The Influence of Psychrotrophs on the Protein Content of Whey

Yates, A.R.; Elliott, John A.

doi:10.1016/s0315-5463(77)73547-3

Cited by 8 publications

(3 citation statements)

References 6 publications

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“…fluorescens at different temperatures, but the bacterial numbers were not reported and whey separation was not typical of large-scale creamery methods. Yates & Elliott (1977) calculated that the growth of unspecified proteolytic psychrotrophic bacteria in whole milk resulted in whey N losses equivalent to reductions of 2-75-4-60% in the protein available for cheese. The lower percentage losses were associated with bacterial populations of approx.…”

Section: Effects On Cultured Milk Productsmentioning

confidence: 99%

Enzymes of psychrotrophic bacteria and their effects on milk and milk products

Law¹

1979

Journal of Dairy Research

210

107

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B. A. LAW lipases (including phospholipases) which, because they are produced extracellularly, can act directly on micellar casein and on the fat globules in milk. They can act in raw milk while it is being stored and the psychrotrophs are multiplying, but they may also continue to act in heat-treated liquid milk and other products. PROTEINASES OF PSYCHROTROPHIC BACTERIA Proteinase-producing groups Some thermoduric bacteria are well known for their ability to produce extracellular proteinases (e.g. Priest, 1977; Law, 1979) and psychrotrophic thermoduric sporeformers have been isolated from milk (see Introduction). However, there have been no definitive reports linking proteinases produced by these organisms with changes in milk or milk products. Proteinase-producing psychrotrophic Gramnegative bacteria are often isolated from milk and references to the identification of such isolates are listed in Table 1. The best represented genus is Pseudomonas, with Ps. fluorescens as the most common species. However, the apparent high incidence of the latter may be due to the ease with which it may be tentatively identified, rather than to its true distribution. The proteinases of several psychrotrophic pseudomonads have been isolated and partly characterized. For example, a, Ps. fluorescens enzyme which gels UHT-sterilized milk (Law, Andrews & Sharpe, 1977) appears to be a thiol proteinase, insensitive to EDTA and inhibited by Co 2+ and Zn 2+ (Alichanidis & Andrews, 1977); it has a nearneutral pH optimum with casein as substrate and its mol. wt is 38400. On the other hand, Barach, Adams & Speck (1976a) isolated an EDTA-sensitive, Zn 2+-containing neutral proteinase (mol. wt 48000) from another Pseudomonas sp. Other psychrophilic Pseudomonas isolates from soil and cold-stored meat produce similar EDTA-sensitive neutral metallo-proteinases (Law, 1979). Protein breakdown in liquid milk Most studies of the degradation of proteins in milk and milk products have concerned the caseins; whey proteins have received little attention. Psychrotroph proteinases may act first during refrigerated handling of raw milk before heat treatment and Law et al. (1977, 1979a) have shown that strains of Pseudomonas and Acinetobacter spp. growing to approx. 10 7 colony-forming units (cfu/ml) and above produce sufficient proteinase to degrade /?-and K-casein to an extent detectable by polyacrylamide-gel electrophoresis (PAGE) and starch-gel electrophoresis (SGE). When milks in which the Pseudomonas sp. had grown were subsequently UHTsterilized and stored at 20 °C, those which had contained 5 x 10 7 and 8 x 10 6 cfu/ml before sterilization gelled after 10-14 d and 8-10 weeks respectively (Law et al. 1977). Uninoculated low-count milks, or milks containing only 8 x 10 5 cfu/ml of the pseudomonad remained liquid for at least 20 weeks after sterilization, although a sediment gradually formed in the latter. The /?-and /e-caseins were extensively degraded in gelled UHT milks and some loss of a sl-casein was seen. Whey proteins were not detectably degraded....

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Section: Effects On Cultured Milk Productsmentioning

confidence: 99%

Enzymes of psychrotrophic bacteria and their effects on milk and milk products

Law¹

1979

Journal of Dairy Research

210

107

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“…The actual losses, however, occurred when the milk was stored 5 or more days. O'Leary et al (38) reported a loss of yield of 0.5%/day when Cheddar cheese was made from milk stored at 5-10°C for 6 d. Others have also observed a reduced yield of cheese when cheesemilk was contaminated with psychrotrophs (2,7,14,20).…”

Section: Resultsmentioning

confidence: 99%

“…Actively growing psychrotrophs can produce proteolytic enzymes that cause an undesirable breakdown of casein in the milk (1,4,5,12). Results of some research have shown that this breakdown causes loss of protein in whey, resulting in reduced cheese yield (2,6,14,15,20). Yates and Elliott (20) reported a significant increase of protein in whey from cheesemilk inoculated with psychrotrophs, which resulted in 2.75 and 3.5% reduction of protein available for cheesemaking.…”

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confidence: 99%

Growth of Pseudomonas or Flavobacterium in Milk Reduced Yield of Cheddar Cheese

Ellis

Marth

1984

Journal of Food Protection

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Cheddar cheese was manufactured from milk which was artificially contaminated with proteolytic species of Pseudomonas or Flavobacterium and stored at 7°C. Cheese was analyzed for moisture content and yield was determined on a dry matter basis. Bacterial counts were made during 7 d of milk storage. Pseudomonas isolates grew to larger populations and faster than did Flavobacterium isolates. Yield of cheese decreased as time of storage was extended beyond 3 d and psychrotrophic populations increased. Greatest losses were observed after 5–7 d of storage with psychrotrophic bacterial counts of 106–108/ml. Overall average decreases in yield of cheese caused by Pseudomonas spp. or by Flavorbacterium spp. were 0.53% and 0.39% per day, respectively, when divided equally over a 7-day period. However, losses generally were not evident until milk was held for 5 d. Numbers of and kind of psychrotrophic bacteria, and multiplication and metabolic activity of these bacteria, when present in milk, are among the factors important in causing a reduction of cheese yield.

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Oxygen tension measurement as a means of detecting incipient spoilage of raw milk by psychrotrophic bacteria?

Rowe¹,

Gilmour²

1986

International Journal of Food Microbiology

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The Influence of Psychrotrophs on the Protein Content of Whey

Cited by 8 publications

References 6 publications

Enzymes of psychrotrophic bacteria and their effects on milk and milk products

Enzymes of psychrotrophic bacteria and their effects on milk and milk products

Growth of Pseudomonas or Flavobacterium in Milk Reduced Yield of Cheddar Cheese

Oxygen tension measurement as a means of detecting incipient spoilage of raw milk by psychrotrophic bacteria?

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