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The effect of freezing and bacterial growth on the discoloration of beef was assessed by measuring myoglobin derivatives myoglobin (MB), oxymyoglobin (MBO(2)), and metmyoglobin (METMB) on the surfaces of fresh and frozen-thawed packaged beef cuts stored at 2 degrees C and analyzed after 0, 3, 6, 9, and 12 days of storage. MB, MBO(2), and METMB concentrations were measured spectrophotometrically. Frozen-thawed beef samples experienced less "blooming" (conversion of MB to MBO(2)) and more rapid discoloration than fresh cuts during storage. By day 3, >20% METMB was formed in the frozen-thawed samples, whereas the fresh samples reached this value after day 6 of storage. The rates of MB oxidation were similar (P > 0.05) for sterile and frozen-thawed inoculated (Pseudomonas fluorescens at a rate of 1.5 colony forming units/cm(2).cm(2) area) samples from day 0 through day 6 of storage. For storage periods of less than a week, bacterial growth is not a major cause of meat discoloration. After day 6, the high bacterial growth rate resulted in a rapid increase in METMB formation. Possible mechanisms for MB oxidation in frozen-thawed beef are suggested.

The study objective was to evaluate the effect of endocrine and mechanical (gel release) signaling on bovine mammary epithelial cell ultrastructure and gene expression. Cultures receiving only one stimulus demonstrated partially differentiated ultrastructure, which included abundant polysomes, limited rough endoplasmic reticulum, and absence of secretory products, whereas the 2 stimuli together induced a more complete lactogenic phenotype that included increased rough endoplasmic reticulum, abundant lipid droplets, and secretory vesicles containing casein micelles. The structural data indicated that although synthesis of milk components was initiated, the copious synthesis and secretion associated with stage II lactogenesis was not evident. Microarray analysis revealed that both prolactin and gel release independently regulated several genes linked to a wide array of cellular activities. In combination, they regulated fewer genes targeted to lactogenesis. Genes regulated by the combination treatment included claudin 7, multiple caseins, xanthine oxidoreductase, and several protein synthesis, packaging, and transport genes. Genes related to structural activity including keratin 15 (morphogenesis), alpha-spectrin (cell shape via actin cytoskeleton), and chitinase-like protein 1 (tissue remodeling) were up-regulated by the combination treatment as was the transcription factor Kruppel-like factor 2 (KLF-2). However, Snail 2, which down-regulates and inhibits tight junction components, was repressed in response to the combination treatment. These results suggest coordination between endocrine and physical signals at the genomic level that produces a more specific and targeted transcriptional response associated with stage I lactogenesis. A molecular pathway analysis of the differentially expressed genes revealed that genes regulating cell signaling were linked to those regulating cell structure and adhesion.

Niacin induces peripheral vasodilatation via prostaglandin D (PGD) and E (PGE) release by Langerhans cells in skin. We evaluated if niacin alone or in combination with PGD and PGE alters expression of heat shock proteins (HSP) 27 and 70. Bovine mammary epithelial cells (BMEC) were cast in collagen in 24‐well plates containing growth media (GM) composed of DMEM/F‐12, insulin, EGF, IGF‐I, BSA and antibiotics at 37°C, 5% CO2. Cultures grew into ductal structures with media changes at 48 hr intervals. On day 8 cultures were divided into Controls (C) receiving GM, GM with niacin (0.5, 1.0, or 10.0 mM), PGD2 (10 or 24 uM), PGD2 with PGE1 (both at 24uM) alone or in combination with niacin. Half were placed into incubators at 37°C (TN) and the remainder at 42°C (HS) for 8 h. At 0h and 8h, replicates were pooled, placed in TRIzol and stored at −80°C until extracted for RNA. Isolated RNA was reverse transcribed into cDNA. Expression of HSP's‐27 and 70 was measured by q‐ PCR. Addition of PGD increased HSP‐27 and 70 gene expression in HS, (P<.0001). Peak fold increases in HSP‐70 expression at 8 hr over time zero differed between C and PGD, (−2.4 vs. 9.3, P<.0001) and were greater for Hsp‐27 (−115 vs +10, P<.0001). Addition of PGE increased HSP‐27 and 70 expression compared to C and PGD alone (P<.05). We conclude that niacin with PGD or PGD+PGE alters HSP‐27 and Hsp‐70 gene expression in BMEC during HS.

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