Fluid milk vitamin fortification compliance in New York State.

Current US regulations, as specified in the Pasteurized Milk Ordinance, require vitamin A fortification of all reduced fat fluid milk products. The addition of vitamin D is optional in all fluid products. Acceptable vitamin concentrations in fortified milks are 2000 to 3000 International units per quart for vitamin A and 400 to 600 International units per quart for vitamin D. Vitamin A and D levels were analyzed in fortified milk products collected over a 4-yr period in New York State. Samples of whole fat, 2% fat, 1% fat, and nonfat milks were collected twice per year from up to 31 dairy processing plants. For vitamin A, 44.5% of 516 samples were in compliance with current regulations, and 47.7% of 648 samples were within the acceptable range for vitamin D. Most milk samples that were out of compliance were underfortified.

Microbiological and chemical quality of raw milk in New York State.

Between December 1993 and January 1996, samples of raw milk from bulk tanks were collected by licensed milk haulers at the time of pick-up from 855 randomly selected farms in New York State (representing approximately 10% of all dairy farms in the state). The milk was examined for microbial and chemical qualities. Bacterial numbers were determined by standard plate count, laboratory-pasteurized count, coliform count, heat-resistant spore-forming psychrotroph count, aerobic spore count (mesophilic), rapid psychrotrophic count, and preliminary incubation count. The frequency distributions for these counts are presented. Paired correlation analyses between the microbiological parameters showed low correlations between test results; no correlation coefficients were > 0.8. The four highest positive correlation coefficients were found between standard plate count and rapid psychrotrophic count (0.7685), rapid psychrotrophic count and preliminary incubation count (0.6648), standard plate count and preliminary incubation count (0.5800), and aerobic spore count and laboratory-pasteurized count (0.5393). All other correlation coefficients were < 0.5. Milk freezing points and acid degree values were determined for all samples. Frequency distributions for these results are also presented.

Evaluation of adenosine triphosphate-bioluminescence hygiene monitoring for trouble-shooting fluid milk shelf-life problems.

An ATP-bioluminescence hygiene monitoring system was used to evaluate food contact surfaces in four fluid milk plants experiencing shelf-life problems. Postpasteurization surfaces, including gaskets, pipe fittings, valves, filler parts, and hand-washed items, were evaluated. Swab results, measured in relative light units proportional to total recovered ATP, were compared with results from the standard method of microbiological swab contact for adjacent sites of equal area. Microbiological procedures included standard plate count, coliform count, and Gram-negative bacteria count. Standard plate counts were < 1, 1 to 50, and > 50 cfu in 65, 22, and 13% of swabbed sites of < 100 RLU (relative light units); in 9, 36, and 55% of sites of 100 to 150 RLU; and in 22, 18, and 60% of sites of > 50 RLU, respectively. Thirteen sites were found with standard plate counts > 10,000 cfu per site and identified with the hygiene monitoring system (> 150 RLU). Gram-negative bacteria were the dominant bacterial type in a majority of these samples. Gram-negative bacteria were detected in a total of 22 sites tested; mean counts were 2100 cfu per site for Gram-negative bacteria and 20 cfu per site for coliform bacteria. Although limited to use on accessible sites, the hygiene monitoring system proved to be an effective, rapid tool for identifying the possible sources of postpasteurization contamination in the fluid milk plants evaluated.

Influence of milking three times a day on milk quality.

Lactations were divided into three periods: early (1 to 99 d), mid (100 to 199 d), and late (200 to 299 d). One hundred Holsteins were randomly split into four groups that were balanced for parity. Groups 222 and 333 were milked twice and three times a day, respectively, throughout lactation. Group 233 was switched from twice to three times daily milking at 100 d, and group 223 was switched at 200 d. Compared with group 222, milk yield for group 333 increased by 10.4%, and fat and protein yields increased by 4.7 and 7.3%, respectively. Mean milk SCC for all groups was < 175,000 cells/ml within each lactation period. The percentage of CP was lower for cows milked three times a day than for cows milked twice a day during each stage of lactation (early, 2.78 and 2.91; mid, 3.08 and 3.19; and late, 3.16 and 3.28, respectively). Casein as a percentage of CP was significantly higher for cows milked three times a day during midlactation. The acid degree values (milliequivalents of FFA/ 100 g of fat) were significantly higher for milk from cows milked three times a day than for cows milked twice a day during early and midlactation, (early, 0.75 and 0.55; mid, 0.82 and 0.61; and late, 0.88 and 0.75, respectively). No differences were detected in milk flavor or plasmin activity because of milking frequency. Casein as a percentage of CP decreased, and plasmin activity increased, as parity and stage of lactation increased.

Cheddar cheese: influence of milking frequency and stage of lactation on composition and yield.

Cheddar cheese was made from milk collected from two groups of cows milked either two or three times daily during early, mid, and late lactation. Milk from cows in late lactation had lower casein as a percentage of true protein and a higher acid degree value than did milk from cows in early lactation. Milk from cows milked three times daily had lower concentrations of milk fat and casein and higher acid degree values than did milk from cows milked twice daily, and thus this milk would be expected to result in decreased cheese yield. Cheese composition was not affected by milking frequency. Stage of lactation effects on cheese composition were confined to differences in salt content and a trend for higher moisture in cheese made from milk of cows in late lactation. Stage of lactation influenced the pH and degradation of alpha s-casein in cheese during aging. Fat and protein losses in whey at draining were higher for milk from cows in late lactation than from milk from cows in early lactation. The typical differences in fatty acid composition of milk from cows in early lactation that cause lower melting point may have caused higher fat loss in press whey. Fat loss in whey at draining was higher in cheese made from milk from cows milked three times daily than in cheese made from milk from cows milked twice daily, but the protein loss was not influenced. The ADV of milk was positively correlated to the fat loss in whey. Lower recoveries of fat and protein in cheese from milk of cows in late lactation were observed and may cause small but economically important decreases in cheese yield. Low SCC of milk from cows in late lactation may have minimized the changes in cheese composition and yield from stage of lactation.

Selection of tests for monitoring the bacteriological quality of refrigerated raw milk supplies.

Raw milk samples were collected from 10 producer bulk tanks. Samples were then subdivided so that milks were subsequently stored at 1.7, 4.4, 7.2, and 10.0 degrees C for 24 and 48 h. After storage, samples were analyzed by seven plating methods: standard plate count, psychrotrophic bacterial count, rapid psychrotrophic count, preliminary incubation count, mesophilic plate count, laboratory pasteurized count, and coliform count by violet red bile agar technique. Impedance protocols on a Bactometer Model 123 for total count, psychrotrophic count, mesophilic count, and coliform count were also used to evaluate the bacteriological quality of the milks. Bacterial counts and impedance detection times were analyzed using nonparametric statistics. Impedance protocols for total count and psychrotrophic count were the best indicators of bacteriological quality. Preliminary incubation count was the best of the plating methods. The laboratory pasteurized count performed poorly. Impedance measurements provided information in the shortest time.

Comparison of dry culture medium and conventional plating techniques for enumeration of bacteria in pasteurized fluid milk.

Standard plate counts, psychrotrophic bacterial counts, and coliforms were determined by conventional plating techniques and by Petrifilm TM plates, a dry culture medium, for 48 commercially processed milk samples (24 whole milk and 24 skim milk). The Petrifilm SM plate counts were compared with counts on standard methods agar for the standard plate count, psychrotrophic bacterial count, and rapid psychrotrophic bacterial count. The Petrifilm violet red bile plate counts were compared with counts on violet red bile agar for coliform test with a solid medium and the preliminary incubation method for detection of coliforms. Standard plate counts were determined within 24 h of packaging and after 7, 10, and 14 d of storage at 6.1 degrees C. Psychrotrophic bacterial counts and coliform counts were determined with 24 h of packaging and after 7 d storage. There was a strong linear relationship between Petrifilm SM and standard methods agar plates (excluding counts on samples plated within 24 h of packaging) and for the psychrotrophic bacterial count method. Petrifilm SM had a weak linear relationship with Standard Methods Agar plates for the rapid psychrotrophic bacterial count. Coliform counts determined on Petrifilm violet red bile plates were generally within the same range as counts on violet red bile agar plates. The positive predictive values for the Petrifilm violet red bile plates and violet red bile agar plates were essentially the same for samples plated within 24 h of packaging.

Effects of premilking udder preparation on bacterial population, sediment, and iodine residue in milk.

Udder preparations that wet both udder surfaces and teats had the highest standard plate count in milk compared with methods that wet teats only. Physical action of cleaning teats with a dry towel lowered bacterial count compared with preparations wetting both udder surfaces and teats. Methods resulting in lowest bacterial counts were the use of water hose, wet towel, or premilking disinfectant teat dip followed by drying with paper towels. Counts of coliform and Staphylococcus sp. followed similar trends. In most comparisons, addition of udder wash sanitizer was of marginal or no benefit. Standard plate count of teat rinses after udder preparation confirmed the benefit of cleaning and drying teats. Physical manipulation of teats during cleaning was essential for lowering sediment in milk. Drying of teats with a paper towel for at least 10 s after dipping with a 1% iodophor disinfectant dip was essential for reducing iodine residue. Both premilking and postmilking disinfectant teat dipping with a 1% iodophor teat dip caused higher iodine residue in milk than premilking disinfectant dip with subsequent drying. A .5% iodophor teat dip contributed less iodine in milk than a 1% iodophor teat dip. Premilking udder preparation affects bacterial count, sediment, and iodine residue in milk.