Pseudomonas spp.: Are Food Grade Organic Acids Efficient against These Spoilage Microorganisms in Fresh Cheeses?

Erica Tirloni,Cristian Bernardi,Simone Stella

doi:10.3390/foods10040891

Abstract

Psychrotolerant Pseudomonas spp. are among the most common spoilage agents in fresh, soft and semi-soft cheeses; therefore, hurdles inhibiting their growth are in strong demand by producers. This study aimed to establish Minimal Inhibiting Concentrations (MICs) of lactic and acetic acid towards P. fluorescens and to evaluate the efficacy of a cheese surface treatment with these two organic acids. MICs were determined in Brain Heart Infusion broth at 30 °C: the inhibition was achieved at a concentration of 49.96 mM and 44.40 mM of acetic and lactic acid, respectively. Two series of inhibition tests were performed on fresh “Primo sale” cheese, inoculated with P. brenneri MGM3, then dipped into different acid solutions (acetic acid: 49.96, 99.92 and 149.88 mM; lactic acid: 44.40, 88.80 and 133.20 mM) and stored at 6 °C. P. brenneri MGM3 were enumerated, including a control series. A significantly lower growth was revealed at the highest concentrations tested, both for acetic (p < 0.01) and lactic acid (p < 0.05) if compared to control samples. A conditioning of “Primo sale” surface with organic acid solutions could be a useful hurdle for Pseudomonas inhibition and shelf-life extension; it should be applied in combination with other mild interventions to fight spoilage and maintain the original product characteristics.

Highlights

A large proportion of food gets spoiled before reaching the end consumer
Minimal Inhibiting Concentrations (MICs) were determined in Brain Heart Infusion broth at 30 ◦C: the inhibition was achieved at a concentration of 49.96 mM and 44.40 mM of acetic and lactic acid, respectively
Two series of inhibition tests were performed on fresh “Primo sale” cheese, inoculated with P. brenneri MGM3, dipped into different acid solutions and stored at 6 ◦C

Summary

Introduction

A large proportion of food gets spoiled before reaching the end consumer. According to the Food and Agriculture Organization of the United Nations, one-third of the food produced for human consumption is spoiled or wasted [1]. Spoilage of food for human consumption is a world-wide issue that is of particular interest for stakeholders, food producers and consumers. Psychrotolerant Pseudomonas spp. are among the most common bacteria implicated in spoilage, especially of refrigerated food with a prolonged shelf life, where they are likely selected [4,5,6]. Pseudomonas spp. produce thermotolerant lipolytic and proteolytic enzymes that reduce the quality and the shelf-life of raw and processed milk [10]. These bacteria are inactivated by the thermal processes currently applied through the production of most dairy products, but they can enter the food production chain as post-process contaminants, due to the contact of the final product with soil, water or raw material [11]. Pseudomonads are recognized to be able to colonize environmental production as well as equipment and facilities for long periods, thanks to their ability to produce persistent biofilms [12,13]

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