Dairy Science and Food Technology

Scientific, information & consultancy services for the food industry

 








 




 

 






 

 








 





 

 





 






 

 



 

Copyright Protected

Content copyright protected

Science Services

DSFT has been providing science based consultancy services globally since 2002.
  
Click to learn more.

It can be difficult for entrepreneurs to obtain starter cultures for trials. This article provides contact details of some culture suppliers.

The isolation of lactic acid bacteria from raw and pasteurized milk is discussed.

Mr George DoranGeorge Doran graduated with a 2:1 honours degree in Food Technology from the College of Agriculture and Food Technology in Northern Ireland in 2015. Mr Doran's final year research project was entitled "An Investigation of Biofouling in Two Mozzarella Cheese Manufacturing Plants".  

 George completed his food technology internship at Cottage Catering, Dromore, N. Ireland and gained experience in Quality Assurance, New Product Development and Production.

George has achieved several academic distinctions and has extensive work experience gained through part-time work in the security and retail sectors.

Included amongst George's achievements are:

  • Member of the winning team for the Chesapeake Product Development Challenge in December 2013
  • Represented IFST Ecothrophelia in London at Food Matters Live in November 2014

Contact

Model probability of detecting a pathogen in food using the Poisson Distribution.

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.

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.

Introduction

Refrigerated storage of raw milk is used to limit the growth of microorganisms in milk prior to processing. It has been known for some time that the quality and yield of cheese produced from bulk cooled milk may be adversely affected by this procedure (Weatherup et al., 1988; Weatherup and Mullan, 1993). The reduced yield and poor quality may be due to physico-chemical changes in the state of several milk components e.g. dissociation of micellar casein, mainly Κ-casein into a soluble phase, occurs during the first 48 h of storage at 4° and 7° C. This results in losses of fat and curd fines, weaker curd, more moist curd and a slightly lower yield. Partial reversal of dissociation occurs after further storage. The reduced yield and quality can also be due to the activity of proteases and lipases produced by psychrotrophic bacteria.

Despite the work that has been done over many years milk is still being stored for extended periods (1-3+ days on some farms) and cheesemakers are again (2019) reporting problems with the yield and quality of cheese produced using this milk.

Following several queries related to milk quality and cheese manufacture I am providing a report written by Wilf Weatherup and me some years ago that may be helpful.

A simple calculator has been provided using the total viable count of milk prior to pasteurisation and a regression equation to predict the grade value of Cheddar cheese.

These products are similar but can differ markedly from each other e.g. traditional Italian gelato is significantly different than mass produced, commercial ice cream in Ireland, GB and the US. However, high end artisan produced ice cream made using batch processes can be similar.

Traditional Italian gelato generally contains around 8% milk fat, has a low overrun usually (< 18%) and is served from a cabinet held at around -11°-12°C. The physical properties are usually different.  Because of the higher temperature of storage and the concentration of sugars, gelato is served and eaten in a highly viscous, semi-frozen state. The texture is often described as being smooth and dense. Fruit-flavoured gelato is also characterised by intense natural fruit flavours and is quite sweet although natural fruit-like sour notes may be evident.

Traditional gelato is produced using batch production methods and is generally consumed within a short time from manufacture.

While there are differences between these products the scientific principles that underpin their production are similar and in the articles that follow, I will often use the terms ice cream and gelato interchangeably. Please accept that I do not equate the quality and eating experience of traditional Italian gelato with mass-produced commercial ice cream.

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

This section gives an overview of developments in this area including opportunities for novel functional foods. The rare involvement of lactobacilli and starter bacteria in human infections is mentioned and a summary of traditional microbiological approaches to the enumeration of probiotic bacteria is included.

The last major update to this article was published in February 2008, since then there have been a number of significant developments. These include the failure of major European dairy companies to obtain ratification by the EFSA of health claims for probiotic products, the deaths of patients on a probiotic trial in the Netherlands, evidence that perhaps some bacteria designated as probiotics may have the potential to aggravate allergies in neonates. Additionally one major researcher has questioned where any strain of Lb. acidophilus has been shown to meet the criteria for a probiotic! However, there has been other more positive research indicating that particular strains of bacteria, in particular lactic acid bacteria, do have the potential to enhance immunity, reduce allergy, and to alleviate distant site infection. This work has very clearly shown that dairy companies and others have a responsibility to use only well characterised strains that have been shown to have probiotic effects in medical trials. Interesting Reid (2007) has stated "a potential major problem for probiotics is the misuse of the term. This can arise from products being poorly manufactured, or being referred to as probiotic without any relevant documentation. The net effect, deleterious to the overall field of probiotics, might be that such products are found to be ineffective, when in fact they were not even probiotic in the first place." Interestingly there is now a growing consensus that there is a world-wide, critical shortage of well qualified food scientists and technologists in commercial food manufacturing. These developments will be taken into consideration in the next major update to this article.

The next major update will summarise recent work on the gut flora and how this complex flora is thought to influence health. Recent research suggests that the gut flora can influence mood e.g. depression and its modification may have the potential to influence body mass and obesity. The main evidence for the latter has come from animal studies and anecdotal accounts of the consequences of faecal microbiota transplants also known as a stool transplants. This work suggests very significant potential for new generation probiotic products.

Gut problems e.g. dyspepsia (indigestion) are common and the Internet has many sites advocating probiotics for treating a range of symptoms. This article, while it may be of interest to the general public, does not promote the medical use of commercial yoghurt products, none of which currently have EFSA endorsements as probiotics in Europe, to treat gastrointestinal problems. I am aware of people experiencing dyspepsia who treated their symptoms with commercial yoghurt products and subsequently found that they had a range of physical medical conditions ranging from ulcers, hiatus hernia to more malign conditions that required surgical intervention. I am positive about the potential health benefits of probiotics but urge readers with health issues to discuss their problems with physicians, who certainly in Europe, take care not to do harm before self treating with yoghurt type products.

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. 

Subcategories

 

 

We use cookies to improve our website and your experience when using it. To find out more about the cookies we use, see our Privacy and Cookie Policy.

info_icon articles