青豆速冻过程冻结时间的数值计算

青豆近似为球状，采用完全隐式差分法，建立描述近似青豆的球状食品冻结过程传热特性的偏微分方程：通过数值计算获得青豆冻结时间的数值解，并与实验值比较。结果表明：数值法计算结果与实测值吻合较好，具有较高的精度。     

FREEZING OF COOKED MEAT: INFLUENCE OF FREEZING RATE AND RECONSTITUTION METHOD ON QUALITY AND YIELD

The combined effects of freezing rate, frozen storage and reconstitution method on meat quality and yield were studied in multifactorial experiments using pan-fried 1.5 cm slices of longissimus muscles and deep-fat fried meat patties. On the whole, a slight improvement in sensory quality and yield was seen with increasing freezing rate, except that liquid nitrogen immersion freezing influenced flavor negatively. In contrast with earlier results of ours with raw beef, an advantage was now seen for reconstitution after previous thawing over reheating directly from the frozen state, and pan frying gave better sensory quality but lower yield than continuous microwave reheating. Tenderness of sliced, cooked beef tended to increase during frozen storage, while the opposite was earlier observed for frozen raw beef. Otherwise, a general trend was seen towards decreasing yield and sensory quality during frozen storage. A number of significant interactions between variables was obtained, suggesting that their influence on quality and yield is interrelated in a rather complex manner.     

EFFECT OF PRESSURE-SHIFT FREEZING VERSUS AIR-BLAST FREEZING OF CARP (CYPRINUS CARPIO) FILLETS: A STORAGE STUDY

Intact carp (Cyprinus carpio) fillets were packaged under vacuum and pressurized at 100, 140, 180 and 200 MPa at 4C for 15 or 20 min. Changes in the lipid fraction and color of the fillets as well as the electrophoretic profiles of the fish proteins were studied to establish the best conditions (time and pressure) for pressure‐shift freezing the carp fillets. Thiobarbituric acid (TBA) values, free fatty acid (FFA) content and color parameters (L*, a*, b*) increased as the pressure level and pressurization time were increased. After 15 min of treatment at any pressure level, the intensity of the protein band with MW < 36 kDa decreased. With these results, the carp fillets were frozen using either pressure‐shift freezing (PSF) (140 MPa, ?14C for 12 min) or air‐blast freezing (ABF) (?20C for 4 m/s) and then stored at ?20C for 75 days. Changes in TBA values, FFA content, texture, total drip losses and size of ice crystal were evaluated. The TBA values and FFA content were relatively lower in the PSF samples than in the ABF samples. The freezing procedure did not seem to have a significant effect (P > 0.05) on the texture of carp fillets. PSF was more effective in reducing total drip losses in cooked samples compared to ABF treatment. Ice crystals found in the PSF fish samples were mainly intracellular, smaller and more regular in shape than those found in the ABF samples.