| In order to get valuable information for development of potential commercial fat products from 36 yak,the fatty acid composition of the kidney from yak grown in Gansu province,China was investigated by use of gas chromatographic method, Which is also the first report of fatty acid profile of yak kidney.After grasped the varation of PV and TBARS,the composition and change of fatty acid extracted from yak kidney were analyzed at 15±1℃.In addition,effect of different oxygen and light on the variation of fatty acid from yak kidney during initial stages of autoxidation were studied in this paper.The main results indicated as follow:(1) Totally,15 different fatty acids have been identified.The major fatty acids are oleic acid(33.3%),stearic acid(20.2%) and palmitic acid(18.4%).Among the identified SFAs,stearic acid(C18:0) and palmitic acid(C16:0) comprised the largest proportions of fatty acid in yak kidney,which is 20.02%and 18.4%respectively,then following arachidic acid(C20:0) and myristic acid(C14:0).Only two monounsaturated fatty acids(MUFA),oleic acid(C18:1) and palmitoleic acid(C16:1), have been identified,which constitutes 33.30%and 4.55%of total FA.Meanwhile,6 polyunsaturated fatty acids(PUFA) have also been identified,of which conjugated linoleic acid(CLA,c9t11C18:2),an excellent inhibitor of tumor growth even at low concentrations,is the most abundant one,which constitutes 27.4%of identified PUFA. The important nutritionally essential omega-3 fatty acids and omega-6 fatty acids have also been identified in yak kidney.Omega-3 fatty acids,including alpha linolenic acid(ALA,C18:3(n-3)),eicosapentaenoic acid(EPA,C20:5(n-3)),and docosahexaenoid acid(DHA,C22:6(n-3)),compromise 27.5%of total PUFA,and omega-6 fatty acids,including linoleic acid(LA,C18:2(n-6)) and arachidonic acid (AA or ARA,C20:4(n-6)),compromise 45.1%of total PUFA.More interestingly,it doesn't contain odd number fatty acid in identified fatty acid of yak kidney.(2)The TBARS value only slightly increased within the first 15 days(induction period);after a moderate increase(15-25 days)(P＜0.01),the TBARS increased significantly up to 45 days which suggests that lipid oxidation mainly occurs at this period.The TBARS value between 45-50 days(P＞0.05) storage is not changed,the PV value of the yak kidney fat during storage at 15±1℃was continuously increased up to 35 days representing the first stage of lipid oxidation.The flat portion of the curve(1-15 days) prior to the rapid rise(15-35 days) in peroxide concentration is an indication of the induction period(i.e.,stability) during the first stage.In contrast, after reaching the maximum values(14.9±1.2) on a prolonged storage(after 35 days), This indicates that probably the produced hydroperoxides are unstable and highly susceptible to further changes that may forms secondary oxidation products in the later stages of lipid oxidation.(3) The initial stage of kidney fat happened in 0-25d at 15±1℃during store times.Saturated fatty acids(SFA) increases from 49.68%to 55.96%,while polyunsaturated fatty acids(PUFA) and monounsaturated fatty acids(MUFA) decreased from 10.73%to 6.95%,and from 37.85%to 28.22%,respectively.The content of all the functional fatty acid,except CLA and LA,started to decrease after 10 days storage(p＜0.05).(4) The PV and TBARS value correlate(negatively,≤0.926) well with the stability of most MUFA and PUFA.When PV and TBARS value increased,it indicates that the amount of C16:1,C18:1,ALA,ARA,EPA and DHA decreased. Even the changes of CLA and LA can not be well(≥0.891) indicated by the PV and TBARS value,it is still possible to get a rough idea about the changes of the FA in yak kidney fat during the commercial product development process.(5) TBARS undering 20 Lux,964 Lux and 1550 Lux increased wavily during initial stage.The variation of TBARS undering 20 Lux did not change the previous 30 days,followed by a rapid increase.Importantly,TBARS of 20 Lux is lower than that of 964 Lux and 1550 Lux,and former laster than laster about 15d.Under anaerobic conditions lagger than aerobic oxidation of lipid oxidation,and a larger difference in oxidation rate;4±1℃TBARS significantly lags behind the changes in 15±1℃,and the lag period of 10 days,occurred in the last initial-oxidation,which reflects that the lower temperature could inhibit the rate of peroxide formation and postpone fat oxidation ultimately.During this period,9±1℃TBARS changes between that of 4±1℃and 15±1℃,which reflects that the temperature on the lipid oxidation and fatty acid composition changes is moderate and uniform,similar to the effects of continuous symptoms.(6) This article holds that lipid oxidation undering anaerobic conditions later than aerobic oxidation,and a larger difference in oxidation rate.In addition,there may be threshold partial pressure of oxygen in the boundaries,Around both threshold,the rate of lipid oxidation and the degree of difference were different large.However,the existence of this phenomenon needs to be done in order to verify in further work. |
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