The effect of electrical stimulation on post mortem myofibrillar protein degradation and small heat shock protein kinetics in bull beef.

This study aimed to determine the effect of electrical stimulation and ultimate pH (pHu) on shear force, myofibrillar protein degradation and small heat shock protein (sHSP) concentrations in M. longissimus lumborum (LL). The LL from both sides of carcasses (n=15) was excised with low voltage electrical stimulation (ES) applied to an LL muscle from one side, while the opposing LL muscle was not stimulated (NS). Muscles were categorised into low (pHu<5.8), intermediate (5.8≤pHu<6.2) and high pHu (pHu≥6.2) and aged for up to 28days post mortem at -1.5°C. High pHu meat tenderised faster which corresponded with the faster degradation of titin and desmin in this group compared with low and intermediate pHu meat. Electrical stimulation significantly affected the variable levels of αß-crystallin and HSP20 with higher concentrations of these sHSP in ES muscles at later ageing timepoints compared with NS muscles.

The protection of bovine skeletal myofibrils from proteolytic damage post mortem by small heat shock proteins.

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 αß-crystallin, desmin, titin, HSP20, HSP27 and µ-calpain. Results showed that αß-crystallin associated with desmin, titin, HSP20, HSP27 and µ-calpain. Exogenous αß-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 28 days post mortem. µ-Calpain autolysed faster in high ultimate pH (pH(u)) meat (pH(u)≥6.2) and this was concomitant with the more rapid degradation of titin and filamin in this pH(u) group. Desmin stability in intermediate pH(u) meat (pH(u) 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.

The development of meat tenderness is likely to be compartmentalised by ultimate pH.

Bull Musculus longissimus dorsi (n=63) were categorised into high (pH≥6.2), intermediate (pH 5.8-6.19) and low (≤5.79) ultimate pH (pHu) and aged up to 28 days post mortem at -1°C. High pHu samples were acceptably tender at 1 day 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.

Small heat shock proteins and their role in meat tenderness: a review.

The eating quality of meat is a result of complex interactions between the biological traits and biochemical processes during the conversion of muscle to meat. It was hypothesised that muscles inevitably engage towards apoptotic cell death due to the termination of oxygen and nutrient supply to the muscle following exsanguination. Thus, factors that regulate the process of apoptotic cell death of muscle cells are believed to ultimately influence meat quality. Proteomic studies have associated the regulation of small heat shock proteins (sHSPs) with various meat quality attributes including tenderness, colour, juiciness and flavour. Due to the anti-apoptotic and chaperone functions of sHSPs, they are proposed to be involved with the eating quality of meat. In this review, we discuss the possible chaperone and anti-apoptotic role of sHSPs during the conversion of muscle to meat and consider the repercussions of this on the development of meat tenderness.

Small heat shock proteins and toughness in intermediate pHu beef.

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 αß-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.

Near infrared spectroscopy as an on-line method to quantitatively determine glycogen and predict ultimate pH in pre rigor bovine M. longissimus dorsi.

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