Effect of different chilling rates on the quality parameters of mule duck fatty liver.

The aim of this experiment was to study the effect of chilling rates on the quality features of fatty livers. Three different chilling rates were applied: ultra-fast (UF), fast (FA), and slow (SL). Technological and proteomic results were compared at time T1 when the internal temperature of livers reached 10°C and at time T2=24 h post mortem. Samples from the UF group reached the T1 temperature at 50 min post mortem and had the least hard livers and the lowest cooking loss percentage (25±9%) at time T2=24 h post mortem (P-value of <0.01). The FA and SL groups reached the T1 temperature after 120 and 210 min post mortem and presented higher melting (36±9 and 41±9%, respectively, at time T2) and harder livers compared to the UF group. In parallel, we conducted semi-quantifications of proteins by electrophoresis and proteolytic activities by mono-dimensional zymography for three families of proteases: Matrix metalloproteases (MMP), Cathepsins, and Calpains. The proteomic assays revealed less modified proteolytic activities in samples from the UF group, and less associated proteins degradations than in samples from the FA and the SL groups. Effects of the different chilling rates were mainly significant at time T2 (24 h post mortem). As a conclusion we were able to highlight an indirect positive relation between proteolysis and melting yield in ducks' fatty liver.

Proteolytic activity alterations resulting from force-feeding in Muscovy and Pekin ducks.

We investigated liver protease activity in force-fed and non-force-fed ducks using zymography gels to better understand mechanisms underlying liver steatosis in palmipeds. Male Muscovy and Pekin ducks were slaughtered before and after a short period (13 d) while they were conventionally fed or force fed. The force-fed regimen contained a high level of carbohydrates and was delivered in large doses. Main hepatic proteases (matrix metalloprotease-2, calpains, and cathepsins) were extracted from raw liver and specifically activated within electrophoretic gels. Both force-fed Muscovy and Pekin ducks presented higher liver weights and BW associated with lower matrix metalloprotease-2 and m-calpain hepatic activities. On the other hand, hepatic cathepsin activity was not affected by force feeding. It was concluded that Muscovy and Pekin duck hepatic proteases are affected similarly by the force feeding. Thus, this cannot explain differences observed between Muscovy and Pekin ducks regarding their ability to develop hepatic steatosis generally reported in literature.