Influence of guar gum on the thermal stability of Listeria innocua, Listeria monocytogenes, and gamma-glutamyl transpeptidase during high-temperatureshort-time pasteurization of bovine milk

Mathematical models describing the thermal inactivation of gamma-glutamyl t ranspeptidase (TP) and Listeria innocua in milk during high-temperature sho rt-time (HTST) pasteurization were validated with data from TI: L. innocua, and L. monocytogenes trials in guar gum-milk. Holding tube times were dete rmined for turbulent flow using water, and for laminar flow using a guar gu m (0.27% wt/wt)-sucrose (5.3% wt/wt)-water mixture. Inactivation of TP and L. innocua was lower in a solution of guar gum (0.25% wt/wt) in whole milk than was predicted by models derived from studies with whole milk alone. Us e of laminar flow timings improved model fit but did not completely account for the observed protective effect. L. monocytogenes survival was close to that predicted by the L. innocua model, although some protection was affor ded this pathogen under laminar flow. Considerable intertrial variability w as noted for L. monocytogenes. Risk analysis simulations using @RISK, a Lot us 1-2-3W add-in, were used to account for intertrial variability. Simulate d log(10) %reductions consistently underpredicted experimental L. monocytog enes survival (fail-safe), thus the L. innocua model derived in milk is sui table for estimating L. monocytogenes survival in viscous products. Increas ed thermal tolerance during laminar flow may be attributed to the protectiv e effect of stabilizer.