352 FOOD SCIENCE APPLICATIONS 



For a short period after death, corresponding rather closely to the onset, 

 duration, and resolution of rigor mortis, there is little change in the num- 

 bers of bacteria present. This period has been likened to the classical lag 

 phase observed in newly inoculated laboratory cultures of bacteria. It is 

 succeeded by a period of gradually accelerating growth associated with 

 organoleptic changes in the fish, typified by a loss of the characteristic 

 fresh fish flavor. Next the bacterial population enters a phase of more or 

 less exponential growth corresponding to the initial appearance of such 

 well known spoilage indicator substances as trimethylamine and other 

 related bases. This phase is of short duration and is succeeded by a more 

 or less stationary terminal growth period, during which there is little 

 change in numbers among the surface bacterial populations. Despite the 

 absence of quantitative bacterial change, this is the period of maximum 

 spoilage activity terminating, practically, when the fish is approaching 

 putridity. 



It is well established by experiment and observation that this classical 

 growth sequence occurs in all fish and shellfish samples held under chill- 

 ing conditions (i.e., greater than 32°F, less than 50°F) and applies equally 

 to whole fish and to fillets or pieces. Of course special treatments, such as 

 pasteurization, antibiotic ices, nitrite, etc., may affect the timing of events 

 and perhaps lengthen part of the growth curve (usually the lag and ac- 

 celerating growth phases.) 



Qualitative. The qualitative alterations in the bacterial populations 

 which accompany these quantitative changes are not well established. 

 However, recent work has provided some information on this point. The 

 predominant gram negative rod floras of living fish are frequently altered 

 by the handhng procedures which precede stowage in ice so that gram 

 positive organisms such as Micrococcus and Corynebacterium attain a tempo- 

 rarily important quantitative position in the surface bacterial populations. 

 This is also frequently true in the case of filleted products. However, 

 during the apparent lag period and the phase of accelerating growth, 

 qualitative changes in the flora re-establish the predominance of the gram 

 negative rod forms so that by the time logarithmic growth is under way 

 usually over 90 per cent of the total bacteria present are of this type. 



At the same time changes occur in the balance of physiological types 

 among the gram negative organisms. The comparatively slow-growing 

 Achromobacter Siud Flavobacterium show a steady decline in relative signifi- 

 cance and the rapidly growing Pseudomonas (more correctly perhaps 

 "pseudomonad^') types become completely predominant. By the time the 

 lag phase is well advanced Pseudomonas types may constitute from 70 to 

 alrriost 100 per cent of the total population present. There is also appar- 

 ently a shift in balance among pseudomonad types themselves, typified by 

 a reduction in the relative occurrence of typical marine forms and an in- 



