Evaluation of the Antimicrobial Activity and Efficacy of Natural Preservatives Against Spoilage Microorganisms in Fermented Dairy Products

Abstract

This study investigated the preservative efficacy of six natural compounds, clove essential oil, nisin, infused olive oil, garlic extract, ginger extract, and extra virgin olive oil, across five culturally significant fermented dairy products: yogurt (FDP-01), kefir (FDP-02), paneer (FDP-03), shrikhand (FDP-04), and misti doi (FDP-05). The objective was to evaluate their antimicrobial, physicochemical, and sensory impact over a 21-day refrigerated storage period, with emphasis on microbial suppression, shelf-life extension, and consumer acceptability.

Microbial screening was performed against dominant spoilage organisms, including Bacillus subtilis, Pseudomonas fluorescens, Escherichia coli, Candida albicans, and Penicillium spp. Zone of inhibition assays, MIC/MBC/MFC determinations, and multivariate ranking revealed clove essential oil and nisin as the most potent agents, with MIC values ≤0.5 mg/mL and complete inhibition of fungal growth at low concentrations. Their efficacy was further validated through declining total viable counts (TVC) in treated samples, maintaining microbial loads below spoilage thresholds throughout storage.

Physicochemical parameters (pH, titratable acidity, viscosity) were monitored at 7-day intervals using standard methods. Control samples exhibited progressive acidification and viscosity loss, while clove oil and nisin treatments preserved structural integrity across all matrices. In paneer and misti doi, nisin proved particularly effective in minimizing curd separation and proteolytic degradation. Strong inverse correlations were observed between microbial proliferation and both pH (r = –0.88) and viscosity (r = –0.76), affirming the biochemical role of microbial control in spoilage prevention.