Pomegranate by-products as ruminant feeds: Effects on meat quality

Increasing demand and production of pomegranate has led to a large amount of by-products that might be used in ruminant feeding. In this PhD thesis, we have investigated the effect of dietary whole pomegranate by-product (WBP) on performance and meat quality of lambs. The WBP was collected from a processing company after squeezing to obtain juice, and it included peels, seeds, membranes and small residual parts of pulp. These parts of pomegranate are particularly rich in bioactive compounds: seeds contain a high amount of lipids, which are mainly characterised by conjugated linolenic acids (CLnA) and among which, the punicic acid (C18:3 c9 t11 c13) is the predominant. Whereas, pomegranate peels are a valuable source of phenolic compounds, and in particular tannins. In the first study (Chapter 5), seventeen lambs were assigned to two experimental treatments and fed a cereal-based concentrate (CON) or the same concentrate where 200 g/kg DM of barley and corn were replaced by whole pomegranate by-product (WPB). After 36 days of trial the lambs were slaughtered and samples of rumen digesta, liver and muscle were collected. The dietary treatment did not affect all the animal performance parameters. While, total polyunsaturated FA (PUFA), linolenic, rumenic (RA), and vaccenic (VA) acid were increased in liver and muscle of WPB lambs (P < 0.05). Punicic acid and three isomers of conjugated linolenic acid were detected exclusively in the rumen and tissues of WPB-lambs. The C18:1 t10/t11 ratio in rumen digesta or in tissues was reduced by feeding WPB (P < 0.001), suggesting that the WPB prevented the t10-shift rumen biohydrogenation pathway. The second study (Chapter 6) was designed to fill in the knowledge gaps found in the first study. Indeed, it remains unclear whether this effect on FA metabolism was due to the action of the bioactive CLnA or of the tannins or perhaps to their interaction. Therefore, two in vitro experiments were conducted: the first one tested the effects of pomegranate oil and tannins, alone or in combination, on the biohydrogenation process, and the second one compared the ruminal responses to by-products rich in CLnA (pomegranate seeds, PS), in tannins (pomegranate peels and pulp, PPP) or in both bioactive components (i.e., the whole pomegranate by-product; WPB). Three cannulated ewes were used as donors of inocula for batch cultures of rumen microorganisms. Incubations lasted for 12 and 24 h and were repeated on 3 different days. The consistency in the results from both trials would confirm that pomegranate tannins and CLnA played different roles in modulating ruminal FA composition. Specifically, tannins would favour the accumulation of potentially health-promoting FA present in dietary lipids (e.g., 18:2n-6 or 18:3n-3) and cis-9 trans-11 conjugated linoleic acid (CLA), whereas the observed increase in trans-11 18:1 would mainly derive from the biohydrogenation of CLnA isomers. Changes in ruminal fermentation parameters showed that pomegranate tannins protected dietary protein from degradation. Nevertheless, a negative impact on in vitro ruminal fermentation was observed when 20% of by-products were included in the diet. Finally, there seem to be no evident synergistic but additive effects between pomegranate bioactive compounds (i.e., tannins and CLnA) on ruminal biohydrogenation or fermentation. The third study (Chapter 7) investigated the effect of including whole pomegranate by-product in lamb diet on meat oxidative stability, using the meat samples from the first experiment. Meat from WPB-fed lambs had a greater concentration of vitamin E (α- and γ-tocopherols), polyunsaturated fatty acids (PUFA), highly peroxidizable PUFA and a higher peroxidability index (P < 0.05). Feeding WPB limited the formation of metmyoglobin (P = 0.05) and reduced lipid oxidation (TBARS values) after 7 days of storage for fresh meat (P = 0.024) or 4 days for cooked meat (P = 0.006). Feeding WPB increased meat antioxidant capacity (ORAC assay) in the lipophilic fraction (P = 0.017), but not in the hydrophilic. These results suggest that vitamin E in the pomegranate by-product contributed to the higher antioxidant capacity of meat from the WPB-fed lambs.