Effect of different freezing rates on the texture and quality parameters of selected fruit and vegetable

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Food Engineering, Turkey

Approval Date: 2015




The freezing rates of strawberry and green bean were determined at -23, -26 and -27°C in a home type freezer. For the estimation of freezing rate, the temperature-time data was obtained with a thermocouple embedded inside the sample. The freezing rates of strawberry were 0.75, 0.93 and 1.02 cm/h at -23, -26, and -27°C, respectively. For green bean, the freezing rates were 0.36, 0.50, 0.57 cm/h at -23, -26, -27°C, respectively. In three freezing rates studied, cellular integrity was examined with NMR relaxometry analysis. NMR relaxometry analysis showed that the freezing rates studied did not keep the cellular integrity in strawberries. However, cell integrity of green bean was kept better after freeze-thawing in comparison to strawberry. Packaged strawberries and green beans were frozen stored at -27°C for 3 months to determine some quality parameters such as L-ascorbic acid, total phenolic content, antioxidant activity and color change. Total phenolic content and antioxidant activity change of selected samples did not decrease a value lower than 80% during the frozen storage at -27°C. L-ascorbic acid losses were approximately 42 and 27 % for 13 weeks of frozen storage of strawberry and green bean, respectively. The degradation rate of ascorbic acid was lower in green bean in comparison to strawberry. A significant change in color was not observed for the selected samples. Home freezing should be done appropriately to preserve the nutritional content and texture of fruits and vegetables. The approximations and analyzes used in this study, can be a base to design and produce a convenient deep freezer systems.