EFFECT OF TEMPERATURE ON THE QUALITY OF MUSCLE FOODS

Heating/cooking alters a food's flavor precursors yielding a product with a new pleasing taste. While heating to a high temperature destroys most pathogens thereby enhancing safety, it also alters the food's flavor by changing the precursors and final flavor components of the food. For example, heating meat to above 77C not only destroys many foodborne pathogens but also causes major changes in level of desirable flavor precursors. Many of these changes are due to alteration in activity of endogenous hydrolytic enzymes as well as heatinduced structural and functional changes. Heating induces differential production and distribution of flavor principles and flavor precursors. A secondary effect of temperature on food-flavor is its direct affect on analysis of flavor volatiles, i.e., high purge temperatures bias analysis of flavor components by production of new and destruction of existing components. This paper focuses on the structure/function relationship of meat proteins and their proteolytic products as they relate to meat flavor and end-point cooking temperature. The paper also will address the effect of analytical temperature on meat flavor analysis.     

酶制剂对国产面粉烘培品质的影响

主要研究4种酶制剂对国产面粉烘焙品质的影响.研究结果:国产面粉通过添加酶,使其烘焙品质有了明显改善,制作的面包比容、弹性、黏聚性增加;硬度和咀嚼度降低,经改良的国产面粉能制作出高品质面包.     

EFFECT OF LIPASE ENZYME ON THE RIPENING OF WHITE PICKLED CHEESE

The effect of addition of pregastric lipase enzyme on the accelerated ripening of white pickled cheese was investigated. Commercial pregastric lipase was added to milk before rennet addition at a level of 0,5, 8, 11 g per 100 L of milk and cheeses were made from this milk. Total solids, fat, total nitrogen, salt, titratable acidity, pH and free fatty acids (C₂-C_18:1) were analysed in the samples during 1–90 days of ripening period at 15 days intervals. Total solids, fat, total nitrogen, salt, titratable acidity, and pH of cheeses slightly increased during the ripening period. Free fatty acids and volatile free fatty acid contents in cheeses made from pregastric lipase added milk were affected by pregastric lipase and their contents were increased significantly (P<0.01) during the ripening period. Particularly, when cheese had a high level (11 g per 100 L milk) pregastric lipase, the amounts of butyric, caproic and caprylic acids in white pickled cheese were quite high. The relative amounts of volatile free fatty acids varied with storage time and pregastric lipase levels.     

不同酶种及助剂对酶活影响的研究

几种生物酶应用于棉织物前处理．采用DNS法和紫外分光光度法研究了生物酶的专一性和不同酶种及助剂对酶活的影响．结果表明，淀粉酶、纤维素酶及果胶酶均具有良好的专一性，不同种类酶之间及与所选用的非离子助剂均有较好的相容性，为混合酶前处理的一浴法研究提供了理论基础．     

超临界状态对酶的影响研究进展

超临界状态下的酶催化反应是近年来生物工程研究的新领域。重点从超临界状态对酶的稳定性和活性的影响、超临界状态下酶的纯化及其失活机制等方面进行了综述。     

TRIALS ON THE ANTIBACTERIAL EFFECT OF GLUCOSE OXIDASE ON CHICKEN BREAST SKIN AND MUSCLE

Use of glucose oxidase as a possible means to inhibit microbial growth on processed poultry was evaluated. Muscle and skin sections of chicken breast were inoculated with Pseudomonas spp. or Salmonella typhimurium and subjected to either: (1) 60 s dip in 2 units of glucose oxidase without glucose supplementation or (2) 60 s dip in 2 units of glucose oxidase with 4% glucose supplementation. Control groups were dipped in sterilized, distilled water. The Pseudomonas and Salmonella populations were determined for each section. Neither enzyme treatment reduced the initial Pseudomonas or Salmonella populations nor did the treatments inhibit the growth of Pseudomonas during the storage period . Salmonella was inhibited by the low temperature. Therefore, a glucose oxidase enzyme treatment has little potential for extending the shelf-life of chicken .     

EFFECT OF POSTMORTEM AGING ON CHICKEN MUSCLE LIPIDS

Neutral lipids of fresh chicken breast muscles are shown to be triglycerides, sterols and sterol esters with only traces of mono- and diglycerides and free fatty acids. Phospholipids include measurable quantities of phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl inositol, phosphatidyl serine, sphingomyelin, diphosphatidyl glycerol, lysophosphatidyl choline and lysophosphatidyl ethanolamine. Fatty acid analyses of several of the lipid fractions are also included. Decreases in phosphatidyl choline and phosphatidyl ethanolamine coupled with increases in lysophosphatidyl choline, lysophosphatidyl ethanolamine and free fatty acids after 48 hr postmortem in the cold indicate phospholipase A activity concurrent with other postmortem changes. The significance of the results is discussed.     

EFFECT OF REDOX AGENTS ON VISUAL CURE IN REFRIGERATED PICKLES1

Nonpasteurized-refrigerated cucumber pickles were treated with oxidants and reductants to determine their effects on development of translucence (cure) appearance and changes in cell wall pectic substances and protein of mesocarp tissue. Similar responses were obtained for different oxidants that inhibited curing and for different reductants that accelerated curing. Calcium did not affect curing when applied alone or in combination with the redox agents. Levels of pectic substance fractions were not altered in cell walls from mesocarp tissue cured by sodium metabisulfite (SMBS), and only minor changes occurred in cell walls from mesocarp tissue inhibited from curing by hydrogen peroxide. Levels of protein and sulfhydryls were altered by the redox treatments. Peroxide protected against loss in protein content and sulfhydryl levels were substantially lowered. The reductant SMBS enhanced the amount of sulfhydryls and reduced disulfide groups. Therefore, changes in protein characteristics appear to be related to curing of pickle mesocarp tissue. Further studies on curing will include redox agents that were found to regulate the curing process.