Polifenoles del romero en la dieta del corderoefecto sobre la calidad y capacidad de conservación de la carne

Abstract

Abstract The collection of papers gathered in the present PhD thesis focuses on the practical application of a dietary rosemary extract (DRE) obtained by the second distillation of the leaves from which the essential oil has already been removed, in which the active principles are diterpenes carnosic acid and carnosol, both present in the same proportion. The use of this DRE in animal feeds has previously been patented by the research team with the aim of improving the quality and the endogenous conservation capacity of lamb meat in a healthy, ecological and economically viable way. In the first paper, "Relationship between antioxidant status and oxidative stability in lamb meat reinforced with dietary rosemary diterpenes", published in the journal Food Chemistry, we established the relationship between the concentration of the diterpenic metabolite deposited in muscle resulting from the dietary consumption of DRE, the antioxidant capacity of the fresh meat and the main physico-chemical (CIELabcolor, hexanal, TBARS and total carbonyls) and sensorial (appearance and rancidity) parameters used for the assessment of the oxidative spoilage of meat. The intake of 200 and 400 mg DRE/kg feed by the fattening lambs resulted in a dose-dependent deposition of functional levels of the diterpenic metabolite C19H22O3 in muscle, which improved the oxidative stability of the resulting lamb loin fillets (Longissimusthoracicus et lumborum) kept at 4 ºC in a protective atmosphere (70% O2/30% CO2) and constant illumination (800 lx), and analysed at different storage periods of between 0, 7, 11 and 14 days. A correlation (P<0.05) was established between the muscular deposition concentration of the diterpenic metabolite and the antioxidant capacity of the fresh meat, measured by means of the radical scavenging techniques (DPPH and TEAC) and the ferric reduction antioxidant power (FRAP). The antioxidant capacity was better correlated (P<0.05) with changes in the values of the CIELabcolor, TBARS and sensorial scores than with the increase in hexanal and total carbonyls coming from myofibrillar proteins. FRAP and DPPH assays were seen to be more accurate than TEAC for predicting the chilled meat oxidative spoilage and, particularly, for assessing the antioxidant effectiveness of the tested DRE on meat. Therefore, evaluation of the antioxidant capacity in fresh meat allows the oxidative spoilage of meat kept in retail conditions to be predicted. Thus, it would be possible to avoid or simplify the shelf-life studies needed for testing this kind of dietary supplement. The next step was to explore the commercial possibilities of the DRE, comparing it with a vitamin E supplement, the reference antioxidant in animal feeding. In the second paper, "Antioxidant and antimicrobial effects of dietary supplementation with rosemary diterpenes (carnosic acid and carnosol) vs vitamin E on lamb meat packed under protective atmosphere", published in the journal Meat Science, two equivalent doses of DRE and ?-tocopherol (600 mg/kg feed) were compared with the aim of evaluating their relative advantages and limitations. For this purpose, different microbiological (TVC, LAB, Enterobacteriaceae, E.coli and Salmonella spp.), physico-chemical (CIELabcolor, TBARS and total carbonyls) and sensorial (appearance and rancidity) parameters in loin fillets kept in retail conditions (see above paper) were analysed on days 0, 7, 11, 14 and 18. The combination of a bacteriostatic packaging and the low temperature were seen to be very effective for ensuring meat microbial quality. As a consequence, the whole antimicrobial potential of the DRE could not be unequivocally confirmed. Despite that, the R-diet reached a functional concentration of the diterpenic metabolite in the muscle, which resulted in an increased antioxidant and antimicrobial activity on the meat. In contrast, the E-diet yielded a higher muscular deposition of ?-tocopherol and was more effective (P<0.05) than the R-diet at preventing meat oxidation and resulting sensorial consequences. Both dietetic treatments allowed an increase in the shelf-life of lamb meat, assessed as the loss of freshness, up to 5 (R-diet) and 10 (E-diet) days, respectively. Compared with vitamin E, the lower bioavailability of the rosemary diterpenes would limit its potential for preserving meat. However, it did seem to reinforce the endogenous antioxidant mechanisms, regenerating and protecting vitamin E against degradation reactions. Finally, we looked at a new application for increasing the technological value of the DRE, based on promoting the preservative activity of sulphites. In the third paper, "Use of dietary rosemary diterpenes to extend the preservation of sulphited-lamb products", published in the journal Small Ruminant Research, we studied the possibility of using DRE supplementation to reduce the sulphites required for preserving meat products. The lamb diet was supplemented with 400 mg DRE/kg feed and patties were formulated with meat from supplemented (R) or not (C) lambs and increasing doses of SO2 (0, 150, 300 and 450 mg/kg meat), yielding 8 different treatments: C0, C150, C300, C450, R0, R150, R300 and R450. Different physico-chemical (CIELab color, pH, WHC, TBARS, total carbonyls and VOCs), microbiological (TVC, LAB and E.coli/coliforms) and sensorial (appearance and odour) parameters were analysed in meat patties kept in retail conditions (see above paper) at days 0, 4, 8 and 12. The use of meat obtained from lambs supplemented with DRE delayed discoloration, lipid oxidation, odour spoilage and the rancidity on meat patties. DRE supplementation extended from 7.9 to 12.3 days the shelf-life, assessed as the loss of freshness, of the patties formulated with 450 mg SO2/kg meat, the maximum legal dose permitted, although it was less effective when lower SO2 doses were employed. Therefore, the meat processing of lamb meat reinforced with rosemary diterpenes seems to be a promising strategy for the manufacture of raw meat products with added sulphites. Taking into account the results obtained, it can be concluded that the potential application of rosemary diterpenic extracts on the animal feeding would be based on its dual potential effect, as antioxidant and antimicrobial, on meat, and on its synergism with sulphite activity. The dietary use of DRE would take advantage and increase the value of the leaf by-products generated from rosemary distillation. However, diterpene intake needs to be optimised to increase even further the shelf-life of meat and meat products, without the use of preserving additives.