| This thesis aims to study the mechanisms whereby variations in dietary components may affect connective tissue contribution to meat toughness. In the in vivo study, the different planes of nutrition had a tendency towards muscle-specific effects on collagen characteristics. These results correlated with the cell biology study on fibroblasts isolated from three bovine muscles, in which there were phenotypic differences in growth behaviour and cell activity of the collagen-degrading enzymes, the matrix metalloproteinases (MMPs), which may be related to or even trigger muscle-specific responses in collagen metabolism found in chapter 1. Vitamins C and E, alone and synergistically, increased both the activity of MMPs and the synthesis of collagen from fibroblasts of semitendinosus (ST) and longissimus (LD) muscles, but to different extents. Cells from LD expressed more MMP activity than do cells from ST muscle, while the latter produced more soluble collagen than LD. Oxidative stress, originating in animals due to an imbalance in the removal of ROS and the content of antioxidants, down-regulated collagen metabolism exerted by IMCT fibroblasts in both muscles. However, the decrease in collagen synthesis was more marked in cells derived from LD than in cells from ST muscle. Vitamins C and E exerted a counteracting effect to oxidative stress environments in both cell lines, suggesting the importance of ensuring the correct administration of these nutrients in the animals' diets in order to hinder ROS and avoid negative effects on collagen contribution to meat tenderness. In conclusion, complex interactions between dietary components and exogenous factors such as stress and muscle-specific collagen metabolism could be affecting background toughness. This, partly, could be a potential reason driving the inconsistent meat tenderness that the meat industry is facing nowadays. Based on the results at the cellular level, it would be interesting to study further the effect that vitamins, as well as other micronutrients and their interaction with animal stress may have on collagen metabolism in vitro. Those results will provide insights as to the correct manipulation of micronutrients, in in vivo trials, in order to try the reduction of background toughness contribution to final beef tenderness. |
