Dairy Science and Food Technology

Scientific, information & consultancy services for the food industry

 








 




 

 






 

 








 





 

 





 






 

 



 

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DSFT has been providing science based consultancy services globally since 2002.
  
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The Dairy Science and Food Technology (DSFT) website provides scientific and technological information, Cloud-based tools and consultancy services for food scientists and technologists working in industry and in colleges and universities. A discussion forum and interactive content through "On Line" calculators are also provided. Writing/citation resources including a Harvard-type reference wizard and a range of citation-wizards can also be accessed.

There are sections on starter cultures, probiotics, cheese science and technology, bioactive peptides, ice cream, wine making, modelling in food technology, thermal processing and modified atmosphere packaging and labelling. Some general health information including reference to allergy and food intolerance is also presented.

The effect of modified atmosphere packaging (MAP) on dairy products, raw meat, raw poultry , cooked meat and fruit and vegetables is discussed.

Dairy products

 MAP has the potential to increase the shelf life of a number of dairy products.  These include fat-filled milk powders, cheeses and fat spreads.  In general these products spoil due to the development of oxidative rancidity in the case of powders and or the growth of micro-organisms, particularly yeasts and moulds, in the case of cheese.

Whole milk powder is particularly susceptible to the development of off-flavours due to fat oxidation.  Commercially the air is removed under vacuum and replaced with N2 or N2/CO2 mixes and the powder is hermetically sealed in metal cans. 

Due to the spray drying process air tends to be absorbed inside the powder particles and will diffuse into the container over a period of 10 days or so.  This typically will raise the residual O2 content to 1%-5% or higher.  Because some markets require product with low levels of residual O2(<1%) some manufacturers re-pack the cans after 10 days storage.  Use of O2 scavenging may also be useful. 

Model probability of detecting a pathogen in food.

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.

Growth and acid production by starter cultures may be inhibited by bacterial viruses, bacteriophages, or added substances including antibiotics, sterilant and detergent residues, or  free fatty acids produced by or as a result of the growth of microorganisms, and natural often called indigenous antimicrobial proteins.

Milk should not contain antibiotic residues.  Milk production in the UK is regulated by the Dairy Products (Hygiene) Regulations 1995.  These regulations include the standards for raw milk.  Prior to 1990 milk was deemed to be contaminated if an antibiotic concentration of > 0.01 international units (iu) /ml was present, the standard has now been increased to 0.006 iu/ml.  Manufacturers buying milk from producers impose stringent financial penalties on farmers producing contaminated milk and have procedures to exclude this from the food chain.  Despite legislation and financial penalties, there is evidence to suggest that residues occasionally still cause problems.  In a survey of the causes of slow acid production by cheese starters in the UK (Boyle and Mullan, 2000, unpublished results) found that, some 28 % of respondents attributed slow acid problems to antibiotics. 

Introduction

There will be occasions when a food manufacturer wishes to use a different, but equivalent lethal thermal process. How does the processor calculate the equivalent process?

This article explains how to calculate an equivalent thermal or heat process at a higher or lower temperature and provides access to a free On Line calculator for checking your calculations.

Providing that the F value at Tref and the z value are known then the F value at the required temperature, T, can be calculated using equation 1.

Equation 1.  heq1 articles

 

Equation 1 has been derived from Stumbo (1973).

The use of high temperature short time heat treatment (HTST) of milk (72°C for 15 seconds) to destroy pathogenic bacteria, reduce the number of spoilage organisms and increase shelf life is well established (Juffs and Deeth, 2007).

The history of pasteurization (pasteurisation is also valid) is fascinating and is notable for its public health success and for the insights of many scientists and engineers. Prior to the introduction of pasteurization, consumption of raw cow milk was a major source of infection by bacteria causing tuberculosis. Pasteurization has eliminated heat-treated-milk as a source of infection. Regrettably raw milk and raw milk products remain a major source of new cases of bovine tuberculosis.

Scoop of ice cream

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. A condensed version of this article is available in the Food Science and Technology OnLine Journal (Mullan, 2018).

Download Excel spreadsheets for calculating the freezing point depression curves of ice cream and gelato mixes.

There is an extensive range of flavoured ice creams (Plate 1) however there is frequently a marked difference in hardness between flavours, e.g. the chocolate flavour is often harder, more difficult to scoop, than the vanilla or strawberry flavours.

Range of flavoured ice creams

Ice cream and gelato manufacturers produce products with a range of favours. There are often significant variations in sweetness and hardness between flavours. This article provides an explanation of sweetness, how it is measured and how it can be controlled.

Relative sweetness and the Potere Dolcificante method are discussed and calculations are used to explain the differences. The limitations and disadvantages of using numerical values of sweetness are explained. Since sweetness and hardness are closely related the reader is also referred to the article on controlling hardness or resistance to scooping.

Starter bacteria in yoghurt

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

Summary

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 monocyotgenes, 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.

Chemical differences between cheeses

What makes one cheese e.g. Cheddar different from another e.g. Gouda or Emmental?

Can you explain why Gouda cheese is different than Cheshire or what makes Emmental different than Cheddar?

What about other cheeses too? And, we need an answer that is more sophisticated that saying the level of starter addition is different! There are many ways in which traditional cheeses can be described or classified.

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