Low-acid Canned Foods Research Articles

LysGR1, a novel thermostable endolysin from Geobacillus stearothermophilus bacteriophage GR1.

Geobacillus stearothermophilus is a highly thermophilic, spore-forming Gram-positive bacterium that causes flat sour spoilage in low-acid canned foods. To address this problem, we isolated G. stearothermophilus-infecting phage GR1 from the soil and characterized its endolysin LysGR1. Phage GR1 belongs to the Siphoviridae family and possesses a genome of 79,387 DNA bps with 108 putative open reading frames. GR1 demonstrated a very low degree of homology to previously reported phages, indicating that it is novel. The endolysin of GR1 (LysGR1) contains an N-terminal amidase domain as an enzymatically active domain (EAD) and two C-terminal LysM domains as a cell wall binding domain (CBD). Although GR1 is specific to certain strains of G. stearothermophilus, LysGR1 showed a much broader lytic range, killing all the tested strains of G. stearothermophilus and several foodborne pathogens, such as Clostridium perfringens, Listeria monocytogenes, and Escherichia coli O157:H7. LysGR1_EAD, alone, also exhibits lytic activity against a wide range of bacteria, including Bacillus cereus, which is not terminated by a full-length endolysin. Both LysGR1 and its EAD effectively remove the G. stearothermophilus biofilms and are highly thermostable, retaining about 70% of their lytic activity after a 15-min incubation at 70°C. Considering the high thermal stability, broad lytic activity, and biofilm reduction efficacy of LysGR1 and its EAD, we hypothesize that these enzymes could act as promising biocontrol agents against G. stearothermophilus and as foodborne pathogens.

Quantitation of α-Dicarbonyls, Lysine- and Arginine-Derived Advanced Glycation End Products, in Commercial Canned Meat and Seafood Products.

Commercial sterilization is a thermal processing method commonly used in low-acid canned food products. Meanwhile, heat treatment can significantly promote advanced glycation end product (AGE) formation in foodstuffs. In this research, the validated analytical methods have been developed to quantitate both lysine- and arginine-derived AGEs and their precursors, α-dicarbonyls, in various types of commercial canned meat and seafood products. Methylglyoxal-hydroimidazolone 1 was the most abundant AGEs found in the canned food products, followed by Nε-(carboxyethyl)lysine, Nε-(carboxymethyl)lysine, and glyoxal-hydroimidazolone 1. Correlation analysis revealed that methylglyoxal and glyoxal were only positively associated with the corresponding arginine-derived AGEs, while their correlations with the corresponding lysine-derived AGEs were not significant. Importantly, we demonstrated for the first time that total sugar and carbohydrate contents might serve as the potential markers for the prediction of total AGEs in canned meats and seafoods. Altogether, this study provided a more complete view of AGEs' occurrence in commercial canned food products.

Viability of bacterial spores surviving heat-treatment is lost by further incubation at temperature and pH not suitable for growth

Spores from 21 strains from different genera were heat-treated and stored in different sets of process conditions (4 temperatures and 3 pH levels) defined to prevent growth. In these conditions, spores surviving the heat treatment progressively lost viability during storage. Different inactivation curve shapes (linear, shoulder and tailing) and different sensitivities to storage were observed. B. coagulans showed the fastest inactivation kinetics, with more than 4-log reduction of spore population within 24 h after heating and G. stearothermophilus displayed slower inactivation kinetics, whereas all the anaerobic strains studied (M. thermoacetica and Thermoanaerobacterium spp.) proved resistant to storage conditions, with no destruction detected during 90 days in most cases. Inactivation rates were relatively unaffected by sub-lethal pH but sharply accelerated by temperature: Inactivation became faster as temperature increased (in the 8 °C–55 °C temperature range), with growth blocked by low pH in sub-lethal temperatures.There were changes in surviving spore numbers after the heat-treatment phase. This has implications and applications in canned food industries, as the probability of a retorted sample testing as non-stable, meaning possible spoilage, may decrease with time. In simple terms, a batch of low-acid canned food that tests as non-shelf-stable after an incubation test i.e. positive growth conditions, may later become negative if stored at room temperature (below the minimal growth temperature for thermophilic spores), which may change the marketability of the batch.

Facility Registration and Initial Regulatory Compliance Activities for Acidified Food and Low-Acid Canned Food Processors in Florida

Food businesses are subject to a wide range of regulatory requirements. Food entrepreneurs who want to produce and sell acidified foods or low-acid canned foods must abide by specific FDA regulations. This new 3-page document intends to clarify the initial steps food entrepreneurs must implement to comply with these regulations. This factsheet is one in a Food Entrepreneurship in Florida series, which assists beginning and established food entrepreneurs by providing them information on topics highly relevant to starting and running a food business: regulations, safety, labeling, processing, and marketing. Written by Matthew Krug and Soohyoun Ahn, and published by the UF/IFAS Food Science and Human Nutrition Department, February 2019. http://edis.ifas.ufl.edu/fs318

Temperature impacts the sporulation capacities and spore resistance of Moorella thermoacetica

Temperatures encountered in cannery allow growth of thermophilic spore-forming bacteria, including the strictly anaerobe Moorella thermoacetica, which grows optimally from 55 °C to 65 °C and is the main cause of spoilage of low-acid canned foods (LACFs) at high temperature. Resistance to wet-heat, biocides and UV-C of spores formed at different temperatures was assessed either for a selection of M. thermoacetica strains or for the strain M. thermoacetica ATCC 39073. Spores formed at 45 °C were significantly more sensitive to wet-heat than spores produced at 55 °C, while spores produced at 65 °C were as heat-resistant as spores produced at 55 °C. Spores of M. thermoacetica ATCC 39073 produced at 45 °C were significantly less resistant to peracetic acid than spores formed at 55 °C, while no difference in sensitivity to H2O2 or to UV-C treatment was observed whatever the sporulation temperature. However, both types of treatment enabled at least a 3.3 log CFU/mL reduction of M. thermoacetica ATCC 39073 spores. M. thermoacetica spores thus showed higher resistance properties when sporulation temperature was close to optimal growth temperature. These findings suggest food spoilage due to M. thermoacetica species could be controllable by holding temperatures below optimal growth temperature from the blanching step to the can filling step.

Spore-forming bacteria responsible for food spoilage

This review explores the main spore-forming bacteria involved in the spoilage of various processed foods. Bakery products are specifically spoiled by Bacillus species, the dominant one being Bacillus amyloliquefaciens, while different Clostridium species classically contaminate refrigerated vacuum-packed meats. These two genera have also been isolated from milk products, even when milk is pasteurized, sterilized, dehydrated or fermented, according to heat treatment and storage temperature. Finally, the most heat-resistant microorganisms are isolated in low-acid canned foods, the three predominant species being Geobacillus stearothermophilus, Moorella thermoacetica and Thermoanaerobacterium spp.

Contamination pathways of spore-forming bacteria in a vegetable cannery

Spoilage of low-acid canned food during prolonged storage at high temperatures is caused by heat resistant thermophilic spores of strict or facultative bacteria. Here, we performed a bacterial survey over two consecutive years on the processing line of a French company manufacturing canned mixed green peas and carrots. In total, 341 samples were collected, including raw vegetables, green peas and carrots at different steps of processing, cover brine, and process environment samples. Thermophilic and highly-heat-resistant thermophilic spores growing anaerobically were counted. During vegetable preparation, anaerobic spore counts were significantly decreased, and tended to remain unchanged further downstream in the process. Large variation of spore levels in products immediately before the sterilization process could be explained by occasionally high spore levels on surfaces and in debris of vegetable combined with long residence times in conditions suitable for growth and sporulation. Vegetable processing was also associated with an increase in the prevalence of highly-heat-resistant species, probably due to cross-contamination of peas via blanching water. Geobacillus stearothermophilus M13-PCR genotypic profiling on 112 isolates determined 23 profile-types and confirmed process-driven cross-contamination. Taken together, these findings clarify the scheme of contamination pathway by thermophilic spore-forming bacteria in a vegetable cannery.

Thermophilic spore-forming bacteria isolated from spoiled canned food and their heat resistance. Results of a French ten-year survey

Thermal processing of Low Acid Canned Foods (LACF), which are safe and shelf-stable at ambient temperature for several years, results in heat inactivation of all vegetative microorganisms and the partial or total inactivation of spores. Good Manufacturing Hygienic Practices include stability tests for managing the pathogen risk related to surviving mesophilic bacterial spores. LACF are also often submitted to additional incubation conditions, typically 55°C for 7days, to monitor spoilage by thermophiles. In this study we identified the bacterial species responsible for non-stability after prolonged at 55°C of incubation of LACF from 455 samples collected from 122 French canneries over 10years.Bacteria were identified by microsequencing or a recent developed tool for group-specific PCR detection (SporeTraQ™). A single species was identified for 93% of examined samples. Three genera were responsible for more than 80% of all non-stability cases: mostly Moorella (36%) and Geobacillus (35%), and less frequently Thermoanaerobacterium (10%). The other most frequent bacterial genera identified were Bacillus, Thermoanaerobacter, Caldanaerobius, Anoxybacillus, Paenibacillus and Clostridium.Species frequency was dependent on food category, i.e. vegetables, ready-made meals containing meat, seafood or other recipes, products containing fatty duck, and related to the intensity of the thermal treatment applied in these food categories. The spore heat resistance parameters (D or δ and z values) from 36 strains isolated in this study were determined. Taken together, our results single out the species most suitable for use as indicators for thermal process settings. This extensively-documented survey of the species that cause non-stability at 55°C in LACF will help canneries to improve the management of microbial contamination.

Conditions associated with Clostridium sporogenes growth as a surrogate for Clostridium botulinum in nonthermally processed canned butter

The objective of this study was to better understand the effect of butter composition and emulsion structure on growth and survival of Clostridium sporogenes, used as a surrogate for C. botulinum in canned butter. The lack of a thermal process step in commercially available canned butter raises questions of potential safety, because it is hermetically sealed and generally exhibits anaerobic growth conditions, which are optimal for Clostridium botulinum growth. Without thermal processing, low-acid canned foods must have inhibitory factors present to prevent C. botulinum growth. Some potential intrinsic inhibitory factors, or hurdles, within butter include: reduced water activity, acidity in cultured products, elevated salt content, and the micro-droplet nature of the aqueous phase in the butter emulsion. It was hypothesized that a normal, intact butter emulsion would have sufficient hurdles to prevent C. botulinum growth, whereas a broken butter emulsion would result in a coalesced aqueous phase that would allow for C. botulinum growth. Batch-churned butter was inoculated with C. sporogenes; butter samples with varying salt contents (0, 0.8, 1.6, and 2.4% wt/wt NaCl) were prepared and stored in coated steel cans for varying times (1 or 2 wk) and temperatures (22 or 41°C) to determine temperature and emulsion structure effects on C. sporogenes growth. Samples stored at 41°C showed a significant increase in C. sporogenes growth compared with those stored at 22°C. Furthermore, NaCl addition was found to have a significant effect on C. sporogenes growth, with 0.8% NaCl promoting more growth than 0%, but with decreases in growth observed at 1.6 and 2.4%. Uninoculated control plates were also found to have bacterial growth; this growth was attributed to other anaerobic bacteria present within the cream. It was concluded that removal of the hurdle created by the micro-droplet size of the emulsion aqueous phase could result in C. botulinum growth even at elevated salt levels and, therefore, home preparation of canned butter is not advisable. It is also possible that commercially canned butter, if heat abused, could potentially allow for C. botulinum growth and, therefore, consumption is not recommended.

Draft Genome Sequence of a Clostridium botulinum Isolate from Water Used for Cooling at a Plant Producing Low-Acid Canned Foods

Clostridium botulinum is a pathogen of concern for low-acid canned foods. Here we report draft genomes of a neurotoxin-producing C. botulinum strain isolated from water samples used for cooling low-acid canned foods at a canning facility. The genome sequence confirmed that this strain belonged to C. botulinum serotype B1, albeit with major differences, including thousands of unique single nucleotide polymorphisms (SNPs) compared to other genomes of the same serotype.

PCR Detection of Thermophilic Spore-Forming Bacteria Involved in Canned Food Spoilage

Thermophilic bacteria that form highly heat-resistant spores constitute an important group of spoilage bacteria of low-acid canned food. A PCR assay was developed in order to rapidly trace these bacteria. Three PCR primer pairs were designed from rRNA gene sequences. These primers were evaluated for the specificity and the sensitivity of detection. Two primer pairs allowed detection at the species level of Geobacillus stearothermophilus and Moorella thermoacetica/thermoautrophica. The other pair allowed group-specific detection of anaerobic thermophilic bacteria of the genera Thermoanaerobacterium, Thermoanaerobacter, Caldanerobium and Caldanaerobacter. After a single enrichment step, these PCR assays allowed the detection of 28 thermophiles from 34 cans of spoiled low-acid food. In addition, 13 ingredients were screened for the presence of these bacteria. This PCR assay serves as a detection method for strains able to spoil low-acid canned food treated at 55°C. It will lead to better reactivity in the canning industry. Raw materials and ingredients might be qualified not only for quantitative spore contamination, but also for qualitative contamination by highly heat-resistant spores.

Effect of enterocin EJ97 against Geobacillus stearothermophilus vegetative cells and endospores in canned foods and beverages

Geobacillus stearothermophilus is a thermophilic bacterium typically responsible for the flat-sour spoilage of low-acid canned food with high water activity. Control of vegetative cells and spores of G. stearothermophilus strains CECT 48 and CECT 49 by enterocin EJ97 produced by Enterococcus faecalis EJ97 is described. Both strains were highly sensitive to EJ97 in a culture medium. In samples from canned foods inoculated with a cocktail of vegetative cells or endospores of the two strains and stored at 45 °C for 30 days, viable cell counts were reduced below detection levels. The time course of microbial inactivation depended on the food sample and bacteriocin concentration. Dormant endospores were resistant to EJ97 short-time treatments (5 min), but endospores activated to germinate by heat became bacteriocin sensitive. The simultaneous application of enterocin EJ97 and heat treatments (90 and 95 °C) on dormant endospores had an increased antimicrobial effect that depended both on the bacteriocin concentration and the heat temperature. Results from this study strengthen the potential of enterocin EJ97 for biopreservation against G. stearothermophilus in canned vegetable foods and drinks.

Preliminary validation of on-line correction of process deviations without extending process time in batch retorting: Any low-acid canned foods

This short communication describes a practical and efficient method for on-line correction of thermal process deviations during retort sterilization of canned foods without upsetting retort operating schedules in large cook room operations. The strategy is a modification of a recently developed “proportional-corrected” process method that accomplishes the on-line correction after recovery of the deviation by operating the retort at a temperature sufficiently above the normal retort temperature so as to reach the specified target lethality within the remaining process time. In this way, on-line correction of the process deviation is accomplished without extending the normal process time specified for that batch cook, and smooth uninterrupted operation of a retort battery system in large cook rooms is assured. The method is intended for easy implementation in any cannery around the world with no need for on-site access to computer-based control systems and/or computer software of any kind.

Optimum on-line correction of process deviations in batch retorts through simulation

This paper describes broader applications of computer-based batch retort control systems that make use of mathematical models to accomplishing on-line correction of unexpected process deviations in thermal processing of low-acid canned foods. Current systems over extend process time with costly consequences to product quality and retort operating schedules in cook room operations. These problems are addressed by describing novel control strategies that also treat the retort temperature as a control variable, rather than just process time alone. On-line correction is accomplished by choosing an optimum higher constant retort temperature for the remainder of the process that will deliver the specified target lethality within the original process time remaining. The paper also describes on-line correction of process deviations occurring during a pre-programmed variable or dynamic retort temperature process that might be chosen to maximize nutrient retention in a conduction-heated food. In this situation, an optimum combination of retort temperature and process time is chosen for the remainder of the process that will deliver the maximum possible nutrient retention without compromising the specified final target lethality. Examples are given for the case of solid product undergoing a conduction-heating process in different shaped containers (cylindrical can and retort pouch), as well as liquid product undergoing forced convection heating in cylindrical cans under mechanical agitation.

Immunoassay Kit Used to Detect the Presence of Bovine Material in Processed Foods

The Tepnel Bio Kit for the detection of beef in cooked foods was assessed to determine its validity in demonstrating if food being imported into New Zealand contains beef material. The test suffered no interference from the presence of other common nonbovine species meats accepted as food within New Zealand and it detected beef in cooked samples of mixed meats when the proportion of beef in the mixture was >2 or >1%, depending on other meat species present. The documentation supplied with the kit indicates that the specific proteins it measures in cooked beef are stable to 130 degrees C. This was confirmed in the literature when the kit was used to test meat and bone meal cooked to at least 133 degrees C. However, our results showed these proteins to be much less stable when heated to elevated temperatures in moist food under pressure, and samples containing beef ceased to be positive by the immunoassay test after being autoclaved to 121 degrees C. This suggests that the test may not be able to detect even relatively high levels of beef in low-acid canned foods, which are normally retorted under pressure to approximately 121 degrees C.

Calculating FT-Values for Heat Preservation of Shelf-Stable, Low-Acid Canned Foods using the Straight-Line Semilogarithmic Model

This is a review paper illustrating how the heat process FT-value for low-acid canned foods can be estimated using measured values of the numbers and resistance of the spoilage organisms and an appropriate model. Heat process FT-values are calculated using the straight-line semilogarithmic model for preservation against public health, mesophilic spore economic and thermophilic spore economic spoilage. The microbiological characteristics of each type of preservation hazard are reviewed. Several appropriate values of DT and N0 are used in the illustration calculations of FT. The presentation is summarized graphically by placing the FT-value lines calculated using the model for preservation against public health, mesophilic spore and thermophilic spore hazards all on the same graph. This gives a visual picture of the relative magnitude of the FT-value for the different types of spoilage hazard.

Factors Important in Determining the Heat Process Value, FT, for Low-Acid Canned Foods

In this monograph an attempt is made to put into perspective several factors that impinge on the heat process value, FT. In the heat processing of low-acid canned foods (LACF), there are three specific types of final product spoilage that concern the food microbiologist and the food manufacturer. These three areas are discussed in some detail. The order to follow in the design of LACF and endpoint values are suggested. Use of descriptive and numerical terms for the endpoint of the LACF heat preservation process is discussed. The origin of the term, “commercial sterility,” is reviewed; reasons for replacing this term (in the future) with a specification are presented. The several faces of the widely-used heat process value, FT, are examined. The use of a safety factor to take care of unknown processing conditions is proposed. Suggested safety factors are listed. The classical research of Esty and Meyer on resistance of Clostridium botulinum is reviewed and interpreted using the simple logarithmic model. The often-quoted but poorly-understood term, 12D, is discussed.

Post-Processing Spoilage of Low-Acid Canned Foods by Mesophilic Anaerobic Sporeformers

Over a period of 4 years, 770 low-acid canned food spoilage incidents were investigated to determine the cause of spoilage. In 27 of these, the cause was attributed to the growth of bacteria of the Clostridium genus that had entered the cans as a result of post-processing leakage. No correlations were found that might explain the occurrence of this mesophilic anaerobic type of spoilage. It appears to be a random event, probably linked to cannery insanitation. A variety of species was found, consisting of both proteolytic and non-proteolytic types. Clostridium botulinum was not isolated from any of the canned foods examined, nor were any of the samples found to contain botulinal toxin. Container leak test methodology and principles are discussed.

Botulism Risk from Post-Processing Contamination of Commercially Canned Foods in Metal Containers

This report focuses on the potential public health risks of Clostridium botulinum from post-process contamination of commercially produced foods in metal containers. This review examines the environmental sources of C. botulinum, the effect of sanitizers in cannery cooling water and the botulism incidents involving U.S. canned foods. There is no evidence that leaker spoilage due to container defects is increasing. The post-processing contamination of commercially produced foods in metal containers by C. botulinum is a rare event which occurs randomly. Based on historical information, its probability of occurring is very small. This is a probability which compares well with the risk associated with the minimum acceptable thermal process of low-acid canned foods.

Regulatory Aspects of Post-Processing Microbiological Contamination of Low-Acid Canned Foods

Various Canadian regulations pertinent to post-processing microbiological contamination of low-acid canned foods are reviewed, As an example of the dilemma presented to the regulatory agency, a typical case history is presented. The case concerns a canned fish product suspected of causing staphylococcal intoxication in two persons. The results of the following investigation are presented and the reader asked to be the judge.