Comparative Growth Inhibition of Bread Spoilage Fungi by Different Preservative Concentrations Using a Rapid Turbidimetric Assay System

Abstract

Bread and intermediate moisture bakery products are mainly spoiled by yeasts and filamentous fungi. The inoculum load and preservation system used determines their shelf life. To extend the shelf life of such commodities, the use of chemical preservatives is the most common way to try and control the initiation of mold spoilage of bread. This study has utilized a rapid turbidimetric assay system (Bioscreen C) to examine the temporal efficacy of calcium propionate (CP) and potassium sorbate (PS) for controlling the growth of important bread spoilage fungi. The objectives were to compare the temporal growth of strains of three important spoilage fungi Hyphopichia burtonii (HB17), Paecilomyces variotii (PV11), and Penicillium roqueforti (PR06) isolated from visibly molded bread to (a) different concentrations of CP and PS (0–128 mM), (b) temperatures (25°C, 30°C), (c) water activity (aw; 0.95, 0.97), and (d) pH (5.0, 5.5). All three abiotic factors, pH, aw, and temperature, and preservative concentrations influenced the relative growth of the species examined. In general, PS was more effective than CP in inhibiting the growth of the strains of these three species. In addition, the Time to Detection (TTD) for the efficacy of the preservatives under the interacting abiotic factors was compared. The strain of Paecilomyces variotii (PV10) was the most tolerant to the preservatives, with the shortest TTD values for both preservatives. P. roqueforti was the most sensitive with the longest TTD values under all conditions examined. These results are discussed in the context of the evolution of resistance to food-grade preservatives by such spoilage fungi in bakery products.

Heterogeneity in stress resistance of Paecilomyces variotii and related food spoilage fungi

“…For every P. variotii strain used in this study, a higher MIC for sorbic acid was found than previously reported for a P. variotii strain isolated from a South American soft drink production facility (Stratford et al, 2009). In another study, a P. variotii strain isolated from bakery products was able to grow at extremely high concentrations of potassium sorbate up until 128 mM in Yeast Extract Sucrose broth at pH 5.0 (Garcia et al, 2021). This concentration corresponds to 45 mM undissociated sorbic acid, which is more than 4 times higher than the highest MIC found in this study.…”

“…Minimum inhibitory concentrations (MICs) for sorbic acid were 1.4 -4.4-fold higher when compared to that of a P. variotii strain isolated from a South American soft drink facility (Stratford et al, 2009). On the other hand, up to four time higher MIC values were found for a P. variotii strain isolated from bakery products, albeit in a different experimental setup (Garcia et al, 2021). Although heat resistance was not significantly correlated with sorbic or benzoic acid resistance, the two most sorbic acid resistant strains, DTO 195-F2 and DTO 282-E5, were also heat resistant.…”

“…In fact, it was recently suggested that this fungus can even grow at temperatures below 0 °C, based on cardinal values of growth models (Nguyen Van Long et al, 2021). On the other hand, halotolerant species such as A. niger have the ability to grow in highly acidified environments down to pH 1.4 (Schuster et al, 2002), while other species can grow at high concentrations of weak acids that are widely used as preservatives, such as sorbic, benzoic and propionic acid (Garcia et al, 2021). Xerophilic fungi are specialized in growing at low water activity ( a w < 0.85).…”

Vegetable fermentations brined with low salt for reclaiming food waste

“…About 1% acetic acid prevents the proliferation of Clostridium botulinum and the consequent production of toxin in cucumber fermentations brined with 6% NaCl (Ito et al., 1976; Koukou et al., 2021). Potassium sorbate was incorporated into the fermentation cover brines anticipating that the activity of the indigenous yeasts and molds could induce undesirable chemical and physical changes in the vegetables (Etchells et al., 1961; Garcia et al., 2021; Guillou et al., 1992; Mehyar et al., 2011; Pérez‐Díaz et al., 2015; Stratford et al., 2020). Yeast growth is sporadically observed in vegetable fermentations particularly under aerobic conditions and with shredded substrates (Etchells et al., 1947).…”

Natural Variation and the Role of Zn2Cys6 Transcription Factors SdrA, WarA and WarB in Sorbic Acid Resistance of Aspergillus niger

“…Commonly found food-spoiling Ascomycetes include, for example, A. niger, Paecilomyces variotii and Penicillium roqueforti [2]. Therefore, preservative resistances of Ascomycetes have been investigated before, especially in relation to specific food products such as bread [23][24][25][26].…”