Better Tasting Milk

Lower somatic cell counts help you protect that important fluid market.

Researchers have provided another good reason to follow a proven mastitis control program to keep somatic cell counts (SCCs) as low as possible. Low-SCC raw milk minimizes the possibility of off-flavours developing in pasteurized, fluid milk and turning consumers off this important product.

Fluid milk sales represented 43 per cent of the milk marketed by Dairy Farmers of Ontario (DFO) in 1999. The average Ontario resident consumes about 88 litres of fluid milk per year. DFO invests millions of dollars annually in promotion to get consumers to drink more. So it’s in your best interest to strive to market a clean, sweet-tasting product to these consumers.

"We must recognize that once milk leaves the farm, it doesn’t get any better," DFO board member Jean-Guy Séguin said in a recent Ontario Milk Producer article. "We must assure high quality to the consumer or our sales and producer incomes will be negatively affected."

The fluid market and factors that may affect consumption are important enough that DFO has conducted nine "Barrier" studies since 1989. These studies help DFO understand why consumers may or may not buy fluid milk.

In the 1999 study, at least 58 per cent of consumers agreed strongly with one or more of the barriers that limited their fluid milk purchases. With this high level, you can’t afford to add any more reasons for them to back off from your product.

Most research studies have examined the effects of mastitis on raw milk quality. It’s well known, for example, that high SCCs affect cheese yields, but this has little direct bearing on you as an individual producer. If poor flavour quality turns consumers off fluid milk, you have more cause for concern. If milk tastes "bad" before the pull, or best-before, date, and the consumer returns the product to the store, then the dairy industry loses both dollars and confidence in the product.

Only limited work had been done on the quality of pasteurized milk from high-SCC cows or herds. That changed when Cornell University researchers conducted a study to determine the effect of raw milk SCCs on the quality of pasteurized fluid milk during 21 days of shelf life. The February 2000 issue of the Journal of Dairy Science (83:264-274) published their research article, Effects of Somatic Cell Count on Quality and Shelf-Life of Pasteurized Milk. It gives us proof that shipping low-SCC milk from the farm is a critical component in maintaining high-quality pasteurized fluid milk acceptable to consumers.

The researchers selected eight Holstein cows producing low-SCC milk with no mastitis-causing pathogens or off-flavours in it. Milk was collected four times before and four times after the researchers infected the cows with the contagious mastitis bacteria Streptococcus agalactiae. Average SCCs were 45,000 cells per millilitre before infection and 849,000 after infection.

Pasteurized, homogenized 2 per cent milk from the pre- and post-infection periods was stored at five degrees C. The researchers analysed the milk for fat breakdown, protein breakdown, bacteria counts and flavour quality at one, seven, 14 and 21 days after processing.

Bacteria counts of both the high- and low-SCC milks were low, with no difference between them. This assured the researchers that the bacteria counts wouldn’t cause shelf-life problems.

On the other hand, there were significant differences in the amount of fat and protein breakdown, and resulting differences in flavour between the high- and low-SCC milks. Acid degree value was used as an index of fat breakdown and casein as a percentage of true protein as an index of protein breakdown.

Over the 21 days of storage the fat broke down three times faster and the protein two times faster in the high-SCC milk than in the low-SCC milk. These higher levels were excellent indicators of why off-flavours were detected in high-SCC milk.

To measure flavour quality effectively, a trained panel of 12 individuals evaluated the pasteurized milk for aroma (seven traits), taste (10 traits) and aftertaste (four traits).

Results shown in the graph above make it clear that between days 14 and 21 the high-SCC milk developed pronounced off-flavours to a degree where consumers wouldn’t want to drink it. The predominant off-flavour identified was rancid. It’s been described as "soapy, bitter, unclean and a lingering aftertaste."

The breakdown of butterfat causes rancid off-flavours. With high-SCC milk, the butterfat is more susceptible to breakdown during refrigerated storage. Other factors, such as stage of lactation, cooling rate of milk, feed quality and quantity, and mechanical handling of the milk, can also play a role in rancid off-flavour development. This trial controlled those factors.

The researchers concluded that using low-SCC milk and careful milk-handling procedures would make it possible to extend the refrigerated shelf life of fluid products without concern about rancid off-flavours developing. Further research would be helpful to determine at what SCC threshold levels off-flavours develop. It could also look at whether a few high-SCC cows in a medium- to low-SCC herd can cause rancid off-flavours.

This research established a definite connection between low SCCs and a longer shelf-life for pasteurized milk. Assuring high-quality raw milk can assure high-quality processed products, one of the keys to our industry’s long-term health.

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This article first appeared in the June 2000 Ruminations column of the Ontario Milk Producer magazine.

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