A pilot study on spoilage dynamics in industrially produced Paneer Shahri, a traditional Iranian fresh cheese

Introduction Paneer Shahri is a traditional Iranian fresh cheese with high moisture and near-neutral pH, making it susceptible to microbial spoilage. This study aimed to assess spoilage-related changes in Paneer Shahri during storage. Methods Microbial, physicochemical, textural, and sensory changes in industrially produced, enzyme-coagulated Paneer Shahri were evaluated during cold storage (8 °C) over 34 days. Results Despite pasteurization, spoilage was primarily driven by non-starter lactic acid bacteria (NSLAB), including Lactococcus lactis, Enterococcus faecalis, and Lacticaseibacillus rhamnosus. These bacteria, all proteolytic and psychrotrophic, were consistently recovered throughout storage and became dominant members of the microbial community. Fermentation of residual lactose by LAB led to a significant decline in pH and an increase in titratable acidity, creating acidic conditions that further supported LAB persistence. Proteolysis contributed to texture softening, as reflected by declining chewiness, gumminess, springiness, and cohesiveness. Biogenic amine production by E. faecalis, particularly tyramine, was observed, posing a potential safety concern during prolonged storage. No Enterobacteriaceae, coagulase-positive staphylococci, or aerobic spore-formers were detected, and lipolysis remained negligible throughout the storage period. Yeasts and molds appeared only in the late stages of storage, and sensory analysis revealed declining smell and overall acceptability, consistent with microbial and biochemical spoilage markers. Discussion These findings highlight the metabolic activity and persistence of NSLAB as key drivers of spoilage in the absence of classical pathogens, emphasizing the importance of monitoring LAB activity to extend shelf life in fresh high-moisture cheeses.