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PubMed1999

Class IIa bacteriocins from lactic acid bacteria: antibacterial activity and food preservation.

In the last decade, a variety of ribosomally synthesized antimicrobial peptides, or bacteriocins, produced by lactic acid bacteria have been identified and characterized. As a result of these studies, insight has been gained into various fundamental aspects of biology and biochemistry such as bacteriocin processing and secretion, mechanisms of cell immunity, and structure-function relationships. In parallel, there has been a growing awareness that bacteriocins may be developed into useful antimicrobial food additives. Class IIa bacteriocins can be considered as the major subgroup of bacteriocins from lactic acid bacteria, not only because of their large number, but also because of their significant biological activities and potential applications. The present review provides an overview of the knowledge available for class IIa bacteriocins and discusses common features and recent findings concerning these substances. The activity and potential food applications of class IIa bacteriocins are a major focus of this review.

Journal Article↗
PubMed2000

Use of a ground beef model to assess the effect of the lactoperoxidase system on the growth of Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus in red meat.

The ability to preserve food in a state that is both appetising and nutritious is a basic requirement for health. Food poisoning represents a major source of illness and loss of productivity in many developed countries. Of particular concern in recent years are outbreaks of food poisoning associated with Escherichia coli O157:H7 or Listeria monocytogenes, many of which have been associated with the consumption of ground meat. Many of the chemicals presently licensed for use as food preservatives are increasingly being questioned with regard to their effects on humans, creating pressure on food suppliers to consider the use of 'natural' alternatives to these chemical agents. The potential use of one such agent, the lactoperoxidase system (LPS), for use in ground meat preparations is examined in this study. The degree of inhibition of growth of E. coli O157:H7, L. monocytogenes L45 and S. aureus R37 by LPS was examined in a broth system at 37 degrees C and in a ground beef system at 0, 6 and 12 degrees C. The degree of inhibition by LPS of natural populations of microorganisms present in ground beef obtained from eight retail outlets and incubated at room temperature was also examined. For each of the strains examined, sensitivity from most to least sensitive followed the order L. monocytogenes L45, S. aureus R37 and E. coli O157:H7. In each case the ability of LPS to inhibit growth was highly temperature dependent and maximal at a temperature permissive but not optimal for growth of the test strain. The numbers of bacteria detected in ground beef obtained from retail outlets varied considerably between the eight samples. In all cases, numbers of bacteria increased markedly in the uninhibited control over the 4 h incubation time and, with the exception of one faecal coliform count, growth of the microbial populations was strongly inhibited by the presence of LPS. It was concluded that LPS could potentially be applied to a considerably wider range of food products than those to which it is presently restricted.

Animals↗
PubMed1999

Production of acylated homoserine lactones by psychrotrophic members of the Enterobacteriaceae isolated from foods.

Bacteria are able to communicate and gene regulation can be mediated through the production of acylated homoserine lactone (AHL) signal molecules. These signals play important roles in several pathogenic and symbiotic bacteria. The following study was undertaken to investigate whether AHLs are produced by bacteria found in food at temperatures and NaCl conditions commercially used for food preservation and storage. A minimum of 116 of 154 psychrotrophic Enterobacteriaceae strains isolated from cold-smoked salmon or vacuum-packed chilled meat produced AHLs. Analysis by thin-layer chromatography indicated that N-3-oxo-hexanoyl homoserine lactone was the major AHL of several of the strains isolated from cold-smoked salmon and meat. AHL-positive strains cultured at 5 degrees C in medium supplemented with 4% NaCl produced detectable amounts of AHL(s) at cell densities of 10(6) CFU/ml. AHLs were detected in cold-smoked salmon inoculated with strains of Enterobacteriaceae stored at 5 degrees C under an N(2) atmosphere when mean cell densities increased to 10(6) CFU/g and above. Similarly, AHLs were detected in uninoculated samples of commercially produced cold-smoked salmon when the level of indigenous Enterobacteriaceae reached 10(6) CFU/g. This level of Enterobacteriaceae is often found in lightly preserved foods, and AHL-mediated gene regulation may play a role in bacteria associated with food spoilage or food toxicity.

Animals↗
PubMed1988

Preservation of food products by irradiation.

The use of irradiation to preserve food has the potential to significantly enhance our capacity to maximize the quality and quantity of the food we consume. In a world in which distribution of food occurs across continents and in which malnourished populations are in dire need of basic food products, any safe, effective, and efficient means of preserving food is more than welcome. Irradiation, as a method for food preservation, has been studied for more than 30 years. This discussion focuses on this most recent method for the preservation of food with particular emphasis on its effects on the safety, nutritive, and aesthetic values of the food preserved by irradiation. The use of ionizing radiation as a method to preserve foods is one that has been demonstrated to be effective for a variety of food classes. Irradiation offers a means to decontaminate, disinfest, and retard the spoilage of the food supply. At the same time, it appears that the wholesomeness of these food products is maintained. Nutritive value can be sustained by use of effective doses of radiation. Concerns over the safety of irradiated food are rooted in questions regarding the potential induction of radioactivity, harmful radiolytic products, and pathogenic radiation-resistant or mutant strains of microorganisms. Research findings have allayed concerns over safety. However, more research is necessary to conclusively resolve these safety issues. Food irradiation is a promising technology that has and will contribute to our ability to feed the people of this world. This technology is but one of many available ways to preserve our greatest natural resource, the food supply. Enhancement of the ability to preserve food by irradiation will facilitate the distribution of food from fertile developed regions to the malnourished peoples of underdeveloped countries. It is in diminishing the problem of malnourishment and starvation that irradiation as a means to preserve food may find the greatest acceptance.

Food Irradiation↗
PubMed1985

[Physical preservation of food].

Physical preservation procedures are mostly aimed at prolonging the durability of foods by slowing down or repressing the spoilage mechanisms by the alteration of relevant parameters. Of these mechanisms of microbiological, enzymatic, chemical and mechanical type, especially the first-named are dealt with. Growth and multiplication of micro-organisms can be influenced by temperature, water activity and high-energy radiation. Depending on the susceptibility to deterioration of the products and the intensity of the processes based on these parameters, different degrees of durability are obtained. Micro-organisms are killed by the application of high temperatures in conjunction with the treatment times required in a given case. Relatively mild treatments affect only the vegetative forms (pasteurization), whereas more aggressive treatments are required to kill spores as well (sterilization). Recontamination of the products which were subjected to the two procedures must be avoided. Pasteurized foods require additional cold storage to prevent the spores from sprouting. Low temperatures reduce and repress the growth of micro-organisms (refrigeration) or prevent any activity of the micro-organisms (deep-freezing). The latter deprives the micro-organisms of the water they need for their growth. The same principle applies to another method of preservation where so much water is extracted from the product that the residual humidity no longer allows the micro-organisms to be active (drying). Ionising radiation can be used to reduce a potential risk to hygiene, to influence physiological processes, to control insects and to lengthen the durability of fresh food in the short term. Finally optimum product quality can be maintained by combining various procedures. If such methods cope with controlling the microbiological situation, attention must nevertheless be given to the other spoilage mechanisms as well, as they may prove to be limiting factors with respect to product quality.

Bacteria↗
PubMed2000

Loss of Cmk1 Ca(2+)-calmodulin-dependent protein kinase in yeast results in constitutive weak organic acid resistance, associated with a post-transcriptional activation of the Pdr12 ATP-binding cassette transporter.

Yeast cells display an adaptive stress response when exposed to weak organic acids at low pH. This adaptation is important in the spoilage of preserved foods, as it allows growth in the presence of weak acid food preservatives. In Saccharomyces cerevisiae, this stress response leads to strong induction of the Pdr12 ATP-binding cassette (ABC) transporter, which catalyses the active efflux of weak acid anions from the cytosol of adapted cells. S. cerevisiae cells lacking the Cmk1 isoform of Ca2+-calmodulin-dependent protein kinase are intrinsically resistant to weak acid stress, in that they do not need to spend a long adaptive period in lag phase before resuming growth after exposure to this stress. This resistance of the cmk1 mutant is Pdr12 dependent and, unlike with wild-type S. cerevisiae, cmk1 cells are capable of performing Pdr12-specific functions such as energy-dependent cellular extrusion of fluorescein and benzoate. However, they have neither higher PDR12 gene promoter activity nor higher Pdr12 protein levels. The increased Pdr12 activity in cmk1 cells is therefore caused by Cmk1 exerting a negative post-transcriptional influence over the activity of the Pdr12 ABC transporter, a transporter protein that is constitutively expressed in low-pH yeast cultures. This is the first preliminary evidence that shows a protein kinase, either directly or indirectly, regulating the activity of a yeast ABC transporter.

ATP-Binding Cassette Transporters↗