Evaluation of the Antifungal Activity of Non-Starter Lactic Acid Bacteria (NSLAB) Cultures Using a Caciotta Cheese Model System

Introduction:  Due to their low pH, nutritional profile, and storage conditions, dairy products are very susceptible to the growth of filamentous fungi that can cause alterations in the cheese rind and texture, which leads to significant economic losses. Lactic acid bacteria are well known for their ability to produce a number of fungal inhibitory metabolites, such as organic acids, cyclic dipeptides, proteinaceous compounds, and fatty acids. So, these bacteria could be good candidates for cheese biopreservation.

Purpose:  In this study, different non-starter lactic acid bacteria (NSLAB) cultures, containing Lactobacillus spp. strains previously selected for their in vitro antifungal properties, were used as an adjunct in the laboratory-scale manufacturing of Caciotta cheese, in order to evaluate their ability to inhibit Penicillium spp. and Aspergillus spp. strains.

Methods:   Two trials were performed. In each trial, three cheese batches were produced: a control batch containing the commercial starter cultures; a batch containing the starter with one Lactobacillus spp. strain; and a batch containing the starter with the multi-strain NSLAB culture. In the first trial, the mold suspensions were applied to the surface of one week old control and experimental cheeses. In the second trial, the mold suspension was inoculated into the milk after the addition of cultures.

Results: The addition of selected NSLAB cultures delayed the mycelial growth of both Penicillium chrysogenum and Aspergillus flavus, as well as that of environmental fungi, on the cheese surface. A stronger antifungal effect was observed in cheeses produced with multi-strain NSLAB cultures and mould inoculated into the milk. This effect resulted in a growth reduction of P. chrysogenum by 2.5 - 3.0 log units after 30 days of storage.

Significance:  Our results indicate that selected NSLAB cultures could have an application as novel preservatives used to extend shelf-life and prevent fungal spoilage of cheese during storage at 8°C.