在线观看亚洲精品专区-在线观看亚洲免费-在线观看亚洲免费视频-在线观看亚洲欧美-欧美freexxx-欧美free嫩交video

食品伙伴網服務號
 
 
當前位置: 首頁 » 專業英語 » 專業知識 » 正文

食品微生物 Chapter 2: Basic aspects

放大字體  縮小字體 發布日期:2005-06-01

Diversity of microbial Life
There is considerable diversity in water and food borne microorganisms which are capable of causing human disease. Although bacteria have been the main focus of attention it should be recognised that this is primarily due to the relative ease with which these organisms can be cultured compared with viruses. In fact the small round structured viruses which caused such considerable numbers of viral gastroenteritis cannot yet be cultured in the laboratory. A review of waterborne diseases from 1991-2000 in the USA has been released and has copious amounts of information (URL waterborne diseases USA)). 

Bacterial cell structure
It is important to understand at least the basic structure of the microbial cell wall. The difference in structure between Gram negative and Gram positive organisms explains the staining reactions and this is a basic technique used in microbiology. The detailed structure of the outer cell membrane of Gram negative organisms (Fig 2.1 and 2.2 , p14 and 15) demonstrates the usefulness of serology in identifying isolates, especially in epidemiological studies. If you do not understand the ’O157:H7’ term used for certain pathogenic strains of E. coli then study again the cell wall structure. 

Microbial growth curves
Bacterial multiplication is often represented by the classic growth curve (Fig 2.3, p17). The curve is divided into several phases; lag, exponential (or logarithmic), stationary and death. To review how bacteria grow you can visit the Cells Alive Web site.

It is important to understand the factors affecting these phases as they determine whether an organism is capable of growing in food. Ultimately it may be possible to accurately predict the extent of microbial growth and this topic is covered in more detail later. An example of predictive microbiology is Microfit (UK) for which you enter in your viable counts at known time intervals and the programs predicts the starting inoculum size, lag period, doubling time and maximum number of cells.

Rates of microbial death, D and Z values
There are a number of terms used to describe microbial death: 

D value 
Z value 
P value 
F value 
The D value is the ’decimal reduction’ time. This is the time required at any given temperature to reduce the viable count by 1 log order (in other words 90%). Although ’maths’ might not be your forte, determining D and Z values is not too difficult. There are some examples given (Fig 2.4, p19) and basic data to try out for yourself at Exercises (Temperature treatment) of the Blackwell’s host site. You can then compare your results with a comprehensive summary of published values (Table 2.3, p21-22). 


Food additives and contact materials
I have not majored on food additives nor contact materials (active packaging) in the books, but here are some useful web sites if you are interested. I’ll work on this matter as time allows, especially since I’m on an EU FSA scientific panel for this topic.

EAFUS (FDA-CFSAN) database 
JECFA 61st meeting (10-19th June 2003, ftp file) 
EU guidelines concerning food additives 
EU administrative guidance 
Nutrient sources 
Enzymes 
Flavourings 
Food contact materials 
Food contact materials guidelines (121 pages) 
Synoptic document (388 pages) 

Intrinsic and extrinsic factors affecting microbial growth
Factors (web site) affecting microbial growth can be divided into two categories; intrinsic and extrinsic (Table 2.6, p25). These can be reviewed at the FDA (USA) Bad Bug Book. Water activity, pH and temperature are the most important factors However water activity and pH are not always that easy to measure. The reason being that water activity is not the same as moisture, it is the amount of ’unbound’ water that is available to the microorganisms. Additionally food being so heterogeneous means that different regions of a food will have different water activity values and should not be simply ’averaged’. Similarly the pH of a food (web site) can vary from zone to zone.

A general site covering can be found at this Web site.

To test your knowledge of microbial growth factors try these quizzes: 

Growth parameters 
pH values of foods 
Predictive Microbiology
Since bacterial growth follows a mathematical pattern it is possible to develop computer programs which will predict the rates of bacterial growth and death under defined environmental conditions (ARTICLE). A number of computer software programs are available, such as: 

Food Micromodel (UK) 
Pathogen Modeling Program (PMP) (USA) 
Combase; Common database for foodborne bacteria 
Since the Pathogen Modeling Program can be freely downloaded from the USDA this program has been used for demonstration purposes. The latest version is 6.1. Although this is a more recent version than the one I used for the book, the main difference only the updated use of the WindowsTM display environment and not the data generated.

Once you have learned how to use the program try the examples given at Exercises (Predictive Modeling) of the Blackwell’s host site. 

更多翻譯詳細信息請點擊:http://www.trans1.cn
 
[ 網刊訂閱 ]  [ 專業英語搜索 ]  [ 加入收藏 ]  [ 告訴好友 ]  [ 打印本文 ]  [ 關閉窗口 ] [ 返回頂部 ]
分享:

 

 
推薦圖文
推薦專業英語
點擊排行
 
 
Processed in 0.070 second(s), 14 queries, Memory 0.9 M
51La
主站蜘蛛池模板: 欧美五月| 国产毛片农村妇女aa板 | 4388x17亚洲最大成人网 | 正在播放国产巨作 | 国产在线免 | 久久的色偷偷 | 两人性潮高免费视频看 | 年轻护士3的滋味 | 日本亚洲欧美国产日韩ay高清 | 久青草视频免费视频播放线路1 | 花怜write. as | 免费一区二区三区 | 美女网站在线观看视频18 | 成人综合婷婷国产精品久久免费 | 18年大片免费在线 | 国产高清一级视频在线观看 | 男人扒开美女尿口无遮挡图片 | 人人洗澡人人洗澡人人 | 在线免费看黄视频 | 亚洲欧美高清在线 | 天天做天天摸天天爽天天爱 | 五月激情网站 | 成熟女性毛茸茸xx免费视频 | 天天怕夜夜怕狠狠怕 | 黄色一级大片视频 | 欧美一区二区三区在线 | 日韩一级视频免费观看 | 你懂的在线视频播放 | 神马影视午夜 | 女同毛片免费网站 | 日韩毛片免费在线观看 | 五月天六月丁香 | 四虎在线免费视频 | 狠狠色丁香婷婷综合小时婷婷 | 在线免费看高清视频大全 | 爱爱欧美 | 在线观看www妖精免费福利视频 | 色五阁| 午夜影院在线观看 | 又长又大又粗又硬3p免费视 | 在线中文天堂 |
微信二维码