| Volatile compounds play an important role in the flavor formation of animal products, and volatiles in adipose tissues determine the species flavor of animal products. Hu sheep is a local breed with high lambing productivity in southern China. Investigation of aromatic active compounds in Hu sheep adipose tissue can provide important information for its breeding and consumers. Five experiments were conducted in this study. Firstly, the effect of animal factors including castrated, breed, age, gender and adipose tissue location on volatile compounds in Hu sheep adipose tissues were investigated, and the formative factors of main volatile compounds were further investigated (Experiment1and2). Then, using soybean oil and antioxidant as two factors, the effect of diet on Hu sheep growth performance, antioxidant ability, fatty acids profile and flavor characteristic of adipose tissues were investigated (Experiment3,4and5).1. Effects of castration, breed and age on volatile composition of fat tissue (Experiment1)In order to investigate the effects of castration, breed and age on volatile profiles in sheep fat tissue, SPME and GC-MS technique were used to extract and analyze the volatile compounds of the perirenal fat (PF) and subcutaneous fat (SF) tissues of wether, goat,10-month Hu sheep and24-month Hu sheep. The principal component analysis, and ANOVA were used to analyze the data. It is found that aldehydes were the main components of fat tissues, E-2-nonenal, E-2-octenal, E-2-decenal, nonanal, heptanal and2-undecanone were found to be the main volatiles. Castration had no effects on volatile levels in both adipose tissues. The SF of Hu sheep had more volatiles than that of goat (P<0.05). The SF of10-month Hu sheep had more volatiles than that of24-month Hu sheep (P<0.05). Main volatiles were all found higher in SF than in PF of both Hu sheep and goat (P<0.05). It can be suggested that, aldehydes were the main volatiles that determine adipose tissues’flavor. Species and age influenced the flavor compounds profile, but castration had no effect on the flavor compounds of goat adipose tissues.2. Effects of gender and fat location on fat quality of Hu sheep (Experiment2)In experiment two, the volatile compounds characteristic of the PF and SF tissues of male and female Hu sheep were investigated. The volatile compounds were determined by SPME-GC-MS, the fatty acids profile was analyzed by GC, and the malondialdehyde level and superoxide dismutase activity of fat tissues were also evaluated. The results were analyzed by PCA and two-way ANOVA. The PCA results showed that aldehydes and unsaturated fatty acids play the key role in distinguishment of ram SF from other fat tissues, and phenols and esters were the key factor in ewe SF’s part. A total of17volatile compounds were found as the key ones, including higher level of E-2-pentenal, heptanal, E-2-octenal, nonanal, E-2-nonenal, E,E-2,4-nonadienal, E-2-decenal,2-undecenal,2-decanone and4-chloro-octane in SF, and higher level of E-2-pentenal, E-2-hexenal, octanal, E-2-octenal, nonanal, E,E-2,4-nonadienal and4-chloro-octane in ewe fat tissues than rams (P<0.05). Unsaturated and monounsatulated fatty acids were higher in ram than ewe (P<0.05), and higher in the SF than PF (P<0.05). The step-wise regression analysis showed that aldehydes were closely correlated with unsaturated fatty acids, especially for C20:2. The antioxidation level of SF was higher than that of PF (P<0.05). It is suggested that higher content of unsaturated fatty acid is the direct cause of higher aldehydes in SF, even though the SF had higher antioxidation level than PF.3. Effect of soybean oil and antioxidant on finishing hu sheep growth performance, ruminal fermentation and serum antioxidant ability (Experiment3)In order to investigate the relationship between fatty acid profile and flavor charecteristic, and provide theory reference to practical feeding industry, animal experiment was conducted with two-factorial design in this experiment. Factor one was soybean oil which is rich in unsaturated fatty acids, and in consideration of the UFA is easy to oxidation reaction, antioxidant was as the second factor. In this experiment, feed intake and average daily gain was valued, ruminal fermentation was dertermined, and serum antioxidant ability was analyzed. The results showed that the the final weight of oil Hu sheep was lower than that of control group (P<0.05). The runimal acetic acid increased and butyric acid decreased in soybean oil group (P0.05). The serum GSH-Px activity was improved by antioxidant treatment (P<0.05). Therefore, oil diet can influence hu sheep growth performance, and antioxidant addition can improve sheep antioxidant ability.4. Effect of soybean oil and antioxidant on antioxidant ability and fatty acids profile of hu sheep adipose tissues (Experiment4)In order to investigate the effect of soybean oil and antioxidant on nutritional quality and antioxidant ability of hu sheep adipose tissue, in this experiment, the activity of catalase and SOD of hu sheep PF and SF in four treatment groups were evaluated, and the fatty acid profiles of adipose tissues were analyzed by GC. The result showed that no effect of soybean oil on the antioxidant ability of SF, but negative effect was found with SOD activity in PF (P<0.05). No change was found in SF fatty acid profile, but in PF, the fatty acid profile were influenced a lot by soybean oil diet, with decreasing total fatty acids amount and reducing percentage of UFA (P<0.05), the PCA results showed distinction between control diet and oil diet. And no significant influence was detected with antioxidant factor. It can be suggestted that the fatty acids profiles of different adipose tissues had different responses to diet effect, SF tended to be stable and PF changed much.5. Effect of soybean oil and antioxidant on flavor charecteristic of finishing hu sheep (Experiment5)In order to investigate the effect of soybean oil and antioxidant on Hu sheep adipose tissue flavor, the flavor finger-print of Hu sheep SF and PF was determined by electronic nose, and the volatile profile of all the tissues were analyzed by GC-MS. The results showed that obvious effect of soybean oil treatment on SF and PF flavor. Soybean oil had no effect on SF volatile but decreased the content of aldehydes in PF (P<0.05). DFA result from electronic nose showed clear distinction between oil diet and control diet, and similar distribution of four treatment groups was also found with volatile profiles’ results. The effect of antioxidant was not as strong as oil treatment, no sharp distinction between oil group and oil plus antioxidant group. It can be inferred that the Hu sheep flavor can be modified by soybean oil diet, PF flavor can be changed through decreased aldehydes by oil diet, and the SF flavor can be modified by comprehensive influence from whole volatiles.In summary, the volatile compounds of adipose tissue were very complex. The volatiles varied amoung different species, ages, genders and adipose tissue locations of animal. Aldehydes played a key role on this variation, with unsaturated fatty acids as the relative factor. The flavor charecteristic of Hu sheep adipose tissues were influenced by soybean oil treatment. Soybean oil decreased unsaturated fatty acids and aldehydes of Hu sheep PF, but did not modify the fatty acids and volatiles profile of SF. Therefore, the volatiles of SF were more varied than that of PF under physiological factors. While, the flavor of PF was more sensitive than that of SF under oil treatment, which aldehydes played esential role in changing adipose tissues flavor. |
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