Kinetic parameters of microbial thermal death in goat cheese whey and growth of surviving microorganisms under refrigeration

Abstract

AbstractWhey is a byproduct of cheese production and, in smallholdings, is usually destined for animal feed or improperly disposed. To create alternatives for whey use, microbiological stabilization is the first step. Therefore, this study evaluated the kinetic parameters of the native microbiota thermal death (62–85°C) in goat cheese whey (GCW) and the growth of survivors after thermal processing performed at three different time–temperatures. The results showed that the come‐up time inactivated 1.0–1.8 log CFU/ml (≤71°C), 3.8 log CFU/ml (75°C), and more than 8 log CFU/ml (≥80°C). The inactivation data at 62, 65, 68, 71, and 75°C were fitted to the Bigelow model, from which D values of 65.7, 31.0, 11.7, 5.4, and 1.2 min, respectively, were determined. Using a first‐order equation, the z value was calculated as 7.5°C (R2 = 0.99). Processes time–temperatures were selected to achieve 2.5 (71°C/20 min), 0.5 (75°C/5 min), and <0.1 log CFU/ml (80°C/1 min) survivors. During the shelf life, microbiological growth was observed in all samples, reaching total bacterial counts (TBC) and psychrotrophic bacteria (TPC) >3 log CFU/ml between 14 and 28 days, with a predominance of non‐acidifying psychrotrophic bacteria. From the results, the time–temperature of 75°C/5 min was established as the best option for GCW processing, ensuring counts <2 log CFU/ml for up to 21 days.Practical ApplicationsThis study showed that the time–temperatures 71°C/20 min, 75°C/5 min, or 80°C/1 min, applied in a batch pasteurization process, were able to inactivate more than 5 log CFU/ml of the native microbiota of goat cheese whey. However, the shelf life of the product at 7°C was limited to 21 days due to the growth of the surviving population, even for samples that reached <0.1 log CFU/ml immediately after heating. Therefore, if extended shelf life is needed, additional barriers to microbial growth should be used. These data can be readily applied by artisanal goat cheese producers as a way to stabilize whey for later use, either in the development of whey beverages or for the use of whey as an ingredient in products.