No abstract

Changes in chemical and physical properties of frozen red hake fillets were determined as a function of time. The decrease in protein extractability could be partly reversed by mercaptoethanol. Sodium dodecylsulfate greatly reduced the loss in extractability. Polypeptides that would not enter 10% polyacrylamide gels after treatment with SDS and mercaptoethanol were formed during frozen storage. The rate of decrease of the myosin heavy chain followed first order kinetics with a rate constant of -0.054 per week at -7°C and closely paralleled the appearance of the "cross-linked" peptides. Uniaxial compression moduli ,correlated well with the dimethylamine produced and the loss of the myosin heavy chain after SDS-PAGE.

Three forms of minced red hake muscle representing whole‐mince, mince with the low molecular weight fraction removed (reconstituted‐minced) and mince with low and high molecular weight soluble fractions removed (washed‐minced) were stored frozen with added Fe+2 and ascorbate (trimethylamine oxide (TMAO) was added when necessary). The production of DMA and free formaldehyde was measured as were the decreases in water‐soluble and salt‐soluble proteins and TMAO as a function of increasing concentrations of ascorbate. Dimethylamine (DMA) production and loss of overall protein extractability were greatest in minced muscle, followed by reconstituted‐minced muscle, and least in washed‐minced muscle. The minced muscle lost water‐soluble proteins, however, less rapidly than the reconstituted‐minced muscle. The percentage of formaldehyde that was bound was highest in the minced, next in the reconstituted‐minced and least in the washed‐minced muscle. This supports earlier data and indicates that formaldehyde reacts with both the small molecular weight fraction and the water‐soluble proteins as well as the contractile proteins. Loss of protein extractability in all samples appeared to be heavily dependent on hydrophobic interactions. Disulfide interactions appeared to occur to some extent in the reconstituted‐minced and washed‐minced muscle but were a minor factor with the minced muscle samples. Surface hydrophobicity of the proteins was inversely related to their extractability. In the sample of minced muscle with the highest concentration of added ascorbate where approximately 79% of the proteins became inextractable, some 2% of the muscle proteins were covalently linked in polymers with molecular weights greater than that of the myosin heavy chains. The data indicate that cross‐linking of protein components occurs as well as hydrolysis of a considerable amount of the protein.

Optimum conditions for microwave inactivation of myrosinase in Canola seeds were investigated with a response surface design. The linear effect of variables (i.e. moisture content, microwave power and exposure time), the second order of exposure time and interaction between exposure time and microwave power were significant for the enzyme inactivation response (PcO.05). A significant (1%) regression equation which could predict the extent of enzyme inactivation at practical levels of moisture, and microwave power was tested. The coupled microwave energy required for complete enzyme inactivation was moisture dependent. The energy required was independent of seed variety. Microwave treatment caused significant increases in the yellow color and sulfur content of the seed oils.

Polyphenoloxidase in Wild Rice (Zizania palustris )Yaw J. Owusu-Ansah Polyphenoloxidase (PPO) was isolated from wild rice (Zizania palustris). Partial purification by acetone precipitation and dialysis of the crude extract yielded a 2.8-fold purification of the activity of the extract. The optimum p H and temperature of the enzyme were 7.8 and 25 "C, respectively. The enzyme catalyzed the oxidation of o-diphenols but not monophenols. Thermal inactivation data indicated fmborder kinetics with an apparent activation energy of 20 kJ/mol. Polyacrylamide gel electrophoresis showed the PPO to be isoenzymes with molecular weights of 116 000, 48 000,42 000, and 35 000, respectively.Polyphenoloxidase (PPO; o-diphenok02 oxidoreductase,