R.J. Baer

Alteration of the Fatty Acid Content of Milk Fat

Milk fatty acid composition can be influenced by several factors, many of which are interactive. These include stage of lactation, seasonal variation, low milk fat syndrome, feeding, genetic variation, and changes in the energy status of the cow due to administration of bovine somatotropin. Utilization of feeding, genetic variation, and bovine somatotropin should produce a milk fat lower in saturated and higher in unsaturated fatty acids. This may be beneficial to consumers, as many health professionals are recommending diets lower in saturated fatty acids. Giving consumers the option of purchasing low saturated fatty acid dairy products may also assist in alleviating the current milk fat surplus in the dairy industry.

Influence of milk fat higher in unsaturated fatty acids on the accuracy of milk fat analyses by the mid-infrared spectroscopic method

An experiment was conducted to investigate the reliability of milk fat measurement by the mid-infrared spectroscopic method when analyzing milk fat containing greater than normal amounts of unsaturated fatty acids. Sixteen mid-lactation Holstein cows were divided into four treatments including a control (C), control with bovine somatotropin (C+), bovine somatotropin and added dietary fat from sunflower seeds (Sun+), or bovine somatotropin and added dietary fat from safflower seeds (Saff+). Milks were sampled weekly for 16 weeks (n=256). Unsaturated fatty acid percentages in milk fat were 25.0, 28.4, 39.6, and 37.9 for C, C+, Sun+, and Saff+ treatments, respectively. Milk fat percentages measured by the Mojonnier fat extraction and mid-infrared spectroscopic methods were 2.99, 2.97; 3.06, 3.01; 2.73, 2.56; and 2.86, 2.74 for C, C+, Sun+, and Saff+ treatments, respectively. Results indicate the mid-infrared spectroscopic method underestimates the fat content in milk which is higher in unsaturated fatty acids. Dairy producers feeding diets with added fat from unsaturated fat sources may be underpaid for milk fat content when the milk is analyzed by the mid-infrared spectroscopic method. A possible remedy for this problem may be to have milk plants calibrate the mid-infrared spectroscopic instrument with milk samples containing higher than normal amounts of unsaturated fatty acids in milk fat.

Effect of storage temperature on quality of light and full-fat ice cream

Ice cream quality is dependent on many factors including storage temperature. Currently, the industry standard for ice cream storage is -28.9 °C. Ice cream production costs may be decreased by increasing the temperature of the storage freezer, thus lowering energy costs. The first objective of this research was to evaluate the effect of 4 storage temperatures on the quality of commercial vanilla-flavored light and full-fat ice cream. Storage temperatures used were -45.6, -26.1, and -23.3 °C for the 3 treatments and -28.9 °C as the control or industry standard. Ice crystal sizes were analyzed by a cold-stage microscope and image analysis at 1, 19.5, and 39 wk of storage. Ice crystal size did not differ among the storage temperatures of light and full-fat ice creams at 19.5 or 39 wk. An increase in ice crystal size was observed between 19.5 and 39 wk for all storage temperatures except -45.6 °C. Coldness intensity, iciness, creaminess, and storage/stale off-flavor of the light and full-fat ice creams were evaluated at 39 wk of storage. Sensory evaluation indicated no difference among the different storage temperatures for light and full-fat ice creams. In a second study, light and full-fat ice creams were heat shocked by storing at -28.9 °C for 35 wk and then alternating between -23.3 and -12.2 °C every 24h for 4 wk. Heat-shocked ice creams were analyzed at 2 and 4 wk of storage for ice crystal size and were evaluated by the sensory panel. A difference in ice crystal size was observed for light and full-fat ice creams during heat-shock storage; however, sensory results indicated no differences. In summary, storage of light or full-fat vanilla-flavored ice creams at the temperatures used within this research did not affect quality of the ice creams. Therefore, ice cream manufacturers could conserve energy by increasing the temperature of freezers from -28.9 to -26.1 °C. Because freezers will typically fluctuate from the set temperature, usage of -26.1 °C allows for a safety factor, even though storage at -23.3 °C did not affect ice cream quality.

Microbiological Safety of Blue and Cheddar Cheeses Containing Naturally Modified Milk Fat

Milk containing naturally modified fat was obtained by feeding lactating dairy cows a Control diet and two experimental diets containing either extruded soybeans or sunflower seeds. Milk from cows fed the experimental diets contained higher levels of both long chain (C18-C18:2) and unsaturated fatty acids than the milk from cows fed the Control diet. Each milk was pasteurized, standardized to 3.6% milk fat, and inoculated with Listeria monocytogenes (strains Scott A and V7), Salmonella typhimurium and Salmonella senftenberg , before manufacturing into Blue or stirred-curd Cheddar cheeses. Populations of L. monocytogenes and Salmonella spp. were monitored during manufacture and aging using Oxford and Xylose Lysine Desoxycholate agars, respectively. During the manufacture of Blue and Cheddar cheese, and during the aging of Blue cheese, behavior of Salmonella spp. and L. monocytogenes in the experimental cheese was similar to the Control cheese. During aging of Cheddar cheese, the rate and extent of decline of Salmonella spp. and L. monocytogenes varied among the cheeses. Declines correlated with the accumulation of specific fatty acids, namely C12, C14, C18:1 and C18:2. These fatty acids were also found to be inhibitory to S. typhimurium and L. monocytogenes when incorporated into tryptic soy agar plates at 37°C. Therefore, the natural fat modification of Blue and Cheddar cheeses enhanced the safety of these cheeses.