High-pressure processing – effects on microbial food safety and food quality

High-pressure processing (HPP) is a nonthermal process capable of inactivating and eliminating pathogenic and food spoilage microorganisms. This novel technology has enormous potential in the food industry, controlling food spoilage, improving food safety and extending product shelf life while retaining the characteristics of fresh, preservative-free, minimally processed foods. As with other food processing methods, such as thermal processing, HPP has somewhat limited applications as it cannot be universally applied to all food types, such as some dairy and animal products and shelf-stable low-acid foods. Herein, we discuss the effects of high-pressure processing on microbial food safety and, to a lesser degree, food quality.     

Bacteriocins from lactic acid bacteria and their potential in the preservation of fruit products

Bacteriocins produced by lactic acid bacteria (LAB) are well-recognized for their potential as natural food preservatives. These antimicrobial peptides usually do not change the sensorial properties of food products and can be used in combination with traditional preservation methods to ensure microbial stability. In recent years, fruit products are increasingly being associated with food-borne pathogens and spoilage microorganisms, and bacteriocins are important candidates to preserve these products. Bacteriocins have been extensively studied to preserve foods of animal origin. However, little information is available for their use in vegetable products, especially in minimally processed ready-to-eat fruits. Although, many bacteriocins possess useful characteristics that can be used to preserve fruit products, to date, only nisin, enterocin AS-48, bovicin HC5, enterocin 416K1, pediocin and bificin C6165 have been tested for their activity against spoilage and pathogenic microorganisms in these products. Among these, only nisin and pediocin are approved to be commercially used as food additives, and their use in fruit products is still limited to certain countries. Considering the increasing demand for fresh-tasting fruit products and concern for public safety, the study of other bacteriocins with biochemical characteristics that make them candidates for the preservation of these products are of great interest. Efforts for their approval as food additives are also important. In this review, we discuss why the study of bacteriocins as an alternative method to preserve fruit products is important; we detail the biotechnological approaches for the use of bacteriocins in fruit products; and describe some bacteriocins that have been tested and have potential to be tested for the preservation of fruit products.     

食源性致病菌群体感应信号分子的检测

群体感应(Quorum sensing,QS)在食物中毒导致的食源性疾病暴发机制和食物腐败变质中起主要作用,QS影响致病菌的细胞被膜形成和致病性。文中通过深入了解食源性致病菌的QS信号分子,综述了革兰氏阴性和革兰氏阳性菌产生的信号分子类型,同时介绍了检测QS信号分子的不同技术,并根据QS机制在食品中的影响提出了思考和建议,为监控食源性致病菌提供依据。     

Recent findings in pulsed light disinfection

Nonthermal disinfection technologies are gaining increasing interest in the field of minimally processed food in order to improve the microbial safety or to extend the shelf life. Especially fresh‐cut produce or meat and fish products are vulnerable to microbial spoilage, but, due to their sensitivity, they require gentle preservation measures. The application of intense light pulses of a broad spectral range comprising ultraviolet, visible and near infrared irradiation is currently investigated as a potentially suitable technology to reduce microbial loads on different food surfaces or in beverages. Considerable research has been performed within the last two decades, in which the impact of various process parameters or microbial responses as well as the suitability of pulsed light (PL) for food applications has been examined. This review summarizes the outcome of the latest studies dealing with the treatment of various foods including the impact of PL on food properties as well as recent findings about the microbicidal action and relevant process parameters.     

Well-known quorum sensing inhibitors do not affect bacterial quorum sensing-regulated bean sprout spoilage

AIM: To investigate the potential of quorum sensing inhibitors (QSI) as food preservative agents in a food product, where bacterial spoilage is controlled by quorum sensing (QS). METHODS AND RESULTS: The effects of well-known QSI were tested on spoilage phenotypes and on QS-regulated genes of a bean sprout spoiling bacterial isolate (Pectobacterium A2JM) in laboratory substrates and in a bean sprout model system. The acylated homoserine lactones (AHL) analogues PenS-AHL and HepS-AHL decreased the specific protease activity of Pectobacterium A2JM in broth but did not reduce the expression of a QS-regulated secretion protein, and were without effect on soft rot of bean sprouts. The QSI ProS-AHL, furanone C-30, patulin, penicillic acid and 4-nitropyridine-N-oxide did not have any effect on protease activity, on gene expression or bean sprout appearance at nongrowth inhibitory concentrations. Extracts from garlic and bean sprouts induced the QS system of Pectobacterium in bean sprouts and a broth system, respectively. CONCLUSIONS: Among the several well-known QSI compounds, only PenS-AHL and HepS-AHL, inhibited QS-regulated protease activity of Pectobacterium A2JM in broth cultures, but had no effect on bean sprout spoilage. SIGNIFICANCE AND IMPACT OF THE STUDY: The QSI compounds must be selected in the specific system in which they are to function and they cannot easily be transferred from one QS system to another.     

Presence of acylated homoserine lactones (AHLs) and AHL-producing bacteria in meat and potential role of AHL in spoilage of meat

Quorum-sensing (QS) signals (N-acyl homoserine lactones [AHLs]) were extracted and detected from five commercially produced vacuum-packed meat samples. Ninety-six AHL-producing bacteria were isolated, and 92 were identified as Enterobacteriaceae. Hafnia alvei was the most commonly identified AHL-producing bacterium. Thin-layer chromatographic profiles of supernatants from six H. alvei isolates and of extracts from spoiling meat revealed that the major AHL species had an R(f) value and shape similar to N-3-oxo-hexanoyl homoserine lactone (OHHL). Liquid chromatography-mass spectrometry (MS) (high-resolution MS) analysis confirmed the presence of OHHL in pure cultures of H. alvei. Vacuum-packed meat spoiled at the same rate when inoculated with the H. alvei wild type compared to a corresponding AHL-lacking mutant. Addition of specific QS inhibitors to the AHL-producing H. alvei inoculated in meat or to naturally contaminated meat did not influence the spoilage of vacuum-packed meat. An extracellular protein of approximately 20 kDa produced by the H. alvei wild-type was not produced by the AHL-negative mutant but was restored in the mutant when complemented by OHHL, thus indicating that AHLs do have a regulatory role in H. alvei. Coinoculation of H. alvei wild-type with an AHL-deficient Serratia proteamaculans B5a, in which protease secretion is QS regulated, caused spoilage of liquid milk. By contrast, coinoculation of AHL-negative strains of H. alvei and S. proteamaculans B5a did not cause spoilage. In conclusion, AHL and AHL-producing bacteria are present in vacuum-packed meat during storage and spoilage, but AHL does not appear to influence the spoilage of this particular type of conserved meat. Our data indicate that AHL-producing H. alvei may induce food quality-relevant phenotypes in other bacterial species in the same environment. H. alvei may thus influence spoilage of food products in which Enterobacteriaceae participate in the spoilage process.     

A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods

A ckland , M.R. & R eeder , J.E. 1984. A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods. Journal of Applied Bacteriology 56 , 415–419.
A rapid method for the detection of lactic acid in preserved foods has been developed, based upon a chemical spot test which does not require solvent extraction or derivatisation of the lactic acid in the sample. The test can be completed within 5 min and was shown to confirm microbial spoilage detected by cultural techniques in a range of preserved foods. In addition the test was able to indicate microbial spoilage in samples where cultural techniques failed because the spoilage organisms were dead. The test may not be appropriate for products which have a naturally high lactic acid content.     

A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods

A rapid method for the detection of lactic acid in preserved foods has been developed, based upon a chemical spot test which does not require solvent extraction or derivatisation of the lactic acid in the sample. The test can be completed within 5 min and was shown to confirm microbial spoilage detected by cultural techniques in a range of preserved foods. In addition the test was able to indicate microbial spoilage in samples where cultural techniques failed because the spoilage organisms were dead. The test may not be appropriate for products which have a naturally high lactic acid content.     

Food color ‘Azorubine’ interferes with quorum sensing regulated functions and obliterates biofilm formed by food associated bacteria: An in vitro and in silico approach

Quorum sensing (QS) plays a crucial role in different stages of biofilm development, virulence production, and subsequently to the growth of bacteria in food environments. Biofilm mediated spoilage of food is one of the ongoing challenge faced by the food industry worldwide as it incurs substantial economic losses and leads to various health issues. In the present investigation, we studied the interference of quorum sensing, its regulated virulence functions, and biofilm in food-associated bacteria by colorant azorubine. In vitro bioassays demonstrated significant inhibition of QS and its coordinated virulence functions in Chromobacterium violaceum 12472 (violacein) and Pseudomonas aeruginosa PAO1 (elastase, protease, pyocyanin, and alginate). Further, the decrease in the production EPS (49–63%) and swarming motility (61–83%) of the pathogens was also recorded at sub-MICs. Azorubine demonstrated broad-spectrum biofilm inhibitory potency (50–65%) against Chromobacterium violaceum, Pseudomonas aeruginosa, E. coli O157:H7, Serratia marcescens, and Listeria monocytogenes. ROS generation due to the interaction between bacteria and azorubine could be responsible for the biofilm inhibitory action of the food colorant. Findings of the in vitro studies were well supported by molecular docking and simulation analysis of azorubine and QS virulence proteins. Azorubine showed strong binding to PqsA as compared to other virulent proteins (LasR, Vfr, and QscR). Thus, it is concluded that azorubine is a promising candidate to ensure food safety by curbing the menace of bacterial QS and biofilm-based spoilage of food and reduce economic losses.     

Pulsed-light system as a novel food decontamination technology: a review

In response to consumer preferences for high quality foods that are as close as possible to fresh products, athermal technologies are being developed to obtain products with high levels of organoleptic and nutritional quality but free of any health risks. Pulsed light is a novel technology that rapidly inactivates pathogenic and food spoilage microorganisms. It appears to constitute a good alternative or a complement to conventional thermal or chemical decontamination processes. This food preservation method involves the use of intense, short-duration pulses of broad-spectrum light. The germicidal effect appears to be due to both photochemical and photothermal effects. Several high intensity flashes of broad spectrum light pulsed per second can inactivate microbes rapidly and effectively. However, the efficacy of pulsed light may be limited by its low degree of penetration, as microorganisms are only inactivated on the surface of foods or in transparent media such as water. Examples of applications to foods are presented, including microbial inactivation and effects on food matrices.     

Application of Bacteriocins in the Control of Foodborne Pathogenic and Spoilage Bacteria

Bacteriocins are antimicrobial peptides or proteins produced by strains of diverse bacterial species. The antimicrobial activity of this group of natural substances against foodborne pathogenic, as well as spoilage bacteria, has raised considerable interest for their application in food preservation. Application of bacteriocins may help reduce the use of chemical preservatives and/or the intensity of heat and other physical treatments, satisfying the demands of consumers for foods that are fresh tasting, ready to eat, and lightly preserved. In recent years, considerable effort has been made to develop food applications for many different bacteriocins and bacteriocinogenic strains. Depending on the raw materials, processing conditions, distribution, and consumption, the different types of foods offer a great variety of scenarios where food poisoning, pathogenic, or spoilage bacteria may proliferate. Therefore, the effectiveness of bacteriocins requires careful testing in the food systems for which they are intended to be applied against the selected target bacteria. This and other issues on application of bacteriocins in foods of dairy, meat, seafood, and vegetable origins are addressed in this review.     

Application of bacteriocins in the control of foodborne pathogenic and spoilage bacteria

Bacteriocins are antimicrobial peptides or proteins produced by strains of diverse bacterial species. The antimicrobial activity of this group of natural substances against foodborne pathogenic, as well as spoilage bacteria, has raised considerable interest for their application in food preservation. Application of bacteriocins may help reduce the use of chemical preservatives and/or the intensity of heat and other physical treatments, satisfying the demands of consumers for foods that are fresh tasting, ready to eat, and lightly preserved. In recent years, considerable effort has been made to develop food applications for many different bacteriocins and bacteriocinogenic strains. Depending on the raw materials, processing conditions, distribution, and consumption, the different types of foods offer a great variety of scenarios where food poisoning, pathogenic, or spoilage bacteria may proliferate. Therefore, the effectiveness of bacteriocins requires careful testing in the food systems for which they are intended to be applied against the selected target bacteria. This and other issues on application of bacteriocins in foods of dairy, meat, seafood, and vegetable origins are addressed in this review.     

Rapid and quantitative detection of the microbial spoilage of meat by fourier transform infrared spectroscopy and machine learning

Fourier transform infrared (FT-IR) spectroscopy is a rapid, noninvasive technique with considerable potential for application in the food and related industries. We show here that this technique can be used directly on the surface of food to produce biochemically interpretable "fingerprints." Spoilage in meat is the result of decomposition and the formation of metabolites caused by the growth and enzymatic activity of microorganisms. FT-IR was exploited to measure biochemical changes within the meat substrate, enhancing and accelerating the detection of microbial spoilage. Chicken breasts were purchased from a national retailer, comminuted for 10 s, and left to spoil at room temperature for 24 h. Every hour, FT-IR measurements were taken directly from the meat surface using attenuated total reflectance, and the total viable counts were obtained by classical plating methods. Quantitative interpretation of FT-IR spectra was possible using partial least-squares regression and allowed accurate estimates of bacterial loads to be calculated directly from the meat surface in 60 s. Genetic programming was used to derive rules showing that at levels of 10(7) bacteria.g(-1) the main biochemical indicator of spoilage was the onset of proteolysis. Thus, using FT-IR we were able to acquire a metabolic snapshot and quantify, noninvasively, the microbial loads of food samples accurately and rapidly in 60 s, directly from the sample surface. We believe this approach will aid in the Hazard Analysis Critical Control Point process for the assessment of the microbiological safety of food at the production, processing, manufacturing, packaging, and storage levels.     

Lactic acid bacteria in a changing legislative environment

The benefits of using lactic acid bacteria in the food chain, both through direct consumption and production of ingredients, are increasingly recognised by the food industry and consumers alike. The regulatory environment surrounding these products is diverse, covering foods and food ingredients, processing aids, feed additives and dietary supplements. On a global basis, there are different approaches taken by the various regulatory authorities. While in Europe, the national legislation is gradually being harmonised, predominantly through the Novel Foods Regulation, there is still a wide disparity between the stringency of regulation of microbial products fed to animals and the comparatively relaxed approach to non-novel microbial products intended for human consumption. In the United States, the onus is on self-regulation of the manufacturer, with the Generally Recognised As Safe (GRAS) and Dietary Supplement Health Education Act (DSHEA) notification schemes encouraging industry to be more open about the ingredients they market. In Japan, the Foods for Special Health Use system continues to gain recognition as more products are approved, and is a potential model for other countries in regulating functional foods. Despite the different approaches to regulating these products, safety of microorganisms such as lactic acid bacteria in the food chain is paramount in all countries. This paper discusses the regulatory requirements of microbial products, predominantly lactic acid bacteria within the global markets, focusing mainly on the developments in Europe.     

Food applications of bacterial cell wall hydrolases

Bacterial cell wall hydrolases (BCWHs) display a remarkable structural and functional diversity that offers perspectives for novel food applications, reaching beyond those of the archetype BCWH and established biopreservative hen egg white lysozyme. Insights in BCWHs from bacteriophages to animals have provided concepts for tailoring BCWHs to target specific pathogens or spoilage bacteria, or, conversely, to expand their working range to Gram-negative bacteria. Genetically modified foods expressing BCWHs in situ showed successful, but face regulatory and ethical concerns. An interesting spin-off development is the use of cell wall binding domains of bacteriophage BCWHs for detection and removal of foodborne pathogens. Besides for improving food safety or stability, BCWHs may also find use as functional food ingredients with specific health effects.     

Presence of Acylated Homoserine Lactones (AHLs) and AHL-Producing Bacteria in Meat and Potential Role of AHL in Spoilage of Meat

Quorum-sensing (QS) signals (N-acyl homoserine lactones [AHLs]) were extracted and detected from five commercially produced vacuum-packed meat samples. Ninety-six AHL-producing bacteria were isolated, and 92 were identified as Enterobacteriaceae. Hafnia alvei was the most commonly identified AHL-producing bacterium. Thin-layer chromatographic profiles of supernatants from six H. alvei isolates and of extracts from spoiling meat revealed that the major AHL species had an R_f value and shape similar to N-3-oxo-hexanoyl homoserine lactone (OHHL). Liquid chromatography-mass spectrometry (MS) (high-resolution MS) analysis confirmed the presence of OHHL in pure cultures of H. alvei. Vacuum-packed meat spoiled at the same rate when inoculated with the H. alvei wild type compared to a corresponding AHL-lacking mutant. Addition of specific QS inhibitors to the AHL-producing H. alvei inoculated in meat or to naturally contaminated meat did not influence the spoilage of vacuum-packed meat. An extracellular protein of approximately 20 kDa produced by the H. alvei wild-type was not produced by the AHL-negative mutant but was restored in the mutant when complemented by OHHL, thus indicating that AHLs do have a regulatory role in H. alvei. Coinoculation of H. alvei wild-type with an AHL-deficient Serratia proteamaculans B5a, in which protease secretion is QS regulated, caused spoilage of liquid milk. By contrast, coinoculation of AHL-negative strains of H. alvei and S. proteamaculans B5a did not cause spoilage. In conclusion, AHL and AHL-producing bacteria are present in vacuum-packed meat during storage and spoilage, but AHL does not appear to influence the spoilage of this particular type of conserved meat. Our data indicate that AHL-producing H. alvei may induce food quality-relevant phenotypes in other bacterial species in the same environment. H. alvei may thus influence spoilage of food products in which Enterobacteriaceae participate in the spoilage process.     

液质发酵食品中微生物群落及与乳酸菌间相互作用研究进展

液质发酵食品发酵过程中微生物组成复杂,复杂的微生物发酵体系会影响微生物的生长和代谢,继而改变微生物的群落结构与功能,最终影响液质发酵食品的品质.乳酸菌在食品发酵中对形成风味物质、提高营养价值、抑制腐败菌生长具有重要的作用.本文主要对近年来食醋、酱油和饮料酒等液质发酵食品中微生物群落及与乳酸菌间相互作用关系进行综述,了解...     

Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage

The microbial spoilage of meat and seafood products with short shelf lives is responsible for a significant amount of food waste. Food spoilage is a very heterogeneous process, involving the growth of various, poorly characterized bacterial communities. In this study, we conducted 16S ribosomal RNA gene pyrosequencing on 160 samples of fresh and spoiled foods to comparatively explore the bacterial communities associated with four meat products and four seafood products that are among the most consumed food items in Europe. We show that fresh products are contaminated in part by a microbiota similar to that found on the skin and in the gut of animals. However, this animal-derived microbiota was less prevalent and less abundant than a core microbiota, psychrotrophic in nature, mainly originated from the environment (water reservoirs). We clearly show that this core community found on meat and seafood products is the main reservoir of spoilage bacteria. We also show that storage conditions exert strong selective pressure on the initial microbiota: alpha diversity in fresh samples was 189±58 operational taxonomic units (OTUs) but dropped to 27±12 OTUs in spoiled samples. The OTU assemblage associated with spoilage was shaped by low storage temperatures, packaging and the nutritional value of the food matrix itself. These factors presumably act in tandem without any hierarchical pattern. Most notably, we were also able to identify putative new clades of dominant, previously undescribed bacteria occurring on spoiled seafood, a finding that emphasizes the importance of using culture-independent methods when studying food microbiota.     

Fermented foods, feeds and beverages

There has been a proliferation of books and papers dealing with the indigenous fermented foods/beverages of the world. It is anticipated that these foods/beverages will play an ever-increasingly important role in feeding both the developing and the developed world as population increases from approximately 4.5 billion to 6 billion by the year 2000 and to 8 to 12 billion people in the 21st century. The indigenous fermented foods consist of microbial protein grown on edible substrates. Microbial or single cell protein (SCP) per se continues to receive research and development attention. It is likely to play an important role in feeding animals in the future when it becomes competitive with soy protein. It may play a direct role in feeding humans in the future after its safety for feeding animals has been adequately demonstrated and it has been shown that it can be processed into foods acceptable to humans. At the present time, mushrooms, a form of microbial protein highly acceptable to humans, which can be grown readily on ligno-cellulosic and other agricultural and food processing wastes, offer considerable opportunity for expanding man's food supply.