Virginia Polytechnic Institute and State University

Susan Duncan, Dairy and Sensory Evaluation

Bill Eigel,                Food Biochemistry

Joe Marcy:               Food Processing

Merle Pierson: Food Microbiology

 Sean O’Keefe: Food Chemistry

Susan Sumner:   Food Safety

Walter Hartman:    Dairy Plant Manager whartman@vt.edu

Kim Waterman:  Dairy Chemistry    Kwater@vt.edu

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Effects of UV Irradiation on the Reduction of Bacterial Pathogens and

Chemical Indicators of Milk

This research was conducted by Kristen Matak (PhD, Food Science and Technology, 2004)

Consumer demand for fresher and minimally processed foods has brought about a movement to find effective, non-thermal processing technologies for the treatment of milk. The influence of temperature on bacterial reduction in UV irradiated milk was tested. Commercially processed skim, reduced fat (2%), and whole milk samples were inoculated with a naladixic acid resistant E. coli O157:H7 surrogate (ATCC 25922), maintained at 4 o C and 20 o C, respectively, and then exposed to a UV light dose between 5.3-6.3 mJ/cm 2 for approximately 1.5 sec using the CiderSure 3500 apparatus (FPE Inc., Macedon, NY). Bacterial populations before and after UV exposure were enumerated. Results indicated that processing temperature was not significantly related to bacterial reduction. Skim milk samples had a greater bacterial reduction, regardless of processing temperature compared to reduced fat milk and whole milk samples. Solids such as milk fat, protein, lactose and minerals in the milk have a greater effect over bacterial reductions than processing temperatures.

Traditional goat cheeses are produced using unpasteurized milk, which increases the food safety concerns for these types of products. Fresh goat's milk was inoculated to 10 7 cfu/ml with Listeria monocytogenes (L-2289) and exposed to UV light using the CiderSure 3500 apparatus. Inoculated milk was exposed to an ultraviolet dose range between 0 and 20 mJ/cm 2 to determine the optimal UV dose. A greater than 5-log reduction was achieved (p < 0.0001) when the milk was processed 12 times for a cumulative exposure time of roughly 18 sec and a cumulative UV dose of 15.8 +/- 1.6 mJ/cm 2 . The results of this study indicate that UV irradiation could be used for the reduction of L. monocytogenes in goat milk.

Organoleptic properties of goat milk treated with UV technology were assessed. Olfactory studies were conducted and a highly significant difference was observed between the odor of fresh goat milk and UV processed milk. The extent of lipid oxidation and hydrolytic rancidity was measured by thiobarbituric acid reactive substances (TBARS) and acid degree values (ADVs). Results indicated that as the UV dose increased, there was a significant increase in TBARS values and ADVs of the milk samples. Milk samples were processed using the UV processor under the same conditions as previously described but without exposure to the UV source to determine if agitation from pumping was causing off-flavors by way of hydrolytic rancidity. The ADVs from these samples increased at the same rate as the UV irradiated samples; however, sensory studies indicated that the increase of free fatty acids (FFA) was not enough to cause detectable off-odors in the milk. Solid phase microextraction and gas chromatography (SPME-GC) was utilized to quantify the production of volatile compounds that were formed due to UV processing. Pentanal, hexanal and heptanal were identified after as little as 1.3 mJ/cm 2 UV dose. Peak areas were measured and analyzed after 7.8 mJ/cm 2 and 15.6 mJ/cm 2 and were determined to increase significantly as UV dose increased (p < 0.05). The chemical analyses supported the findings from the sensory studies. The outcome of this research showed that UV irradiation at the wavelength 254 nm was detrimental to the sensory quality of milk. When developing novel technologies, safety, sensory properties and consumer acceptance are important factors for the success of the technology.

HOT TOPICS AND DAIRY ISSUES

  Cheese Sales Approach $40 Billion

Americans are developing broader tastes in cheese and most of the cheese they are eating is made in the U.S. , reports a new study sponsored by the California Milk Advisory Board (CMAB). Trends toward increased consumption of U.S. produced cheeses and growth of specialty cheeses were observed. The study, “U.S. Cheese Consumption Trends, 1994-2003,” reports that the steady growth in natural cheese consumption that the U.S. has seen for more than two decades is being supplied by domestic production and not imports. Americans consumed 8.8 billion pounds of cheese in 2003 with a total market value of $39.9 billion, according to the study.

  Milk and Ovarian Cancer

Researchers in Sweden have been tracking more than 60,000 women for 13 years in an attempt to gather evidence linking milk consumption to an increased risk of ovarian cancer. This is one of the biggest studies to be conducted since the possibility of the link was introduced in the late 1980s. Researchers found that milk and yogurt appeared to increase chances of ovarian tumor, but other dairy products like cheese, butter and ice cream did not. It was emphasized that the study was still ongoing. The Swedish team, from the Karolinska Institute in Stockholm , investigated possible links on their own soil because Sweden has one of the highest rates of ovarian cancer in the world and also consumes large quantities of dairy products.

One theory is that galactose, a sugar that is naturally present in milk, is responsible. Scientists believe that too much galactose is toxic to ovaries and can prompt the body to produce certain hormones that allow serious types of ovarian cancer to develop.

Women who have been through menopause, have never had children, or have a family history of the disease are most at risk.

Exports to Chile Rise and U.S. Butter Imports Increase

USDA data shows that U.S. exports of cheese and ice cream to Chile more than doubled in the first 6 months since the new U.S.-Chile Free Trade Agreement has been in effect. From January to June 2004, USDA reports more than 190% growth in export volume over the first 6 months of 2003. U.S. exporters sent Chile $1.4 million worth of American cheese and $115,000 worth of ice cream. U.S. imports of Chilean dairy products are also greater than last year's, but to a lesser degree. Prior to the enactment of the new trade agreement, Argentina and Uruguay supplied one-half to two-thirds of Chile 's dairy imports. The U.S. dairy product exports were hindered by restrictions caused by differences in inspection regulations and grading standards, as well as a 6% tariff rate.

The National Milk Producers Federation (NMPF) charges that butter imports have jumped 89% over last year, and U.S. milk producers are very unhappy over rising imports of foreign butter. If imports rise to the safeguard level of 13,754 metric tons of butter, the U.S. is entitled to impose higher tariffs, and NMPF is urging USDA to immediately impose the higher tariffs as soon as imports reach that threshold.