Inhibitory effect of Limosilactobacillus reuteri and nisin against Listeria monocytogenes in pasteurised Halloumi cheese

Background Halloumi cheese (HC) is a hard or semihard cheese that is characterised by having high water activity ( a w ), moderate pH and bountiful nutrients, making it a suitable environment for foodborne pathogens to proliferate. As ready‐to‐eat foods, cheeses should be free from Listeria monocytogenes and other pathogens. Aim The probiotic bacteria Limosilactobacillus reuteri and nisin were tested for their potential to inhibit L. monocytogenes in HC (10.0% brine) under various temperatures (4, 10 and 24°C). Methods Limosilactobacillus reuteri and L. monocytogenes were inoculated into HC at an initial level of ca. 10 6 –10 7 cfu/ml and 10 5 –10 6 cfu/g of brine, respectively. Nisin was added to the brine solution at the levels of 500, 1000 and 1500 IU/ml. The inhibitory effect of L. reuteri and nisin on L. monocytogenes was monitored for a 30‐d storage. Total mesophilic bacterial count (TBC) and yeast and mould counts were determined. The a w , salt content and pH changes were measured. Major Findings Limosilactobacillus reuteri grew in HC at all temperatures, but more preferably at 10 and 24°C. L. reuteri resulted in an evident antimicrobial activity against L. monocytogenes . The magnitude of reduction ranged between 1.0 and 2.5 log compared to the control. TBC and yeast and mould counts were significantly lower in the L. reuteri ‐treated and nisin treated HC compared to the control. The a w of the HC ranged between 0.94 and 0.97, and the salt content increased with time, reaching to >6.4% by the end of storage. The pH dropped, especially at 24°C from ca. 6.6 to <5.4 by the end of the storage. Scientific or Industrial Implications The study demonstrated that L. reuteri , as a probiotic, could considerably pose an antimicrobial potency against L. monocytogenes . Nisin was unequivocally effective in inhibiting the growth of L. monocytogenes in HC .