内源蛋白酶在肉嫩化中的作用(综述)

本文阐述了与肉成熟有关的两类蛋白酶,即钙激活蛋白酶和溶酶体组织蛋白酶,并分别就两类酶的分类、影响酶活性的因素、在肉嫩化中的作用、分离提纯及活性测定方法等作了介绍.     

Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets

The aim of the present experiment was to measure the protease activities in ice-stored and super-chilled Atlantic salmon (Salmo salar) fillets, and the effect on texture. Pre-rigour fillets of Atlantic salmon were either super-chilled to a core temperature of −1.5 °C or directly chilled on ice prior to 144 h of ice storage. A significantly higher calpain activity was detected in the super-chilled fillets at 6 h post-treatment compared to the ice-stored fillets and followed by a significant decrease below its initial level, while the calpastatin activity was significantly lower for the super-chilled fillets at all time points. The cathepsin B + L and B activities increased significantly with time post-treatment; however, no significant differences were observed at any time points between the two treatments. For the ice stored fillets, the cathepsin L activity decreased significantly from 6 to 24 h post-treatment and thereafter increased significantly to 144 h post-treatment. There was also a significantly lower cathepsin L activity in the super-chilled fillets at 0 h post-treatment. No significant difference in breaking force was detected; however, a significant difference in maximum compression (F_max) was detected at 24 h post-treatment with lower F_max in the super-chilled fillets. This experiment showed that super-chilling had a significant effect on the protease activities and the ATP degradation in salmon fillets. The observed difference in F_max may be a result of these observed differences, and may indicate a softening of the super-chilled salmon muscle at 24 h post-treatment.     

Textural assessment of clenbuterol treatment in beef

Eight Charolais heifers (ca. 300 kg) were fed a diet containing either 0 (control) or 1 ppm clenbuterol during 5 weeks. Daily live weight gain was higher (p<0.01), by about 34%, in treated animals. They were slaughtered after a week of withdrawal. Activity of μ-calpain of meat from clenbuterol-fed heifers was lower (p<0.01) immediately post mortem, while activity of calpastatin was higher (p<0.05) than in meat from controls. According to sensory and instrumental data, meat from clenbuterol-fed heifers did not tenderise during aging, and was tougher (p<0.05) than control meat at 8th day post mortem. Both principal component analysis and multivariate discriminant analysis of a pool of data of the textural profile showed differences due to clenbuterol treatment at 24 h. The slope after yield (calculated from the Warner–Bratzler shearing force–deformation curve), was the only textural parameter affected (p<0.05) at 24 h by the treatment.     

Evidence for post-mortem m-calpain autolysis in porcine muscle

The objective of the present work was to characterize changes in calpain activity in pork post-mortem. Samples from pig M. longissimus dorsi and M. semimembranosus were collected three days post-mortem from 75 animals and analyzed with casein zymography. The results indicated post-mortem autolysis of m-calpain as two m-calpain bands were observed on the zymogram gel. Use of M. longissimus dorsi from three pigs collected at different times during storage further confirmed post-mortem autolysis of m-calpain. The activity of the autolyzed form of m-calpain was detectable at day 3 and further increased at day 6. The results also showed a decrease in the non-autolyzed m-calpain activity during post-mortem storage. Collectively, these results suggest that m-calpain is active post-mortem in porcine muscles.     

The efficiency of electrical stimulation to counteract the negative effects of β-agonists on meat tenderness of feedlot cattle

Beta agonists used as growth enhancers are known to affect the aging potential of beef muscle negatively. On the other hand, procedures like electrical stimulation could accelerate rigor and the aging process. In this study, 20 out of 40 young steers received no beta agonist (C), the remaining twenty steers received a beta agonist (zilpaterol hydrochloride) (Z) for the 30 days prior to slaughter followed by 4 days withdrawal.     

Factors regulating lamb longissimus tenderness are affected by age at slaughter

The objective of this experiment was to determine age-related changes in collagen concentration, sarcomere length, calpain (μ- and m-) and calpastatin activities, postmortem proteolysis and Warner–Bratzler shear force (WBSF) in ovine longissimus thoracis et lumborum. Rambouillet lambs were slaughtered at 2, 4, 6, 8 and 10 months of age and samples of longissimus were collected at 0, 2 and 10 days postmortem. Collagen concentration and sarcomere lengths were determined from the cores used for WBSF measurements and reflected changes in the background toughness. Longissimus collagen concentration did not change (P>0.05) due to lamb age. Sarcomere lengths also showed age-related changes, increasing (P<0.05) from 1.35 μm at 6 months to 1.48 and 1.55 μm at 8 and 10 months, respectively. The extent of calpain mediated proteolysis determines the improvement in meat tenderness with postmortem storage. The most notable change in the calpain proteolytic system was the decline (P<0.05) in calpastatin activity from 4.18 to 1.91 U/g muscle between 2 and 10 months. The activity of μ-calpain showed a 16% increase (P<0.05) from 4 to 6 months, before it dropped again at 8 and 10 months. There was a gradual decline (P<0.05) in m-calpain activity with age, and by 10 months m-calpain activity had reduced to 80% of 2 months levels. The ratio of μ-calpain to calpastatin activities increased (P<0.05) from 2 to 6 months (from 0.31 to 0.56) with no further changes (P>0.05) at 8 or 10 months. There were no age-related changes (P>0.05) in desmin degradation at day 2, however, examination of day 10 samples showed increased (P<0.05) degradation from 2 to 6 months. Thus, the changes observed in the ratio of μ-calpain to calpastatin activities are reflected in the extent of postmortem proteolysis. Meat tenderness was measured using WBSF at 2 and 10 days postmortem. Because little proteolysis had taken place at 2 days postmortem, the decline in day 2 WBSF from 6 to 8 months could be explained by changes in sarcomere length. However, at 10 days postmortem, where WBSF was shown to decrease from 2 to 8 months, the improvement in tenderness could be explained by the amount of postmortem proteolysis. The data presented in this paper show evidence that sarcomere length is the main determinant of background toughness in ovine longissimus, and that postmortem proteolysis, resulting from μ-calpain activity regulated by calpastatin, is the main determinant of ovine longissimus tenderization during aging. Thus, lamb longissimus tenderness after refrigerated storage is determined by postmortem proteolysis and its interaction with sarcomere length.     

Proteins and proteolytic activity changes during refrigerated storage in sea bass (Dicentrarchus labrax L.) muscle after high-pressure treatment

Contrary to other preservation methods like thermal treatments, high pressure can destroy microorganisms without affecting the nutritional quality, color, or food texture. The firm texture of fish flesh is an important quality parameter. During the refrigerated storage, the tissue becomes softer and the muscle is deteriorated by different proteases. The aim of this study was to study the modification of the fish muscle proteins after high-pressure treatment during the refrigerated storage and to evaluate the effect of high-pressure treatment level on the post-mortem protein changes and enzyme activities. The calpain activity decreased with the high-pressure treatment and evolved differently during the refrigerated storage, depending on the level of pressurisation. Its inhibitor, the calpastatin was not affected by high pressure, but its inhibiting potential decreased during the post-mortem storage. The activities of cathepsins were modified by the high-pressure treatment and the time of storage, but depended according to their class. The electrophoresis profiles showed that sarcoplasmic proteins were modified according both the high-pressure treatment and the period of storage. For the myofibrillar proteins, the only changes were due to the high-pressure treatment.     

Effects of high-pressure processing on proteolytic enzymes and proteins in cold-smoked salmon during refrigerated storage

The present paper describes the effects of high-pressure processing on the activity of proteolytic enzymes in cold-smoked salmon and enzyme extracts for pressures up to 300 MPa. The activities of the three enzymes, cathepsin B-like, cathepsin B + L-like and calpains were reduced at all pressure levels of up to 300 MPa (at ca. 9 °C for 20 min) in crude enzyme extracts prepared from cold-smoked salmon. Calpain almost completely inactivated at 300 MPa. High-pressure did not influence general proteolytic activity but activated the enzymes in muscles at higher pressure levels studied until 18 days of storage. An increase in the activity of cathepsin B + L-like and calpain was seen after 12 days of refrigerated storage. Myosin heavy chain was less affected at higher pressure levels (300 MPa) only as shown by Sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) of proteins and further refrigerated storage had no obvious effects on proteins.     

Energy supply patterns for finishing steers: Feed conversion efficiency, components of bodyweight gain and meat quality

The objective was to determine the effect of pre-slaughter growth rate on feed efficiency, components of body growth and on the tenderness of longissimus muscle from steers reared to a common age and carcass weight. Sixty Friesian steers were group-housed and offered grass silage ad libitum and 3.5kg concentrates per animal daily for 5 months and then 5kg concentrates and 1kg grass hay for 1month before the experiment began. The animals were then weighed and in a randomised block were assigned to one of 5 groups, for slaughter at the beginning of the experiment or to be offered concentrates and hay (900 and 100g/kg total diet, respectively) to achieve target growths of: 0.72kg/day continuously for 17 weeks, 0.36kg/day for the first 8 weeks and 1.08kg/day for the final 8 weeks (low-high), 1.08kg/day for the first 8 weeks and 0.36 for the final 8 weeks (high-low) or 0.36kg/day for the first 2 weeks, 0.72kg/day during weeks 4 and 14 and 1.08kg/day for the final 2 weeks (pulse). One week was allowed for transition to the different dietary allowances within each energy supply pattern. The mean age at the beginning and end of the study was 18 and 22.5 months, respectively. After slaughter, the weight of the carcass and kidney+channel fat depot were recorded, the pistola hind quarter was dissected into fat, lean and bone and the tenderness of the m. longissimus thoracis et lumborum (LTM) muscle was measured instrumentally and using a trained taste panel after 2, 7 or 14 days ageing. The pattern of energy supply did not affect carcass weight, fat score or kidney+channel fat weight. The pistola hind quarter from animals offered the low-high energy pattern had a similar composition to the continuously-fed animals but contained more muscle than that from animals offered high-low or pulse energy patterns. After 14 days ageing, LTM from the continuously-fed animals was more tender than that from animals offered the other energy supply patterns but shear force did not differ between supply patterns. The data do not support the hypothesis that pre-slaughter growth rate increases tenderness but suggest that energy supply pattern can influence body composition of finishing cattle.