Predicting the safety and stability of products preserved with acetic acid using the CIMSCEE model

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Written by Michael Mullan

Commercially, cold-filled acidic pickles, sauces (e.g. salad cream, mayonnaise), and food dressings are preserved, and their microbiological safety and stability are assured, by the use of acetic acid, salt (NaCl), and sugar. This article provides an overview of a preservation model and access to the model to enable the effect of sauce components and pH to be investigated.

Comite´ des Industries des Mayonnaises et Sauces Condimentaires de la Communaute´ Économique Européenne (1992) (CIMSCEE) has provided guidance on a safety value, Σs, for a microbiologically safe product preserved using acetic acid and a stability value, Σ, above which microbial spoilage should not occur.

A safe product has been defined as one which is so formulated that when an inoculum of viable cells of Escherichia coli is  added to the product this is reduced by 3 log cycles in less than 72 h. Products exhibiting this level of antibacterial activity have a CIMSCEE safety value (Σs) of greater than 63. Σs is calculated using equation 1. A microbiologically stable product is one that will not support microbial growth at ambient temperature and has a Σ value of greater than 63. Σ is calculated using equation 2.

Equation 1. Σs =15.75 (1 - ɑ) (total acetic acid* %) + 3.08 (salt* %) + (hexose* %) + 0.5 (disaccharide* %) + 40 (4-pH). Note, values with an * must be calculated as water phase values.

Equation 2. Σ =15.75 (1 - ɑ) (total acetic acid* %) + 3.08 (salt* %) + (hexose* %) + 0.5 (disaccharide* %). Note, values with an * must be calculated as water phase values.

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Calculators for determining the F or P value of a thermal process

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Written by Michael Mullan

The Dairy Science and Food Technology website contains several free, On Line calculators, for determining the cumulative lethality (F, B*, P or PU) of thermal processes, the concentration of Thermal Process Indicators (TTI) following UHT treatment of milk and several other process indicators.

These calculators are listed on the Calculators and Models page under Thermal Processing e.g.

• Calculator for determining the lethality (F, value) of a thermal process using the Trapezoid and Simpson's rules. This unique calculator works with thousands of pasted values e.g. from a data logger.
• Calculator for determining the lethality (F, B* values) and chemical changes (C* value, formation of HMF, Lactulose, Furosine, and destruction of thiamine) in heated milk integrated using the Trapezoid and Simpson's rules.
• Calculator for determining the lethality (F, B* values) and chemical changes (C* value) for generic high-temperature processes using the Trapezoid and Simpson's rules. 
• Determine the accuracy of 3 algorithms for predicting the concentration of lactulose in milk after defined heat treatment.

The lethality calculators convert temperature readings to lethal rates, plot the lethal rates against time, and determine appropriate lethality values or chemical indicators for a heat process whether using hot water, saturated steam or dry heat. The area under the time-lethality curve is determined by numerical integration using the industry standard method, the trapezoid rule or the more accurate Simpson's rules or both for comparative purposes. In general, the more values, the more accurate the value for F or P will be. One of the calculators will also upload CSV files of a thermal process and provides a facility for free, independent validation of a thermal process.

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Reliability of microbial sampling in assuring food safety and calculation of prevalence following negative tests

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Written by Michael Mullan

Microbial testing is still important but it is critical to understand its limitations in assuring food safety.

Despite the global use of HACCP systems and a legal requirement for the use of HACCP in many jurisdictions' food poisoning remains an endemic problem and large numbers of people continue to be hospitalised, die and as a result companies either face substantial legal costs and / or in many cases are forced to cease trading.

While the use of HACCP systems significantly reduces the need for microbiological end point testing of foods, sampling schemes and microbial analysis have important roles in system validation and quality assurance. This article also provides access to three free On-Line calculators that enable the probability of detecting a pathogen in a food, the number of samples required to test to meet a food standard and how to calculate the prevalence of a pathogen when all the samples taken for testing return negative results.

This raises an issue concerning the adequacy of sampling schemes and microbial analysis in commercial food manufacture.

In September 2015 the US Centers for Disease Control and Prevention reported on a multistate outbreak of listeriosis allegedly caused by Mediterranean-type soft cheeses. Some 30 people were affected, twenty-eight people were hospitalized and three deaths were reported. However, listeria were not isolated from the cheeses produced by the manufacturer concerned.

Further information on the mathematics of microbial sampling

Perfect ice cream or gelato. Getting the hardness or "scoopability" just right.

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Written by Michael Mullan

In this article we will explore how to use mix composition to control the hardness or "scoopability" of ice cream or gelato. The serving temperature which influences the concentration of ice present will also be considered. The volume of air added during freezing (overrun), the manufacturing process and the concentration and type of emulsifier can also affect hardness. 

However, these effects are generally less significant than the concentration of sweeteners used and serving temperature. This article should be read in conjunction with the article on the sweetness of ice cream. 

This article originally had the title "Goldilock's ice cream. Controlling hardness or scoopability." Goldilocks was a character from "Goldilocks and the Three Bears" a British 19th-century fairy tale and I originally thought that everyone would understand if an ice cream was acceptable to Goldilocks it had to be good! I have changed the title to reflect that many readers have not read this fairy tale and I may have been inadvertenly confusing people.

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Microbiology of starter cultures

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Written by Michael Mullan

This article discusses the origins and role of starters in dairy fermentations, the ecology of starter bacteria, the classification of starter bacteria,  the types of starter culture used and concludes with some observations on artisanal cultures. The author has  provided a broader perspective on the use of starter cultures in food fermentations in the Encyclopedia of Food Microbiology. The chapter can be downloaded from Elsevier Ltd. This article should be read in conjunction with the article  discussing the major functions of starters in dairy fermentations and the relative importance and effectiveness of the antimicrobial agents produced by starters. Note the classification of many bacteria previously known as lactobacilli has changed see https://www.dairyscience.info/index.php/site-news/430-nomenclature-lab.html.

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Functions of starters in dairy fermentations. The importance and effectiveness of their antimicrobial mechanisms

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Written by Michael Mullan

This article discusses the major functions of starters in dairy fermentations. Recent research on the relative importance of the antimicrobial agents produced by starters is included. The importance of undissociated lactic acid (HLac) is discussed with regard to the inhibition of the growth of Listeria monocytogenes, Escherichia coli and Staphylococcus aureus.

The author recommends that regulators should require manufacturers of raw milk cheeses to meet a minimum value for HLac that must be achieved prior to product release for retail sale.

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