Cryochemistry of plant tissue. Protein interactions

Mechanism of freeze-thaw injury and recovery: A cool retrospective and warming up to new ideas

Understanding cellular mechanism(s) of freeze-thaw injury (FTI) is key to the efforts for improving plant freeze-tolerance by cultural methods or molecular/genetic approaches. However, not much work has been done in the last 25+ years to advance our understanding of the nature and cellular loci of FTI. Currently, two FTI lesions are predominantly implicated: 1) structural and functional perturbations in plasma membrane; 2) ROS-induced oxidative damage. While both have stood the test of time, many questions remain unresolved and other potentially significant lesions need to be investigated. Additionally, molecular mechanism of post-thaw recovery (PTR), a critical component of frost-survival, has not been well investigated. Mechanistic understanding of repair after reversible injury could expand the options for strategies to improve frost-hardiness. In this review, without claiming to be exhaustive, I have attempted to synthesize major discoveries from last several decades on the mechanisms of FTI and the relatively little research conducted thus far on PTR mechanisms. It is followed by proposing of hypotheses for mechanism(s) for irreversible FTI or PTR involving cytosolic calcium and ROS signaling. Perspective is presented on some unresolved questions and research on new ideas to fill the knowledge gaps and advance the field.

Some aspects of protein changes in frozen foods

In the past decades many results on changes of food proteins caused by freezing and their relation to quality changes were found. Recently especially the nutrition physiological viewpoint of these alterations has aroused considerable interest. In the present paper the attempt is made to outline some aspects of these changes which are usually referred to as "denaturation" caused by freezing. After a description of the phenomena observed and their measurement, a survey of the main causes presumed for the "denaturation" of fish muscle proteins by freezing is given. With special consideration of the molecular range it can be said that generally aggregation phenomena prevail and that the participating molecules, or part of them, may still be native or more or less changed in their conformation before or during aggregation. Definite judgement of the nutritional properties of the altered proteins in frozen foods is possible only when convincing results of feeding experiments will be available.