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.
TABLE 1: Major functions of starters in milk fermentations
Whey expulsion (syneresis)
Flavour compound production
Formation of diacetyl and acetaldehyde
Lowering of pH and redox potential
Production of antibiotic substances e.g. bacteriocins such as nisin
Production of hydrogen peroxide
Formation of D-leucine
Production of lactate/lactic acid
Production of openness to facilitate 'blue veining'
Body and viscosity improvement
Increase cheese yield?
Result in reduced use of milk powder in yoghurt manufacture
Reduce potential for gas and off-flavour development
Make products more acceptable to the lactose intolerant
Lowering of redox potential
Aids flavour development
Although lactic acid production is the major task required of starters in many milk fermentations, starters have other - sometimes equally important - roles.
The preservative properties of starters have been used to extend the shelf life of products e.g. Cottage cheese and to inhibit the growth of psychrotrophic micro-organisms in silo milk in cheese factories. The mechanism for these effects involves competition for nutrients, decrease in pH, the formation of inhibitory compounds, lowering of redox potential and possibly activation of the lactoperoxidase system.
The production of openness e.g. slits or seams, is important in some varieties of blue-veined cheese such as Cambazola or Blue Brie and can be achieved by the use of starters containing strains of Lc. lactis subsp. lactis biovar. diacetylactis and/or Leuconstoc species.
Some starters produce complex polysaccharide-type materials which can be utilised by technologists to improve the body or viscosity of products such as yoghurt, increase cheese yield or to produce the essential product characteristics (ropiness) of Finnish long milk - Viili.
LAB starters, particularly strong acid producers, have the potential to significantly lower the oxidation–reduction (Eh) potential in dairy products, particularly in cheese or in liquid products in sealed systems. The Eh of raw milk is about +150 mv, whereas Cheddar cheese has an Eh of around -250 mv. Reduction of Eh to such low values creates an environment in which only facultative or obligate anaerobic microorganisms can grow. Low redoxpotential is also an essential requirement for the formation of the typical flavour of Gouda and Cheddar cheeses.
Cheddar cheese at the start of pressing contains about 0.5% (w/w) lactose. Failure of starters to utilise residual lactose (due to phage-induced cell lysis) during pressing and in the first few weeks of maturation may result in sweet cheese and/or gas production by heterofermentive non-starter bacteria.
Because acid production by the starter influences syneresis, variations in starter activity may result in variations in the moisture content of the final cheese. Obviously these effects have the potential to affect the profitability of dairy plants.
In cheesemaking, lysis of starter cells can result in problems which range from slow acid production to completely lost vats. Lysis of starters during the early stages of cheesemaking may result in cheese of high pH, high lactose content, high redox potential and low lactic acid and lactate content.
Disruption of starter functions can have a range of consequences. These range from major product quality problems, including the growth of pathogens e.g. Staphylococcus aureus (especially if raw milk has been used), to lost product.
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How to cite this article
Mullan, W.M.A. (2005) .
[On-line]. Available from: https://www.dairyscience.info/industrial-significance-of-lactococcal-bacteriophages.html . Accessed: 4 March, 2024.
Updated August 2016.