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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.
This article discusses the major functions of starters in dairy fermentations. Recent research on the relative importance of the antimicrobial agents produced by starters is included. The importance of undissociated lactic acid (HLac) is discussed with regard to the inhibition of the growth of Listeria monocyotgenes, Escherichia coli and Staphylococcus aureus.
The author recommends that regulators should require manufacturers of raw milk cheeses to meet a minimum value for HLac that must be achieved prior to product release for retail sale.
Characteristics - Toma del Lait brusc is a typical Piedmont cheese with a cylindrical appearance and flat surfaces. The cylindrical shape has a diameter of 25-35 cm, an edge of 12-18 cm and a weight of 4-8 kg. Ripening lasts at least 60 days but frequently is longer e.g. 180 days. The crust is wrinkled, hard, and reddish-grey with yellow and white highlights. The dough is ivory-white or dark-yellow with small holes. Typical greenish-blue veins due to mould growth may be present in ripened cheese. The texture is consistent, compact and very friable. In young cheeses, the odour is fine and delicate, becoming very strong and persistent in aged products. The taste is mainly sweet and fine but savoury, salty and intense in aged products.
Production area - The cheese is produced in the high pastures throughout Turin province.
Peroxidases catalyse reactions in which hydrogen peroxide is reduced and a suitable electron donor is subsequently oxidised. A wide variety of organic and inorganic substances can serve as electron donors, but substrate specificity varies between various peroxidases.
- Written by Nupur Goyal and D.N. Gandhi
- Written by Claire Towler
As more pressure is applied to reducing production costs, attention is increasingly being given to maximising the yield of high moisture cheeses including Cottage cheese. While yield is important, cheese quality must also be considered whenever attempts are being made to improve or optimise yield.
Models in food technology, at the simplest level, are equations showing the relationship between two or more variables. Dunn (1986) defined a mathematical model of a process as a 'system of equations whose solution, given specified input data, is representative of the response to a corresponding set of inputs'.
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.