042: Tracking Population Shifts of Non-Starter Lactic Acid Bacteria in the Presence of Spore Formers During Cheese Ripening

Introduction

Cheese ripening is influenced by microbial interactions, with non-starter lactic acid bacteria (NSLAB) playing a key role in flavor and texture development. However, spore formers can disrupt this balance, causing spoilage. This study examines the impact of spore formers on NSLAB dynamics and identifies dominant strains to enhance cheese quality and stability.

Methods

Pasteurized and standardized milk (110 L per batch) from Davis Dairy Plant, SDSU, Brookings, was used to produce Cheddar cheese. Two independent trials with three treatments: control (C), incorporated with inulin (1% w/v)(T1) and the mixture of aerobic (Bacillus licheniformis) and anaerobic spore former (Clostridium tyrobutyricum) (2 log10 CFU/ml) (T2), were made and stored at 7°C for six months. The physicochemical (pH, moisture, fat, protein) and microbiological analyses (spore counts, total plate count on TSA, Lactococcus on M17, and Lactobacilli on MRS) were done monthly in triplicates. Species and strain identification were performed using 16S rRNA sequencing and MALDI-TOF.

Results

At the start, the NSLAB counts were similar (2 log10CFU/g) in all three treatments; however, the trends showed that the NSLAB count increased faster in T1 (9-9.5 log10CFU/g) samples than in the C and T2 (8-8.2 log10CFU/g) after three months, reaching 10.5 log10CFU/g in T1 compared to C and T2 (8.5 log10CFU/g) after six months of ripening. The most dominant species of NSLAB was Lactobacilli, and the most dominant was Lb. rhamnosus, even in the presence of spore formers. In the case of spore counts, the spores count of T1 (≤1 log10CFU/g) was significantly lower than T2 (2.5 log10CFU/g) and comparable to C (1.2 log10CFU/g). This was supported by the presence of slits and gas holes in T2 cheese samples, while no defects were found in T1. There was no significant difference found in fat, protein, moisture, and pH, and all the parameters were within the acceptable range.

Significance

This study provides a foundation for future approaches to enhance cheese quality by examining the effects of spore formers treatments on cheese and NSLAB with and without inulin addition during ripening. It highlights the potential of inulin and NSLABs to control cheese spoilage during ripening more effectively.

Authors: Rakesh Kaushik, Sanjeev Anand