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- Discovery of bacteriophages for lactococci
- Bacteriophages for lactic acid bacteria
- Bacteriophage lysins
- Morphology and classification of bacteriophages
- Enumeration of bacteriophages
- Isolation and purification of bacteriophages
- Preparation and storage of high titre lactococcal lysates
- Industrial significance of lactococcal bacteriophages
- Bacteriophage control in cheese manufacture
Any agent which inhibits starter activity or kills a strain with an essential function e.g. aroma production can have serious detrimental effects on the quality of the product being produced. Infection with bacteriophage is the major single cause of fermentation failure or of problems in fermentation processes utilising lactic acid bacteria.
The major functions of starters in dairy fermentations are shown in table 1. See the section on starters also.
The infection of a growing bacterial culture with phage is initiated by the adsorption of the phage to the host cell. The specificity of adsorption of lactococcal phages and the location of phage receptor substances have been studied and has been reviewed (Lawrence et. al., 1976).
Bradley (1967), in a classic review paper, summarised the principles of phage morphology and outlined six basic morphological types (fig. 1). The tailed phages, Bradley's groups A-C account for some 96% of all phages isolated to date and as discussed below belong to the order Caudovirales. Only phages in Group A have contractile tails. All tailed bacteriophages have a nucleic acid core surrounded by a protein coat. Phages active against lactic acid bacteria are approximately tadpole or sperm shaped and have a distinct head terminating in a tail with a hollow core.
Phages attacking lactic acid bacteria belong to Groups A, B and C and contain double stranded DNA. Phages in Groups D and F contain single stranded DNA, however, Group E phages contain single-stranded RNA.
There are many reasons why information on the concentration of bacteriophage in a sample may be required. These include the determination of:
Over 99% of phages detected using microscopy have not been cultured. This article explores factors that influence plaque formation and if addressed may help in phage isolation.
Current data indicate that some 1031 bacteriophages exist globally, including about 108 genotypes. Some phages form very tiny or micro plaques. These can sometimes be so small that it is almost impossible to see them. Frequently 'new' phages can be observed using e.g. electron microscopy under conditions where there is strong evidence of a potential host yet it can be very time consuming or in some instances not possible to get the phage to form plaques. Less than 1% of the phages observed using microscopy have ever been grown in culture, this is sometimes called "the great plaque count anomaly".
How do you isolate a bacteriophage (phage) and obtain a pure phage preparation? This is achieved by plating a phage suspension using the double agar method, and a susceptible host strain, to obtain plaques and further purifying the phage contained within the plaque.
The effect of modified atmosphere packaging (MAP) on dairy products, raw meat, raw poultry , cooked meat and fruit and vegetables is discussed.
Summary in Italian
Nel Mondo vi è un elevato numero di bevande ottenute dalla fermentazione alcolica di liquidi zuccherini quali succhi vegetali, miele, latte ecc., ma le più importanti per diffusione e quantità prodotte sono senza dubbio il vino, la birra ed il sidro. Lo scopo di questo breve articolo è quello di riassumere la storia e la tecnologia produttiva di una di queste bevande, ottenuta dalla fermentazione dell'uva, il vino. Conosciuto già dagli Egizi, il vino ha accompagnato con alterne vicende l'uomo in tutta la sua storia, divenendo nella cultura cristiana simbolo, con il pane, dell'unione stessa con Dio. Prodotto in quasi tutto il modo anche in virtù dell'ampio areale di coltivazione dell'uva, il vino si presenta al consumatore in varie tipologie (rosso, bianco, rosato, dolce, secco, spumante ecc.) volte ad interpretare al meglio le caratteristiche della materia prima ed a soddisfare le esigenze del consumatore stesso. Alla base di queste diverse tipologie di prodotti vi sono altrettante tecnologie venutesi a definire nei secoli ed i cui aspetti fondamentali vengono descritti in queste pagine con la speranza di stimolare il lettore ad approfondirne lo studio sui numerosi testi specialistici attualmente disponibili.
I get lots of queries from companies and individuals either requesting recommendations for people who might be suitable for dairy science, dairy technologist, food technologist jobs or for advice from food job seekers on vacancies in particular job areas. I regret that I can no longer respond directly to these queries, I simply do not have the time to do so.
The Ulster Farmers Union has Insurance and Agriculture Business Opportunities at Senior Group Manager and Assistant Group Manager level in Northern Ireland. More information is available at the UFU website.
Based in Belfast., Northern Ireland
£19,028 - £29,597; commensurate with experience.
The Ulster Farmers' Union, Northern Ireland's leading farming organization, wishes to appoint a Communications Officer.
Working in the UFU Membership and Communications Department, main duties and responsibilities will include: working effectively and efficiently in a dynamic team environment to produce news releases and publications; building and maintaining good relations with the media; developing the UFU Website and E-communications; and coordinating the UFU presence at events such as the Balmoral Show.
This is an exciting opportunity to work in a very busy, diverse and rewarding environment.
So if you have a commitment to the local agriculture industry, a demonstrable interest in press/public relations, have strong ICT skills and possess a third level qualification in an agriculture related subject, then contact the Ulster Farmers' Union for full details and an application form. Tel: 02890 370222 or download the application form from www.ufuni.org.
The closing date for receipt of applications is Friday 30 July 2010 at 12 noon.
National Milk Laboratories (a subsidiary of National Milk Records plc) provide milk testing services to the GB dairy industry, not only undertaking milk payment testing for circa 95% of all dairy farms, but also offering microbiological and disease testing services to help our farmers and milk buyer customers produce high quality milk and products for the consumer.
Due to retirement, a vacancy for a Laboratory Manager has arisen at our Kelvin Avenue, Hillington, Glasgow laboratory. The successful job holder will be expected to take responsibility for all aspects of laboratory operations which operate 20 hours / day, 365 days / year. You will need to demonstrate strong technical and staff management skills, along with business awareness and confidence in order to represent the NML business to existing and potential customers. The ability to apply technical knowledge to improve the efficiency and effectiveness of existing service provision as well as facilitating the introduction of new testing services will be important aspects of the role.
Applications are invited from candidates who possess the skills and aptitude to fulfil this important role within NML. Please apply in writing, enclosing your CV to Tony Craven, NMR Group Operations Manager, National Milk Records, Skipton Road, Harrogate, North Yorkshire, HG1 4LG (post or e mail to email@example.com), stating why you feel you are the person most suited to this role. If you require further information, Tony can be contacted on 01423 851350. Closing date 9th April 2010.
Cheese and Dairy Processing Advisor with The Women’s Association ZamZam, Tajikistan.
What’s the context and purpose of the role?
Tajikistan is a poor country, where most of the people live below the poverty line, particularly in rural areas. ZamZam was established in 2006 with the aim of creating income generating activities for poor women living in the Muminabad district of Tajikistan. A project was set up to produce and process dairy products and you’ll work with the staff of ZamZam to increase the reach of this project and extend the range of products. This placement will give you scope to get involved in all areas of the production and marketing of milk and cheese, with the goal of improving product sales. By allowing these vulnerable women to process and sell dairy products, you’ll enable them to earn a living and access better health and education for their families.
What does the role involve?
- Advising around 30 women on milk storage to improve the shelf life of products.
- Providing technical training (composition of milk product, chemical and biological components) to improve the quality of produce.
- Recommending dairy products to diversify current output.
- Training women at ZamZam on cheese production.
- Developing packaging and labeling of products.
- Reviewing current practices and recommending ways to increase milk production.
What skills, experience and personal qualities are needed for the role?
You’ll have a minimum of 5 years’ experience working in a hands-on role in cheese and dairy production. Ideally you’ll have experience of small-scale production and will be familiar with packaging and marketing of dairy products. You’ll be able to train others in basic computer skills (excel and word) and will be comfortable working with and training a wide range of people through the help of an interpreter.
You’ll be able to show initiative and work with little supervision. Finally the ability to work effectively with limited resources and retain a positive and flexible approach is a must for VSO volunteers, as is a good sense of humour!
And the rest…
You’ll be living and working in Muninabad District, in the Southwest of Tajikistan (part of the Kathlon Province). People in the area are mainly involved in agricultural work such as growing wheat and potatoes or raising livestock. Kulyab, 40kms away, is a bigger city with a railway and international airport. The region has a temperate climate with cold winters, warm summers and little rainfall from July – October. There are no safety concerns and locals are hospitable and welcoming to foreigners. A willingness to learn basic Tajik will come in useful and the effort shown in learning their language is very much appreciate by the Tajiks. However you will also be provided with an interpreter.
This is a short-term volunteering position for 6-months. In return, you will be provided with valuable training before your placement, a local salary, return flights, accommodation and insurance. When you return to your home country, VSO will help you to resettle and we’ll invite you to stay involved with us through campaigning, development awareness raising and fundraising.
For more information contact Hannah Gilman .
A Dairy Quality Control Advisor at Lilongwe Dairy, Malawi added 29 January 2009.
What’s the context and purpose of the role?
What does the role involve?
What skills, experience and personal qualities are needed for the role?
You’ll have several years’ experience working in the Dairy sector, specifically in quality control. You’ll be able to create quality control inspection and testing plans and also be confident in training others to undertake and analyse tests on raw milk. You’ll be working with few resources, so it’s essential to make inventive use of what’s already there. You’ll need a positive outlook and an ability to work with a wide range of people in solving problems. By involving the staff members in decisions, you’ll find it easier to make changes, so an outgoing nature will be very useful.
And the rest…
Dairy scientist added 20 November, 2007.
Kate Yuxl from the ChinaClick2 Group is seeking to recruit an experienced dairy scientist. Details of the vacancy are given below.
This is an excellent opportunity to join an established dairy company. Our clients are a leading China dairy manufacturer. Currently, they require an leader with experience and understanding of product development to join their technical research team. Their research centre is located in Europe.
Within this role your key responsibilities will include significant input into new product research. Working within the team, you will also need to routinely communicate effectively and efficiently with other departments, providing technical expertise when required.
The successful candidate will ideally possess the following attributes:
• Tertiary qualification in Dairy Technology/Science or similar ;
• 10 or more years practical dairy product development experience;
• The ability to apply technical and analytical techniques;
• A proven ability to complete projects within tight deadlines;
• Excellent communication and organisational skills;
• Able to work as leader of a team.
This is an excellent opportunity for someone looking to get into Dairy Development with a progressive organisation. For a confidential enquiry or to apply for this position please email firstname.lastname@example.org
Note: If this vacancy is not exactly what you are seeking, then please contact me in confidence to discuss your individual requirements.
Cheese maker added 15 April, 2007.
Please contact Diane@mkandassoc.com for additional information or call (724) 285-7474.
Technologists producing acidic foods such as pickles and sauces often find it difficult to get information on the processing conditions required to obtain commercial sterility or how to calculate the processing time at a higher temperature. Following the experience of working with processors experiencing technical issues, including spoilage problems and difficulties in exporting products, I have produced a concise Ebook (Thermal processing of acid fruit and vegetable products. Significant microorganisms, recommended processing time / temperatures, and public health significance of spoilage) that may be helpful. Currently the Ebook (figure 1):
Many students have problems in understanding the mathematics describing the destruction of microorganisms by heat. Log reductions of pathogens and equivalent time-temperature treatments along with the associated lethalities account for a large part of the harder to understand topics. The quiz below is a simple test of of some of the basic concepts. Note Z value is not dealt with in this quiz. If there is sufficient interest I will provide the answers.
Heat Processing Quiz
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 has been derived from Stumbo (1973).
This article investigates how to calculate the lethal effects of UHT treatment and the usefulness of TTIs for differentiating sterilised, direct and indirectly processed UHT-treated milk. The importance of accessing accurate temperature time-data and knowing holding tube dimensions, flow rate, average and minimum holding time and the flow characteristics (Reynolds number) are discussed. The reliability of a model developed by Claeys et al. (2003) to predict the effects of UHT-processing on hydroxymethylfurfural, lactulose and furosine concentrations in milk is discussed. Free On Line calculators for calculating holding time, average flow rate, holding tube length in UHT and HTST plants are provided. A free On Line calculator programmed using the thermal constants calculated by Claeys et al. (2003) is provided to calculate hydroxymethylfurfural, lactulose and furosine concentrations following heat treatment in skim, semi fat and full fat milks. This calculator also calculates F0, B*, C* and % destruction of thiamine. Two methods of numerical integration are used to measure the cumulative lethal and chemical effects of UHT treatment, namely the Trapezoid and Simpson's rules.
Typical UHT treatments involve heating milk to 137℃ to 150℃ in a continuous-flow process and holding at that temperature for one or more seconds before cooling rapidly to room temperature. The milk is then aseptically packaged to give a product that is stable for several months at ambient temperature.
In Europe, UHT treatment is defined as heating milk in a continuous flow of heat at a high temperature for a short time (not less than 135 °C in combination with a suitable holding time, not less than a second) such that there are no viable microorganisms or spores capable of growing in the treated product when kept in an aseptic closed container at ambient temperature (Reg EC 2074/2005).
Can you destroy Mycobacterium avium subsp. paratuberculosis (MAP) by pasteurization? How important is holding time compared with holding temperature? Use the powerful free tools in this section to answer these questions.
An article on thermal process modelling has been added. This article calculates the effect of HTST treatment on the number of log reductions of major milk pathogens and discusses the temperature milk should be pasteurized if Mycobacterium avium subsp. paratuberculosis (MAP) was designated as a human pathogen. The log reductions refer to log10 or decimal (10 fold) reductions in the concentration of viable bacteria.
Dry heat sterilisation is widely used for glassware and materials that are not suitable for sterilisation using saturated steam. A range of temperatures and times are used. Currently a temperature of at least 170°C for 30-60 minutes is widely used. The term is not particularly precise since variable concentrations of water may be present in the oven used (Sandle, 2013).
Spreadsheets for calculating F, B*, C* values of thermal processes and the concentration of Time Temperature Indicators.
DSFT has an extensive range of free-On Line resources for undertaking a wide range of thermal process calculations including dry heat sterilisation (FH) and depyrogenation (FD or FP). This page provides access to a range of Microsoft Excel spreadsheets that can be downloaded for a small donation and will work on a PC or Mac without access to the Internet. In general these spreadsheets are similar to their corresponding free applications on this website.
A number of the spreadsheets have lite or demonstration versions for evaluation prior to purchase. If you want to test a version that does not offer a test version contact me and I can arrange to provide this.
These donations are important. They contribute towards the running costs of the website and enable me to provide free access to the website rather than require a subscription.
MICROSOFT EXCEL LETHAL RATE CALCULATORS AND TEMPERATURE TIME INTEGRATORS FOR THERMAL PROCESSES
This section provides the context to using Excel to calculate the cumulative lethal effects (at all stages during processing) of heat on microorganisms and provides an explanation of how the Excel spreadsheets and On Line calculators available for download from the Dairy Science and Food Technology (DSFT) work.
Here we provide an overview of the background, including a summary of the underlying mathematics, required to produce an Excel spreadsheet for performing basic thermal processing calculations. Note I am not providing a guide to using spreadsheets but basic information that a competent Excel user should be able to use to make their own thermal processing spreadsheet.
- 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.
DSFT provides a range of thermal processing consultancy services to food and pharmaceutical manufacturers. These include:
- Independent validation of the antimicrobial effectiveness of the heat treatments used in processing.
- Calculation of the average holding time used in processing HTST and HHST products.
- Determination of the flow type and calculation of the minimum holding or residence time of the fastest flowing particles in HTST and HHST products.
- Determination of the F values and the number of logarithmic (log10) reductions of designated microorganisms following heat treatment.
- Advice on equivalent heat processes to meet legislative and other requirements.
- Benchmarking of company processes against statutory and international best practice.
- Advice on alternative methods to microbiological examination for providing additional assurance of adequate heat treatment e.g. the phosphatase test is of no value in providing assurance that a temperature >80°C was used in milk processing. Additional tests that confirm higher temperatures than e.g. normal milk-pasteurization temperatures can be provided. The merits of incorporating these into routine quality assurance testing will be explained.
Small, and even large companies, frequently find it difficult to contact potential new supplier or service partners. This is a particular problem for some small companies attempting to operate testing laboratories.
However, there are companies who provide exemplary customer service and work hard to meet customer needs. The following is a list of these companies that provide exemplary customer service in the laboratory service area.
The nature of polyphosphate
The articles on the Lactoperoxidase system by Michael Mullan include material produced with former colleagues, in particular Professor Lennart Bjorck (SE), Dr Ir. J Stadhouders (NL) and Professor Dr W Heeschen (DE), on International Dairy Federation Group IDF F19, 'Indigenous antimicrobial proteins in milk'.
The work of the group was initially focused, after a request in 1982 from the Joint FAO/WHO Committee of Government Experts for technical advice from IDF on the use of the lactoperoxidase system for preservation of raw milk. This work resulted in a "Code of Practice", which was published in 1988 (Bulletin of IDF No. 234/1988).
The author presented a paper on behalf of the Group entitled"Significance of the Antimicrobial Proteins of Milk to the Dairy Industry" at the IDF Cheese Week at Rennes, France 1988. This draft Django platform.document formed the basis of a more extensive monograph entitled the 'Significance of the indigenous antimicrobial agents of milk to the dairy industry' published by IDF in 1991 (IDF bulletin . 264/1991). More recently a monograph,'Determination of indigenous antimicrobial proteins of milk' (IDF No. 284/1993), detailing methods for the analysis of these antimicrobial proteins in milk was published.
Michael Mullan also gratefully acknowledges collaborative work with former colleagues Dr Bob Crawford (deceased), Dr Bo Ekstrand, Dr Nigel Wade, Dr Tony Waterhouse and the late Mr Arthur Walker at the WSAC at Auchincruive. The WSAC is now part of the SRUC.
The animal feeding trials at Auchincruive were led by Dr Tony Waterhouse. Studies on the production of lactoperoxidase containing feeding materials and the development of a milk replacer containing a stable and functional lactoperoxidase system were led by the author. Michael Mullan gratefully acknowledges the detailed biochemical work by Dr Bo Ekstrand that was critical to these developments and the excellent scientific support work undertaken by Margaret McDougall and Marion Muir. Bo Ekstrand's post doctoral research was funded by Astra-Ewos. The low heat skim milk powder that formed the lactoperoxidase source for the milk replacer was produced in collaboration with Mr John Hynd, the manager of the Scottish Milk Marketing Board creamery at Stranraer in Scotland.
Arthur Walker died in 2002. Arthur was a person dedicated to the education of young people and had an extraordinary positive attitude to life. He isolated many of the bacteriophages that were in the Auchincruive phage collection when I went to Scotland in 1977. Most of these had been isolated from technical investigations of slow-acid problems with single-strain starters such as C2 at the then SMB factories at Stranraer and Dalbeattie. Hence my designation of the C2 phage that I studied as part of my PhD, as ØC2(W).
Some of the work on phage enumeration discussed by Michael Mullan was undertaken at University College Cork, Ireland working with Professors Charlie Daly and Pat Fox. Their generous help and advice over many years is gratefully acknowledged.
I have included a range of calculators e.g. aids for determining yield, milk component retention in cheese manufacture, ice-cream mix composition and the F-value of thermal processes. Wizards to help students produce correctly cited references have also been included. These aids are included for the use of students and trainees and are not intended for commercial use or to replace support from lecturers and tutors.
It is a condition of using this website that you accept that you use all software and educational material at your own risk including any that you obtained after donation and download.
I accept no liability and cannot be held accountable for any losses/damages/problems/consequences arising from the use or interpretation of any material that I have provided for educational use including any errors made by me or others.
The general conditions concerning donation and use of spreadsheet and subscription services are given at https://www.dairyscience.info/index.php/technology/181-spreadsheets.html .
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This article explains how to convert numbers to scientific notation and back again to standard format. It also contains two calculators that will enable calculations to be checked and that provide feedback on common data entry input errors.