鸡肉盐溶蛋白质热诱导凝胶质构的研究

采用L9（3^4）正交试验法研究磷酸盐和氯化钙复合作用对鸡胸和鸡腿肉热诱导凝胶的硬度和弹性的影响。结果表明，鸡胸肉和鸡腿肉热诱导凝胶的硬度有极显著差异（p〈0．01），二者凝胶的弹性无显著差异（p〉0．05）。就鸡胸内而言。氯化钙、三聚磷酸盐和焦磷酸盐对其硬度均有极显著影响（p〈0．01），三聚磷酸盐和焦磷酸盐对其凝胶的弹性有显著影响（p〈0．05）；而对于腿内来讲。焦磷酸盐对其硬度有极显著影响（p〈0．01），氯化钙和三种磷酸盐对凝胶的弹性均有显著影响（p〈0．05）。     

HEAT-INDUCED GELATION AND PROTEIN-PROTEIN INTERACTION OF ACTOMYOSIN1

Natural actomyosin (NAM) and “crude” actomyosin formed gels yielding maximum strengths (from back extrusion force) at pH 5.0 and 5.5, respectively. At pH 6.0, NAM gels had a least protein concentration endpoint (LCE) value of 6 mg/ml. Gel strength increased exponentially with an increase of NAM concentration from 3.75–10 mg/ml. With constant time (30 min)-temperature heating, NAM gel forces increased by 20.5% (NS, P>0.05) in the 30–80°C range. Arrhenius plots of NAM interaction in solution and in gelation at pH 6.0 indicated two different reaction mechanisms within the temperature zones above and below approximately 35°C for solutions and 40°C for gels. Similarity of interaction slopes above the 35–40°C region suggested one reaction mechanism for NAM molecular aggregation in solution and gelation.     

FERMENTATIONS IN THE PRESENCE OF AMYLOGLUCOSIDASE

The addition of amyloglucosidase to fermenting wort produced changes in the spectrum of carbohydrates. Some oligosaccharides were broken down to a larger extent than others, and maltotriose and maltose were depleted at a higher rate than under normal conditions. It was also noted that the glucose concentrations increased in fermentations to which amyloglucosidase had been added. In order to determine whether the reduction in maltotriose and maltose was caused by the enzyme alone or by assimilation as well as enzymic degradation, maltotriose depletion rates were compared in fermentations with Sacch. cerevisiae and with Sacch. uvarum. The results indicated assimilation as well as degradation. Further evidence of maltotriose fermentation was obtained when glucose was continuously pumped into a fermentor at a rate approximating to the glucose formation by the enzyme. Also, under these experimental conditions, it was found that glucose levels increased, while maltose and maltotriose concentrations decreased. However, the observed increase in glucose during the fermentation was lower than would be expected from the mechanical addition, indicating a simultaneous uptake of glucose, maltose and maltotriose.     

INITIAL POSTMORTEM PORCINE MUSCLE PH EFFECT ON HEAT-INDUCED GELATION PROPERTIES

Heat-induced gelation properties of the semimembranous muscle from induced DFD (dark, firm and dry) and normal pigs were characterized to evaluate the effect of muscle pH on strength and cooking loss of gels induced by a heating at 0.7C/min. The pH of muscle slurries (10% protein with 2% Nacl) were adjusted to 5.5, 6.0, 6.5, or 7.0 with 1 M 2-[N-Morpholino] ethanesulfonic acid buffer. Muscle with a high initial pH (DFD) had lower cooking losses at all adjusted pHs. Force required to penetrate the gel (Pf), force required to move plunger through the gel (Fp), and viscosity index of the gel were consistently higher for DFD muscle at each adjusted pH except pH 5.5. These results indicate that ultimate pH influences the thermal gelation properties of a meat product if the pH is ≥ 6.0. DFD muscle had desirable protein functionality and cooking yield.     

HEAT-INDUCED TRANSITIONS IN THE PROTEIN-PROTEIN INTERACTION OF BOVINE NATURAL ACTOMYOSIN1

Protein-protein interaction of bovine natural actomyosin (NAM) was studied by means of optical density changes resulting from discrete particle formation in the temperature range of4°C to 70°C. From Arrhenius plots, the apparent heat of activation (ΔH_a) at pH 5.5 (17.1 kcallmole) was significantly (P<0.05) lower than activation energies in the pH range of 6.0 to 7.5. The lower Δ H_a resulted in initiation of protein-protein interaction at a temperature near 16°C at pH 5.5, whereas interaction did not proceed until the temperature approached 37°C at pH 6.0 and above. Derivative curves (dOD/dT) at pH 5.5 and 6.0 showed two distinct NAM thermal transition regions. Tm₁ occurred at 43.0°C at pH 5.5 and 48.5°C at pH 6.0, with the 5.5°C difference possibly arising from effects of proton binding in altering protein conformation. Only a 1.5°C difference in Tm₂ (56.0°C at pH 5.5 versus 57.5°C at pH 6.0) was found. Although the overall heat-mediated NAM aggregation (in dilute solution) was found to follow first order kinetics by two evaluation methods, the existence of two thermal transitions supports a two-step reaction mechanism proposed for the formation of protein gels (in higher concentration solutions).     

INFLUENCE OF NACL LEVEL AND FREEZING ON ACTIN AND MYOSIN CONTENT OF EXUDATE FROM CHUNKED AND FORMED LAMB ROASTS

The influence of NaCl levels and freezing on bind characteristics and protein exudate of chunked and formed lamb roasts were evaluated. Roasts prepared from frozen lean had lower shear values and Instron peak loads than did roasts prepared from fresh lean. Freezing of lean prior to processing lowered percentage actin in exudate but significant (P<.05) NaCl level × freezing interactions existed for percentage actin and myosin. Increasing NaCl levels from .5 to 2.0% decreased cook loss in all roasts made from fresh and frozen meat and increased Instron measures of bind in roasts made from fresh but not frozen meat. Effects of freezing and NaCl level on extractability and functionality of the myofibrillar proteins into the exudate at meat chunk surfaces is probably responsible for the observed differences in bind.     

RHEOLOGICAL PROPERTIES OF HYDROCOLLOIDS IN THE PRESENCE OF SUCROSE AND MILK

Apparent viscosities of guar gum, locust bean gum, and sodium carboxymethylcellulose were measured at shear rates of 16-2620s^-1 in water, sucrose, milk, and sucrose/milk solutions. The effect of different heat treatments was also studied. For all solutions, a power law equation described the variation of relative viscosity with shear rate allowing comparison of their non-Newtonian behaviour. With the neutral hydrocolloids, the hydration was limited by the presence of sucrose and milk which reduced the effective length of the polymer molecules. The behaviour of the polyanionic hydrocolloid, Na CMC, although influenced by milk and sucrose separately, was controlled by milk in a milk/sucrose mixture. This is due to milk salts which reduced the intramolecular repulsions along the polyanion and substantially lowered its effective hydrated length.     

HEAT-INDUCED CHANGES IN EXTRACTABILITY OF BEEF MUSCLE COLLAGEN

Alterations in the extractability of collagen due to heating of beef muscle were determined and compared with shear and penetrometer values. Strips were heated in a water bath programmed to reproduce the internal temperature curve of a roast in a 163°C oven. Samples were removed at internal temperatures of 58, 67, 75 and 82° C. Data were collected on weight of raw and heated meat, amount of juice expressed during heating, moisture, fat and nitrogen content of the meat and juice, total and extractable collagen, and shear force and depth of penetrometer penetration. Solubilized collagen in the heated meat was determined by extraction with water at 40°C. The amount of soluble collagen increased with increasing internal temperature. Comparison of the solubilized collagen data with shear and penetrometer readings suggested that the changes in the contractile fibers influenced texture more than did the changes in the collagen of these muscles under these heating conditions.     

CHARACTERIZATION OF THE PROTEASES INVOLVED IN HYDROLYZING PADDLEFISH (POLYODON SPATHULA) MYOSIN

An extract from paddlefish surimi possessed activities of B, L, and H‐like cathepsins. The optimal pH was around 5.0 for cathepsins B and L, and was between 6.0–6.5 for the H‐like cathepsin. The enzyme activities were not impaired by heating at 40Cfor 20 min. However, the protease extract lost about 20% of its cathepsin B, 50% B+L, and 90% H‐like cathepsin activities after heating at 50C for 20 min. The activity of H‐like cathepsin was not inhibited by E‐64, suggesting that it did not belong to ike known cysteme protease group. The protease extract was capable ofhydrolyzing myosin heavy chain, producing a major fragments) around 140 kDa. Degradation of myosin by the protease extract was substantially reduced by protease inhibitors including E‐64, a protease inhibitor mixture, and bovine plasma powder.     

HEAT-INDUCED OFF-FLAVOR IN AVOCADO FLESH

SUMMARY— The off-flavor induced in the Fuerte avocado by heating at 100°C for 20 min has been examined. Isolates which exhibited off-flavor were obtained by ethanol extraction of freeze-dried avocado puree. The ether-soluble portion of these extracts was separated by silicic acid column chromatography and thin-layer chromatography. The presence of off-taste in individual fractions was determined by a quantitative taste assay using ethanol-extracted pulp or filter paper as taste medium. Fraction II from a silicic acid column possessed the most dominant off-taste and represented 0.6% of the original avocado flesh. It was a mixture which varied in polarity between that of neutral lipid and phospholipid. Separation of Fraction II by TLC showed the presence of at least 12 components. Separation of the analogous fraction from unheated control samples showed the presence of the same components in similar amounts. Only pheophytins a and b, which were formed by heating, ware missing from the control. Attempts to isolate further by TLC and to characterize substances responsible for off-taste resulted in a significant reduction in off-taste intensity of heat-treated isolates as well as the appearance of similar off-taste in the analogous control. The attenuation is partially accounted for by a synergistic effect involving separated zones from the chromatogram. The over-all off-flavor involved most isolates, though substances responsible were present in quantities undetected by chromatographic techniques     

THE THERMAL STABILITY OF ASPERGILLUS ORYZAE ALPHA-AMYLASE IN PRESENCE OF SUGARS AND POLYOLS

The aim of this study was to test whether it is possible to estimate the heat stability of Aspergillus oryzae alpha‐amylase (α‐amylase) based on the amount of hydroxyl (OH) groups provided in a buffer solution. The thermal stability of the enzyme in a presence of different sugars (sucrose and trehalose) and polyols (mannitol, sorbitol, lactitol and glycerol) was investigated in the temperature range of 62–68C on a kinetic basis. It was investigated if the protective effect of additional substances was correlated to the number of hydroxyl groups (nOH) provided by each of them (per volume unit of the enzyme solution nOH). All additives showed a protective effect on the enzyme's heat stability, which was strongly dependent on the added compound concentration. Among all stabilizing compounds investigated, sucrose exhibited the largest protective effect. The decimal reduction time of α‐amylase activity increased by 33.9 times when 420 mg/mL of sucrose was added to the environment. When the same concentration of trehalose was used, the D‐value increased by 6.4 times compared to the value in the buffer system. The nOH provided in the enzyme solution could not be related to the D‐values for the enzyme thermal inactivation, meaning that the enzyme heat stability was not dependent on the nOH.