Risks of Suppressing Lactic Acid Process by Residual Disinfectants

Cheese production is a complex biotechnological process that places high demands on the quality of raw milk, including the absence of bacterial growth inhibitors. Residual amounts of disinfectants may accidentally act as such inhibitors. Industrial dairy producers prefer peracetic acid- and hydrogen peroxide-based disinfectants due to their strong biocidal activity. Omitting the final rinse is a common violation of equipment disinfection protocols. As a result, residual disinfectants may enter dairy products. If they enter a milk mix intended for cheese production, they can inhibit the growth of starter microflora, disrupt production processes, and reduce the safety and quality of the finished product. This article describes the effect of a residual peracetic acid-based disinfectant on the reactivation, development, and acid-forming activity of lactococci and thermophilic streptococci, which are the main acid-forming microorganisms in cheese starters. Lactococci and thermophilic streptococci cultures were used as dry bacterial starters, simulating the direct inoculation of starter cultures into the cheese vat. The inhibitory effect of the disinfectant was studied at peracetic acid concentrations of 0.01; 0.005; 0.001; 0.0005 and 0.00006%. Standardized microbiological analysis made it possible to quantify the development of starter microflora and assess its acid-forming activity. A concentration of 0.01% had a bactericidal effect on lactococci and thermophilic streptococci; 0.005% peracetic acid demonstrated a bactericidal or bacteriostatic action; concentrations of ≤0.001% caused developmental inhibition.