Enhanced lactose cheese milk does not guarantee calcium lactate crystals in finished cheddar cheese.

Three experimental batches of Cheddar cheese were manufactured in duplicate, with standardization of the initial cheese-milk lactose content to high (5.24%), normal (4.72%, control), and low lactose (3.81%). After 35 d of aging at 4.4 degrees C, the cheeses were subjected to temperature abuse (24 h at 21 degrees C, unopened) and contamination (24 h at 21 degrees C, packages opened and cheeses contaminated with crystal-containing cheese). After aging for 167 d, residual cheese lactose (0.08 to 0.43%) and L(+)-lactate concentrations (1.37 to 1.60%) were high and D(-)-lactate concentrations were low (<0.03%) for all cheeses. No significant differences in lactose concentrations were attributable to temperature abuse or contamination. No significant differences in L(+)- or D(-)-lactate concentrations were attributable to temperature abuse. However, concentrations of L(+)-lactate were significantly lower and D(-)-lactate were significantly higher in contaminated cheeses than in control cheeses, indicating inoculation (at d 35) with heterofermentative nonstarter lactic acid bacteria able to racemize L(+)-lactate to D(-)-lactate. The fact that none of the cheeses exhibited crystals after 167 d demonstrates that high cheese milk or residual lactose concentrations do not guarantee crystal formation. Contamination with nonstarter lactic acid bacteria can significantly contribute to D(-)-lactate accumulation in cheese.

Nonstarter lactic acid bacteria and aging temperature affect calcium lactate crystallization in cheddar cheese.

The occurrence of unappetizing calcium lactate crystals in Cheddar cheese is a challenge and expense to manufacturers, and this research was designed to understand their origin. It was hypothesized that nonstarter lactic acid bacteria (NSLAB) affect calcium lactate crystallization (CLC) by producing D(-)-lactate. This study was designed to understand the effect of NSLAB growth and aging temperature on CLC. Cheeses were made from milk inoculated with Lactococcus lactis starter culture, with or without Lactobacillus curvatus or L. helveticus WSU19 adjunct cultures. Cheeses were aged at 4 or 13 degrees C for 28 d, then half of the cheeses from 4 and 13 degrees C were transferred to 13 and 4 degrees C, respectively, for the remainder of aging. The form of lactate in cheeses without adjunct culture or with L. helveticus WSU19 was predominantly L(+)-lactate (> 95%, wt/wt), and crystals were not observed within 70 d. While initial lactate in cheeses containingL. curvatus was only L(+)-lactate, the concentration of D(-)-lactate increased during aging. After 28 d, a racemic mixture of D/L-lactate was measured in cheeses containing L. curvatus; at the same time, CLC was observed. The earliest and most extensive CLC occurred on cheeses aged at 13 degrees C for 28 d then transferred to 4 degrees C. These results showed that production of D(-)-lactate by NSLAB, and aging temperature affect CLC in maturing Cheddar cheese.

Yogurt consumption does not enhance immune function in healthy premenopausal women.

Fermented milk products may protect against breast cancer by stimulating immunologic activity. Twenty-five women [24.0 +/- 0.7 (SE) yr] were assigned randomly to two groups: control (n = 12) and yogurt treatment (n = 13). Controls refrained from yogurt products for three months, whereas the yogurt treatment group consumed two cups (454 g/day) of commercially produced yogurt for three consecutive months. Prior yogurt consumption did not exceed 4-6 cups/mo, and subjects consumed their usual diet during the study. Three-day diet records and fasting midluteal blood samples were obtained during subjects' first, second, and fourth menstrual cycles (baseline, Month 1, and Month 3, respectively). Macronutrient intakes differed between groups only for carbohydrate. Calcium intake increased for yogurt consumers during intervention. Lymphocyte proliferation induced by concanavalin A, phytohemagglutinin, and pokeweed mitogen, interleukin 2 production, and cytotoxic T lymphocyte-mediated cytotoxicity was assessed after baseline and Months 1 and 3 for both groups. No significant immune differences between the control and yogurt treatment group were observed for concanavalin A, phytohemagglutinin, pokeweed mitogen, interleukin-2, or cytotoxicity. In conclusion, three months of yogurt consumption did not enhance ex vivo cell-mediated immune function in young women.

Survey of the conjugated linoleic acid contents of dairy products.

The objective of this research was to determine the content of conjugated linoleic acid, an anticarcinogen, in dairy products. Fifteen cheeses, three fermented dairy products (other than cheeses), and four fluid milk products (two brands for each product) were included in the survey. Total lipids, fatty acids, protein, moisture, and titratable acidity were also measured to determine the relationship between the content of these constituents and conjugated linoleic acid content. The conjugated linoleic acid content of cheeses ranged from 3.59 to 7.96 mg/g of lipid. Blue, Brie, Edam, and Swiss cheeses had significantly higher conjugated linoleic acid content than the other cheeses. Sharp Cheddar cheeses tended to have higher conjugated linoleic acid content than the medium Cheddar cheeses, but the increase was not significant. The conjugated linoleic acid content of the other fermented dairy products ranged from 3.82 to 4.66 mg/g of lipid, and cultured buttermilk had the highest content. The conjugated linoleic acid contents of four fluid milks ranged from 3.38 to 6.39 mg/g of lipid and were not significantly different from one another. Multiple linear regressions of conjugated linoleic acid content and the total fatty acid content indicated a relationship between conjugated linoleic acid content and the content of precursors and intermediates of conjugated linoleic acid formation, including linoleic and oleic acids.

Inhibitory effect of conjugated dienoic derivatives of linoleic acid and beta-carotene on the in vitro growth of human cancer cells.

The effects of physiologic concentrations of conjugated linoleic acid (CLA) and beta-carotene were assessed on human (M21-HPB, malignant melanoma; HT-29, colorectal; MCF-7, breast) cancer cells. The incubation of cancer cells with CLA showed significant reductions in proliferation (18-100%) compared to control cultures. M21-HPB and MCF-7 cell mortality was dose- and time-dependent. beta-Carotene was inhibitory to breast cells only. MCF-7 cells supplemented with CLA incorporated significantly less [3H]leucine (45%), [3H]uridine (63%) and [3H]thymidine (46%) than control cultures. M21-HPB and HT-29 cells supplemented with CLA incorporated less [3H]leucine (25-30%). These in vitro results suggest that CLA and beta-carotene may be cytotoxic to human cancer cells in vivo.

Effects of pH and Water Activity on Microbiological Stability of Salad Dressing.

The water activity and pH of an experimental starch-based salad dressing were varied to evaluate inhibitory effects on microorganisms selected from groups known to be principal dressing spoilage agents. Dressing samples were inoculated with Lactobacillus fructivorans , Zygosaccharomyces bailii , or a yeast isolated from a spoiled commercial salad dressing. Both yeast and L. fructivorans displayed a minimum growth pH of approximately 3.55 to 3.60. The minimum aw observed was 0.89 for yeast growth and 0.91 for L. fructivorans . Combinations of aw and pH which imparted microbial stability without use of preservatives are described.

Effect of vitamin A deficiency on mammary gland development and susceptibility to mastitis through intramammary infusion with Staphylococcus aureus in mice.

Weanling mice were fed 0 or 150 micrograms retinol equivalent/kg of diet for 5 weeks, were bred, and allowed to complete gestation. On day 3 of lactation, all mice were separated from their litters for 1 hour and were then anesthetized. The 4th right or left mammary gland was inoculated with 0.1 ml of S Aureus (10(10) colony-forming units/0.1 ml). Exactly 24 hours after inoculation, the mice were euthanatized and the mammary glands were removed and fixed for histologic evaluations. Vitamin A-deficient dams had smaller litter size and lower liver stores of vitamin A; however, deficiency was not severe enough to produce external signs of vitamin A deficiency in the dams. Morphologic studies showed large areas of adipose tissue, greatly reduced ductal and lobule-alveolar development, and decreased total secretory activity in mammary glands from vitamin A-deficient females. On the other hand, mammary glands from vitamin A-supplemented mice had extensive lobule-alveolar development and highly distended alveoli. Extensive necrosis of alveolar tissue was observed in staphylococcus-infused mammary glands of all mice. Large numbers of leukocytes and cell debris were present in the lumen of alveoli and ducts. However, mammary glands from vitamin A-deficient females had more extensive pathologic damage compared with corresponding glands from vitamin A-supplemented mice. Results indicted that vitamin A-deficient mice had reduced mammary development and increased pathologic damage to the mammary gland after intramammary challenge with staphylococcus.

Effect of dietary vitamin A on resistance to experimental Staphylococcus mastitis in mice.

Weanling mice (118) were fed a purified diet free of vitamin A for 3 wk and subsequently assigned to diets containing 10, 100 (4000 IU vitamin A/kg diet), or 300% of National Research Council recommended vitamin A. After 3 wk on the treatment diet all mice were bred and allowed to complete gestation. At 24 h postpartum, the left fourth abdominal mammary gland of each mouse was inoculated with Staphylococcus aureus (10(8) cells in .1 ml of saline/gland), and mammary gland infection was observed daily for 6 consecutive days. Liver vitamin A content was lowest in mice for 10% and highest for 300%. However, mice fed 10% showed normal growth and reproduction by small treatment differences in body weight changes, litter size at birth, and average pup weight. Mice fed 10 and 100% vitamin A showed more severe mammary gland inflammation after intramammary inoculation as opposed to mice fed 300%. Severity of mastitis in mice fed 100% vitamin A was similar to 10%. The number of mice classified as mastitic was also similar between 10 and 100% on days 1 and 2 postinoculation; however, on day 3 postinoculation mice fed 100% had a lower incidence of mastitis as opposed to 10%. Severity of mammary inflammation on days 4 through 6 were similar to those on day 3. Results showed a protective effect of dietary vitamin A supplementation against experimental Staphylococcus aureus mastitis in mice.

Impedance Measurements in Raw Milk as an Alternative to the Standard Plate Count 1.

Electrical impedance, using the Bactometer 32, was evaluated as an alternative method to the Standard Plate Count (SPC) to determine the initial microbial count of raw milk samples. The raw milk samples were obtained from farm bulk tanks on commercial dairy farms. Analyses were started within 24-36 h after collection. The impedance method was used to evaluate the samples as raw milk, raw milk plus yeast extract, raw milk given preliminary incubation (18 h at 13 C) or raw milk given preliminary incubation plus yeast extract. The yeast extract (1% final concentration) was added after the milk was placed in the module wells. The geometric mean SPC of each of these four groups was 4.51, 4.37, 4.96 and 5.14, and the corresponding mean detection times with Bactometer 32 were 10.13, 8.80, 8.28 and 6.11 h, respectively. The correlation coefficient of detection time to SPC was -0.77, -0.88, -0.78 and -0.79, respectively, for the four sample groups. When specific detection cut-off times (approximately 7 h) were selected and a maximum SPC of 100,000 CFU/ml was selected, 85.2%, 97.2%, 81.0% and 83.6%ofthe samples in the above four groups were correctly classified.

Antimicrobial Effect of Butylated Hydroxyanisole and Butylated Hydroxytoluene on Staphylococcus aureus 1.

The antimicrobial effect of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on three enterotoxigenic strains of Staphylococcus aureus in Brain Heart Infusion broth (BHI) was evaluated by turbidity measurements. Also, the interaction of these compounds with pH and NaCl on growth of S. aureus strain 100 was measured. Inhibition of S. aureus growth increased with an increase in the concentration of BHA and/or BHT. Complete inhibition of S. aureus growth occurred in BHI with 1.12 µmole of BHA/ml or 0.70 µmole of BHT/ml as well as with a combination of 0.25 µmole of both BHT and BHA/ml. Inhibition of S. aureus growth by BHA or BHT was substantial at pH 7.0 and with 2% NaCl. When 0.84 µmole or greater of BHA/ml and 0.47 µmole or greater of BHT/ml were added to BHL, growth of S. aureus 100 was inhibited to the extent that enterotoxin A could not be detected after 24 h of incubation.

Effect of Neutral Fats and Fatty Acids on Aflatoxin Production 1.

The influence of neutral fats and fatty acids on aflatoxin production by Aspergillus flavus (ATCC 15546) was investigated using a chemically defined medium (glucose-salts-amino acids). The fat-fortified medium was inoculated with A. flavus spores and incubated at 28 C; samples were solvent-extracted at 3-, 6-, 9-, and 14-day intervals and aflatoxin content quantitated fluorometrically. Increasing concentrations of tricaprylin (15% >10% >5%) repressed aflatoxin G2 synthesis more than B1 synthesis as compared to the control. Maximum concentrations of G1 and B1 were attained within 3 to 6 days and then declined. Increasing amounts of tricaprylin had little influence on B1 degradation following 3 days of incubation whereas G1 degradation was pronounced after 3 days. Tristearin fortification of the medium produced results comparable to those obtained with tricaprylin. Within the 14-day incubation period, G1 degradation rates exceeded those of B1 in both the control and fortified samples. As compared to the control, both the 15% linoleic acid and the 15% stearic acid fortification of the medium repressed B1 and G1 synthesis; however, the difference became less pronounced with incubation time. The 15% stearic acid fortification facilitated greater B1 yields than the 15% linoleic acid until the 9th day at which time B1 accumulation in the linoleic acid fortification surpassed that of the stearic acid. The G1 level in the 15% stearic acid-fortified medium attained 1300 µg within 3 days and declined to a trace at 14 days. Aflatoxin G1 synthesis in the 15% linoleic acid-fortified medium was completely repressed throughout the entire incubation period.

Growth and Enterotoxin A Production by Staphylococcus aureus in Fluid Dairy Products 1.

Staphylococcus aureus strain 100 grew better in skim milk and whole milk (3.5% fat) than in half and half (10.5%), and whipping cream (30% fat) at 37 C. Enterotoxin A production was 1.14, 0.88, 0.24, and 0.18 µg per 100 g of skim milk, whole milk, half and half, and cream, respectively. Sufficient cell numbers were not obtained for enterotoxin production after 16 h at 22 C in these same media.

Thermal resistance of pseudomonas fragi in milk containing various amounts of fat.

Similar populations of Pseudomonas fragi were grown at 25 C for 20 hr or at 7 C for 7 days in milk containing 0, 10, and 20% fat; they were then heated at 48, 50, and 52 C in milk containing 0, 10, and 20% fat. After inoculation, the heating medium contained 2.1 x 10(6) to 6.9 x 10(6) organisms per milliliter. The P. fragi cells grown in skim milk had greater thermal resistance (D(52) = 3.0 to 3.1) than those grown in milk containing fat (D(52) = 1.9 to 2.5). The organisms grown at 7 C for 7 days in milk containing 10% fat were more resistant (D(52) = 3.0) than those grown in the same medium at 25 C for 20 hr (D(52) = 2.0). The presence of 0 to 20% milk fat in the heating medium had no apparent effect on the thermal resistance.