Microbiological Challenge Testing Research Articles

Growth potential of Listeria monocytogenes strains in mixed ready-to-eat salads

In this study, a microbiological challenge test in three artificially contaminated retail mixed mayonnaise-based ready-to-eat salads stored at refrigerator temperatures (3 °C and 7 °C) for 48 h was carried out. Shrimp–tomato salad, smoked ham salad and garlic cheese salad were separately contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes, Enterobacteriaceae, staphylococci and total plate count (CFU/g) was determined. Listeria monocytogenes growth potential in the salads was calculated and evaluated. A significant increase in total plate count and L. monocytogenes count throughout storage of all three investigated salads was found. Enterobacteriaceae levels were high at the beginning in all salads but significantly ( p < 0.05) decreased throughout the experiment depending on the temperature. All investigated L. monocytogenes strains demonstrated growth at both temperatures but expressed different growth potential. Especially garlic cheese salad and smoked ham salad were able to support the growth of Listeria. Shrimp–tomato salad supported growth the least. The growth potential increased with the increasing temperature and exceeded 0.5 log 10 CFU/g in many cases. If the potential for growth is > 0.5 log 10 CFU/g, food products can potentially endanger human health. Reference strain (ATCC 7644) showed the least growth potential almost in all cases in comparison with strains isolated from frozen pollock loins and from thermally treated specialty sausage containing preservatives. To eliminate the occurrence of microbiological risks, the shelf-life of the studied salads was estimated.

Determination of DB10B values of single and mixed cultures of bacteria after gamma irradiation

The DB10B value of bacteria represents the absorbed radiation dose required to inactivate 90 % of a viable populati-on or reduce the population by a factor of 10. DB10B values of 3 bacterial isolates (Escherichia coli, Staphylococ-cus aureus and Salmonella parathyphi B) were determined using single and mixed cultures to assess the effect of microbial competition on radiosensitivity. The isolates were inoculated into wakye substrate and exposed to &gamma;-radiation doses of 0, 100, 300, 450, 600, 750, 850 Gy from a P60PCo source at a dose rate of 2.20 kGy/h in air. Enumeration of survivors of the isolates was carried out using serial dilution and pour plate methods. The survi-ving fraction of isolates decreased with increased irradiation doses. DB10B values of E. coli, S. aureus and S. parat-hyphi B were respectively 0.27, 0.33 and 0.44 kGy when inoculated as single cultures, and 0.24, 0.28 and 0.32 kGy respectively when inoculated as mixed cultures. DB10B values were lower for mixed cultures compared to single cultures, which might indicate reduced resistance to &gamma;-radiation as a result of competition among the isolates. Microbiological challenge tests based on the DB10B values may result in delivery of higher irradiation doses, but the extra dose could serve as safety margin to enhance the food preservative capacity of radiation processing.

MIXTURES OF BEEF TRIPE, BEEF LIVER AND SOYBEANS APPLIED TO FOOD DEVELOPMENT

A nutritive sausage-type product was developed with beef tripe, beef liver and soybeans as ingredients. A three-component mixture design was used to obtain seven different formulations (minimum of each main ingredient: 16.5%, maximum: 67.0%). Ingredients were ground, mixed and packed tightly with a polypropylene film to obtain a roll. Pieces were cooked in boiling water for 90 min. The composition of the obtained products varied within the following ranges: proteins 17.32–25.56 g/100 g, lipids 3.22–3.87 g/100 g, crude fiber 1.50–4.50 g/100 g, minerals 1.44–2.72 g/100 g. Total iron levels varied between 1.39 and 2.98 mg/100 g and calcium levels between 15.07 and 34.01 mg/100 g. Surface response analysis was applied to parameters obtained from texture profile analysis (hardness, adhesiveness, cohesiveness and elasticity). Products hardness increased when the soy content increased; on the contrary, formulations enriched in beef tripe were those of higher elasticity and cohesiveness. Color was mainly determined by the incorporation of liver. A nontrained panel was used to evaluate the acceptance of the different formulations. The most accepted one was that with equal proportions of the three main ingredients. Microbiological challenge testing showed that the thermal treatment was enough for assuring the product safeness even in samples with high initial microbial charge.

Microbiological Challenge Testing

Comprehensive Reviews in Food Science and Food SafetyVolume 2, Issue s2 p. 46-50 Microbiological Challenge Testing First published: 20 November 2006 https://doi.org/10.1111/j.1541-4337.2003.tb00051.xCitations: 26AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume2, Issues2April 2003Pages 46-50 RelatedInformation

The HACCP concept: specification of criteria using quantitative risk assessment

An important aspect of the hazard analysis critical control point (HACCP) system is the specification of criteria (setting of critical limits) to ensure that the activities at a specified critical control point (CCP) are under control. An approach is presented here that allows criteria to be specified in relation to potentially hazardous micro-organisms. It is based on the identification of such organisms, and information on numbers present in (raw) food materials. Storage tests, microbiological challenge testing and mathematical models are tools to predict growth or death of these organisms during processing and post-distribution handling. Thus, information can be obtained on the likely bacterial load at the time of consumption. Ultimately, quantitative risk assessment can be used to judge acceptance or non-acceptance of the product. If microbial levels are acceptable, criteria can be established at specific CCPs. This implies a complete description of activities at each CCP and takes account of parameters such as temperature, time, water activity and pH.

Microbiological challenge testing for ensuring safety of food products

Microbiological challenge testing (MCT), storage testing, and predictive modelling are tools to stimulate or to test what can happen to a food product during processing, distribution and subsequeny handling. MCT is carried out if the microorganism of interest is suspected to be present in low numbers or only incidentally, and should be applied if full knowledge about the characteristics of a potential hazardous microorganism does not exist. MCT involves: (a) an appropriate experimental design; (b) an inoculation procedure; (c) a test procedure; and (d) interpretation of results. If MCT is carried out properly, information is obtained on the types of microorganisms capable of growth in the product, so that risks of food poisoning can be assessed. Therefore, the information obtained can be the basis for setting safety criteria at the critical control points in a food processing operation. However, it remains necessary to verify the test results under field conditions.

The HACCP concept: specification of criteria using quantitative risk assessment

An important aspect of the hazard analysis critical control point (HACCP) system is the specification of criteria (setting of critical limits) to ensure that the activities at a specified critical control point (CCP) are under control. An approach is presented here that allows criteria to be specified in relation to potentially hazardous microorganisms. It is based on the identification of such organisms, and information on numbers present in (raw) food materials. Storage tests, microbiological challenge testing and mathematical models are tools to predict growth or death of these organisms during processing and post distribution on handling. Thus, information can be obtained on the likely bacterial load at the time of consumption. Ultimately, quantitative risk assessment can be used to judge acceptance or non-acceptance of the product. If microbial levels are acceptable, criteria can be established at specific CCPs. This implies a complete description of activities at each CCP and takes account of parameters such as temperature, time, water activity and pH.

Stability of spores of Bacillus cereus stored on silicagel

Spores of four different strains of Bacillus cereus were stored on silicagel at 22°C and in physiological saline solution at −20°C for a period of 260 days. At different intervals the spores were tested for survival, heat sensitivity and capacity to germinate. There was no clear change in any of the parameter tested, so storage on silicagel can be a good alternative for storage as a frozen suspension. Spores stored in this way can easily be exchanged for reference material and used for microbiological challenge testing.

A user's guide to microbial challenge testing for ensuring the safety and stability of food products

This article describes the development of a user's guide to microbiological challenge testing (MCT), which seeks to ensure the safety of different food products. Before undertaking such a test, each situation must be carefully reviewed and both relevant micro-organisms and the risks involved must be established. Only in the absence of the necessary information will a MCT be required. The test involves: (1) an appropriate experimental design; (2) an inoculation procedure; (3) a test procedure; and (4) interpretation of results; The results are evaluated in relation to set safety criteria and, if satisfactory, should be confirmed under field conditions (verification). Based on this approach, a practical example is given to predict the safety and stability of vacuum-packed cooked potatoes.