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

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.

Storage environment/packaging materials impacting bread spoilage under ambient conditions: A comparative analysis

Packaging in bread-making industry is one of priorities to satisfy the peculiar requirements of freshness in bread. A suitable packaging material allows for both rapid heat exchange with the environment and water vapour evaporation in order to prevent condensation inside the bread package. The effectiveness of some storage media/packaging materials in preventing bread spoilage under ambient temperature was studied. Bread staling, microbiological stability and organoleptic changes were evaluated as a function of storage time. The functional properties (water and oil absorption capacities and water oil absorption indices) of the bread were estimated .The water absorption capacity (WAC) of bread was in the range of 144-221 g/100 g sample, while the oil absorption capacity (OAC) range was 113-132 g/100 g. Water Oil Absorption Capacity (WOAI) for each of the packaging materials was < 2.0, which indicates the lipophilic nature. All the bread slices stored under different media/packaging materials, except perforated bowl and transparent plastic bowl exhibited sensory scores of 2.5 and above. Microbial growth manifested in bread kept in perforated and transparent plastic containers compared to the bread kept in cellophane and aluminum plate. This study clearly shows differences in the rates of staling, microbial stability and physical/chemical changes at different storage conditions.