Initiation of germination of bacterial spores by hydrostatic pressure.
TL;DR: Hydstatic pressure initiated germination of bacterial spores in nutrient-free media and potentiated L-alanine and closely related α-amino acids, but not their breakdown products, potentiated germination initiated by pressure.
Abstract: SUMMARY: Hydrostatic pressure initiated germination of bacterial spores in nutrient-free media. Those spores which were most dormant towards chemical germinants at I atmosphere pressure were also the most resistant to germination by pressure treatment. Germination by high pressure treatment was characterized by temperature and pH optima, like germination at atmospheric pressure. Germination initiated by pressure was inhibited by metabolic poisons and was potentiated by low concentrations of various nutrients including some of those which are normally germinative (at higher concentrations) at atmospheric pressure. In particular, L-alanine and closely related α-amino acids, but not their breakdown products, potentiated germination initiated by pressure. Study of potentiation by D-alanine (which strongly inhibits germination initiated by L-alanine at I atmosphere pressure) revealed that high pressures caused an increase in the rate of racemization of alanine by spores. Germination by pressure probably resulted from acceleration of some germination reaction which is normally negligibly slow at a pressure of I atmosphere, and also from an increase in permeability of some barrier within the spore to L-alanine and related α-amino acids.
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TL;DR: Taking into account the baroprotective effects of some food constituents and the strong resistance of some microbial strains, recent research aims at combined processes in which high pressure is associated with moderate temperature, CO2, other bacteriostatic agents, or to nonthermal physical processes such as ultrasounds, alternative currents, high-voltage electric pulses, and so forth.
Abstract: High pressure (1 to 10 kbars, i.e. 100-1000 MPa) affects biological constituents and systems. Several physicochemical properties of water are modified, such as the density, the ionic dissociation (...
727 citations
TL;DR: In this article, a variety of methods are evaluated for the in situ measurement of an intrinsic food component before and after treatment, and physical mathematical method, in which the actual temperature-pressure-time profile is combined with the kinetics of the attribute under consideration.
Abstract: An important issue in the application of high pressure technology in the food preservation/processing industry is regulatory approval, which focuses upon microbiological and toxicological safety of food products. High pressure preservation processes should reduce the microbial load to the same level achieved by traditional technologies, while delivering higher-quality products. Combination of high pressure with other treatments (e.g., mild temperature elevation, refrigerated storage, acidification) during processing and storage is a likely route the food industry will take, as the inactivation of bacterial spores and some pressure-resistant enzymes at room temperature cannot be achieved by pressure alone. Several authors suggest that the most safe and economically feasible use of high pressure is in combination with moderately elevated temperature (Gould & Sale, 1970; Knorr, 1993). From the point of view of those who define hazard analysis of critical control points (HACCP) guidelines (risk analysis method carried out to guarantee safety and quality of food products throughout the production chain) or “novel food” regulations (directives that have to be taken into account when introducing new products, new ingredients, or new processing techniques on the market), and also from an engineering point of view, methods to determine the impact of pressure processes on food safety and quality are indispensable. A variety of methods could be evaluated for this purpose: (1) the in situ method, in which the change of an intrinsic food component is measured before and after treatment; (2) the physical mathematical method, in which the actual temperature-pressure-time profile is combined with the kinetics of the attribute under consideration; or (3) the use of process history indicators, which are devices that mimic the change of the attribute under consideration when submitted to the same temperature-pressure-time profile. All these methods rely largely on kinetic models. In this context, quantitative kinetic studies on the combined effect of pressure and temperature on several aspects of food safety and quality (pathogenic/spoilage microorganisms, enzymes related to food quality, nutritional and sensorial quality characteristics) are required. From an engineering point of view, such kinetic data are very important for evaluation of process uniformity, for process validation, and for process optimization.
538 citations
TL;DR: High hydrostatic pressure has the potential to produce high quality foods that are microbiologically safe and with an extended shelf-life, and a knowledge of how these factors interact is necessary in order to select the optimum processing conditions for foods.
Abstract: High hydrostatic pressure has the potential to produce high quality foods that are microbiologically safe and with an extended shelf-life. Micro-organisms vary in their response to high pressure. Bacterial spores are the most resistant group and they cannot be significantly inactivated by pressure alone. Combination treatments using high pressure and heat have been proposed as a method of producing shelf-stable low acid foods. Viruses are less resistant than bacterial spores and their infectivity can be abolished without destroying their ability to elicit antibodies, leading to the possibility of vaccine production. Yeasts, moulds and vegetative bacteria vary in their response to pressure, depending on factors such as species, strain, processing temperature and substrate, and these are reviewed in the paper. A knowledge of how these factors interact is necessary in order to select the optimum processing conditions for foods. A number of pressure-treated foods are already commercially available and these are discussed in the paper.
438 citations
Cites background from "Initiation of germination of bacter..."
...However, relatively low pressures (below 200 MPa) can trigger spore germination (Gould and Sale 1970)....
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TL;DR: The aim of this review is to provide an overview of the microbiological aspects of the most relevant nonthermal technologies for microbial inactivation currently under study, including irradiation, high hydrostatic pressure, pulsed electric field and ultrasound under pressure.
Abstract: The increasing consumer demand for 'fresh-like' foods has led to much research effort in the last 20 years to develop new mild methods for food preservation. Nonthermal methods allow micro-organisms to be inactivated at sublethal temperatures thus better preserving the sensory, nutritional and functional properties of foods. The aim of this review is to provide an overview of the microbiological aspects of the most relevant nonthermal technologies for microbial inactivation currently under study, including irradiation, high hydrostatic pressure, pulsed electric field and ultrasound under pressure. Topics covered are the mechanisms of inactivation, sensitivity of different microbial groups and factors affecting it and kinetics of inactivation.
395 citations
Cites background from "Initiation of germination of bacter..."
...Pressure itself at a moderate level induces spore germination (Gould and Sale 1970)....
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TL;DR: Some successful combinations of different nonthermal technologies, such as high hydrostatic pressure, ultrasound, pulsed electric fields, and irradiation, with traditional or emerging food preservation technologies are reviewed.
Abstract: In the last 2 decades, consumer demand for fresher, higher quality, and safer food has promoted research on nonthermal methods of food preservation for the inactivation of microorganisms and enzymes as an alternative to thermal processes. However, the high resistance of certain enzymes and microorganisms to nonthermal processes, especially bacterial spores, limit their application. To expand the use of nonthermal processes in the food industry, combinations of these technologies with traditional or emerging food preservation techniques are being studied. The use of nonthermal processes in combination with other preservation technologies presents a number of potential benefits to food preservation. The purpose of this article is to review some successful combinations of different nonthermal technologies, such as high hydrostatic pressure, ultrasound, pulsed electric fields, and irradiation, with traditional or emerging food preservation technologies.
373 citations
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TL;DR: Spores of various species of the genera Bacillus and Clostridium were inactivated by hydrostatic pressures up to 8000 atmospheres, suggesting that pressure caused inactivation of spores by first initiating germination and then inactivating the germinated forms.
Abstract: SUMMARY: Spores of various species of the genera Bacillus and Clostridium were inactivated by hydrostatic pressures up to 8000 atmospheres. Inactivation was a function of holding time at pressure rather than of the compression and decompression stages. Inactivation generally proceeded more rapidly at high than at low temperatures; below about 50° there was a well defined optimum pressure for inactivation, but above about 50° an increase in pressure up to 8000 atmospheres caused progressively more inactivation.
Inactivation was decreased at extremes of pH value and by high ionic strength solutions. A proportion of the spores pressurized under certain conditions became heat-sensitive. These observations, and the chemical, phase-contrast, and electron-microscopic changes seen in pressurized spores, suggested that pressure caused inactivation of spores by first initiating germination and then inactivating the germinated forms.
264 citations
153 citations
TL;DR: The effect of hydrostatic pressures as high as 1,700 atm at 25 C on the heat and radiation resistance of Bacillus pumilus spores was studied and phosphate-buffered spores were more sensitive to compression than spores suspended in distilled water.
Abstract: The effect of hydrostatic pressures as high as 1,700 atm at 25 C on the heat and radiation resistance of Bacillus pumilus spores was studied Phosphate-buffered spores were more sensitive to compression than spores suspended in distilled water Measurements of the turbidity of suspensions, the viability, refractility, stainability, dry weight, and respiratory activity of spores, and calcium and dipicolinic acid release were made for different pressures and times Initiation of germination occurred at pressures exceeding 500 atm and was the prerequisite for inactivation by compression The rate of initiation increased with increasing pressure at constant temperature This result is interpreted as a net decrease in the volume of the system during initiation as a result of increased solvation of the spore components
127 citations
TL;DR: A mixture of l-alanine and inosine and various ions was the best germinative solution for most strains, but not all ions were effective and some anomalous germination patterns were encountered.
Abstract: Foerster, Harold F. (University of Texas, Austin), and J. W. Foster. Response of Bacillus spores to combinations of germinative compounds. J. Bacteriol. 91:1168-1177. 1966.-Spores of 21 strains of Bacillus megaterium and 25 other strains representing 13 species of Bacillus were produced under standardized conditions. The germination of a washed spore suspension of each strain was measured as a response to various combinations of 30 different germinative compounds. The strains were first typed with respect to their response to "primary" germination compounds, i.e., glucose, l-alanine, inosine, and l-alanine-inosine mixture, and also Na(+) and K(+). The second stage was the determination of the response to various organic and inorganic anions and cations, each strain being supplied with the "primary" compounds best for it. Marked differences in germination patterns were observed among species and strains of the same species. No relation to established taxonomic lines was evident. A nonspecific requirement for ions was found for all strains, but not all ions were effective. A striking degree of interchangeability of germinative chemicals was found. "Fractional germination" was very common. A mixture of l-alanine and inosine and various ions was the best germinative solution for most strains. Some anomalous germination patterns were encountered. Those studied included a strain whose cells lysed spontaneously upon germination and other strains for which l-leucine had striking germinative powers.
102 citations