Masanori Matsuishi

Denaturation of actin and myosin in myofibrils induced by heating at 50°C was investigated to reveal the mechanism of irreversible liberation of actin from myofibrils on heating at lower temperatures than conventional cooking. Denaturation of these proteins was determined by Mg2+-ATPase (adenosine triphosphatase) and Ca2+-ATPase activities. When minced meat was heated for 20 min, actin was liberated accompanying denaturation of 80% of actin and 50% of myosin. Heating of the myofibrillar fraction (MFF) isolated from meat homogenate induced much slower denaturation of actin than myosin. When MFF was heated with sarcoplasmic fractions, denaturation of actin was facilitated, suggesting that sarcoplasmic fractions contain factors to facilitate actin denaturation. Inosine-5′-monophosphate, a component of sarcoplasmic fractions, was shown to have no effect on actin and myosin denaturation. These results suggest that heating meat at 50°C dissociates binding (‘Bond A’) between actin and myosin participating in ATPase activities, resulting in denaturation of both proteins under influence of sarcoplasmic components. Although denaturation of actin and myosin disrupted Bond A, actin was not liberated simultaneously, suggesting the presence of another bond (‘Bond B’, more heat-stable than Bond A) between both proteins and necessity of disruption of Bond B for actin release from myofibrils.

The objective of this study is to identify the properties and responsible compounds for the aromatic roast odor (retort beef aroma) that commonly occurs in canned beef products and could contribute to their palatability. The optimal temperature for generating retort beef aroma was 121 degrees C. An untrained panel evaluated both uncured corned beef and canned yamato-ni beef and found that they had an aroma that was significantly (P<0.01) similar to the odor of 121 degrees C-heated beef than 100 degrees C-heated beef. The panel also noted that the aroma of 121 degrees C-heated beef tended to be (P<0.1) preferable than that of 100 degrees C-heated beef. These results suggest that retort beef aroma is one constituent of palatability in canned beef. GC-MS (gas chromatography-mass spectrometry) analysis of the volatile fraction obtained from 100 degrees C- and 121 degrees C-heated beef showed that the amounts of pyrazine, 2-methylpyrazine and diacetyl were higher in the 121 degrees C-heated beef than in the 100 degrees C-heated beef. GC-sniffing revealed that the odor quality of pyrazines was similar to that of retort beef aroma. Therefore, pyrazines were suggested to be a candidate responsible for the retort beef aroma. Analysis of commercial uncured corned beef and cured corned beef confirmed the presence of pyrazine, 2-methylpyrazine and 2,6-dimethylpyrazine.

The object of the present study was to reveal the action of inosine-5'-monophosphate (IMP) toward myofibrils in postmortem muscles. IMP solubilized isolated actomyosin within a narrow range of KCl concentration, 0.19-0.20mol/L, because of the dissociation of actomyosin into actin and myosin, but it did not solubilize the proteins in myofibrils with 0.2mol/L KCl. However, IMP could solubilize both proteins in myofibrils with 0.2mol/L KCl in the presence of 1m mol/L pyrophosphate or 1.0-3.3m mol/L adenosine-5'-diphosphate (ADP). Thus, we presumed that pyrophosphate and ADP released thin filaments composed of actin, and thick filaments composed of myosin from restraints of myofibrils, and then both filaments were solubilized through the IMP-induced dissociation of actomyosin. Thus, we concluded that IMP is a candidate agent to resolve rigor mortis because of its ability to break the association between thick and thin filaments.

Water-holding capacity (WHC) of heat-induced pork gels was examined. The heat-induced gels were obtained from meat homogenates prepared by adding nine volumes of 0.3-0.5mol/L NaCl solutions containing 9-36mmol/L disodium inosine-5-monophosphate (IMP) or 9mmol/L tetrapotassium pyrophosphate (KPP) to minced pork. IMP at 36mmol/L enhanced the WHC to the same level as attained by KPP. Physical and sensory properties of heat-induced gels were also examined. The heat-induced gels were prepared from porcine meat homogenates containing 0.3mol/L NaCl and 9-36mmol/L IMP or 9mmol/L KPP. IMP at 36mmol/L enhanced the values of hardness, cohesiveness, gumminess and springiness, measured with a Tensipresser, and several organoleptic scores to the same level as the score attained by KPP. Thus, it is concluded that IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages.