|M.Sc Student||Iliassafov Lubov|
|Subject||Loss of Crispness in Frozen Pre-fried Foods and Methods for|
|Department||Department of Biotechnology and Food Engineering||Supervisor||Dr. Eyal Shimoni|
|Full Thesis text|
This research studies the phenomenon of crispness loss in coated pre-fried foods such as pre- fried coated turkey breasts. These products are characterized by crispness of the outer crust side with a soft and moist interior that cause these products to be favored by consumers in many countries. In order to understand the loss of crispness mechanism, the physical changes occurring during processing and storage of coated turkey breasts were studied in detail. Initially, sensory, mechanical and acoustic properties of coated turkey breasts after frying, microwave and oven reheating were measured. These results showed that the initial slope (rheological parameter) of the force-deformation curve had a good correlation (r=0.94) with sensory crispness and can may be used as an indicator for crispness quantitative evaluation. Developed acoustic signature classifying model (ASCM) for evaluation the crispness of pre-fried coated turkey breast showed a good performance in initial slope/sensory grade predictions for fried and microwave reheated coated turkey breasts.
For understanding the mechanism of crispness loss, the changes of water activity of the breading (outside layer of coating) as a result of moisture migration was investigated. We found that water activity may also be used as an indicator for changes, which occur during processing and storage. A significant increase in water activity occurs during the first days of storage. During the microwave reheating, the water activity values in the coatings increase and a non-crispy, soggy surface was obtained, this was confirmed by sensory tests. The results of the mechanical tests showed that crispness loss depended on the moisture migration that occurred during storage, and less on the microwave heating.
For crispness loss reduction, classic formulation of breading was changed according to the following concepts: reduction of moisture migration and reduction of microstructure changes. The use of crushed fried croutons or baked breading, with incorporated lipid layers as a barrier for moisture migration, improved the sensory crispness. However, the oil content increased significantly and the adhesion of these breading decreased. In order to reduce microstructure changes, starch cristallinity was increased by including high amylose corn starch (HACS) in the formula of breading production. The results of the mechanical, sensory, DSC analysis and SEM images, showed that using breading with high amylose corn starch significantly improved crispness of microwave reheated coated turkey breast samples. These findings can be taken into account when new formulations for reduction loss of crispness are developed.