RELATIONSHIP OF FREEZING PRESERVATION PARAMETERS TO TEXTURE-RELATED STRUCTURAL DAMAGE TO THERMALLY PROCESSED CRUSTACEAN MUSCLE

Abstract

Selected freezing preservation parameters applied to thermally processed blue crabs and shrimp were evaluated by means of scanning electron microscopy to determine the relationship of the parameters to texture-related structural damage brought about by ice crystal formation and growth. Ice crystal growth and tissue disruption occurs largely during post-freezing frozen storage, the rate of freezing merely setting the pattern of subsequent crystal growth. Damage is more severe with slow (sharp) freezing due to growth of large extracellular ice crystals, causing tissue dehydration and shrinkage and compaction. This also leads to greater drip loss upon thawing. Rapid freezing in “Freon” food freezant or in liquid nitrogen (LN₂) results in less disruptive intracellular crystal formation and growth, the water tending to remain in the tissue upon thawing. Immersion in LN₂ caused noticeable stress-cracking of the tissue, but there was no evidence of significant ice crystal growth during subsequent warming to freezer storage temperatures. Ice crystal growth during — 29 °C storage was at least one-third slower than at — 10 °C, underscoring the overriding importance of good holding conditions following rapid freezing. It can be concluded that the various fast freezing methods are essentially equally suitable as long as the freezing rate is well within the limit for promoting formation of tiny intracellular ice crystals (i.e. on the order of a few to several minutes). Double freezing of shrimp, a common commercial practice, doesn't appear to result in significant damage to tissue over and above that which develops during post-thermal processing frozen storage. It is advisable to upgrade frozen storage systems in the distribution channels to the level of sophistication of modern freezing systems, and to hold product for as short a time at as low a subfreezing temperature as is practical.