The effect of steam pelleting of a dry dog food on the Maillard reaction

During processing of pet foods, the Maillard reaction (MR) can occur, which reduces the bioavailability of essential amino acids like lysine and results in the formation of advanced Maillard reaction products (MRPs). This study examined the effect of conditioning temperature (65 and 90 °C) and die hole length (ø 5 × 45, 65, and 80 mm) during pelleting processing of a standard dry dog food on selected indicators of the MR (total lysine, reactive lysine, fructoselysine, ɛ-N-carboxymethyllysine, (5-hydroxymethyl)-2-furfural, lysinoalanine), browning development and CIE-Lab color. Steam pelleting variables did not cause a significant loss of lysine or change in color and absorbance values. Analyzing the unprocessed ingredient mix suggests that the choice of the ingredients used in the ingredient mix, rather than the pelleting process applied, is responsible for the RL/TL ratio observed in the dry standard dog food used in this study. MRP content increased during steam pelleting (fructoselysine: 366.2 to 538.8 mg/kg DM; ɛ-N-carboxymethyllysine: 12.6 to 14.8 mg/kg DM; lysinoalanine: 5.7 to 7.7 mg/kg DM; P<0.05). Increasing conditioning temperature from 65 to 90 °C increased fructoselysine (475.9 to 601.6 mg/kg DM; P<0.01) and ɛ-N-carboxymethyllysine (14.3 to 15.1 mg/kg DM; P=0.003). An increased die hole length of 80 mm decreased fructoselysine content compared to 45 and 65 mm (461.3 vs. 573.3 and 581.6 mg/kg DM; P<0.01) but increased lysinoalanine content (8.8 vs. 7.4 and 6.8 mg/kg DM; P=0.002). Analyzing total and reactive lysine and absorbance values are not accurate enough to predict the MR and formation of MRPs during processing.