Classification of food spoilage bacterial species and their sodium chloride, sodium acetate and glycine tolerance using chemometrics analysis and Raman spectroscopy

The purpose is classification of stress tolerances of spoilage bacteria using Raman spectra and chemometrics. We obtained Raman spectra of six spoilage bacteria. Classification models were constructed with support vector machine and classified food-related stress tolerance with 90% accuracy, which provides bacterial characteristics specific to environment reducing food spoilage.

Allyl isothiocyanate encapsulated halloysite covered with polyacrylate as a potential antibacterial agent against food spoilage bacteria

Allyl isothiocyanate (AITC) is a highly volatile organic compound that is a potential antibacterial agent against food spoilage bacteria. Naturally formed halloysite nanotubes (HNTs) have a length of 1 μm and diameter ranging from 10 to 50 nm. The biocompatibility of HNT allows safe release of drugs to bacterial cells at a relatively low concentration compared to other systems. We encapsulated AITC inside HNTs that were then coated with sodium polyacrylate (PA). The HNT-AITC-PA nanocomposites (NCs) were characterized by Fourier-transform infrared spectroscopy, thermal gravimetric, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. In vitro antibacterial activity was evaluated against gram positive (Staphylococcus aureus) and gram negative (Escherichia coli) bacteria capable of food spoilage. HNT-AITC-PA NCs effectively inhibited the growth of both bacteria. The activity was pronounced against E. coli at 100 μg/mL, with concentrations of 25 μg/mL and 200 μg/mL reducing the viable cell population by 41% and 96%, respectively. Thus, HNT-AITC-PA NCs are a novel and promising material against food spoilage bacteria for use in active antibacterial food packaging.

Stochastic modeling of variability in survival behavior of Bacillus simplex spore population during isothermal inactivation at the single cell level using a Monte Carlo simulation

The control of bacterial reduction is important to maintain food safety during thermal processing. The goal of this study was to illustrate and describe variability in bacterial population behavior during thermal processing as a probability distribution based on individual cell heterogeneity regarding heat resistance. Toward this end, we performed a Monte Carlo simulation via computer, and compared and validated the simulated estimations with observed values. Weibullian fitted parameters were estimated from the kinetic survival data of Bacillus simplex during thermal treatment at 94 °C. The variability in reductions of bacterial sporular populations was illustrated using Monte Carlo simulation based on the Weibull distribution of the parameters. In particular, variabilities in viable spore counts and survival probability of the B. simplex spore population were simulated in various replicates. We also experimentally determined the changes in survival probability and distributions of survival spore counts; notably, these were successfully predicted by the Monte Carlo simulation based on the kinetic parameters. The kinetic parameter-based Monte Carlo simulation could thus successfully illustrate bacterial population behavior variability during thermal processing as a probability distribution. The simulation approach may contribute to improving food quality through risk-based processing designs and enhance risk assessment model accuracy.

Purification and characterization of enterocin FH 99 produced by a faecal isolate Enterococcus faecium FH 99

Enterococcus faecium FH 99 was isolated from human faeces and selected because of its broad spectrum of inhibitory activity against several Gram-positive foodborne spoilage and pathogenic bacteria. Ent. faecium FH 99 accumulates enterocin in large number in early stationary phase of the growth. The enterocin FH 99 was stable over a wide pH range (2-10) and recovered activity even after treatment at high temperatures (10 min at 100°C). The enterocin was subjected to different purification techniques viz., gel filteration, cation exchange chromatography and reverse-phase high-performance liquid chromatography. The activity was eluted as one individual active fraction. SDSPAGE revealed a molecular weight of less than 6.5 kDa. Studies carried out to identify the genetic determinants for bacteriocin production showed that this trait may be plasmid encoded as loss in both of the plasmids (size>chromosomal DNA) led to loss in bacteriocin production by Ent. faecium FH 99. Ent. faecium strain FH 99 is a newly discovered high bacteriocin producer with Activity Units 1.8 × 10(5) AU ml(-1) and its characteristics indicate that it may have strong potential for application as a protective agent against pathogens and spoilage bacteria in foods.