Experimental studies and modeling the behavior of anaerobic growth of Clostridium perfringens in cooked rice under non-isothermal conditions

How can packaging, source and food safety management system affect the microbiological quality of spices and dried herbs? The case of a developing country

Spices and herbs are widely used in almost all types of food preparation and their microbial contamination may cause spoilage and pose public health risk. Thus, the aim of this study was to assess the effect of packaging, source and a food safety management system (FSMS) on the microbiological quality of spices and dried herbs in a developing country, like Lebanon. For this, a total of 96 composite samples of thirteen most commonly consumed types of spices and dried herbs were collected twice at three-month interval. Each type was purchased in 5 common brands from 4 categories: packaged in companies with FSMS, packaged in companies without FSMS, packaged imported, and unpackaged. Total aerobic mesophilic bacteria (TAMB), sulfite reducing anaerobic bacteria, C. perfringens, coliforms, E. coli, yeasts and molds were found in 89%, 43%, 18%, 15%, 1% and 54% of the samples, respectively. All samples were negative for Salmonella. One per cent, 4%, 6%, 1% and 7% of the samples had unacceptable levels of TAMB, coliforms, sulfite reducing anaerobic bacteria, E. coli, yeasts and molds, respectively. Among the four categories, imported samples had the lowest microbiological load, followed by locally packaged in companies with FSMS, then locally packaged in companies without FSMS and the highest microbiological load was for the unpackaged spices and dried herbs. This study highlighted the importance of storage conditions, good hygienic practices, process controls and FSMSs in the spices and dried herbs sector.

Validation of a Simple Two-Point Method To Assess Restaurant Compliance with Food Code Cooling Rates

ABSTRACT

Outbreaks from improperly cooled foods continue to occur despite clearly described Food Code cooling guidelines. It is difficult for regulators to enforce these guidelines because they are typically in an establishment for less than the 6 h needed to document proper cooling. Prior research proposed using a novel method to estimate cooling rates based on two time-temperature points, but this method has not yet been validated. Time-temperature profiles of 29 different foods were collected in 25 different restaurants during cooling. Cooling curves were divided into two categories: typical (21 foods) and atypical (eight foods) prior to further analysis. Analysis of the typical cooling curves used simple linear regression to calculate cooling rates. The atypical cooling profiles were studied using Monte Carlo simulations of the cooling rate. Almost all linearized typical cooling curves had high (>0.90) R2 values. Six foods with typical cooling profiles that did not pass Food Code cooling times were correctly identified by the two-point model as having slow cooling rates. Three foods that did not pass Food Code cooling times were identified by the two-point model as having marginal cooling rates. Ten of 12 foods identified by the two-point model as having acceptable cooling rates met Food Code cooling times. Most (six of eight) foods that were considered to have atypical cooling curves failed to meet the Food Code cooling times. The two-point model was also able to determine whether these foods would fail based on Food Code guidelines depending upon the simulation criteria used. Our data show that food depth has a strong influence on cooling rate. Containers with a food depth ≥7.6 cm (3 in.) were more likely to have cooling rates slower than the U.S. Food and Drug Administration Model Food Code cooling rate. This analysis shows that the two-point method can be a useful screening tool to identify potential cooling rate problems during a routine restaurant inspection visit.

HIGHLIGHTS

Modeling for Survival of Clostridium perfringens in Saeng-sik, a Powdered Ready-to-Eat Food with Low Water Activity

HIGHLIGHTS

We developed a mathematical model to predict the survival of C. perfringens in food. C. perfringens vegetative cells and spores were inoculated into dried powder food. The a_w of saeng-sik was below 0.1. Weibull and Davey models can successfully describe the survival of C. perfringens. The developed model can be applied to samples with different microbial communities.

Assessment of microbial safety and quality changes of brown and white cooked rice treated with atmospheric pressure plasma

The microbial and physicochemical properties of brown and white cooked rice treated by atmospheric pressure plasma (APP). APP was produced (250 W, 15 kHz, ambient air) and applied to brown and white cooked rice for 5, 10, and 20 min. The 20-min plasma treatment reduced in bacterial counts by 2.01 log CFU/g when cooked rice were inoculated with Bacillus cereus or Escherichia coli O157:H7. The pH of the brown cooked rice was decreased by the 5-min plasma. The hardness values of APP-treated brown and white cooked rice were lower than untreated samples. The reducing sugar contents of brown and white cooked rice were significantly higher than those in untreated samples. Lipid oxidation of APP-treated brown and white cooked rice were higher compared to untreated samples. These results indicate that APP improves microbial quality, although further studies should be conducted to change the physicochemical qualities of brown and white cooked rice induced by APP.

Evolution of model specific relative growth rate: Its genesis and performance over Fisher's growth rates

Growth curve models play an instrumental role to quantify the growth of biological processes and have immense practical applications across disciplines. In the modelling approach, the absolute growth rate and relative growth rate (RGR) are two most commonly used measures of growth rates. RGR is empirically estimated by Fisher (1921) assuming exponential growth between two consecutive time points and remains invariant under any choice of the underlying growth model. In this article, we propose a new measure of RGR, called modified RGR, which is sensitive to the choice of underlying growth law. The mathematical form of the growth equations are utilized to develop the formula for model dependent growth rates and can be easily computed for commonly used growth models. We compare the efficiency of Fisher's measure of RGR and modified RGR to infer the true growth profile. To achieve this, we develop a goodness of fit testing procedure using Gompertz model as a test bed. The relative efficiency of the two rate measures is compared by generating power curves of the goodness of fit testing procedure. The asymptotic distributions of the associated test statistics are elaborately studied under Gompertz set up. The simulation experiment shows that the proposed formula has better discriminatory power than the existing one in identifying the true profile. The claim is also verified using existing real data set on fish growth. An algorithm for the model selection mechanism is also proposed based on the modified RGR and is generalized for some commonly used other growth models. The proposed methodology may serve as a valuable tool in growth studies in different research areas.

Propidium Monoazide Quantitative Real-Time Polymerase Chain Reaction for Enumeration of Some Viable but Nonculturable Foodborne Bacteria in Meat and Meat Products

Foodborne infections due to bacterial pathogens are increasing worldwide. Given the surreptitious nature of viable but nonculturable (VBNC) bacteria, they largely remain a threat to public health and food safety due to their non-detectability through conventional plate count techniques. Hence, species-specific quantitative real-time polymerase chain reaction (PCR) (qPCR) alone and combined with the use of propidium monoazide (PMA) was used along with the plate count method to quantify VBNC Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, and Enterobacteriaceae in fresh and processed meat samples. The major bacterial pathogen isolated was S. aureus (93%) followed by Enterobacteriaceae (80.33%), C. perfringens (26.33%), and B. cereus (21.33%); their total viable counts were mostly recorded in raw meat than examined meat products. PMA quantitative real-time PCR (PMA qRT-PCR) could detect and quantify VBNC bacteria in 90.48% of culture-negative samples. It affirmed the presence of VBNC S. aureus (n = 10), B. cereus (n = 8), C. perfringens (n = 6), and Enterobacteriaceae (n = 12) in either single or mixed bacterial contamination. The log₁₀ mean values of VBNC bacterial counts were highly reported for C. perfringens and S. aureus (9.60 ± 0.449 and 8.27 ± 0.453 CFU/g, respectively) followed by Enterobacteriaceae (6.95 ± 0.564 CFU/g) and B. cereus (6.69 ± 0.749 CFU/g). Sequencing of rpoB gene of Enterobacteriaceae enabled the identification of Klebsiella pneumoniae complex, Enterobacter cloacae complex, and Salmonella Typhi, which have been reported to be capable of entry into the VBNC state. To our knowledge, this is the first report at least in Egypt that records the presence of VBNC cells in meat samples representing a strong threat to public health and food safety. Moreover, PMA qRT-PCR allowed a quick and unequivocal way of enumeration of VBNC foodborne bacteria.