Academic literature on the topic 'Food preservation/microbiology'

Introduction: Microbes perform better functions for agricultural production by promoting various direct and indirect mechanisms in soil and plants. If agricultural development is to satisfy the needs of an increasing global population, a deeper understanding of soil microbiology is needed. Furthermore, microbial biota such as yeast, bacteria etc., plays a significant role in food preservation by various mechanisms. Review results: Despite their pathogenicity, microbes play a substantial role in dispensing an assortment of fermented drinks and foods in the food industry and home. Probiotics, fermented foods and alcoholic beverages are flattering extra popular due to their health benefits and flavour. Furthermore, they increase the yield and growth of plants by improving mineral availability to the plants and by another mechanism. Review implementation: This present review also discusses the various organisms used in the agricultural processing of beverages and food and the benefits of using the following microbes in the beverage and food industry.

ABSTRACTFood spoilage may be defined as a process that renders a product undesirable or unacceptable for consumption and is the outcome of the biochemical activity of a microbial community that eventually dominates according to the prevailing ecological determinants. Although limited information are reported, this activity has been attributed to quorum sensing (QS). Consequently, the potential role of cell-to-cell communication in food spoilage and food safety should be more extensively elucidated. Such information would be helpful in designing approaches for manipulating these communication systems, thereby reducing or preventing, for instance, spoilage reactions or even controlling the expression of virulence factors. Due to the many reports in the literature on the fundamental features of QS, e.g., chemistry and definitions of QS compounds, in this minireview, we only allude to the types and chemistry of QS signaling moleculesper seand to the (bioassay-based) methods of their detection and quantification, avoiding extensive documentation. Conversely, we attempt to provide insights into (i) the role of QS in food spoilage, (ii) the factors that may quench the activity of QS in foods and review the potential QS inhibitors that might “mislead” the bacterial coordination of spoilage activities and thus may be used as biopreservatives, and (iii) the future experimental approaches that need to be undertaken in order to explore the “gray” or “black” areas of QS, increase our understanding of how QS affects microbial behavior in foods, and assist in finding answers as to how we can exploit QS for the benefit of food preservation and food safety.

Lactic acid fermented fruit and vegetables are normally obtained following a natural spontaneous fermentation in which no starter cultures are added. It could be expected that a suitable starter culture would help standardise production. Several lactic acid bacteria were selected for a series of physiological studies, in a defined medium (MRS broth) and in carrot juices, under varying conditions of growth temperature, salt concentration and carbohydrate source. Based on these, the homofermenter Lactobacillus pentosus and the heterofermenter Leuconostoc mesenteroides were tested as potential starters, in single and mixed cultures, for the fermentation of carrots (Daucus carota), as a novel fermentable substrate, and cabbage (Brassica oleracea) into sauerkraut. Fermentations were performed in the presence of the natural microflora. Sugar catabolism and acid production were monitored through H.P.L.C. In the fermentation of carrots Leuconostoc mesenteroides played a major role, with no homofermenters present. For sauerkraut, the mixed starter culture composed of Leuconostoc mesenteroides and Lactobacillus pentosus gave the closest resemblance to the product normally obtained following a natural commercial fermentation. The inclusion of the heterofermenter provided the required acid balance for correct product flavour and aroma by enhancing production of acetic acid. Acetate is also a better antimicrobial than lactate. A shorter fermentation time was also obtained, reducing the time from 3-4 weeks in the natural fermentation to only 7 days with the use of the mixed starter. When reduced salt concentrations were tried, 1% NaCl (w/w) resembled the spontaneous fermentation more closely, in regard to microbial sequence, pH and total acidity. Different ratios of the two lactic acid bacteria in combination were tried, the best being that in which L, mesenteroides and L. pentosus were initially present in the same proportions. Survival of Listeria monocytogenes in fermenting sauerkraut was shorter when starter cultures were used, but no difference was detectable between mixed and single cultures.

Thesis (MScVoedselwet)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Red meat has a limited shelf-life at refrigerated temperatures, where spoilage is mainly due to the proliferation of bacteria, yeast and moulds, acquired during the dressing process. In addition, almost a fifth of food-borne disease outbreaks, caused by microorganisms such as Escherichia coli 0157:H7, Listeria monocytogenes and Staphylococcus aureus are associated with red meat. To improve the microbiological quality of red meat, systems such as HACCP, GHP and GMP are currently practiced; however, these practices are not able to extend the shelf-life of these products. At present suitable food-grade preservatives are recommended, but the use of some of these preservatives is increasingly being questioned with regard to their impact on human health. Additionally, food service customers demand high quality products that have a relatively long shelf-life, but still prefer the appearance of minimally processed food. All these factors challenge the food manufacturing industry to consider more natural means of preservation. Antimicrobial metabolites of food grade bacteria, especially lactic acid bacteria, are attracting increasing attention as food preservatives. Bacteriocins are antimicrobial peptides (3 to 10 kDa) with variable activity spectra, mode of action, molecular weight, genetic origin and biochemical properties that are bacteriostatic or bactericidal to bacteria closely related and bacteria confined within the same ecological niche. Micro-organisms were isolated from beef, lamb and pork, obtained from four commercial retailers. The number of viable cells three days after the sell-by date at 4ºC ranged from 80 cfu.g-1 to 1.4 × 108 cfu.g-1. Fifty-three percent were Gram-negative bacteria, 35% Gram-positive and 12% yeast. The microbial population of the meat was greatly influenced by the origin, i.e. the retailer. Bacteriocins produced by Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 and Pediococcus pentosaceus ATCC 43201 were screened for activity against bacteria isolated from the different meat samples. Sixteen to 21% of the isolates, identified as members of Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus and Bacillus were sensitive to the bacteriocins. Curvacin DF 38, plantaricin 423 and caseicin LHS (2.35 to 3.4 kDa) had the broadest activity range and inhibited species of Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. The bacteriocins remained stable at 121ºC for 20 min, in buffers with a pH ranging from 2 to 10 and in NaCl concentrations of between 0.1 and 10% (m/v). Like most peptides, they were sensitive to proteolytic enzymes. Curvacin DF 38 is sensitive to amylase, suggesting that the bacteriocin might be glycosylated. To assess the efficiency of curvacin DF 38, plantaricin 423 and caseicin LHS as meat preservatives, they were partially purified by ammonium sulphate precipitation and separation in a Sep Pak C18 cartridge. The shelf-life of pork may be extended by up to two days. Meat samples treated with bacteriocins were darker than the control (untreated) sample. Descriptive sensory evaluation by a seven-member panel indicated that there were significant differences (P ≤ 0.05) regarding the aroma, sustained juiciness, first bite and metallic taste attributes of the control and the 4 day-treated samples. The control and 2 day-treated samples and the 2 day- and 4 day treated samples did not differ significantly regarding these attributes. There were no significant differences regarding the initial juiciness, residue and pork flavour attributes. Concluded from the results obtained in this study, bacteriocins produced by Lb. curvatus DF 38, Lb. plantarum 423 and Lb. casei LHS effectively extended the shelf-life of pork loins by up to 2 d at refrigerated temperatures with no drastic changes on sensory characteristics. In edition, the stability of these bacteriocins broadens their application as preservatives in many foods.
AFRIKAANSE OPSOMMING: Die rakleeftyd van rooivleis by yskastemperature is beperk, waar bederf hoofsaaklik deur die vermenigvuldiging van bakterieë, giste en swamme veroorsaak word. Die meeste van hierdie kontaminante is afkomstig van die slagtingsproses. Byna ’n vyfde van alle uitbrake van voedselvergiftigings wat deur organismes soos Escherichia coli 0157:H7, Listeria monocytogenes en Staphylococcus aureus veroorsaak word, word met rooivleis geassosieër. Die praktyke HACCP, GMP en GHP word tans toegepas om die mikrobiologies kwaliteit van vleis te handhaaf, maar is egter nie voldoende om die rakleeftyd van rooivleis the verleng nie. Die preserveermiddels wat huidiglik aanbeveel word vir dié doel, word toenemend bevraagteken aangaande die invloed daarvan op die menslike gesondheid. Hierby is daar ’n aanvraag na hoë kwaliteit, ongeprosesseerde produkte met ’n verlengde rakleeftyd. Gevolglik word die voedsel vervaardigings industries aangemoedig om meer natuurlike vorms van preservering the oorweeg. Die aandag word tans op die anti-mikrobiese metaboliete van voedselgraad microbes, veral melksuurbakterieë, gevestig. Bakteriosiene is anti-mikrobiese peptiede (3 tot 10 kDa) met verskeie aktiwiteitsspektra, werkswyse, molekulêre massa, genetiese oorsprong en biochemiese eienskappe. Bakteriosiene is meestal bakterie-dodend of - staties teen taksonomies naby geleë organismes en organismes vanuit dieselfde ekologiese nis. Mikroörganismes is geïsoleer vanuit bees-, skaap- en varkvleis, verkry vanaf vier supermarkte. Die aantal lewensvatbare selle per gram (cfu.g-1) het drie dae na die “verkoop”-datum by 4ºC vanaf 80 cfu.g-1 tot 1.4 × 108 cfu.g-1 gevarieër. Drie en vyftig persent van die isolate is as Gram-negatief, 35% as Gram-positief en 12% as giste geïdentifiseer. Die sensitiwiteit van hierdie isolate teen bakteriosiene wat deur Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb. salivarius 241 en Pediococcus pentosaceus ATCC 43201 geproduseer is, is vervolgens getoets. Tussen 16% en 21% van die isolate was sensitief teen die bacteriosiene en is onder andere as Klebsiella, Shigella, Staphylococcus, Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus en Bacillus geïdentifiseer. Die bakteriosiene met die wydste aktiwiteitsspektrum, naamlik, curvacin DF 38, plantaricin 423 en caseicin LHS is verder ondersoek. Hierdie antimikrobiese peptiede (2.35 tot 3.4 kDa) toon aktiwiteit teen spesies van Lactobacillus, Pediococcus, Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. Die bakteriosiene is stabiel by 121ºC vir 20 min, in buffers met ‘n pH-reeks van tussen 2 en 10 en soutkonsentrasies vanaf 0.1% tot 10%. Soos die geval by meeste peptiede is hierdie bakteriosiene sensitief vir proteolitiese ensieme. Curvacin DF 38 is ook sensitief vir amylase, wat daarop dui dat hierdie bakteriosien moontlik geglikosileer is. Die effektiwiteit van curvacin DF 38, plantaricin 423 en caseicin LHS as preserveermiddel in voedselsisteme is getoets deur dit te suiwer (ammonium sulfaat presipitasie en Sep Pak C18 kolom) en op vark lendestukke aan te wend. Mikrobiese analise het bewys dat die rakleeftyd van vark met sowat 2 dae verleng kan word. Volgens die vleiskleurevaluering was die bakteriosien behandelde vark donkerder as die kontrole. Die aroma-, sappigheid-, tekstuur- en metaalgeur-eienskappe van die kontrole en die 4-dag behandelde monster het volgens ‘n opgeleide sensoriese paneel betekenisvol verskil (P ≤ 0.05). Die kontrole en die 2-dag behandelde en die 2-dag behandelde en die 4-dag behandelde monsters het nie betekenisvol verskil nie. Daar was geen betekenisvolle verskil aangaande die aanvanklike sappigheid-, residu- en varkgeur-eienskappe nie. Hierdie sensoriese eienskappe is belangrik ten opsigte van die verbruiker se aanvaarding van die produk. Vervolgens kan uit hierdie resultate afgelei word dat die bakteriosiene wat deur Lb. curvatus DF 38, Lb. plantarum 423 en Lb. casei LHS geproduseer word voldoende is om die rakleeftyd van vark lendestuk by 4ºC met 2 dae te verleng met min of geen effek op die sensoriese persepsie van die vleis. Hierdie bakteriosiene is ook stabiel onder verskeie kondisies wat die toepassing as preserveermiddel aansienlik verbreed.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016.
Microbial spoilage has been reported in various food products and this has led to increased food, fruit and beverage losses, thereby threatening economic growth, food safety and security. Furthermore, statistics have shown that more than 30% of agricultural produce in developing countries, mostly in Africa, is lost owing to microbial spoilage. Beverages, food and fruits are predominant contributors to the South African export market. In recent years, contamination of these products resulting in spoilage has been a problem, although partial spoilage control has been achieved using chemical preservatives such as dimethyl dicarbonate, sodium benzoate, potassium sorbate, and sulphur dioxide (SO2). However, prolonged exposure to these chemical preservatives can cause human health problems such as skin and/or eyesight damage, muscle and stomach pain, cardiovascular disease and the impairment of brain function. To mitigate such health concerns, biologically benign alternatives are deemed suitable, providing the rationale for this study.

High pressure (HP) kinetics of the microbial destruction and changes in the physicochemical characteristics of milk and pork were studied. Raw milk samples containing indigenous microflora of approximately 106 CFU/mL were heat sealed in dual peel sterilization pouches and subjected to HP treatment from 150--400 MPa with holding times ranging 5--120 min. The kinetic parameters (rate constant, k and decimal reduction time, D) for the microorganisms, alkaline phosphatase, color and viscosity were evaluated, based on first order kinetics and the pressure dependence of kinetic parameters was evaluated using pressure destruction time (PDT) and Arrhenius models. Kinetic data was well described by the first order model (R 2 > 0.90).
The application of pressure pulse was explored for pressure destruction of microorganisms as well as changes in physical-chemical characteristics of pork chops. Pork chops (2 days post-rigor) were subjected to HP treatment from 200--350 MPa for 0--120 min. Results showed that pressure changes of pork variables followed a dual effect consisting of an instantaneous pressure kill (IPK) with the application of pressure pulse (no holding) and a subsequent first order rate of destruction during the pressure hold time. The IPK values were pressure dependent and increased with pressure level. Parameters k and D indicated a higher rate of pressure destruction of microorganisms compared to quality attributes.
Kinetics of pressure destruction of Listeria monocytogenes Scott A were studied in relation to those of indigenous microorganism of milk and pork. The IPK was more pronounced with L. monocytogenes than with indigenous microflora. However, the kinetic parameters (k and D values) indicated a larger pressure resistance for L. monoctyogenes. HP processes were developed based on the standard plate count (SPC) kinetic data for indigenous microflora of milk as well as L. monocytogenes in milk and pork. The results showed that SPC kinetics permitted good estimation of microbial destruction in low pressure-lethality processes of milk and pork but its application at higher pressure-lethality levels were inaccurate. On the other hand, processes established based an destruction of L. monocytogenes were more predictable. Pressure pulse application to microbial lethality was also well predicted.
The shelf-life of milk and pork increased with the level of applied pressure lethality, but Q10 values suggested that low storage temperature was nevertheless required to control microbial growth and maintain quality. Storage of HP treated park offered some improvement in the texture but resulted in large color changes and drip losses. L. monocytogenes were not detected in any of the stored milk samples HP treated to achieve a lethality ≥10D.

Thesis (M. Tech. Environmental health) -- Central University of technology, Free State, 2011
Although the application of low pH is common practice in food preservation, the emergence of acid tolerance has been reported world-wide amidst a growing concern that preservation with weak acids, such as organic acids may be influenced as a result of food-borne bacteria becoming acid tolerant or acid resistant. The present study was conducted to assess the acid tolerance of a wide range of bacterial species and consequently the sustainable application of organic acids as food preservatives in particularly acidic foodstuffs. Acid tolerance was determined in 19 bacterial strains predominantly associated with food spoilage and food poisoning. After exposure to hydrochloric acid 16% of the isolates were found to be intrinsically tolerant to low pH and included amongst others the enteric bacteria Escherichia coli and Salmonella spp. The latter organisms are known causative agents in food spoilage and poisoning, and the results highlight the predicaments related to their ability to survive in acidic foodstuffs as well as the human gastric environment. Bacterial strains were further exposed to increasing concentrations of various acidic foodstuffs in order to determine the development of acid tolerance by gradual decrease in pH, as opposed to exposure to acid shock. After induction, the protein profiles of resulting acid tolerant isolates were compared with those of the original un-induced strains. Exposure to acidic foodstuffs resulted in various survival profiles, where not only pH but also the type of acidulant (foodstuff or inorganic acid) were found to be contributing factors in acid tolerance development. Bacterial protein composition after exposure to acidic foodstuffs showed considerable variation which may be indicative of acid tolerance development whereas the mechanisms involved may be the result of multiple modifications in bacterial composition. After the induction of acid tolerance, susceptibility of induced strains to various organic acids were determined at various pH values. This was done to investigate whether acid tolerance would influence the inhibitory activity of organic acids as antimicrobial agents in acidic food. Decreased susceptibility was not significantly demonstrated with the exception of only selected isolates, the latter including E. coli and S. typhimurium. Organic acid activity was found to be much more effective at lower pH values and it would be necessary to elucidate whether this inhibition is the result of a lower pH or more specifically the activity of the organic acids. The effect of exposure to an acidic environment on phenotypic characteristics of Gram-negative bacteria, and more specifically psychrotrophic organisms was evaluated in order to show the combined effect of organic acids and low temperature preservation. The characteristic yellow pigment of various Chryseobacterium species was found to be not as apparent after acid exposure while in some cases the colonies were observed as white. In Pseudomonas aeruginosa the characteristic green pigment was much more prominent after acid exposure. These morphological alterations may be important factors that should be considered in identification procedures employed in food safety laboratories. Finally, the influence of acidic exposure via acidic foodstuffs and also organic acids on the protein composition and outer membrane protein structure of various bacterial cells was investigated. No specific relationships with the MICs (Minimum Inhibitory Concentrations) of organic acids after induction with the selected acidic foodstuffs could be established, although various differences were found in protein expression. From the results, it may be suggested that the outer membrane of various pathogenic bacteria is involved in acid tolerance development and this supports the reports on the importance of membrane integrity in the protection against low pH. In conclusion, the study endeavoured to add to the body of knowledge with regard to alternative food preservation regimes utilising organic acids, either solely or in combination with selected extrinsic and intrinsic parameters.