Effects of different freezing methods on the quality of red shrimp (Aristaeomorpha foliacea)

In this thesis, it is aimed to investigate the effects of different freezing and thawing methods on the quality of red shrimp (Aristaeomorpha foliacea). In the study, the shrimps first brought to the laboratory were divided into two groups. Head and shells of a group shrimps were removed, while the other group of shrimps remained shell-on as a whole. Both groups of shrimps were frozen with three different methods after the pre-cooling process. In the blast freezer (-40°C temperature, 4 m / s air velocity), in a domestic freezer at -18°C and with liquid nitrogen. Frozen shrimps are packed in sealed polyethylene bags without losing time after freezing. Packaged shrimps were stored in the freezer for 30 days at -18ºC. At the end of the storage period, quality control analyses were performed by using three different thawing methods (at ambient temperature, in a refrigerator and in a microwave oven). When the study results were evaluated interms of total volatile basic nitrogen (TVB-N) and trimethylamine (TMA-N) values shrimps frozen with liquid nitrogen were found to be relatively low compared to those frozen by other methods. During 30 days of storage, TVB-N and TMA-N values increased significantly but they did not reach their consumption limit values. The highest TVB-N and TMA-N values were determined in the thawed samples compared to the thawing methods. No significant differences were observed in TVB-N and TMA-N values among the samples thawed in the refrigerator and microwave oven. No significant change was observed in the pH values of frozen shrimps after 30 days of storage. However, in terms of freezing methods, the lowest pH values were determined in shrimps frozen with liquid nitrogen. This was followed by frozen samples in the air blast and domestic freezer. When analyzed in terms of thawing methods, the highest pH values were determined in samples thawed at ambient temperature. The lowest pH values were determined in refrigerated samples. In this study, L *, a * and b * values of shrimps were measured because color is an important feature in the quality and acceptability of shrimps. The L * value, which shows the pale color increase with the increase in brightness, has increased after storage. The highest L * value and the lowest a * value were found in the shrimp frozen with liquid nitrogen. High L * and a * values were determined in the shrimp thawed in the refrigerator. A higher L * value was determined in shell-on shrimps than shell-of shrimp. The freezing process caused the loss of cooking in shrimps. During freezing, water retention capacity decreased and cooking loss increased due to damage of cell membranes. While the freezing methods did not affect the loss of cooking, the loss of cooking increased with thawing in microwave oven. Hardness values of our study samples increased after freezing and 30 days of storage. When we compare the freezing methods, the lowest hardness values were determined in the samples frozen with liquid nitrogen. There was no significant difference between the hardness values of the samples thawed at ambient and refrigerated temperatures. When the thawing methods are compared, it is seen that the highest hardness values are determined in refrigerated thawed samples. Freezing and frozen storage significantly affected the springiness of shrimps. At the end of the frozen storage period of 30 days of shrimps, a significant decrease in elasticity was determined. In terms of freezing methods, the highest springiness values were found in liquid nitrogen-frozen samples and there was no significant difference between blast freezing and deep freezing methods. There was no significant difference in the springiness values between the thawing methods. Removing of shell did not affect springiness values. No significant difference was observed between the freezing and thawing methods in terms of cohesiviness values. Values of shell-off shrimp were higher than shell-on shrimps. A significant increase in chewiness values was determined after freezing and storage for 30 days. In comparison with the freezing methods, the chewiness values of the shrimp frozen with liquid nitrogen were found to be significantly higher than the other methods of shrimp frozen. When the thawing methods were compared, the highest chewiness values were determined in the thawed samples at ambient temperature. Storage time and freezing method and shrimp group were statistically significant. The thawing method was statistically insignificant. After 30 days storage of shrimps, a significant decrease in the sensory values of shrimps was determined. This shows that freezing and frozen storage have undergone quality loss of shrimps. Freezing method, thawing method and removing of shell of shrimpl showed no significant effect on sensory values. As a result, it was determined that the freezing and frozen storage affected the physical and chemical properties of the shrimps. According to the results of this study, it was observed that freezing of shrimps by freezing in air blast and thawing in refrigerator with low temperature were more suitable than other methods. In addition, altough the shrimp frozen with shell-off gives better results in terms of deterioration parameters, textural losses can be seen.