Effect of ozone pretreatment on fish storage life at low temperatures.

The purpose of the present study was to determine the effect of ozone pretreatment of live fish on their shelf life and storage characteristics during storage at 0 and 5 degrees C. The evaluation included sensory, chemical, physical, and bacteriological tests at set intervals throughout a storage period of 30 days under two temperature regimes (0 and 5 degrees C). The results of the sensory tests showed that ozone pretreatment of live tilapia prolonged their shelf life by 12 days and improved their quality characteristics during storage at 0 degrees C for 30 days. These results were corroborated by the bacteriological tests. The sensory qualities of ozone-treated tilapia stored at 5 degrees C became unacceptable 3 days later than those of control fish. Although the most important factor affecting the fish shelf life is storage temperature, the combination of ozone pretreatment with storage at 0 degrees C appears to be a promising means of prolonging the shelf life.

Temperature dependent characteristics of intestinal glycyl-L-leucine dipeptidase in boreal zone fish.

Three kinds of boreal zone fish were investigated for gastrointestinal glycyl-L-leucine (GL) dipeptide cleaving activity as a function of feeding stage and seasonal changes. The enzyme activity tested in the perch (Perca fluviatilis L.) intestine increased steadily during digestion and rapidly disappeared after completion. The temperature characteristics and the seasonal changes in dipeptide cleaving activity in pike perch (Stizostedion lucioperca L.) and bream (Abramis brama L.) were studied. In summer, the maximal activities in the pike perch and the bream were found at temperatures of 40 and 30 degrees C, respectively. In winter, the temperature of maximal activity in pike perch fell to only 30 degrees C, whereas no changes were observed in bream. The activation energies in bream and pike perch were several times lower in winter than in summer. Seasonal changes in the dipeptide cleaving activity at low temperature relative to that at the temperature of maximal activity were found. At high temperatures, the stability of the enzyme decreases in winter and increases in summer, but in the presence of a substrate the thermal stability of the enzyme increases both in winter and in summer. In our experiments, we found that in these fish, GL dipeptidase was unstable at 0 and -10 degrees C.

Effects of herbal essential oils used to extend the shelf life of freshwater-reared Asian sea bass fish (Lates calcarifer).

Sensory and microbiological characteristics of Asian sea bass (Lates calcarifer) fish raised in a freshwater pond were evaluated during cold storage for 33 days. Whole fish (averaging 400 g each) were stored in a cold storage room at 0 to 2 degrees C. Essential oils of herbs--thyme (Thymus vulgaris) and oregano (Origanum vulgare)--added at 0.05% (vol/vol) were used as preservatives. On the basis of the sensory test results as well as the bacteriological tests, the addition of oregano and thyme essential oils can considerably slow the process of spoilage. The fish treated with these oils were still fit for human consumption after 33 days of storage. The results obtained through sensory tests are corroborated to a great extent by the chemical (hypoxanthine) tests and to a lesser extent by the physical (Cosmos units) tests. The initial total bacteriological counts were 1.7 x 10(3) CFU/cm2 on the fish surface and <10(2) CFU/g in the fish flesh, and in the control treatment (without preservatives), these counts rose continuously, reaching around 10(7) CFU/cm2 on the fish surface and 10(3) CFU/g in the flesh after 33 days of storage at 0 to 2 degrees C. The use of herbal essential oils as preservatives, on the other hand, resulted in a maximal count of 10(5) CFU/cm2 on the fish surface, while the bacterial count in the flesh remained <10(2) CFU/g by the end of the 33-day storage period at 0 to 2 degrees C.

Amylolytic activity in fish intestinal mucosa: temperature effects.

The activity, temperature characteristics and energy of activation of amylolytic enzymes in the intestinal mucosa were studied in six species of fish living in a boreal zone [burbot (Lota lota L.), northern pike (Exos lucius L.), perch (Perca fluviatilis L.), bream (Abramis brama L.), roach (Rutilis rutilis L.), and carp (Cyprinus carpio L.)] and in three species from tropical and subtropical areas [pilchard (Sardina pilchardus W.), jack mackerel (Trachurus trecae C.) and round sardinella (Sardinella aurita V.)]. The amylolytic activity correlated with the feeding habits: it was essentially lower in predators. The enzyme activity at low temperature, relative to the maximal activity, was correlated with the natural environmental temperature where the species lived. At low temperature the relative activity was higher in boreal fish than in tropical and subtropical fish. We found a breakpoint in the Arrhenius plots in all fish species, except for jack mackerel. The energy of activation in predators decreased below the breakpoint in the low-temperature region. The energy of activation in benthophages of the Aral-Ponto-Caspian area was lower at higher temperatures above the breakpoint. A reduction in activation energy in the range of physiological temperatures might indicate adaptation to the environmental temperature.

Effects of storage temperature and preservative treatment on shelf life of the pond-raised freshwater fish, silver perch (Bidyanus bidyanus).

Sensory and microbiological characteristics of pond-raised freshwater silver perch (Bidyanus bidyanus) fish, during cold storage over a period of 25 days were evaluated. Whole fish (averaging 400 g each) were stored in cold storage rooms at either 0 to 2 degrees C, 5 degrees C, or 5 degrees C + potassium sorbate as a preservative. The organoleptic and hypoxanthine test results show that the treatment of potassium sorbate can slow the process of spoilage by about 5 days. Yet, the most important factor affecting the shelf life of these fish is the storage temperature. Keeping the fish at 0 to 2 degrees C can prolong the storage prior to spoilage by 10 days compared with those kept at 5 degrees C. These results obtained through organoleptic tests are corroborated by both the chemical (hypoxanthine and total volatile basic nitrogen) and to some extent by the physical (cosmos) tests. The initial total bacteriological counts were 5 x 10(2) CFU/cm2 for fish surface and <10(2) CFU/g for fish flesh, and these counts rose continuously, reaching about 106 CFU/g (0 to 2 degrees C) and 10(7) CFU/g (5 degrees C) in flesh and 10(7) to 10(8) CFU/cm2 on the surface by the end of the storage period. The addition of potassium sorbate led to a smaller increase in bacterial numbers, especially during the first 15 days. Bacterial composition fluctuated during storage. The initial load on the fish surface was predominantly mesophilic and gram positive and consisted mostly (80%) of Micrococci, Bacillus, and Corynebacterium. During the next 10 days, these bacteria were practically replaced by gram-negative flora comprised mostly of Pseudomonas fluorescens that rapidly increased with storage time and accounted for 95% after 15 days.