This study was conducted to investigate the growth of microorganisms, including pathogenic bacteria such as Cronobacter sakazakii and Bacillus cereus, in Sunsik beverages made of water, milk, soymilk, or honey-water during storage at room temperature. Prepared Sunsik beverages were stored at room temperature and the growth of total aerobic counts, Escherichia coli/coliforms, and yeast and mold were measured. Also, samples inoculated with a cocktail of C. sakazakii or B. cereus spores were stored at room temperature and their growths were determined during storage. Populations of total aerobic counts and coliforms significantly increased with increasing storage time at room temperature, which resulted in higher than 8 log and 7 log after 24 h in all samples except for the honey-water sample, respectively. Levels of total aerobic counts and coliforms were significantly lower in the honey-water sample than in the other samples after 6 and 9 h of storage, respectively. Initial populations of C. sakazakii and B. cereus ranged from 0 to 1 log CFU/mL, respectively, and these populations significantly increased with increasing storage time at room temperature. Therefore, populations of C. sakazakii and B. cereus were approximately 7 to 8 log CFU/mL after 24 h of storage. However, after 12 and 9 h of storage, there were significant differences in levels of C. sakazakii and B. cereus between the honey-water sample and the other samples, respectively. Based on these results, the addition of honey can inhibit microbial growth in Sunsik beverages; however, the best way to avoid pathogen infection would be to consume Sunsik beverages as soon as possible after preparation.

The combined effects of pH, water activity (a(w)), oxygen (O2) and carbon dioxide (CO2) levels on growth and sporulation of 10 common food-borne fungi were studied. The use of a multivariate statistical method (PLS) for the analysis of data showed that the fungi could be grouped according to their physiological response to changes in the four tested factors. Carbon dioxide, a(w) and pH were found to be the most significant factors describing differences and similarities among the fungi. Maximal inhibitory effect of elevated levels of CO2 (5-25%) and decreased a(w) (0.99-0.95) varied among the 10 species from 6 to 77% and from 52 to 100%, respectively. Sporulation of the fungi was sensitive to all tested factors. Furthermore, interaction of CO2 and a(w) displayed a significant effect on sporulation. It was shown that different fungal species associated with the same ecosystem responded similarly to changes in the tested factors. Thus, fungi which are not phylogenetically related may be physiologically related or show a common strategy of life.

Saeng-sikis a powdered ready-to-eat food with very low moisture that contains dried raw materials such as grains, fruits,mushrooms, and seaweeds. This product is consumed as a convenient and nutritious meal replacement. The objective of this study was to develop a mathematical model for predicting the survival of Clostridium perfringens vegetative cells and spores in saeng-sikas a function of temperature and to validate the model using saeng-siksamples with different microbial communities analyzed by matrix-assisted laser desorptionionization time-of-flight mass spectrometry. Kinetic data for C. perfringens survival in saeng-sikfit well to the Weibull model with high goodness off it (R(2) = 0.92 to 0.98). The obtained δ values (required time for first decimal reduction) for each temperature were 19.62 to 864.86 h, and concave curves (p < 1) were observed under all experimental conditions (5 to 40 degree C). Kinetic parameters were further described in a secondary model as a function of temperature using a Davey model (R(2) =0.99). The developed model was validated by the bias factor, accuracy factor, and root mean square error, and the values were within acceptable ranges for predictive models, even for saeng-sik samples with different microbial communities. When saeng-sikwas rehydrated according to the manufacturer’s recommendations, germination and outgrowth of C. perfringens was observed when the sample was subjected to unusual temperatures during storage, such as at 30 degree C for 15 h. C. perfringens spores survived in saeng-sik with very low water activity. Because C. perfringens could germinate and grow under such conditions, care must be taken to avoid initial contamination of C. perfringens during the manufacturing process. Our model developed with samples with different microbial communities provides useful information for next-generation microbiological risk assessment taking into consideration the ecology of the food-associated microbial community.

Fungal growth on solid foods can make them unfit for human consumption, but certain specialty foods require fungi to produce their characteristic properties. In either case, a reliable way of measuring biomass is needed to study how various factors (e.g. water activity) affect fungal growth rates on these substrates. Biochemical markers such as chitin, glucosamine or ergosterol have been used to estimate fungal growth, but they cannot distinguish between individual species in mixed culture. In this study, a real-time polymerase chain reaction (rt-PCR) protocol specific for a target fungal species was used to quantify its DNA while growing on solid food. The measured amount of DNA was then related to the biomass present using an experimentally determined DNA-to-biomass ratio. The highly sensitive rt-PCR biomass assay was found to have a wide range, able to quantify the target DNA within a six orders-of-magnitude difference. The method was used to monitor germination and growth of Penicillium chrysogenum spores on a model porous food (cooked wheat flour) at 25°C and different water activities of 0.973, 0.936, and 0.843. No growth was observed at 0.843, but lag, exponential and stationary phases were identified in the growth curves for the higher water activities. The calculated specific growth rates (μ) during the exponential phase were almost identical, at 0.075/h and 0.076/h for aw=0.973 and 0.936, respectively. The specificity of the method was demonstrated by measuring the biomass of P. chrysogenum while growing together with Aspergillus niger on solid media at aw=0.973.

The objective of the study was to evaluate the combined effects of pasteurization intensity (no heat treatment and 10min at 70, 80 and 90°C), water activity (aw) (0.960–0.990), pH (5.5–7.0) and storage temperature (7 and 10°C) on the survival and outgrowth of psychrotolerant spores of Bacillus cereus FF119b and Bacillus pumilus FF128a. The experiments were performed in both artificial media and a validation was performed on real food products (cream, béchamel sauce and mixed vegetable soup). It was determined that in general, heat treatments of 10min at 70°C or 80°C activated the spores of both B. cereus FF119b and B. pumilus FF128a, resulting in faster outgrowth compared to native (non-heat treated) spores. A pasteurization treatment of 10min at 90°C generally resulted in the longest lag periods before outgrowth of both isolates. Some of the spores were inactivated by this heat treatment, with more inactivation being observed the lower the pH value of the heating medium. Despite this, it was also observed that under some conditions the remaining (surviving) spores were actually activated as their outgrowth took place after a shorter period of time compared to native non-heated spores. While the response of B. cereus FF119b to the pasteurization intensity in cream and béchamel sauce was similar to the trends observed in the artificial media at 10°C, in difference, outgrowth was only observed at 7°C in both products when the spores had been heated for 10min at 80°C. Moreover, no inactivation was observed in cream or béchamel sauce when the spores were heated for 10min at 90°C in these two products. This was attributed to the protective effect of fat in the cream and the ingredients in the béchamel sauce. The study provides some insight into the potential microbial (stability and safety) consequences of the current trend towards milder heat treatments which is being pursued in the food industry.