Functional Lipid Analysis In Tissues Of Different Kinds Of Cattle And Effect Of Thermal Treatme Nts On Lipid Oxidation

The objective of this work was to investigate the nutritional characteristics of five tissues(biceps femoris muscle(BFM), longissimus muscle(LSM), liver(LV), subcutaneous adipose tissue(SAT) and abdominal adipose tissue(AAT) in yak, yellow cattle and water buffalo, and the contents of squalene, tocopherol and fatty acid profile in five tissues of three cattle were determined using Gas Chromatography-Mass Spectrometry(GC-MS), High Performance Liquid Chromatography(HPLC), Ultra Performance Liquid Chromatography(UPLC) and Gas Chromatography(GC). Moreover, this work also investigated the effects of four thermal treatments on lipid oxidation, fatty acid profile and formation of volatile compounds of yak met. The main research contents and results are as follow.(1) The analytical methods of HP-SPME-GC-MS and HPLC-PAD have been developed for the qualitative and quantitative analysis of squalene in yak meat. Firstly, squalene in yak meat was extracted with CAR/PDMS fiber, after separated by HP-5MS column(30 m×0.25 mm I.D. × 0.25μm), and then MS was used to analyzed it qualitatively. It was found that there was the molecular ion peak [C30H50] +(m/z 410) of squalene and some characteristic fragment ions, such as [C5H9] +(m/z 69)、[C6H9+.](m/z 81)、[C7H11]+(m/z 95)and [C10H17] +(m/z 137) etc., which were used to accurately qualitative analysis of squalene in yak meat. Based on qualitative analysis, quantitative analysis of squalene was also investigated. The samples were saponified using 1.0 mol/L KOH solution under 75℃ for 30 min and then extracted with petroleum ether, squalene was separated on Proshell 120 C18(3.0 × 100 mm, 2.7 μm), and then detected using photodiode array detection. Excellent linearity of the calibration curve was observed in the range from 1.0 to 1000 μg/m L and correlation coefficient was 0.9997. The LOD and LOQ were 0.20 and 0.60 mg/L, respectively. The RSD was 1.70% and the recoveries were from 83.78 to 102.4%.(2) Squalene was found in five tissues of yak which live at the Tibet plateau area, and squalene contents in five tissues of yak were significantly different(p<0.05), and high level of squalene(59.82 mg/100g) was found in the BFM. α-、β + γ-and δ-tocopherol were identified in five tissues of yak, and α-tocopherol was accounted for 95.73~96.85% of total tocopherols, and its content in LV(2487.27 μg/100g) was significantly higher than muscular and adipose tissues. Moreover, fatty acid composition in five tissues of yak was also analyzed, the highest content in five tissues of yak was SFA(51.14-58.11 g/100g), followed by MUFA(16.08-46.11 g/100g) and PUFA(2.86-25.81 g/100g). Conjugated linolenic acids(CLA) were also found in BFM(0.36 g/100g), SAT(0.62 g/100g) and AAT(0.77 g/100g) and there were significantly different among the three tisseues(p<0.05).(3) There was a significant difference in squalene content among the five tissues of water buffalo(p<0.01), and the high content of squalene were found in the BFM(257.70 mg/100g) and LSM(125.68 mg/100g). In addition to α-tocopherol, which had been reported, β+γ-, δ-tocopherol isomers were also found in the five tissues of water buffalo. β+γ-tocopherols were found in the LV(52.10 μg/100 g) and AAT(9.33 μg/100g), and high content of δ-tocopherol was observed in the SAT(64.67 μg/100g) and AAT(25.67 μg/100g), respectively. Distribution of fatty acids in five tissues also was investigated, and there was a significant difference in fatty acids among the five tissues(p<0.01). The higher SFA content was showed in the SAT(65.12 g/100g) and AAT(68.83 g/100g) and the higher content of MUFA was indicated in the BFM(44.74 g/100g) and LSM(40.18 g/100g), whereas the higher PUFA content was observed in the LV(24.69 g/100g).The ratios of PUFA/SFA and n-6/n-3 were 0.49 and 3.39, respectively.(4) Squalene was found in the five different tissues of yellow cattle and their contents in the BFM and LSM were 19.07 mg/100 g and 7.81mg/100 g, respectively, which were significantly higher than those of LV, SAT and AAT(p < 0.05). α-tocopherol, accounting for 87.26-93.02%, is the primary component which is composed of the total tocopherols in the five tissues of yellow cattle. The contents of α-tocopherol(1028.10 μg/100g) and total tocopherols(1168.56μg/100g) in the LV were notably higher than those of SAT, AAT, BFM and LSM(p<0.05). This work also found the distribution of fatty acids in five tissues of yellow cattle. BFM(52.03g/100g) and LSM(54.29 g/100g) contained higher contents of SFA, SAT(46.92 g/100g) and AAT(47.54 g/100g) showed higher contents of MUFA, whereas LV(18.24g/100g) indicated higher content of PUFA. The n-6/n-3 rate in the LV was 2.93. Except for LV, CLA was found in the muscular and adipose tissues and their contents in the BFM and LSM were 0.40 g/100 g and 0.38 g/100 g, respectively.(5) This work investigated systematically about the effect of four thermal treatments on the lipid oxidation, fatty acid profile and formation of volatile compounds in yak meat. Roasting, microwaving, boiling and steaming have significantly affected on the lipid oxidation. The highest TBARS value was found in the roasted meat(1.00 mg MDA/kg), and the lowest value was observed in the boiled meat(0.57 mg MDA/kg). The highest and lowest cooking loss were found in the microwaved(39.46 %) and roasted(23.54 %) meat, respectively. Four thermal treatments significantly increased SFA content of intramuscular lipid of yak meat and remarkably decreased contents of MUFA and PUFA, ratios of PUFA/SFA and n-6/n-3. The highly increasing ratio in SFA content in roasted meat was 21.38 %, while the decreasing ratio in MUFA content was 22.90 %; the decreasing ratio in MUFA content in boiled meat was only 17.26 %, whereas the reducing ratio in PUFA content in boiled meat was 32.37 %. A total of 38 volatile compounds in four cooked yak meat were separated and identified using SPME-GC-MS, and classified into 8 chemical families: aldehydes 11, linear hydrocarbon 4, ketones 3, alcohols 4 acids 4, cyclic hydrocarbons 3, esters 6, nitrogen and sulfur compounds 3. The high contents of volatile compounds(808.47 AU × 106/g) were found in the steamed meat among the four cooked meat, the aldehydes, especially hexanal and heptanal, were the primary volatile compounds of cooked meat.