Aerobic spore-forming bacteria associated with ropy bread: Identification, characterization and spoilage potential assessment

Aerobic spore-forming (ASF) bacteria have been reported to cause ropiness in bread. Sticky and stringy degradation, discoloration, and an odor reminiscent of rotting fruit are typical characteristics of ropy bread spoilage. In addition to economic losses, ropy bread spoilage may lead to health risks, as virulent strains of ASF bacteria are not uncommon. However, the lack of systematic approaches to quantify physicochemical spoilage characteristics makes it extremely difficult to assess rope formation in bread. To address this problem, the aim of this study was to identify, characterize and objectively assess the spoilage potential of ASF bacteria associated with ropy bread. Hence, a set of 82 ASF bacteria, including isolates from raw materials and bakery environments as well as strains from international culture collections, were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and their species identity confirmed by 16S rRNA and gyrA or panC gene sequencing. A standardized approach supported by objective colorimetric measurements was developed to assess the rope-inducing potential (RIP) of a strain by inoculating autoclaved bread slices with bacterial spores. In addition, the presence of potential virulence factors such as swarming motility or hemolysis was investigated. This study adds B. velezensis, B. inaquosorum and B. spizizenii to the species potentially implicated of causing ropy bread spoilage. Most importantly, this study introduces a standardized classification protocol for assessing the RIP of a bacterial strain. Colorimetric measurements are used to objectively quantify the degree of breadcrumb discoloration. Furthermore, our results indicate that strains capable of inducing rope spoilage in bread often exhibit swarming motility and virulence factors such as hemolysis, raising important food quality considerations.

From wheat grain to flour: a review of potential sources of enteric pathogen contamination in wheat milled products

The number of food safety issues linked to wheat milled products have increased in the past decade. These incidents were mainly caused by the contamination of wheat-based products by enteric pathogens. This manuscript is the first of a two-part review on the status of the food safety of wheat-based products. This manuscript focused on reviewing the available information on the potential pre-harvest and post-harvest sources of microbial contamination, and potential foodborne pathogens present in wheat-based products. Potential pre-harvest sources of microbial contamination in wheat included animal activity, water, soil, and manure. Improper grain storage practices, pest activity, and improperly cleaned and sanitized equipment are potential sources of post-harvest microbial contamination for wheat-based foods. Raw wheat flour products and flour-based products are potentially contaminated with enteric pathogens such as Shiga toxin-producing E. coli (STECs), and Salmonella at low concentrations. Wheat grains and their derived products (i.e., flours) are potential vehicles for foodborne illness in humans due to the presence of enteric pathogens. A more holistic approach is needed for assuring the food safety of wheat-based products in the farm-to-table continuum. Future developments in the wheat supply chain should also be aimed at addressing this emerging food safety threat.

Acidic water tempering and heat treatment, a hurdle approach to reduce wheat Salmonella load during tempering and its effects on flour quality

The cultivation and processing of wheat render it susceptible to microbial contamination from varied sources. Hence, pathogens such as Salmonella can contaminate wheat grains, which poses a food safety risk in wheat-based products. This risk is displayed by the incidence of foodborne illness outbreaks linked to Salmonella-contaminated wheat flour and flour-based products. The purpose of this study was to assess the effectiveness of combining acidic water and heat treatment in reducing the Salmonella load of hard red spring (HRS) wheat grains during tempering. Effective treatments were then evaluated for their effects on wheat flour quality. Tempering with sodium bisulfate (SBS), lactic acid (LA), and citric acid (CA) at 15% w/v alone reduced (p < 0.001) wheat Salmonella load by 3.15, 3.23, and 2.91 log CFU/g, respectively. Heat treatment (55 °C) reduced (p < 0.001) wheat Salmonellaload by 4.1 log CFU/g after 24 h of tempering. Combining both tempering and heat treatments resulted in a greater reduction in Salmonella load as non-detectable levels (<2 log CFU/g) of Salmonella in the wheat grains were obtained after 12 h of tempering with LA (15%) + heat. A similar result were achieved for both SBS (15%) + heat and CA (15%) + heat treatments after 18 h of tempering. Applying the combined treatments in HRS wheat grains resulted in comparable wheat flour baking (volume, texture, and crumb structure) and physicochemical properties (rheology and composition) relative to the control (tempering with water alone). The results from this study has the potential to be utilized for developing more effective methods for improving the food safety of wheat flour against Salmonella contamination.

Non-targeted metabolomics of moldy wheat by ultra-performance liquid chromatography - quadrupole time-of-flight mass spectrometry

Introduction

As one of the staple foods for the world's major populations, the safety of wheat is critical in ensuring people's wellbeing. However, mildew is one of the prevalent safety issues that threatens the quality of wheat during growth, production, and storage. Due to the complex nature of the microbial metabolites, the rapid identification of moldy wheat is challenging.

Methods

In this research, identification of moldy wheat samples was studied using ultra-performance liquid chromatography - quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) coupled with chemometrics. The non-targeted PCA model for identifying moldy wheat from normal wheat was established by using previously established compounds database of authentic wheat samples. The partial least squares-discriminant analysis (PLS-DA) was performed.

Results and discussion

By optimizing the model parameters, correct discrimination of the moldy wheat as low as 5% (w/w) adulteration level could be achieved. Differential biomarkers unique to moldy wheat were also extracted to identify between the moldy and authentic wheat samples. The results demonstrated that the chemical information of wheat combined with the existing PCA model could efficiently discriminate between the constructed moldy wheat samples. The study offered an effective method toward screening wheat safety.

Occurrence of Antibiotic Resistant Bacteria in Flours and Different Plant Powders Used in Cuisine

In recent years, several alimentary diseases have been connected with the consumption or tasting of raw flour and dough. Microbiological quality concern is also raising due to increased consumer demand for plant powders, while some of them can be consumed without prior thermal processing. In this study, we have focused on the occurrence of antibiotic-resistant coliform bacteria and enterococci in flour, plant powder and dough from Slovak retail. Our results indicated the presence of both total and antibiotic-resistant coliform bacteria and enterococci in the flour and powder samples. Lower numbers of the total, as well as resistant bacteria, were detected in flours compared to plant powders. Coliform bacteria isolates were predominantly identified as Klebsiella spp. and Enterobacter spp. Ampicillin resistance appeared in 97% of isolates followed by chloramphenicol resistance (22%) and tetracycline resistance (17%). The presence of the bla_SHV gene was confirmed in 13% of isolates. The tetA and tetE genes were present in 25% of isolates of coliform bacteria. The presence of enterococci was detected only in plant powders. Antibiotic-resistant strains were identified as the following: Enterococcus casseliflavus, E. gallinarium and E. faecium. Despite the isolates showing resistance to vancomycin, the presence of the vanA gene was not detected. The majority of antibiotic-resistant isolates belonged to the group of medium biofilm producers. None of these isolates showed efflux pump overproduction. Antibiotic-resistant coliform bacteria and enterococci were not detected in the processed doughs.

Ropiness in Bread—A Re-Emerging Spoilage Phenomenon

As bread is a very important staple food, its spoilage threatens global food security. Ropy bread spoilage manifests in sticky and stringy degradation of the crumb, slime formation, discoloration, and an odor reminiscent of rotting fruit. Increasing consumer demand for preservative-free products and global warming may increase the occurrence of ropy spoilage. Bacillus amyloliquefaciens, B. subtilis, B. licheniformis, the B. cereus group, B. pumilus, B. sonorensis, Cytobacillus firmus, Niallia circulans, Paenibacillus polymyxa, and Priestia megaterium were reported to cause ropiness in bread. Process hygiene does not prevent ropy spoilage, as contamination of flour with these Bacillus species is unavoidable due to their occurrence as a part of the endophytic commensal microbiota of wheat and the formation of heat-stable endospores that are not inactivated during processing, baking, or storage. To date, the underlying mechanisms behind ropy bread spoilage remain unclear, high-throughput screening tools to identify rope-forming bacteria are missing, and only a limited number of strategies to reduce rope spoilage were described. This review provides a current overview on (i) routes of entry of Bacillus endospores into bread, (ii) bacterial species implicated in rope spoilage, (iii) factors influencing rope development, and (iv) methods used to assess bacterial rope-forming potential. Finally, we pinpoint key gaps in knowledge and related challenges, as well as future research questions.

End-Use Quality of Historical and Modern Winter Wheats Adapted to the Great Plains of the United States

Improving milling and baking properties is important during wheat breeding. To determine changes in milling and baking quality of hard winter wheat, 23 adapted cultivars released in the Great Plains between 1870 and 2013 were grown in triplicate in a single location (Mead, NE, USA) over two crop years (2018 and 2019). Grain yield and kernel hardness index increased by release year (p < 0.05). The observed increase in hardness index was accompanied by a decrease in percent soft kernels (p < 0.05). Diameter and weight decreased with release year in 2019 (p < 0.05), and their standard deviation increased with the release year (p < 0.05). Flour protein content decreased with release year (p < 0.05) and dough mixing quality increased (p < 0.05). No significant relationship was found for baking property variables, but bran water retention capacity (BWRC), which is correlated with whole wheat bread quality, increased with release year (p < 0.05). In conclusion, wheat kernels have become harder but more variable in shape over a century of breeding. Mixing quality showed significant improvements, and loaf volume and firmness remained constant, even in the presence of a decrease in protein concentration. Bran quality decreased across release year, which may have implications for whole grain baking quality and milling productivity.

Shiga Toxin-Producing Escherichia coli in Wheat Grains: Detection and Isolation by Polymerase Chain Reaction and Culture Methods

Shiga toxin-producing Escherichia coli (STEC) are major foodborne pathogens and seven serogroups, O26, O45, O103, O111, O121, O145, and O157, often called top-7 STEC, account for the majority of the STEC-associated human illnesses in the United States. Two Shiga toxins, Shiga toxins 1 and 2, encoded by stx1 and stx2 genes, are major virulence factors that are involved in STEC infections. Foodborne STEC infections have been linked to a variety of foods of both animal and plant origin, including products derived from cereal grains. In recent years, a few STEC outbreaks have been linked to contaminated wheat flour. The microbiological quality of the wheat grains is a major contributor to the safety of wheat flour. The objective of the study was to utilize polymerase chain reaction (PCR)- and culture-based methods to detect and isolate STEC in wheat grains. Wheat grain samples (n = 625), collected from different regions of the United States, were enriched in modified buffered peptone water with pyruvate (mBPWp) or E. coli (EC) broth, and they were then subjected to PCR- and culture-based methods to detect and isolate STEC. Wheat grains enriched in EC broth yielded more samples positive for stx genes (1.6% vs. 0.32%) and STEC serogroups (5.8% vs. 2.4%) than mBPWp. The four serogroups of top-7 detected and isolated were O26, O45, O103, and O157 and none of the isolates was positive for the Shiga toxin genes. A total of five isolates that carried the stx2 gene were isolated and identified as serogroups O8 (0.6%) and O130 (0.2%). The EC broth was a better medium to enrich wheat grains than mBPWp for the detection and isolation of STEC. The overall prevalence of virulence genes and STEC serogroups in wheat grains was low. The stx2-positive serogroups isolated, O8 and O130, are not major STEC pathogens and have only been implicated in sporadic infections in animals and humans.

Draft Genome Sequences of Salmonella enterica subsp. diarizonae Serotype IIIb_61:I,v:1,5,(7) Strains Isolated from Wheat Grains

Salmonella enterica subsp. diarizonae serotypes are primarily involved in reptile-associated salmonellosis in humans. Here, we report the draft genome sequences of three subsp. diarizonae strains belonging to the serotype 61:1,v:1,5,(7), isolated from wheat grains collected at the time of harvest. Strains of serotype of 61:1,v:1,5,(7) have been isolated from feces of reptiles, cattle, and sheep and from infections in humans.

Salmonella enterica subsp. diarizonae serotypes are primarily involved in reptile-associated salmonellosis in humans. Here, we report the draft genome sequences of three S. enterica subsp. diarizonae strains belonging to the serotype IIIb_61:1,v:1,5,(7), isolated from wheat grains collected at the time of harvest. Strains of serotype IIIb_61:1,v:1,5,(7) have been isolated from feces of reptiles, cattle, and sheep and from infections in humans.

Effect of Physical Structures of Food Matrices on Heat Resistance of Enterococcus faecium NRRL-2356 in Wheat Kernels, Flour and Dough

Nonpathogenic surrogate microorganisms, with a similar or slightly higher thermal resistance of the target pathogens, are usually recommended for validating practical pasteurization processes. The aim of this study was to explore a surrogate microorganism in wheat products by comparing the thermal resistance of three common bacteria in wheat kernels and flour. The most heat-resistant Enterococcus faecium NRRL-2356 rather than Salmonella cocktail and Escherichia coli ATCC 25922 was determined when heating at different temperature-time combinations at a fixed heating rate of 5 °C/min in a heating block system. The most heat-resistant pathogen was selected to investigate the influences of physical structures of food matrices. The results indicated that the heat resistance of E. faecium was influenced by physical structures of food matrices and reduced at wheat kernel structural conditions. The inactivation of E. faecium was better fitted in the Weibull distribution model for wheat dough structural conditions while in first-order kinetics for wheat kernel and flour structural conditions due to the changes of physical structures during heating. A better pasteurization effect could be achieved in wheat kernel structure in this study, which may provide technical support for thermal inactivation of pathogens in wheat-based food processing.

Reduction in pathogenic load of wheat by tempering with saline organic acid solutions at different seasonal temperatures

As a raw agricultural commodity, wheat is exposed to microbial contamination; therefore, enteric pathogens may be among its microbiota creating a food safety risk in milled products. This research evaluates (1) the effectiveness of organic acids dissolved in saline solutions to reduce the counts of pathogenic microorganisms in soft and hard wheat, and also investigates the effect of seasonal temperature on (2) survivability of pathogens in wheat kernels and on (3) pathogen inactivation during tempering with saline organic acid solutions. Wheat samples were inoculated with cocktails of either 5 serovars of Salmonella enterica, 5 E. coli O157:H7 or 6 non-O157 Shiga toxin-producing E. coli (STEC) strains to achieve a concentration of ~7 log CFU/g. Inoculated samples were allowed to stand for 7-days at temperatures (2.0, 10.8, 24.2, 32 °C) corresponding to those experienced during winter, spring/fall, and summer (average and maximum) in the main wheat growing regions in the state of Nebraska, USA. Besides water, solutions containing acid (acetic or lactic 2.5% or 5.0% v/v) and NaCl (~26% w/v) were used for tempering the wheat to 15.0% (soft) and 15.5% (hard) moisture at the different seasonal temperatures. The survival of pathogenic microorganisms throughout the resting period, and before and after tempering was analyzed by plating samples on injury-recovery media. The survival rate of pathogenic microorganisms on wheat kernels was higher at temperatures experienced during the winter (2.0 °C) and spring/fall (10.8 °C) months. Regardless of tempering temperature, the initial pathogen load was reduced significantly by all solutions when compared to the control tempered with water (P ≤ .05). The combination of lactic acid (5.0%) and NaCl was the most effective treatment against Salmonella enterica, E. coli O157:H7 and non-O157 STEC, with average reduction values of 1.8, 1.8 and 1.6 log CFU/g for soft wheat and 2.6, 2.4 and 2.4 log CFU/g for hard wheat, respectively. Implementation of organic acids and NaCl in tempering water may have the potential to reduce the risk of pathogen contamination in milled products.

Occurrence and Levels of Salmonella, Enterohemorrhagic Escherichia coli, and Listeria in Raw Wheat

HIGHLIGHTS

Prevalence of Salmonella and E. coli in raw wheat emphasizes the need to cook wheat products. 3,891 grain samples were tested for E. coli and Salmonella; 1,285 were tested for Listeria. Of wheat berries sampled, 0.44% were positive for E. coli and 1.23% were positive for Salmonella. Salmonella diversity was high, indicating various animal sources that are difficult to prevent. Cooking wheat products is the best preventative measure against foodborne illness from wheat.

Tap water is one of the drivers that establish and assembly the lactic acid bacterium biota during sourdough preparation

This study aimed at assessing the effect of tap water on the: (i) lactic acid bacteria (LAB) population of a traditional and mature sourdough; and (ii) establishment of LAB community during sourdough preparation. Ten tap water, collected from Italian regions characterized by cultural heritage in leavened baked goods, were used as ingredient for propagating or preparing firm (type I) sourdoughs. The same type and batch of flour, recipe, fermentation temperature and time were used for propagation/preparation, being water the only variable parameter. During nine days of propagation of a traditional and mature Apulian sourdough, LAB cell density did not differ, and the LAB species/strain composition hardly changed, regardless of the water. When the different tap water were used for preparing the corresponding sourdoughs, the values of pH became lower than 4.5 after two to four fermentations. The type of water affected the assembly of the LAB biome. As shown by Principal Components Analysis, LAB population in the sourdoughs and chemical and microbiological features of water used for their preparation partly overlapped. Several correlations were found between sourdough microbiota and water features. These data open the way to future researches about the use of various types of water in bakery industry.

Contaminants in Grain-A Major Risk for Whole Grain Safety?

Grains are the main energy and carbohydrate sources for human nutrition globally. Governmental and non-governmental authorities recommend whole grains as a healthy food choice. The role of contaminants in (whole) grains and how to mitigate any potential risk following their consumption has not been reported. With this narrative review, we shed light on the potential human health risk from contaminants in whole grains and elaborate strategies to mitigate such risk. We found that grains represent a significant source of food-borne contaminants, the main ones being; mycotoxins including (A) aflatoxin B1; (B) ochratoxin A; (C) fumonisin B1; (D) deoxynivalenol; (E) zearalenone; toxic metals like arsenic, cadmium and lead; as well as process contaminants such as acrylamide. Whole grains usually contain more contaminants than refined products. However, whole grains also provide more nutrients that may reduce the impact of these contaminants. Strict regulatory thresholds aim to minimize the risk of contaminants to public health. The consumer can further impact on the mitigation of any risk by eating a healthy diet filled with nutrient-dense foods such as whole grains and probiotics. The risk posed by contaminants from whole grains do not outweigh the known nutritional benefits of whole grain consumption.

Frankfurters made with pork meat, emmer wheat (Triticum dicoccum Schübler) and almonds nut (Prunus dulcis Mill.): evaluation during storage of a novel food from an ancient recipe

The physical, chemical and microbiological characteristics of reformulated meat-based frankfurters, derived from an ancient Roman cookbook and produced from pork meat, emmer wheat, almond, fish sauce and spices, were investigated during storage. Two different formulations were considered, with pork thigh and pork shoulder muscles, respectively. The products contain 13-16% protein, 14-19% fat, 14% carbohydrates, >7% fibre and a polyunsaturated/saturated fatty acids ratio above 0.4. During the 24 days of storage, both products evidenced a decrease in the pH and increases in the total volatile nitrogen content and TBARs value, whereas, the a_w remained stable. From a microbiological perspective, increases in the total viable count and lactic acid bacteria up to 4.8 log cfu/g occurred during storage, but no pathogens were found. Sensory analyses revealed a change in odour and flavour at 18 days, with the detection of a fermented and rancid taste. Survival sensory analysis defined a shelf life of the products of between 18.6 and 22.7 days.