Development of a Microbial Model for the Combined Effect of Temperature and pH on Spoilage of Ground Meat, and Validation of the Model under Dynamic Temperature Conditions

Abstract

The changes in microbial flora and sensory characteristics of fresh ground meat (beef and pork) with pH values ranging from 5.34 to 6.13 were monitored at different isothermal storage temperatures (0 to 20°C) under aerobic conditions. At all conditions tested, pseudomonads were the predominant bacteria, followed by Brochothrix thermosphacta, while the other members of the microbial association (e.g., lactic acid bacteria and Enterobacteriaceae) remained at lower levels. The results from microbiological and sensory analysis showed that changes in pseudomonad populations followed closely sensory changes during storage and could be used as a good index for spoilage of aerobically stored ground meat. The kinetic parameters (maximum specific growth rate [ max ] and the duration of lag phase []) of the spoilage bacteria were modeled by using a modified Arrhenius equation for the combined effect of temperature and pH. Meat pH affected growth of all spoilage bacteria except that of lactic acid bacteria. The "adaptation work," characterized by the product of max and ( max ؋ ) was found to be unaffected by temperature for all tested bacteria but was affected by pH for pseudomonads and B. thermosphacta. For the latter bacteria, a negative linear correlation between ln( max ؋ ) and meat pH was observed. The developed models were further validated under dynamic temperature conditions using different fluctuating temperatures. Graphical comparison between predicted and observed growth and the examination of the relative errors of predictions showed that the model predicted satisfactorily growth under dynamic conditions. Predicted shelf life based on pseudomonads growth was slightly shorter than shelf life observed by sensory analysis with a mean difference of 13.1%. The present study provides a "readyto-use," well-validated model for predicting spoilage of aerobically stored ground meat. The use of the model by the meat industry can lead to effective management systems for the optimization of meat quality.Fresh meat is a highly perishable food product and unless appropriately actions are taken, e.g., packaged, transported and stored at refrigeration temperatures, can spoil in relatively short time. Factors affecting meat spoilage include intrinsic (e.g., pH, a w , composition, type, and extent of initial contamination) and extrinsic parameters (e.g., temperature and packaging atmosphere). Among these, temperature is considered the most important factor. Although most countries have established regulations with maximum temperature limits for refrigeration storage, in practice these are often violated. Survey studies have shown that temperature conditions higher than 10°C are not unusual during transportation, retail storage, and consumer handling (13,15). Such temperature abuses during any stage of the chill chain may result in an unexpected loss of quality and a significant decrease of meat shelf life.Challenge tests are the main current method used by the meat industry and academia to evaluate product's shelf life. The disadv...

Primary and secondary modeling of Brochothrix thermosphacta growth under different temperature and ph values

“…Note, through these values, that the increase of pH and temperature cause greatly impacts in the μmax lifting. This same relationship was observed by Koutsoumanis et al (2006) in a study with fresh ground beef with pH ranging between 5.34 and 6.13 and stored at different temperatures (0-20 °C). Similarly Leroi et al (2012) in a study with different strains of B. thermosphacta observed increase in μmax.…”

“…An example of the effect of pH on meat microbial kinetics can be seen with work by Koutsoumanis et al (2006), were able to observe the significant effect of ground meat pH (5.34 and 6.13) on a growth kinetics of Pseudomonas, B. thermosphacta and bacteria of the family Enterobacteriaceae, was observed, for example, for B. thermosphacta at 10 °C the growth rate doubles as the pH goes from 5.4 to 6.1.…”

Kinetics of colour and texture changes of beef during storage

“…According to Taoukis and Labuza (1989), it is necessary to know about the quality loss kinetics of a food to predict its shelf life, in this sense, there is much bibliography of mathematical models to quantify and to predict the rate of growth of microorganisms under environmental conditions with the intention of assuring the hygienic quality of food, thus determining its storage life (Koutsoumanis et al 2006;Limbo et al 2010;Shimoni and Labuza 2000). However, there has been little information available on modelling kinetics of colour and texture transformations during refrigerated storage in raw meat.…”

Can potential for dark cutting be predicted by phenotype? Relationship between sex, carcass characteristics, and the incidence of dark cutting beef

“…Dark cutting beef usually has an ultimate pH greater than 5.8 and is discriminated against by retailers because of its reduced shelf life (Koutsoumanis et al 2006) and by consumers because of its abnormal appearance. In compliance with the Canadian Beef Carcass Grading Regulations (Canada Agricultural Products Act SOR/92-541 2014), dark cutting carcasses are downgraded to the Canada dark cutting grade (Canada B4) and their value is usually reduced to that of mature, over 30 mo old cattle.…”