No abstract

Differential scanning calorimetry (DSC) and dynamic oscillatory shear testing were performed to study the influence of inulin (Raftiline HP-gel and Raftiline ST-gel) and oligofructose (Raftilose P95) on the thermal stability and gelation (using glucono-delta-lactone [GDL] as a coagulant) of soy protein isolate (SPI) dispersions. Addition of 10% (w/v) inulin/oligofructose or sucrose increased (P < 0.05) the peak denaturation temperatures (T(m)) of 7S and 11S soy proteins in SPI dispersion (5%[w/v], pH 7.0) by an average of 1.9 and 2.3 degrees C, respectively. GDL induced SPI thermal gelation, and the gel rheology was affected by both the pH decline and the specific temperature of heating. Addition of inulin/oligofructose (8%, w/v) improved the gelling properties of preheated SPI dispersion (8%, w/v) coagulated with GDL, showing 14.4 to 45.6% increase (P < 0.05) in gel rigidity (G' value) at the end of heating (81 degrees C). Microstructural examination revealed a denser protein cross-linking structure and reduced pore sizes in SPI gels containing inulin/oligofructose. In general, inulin was more capable of improving SPI gelation than oligofructose, suggesting that the degree of fructose polymerization in the fructans was of thermal and rheological importance.

Australian red claw crayfish tails were dipped in either 0.06% (w/w) anti-oxidant solutions (tocopherols, propyl gallate, or rosemary extract) or in water and subsequently stored in a )20°C freezer. At the end of 0, 1, 3, and 6 months of storage, the raw muscle samples were analysed for lipid oxidation, the thermal stability of proteins, cooking yield and shear force. Red claw treated with anti-oxidants showed a lower (P < 0.05) thiobarbituric acidreactive substances (TBARS) production than the non-anti-oxidant control (dipped in water). Enthalpy of denaturation (DH) for the myosin head and shear values for the tails decreased (P < 0.05) in all samples after 6 months of storage, while cooking yield was unaffected by storage. Overall, red claw muscle was quite stable and the oxidation, measured as TBARS values, was small (<0.3 mg kg )1 ) but could be further stabilized by anti-oxidant dipping treatments. However the anti-oxidant dipping did not prevent texture softening in red claw muscle during frozen storage.

ABSTRACT. Shell-on tails of 70 juvenile Australian red claw crayfish, Cherax quadricarinatus, were separately packaged in seven sealed plastic freezer bags (10 in each) and stored on ice (0°C) for 0, 1, 3, 5, 7, 10, and 14 days. At the end of each storage period, raw muscle homogenate from five tails (pooled) were analyzed for lipid peroxidation, proteolysis (electrophoreis), and thermal stability (differential scanning calorimetry). The other five tails were individually cooked (2 minutes boiling) to determine cooking yield and toughness (Warner-Bratzler shear). Lipid oxidation occurred during storage (e.g., TBA values increased from 0.341 mg/kg on day 0 to 1.492 mg/kg on day 14, P < 0.05). Myofibrillar and sarcoplasmic proteins were generally resistant to proteolysis, but were destabilized during storage. Transition temperatures for myosin head and actin decreased (P # 0.05) from 50.2°C and 72.6°C on day 0, to 39.4°C and 60.3°C by day 14, respectively; while enthalpy of denaturation for myosin head reduced from 0.324 J/g to 0.116 J/g during this pe- riod. Storage also resulted in a gradual loss in cooking yield, which correlated (R = 20.82, P < 0.05) with progressive toughening of cooked meat. The results indicate that red claw muscle is susceptible to protein denaturation and lipid oxidation, and these chemical changes may be responsible for decreased cooking yield and reduced tenderness of meat during extended refrigeration storage.

The influence of repeated freezing-thawing (F/T, six cycles) treatment on Australian red claw crayfish (Cherax quadricarinatus) muscle quality was investigated. For each F/T cycle. five raw tails were analyzed for lipid oxidation. proteolysis. and thermal stability, and another five tails were cooked to detennine cooking yield and tenderness (shear). Lipid oxidation occurred during repeated Fmtreatment, as evidenced by a marked TBARS increase, i.e., from 0.070 mgkg (fresh) to 1.201 mgkg (cycle 6). While F/T induced small proteolytic and thermal stability changes, it caused a major loss in cooking yield as well as in tenderness of meat. The results showed an overall susceptibility of the main quality traits of red claw muscle to F/Tabuses. n u s , to retain good eating qualities. red claw tails should not be subjected to more than three F/T cycles.