Spoilage potential of a heat-stable lipase produced by Serratia liquefaciens isolated from cold raw milk

Abstract Serratia liquefaciens, a psychrotrophic bacterium isolated from raw milk, has a high potential for proteolytic spoilage. However, its lipolytic potential is underexplored. Thus, this work evaluated the lipolytic activity of 17 isolates of S. liquefaciens and their ability to produce heat-stable lipase. Using p-nitrophenyl palmitate as substrate, high variability of extracellular lipolysis was observed in all isolates of S. liquefaciens, and they were classified as weak, moderate and high lipase producers. Zymography detected a lipase of approximately 65 kDa in the culture supernatant of the moderate and high lipolytic isolates. In tributyrin agar, the hydrolysis halo was formed in a temperature range of 4–37 °C and, at 30 °C, the largest halo was detected. At temperatures of 65, 72, 85 and 95 °C, the lipase half-life times (t1/2) were 29.10, 19.94, 15.08 and 8.41 min and D-values were 96.71, 66.23, 50.10 and 27.95 min, respectively. After simulation of the slow pasteurisation, lipase maintained 47% of its activity, while after rapid pasteurisation, the lipase activity was not altered in skim milk. In conclusion, the ability of S. liquefaciens to secrete heat-stable lipase at refrigeration temperatures reveal the spoilage potential of this species in milk and dairy products.