-specific diets exist, particularly in mildly cooked (fresh) formats. The objective of this study was to quantify MRP (mg/kg DM), including the early-stage MRP fructoselysine (FL) and three advanced MRP (AGE): Nε-carboxymethyllysine (CML), Nε-carboxyethyllysine (CEL), and methylglyoxal-derived hydroimidazolone-1 (MG-H1), in commercially available cat foods in the United Kingdom and United States representing mildly cooked (n = 6), retorted wet (n = 10), and extruded dry (n = 10) formats to better understand dietary exposure and potential biological relevance. This study also estimated daily AGE intake and evaluated associations between dietary macronutrient composition and MRP concentrations. Lastly, total lysine (TL) and reactive lysine (RL), were measured to assess potential processing-related changes in lysine availability. Selected MRP, including AGE were quantified by ultra-performance liquid chromatography-tandem mass spectrometry and compared by one-way ANOVA. FL concentrations differed among diet formats (P < 0.05) and were greater in mildly cooked and retorted wet than in extruded dry. CML concentrations differed among diet formats (P < 0.05), with retorted wet greater than extruded dry, while mildly cooked diets were intermediate. Concentrations of CEL (P < 0.05), MG-H1 (P < 0.05), and total AGE (P < 0.05) were greatest in retorted wet diets, whereas mildly cooked and extruded dry diets did not statistically differ. Estimated daily AGE intake (mg/kg BW0.75) also differed among formats (P < 0.05), with retorted wet diets resulting in greater intake than mildly cooked and extruded dry. Levels of TL (P < 0.05) and RL (P < 0.05) differed among diet formats, with extruded dry containing the lowest levels, although the RL: TL ratio did not significantly differ among formats. Within-format correlations between nutrients and MRP were limited and differed by format. These findings demonstrate that commercially available feline diets differ in concentrations of MRP, including AGE, and estimated AGE exposure, with retorted wet diets exhibiting the greatest values for all AGE among evaluated formats.