Paul L. Sensky

Tenderness - an enzymatic view.

One of the most common causes of unacceptability in meat quality is toughness. Toughness is attributed to a range of factors including the amount of intramuscular connective tissue, intramuscular fat, and the length of the sarcomere. However, it is apparent that the extent of proteolysis of key proteins within muscle fibres is significant determinant of ultimate tenderness. The objective of this manuscript is to describe the main endogenous proteolytic enzyme systems that have the potential to be involved in muscle post-mortem proteolysis and whether the experimental evidence available supports this involvement.

The relationship between slow and fast myosin heavy chain content, calpastatin and meat tenderness in different ovine skeletal muscles.

The present study investigated the relationship between fibre type distribution and slow (MHC-s) and fast (MHC-f) myosin heavy chain content on calpastatin and meat tenderness in longissimus dorsi (LD), tensor fasciae latae (TFL), semitendinosus (ST), trapezius (TZ) and supraspinatus (SS) muscles from six Mule×Charolais rams. Samples taken at slaughter were frozen either in liquid N(2) for analysis of MHC-s and MHC-f by immunoblotting, or in cooled isopentane for histochemical fibre typing. Calpastatin activity and an immunoreactive 135 kDa calpastatin band were analysed in samples taken 24 h postmortem. Shear force was determined on muscle chops taken at 24 h postmortem and conditioned until day 14. The intensity of MHC-s and MHC-f immunopositive bands correlated with %Type I and %Type II fibres identified histochemically (r(2)=0.612 and 0.366, respectively, p<0.001). Muscle specific differences were observed in MHC-s and MHC-f immunoreactivity, fibre type distribution, calpastatin activity, calpastatin 135 kDa immunoreactivity and shear force. MHC-s correlated positively with calpastatin activity (r(2)=0.725, p<0.001) and 135 kDa calpastatin (r(2)=0.228, p<0.01) across all muscle types. The data show that detection of MHC-s can be used to identify fibre type differences between ovine muscles and that this correlates with differences in calpastatin content and inhibitory activity, but not tenderness.

The effect of altered growth rates on the calpain proteolytic system and meat tenderness in cattle

The present study was conducted to determine the effects of growth pattern on the calpain system and meat tenderization. Twenty-four Friesian calves were randomly allocated to three treatment groups: FAST (fast growth rate), SLOW (severely restricted growth rate) and ALTER (restricted growth for 30 days followed by fast growth rate). Four animals from each group were slaughtered on day 32 or 45 after altering the growth rates. Samples of M. longissimus dorsi were rapidly frozen at slaughter for protein analysis by Western blotting. Restricted growth reduced the immunoreactivity of a calpastatin band (135 kDa) measured at 24 h postmortem. Immunoreactivity associated with the large subunit of μ- or m-calpain appeared to be unaffected by growth patterns. Shear force measurements taken after 14 days of conditioning were positively related to 135 kDa calpastatin at 24 h postmortem. In this study there was no clear relationship between shear force and growth pattern.