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Typical pots of UHT milk

Summary

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.

Introduction

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).


Dr Michael Mullan owner of Dairy Science and Food Technology consultancyThe Dairy Science and Food Technology (DSFT) site was designed and created by Dr Michael Mullan. Originally the site was intended as a project aimed at exploring the use of the Internet as a means of communicating with students. DSFT gets around a million 'hits' a year and there are hundreds of links back to the site.

Dr Michael Mullan is a food scientist with industrial, research and teaching experience in many areas of food manufacture. Michael is a graduate from Queens University Belfast (BSc (Hons) Food Science), University College Cork (MSc Dairying), the University of Glasgow (PhD) and the University of Twente (Certificate in Quality Management in Higher Education Institutions).

 Michael Mullan is a Fellow of the Institute of Food Science and Technology (FIFST) and was the secretary, Deputy Chairman, and the UK representative on International Dairy Federation Group F19, Indigenous Anti-Microbial Proteins In Milk.

 

Michael Mullan was Head of the Food Technology Education Branch at the Department of Agriculture's (DARD), Loughry College for many years and had a joint appointment as a Lecturer in Food Technology in the School of Agriculture and Food Science (SAFS) at Queen's University Belfast.

Michael Mullan has worked across a range of food supply roles in DARD including the management of around £20M of EU-Peace projects including farmer-mentoring and group-based capital development projects.  Currently Michael Mullan is the owner of the Dairy Science and Food Technology consultancy. View LinkedIn profile.

Michael Mullan is also a member of the Society of Dairy Technology, the chairman of Cookstown Wild life Trust and a Past President of Cookstown Rotary Club. He has also served two terms as a School Governor. He became the Editor of the International Journal of Dairy Technology (IJDT) in January 2019.

Michael Mullan currently works part time at Dairy Science and Food Technology Services on a range of consultancy matters. Michael does mainly desk based research now but continues to collaborate with academics and their research students on phage control, phage lysin, phage enumeration, application of antimicrobial systems (in particular the lactoperoxidase system), thermal processing, use of compositional indicators to improve cheese quality and mathematical modelling of dairy product manufacture. Current projects include modelling Mycobacterium avium subspecies paratuberculosis destruction during thermal processing and use of TTI's in UHT processing.

Research, consultancy and professional interest areas

The science and technology of the lactoperoxidase-thiocyanate-hydrogen peroxide system and its application in process control, product manufacture and nutrition.
Factors influencing the yield and quality of cheese including open texture defects such as slits and cracks caused by gas production.
Mathematical modelling in food technology including the optimisation of sweetness and hardness in ice-cream / gelato.
The exploitation of lactococci in cheesemaking.
Biology, enumeration and control of lactococcal bacteriophages.
Building high achieving teams using coaching and mentoring techniques.
Curriculum development of food technology courses and the development of quality assurance processes in higher education programmes.
Scientific referee for major journals including Journal of Dairy Research, Journal of Dairy Science, Journal of Agricultural and Food Chemistry, Food Microbiology, Foodborne Pathogens and Disease, and the International Journal of Food Science and Technology.

Past/current membership of committees/groups associated with milk research and development

These include -.
• Secretary, deputy chairman, and UK representative on International Dairy Federation Group F19 (Indigenous Antimicrobial Proteins in Milk).
• Joint organiser and member of the Scientific Committee responsible for the International Dairy Federation Seminar on 'Indigenous Antimicrobial Agents of Milk - Recent Developments'. Uppsalla, Sweden.
• Member of the organising committee of the joint Federation of European Microbiological Societies and International Dairy Federation seminar on the "Antimicrobial Proteins in Milk", University of Bath, Bath, UK.
• Member of the Society of Dairy Technology.
• Fellow of the Institute of Food Science and Technology.
Editor of the International Journal of Dairy Technology.

Contact

Lactococcal bacteriophages

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.

Characteristics - Cevrin di Coazze is a ripened cheese produced from a mixture of goats' and cows' milk.  The concentration of cows' milk must be 60-70%.  Cevrin di Coazze cheese is cylindrical with flat surfaces.  The cylindrical shape has a diameter of 15-18 cm, an edge of 7-10 cm and a weight of 800-1500 g. Ripening lasts at least 20 days but is frequently longer than 120 days.  The crust is smooth and regular but not elastic.  The colour is wrinkled, hard, and reddish-grey with yellow and white highlights depending on its age.  The dough is yellowish with small and sparse holes.  The texture is soft and elastic.  The odour is strong and persistent.  The taste is very savoury and mainly hot, salty and acid in ripened products.

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.

Commercial cheese correctly manufactured with pasteurised milk and lactic starter cultures has a well deserved reputation as a nutritious and safe product. However, under certain circumstances cheese may support the growth of food poisoning bacteria or serve as a ‘vehicle’ for their transmission.

Four pathogens are of particular significance, Listeria monocytogenes, Salmonella species, enteropathogenic Escherichia coli and Staphylococcus aureusListeria monocytogenes, the causal agent of listeriosis, is arguably the most significant of this group.

L. monocytogenes is particularly significant since it can grow / survive for long periods in cheese and cause serious illness leading to death; the death rate arising from listeriosis can exceed 30%. It can also induce abortion in humans and its ability to cross the placenta, and access the brain makes it a particularly dangerous pathogen.

 This article provides an introduction to the binary and ordinal logistic regression models developed by Bolton and Frank (1999) for predicting the probability of L. monocytogenes growing in cheese after 42 days storage at 10°C.

Characteristics of Listeria monocytogenes

L. monocytogenes is a Gram-positive, non-sporing bacterium that can grow in high salt environments (up to 10 % sodium chloride), and over a wide pH (5.0-9.6) and temperature range (< 3° – 45°C); it can grow aerobically and microaerophilically ( Bajard et al., 1996; Pearson and Marth, 1990).

While the organism is relatively sensitive to heat there has been considerable debate regarding its sensitivity to pasteurisation.  While   D 71-72°C  values have generally been reported as < 4s, a D72°C value of 4.6 ± 0.5 s has been reported (Bunning et al., 1992) for heat-shocked cells.  Assuming a D72°C value of 5s and raw milk containing 1000 (a high value) CFU / ml, pasteurisation at 72°C for 15s would be predicted to result in around 1 CFU / ml surviving (see http://www.dairyscience.info/newcalculators/listeria-d.asp) emphasising the critical importance of ensuring  only low concentrations of this pathogen in raw milk.

 DSFT provides a range of consultancy services to ice cream, gelato, sherbet and sorbet manufacturers. These range from help in formulating recipes, reducing costs by replacing expensive imported additives, problem solving, courses in advanced product manufacture, advice on all aspects of HACCP including process validation, providing assistance in discussions with regulatory authorities to independent audits of plant, process and external advice received. Independent nutritional advice on the manufacture and safety of low or sugar-free gelato and ice cream products is also provided.

We can help with the development and commercial production of soya and dairy-free, high protein ice cream-like products with or without sucrose. There are better options than sorbitol and fructose. Science based advice on describing products intended for consumers with health issues can also be provided.

Despite work undertaken over 20-years ago by researchers in Canada many large scale ice cream producers have limited knowledge of the minimum holding time of ice cream mix processed using HTST or HHST heat-processes. Furthermore many lack the evidence that they meet regulatory requirements for holding time. DFST can use your plant data to calculate average holding time, flow type, minimum residence or holding time, the log reductions of major pathogens and advise on any remedial action required.

 

Contact DSFT

Note this article is still in draft form and is available On Line to facilitate editing. It is scheduled to be completed by June 2015.

There are several programming languages used to construct models that will run on web servers. These include Perl, PHP, Python, Classic ASP, JavaScript and ASP.Net. These languages can be used with appropriate databases to develop powerful web-based applications.

PHP has become particularly popular and is fairly easy to learn. Classic ASP is very easy to learn but is increasingly being replaced by ASP.NET. Virtually anyone who can put a spreadsheet together is capable of learning a basic language such as ASP.

The purpose of this article is to show how the calculator for predicting salmonella growth on tomatoes was written in ASP. I would like to encourage lecturers and students to learn how to programme. While ASP is being replaced by ASP.NET the basic premises using in ASP coding can be applied to other languages and even if you decide to learn PHP which is a particularly versatile web language you will be able to apply the concepts learned

Constructing the data entry form

The HTML and ASP code used to construct the data entry form is shown below. For simplicity web page header information, value information in ASP and some form security information has not been shown.

The input form was constructed by writing the code for a table in HTML and adding in HTML text boxes to allow initial number (no), temperature (t) and incubation time (hr) to be entered.

 <%@LANGUAGE="VBSCRIPT" CODEPAGE="1252"%>

<form id="form1" name="form1" method="post" action="sam1.asp">

<table width="75%" border="1" cellspacing="0" cellpadding="1">
<tr>
<th colspan="2" scope="col">Predict the growth of salmonella in cut tomatoes at 10&deg;C to 35&deg;C</th>
</tr>
<tr>
<td width="41%">Initial number of salmonella / gram</td>
<td width="59%"><input name="no" type="text" id="no" value="<%=no%>" /></td>
</tr>
<tr>
<td>Temperature, &deg;C</td>
<td><input name="t" type="text" id="t" value="<%=t%>" /></td>
</tr>
<tr>
<td height="20">Incubation time, hours</td>
<td><input name="hr" type="text" id="hr" value="<%=hr%>" /></td>
</tr>
<tr>
<td height="20" colspan="2"><div align="center">
<input type="submit" name="Predict number of samonella" id="Predict number of samonella" value="Predict number of salmonella" />
</div></td>
</tr>
</table>
<p>&nbsp;</p>
</form>


 

Writing the data processing script

A simplified version of the processing script is given below. The notes which are preceded by a ' explain how the script works.

<%@LANGUAGE="VBSCRIPT" CODEPAGE="1252"%>


<% Option Explicit
'Use of option explicit will ensure that error messages are displayed if there are coding problems. These are helpful in finding solutions. %>

<%


'List variables

Dim no
Dim t
Dim hr

'no, t and hr are values that have been entered on the form
Dim r
Dim g
Dim gen
Dim pop

'r,g,gen, pop are the products of calculations that will be undertaken

'We will now obtain the information from the entry form to perform the calculation

no=CSng(Request.form("no"))
t=CSng(Request.form("t"))
hr=CSng(Request.form("hr"))


'Taking information from the form we will calculate r,g, gen and pop. This could easily be done in one calculation. The calculation has been broken down into its component parts so that it can be followed more easily.

'For an explanation of the calculation please see http://www.dairyscience.info/index.php/food-model/258-predict.html
 
r=0.026*(t)-0.1065
g=1/(r*r)  'note r is the square root of the growth rate, we need to obtain the growth rate by multiplying r by r
gen=hr/g
pop = no*2^gen

'We next need to provide the results of the calculation for pop which is the total number of salmonella after growth at the temperature chosen for the time inputted.

If t >9.99 AND t <35.01 THEN ' basic validation to ensure that the results are within the temperature parameters modelled

'The  'If Statement' is used to make a decision to execute code if some condition is True.
 
response.write ("The predicted number of samonella after" & "&nbsp;" & (hr)& "&nbsp;" & "hours has been calculated as" & "&nbsp;" & round(pop,0) & "&nbsp;" & "CFU/g.")
 END IF

'END IF is used to indicate the end of code execution


IF t < 10 THEN
Response.Write ("&nbsp; Caution. This model as not been validated at temperatures <10&deg;C.")
END IF

IF t > 35 THEN
Response.Write ("&nbsp; Caution. This model as not been validated at temperatures >35&deg;C")
END IF
%>

About the data processing script

These scripts will work on a Windows web server or a Windows PC running Microsoft's free IIS or PWS components. They are compressed and must be un-zipped before use. They have been provided free and are not warranted in any way. They are intended for educational use only. They can easily be adapted to work using PHP or JavaScript.

Qualifications/Disclaimer

To be added.

Acknowledgements

I learned ASP, how to use Access Databases and HTML from a former colleague Dr Raymond Martin. Raymond generously helped me correct concatenation and many other errors and though his help I gradually learned how to write quite sophisticated data-base driven ASP applications. I gratefully acknowledge Raymond's help over many years.


How to cite this article

Mullan, W.M.A. (2015). [On-line]. Available from: https://www.dairyscience.info/index.php/cheese-starters/209-articles.html?start=80 . Accessed: 11 December, 2019.  

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