354 FOOD SCIENCE APPLICATIONS 



Handling Effects. The influence of handling procedures on the bac- 

 terial populations in fish is fairly evident from the outline description 

 of the normal situation given above. Rough handling of the fish which 

 results in breaks in the skin barrier or crushing of tissues will facilitate 

 primary penetration of the tissues by bacteria and will hasten spoilage. 

 Dirty ice, re-used ice, or ice stored for long periods in fish rooms will 

 harbor large numbers of psychrophilic fish spoilage bacteria and, there- 

 fore, the use of such ices can bring about a shortening of the lag-acceler- 

 ation phase of bacterial growth again leading to more rapid spoilage. A 

 similar effect will be obtained by exposure of fish to improperly cleaned 

 boxes, pen boards, etc. 



Of all the physical and chemical factors which affect bacterial growth, 

 temperature is probably the most important. The psychrophilic bacteria, 

 which normally cause fish to spoil, grow many times faster at temper- 

 atures close to 70°F than they do at temperatures close to 32°F. Indeed, 

 as Hess^ pointed out many years ago, the effect on bacterial growth of 

 raising the temperature a few degrees in the region of 32°F is out of all 

 proportion to the effect of raising the temperature through the same 

 number of degrees in the region of 70°F. Any laxity in temperature con- 

 trol (e.g., through use of insufficient ice or poor brine cooling) will result 

 in accelerated bacterial growth and more rapid spoilage. 



Filleted and steaked fish are particularly susceptible to the deleterious 

 effects of bad handling since the naked flesh provides an excellent medium 

 for bacterial growth. Theoretically, a fillet carefully prepared from a fresh 

 fish should be nearly sterile, since all bacteria are initially present only 

 on the exterior surfaces of the fish. However, filleting knives, tables and 

 boards, filleter's gloves, static wash water, etc., rapidly accumulate large 

 populations of fish bacteria if proper sanitary precautions are not ob- 

 served. Transposition of these bacteria to the virgin flesh surface can 

 bring about very rapid spoilage of the cut fish. 



Effect of Processing on Fish Bacteria. The primary aim of all process- 

 ing is to interfere in some way with the activities of the spoilage bacteria. 

 Most processes can be defined in terms of three objectives: partial inhi- 

 bition, complete inhibition, and sterilization. 



Partial Inhibition. Partial inhibition is most commonly achieved in 

 practice by maintaining the temperature of the fish or other seafood 

 close to 32°F by the use of ice or refrigerated brine. As was noted earlier, 

 the effect of such low temperatures is to reduce very greatly the rate of 

 multiplication of the spoilage bacteria and thus to delay the onset of the 

 logarithmic growth phase and the corresponding development of gross 

 spoilage. 



Chemical additives, such as nitrites, bcnzoates, etc., operate in a some- 



