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- Discovery of bacteriophages for lactococci
- Bacteriophages for lactic acid bacteria with particular emphasis on lactococci
- Bacteriophage lysins
- Morphology and classification of bacteriophages
- Enumeration of lactococcal 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.
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).
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.
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
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.
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.
Technologists must be able to calculate the cumulative lethality of a heat process normally referred to as F. This is done by defining a reference temperature, e.g. 121.1 °C for a F0 calculation using a low acid food or e.g. 93.3 °C for an acid product, at which the equivalent lethal effects experienced during heating and cooling at lower temperatures are calculated.
The area under the lethality curve is normally calculated using numerical integration. The most commonly used method is the trapezium or trapezoid method. An alternative, more accurate, but slightly more complicated method, is to use Simpson's rule or to be more correct Simpson's rules.
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):
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.
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.
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 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.
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.
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So you want to know how to cite a reference? Here you can use 50 Harvard reference wizards to generate a bibliography, "Works Cited", references or citations to books, speeches, images, legal rulings, websites and many other sources of information using the Harvard style, author-date citation method; the legal rulings are not referenced using the Harvard system but are included because many students need to cite at least one legal citation.
Over the past 10-15 years, there has been an enormous increase in the sources of information available to students; if you are an academic just look at your own thesis and determine how many different citations you used. If you graduated more than 10-years ago it is unlikely that you used more than 10-different reference types. The diversity of information sources that today's students encounter can create difficulties when it comes to correctly citing some sources, particular electronic sources, let alone judging the validity of the source. Perhaps it should not be a surprise that referencing causes so many problems across higher education wherever it is undertaken!
Following my experiences as a research supervisor, teacher, education manager and external examiner I decided that I would try to make referencing a little easier by creating a series of 'wizards'; these are forms in which information is entered, and if entered correctly, will result in a correctly formatted reference. Hopefully through this facility, supervisors may avoid the tautology of citations with ISBN numbers, incorrect Mintel citations and web references!
How to convert numbers to scientific notation and back to standard format?
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.
How do you convert numbers to scientific notation?