Plant secondary compounds in small ruminant feeding: an alternative to synthetic compounds for improving meat quality in low-input farming systems

Abstract

Sheep meat is a source of polyunsaturated (PUFA) and monounsaturated (MUFA) fatty acids that confer beneficial effects to human health, but it also contains high concentration of saturated fatty acids (SFA) that are associated with the development of certain diseases. To attain a healthier intramuscular fatty acid composition, that is, meat with high PUFA to SFA ratio, and low in fatty acids n-6 to n-3 ratio, several strategies focused on animal feeding have been tested. However, a sufficient amount of antioxidants must be present in meat to counterbalance the increase in the content of readily oxidizable unsaturated fatty acids, which is vulnerable to oxidation, and from the associated deterioration of meat colour and proteins, thus antioxidants are crucial in preserving the nutritive value and extending the shelf life of the meat.

The increasing costs of feedstuffs for livestock led to the utilization of cheaper resources as alternatives to reduce the production cost. Here, locally available materials and agro-industrial by-products commonly found in the Mediterranean countries (citrus pulp, carob pulp, and olive cake) were used in feeding trials with lambs and the effects on meat quality were evaluated. These plant-derived materials contain considerable amounts of secondary bioactive metabolites, which affect the fatty acid composition and/or act as antioxidants. Hence, it was hypothesized that at appropriate levels of inclusion in to the lamb diets, these feedstuffs would not negatively affect animal health and productivity, and would represent a strategy to naturally produce a healthy and oxidatively stable meat.

In the first study (Experiment 1), Comisana male lambs were fed for 60 days:a conventional cereal-based concentrate diet, or concentrates in which 24% or 35% dried citrus pulp was included in partial replacement of barley. Following slaughter, the slices of longissimus thoracis et lomborum muscle were packed aerobically and stored for up to 6 days. The inclusion of citrus pulp in the diet effectively inhibited protein oxidation in meat by reducing protein radicals, carbonyl formation, and thiol loss in comparison to the Control. The results showed the ability of citrus pulp to be conveniently included among the ingredients of a concentrate-based diet and to result in an improved oxidative stability of meat proteins.In the second study (Experiment 2), Comisana lambs were fed for 60 days: conventional concentrates or a diet in which cereal concentrates were partially replaced by 24% or 35% carob pulp. The results demonstrated that feeding carob pulp did not affect animal productivity and improved the muscle content of PUFA, among which is rumenic acid, and reduced the SFA concentration and the n-6/n-3 PUFA ratio as compared to the control diet. Moreover, no extensive colour, lipid and protein oxidation in meat were observed over 6 days of aerobic storage. Therefore, dietary carob in lamb diet could be an effective strategy to improve the PUFA content in the meat without compromising animal growth performance and meat oxidative stability. In the third study (Experiment 3), the effect of feeding lambs with diets including linseed and olive cake on the evolution of volatile compounds (VOCs) in meat was assessed. Specifically, Appenninica lambs fed commercial concentrates or diets containing linseed, or olive cake, or combination of both. The VOC profile was determined through SPME-GC-MS analysis of raw and cooked meat The cooked meat showed higher concentrations of VOCs than raw meat and most of these were derived from fatty acid oxidation.Nevertheless, in both raw and cooked meat, none of the lipid oxidation-derived volatiles was significantly affected by the dietary treatments. Therefore, the results suggest that the replacement of cereal concentrates with linseed and/or olive cake in diets for lambs did not cause appreciable changes in VOC profile of meat.