stantan thermocouples, was monitored contin- 

 uously during the freezing experiments. The 

 results are plotted in Figure 1-5. It took ap- 

 proximately 30 sec to freeze the sample by im- 

 mersion in Freon 12. The freezing time was 

 approximately 2 min when using cold nitrogen 

 blast. However, it took 14 min to freeze the 

 same size piece in still cold air. Immersion 

 pi'oved to be by far the fastest method of 

 freezing. 



*100 

 1^ +80 



S +40 

 5 +20 



FREEZING TIME 



Figure 1-5. — Freezing curves of crab meat. 



Comparison of DifFerent Freezing 

 Methods 



Ratings obtained from samples frozen by 

 Freon immersion or by Freon sprays were 

 quite similar to those obtained from samples 

 frozen by intermittent immersion in liquid ni- 

 trogen (Table I-l) . In a few cases, the ratings 

 in these tables also suggest that samples frozen 

 in Freon were slightly better than samples 

 frozen in liquid nitrogen but this difference 

 is not considered significant. 



In comparison with the Freon freezing and 

 the liquid nitrogen freezing methods, the panel 

 ratings for samples frozen by a cold nitrogen 

 gas blast (about — 150° F) were very similar 

 for up to 4 months' storage. After 6 months' 

 storage, the samples frozen by nitrogen blast 

 rated slightly, but not significantly, lower than 

 the immersion-frozen samples (Table I-l). 



Results obtained from panel evaluations of 

 slow-frozen samples indicate that this method 

 was less desirable than any of the other freez- 

 ing methods used in this study. For example, 

 even a low-temperature storage at — 20° F did 



not prevent a gradual loss in quality in these 

 samples, whereas the quick-frozen samples 

 maintained a much better quality at this tem- 

 perature. These results are consistent with 

 the hypothesis that slower freezing rates permit 

 more interactions between solutes in the un- 

 frozen tissue fluids and other tissue components 

 (Love, 1968; van den Berg, 1968). 



Although most of the frozen-stored samples 

 were slowly thawed at room temperature, quick 

 thawing by microwave energy resulted in a 

 product of slightly higher acceptability (Table 

 I-l). 



Comparison of Freezing with Other 

 Preservation Methods 



Panel ratings given to heat-pasteurized sam- 

 ples stored for up to 8 months at -h 34° F (Table 

 1-2) were generally comparable to quick-frozen, 

 vacuum-i^ackaged samples stored at 0° F for 

 the same length of time. In some instances, 

 the ratings for these pasteurized samples ap- 

 peared to lie lower than those received by sam- 

 ples stored at —20° F (Table I-l). On the 

 other hand, heat-sterilized samples were con- 

 sistently downgraded by the panel for their 

 undesirable bluish discoloration as well as their 

 oif-taste (Table 1-2). 



A few samples of crab meat were preserved 

 by freeze-drying, vacuum-packaged, and stored 

 for 6 months at ambient temperature. The 

 panel consistently rated the taste of these sam- 

 ples as unacceptable although their appearance 

 and texture received fair acceptance ratings 

 (Table 1-2). 



Effect of Different Storage Tempera- 

 tures 



Crab meat samples held at dry ice temper- 

 ature (about — 108° F) were rated highly by 

 the taste panel even after 8 months' storage. 

 Quick-frozen samples held at — 20° F were 

 rated somewhat lower during this storage peri- 

 od but their ratings were still generally within 

 the range given to freshly picked, nonfrozen 

 control samples. In contrast, some of the sam- 

 ples held at 0° F, received much lower ratings 

 than comparative samples held at the lower 

 temperatures. Particularly, the ratings of 



