Changes in Lipase and Antioxidant Enzyme Activities during Processing of Cantonese Sausage with D-Sodium Erythorbate

Pork was used as raw material to produce Cantonese sausage, with additions of 0.05% or 0.1% D-sodium erythorbate. The oxidation indices (peroxide value, TBARS value, carbonyl value, and conjugated dienes value) and enzyme activity (total phospholipase, acid lipase, neutral lipase, superoxide dismutase, and glutathione peroxidase) were measured in the sausages at different processing periods. The results showed slowed lipid oxidation in the presence of D-sodium erythorbate, inhibition of total phospholipase, acid lipase, and neutral lipase activities, and increased superoxide dismutase activity, with little change in glutathione peroxidase activities. When increasing D-sodium erythorbate, the superoxide dismutase activity was negatively correlated with the peroxide value at 5 h (P<0.01), the neutral lipase activity was positively correlated with the conjugated dienes value at 15 h (P<0.01), and the total phospholipase activity was positively correlated with the peroxide value at 30 h (P<0.01). This study explored the antioxidant effect of D-sodium erythorbate and provides a theoretical foundation to improve the quality of Cantonese sausage.

Regulation and role of hormone-sensitive lipase in rat skeletal muscle

Intramyocellular triacylglycerol (TG) is an important energy store, and the energy content of this depot is higher than the energy content of the muscle glycogen depot. It has recently been shown that the mobilization of fatty acids from this TG pool may be regulated by the neutral lipase hormone-sensitive lipase (HSL). This enzyme is known to be rate limiting for intracellular TG hydrolysis in adipose tissue. The presence of HSL has been demonstrated in all muscle fibre types by Western blotting of muscle fibres isolated by collagenase treatment or after freeze-drying. The content of HSL varies between fibre types, being higher in oxidative fibres than in glycolytic fibres. When analysed under conditions optimal for“ HSL, neutral lipase activity in muscle can be stimulated by adrenaline as well as by contractions. These increases are abolished by the presence of anti-HSL antibody during analysis. Moreover, immunoprecipitation with affinity-purified anti-HSL antibody causes similar reductions in muscle HSL protein concentration and in measured neutral lipase responses to contractions. The immunoreactive HSL in muscle is stimulated by adrenaline via β-adrenergic activation of cAMP-dependent protein kinase (PKA). From findings in adipocytes it is likely that PKA phosphorylates HSL at residues Ser563, Ser659and Ser660. Contraction probably also enhances muscle HSL activity by phosphorylation, because the contraction-induced increase in HSL activity is elevated by the protein phosphatase inhibitor okadaic acid and reversed by alkaline phosphatase. A novel signalling pathway in muscle by which HSL activity may be stimulated by protein kinase C (PKC) via extracellular signal-regulated kinase (ERK) has been demonstrated. In contrast to previous findings in adipocytes, in muscle the activation of ERK is not necessary for stimulation of HSL by adrenaline. However, contraction-induced HSL activation is mediated by PKC, at least partly via the ERK pathway. In fat cells ERK is known to phosphorylate HSL at Ser600. Hence, phosphorylation of different sites may explain the finding that in muscle the effects of contractions and adrenaline on HSL activity are partially additive. In line with the view that the two stimuli act by different mechanisms, training increases contraction-mediated HSL activation but diminishes adrenaline-mediated HSL activation in muscle. In conclusion, HSL is present in skeletal muscle and can be activated by phosphorylation in response to both adrenaline and muscle contractions. Training increases contraction-mediated HSL activation, but decreases adrenaline-mediated HSL activation in muscle.