第8章 专业英语翻译

1. fully the principles of food sanitation. One must understand the role of microorganisms in food spoilage and poisoning. Microorganisms are found throughout the natural environment. These microorganisms （also called microbes）cause food spoilage through ingestion of food，which contains microorganism's food borne infection because certain disease con microorganisms of public health concern.

3. Microorganisms are also important in connection with food sanitation because certain disease-producing microbes may be transmitted through food. The importance of sanitation practices is to combat the proliferation and activity of food spoilage and food poisoning microorganisms. The microorganisms most common to food are bacteria and fungi. The fungi，which are less common than bacteria，consist of two major microorganisms，molds and yeasts.

4. Molds are multicellular microorganisms with mycelial （filamentous）morphology. These microbes are also characterized by their display of a variety of colors and generally recognized by their mildewy or fuzzy，cotton like appearance. Molds can develop numerous tiny spores that are t found in the air and can be spread by air currents. These spores can produce new mold growth if they are transferred to a location that hears conditions conductive to germination.

5. Mold generally withstands greater fluctuation in PH than bacteria and yeasts and can frequently tolerate more temperature fluctuation. Although molds thrive best at or near a PH of 7.0，a PH range of from 2.0 to 8.0 can be tolerated at ambient temperature than in a colder environment，even though an acid to neutral PH is preferred. Molds thrive better at ambient temperature than in a colder environment ，even though growth can occur below 0℃。

6. Although mold growth is optimal at a water activity （Aw）of approximately 0.85，growth can and does occur below 0.80 .at an Aw of 0.90 or higher，bacteria and yeasts grow more effectively and normally utilize available nutrients for growth at the expense of molds. When the Aw goes below 0.90 molds grow more growth. Yeasts are generally unicellular and differ from bacteria in their larger cell size and morphology，and because they produce buds during the process of reproduction by division.

7. Like molds，yeasts can be spread through the air，or other means，and alights on the surface of foodstuffs. Yeast yeasts prefer an Aw of 0.90-0.94，but can grow below 0.90. These microorganisms grow best in the intermediate acid range；a PH of from 4.0 to 4.5 foods that highly contaminated with yeasts will frequently have a slightly fruity odor.

8. Bacteria are unicellular microorganisms that are approximately 1 \m in diameter with morphology variation from short and elongated rods （bacilli）to spherical or ovoid forms，Cocci are spherically shaped bacteria. Individual bacteria closely combine in various forms according to genera. Some sphere-shaped bacteria occur in clusters similar to a bunch of grapes （i.e.，staphylococci）。

9. Other bacteria （rod shaped of sphere shaped）are linked together to form chains （i.e.，streptococci）。Certain genera of sphere-shaped bacteria also are formed together in pairs （diploid formation；i.e.，pneumococci）or as a group of four （tetrad formation；i.e.，sarcinia），while other genera appear as an individual bacterium. Other bacteria possess flagella and are motile. Bacteria produce various pigments，which range from shades of yellow to dark pigments such as brown or black.

10. Certain bacteria have pigmentation of intermediate colors such as red，pink，orange，blue green，or purple. These bacteria cause food discoloration，especially among foods with unstable color pigments such as meat. Some bacteria also cause discoloration by slime formation.

Some species of bacteria also produce spores. The properties of which vary considerably. Certain spores are resistant of heat，chemicals，and other adverse environmental conditions.

11. Many of these spore-forming bacteria are thermophilic microorganisms，which produce a toxin that will cause food poisoning.

Methods of Killing Microorganisms

Before assessment of methods available for d3estruction of microorganisms，it is important to define death as applied to microorganisms. Microorganisms are considered dead when they cannot multiply，even after being in a suitable growth medium under favorable environmental conditions.

13.This concept differs from dormancy，especially of bacterial spores，since dormant microbes have not lost permanently the ability to reproduce as evidenced by eventual multiplication after prolonged incubation，transfer to a different growth medium，or some form of activation. Regardless of the cause of death，microorganisms follow a logarithmic rate of death.

14. This pattern suggests that the population of microbial cells is dying at a relatively constant rate. Deviations from this death rate can occur due to accelerated effects from a lethal agent （i.e.，sanitizers），effects due to a population mixture of sensitive and resistant cells，of with chain-or clump forming microflora with uniform resistance to the environment.

15. Heat

Application of heat has historically been the most widely used method of killing spoilage and pathogenic bacteria in foods. Heat processing has been considered a way to cook food products and destroy spoilage and pathogenic microorganisms. Therefore，extensive studies have been conducted to determine optimal heat treatment for destruction of microorganisms.

16. A measurement of time required to sterilize completely a suspension of bacterial cells of spores at a given temperature is thermal death time （TDT）。The value of TDT will depend upon the nature of the subject microorganism，number of cells，and factors related to the nature of the growth medium.

17. Another measurement of microbial destruction is decimal reduction time （D value），which is the time in minutes required to destroy 90% of the cells at a given temperature. Again the value depends on the nature of the microorganism，characteristics of the medium，and calculation method for determining the D value. This value is calculated for a period of exponential death of microbial cells （following the logarithmic order of death）。

18.The D value can be determined through an experimental survivor curve.

A thermal resistance curve （phantom thermal death time curve）may be plotted from D values or TDT values at different heating temperatures. The slope of this curve is the Z value. The Z value is defined as the number of degrees that the temperature must be increased to cause a log （90%）reduction in D.

19. The ordinate of this thermal death time curve may also be TDT values. Therefore，the destruction rate of a specific strain of bacteria （or its spores）in a foodstuff is best described by its D and Z values.

Chemicals

Many chemical compounds that destroy microorganisms are not appropriate for killing bacteria in or on a foodstuff.

20 .Those chemicals，which can be used，are applied as sanitizing agents for equipment

and utensils that can contaminate food. The survivor curve of microorganisms treated with chlorine reveals a deviation from the logarithmic order of death that is normally obtained from heat treatment of sanitizing with other bactericidal agents by being S shaped. This deviation cannot be fully explained，but the cell or the necessity of inactivating multiple sites within the cell before death results.

23. Radiation

When microorganisms in foods are irradiated with high-sped electrons （beta rays）have with X-rays （or gamma rays），the log of the number of survivors is directly proportional to the radiation dose. The relative sensitivity of a specific strain of microorganism subjected to specific conditions is normally expressed as the slope of the survivor curve.

24.The log10 of survivors from radiation is plotted against the radiation dosage，and the radiation D or D10，which is comparable with the thermal D value，is obtained. The D10 is defined as the amount of radiation in rads （ergs of energy per 100g of material）required reducing the microbial population by 1 log （90%）。

25.The destruction mechanism of radiation is not fully understood. It appears that death is caused by inactivation if components within the cell through that death is caused by inactivation of components within the cell through energy absorbed within the cell. Inactivation by radiation results in an inability of the cell to divide and produce visible outgrowth.

26.Methods of Inhibiting Microbial Growth

Most methods used to kill microorganisms may be applied in a milder treatment to inhibit microbial growth. Milder treatment of microbial cells through sublethal heating，irradiation，or toxic chemicals frequently causes injury and impaired growth without death. Injury is reflected through an increased lag phase，bitory conditions.

27.Synergistic combinations of inhibitory agents such as irradiation and heat and chemicals can increase microbial sensitivity to inhibitory conditions. Injured cells appear to require synthesis of some essential cell materials，that is，ribonucleic acid or enzymes before recovery is accomplished. The major methods for microbial inhibition will be discussed under the topics that follow.

28. Refrigeration

Freezing and subsequent thawing will kill some of the microflora. Those that survive freezing will not proliferate during frozen storage. Yet，this is not a practical method of reducing the microbial load. Also，microorganisms that survive frozen storage will grow on thawed foods at a rate similar to those，which have not been frozen. Refrigerated storage can be used in conjunction With other methods of inhibition，that is，preservatives，heat，and irradiation.

29. Chemicals

Chemicals that increase osmotic pressure with reduced Aw below the level that permits growth of most bacteria can be used as bacteriostats. Examples include salt and sugar. Nitrite，which is used in cured meats，also functions as a bacteriostat.

30. Dehydration

Reduction of microbial growth by dehydration is another method of reducing the Aw to a level that prevents microbial proliferation. Some dehydration techniques restrict the types of microorganisms that may multiply and cause spoilage. Dehydration is most effective when combined with other methods of controlling microbial growth such as salting and refrigeration.

31. Fermentation

In addition to desirable flavors produced from fermentation，this technique can control microbial growth. Fermentation functions through anaerobic metabolism of sugars by acid-producing bacteria that lower the pH of the substrate，which would be the foodstuff. A pH below 5.0 restricts growth of spoilage microorganisms. Acid products that result from fermentation contribute to a lower may be packed in hermetically sealed containers to prevent spoilage by aerobic growth of yeasts and molds