Enumeration and Identification of Spoilage Lactic Acid Bacteria in Chilled Food Products Using 3M™ Petrifilm™ Lactic Acid Bacteria Count Plate

Introduction: Lactic acid bacteria (LAB) are the major bacteria groups associated to spoilage of food products, particularly in reduced oxygen packaging (ROP). Understanding the diversity of LAB associated to spoilage in ROP product and non-ROP product is essential in improving the product quality and shelf life that will lead to a reduction in food waste.

Purpose:  Assess the impact of storage temperature on the abundance and diversity of LAB in selected ROP food products.

Methods:  A total of 200 ROP chilled food products were purchased from the local retail. A portion of the samples were stored at 4^oC or 25-27^oC for 20h before the microbiological assessment was performed. Total aerobic bacteria (TPC) and LAB in food products were enumerated using 3M^TM Petrifilm^TM Aerobic Count Plate and 3M^TM Petrifilm^TM Lactic Acid Bacteria Count Plate, respectively. About 5-10 LAB colonies were isolated from each sample for bacterial identification.

Results: LAB were detected in 74% of the total samples, that ranged from 1.00-7.48 log₁₀CFU/g, with significantly higher counts in ROP products including chicken sausage, chicken rolls and mushrooms (p<0.01) compared to produce, sauces and starchy foods. The LAB counts in food products stored at room temperature were significantly higher compared to before and after storage at 4°C (p<0.05). ROP products stored at 4°C for 20h did not significantly increase the total bacteria count (p>0.05), but the LAB had a significant increase (p<0.01) with about 1.02 log₁₀CFU/g increment for LAB.

Significance: LAB were present in the majority of the chilled food products included in this study, particularly in ROP products. Refrigeration and ROP arrest only the growth of aerobic bacteria, but not LAB that may cause spoilage. Quantification and control of LAB are essential to optimize shelf life of food ROP products.