Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı 2

The Effect of Nisin and Irradiation Combination on the Shelf Life of Cold Stored Fish
Sea bass (Dicentrarchus labrax), is one of the main aquaculture fish of Turkey and it is an important product both for domestic and export markets. It is usually transported and marketed in cold chain. Therefore, decreasing microbial growth, retarding chemical reactions and increasing shelf life during cold storage may provide economic benefits, and are very important in the view of food safety.
Nisin is an antimicrobial which exhibits antimicrobial activity especially against Gram-positive bacteria in foods. However, it may not be sufficient to inhibit Gram negatives. On the other hand, ionizing radiation is a safe and effective method to inactivate Gram negative microorganisms. It is known that the combination of preservation methods may provide better results in microbial safety as well as the sensory quality. Therefore, the effect of irradiation and nisin combination on the shelf life and microbial quality of cold stored (2±1°C) sea bass fillets was studied.
Sea bass fillets were separated into four groups. The first group was cold stored control (C), second was treated with 0.1% nisin (N), third group was irradiated with 3 kGy (I), and the last group was treated with 0.1% nisin and then irradiated with 3 kGy (NI). All groups were air packed, stored at 2±1°C and sensory, physical, chemical and microbiological analyses were done every other day.
Regarding sensory analyses, the shelf life was 7 days for K group, 11 days for N group, 15 days and17 days for I and NI groups, respectively. The ph value did not exceed the limit of spoilage in any group. The different treatments did not significantly affect the color of samples. The TVB-N contents of K and N samples were acceptable until the 7^th day, then exceeded the limit of spoilage. Irradiated samples (I and NI groups) contained acceptable levels of TVB-N until the 21^th day of cold storage. Similarly non-irradiated samples (K and N) exceeded the acceptability limit for TMA-N at the 13^th day, while I and NI samples contained lower amounts of TMA-N during storage. It was also determined that irradiation increased the TBA values of samples.
As to microbiological results, mesophilic aerobic bacteria counts of K and N samples were above the limit of spoilage at the 9^th and 11^th days, respectively. The acceptability limit for psychrophilic aerobic bacteria was exceeded by K and N groups after 7 days of storage. Either mesophilic or psychrophilic aerobic bacteria counts of NI groups were remained below the limits during the study. Yeast and mould counts of K and N groups were significantly higher (p<0.05) than I and NI groups during cold storage.
As a result, the shelf life of K group samples was 7 days, while it was 11 days for N group, 15 days for I group and 17 days and NI group samples, according to sensory analyses. It was determined that irradiation inhibited bacterial growth, decreased TVB-N and TMA-N values and while combined with nisin maintained a better sensory quality.

ORHAN Yasin
Danışman : Prof. Dr. Özkan ÖZDEN

Anabilim Dalı : Su Ürünleri Avlama ve İşleme Teknolojisi

Programı : İşleme Teknolojisi

Mezuniyet Yılı : 2014

Tez Savunma Jürisi : Prof. Dr. Özkan ÖZDEN

Prof. Dr. Sühendan MOL TOKAY

Prof. Dr. Candan VARLIK

Prof. Dr. Gürbüz GÜNEŞ

Yard. Doç. Dr. Ş. Yasemin TOSUN