Food Microbiology

Food Safety and Modernization Act (FSMA) Preventive Control rules require nut processors validate thermal processes to ensure a desirable log reduction of Salmonella is achieved. Due to the complex nature of nut and nut products, processes and equipment, it is difficult to use one validation study for all and may requires individual equipment be validated at the plant level. In plant validation studies, pathogens such as Salmonella cannot be used due to the risk of contamination, thus the suitability of a non-pathogenic organism, Enterococcus faecium as a surrogate for Salmonella was evaluated for peanut and pecan thermal processing...

A direct microscopic time-lapse method, using appropriate staining for cell viability in a confocal scanning laser microscope, was used for the direct assessment of Salmonella Agona individual cell inactivation in small two-dimensional colonies exposed to osmotic stress. Individual cell inactivation times were fitted to a variety of continuous distributions using @Risk software. The best fitted distribution (LogLogistic) was further used to predict the inactivation of Salmonella populations of various initial levels using Monte Carlo simulation...

For the purpose of investigating the heat resistance mechanism of Alicyclobacillus acidoterrestris, label-free quantification was used to reveal some cellular changes in A. acidoterrestris during heat stress. Totally, 545 differential expression proteins were respectively identified at heat stress of 65 °C for 5 min, of which 258 proteins were up-regulated and 287 proteins were down-regulated. These significantly changed proteins were mapped to 100 pathways and some of them were mostly related to protection or repair of macromolecules such as proteins and DNA, cell wall formation, which indicated that these proteins might play crucial roles in response to heat stress...

To better understand the effects of bacteria on the characteristics of Fu brick tea, we investigated bacterial community structure as well as the predicted functions of identified bacteria and their correlations with chemical compounds during the manufacturing process. Overall, Klebsiella species dominated during the initial stage of processing, but were quickly replaced by Pseudomonas, Lactococcus, Stenotrophomonas, Enterococcus, and Bacillus species, which remained stable until the end of the manufacturing process...

The effect of high pressure processing (HPP) on the microbiota of ripened Iberian ham of different water activity, salt concentration and intramuscular fat content was investigated before and after a 5-month refrigeration period. At the beginning of the refrigeration period, the only significant effects of chemical composition were those of water activity on psychrotrophs and Micrococcaceae in untreated hams, and of the salt-in-lean ratio on lactic acid bacteria in HPP-treated hams. At the end of the refrigeration period, the only significant effect was that of intramuscular fat content on moulds and yeasts in HPP-treated samples...

Although nitrite in powdered milk formula (PIF) is a recognized health risk for infants, the presence of nitrite in PIF has only been investigated as a chemical contaminant during the inspection of end-products. The risk posed by microbial sources of nitrite during the PIF manufacturing process has not been considered. This is the first study to report the taxonomy and physiological characteristics of nitrite-producing bacteria isolated from PIF processing environments. All isolates identified as nitrite-producers (133 out of 501 strains collected over four years) from work-in-process and end-products of PIF were spore-forming bacilli...

Brazilian artisanal cheeses are characterized by the use of raw milk and in some cases, natural starter cultures, known as "pingo", as well as following simple and traditional manufacturing technology. In this study, a large-scale screening of the microbial ecology of 11 different types of artisanal cheeses produced in five geographical areas of Brazil was performed. Besides, the specific origin-related microbial signatures were identified. Clear geography- and technology-based differences in the microbiota were observed...

Bilberry (Vaccinium myrtillus L.) juice was fermented with Torulaspora delbrueckii (TD291 and TD70526) and Schizosaccharomyces pombe (SP3796 and SP70572) in pure fermentation as well as in sequential and simultaneous inoculations with Saccharomyces cerevisiae 1116 (SC1116). Altogether, 56 volatile compounds were identified and semi-quantified with HS-SPME-GC/MS in bilberry products. Yeast fermentation prominently enhanced the aroma complexity of bilberry with a sharp increase in alcohols, esters, aldehydes, and acetals...

Phenolic compounds are well known for their antimicrobial activity. They may provide an interesting solution to ensure food safety by preventing the growth of foodborne pathogens while addressing the wishes of consumers for the use of natural preservatives in food and favoring the reuse of agro-industry byproducts. However, their mechanism of action is still not very well understood. Here, we aimed to decipher the complex mechanism of action of eight phenolic acids by decomposing their effects, such as the general effect of the decrease of extracellular pH (γ(pH)) and specific inhibitory effects of the undissociated (γ(Au )) and dissociated (γ(Ad )) forms...

Listeria monocytogenes is one of the most important foodborne pathogens due to the high hospitalization and mortality rates associated to an outbreak. Several new molecular methods that accelerate the identification of L. monocytogenes have been developed, however conventional culture-based methods still remain the gold standard. In this work we developed a novel Peptide Nucleic Acid Fluorescence in situ Hybridization (PNA-FISH) method for the specific detection of L. monocytogenes. The method was based on an already existing PNA probe, LmPNA1253, coupled with a novel blocker probe in a 1:2 ratio...

Next Generation Sequencing (NGS) combined with powerful bioinformatic approaches are revolutionising food microbiology. Whole genome sequencing (WGS) of single isolates allows the most detailed comparison possible hitherto of individual strains. The two principle approaches for strain discrimination, single nucleotide polymorphism (SNP) analysis and genomic multi-locus sequence typing (MLST) are showing concordant results for phylogenetic clustering and are complementary to each other. Metabarcoding and metagenomics, applied to total DNA isolated from either food materials or the production environment, allows the identification of complete microbial populations...

Cronobacter are opportunistic bacterial pathogens of both infants and adults. We investigated the incidence and distribution of Cronobacter in 1245 samples of cereal and related environments. 39.1% (101/258) rice-related and 46.9% (98/209) wheat-related samples tested positive for Cronobacter, and the positive rate differed notably according to processing method. Cronobacter was found in rice and wheat plants at the tillering, filling and mature stages. Soil, water and swab samples from nearby milling plants were assayed, and results revealed that 6...

To acquire data on contamination with Norovirus in berry fruit and salad vegetables in the United Kingdom, one thousand one hundred and fifty two samples of fresh produce sold at retail in the UK were analysed for Norovirus. Of 568 samples of lettuce, 30 (5.3%) were Norovirus-positive. Most (24/30) lettuce samples which tested positive for Norovirus were grown in the UK and 19 of those 24 samples contained NoV GI. Seven/310 (2.3%) samples of fresh raspberries were Norovirus-positive. Most (6/7) of the positively-testing fresh raspberry samples were imported, but no predominance of a genogroup, or any seasonality, was observed...

Commercial wine fermentation is commonly conducted by inoculated strains of Saccharomyces cerevisiae. However, other non-Saccharomyces yeast species have recently become popular co-inoculants. Co-inoculated yeast species compete with each other for nutrients, and such competition may impact fermentation kinetics and aroma production. Understanding the specific nutrient requirements of non-Saccharomyces strains therefore is essential to better characterize the competitive potential of each strain, and to support rational decision making for nutrient supplementation during wine making...

This study examines the effect of juices and non-Saccharomyces yeasts on physicochemical properties and sensory quality for fruit wines. Here, fruit wines produced from six kinds of fruit juices and eight non-Saccharomyces yeasts were evaluated, and the results show significant phenotypic diversity within these yeasts for wine fermentation on a range of substrates. Substantial variations in indicators such as total acid, sugar content and organic acid content were observed, which were caused by selection of both yeasts and juice types...

Of the 1648 microbial isolates from 133 soil samples collected from 30 diverse locations in the Republic of Korea, two isolates exhibited strong antilisterial activity and ability to grow to high populations (>8.0 log CFU/ml) in Bennett's broth. Isolates were identified as Streptomyces lactacystinicus (strain Samnamu 5-15) and Streptomyces purpureus (strain Chamnamu-sup 4-15). Both isolates formed biofilms on the surface of stainless steel coupons (SSCs) immersed in Bennett's broth within 24 h at 25 °C...

This study compares dynamic tertiary and competition models for L. monocytogenes growth as a function of intrinsic properties of a traditional Brazilian soft cheese and the inhibitory effect of lactic acid bacteria (LAB) during refrigerated storage. Cheeses were prepared from raw or pasteurized milk with or without the addition of selected LAB with known anti-listerial activity. Cheeses were analyzed for LAB and L. monocytogenes counts, pH and water activity (aw ) throughout cold storage. Two approaches were used to describe the effect of LAB on L...

Quantitative Polymerase Chain Reaction (qPCR) is a molecular method commonly used to detect and quantify bacterial DNA on food but is limited by its inability to distinguish between live and dead cell DNA. To overcome this obstacle, propidium monoazide (PMA) alone or with deoxycholate (DC) was used to prevent dead cell detection in qPCR. qPCR methods were used to detect strains of Escherichia coli O157, which can cause infection in humans with an infectious dose of less than 10 cells. A 5 strain E. coli O157:H7 cocktail was inoculated onto beef steaks and treated with interventions used in meat facilities (lactic acid (5%), peroxyacetic acid (200 ppm) or hot water (80 °C for 10 s))...

This study investigated the influences of seawater to oyster ratio on depuration for decontaminating V. parahaemolyticus in raw oysters with a goal of identifying the proper ratio of oyster to seawater capable of improving the efficacy of the depuration process. The water to oyster ratios tested in this study ranged from 1.0 to 2.5 L of artificial seawater (ASW) per oyster (40 oysters in 40, 60, 80 and 100 L ASW). The depuration efficacy for purging V. parahaemolyticus from oysters was highest when we applied a 2:1, followed by 1...

The objective of the present study was the evaluation of Fourier transform infrared (FTIR) spectroscopy and multispectral imaging (MSI), in tandem with multivariate data analysis, as means of estimating the microbiological quality of sea bream. Farmed whole ungutted fish were stored aerobically at 0, 4 and 8 °C. At regular time intervals, fish samples (i.e. cut portions) were analysed microbiologically, while FTIR and MSI measurements also were acquired at both the skin and flesh sides of the samples. Partial least squares regression (PLSR) models were calibrated to provide quantitative estimations of the microbiological status of fish based on spectral data, in a temperature-independent manner...