ROLE OF pH IN GEL FORMATION OF WASHED CHICKEN MUSCLE AT LOW IONIC STRENGTH

This work was designed to test the hypothesis that it is not solubilization of the myofibrillar proteins per se that is required to form good gels at low salt concentrations, but the protein‐containing structures must be disorganized. Gels were made from washed minced chicken breast muscle at 0.15, 0.88, and 2.5% sodium chloride. The gels made with varying salt concentrations were evaluated either at pH 6.0–6.5 or pH 7.0–7.4. Strain values, an indicator of protein quality, were high only at neutral pH in the gels containing 0.15 or 0.88% salt. At 2.5% salt, strain values of gels made at acid pH were superior to those at the low salt concentrations at acid pH, but inferior to gels with 2.5% salt at neutral pH. Poor gels were obtained at 0.15% salt and low pH whether or not there was an intermittent adjustment to neutral pH. A neutral salt wash markedly increased the water content of the mince, suggesting that solubility‐inhibiting proteins were removed. Good quality gels were obtained in the absence of any detectable solubilization of myosin and only minimal solubilization of actin.     

SOLUBILITY OF THE PROTEINS OF MACKEREL LIGHT MUSCLE AT LOW IONIC STRENGTH

Over 90% of the proteins of mackerel light muscle were soluble in solutions of physiological ionic strength or less. To accomplish this solublization, it was necessary to extract certain proteins at moderate ionic strength and neutral pH before extracting the rest of the myofibrillar and cytoskeletal proteins in water. Six proteins were favorably solubilized by sodium chloride solutions of moderate ionic strength at neutral pH under conditions that allowed later dissolution of myofibrillar and cytoskeletal proteins in water. The possibility is suggested that three of these proteins were involved in preventing the solubilization in water of other myofibrillar and cytoskeletal proteins of mackerel light muscle. Based on molecular masses and relative abundance, these proteins could possibly be M-protein (166 kDa), α-actinin (95 kDa) and desmin (56 kDa).     

鸡胸肉肌原纤维蛋白的提取及凝胶特性的研究

研究从鸡胸肉中提取肌原纤维蛋白，探讨不同pH值对肌原纤维蛋白含量的影响。研究结果：在pH7．0时，蛋白含量最大为69．74％，通过SDS—PAGE凝胶电泳分析表明，其主要成分为肌球蛋白、肌动蛋白和肌动球蛋白及其他一些小分子肌原纤维蛋白碎片；在离子强度0．6、pH7．0时提取的肌原纤维蛋白所制备的凝胶的保水性、硬度、胶粘性最大。     

A COMPARISON OF THE WATER HOLDING CAPACITY OF PRE- AND POST-RIGOR CHICKEN, TROUT AND LOBSTER MUSCLE IN THE PRESENCE OF POLYPHOSPHATES AND DIVALENT CATIONS

The water holding capacity (WHC) of rainbow trout (Salmo gairdneri) white muscle and lobster (Homarus americanus) tail muscle did not change from pre- to post-rigor. The trout muscle WHC values were similar to those of post-rigor chicken breast muscle and were not affected by the addition of sodium pyrophosphate (PP_i), Mg, Ca or combinations of these. In contrast, the WHC of lobster muscle was like the WHC of pre-rigor chicken breast muscle. The pre-rigor lobster muscle showed a large increase in WHC values with the addition of pyrophosphate (205% of control) but with the further addition of Mg to the sample the increase was depressed (166% of control). Ca addition to the pyrophosphate sample even more markedly depressed the WHC (90% of control). In both cases, Mg and Ca seemed to have approximately the same effect on WHC whether PP_i was present or not. Kena, on the other hand, increased the WHC of both pre- and post-rigor trout and lobster muscle. Ca seemed to negate the increasing effect Kena had on WHC. Kena plus Mg caused a large increase in the WHC of the prerigor lobster muscle; the WHC capacity with Kena alone was 123% of control while the WHC with Kena and Mg was 231% of control.     

QUANTITATIVE CHANGES IN WHOLE MYOFIBRILS AND MYOFIBRILLAR PROTEINS DURING FROZEN STORAGE OF TRUE COD

The extractability of whole myofibrils from true cod decreased more rapidly during frozen storage at −40°C than did the extractability of the component myofibrillar proteins. There was a 95% decrease in extractable myofibrils after 6 months in storage, but only a 23% decrease in extractable myofibrillar proteins.     

ROLE OF IONIC STRENGTH IN BIOCHEMICAL PROPERTIES OF SOLUBLE FISH PROTEINS ISOLATED FROM CRYOPROTECTED PACIFIC WHITING MINCE

Biochemical characteristics of Pacific whiting muscle proteins extracted at acidic, neutral and alkaline conditions were investigated as affected by various ionic strength levels. The protein solubility at pH 4 declined, as NaCl was added up to 200 mM, due to protein aggregation through hydrophobic interactions. In contrast, at pH 7 and 10, solubility increased as NaCl was added up to 400 mM after which it remained constant. Changes in total SH content and S_owere highly related to the different molecular weight distributions of the soluble proteins. At pH 4, myosin heavy chain (MHC) was soluble as evidenced by the presence of MHC in the soluble fraction, even though degraded molecules were shown at IS 10–100 mM, and became completely insoluble at IS ≥ 150 mM. At pH 10, the density of the MHC band gradually increased as IS increased and the formation of high MW polymers was observed at IS ≥ 150 mM.     

THE STRUCTURE AND PROPERTIES OF MYOFIBRILLAR PROTEINS IN BEEF, POULTRY, AND FISH

The myofibrillar proteins myosin, actin, tropomyosin, and troponin are involved in the contraction of muscle. They are also an integral part of the unique, highly organized structure of muscle tissue. The chemistry and biochemistry of these proteins has been studied both in vivo and in vitro by scientists from many different fields. The same proteins are of great importance to food scientists because of their role in meat and meat products. This review summarizes some of the important physicochemical and biochemical properties of these proteins that may be important for food scientists.     

THE EFFECT OF SODIUM POLYPHOSPHATES AND OF DIVALENT CATIONS ON THE WATER HOLDING CAPACITY OF PRE-AND POST-RIGOR CHICKEN BREAST MUSCLE

The water holding capacity (WHC) of natural actomyosin (NAM), of both contracted and uncontracted glycerinated myofibrils and of pre- and post-rigor chicken meat was investigated in the presence and/or absence of sodium pyrophosphate (PP_i), Kena, CaCl₂ and MgCl₂. In these experiments PP_i caused a small decrease in the WHC of NAM which was further decreased either by Ca or even further by Mg. PP_i with or without Ca or Mg had almost no effect on the WHC of glycerinated myofibrils. Pre-rigor meat showed a slight decrease in WHC of PP_i which was further decreased with Mg or even further by Ca. With post-rigor meat the WHC increase with PP_i was decreased by the addition of Mg or even further decreased by the addition of Ca. The actual WHC of pre-rigor meat was almost twice that of post-rigor meat. Once rigor had occurred no major changes in WHC were observed up to 5 days. Kena caused a slight decrease in the WHC of NAM. Using myofibrils and the meat samples, Kena gave an increase in WHC. The addition of Ca and Mg again tended to decrease this WHC.     

FACTORS AFFECTING THE SODIUM CHLORIDE EXTRACTABILITY OF MUSCLE PROTEINS FROM CHICKEN BREAST, TROUT WHITE AND LOBSTER TAIL MUSCLES

The amount of protein extracted from chicken breast muscle at low salt (0–50 mM NaCl) increased as the salt concentration of the extracting solutions increased. The addition of 10 mM sodium phosphate buffer pH 7 (P_i) caused a marked increase in protein extractability at all salt concentrations. A particular polypeptide chain of about 150,000 daltons appeared to be particularly sensitive to the extraction conditions. At high salt (0.6M NaCl, 50 mM sodium phosphate buffer pH 7.0) a second extraction still contained significant amounts of protein. The amount of protein extracted was maximized at a 1/20 dilution. On the other hand, the protein extract-ability of trout white muscle, showed a smaller P_i effect and very little dependence on low salt concentration. The protein extractability of lobster flexor muscle showed little change with either increased salt or P_i. For all three muscles extraction over time with either high or low salt remained essentially constant after the first day with the most protein being extracted from lobster muscle and the least from chicken muscle.