The affect of propolis treatment on shelf life and organoleptic, chemical and microbiological properties of smoked trout (oncorhynchus mykiss) fillets

In this study, it was purposed to investigate the changes in microbiological, chemical and sensory properties of vacuum packaged smoked rainbow trout fillets by applying propolis extract (PE) at different doses during production and storage stage. Different PE ratios (0.25%, 0.50%, 1%, and 3%) were applied to the fillets for this purpose, and they were vacuum packed following hot smoking. The samples produced in 5 different groups together with the control group were stored at 4±1 °C. At the production stages (fillet, end of brine) and on the end of smoking (day 0), 7th, 14th, 21st, 28th, 42nd, 56th, 70th and 84th days of storage, the samples were analysed in terms of microbiological (total mesophilic aerobic bacteria, total psychroilph aerobic bacteria, Pseudomonas spp., sulfite-reducing anaerobic bacteria, Lactobacillus spp., lactic streptococcus spp., lipolytic microorganism and yeast-mold counts), chemical (pH, water activity, crude fat, free fatty acid, thiobarbituric acid, total volatile basic nitrogen, moisture, crude ash and salt value), and sensory (colour, odour, flavor, apperance, texture and overall acceptance) qualities. The study was carried out in four replications. The total mesophilic and psychrophilic aerobic bacteria, Lactobacillus spp., Lactic streptococcus spp., lipolytic bacteria and yeast-mold counts decreased in all groups until the end of smoking (day 0), whereas they showed different changes depending on the groups on the storage days and gradually increased in the following storage period. The sulfide reducing anaerobic bacteria numbers were below the detection limit at all stages (except the end of brine). On the other hand, Pseudomonas spp. numbers were remained below the detection limit only on storage days. The samples treated with 3% PE during production and storage had considerably fewer mesophilic and psychrophilic aerobic bacteria than the other groups (p<0,05), but it was effective on Lactobacillus spp. at 14 th and 56 th days, as well as lipolytic bacteria at the ends of brine and at 56 th days of storage (p<0,05). However, it was observed that PE had no effect on lactic Streptococcus spp. and yeast-mold numbers (p>0.05). As a result of the analysis 0.25% PE application did not affect apperantly the microbiological and chemical properties of the product. However, it affected the microbiological, chemical and sensory parameters of the product in groups with 0.50%, 1% and 3% PE, and significant differences were found both between the groups and throughout the storage period. While the control group and the 0.25% PE added group showed signs of spoilage on the 56th day of storage, the 0.50% and 1% PE added groups showed signs of spoilage 14 days after the control, and the 3% PE added group showed signs of spoilage 28 days after the control. In current study, pH and water activity (aw) values in the samples decreased during the production phase and increased during the storage days. The values of crude fat, salt and ash increased steadily throught time, but rapidly at the beginning of production stage. The amounts of TBA and TVB-N increased slowly depending on time in all stages and reached the highest value at the end of the storage (p<0.05). While there was no statistical difference between the groups in terms of TBA values (p>0.05), there was a statistical difference in terms of TVB-N between the control group and the 3% PE group only at 56 days of storage (p<0.05). In the sensory analysis, it was determined that PE applied at different concentrations had a negative effect on the overall acceptance, odour and flavor on the product's sensory properties (p<0.05), but had a positive effect on the color values (p<0.05). As a consequence, the application of propolis to the smoked trout fillets prepared in vacuum packaging has a relatively positive effect on the microbiological and chemical qualities of the product, as well as extending the shelf life from 14 to 28 days depending on the increasing PE concentrations. However, excessive concentration application has a negative affects on the product's sensory properties. For this reason, as a result of this research, it is recommended to use a maximum of 1% PE in this type of products.