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Abstract: This study aimed to determine how small heat shock proteins (sHSPs) protect myofibrillar proteins from μ-calpain degradation during ageing. Immunoprecipitation experiments with M. longissimus dorsi (LD) from Angus heifers (n=14) examined the interaction between αβ-crystallin, desmin, titin, HSP20, HSP27 and μ-calpain. Results showed that αβ-crystallin associated with desmin, titin, HSP20, HSP27 and μ-calpain. Exogenous αβ-crystallin reduced desmin and titin degradations in myofibrillar extracts and attenuated μ-calpain activity. In a second experiment, bull LD (n=94) were aged at −1.5°C for up to 28days post mortem. μ-Calpain autolysed faster in high ultimate pH (pHu) meat (pHu ≥6.2) and this was concomitant with the more rapid degradation of titin and filamin in this pHu group. Desmin stability in intermediate pHu meat (pHu 5.8 to 6.19) may be due to the protection of myofibril-bound sHSPs combined with the competitive inhibition of μ-calpain by sHSPs. [Copyright &y& Elsevier]

Abstract: Bull Musculus longissimus dorsi (n =63) were categorised into high (pH≥6.2), intermediate (pH5.8–6.19) and low (≤5.79) ultimate pH (pHu) and aged up to 28days post mortem at −1°C. High pHu samples were acceptably tender at 1day post mortem and significantly more tender than low pHu meat at all ageing timepoints (p <0.05). Rapid autolysis of μ-calpain in high pHu meat was linked with the more rapid degradation of titin, nebulin and filamin in this pHu group. Desmin degraded faster in low pHu meat and was concurrent with an increase of cathepsin B levels. The results from this study support the hypothesis that beef tenderisation is pHu compartmentalised with tenderness in high and low pHu meat characterised by variable rate of degradation of high and low molecular weight myofibrillar proteins during ageing, which are in turn regulated by μ-calpain and cathepsin B activities. [Copyright &y& Elsevier]

Abstract: Bull M. longissimus dorsi (n=94) categorised into high (n=28), intermediate (n=14) and low (n=52) ultimate pH (pHu) were aged at −1.5°C for 28days. Shear force was higher and more variable (p<0.05) in intermediate pHu samples during ageing. Titin, filamin and desmin degradation was also less extensive in intermediate pHu samples compared to the other two pH categories. The extent of the decline of HSP20, HSP27 and αβ-crystallin concentrations during post mortem ageing was pHu related such that high pHu meat maintained the highest concentration of small heat shock proteins followed by intermediate and low pHu meat. μ-Calpain autolysis was slowest in intermediate pHu and cathepsin B activities remained consistently low during ageing in this group (p<0.05). Meat toughness in the intermediate pHu group may be attributed to the combination of a larger pool of sHSP with a sub-optimal cathepsin B activity and intermediary μ-calpain activities. [Copyright &y& Elsevier]

Abstract: The potential of near infrared (NIR) spectroscopy as an on-line method to quantify glycogen and predict ultimate pH (pHu) of pre rigor beef M. longissimus dorsi (LD) was assessed. NIR spectra (538 to 1677nm) of pre rigor LD from steers, cows and bulls were collected early post mortem and measurements were made for pre rigor glycogen concentration and pHu. Spectral and measured data were combined to develop models to quantify glycogen and predict the pHu of pre rigor LD. NIR spectra and pre rigor predicted values obtained from quantitative models were shown to be poorly correlated against glycogen and pHu (r 2 =0.23 and 0.20, respectively). Qualitative models developed to categorise each muscle according to their pHu were able to correctly categorise 42% of high pHu samples. Optimum qualitative and quantitative models derived from NIR spectra found low correlation between predicted values and reference measurements. [ABSTRACT FROM AUTHOR]