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

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.

Ice cream processors are required to meet or exceed the pasteurisation time temperatures specified in their jurisdiction. Details of minimum requirements are given in Table 1.

Table 1. Minimum temperature-time criteria for pasteurising ice cream mixes in selected countries

Country

Heat treatment*

Regulation/Statutory Instrument and reference

Canada

 

69°C for 30 minutes

80°C for 25 seconds

Code of Good Practice for High-Temperature Short-Time Pasteurizers (HTSTs). (Anon, 1991)

New Zealand

**69°C for 20 minutes

**74°C for 10 minutes

**79.5°C for 15 seconds

**85.5°C for 10 seconds

DPC 3: Animal Products (Dairy): Approved Criteria for the Manufacturing of Dairy Material and Product. (DPC 3, 2010)

UK

65.6°C for 30 minutes
71.1°C for 10 minutes
79.4°C  for 15 seconds 148.8°C for two seconds

The Dairy Products (Hygiene) Regulations 1995. (Anon, 1995)

US

69°C for 30 minutes

80°C for 25 seconds

83°C for 15 seconds

Grade A Pasteurized Milk Ordinance- 2019 Revision. (PMO, 2019)

Notes
*Holding times and temperatures are minimum values. Holding time refers to the minimum residence time of the fastest traveling particle. This depends on whether the liquid flow is laminar or turbulent.
** Applies to ice cream mixes containing particles of diameter less than or equal to 1000 µm.

Introduction

As previously discussed (Mullan, 2016), there will be occasions when a food manufacturer who has been using two different but equivalent thermal processes from a lethality perspective wishes to use a different, but equivalent lethal thermal process. This is straightforward if the z-value is known (Mullan, 2016). How does the processor calculate the equivalent lethal process if z is unknown?

This article explains how to calculate z using the time and temperature values of the two different, but equivalent lethal processes, and provides access to a free On Line calculator for checking your calculations.

It is important that students understand accuracy, precision and error before embarking on research projects and reflect this understanding in reports and dissertations.

There is a free tutorial by Cecil McIntosh on Sophia that explains these concepts and also provide self assessed questions to test understanding.

The editorial group of Wiley is offering Assistant Editor positions based in their Beijing or Shanghai offices in China for their internationally-renowned food science and nutrition journals, including Molecular Nutrition and Food Research. As part of an international team of editors, the focus of this role is on evaluating manuscripts, handling peer review and making decisions on which manuscripts to accept for publication. Link removed.

 Dr Saumya BhaduriDr Saumya Bhaduri received his Master of Science in Biochemistry and PhD in Biochemistry from the University of Calcutta, India. He immigrated to the United States as an NIH Fellow at the University of Nebraska in Lincoln, NE. Dr. Bhaduri worked as a faculty member for 6 years at the Institute of Molecular Virology in St. Louis, MO. He later served as a faculty member at Washington University Medical School in St. Louis, MO. After 5 years in the Pathology Department, Dr. Bhaduri joined the USDA/ARS as a Senior Scientist in the Eastern Regional Research Centre (ERRC) in Philadelphia, PA.

During his time at the USDA/ARS, Dr. Bhaduri created and established the first molecular biology laboratory at ERRC. He received a year-long sabbatical fellowship in order to further his exploration of DNA sequencing of food borne pathogens at the University of Reading, England. Over the course of his extensive experience at various institutions, Dr. Bhaduri’s major research areas focused on initiation of protein synthesis and genetic code, molecular virology, mapping of the histidine operon, and detection and isolation of foodborne pathogens.

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. 

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