Ice recrystallization

Dissolve 0.26 g of aniline hydrochloride in 2.5 mL of water, add 0.21 g of acetic anhydride followed immediately by 0.25 g of sodium acetate. Warm the mixture, cool it to room temperature, and then in ice. Recrystallize the product from water and wash it with acetone as described above. See Chapter 41 for mechanism. 

Inhibition of Ice Recrystallization. IR inhibition assays were conducted as previously described". Briefly, samples are placed in capillary tubes and snap-frozen at about -35 C. They were then placed in the cryocycler chamber, with the temperature held at -6 C for >16 h. Digital images through crossed polarizing filters were taken of the capillaries immediately after they were placed in the chamber and at the end of the incubation period. Crystal size in the images was compared. Samples were classified as show ing IR inhibition if there was no apparent growth in the crystal size over time. 

Figure 4 Inhibition of ice recrystallization. Samples in 10 pi microcapillaries (740 pm diameter) were frozen and placed at -6°C and examined between crossed polarizing filters. Images were taken prior to, and after overnight incubation, but only the latter images are shown. From left to right samples include sample buffer controls (I, 2), bovine serum albumin, a control protein diluted to 0.2 and 0.02 mg/ ml, respectively (3,4), serial dilutions of 0.2, 0.02 and 0.002 mg/ ml Type I fish antifreeze protein in buffer (5-7), Chryseobacterium sp. cultures (8, 9), and E. coli cultures (10, 11). Note that only the fish AFP and the Chryseobacterium sp. cidtures have crystals too small to be detected at this magnification and the overlying feathery pattern, typical of snap frozen samples, is apparent. Bacterial cultures were at 2 x 10 CFU/ ml. Lines indicate duplicate samples and arrows indicate samples that were diluted.

Donhowe, D.P., and Hartel, R.W. (1996). Influence of Temperature on Ice Recrystallization in Frozen Desserts. 1. Accelerated Storage Studies, International Dairy J. 6, 1191-1208. 

From the mother liquors obtained from the preparation of cocaine, Spath and Kittel (11) isolated a colorless liquid with a strong narcotic odor, which boiled at 78-82 (12 mm.). This, when fractionated, left a small undistilled oily residue which partially crystallized on cooling in dry ice. Recrystallization from petroleum ether yielded colorless needles... 

RL Sutton, A Lips, G Piccirillo, A Sztehlo. Kinetics of ice recrystallization in aqueous fructose solutions. Journal of Food Science 61 741, 1996. 

To date the best advice has been to freeze seafoods quickly and hold them at a very low 300°C), constantly maintained temperature, with an adequate moisture barrier applied to surfaces in contact with air to prevent lyophilization. Thawing should be equally fast to prevent ice recrystallization and tissue damage. Yet these conditions are difficult to achieve economically and logistically, and consequently the public image of the quality of frozen seafood has justifiably been a good notch below that of fresh seafood. 

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