摘要:

Through the years various factors have been implicated in the pinking of cooked poultry and pork. The problem usually appears randomly and mysteriously disappears. Two of the most prominent precursors for the defect appear to be the presence of extraneous residual nitrates/nitrites and high cytochrome c levels.

ISSN:8755-9129    

DOI:10.1080/87559129409541003

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The flavors produced by stewing, broiling, or roasting make meat one of the most popular items in the human diet. No “key” compounds are responsible for meat flavors. However, protein degradation appears essential to the development of meat flavor precursors whose interactions are responsible for characteristic meat flavors. This review examines simulated meat flavor systems based on the protein degradation products produced by acid hydrolysis using strong mineral acids, yeast autolysis, and enzyme degradation of natural meat proteins by pure proteinases. In addition, the contributions to meat flavor made by heating protein hydrolysates in the presence of sugars and organic sulfur compounds are reviewed. This paper also describes the work in applied meat flavor research carried out in the former East Germany.

ISSN:8755-9129    

DOI:10.1080/87559129409541004

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A worldwide shortage of calf rennet for cheese production has existed for several decades. Bovine pepsin and to a certain extent porcine pepsin and plant coagulants have been used as rennet substitutes, but these have not been commercially successful owing to their extensive proteolytic nature and other inherent drawbacks. Investigations to develop other alternatives have resulted in the introduction of various microbial coagulants which have found markets in several countries despite certain shortcomings when compared with traditional calf rennet. However, in some countries, microbial coagulants have not been accepted for regular cheese manufacture because they are believed to result in a reduced yield and a lower quality product; this is particularly applicable to cheddar cheese manufacture. Immobilization of proteases for milk coagulation has received renewed thrust; this may convert renneting of milk to a continuous operation. However, this technique has yet to be applied on an industrial scale; such a process is not likely to be successful since immobilized enzyme technology is dependent on the ability of a small, rapidly diffusing substrate to move quickly around the immobilized enzyme. In contrast, casein micelles are large and diffusion is slow, so the proteolysis rate is very slow. Microbial rennets offer an attractive target for genetic engineers since it may be possible to alter their structure/function characteristics to match those of calf rennet; application of site‐directed mutagenesis could be particularly rewarding. The term “calf rennet,” in the cheese industry, generally refers to an enzyme extract obtained from the fourth stomach (abo‐masum) of 10‐ to 30‐day‐old calves and used to coagulate milk for cheese production. The purified milk‐clotting enzyme present in crude rennet preparations is known as “rennin” or “chymosin.” The designation “chymosin” is now recommended in the international enzyme nomenclature (renin is associated with hypertension and is derived from the kidney). Calf rennet is referred to as “animal rennet” frequently, the term “chymase” appears in the older literature as a synonym for rennet. In more general usage, however, any milk‐clotting enzyme preparation yielding a relatively stable curd is designated as rennet. Christian Hansen is credited with the first industrial production of rennet in 1874 (1). This enzyme was called chymosin (EC 3.4.23.4); it belongs to the group of aspartic proteases and is the standard against which all other types of milk‐clotting enzymes are compared. Since the origin of cheese production, the manufacturing process has always needed soluble enzymes to clot the milk; it has been adapted to the properties of calf rennet, an essential enzyme for this purpose. Rennet coagulates milk rapidly at its natural pH with little further degradation of the milk proteins. The zymogen, prorennin, is converted to chymosin at pH below 5.0, but optimally at pH 2.0 (2). Chymosin, a strong protease, has been crystallized (3) and detailed crystallographic studies of the enzyme have been reported by Bunn et al. (4). Besides a slightly high proteolytic activity, another disadvantage of this enzyme is that it is extracted from the abomasum of the unweaned calf. As the calf ages, chymosin is replaced by pepsin, although in cattle, the secretion of chymosin never comes to a complete stop. Although pepsin can clot milk, it has a tendency to result in higher fat losses because the curd formed has a more open, looser structure than that formed with chymosin; the cheese produced also has a softer body than desired. Pepsin and a commercial product under the trade name Metroclot (5, 6) have, however, been used for the production of a variety of cheeses in the past. The kinetic properties and amino acid composition of chymosin and pepsin have been extensively studied. There is more or less a consensus of opinion in favor of chymosin as the enzyme for cheese making; presently three companies are producing calf chymosin through recombinant DNA technology. The cloned chymosin preparations produced by different microorganisms have been tested in various countries for cheese manufacture. No major differences could be detected among cheeses made with cloned chymosin and those made with the natural enzyme. This review describes the past, present, and future status of rennet substitutes utilized as milk coagulants and applications of modern biological tools to strain improvement and process development.

ISSN:8755-9129    

DOI:10.1080/87559129409541005

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Rapid methods and automation in microbiology are dynamic fields and are constantly moving forward in helping to solve applied microbiology and food safety issues. This article is a review of the current development of this field in the areas of sample preparation, alternative methods for viable cell counts, new methods for estimation of microbial populations and biomass, and new and novel techniques. This article should be of interest to all scientists concerned with the current development of rapid methods and potential application of these techniques in their daily work. The article addresses the basic principles of rapid methods and specific applications of methods, and provides an updated reference list for further investigations by readers.

ISSN:8755-9129    

DOI:10.1080/87559129409541006

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

BIOACTIVE VOLATILE COMPOUNDS FROM PLANTS. Roy Teranishi, Ron G. Buttery, and Hiroshi Sugisawa, editors. ACS Symposium Series 525. American Chemical Society, Washington, DC, 1993, 375 pages, $79.95.

ISSN:8755-9129    

DOI:10.1080/87559129409541007

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129409541008

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129409541002

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor