Natholyn D. Harris

Musty Aroma Compounds Produced by Selected Molds and Actinomycetes on Agar and Whole Wheat Bread

Musty aroma compounds produced by cultures of Streptomycetes odorifer , Streptomycetes griscus , Penicillium roqueforti , Aspergillus flavus , Aspergillus niger , and Botrytis cineria when grown on agar and whole wheat bread were isolated and identified using headspace entrainment and GC-MS analysis. Actinomycete cultures produced the most intense musty aromas, which were attributed to the presence of 2-methylisoborneol and geosmin, whereas P. roqueforti and B. cineria cultures produced an overall musty-fruity odor quality caused by the combination of 2-methylisoborneol and 8-carbon alcohols and ketones. Several musty compounds in the cultures were not identified including an intensely musty, cat-like aroma compound produced by A. flavus . Seven musty aroma-type categories are proposed to assist in defining musty taints produced by microorganisms in food and feedstuffs.

Inhibitory Effect of Lactobacillus bulgaricus on Psychrotrophic Bacteria in Associative Cultures and in Refrigerated Foods

The purposes of this study were two-fold: (a) to determine growth inhibition of Pseudomonas fragi , Achromobacter liquefaciens and Staphylococcus aureus due to Lactobacillus bulgaricus in associative cultures, and (b) to evaluate use of L. bulgaricus to control growth of natural flora in refrigerated tuna and potato salads and ground beef. The antagonistic effects of three concentrations of L. bulgaricus were studied after storage for 5 d at 6°C. Data were analyzed using a Student t Test. Pronounced inhibition was observed toward test organisms. Total growth inhibition of P. fragi and A. liquefaciens was attained due to the third level of L. bulgaricus (1.4 × 106 - 5.7 × 106 cells/ml). Natural flora in test foods were also greatly inhibited. Total growth inhibition of bacteria was attained in potato salad due to the third level of L. bulgaricus (3.9 × 106 cells/g). It was suggested that organic acids and hydrogen peroxide were partially responsible for the inhibition.

Oxidation of cholesterol in commercially processed cow's milk

Pasteurized whole milk, ultra-high temperature heated milk, canned evaporated milk, skim milk and instant nonfat dry milk were analyzed for presence of oxidized cholesterol compounds. Effects of heating whole milk and storage of whole milk lipid extracts were also examined. Analytical thin-layer chromatography data indicate that cholesterol in liquid milk was stable during commercial pasteurization, sterilization and evaporation. However, instant non-fat dry milk contained 7-hydroxy-cholesterol. Heating whole milk for 12 h at 85°C did not produce oxysterols, but GC-MS analysis indicate that storage of whole milk lipids may have produced steroidal ketones.

Effectiveness of oil carrier for antioxidants in fish concentrate

Two levels of antioxidants, 0.02% and 0.002%, were added to a concentrated fish product. Two ways of incorporating antioxidants into fish oil were studied. The oxidation rate of the samples was measured by using an oxygen analyzer and the thiobarbituric acid test. The concentrated fish prepared from fresh mullet was stored for 0 hr, 48 hr, and 96 hr. The use of antioxidants in a vegetable oil carrier did significantly slow the breakdown reaction of fish oil and lowered the oxidation rate of the sample. When vegetable oil was used to serve as an antioxidant carrier, the high level of antioxidant (0.02%) stabilized the fatty product more efficiently than the lower level (0.002%) did. At the level of 0.02% antioxidants, using soybean oil to serve as antioxidant carrier, the fish product was quite stable during storage under the conditions of this study.