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Biomedical subjects

J Olley

Publications and source records attributed to J Olley.

16 recordsLinked to original sources
PubMed2002

A process risk model for the shelf life of Atlantic salmon fillets.

The shelf life of Atlantic salmon (Salmo salar) portions produced for retail distribution is examined and the dominant aerobic spoilage organism is identified. Characterization of the harvesting and processing operations allow the development of a stochastic mathematical model, a process risk model (PRM), which predicts the range of the possible shelf life for the portions under normal retail and distribution. The considered risk is the failure to achieve the nominal 'use by' date. Bacterial counts from surface swabs, water, ice, and fish samples, collected over a period of 9 months, are fitted to distribution functions for use within the model. Comparisons are made between the distributions fitted to the observed bacterial levels and the predicted levels for the slurry water, initial surface contamination on the fish, and for the predicted and observed shelf life. Storage temperature of the packaged salmon portions has the greatest influence on shelf life, with contamination from contact surfaces and other sources being the next most important. The range of bacterial counts on the portions was between -0.6 and 5 log10 cfu/cm2. The model predicts bacterial counts in the slurry water to have an average value of 3.36 log10 cfu/ml, whereas the observed slurry water bacterial counts were 3.35 log10 cfu/ml. The predicted average initial bacterial contamination is 3.31 log10 cfu/cm2 on the fish surface and 3.23 log10 cfu/cm2 on the observed. The average predicted shelf life is 6.5 days, compared to an observed value of 6.2 days at 4 degrees C.

Animals↗
PubMed2002

Predictive microbiology: towards the interface and beyond.

This review considers the concept and history of predictive microbiology and explores aspects of the modelling process including kinetic and probability modelling approaches. The "journey" traces the route from reproducible responses observed under close to optimal conditions for growth, through recognition and description of the increased variability in responses as conditions become progressively less favourable for growth, to defining combinations of factors at which growth ceases (the growth/no growth interface). Death kinetics patterns are presented which form a basis on which to begin the development of nonthermal death models. This will require incorporation of phenotypic, adaptive responses and may be influenced by factors such as the sequence in which environmental constraints are applied. A recurrent theme is that probability (stochastic) approaches are required to complement or replace kinetic models as the growth/no growth interface is approached and microorganisms adopt a survival rather than growth mode. Attention is also drawn to the interfaces of predictive microbiology with microbial physiology, information technology and food safety initiatives such as HACCP and risk assessment.

Bacteria↗
PubMed2000

Histamine fish poisoning revisited.

Histamine (or scombroid) fish poisoning (HFP) is reviewed in a risk-assessment framework in an attempt to arrive at an informed characterisation of risk. Histamine is the main toxin involved in HFP, but the disease is not uncomplicated histamine poisoning. Although it is generally associated with high levels of histamine (> or =50 mg/100 g) in bacterially contaminated fish of particular species, the pathogenesis of HFP has not been clearly elucidated. Various hypotheses have been put forward to explain why histamine consumed in spoiled fish is more toxic than pure histamine taken orally, but none has proved totally satisfactory. Urocanic acid, like histamine, an imidazole compound derived from histidine in spoiling fish, may be the "missing factor" in HFP. cis-Urocanic acid has recently been recognised as a mast cell degranulator, and endogenous histamine from mast cell degranulation may augment the exogenous histamine consumed in spoiled fish. HFP is a mild disease, but is important in relation to food safety and international trade. Consumers are becoming more demanding, and litigation following food poisoning incidents is becoming more common. Producers, distributors and restaurants are increasingly held liable for the quality of the products they handle and sell. Many countries have set guidelines for maximum permitted levels of histamine in fish. However, histamine concentrations within a spoiled fish are extremely variable, as is the threshold toxic dose. Until the identity, levels and potency of possible potentiators and/or mast-cell-degranulating factors are elucidated, it is difficult to establish regulatory limits for histamine in foods on the basis of potential health hazard. Histidine decarboxylating bacteria produce histamine from free histidine in spoiling fish. Although some are present in the normal microbial flora of live fish, most seem to be derived from post-catching contamination on board fishing vessels, at the processing plant or in the distribution system, or in restaurants or homes. The key to keeping bacterial numbers and histamine levels low is the rapid cooling of fish after catching and the maintenance of adequate refrigeration during handling and storage. Despite the huge expansion in trade in recent years, great progress has been made in ensuring the quality and safety of fish products. This is largely the result of the introduction of international standards of food hygiene and the application of risk analysis and hazard analysis and critical control point (HACCP) principles.

Disease Outbreaks↗
PubMed2000

Effect of temperature and salinity stress on growth and lipid composition of Shewanella gelidimarina.

The maximum growth temperature, the optimal growth temperature, and the estimated normal physiological range for growth of Shewanella gelidimarina are functions of water activity (a(w)), which can be manipulated by changing the concentration of sodium chloride. The growth temperatures at the boundaries of the normal physiological range for growth were characterized by increased variability in fatty acid composition. Under hyper- and hypoosmotic stress conditions at an a(w) of 0.993 (1.0% [wt/vol] NaCl) and at an a(w) of 0.977 (4.0% [wt/vol] NaCl) the proportion of certain fatty acids (monounsaturated and branched-chain fatty acids) was highly regulated and was inversely related to the growth rate over the entire temperature range. The physical states of lipids extracted from samples grown at stressful a(w) values at the boundaries of the normal physiological range exhibited no abrupt gel-liquid phase transitions when the lipids were analyzed as liposomes. Lipid packing and adaptational fatty acid composition responses are clearly influenced by differences in the temperature-salinity regime, which are reflected in overall cell function characteristics, such as the growth rate and the normal physiological range for growth.

Culture Media↗
PubMed1997

Development and evaluation of a predictive model for the effect of temperature and water activity on the growth rate of Vibrio parahaemolyticus.

The growth rates of four strains of Vibrio parahaemolyticus were measured and compared in a model broth system. The results for the fastest growing strain, based on 77 combinations of temperature and water activity (aw) using NaCl as the humectant, were summarised in the form of a predictive mathematical model. The model, of the square-root type includes a novel term to describe the effects of super-optimal water activity, and can be used to predict generation times for the temperature range (8-45 degrees C) and water activity range (0.936-0.995) which permit growth of Vibrio parahaemolyticus. Predicted generation times from the model were compared to literature data, using bias and accuracy factors, for both laboratory media and foods. The model was shown to give realistic growth estimates, with a bias value of 1.01, and an accuracy factor of 1.38.

Models, Biological↗
PubMed1987

Model for combined effect of temperature and salt concentration/water activity on the growth rate of Staphylococcus xylosus.

The combined effect of temperature and NaCl concentration/water activity on the growth rate of a strain of halotolerant Staphylococcus is described by the square-root models which had been used previously to model temperature dependence only. The model square root r = b(T-T min) is shown to be a special case of the Bĕlehrádek temperature function which is given by r = a(T-alpha)d. The constant alpha is the socalled 'biological zero' and equivalent to T min in the square-root models. This and the exponent d = 2 were unaffected by changing NaCl concentration/water activity. The Bĕlehrádek-type equations are preferable to the Arrhenius equation in that their parameters do not change with temperature. The constancy of T min allows derivation of a simple expression relating growth rate of strain CM21/3 to temperature and salt concentration/water activity within the range of linear response to temperature predicted by the square-root model.

Animals↗
PubMed1982

A peptide-containing fraction of plasma from schizophrenic patients which binds to opiate receptors and induces hyper-reactivity in rats.

A serum fraction from schizophrenic patients has been investigated for its effect on opiate receptor sites and on behaviour in rats. Serum from schizophrenic patients was ultrafiltered and fractionated on DEAE-Sephadex A-25. The concentration of peptide material eluting under 0.1 M HCl (fraction I) was further purified on Sephadex-G10 and four major peaks were identified (fractions II to V). When injected intracerebroventricularly in rats, fraction II produced a characteristic behavioural syndrome, which included hyperactivity associated with hyperemotionality. The effects were long lasting, bouts of hyperemotionality accompanied by analgesia were recorded over a two-week period. The same fraction from control non-patients produced a transient and much reduced, but qualitatively similar response. There was evidence that fraction III was also active. An in vitro opiate receptor binding test showed that fraction II from schizophrenic patients inhibited [3H]naloxone binding.

Adolescent↗
PubMed1982

Relationship between temperature and growth rate of bacterial cultures.

The Arrhenius Law, which was originally proposed to describe the temperature dependence of the specific reaction rate constant in chemical reactions, does not adequately describe the effect of temperature on bacterial growth. Microbiologists have attempted to apply a modified version of this law to bacterial growth by replacing the reaction rate constant by the growth rate constant, but the modified law relationship fits data poorly, as graphs of the logarithm of the growth rate constant against reciprocal absolute temperature result in curves rather than straight lines. Instead, a linear relationship between in square root of growth rate constant (r) and temperature (T), namely, square root = b (T - T0), where b is the regression coefficient and T0 is a hypothetical temperature which is an intrinsic property of the organism, is proposed and found to apply to the growth of a wide range of bacteria. The relationship is also applicable to nucleotide breakdown and to the growth of yeast and molds.

Bacteria↗
PubMed1978

Temperature function integration and the development and metabolism of poultry spoilage bacteria.

The rate of spoilage of chicken tissues, the development of spoilage bacteria, and the utilization of amino acids by spoilage bacteria as a function of temperature were more accurately described by the general spoilage curve of Olley and Ratkowsky (Food Technol. Aust. 25:66-73, 1973; Food Technol. N.Z. 8:13-17, 1973) than by the linear equation of Spencer and Baines (Food Technol. [Chicago] 18:175-179, 1964). Remaining shelf life of poultry tissues may be predicted at temperatures up to 16 degrees C by using a temperature function integrator which incorporates the general spoilage curve.

Amino Acids↗
PubMed1978

Non-specific neural stimuli and metabolic rhythms in rats.

Ten rats housed in individual metabolism cages in a room next to a teaching laboratory showed rhythmic fluctuations in urination and defaecation. Sectral analysis of the data indicates a weekly rhythm which is attributed to the lack of neural stimuli at the weekend. Regression analysis using a weekly cycle illustrates this effect.

Animals↗
PubMed1976

Protein changes in frozen fish.

Storage of frozen fish brings about a decrease of extractability of myofibrillar proteins. There is also deterioration of the texture and functional properties of the flesh. In model systems, aggregation of myosin, actin, tropomyosin, and whole myofibrils have been described. These changes are caused by concurrent action of partial dehydration due to the freezing out of water, exposure of the proteins to inorganic salts which are concentrated in the remaining nonfrozen fluid, interactions with free fatty acids liberated from phospholipids and with lipid oxidation products, and cross-linking by formaldehyde produced in some species of fish as a result of enzymic decomposition of trimethylamine oxide. The extent of protein alterations increases with time and temperature of storage as well as with advanced disintegration of the tissues and intermixing of their components. The role played by the individual factors and the significance of different types of bonds, i.e., hydrophobic adherences, ionic bonds, and covalent cross-links in particular cases are not yet fully disclosed. Retardation of the deteriorative changes of proteins in frozen fish is possible by avoiding high storage temperatures and oxidation of lipids, removing hematin compounds and other constituents promoting cross-linking reactions, and by adding cryoprotectors like sugars, several organic acids, amino acids, or peptides.

Adenosine Triphosphatases↗
PubMedDate not supplied

Application of predictive microbiology to assure the quality and safety of fish and fish products.

Predictive microbiology offers an alternative to traditional microbiological assessment of food quality and safety. The concept is that a detailed knowledge of the microbial ecology of a food product can be expressed as a mathematical model to enable objective evaluation of the effect of processing, storage and distribution operations on microbial development. Experience to date indicates the need initially to derive a mathematical model in laboratory studies, to validate the model in food products and to incorporate the information into monitoring devices. These may be chemical or physical indicators or electronic integrators or loggers. To enable a correct decision on quality or safety, it is essential that the response of the monitoring device to environmental changes mimics exactly that of the organism of concern. Most monitoring devices currently available record temperature history, but not other environmental factors that influence growth and that, in some circumstances, change during storage. The next generation of monitoring devices may be required to monitor several parameters to take full advantage of increasingly accurate and sophisticated models.

Animals↗
PubMedDate not supplied

Quantitative microbiology: a basis for food safety.

Because microorganisms are easily dispersed, display physiologic diversity, and tolerate extreme conditions, they are ubiquitous and may contaminate and grow in many food products. The behavior of microbial populations in foods (growth, survival, or death) is determined by the properties of the food (e.g., water activity and pH) and the storage conditions (e.g., temperature, relative humidity, and atmosphere). The effect of these properties can be predicted by mathematical models derived from quantitative studies on microbial populations. Temperature abuse is a major factor contributing to foodborne disease; monitoring temperature history during food processing, distribution, and storage is a simple, effective means to reduce the incidence of food poisoning. Interpretation of temperature profiles by computer programs based on predictive models allows informed decisions on the shelf life and safety of foods. In- or on-package temperature indicators require further development to accurately predict microbial behavior. We suggest a basis for a "universal" temperature indicator. This article emphasizes the need to combine kinetic and probability approaches to modeling and suggests a method to define the bacterial growth/no growth interface. Advances in controlling foodborne pathogens depend on understanding the pathogens' physiologic responses to growth constraints, including constraints conferring increased survival capacity.

Bacteria↗