Effect of bioprotective cultures on Listeria monocytogenes in milk and high moisture cheese

Obj 1. ​Determine the antimicrobial activity of cell-free supernatants of LALCULT® Protect LCl against L. monocytogenes in laboratory growth media. Obj 2. Determine the antimicrobial activity of LALCULT® Protect LCl against L. monocytogenes when co-cultured in milk following a typical cheesemaking temperature profile. Obj 3. Assess the survival of L. monocytogenes during the manufacture and storage of Queso Fresco manufactured with either LALCULT® Protect LCl or Lyofast LPAL (Lactplantibacillus plantarum; Sacco) when added as direct vat set or bulk cultures.​ Abstract: ​Listeria monocytogenes contamination continues to pose a threat to cheese safety irrespective of prior milk lethality treatments. This is of particular concern for high moisture cheeses (>50%; e.g., Queso Fresco) that have been shown to support L. monocytogenes growth to high levels. Due to restrictions on the use of most antimicrobial interventions imposed by the Standards of Identity for cheese (21 CFR 133) and the emerging consumer demand for safe yet minimally processed, ""clean label"" foods, the development and validation of more natural control measures are most needed. The use of protective bacterial cultures (PCs) to inhibit the growth of undesirable microorganisms, known as biopreservation, is a promising approach for enhancing the safety of cheese. Previous research in our lab has tested in milk several bacterial cultures that are currently approved as ingredients in all cheeses and do not require additional labeling as promising alternatives. LALCULT® Protect LCl, is a new bioprotective culture of Carnobacterium maltaromaticum; a psychrotolerant and halotolerant lactic acid bacterium with limited aromatic contribution and limited acidification that does not inhibit acidifying cultures. Preliminary data provided by the culture supplier have shown that LCl inhibited the growth of L. monocytogenes in Camembert cheese over the 40-day shelf life, whereas populations increased ~2-3 log CFU/g in cheeses produced with other protective cultures on the market. However, the efficacy of this culture in the production of other cheeses and how this compares to other cultures is not known. One potential limitation in the application of protective cultures in cheese production is the limited growth and antimicrobial metabolite production during cheesemaking when added as direct set cultures in frozen or freeze-dried formats. The use of bulk starter cultures is an option for cheesemakers looking to overcome the lag period and acidification. A similar approach with PCs may be a viable option to enhance their antimicrobial activity in cheese. Thus, the proposed work will determine the efficacy of LC1 to control L. monocytogenes in milk, which will be compare to previous results obtained with other protective cultures available to producers. We will then determine the effect of LC1 and Lyofast LPAL on L. monocytogenes as milk contaminants during the production and storage of Queso Fresco including a comparison of direct set application of protective cultures and a novel bulk culture approach.​