Free And Bound Phenolic Compounds In Tea Seed Oil And Their Antioxidant Mechanism

Tea seed oil,derived from Camellia sinensis(L.)O.Ktze.,was authorized as a new resource food by Chinese Ministry of Health in 2009.It has been reported that tea seed oil contains high levels of phenolic compounds,and nearly 70% of phenolics present are phenolic acids,different with olive oil.However,the common extraction method of phenolic compounds from olive oil is adopted to extract phenolic compounds from tea seed oil.Moreover,research about phenolic forms in tea seed oil is still at an initial stage.composition and antioxidant activity of bound phenolic compounds in tea seed oil has never been uncovered in papers.Antioxidant mechanism of free and bound phenolic compounds,has not been elucidated yet.Neither has the significance of the distribution of different form of phenolic compounds been revealed.Ten representative tea seed samples were collected from main producing origins in four different areas of Camellia sinensis O.Ktze.,and our work was conducted as follows:(1)Deep eutectic solvents(DESs)were screened for extraction of free and bound phenolic compounds and the analysis was performed with UHPLC-Q-tof-MS/MS and UHPLC-QqQ-MS/MS.(2)The free and bound phenolic composition and their antioxidants tested by four different assays of 10 tea seed oil samples were evaluated systematically.Afterwards,the antioxidant mechanisms of free and bound phenolics in tea seed oil were explored based on the measured data.(3)Effect of distribution of free and bound phenolic compounds in tea seed oil on oil oxidation stability was investigated.And the possible factors that affect distribution of free and bound phenolic compounds in tea seed oil were investigated as well.The results and conclusions are as follows:(1)Qualitative and quantitative analysis method performed with UHPLC-Q-tof-MS and UHPLC-QqQ-MS were optimized respectively.In addition to 24 phenolic compounds in tea seed oil reported by our research team,dihydrocaffeic acid and six flavonoid glycosides were identified in this work.The results showed that hydrogen bond donors(HBDs)and temperature affected the extraction rate significantly,83.91 ?g/g free phenolic compounds and 25.71 ?g/g bound phenolic compounds were extracted from tea seed oil by the DES with glycerol as HBD under 50?,51.0% and 93.2% higher than conventional 60%(v/v)methanol/water,respectively.(2)There were 31 and 30 phenolic compounds identified in free and bound forms,respectively,including phenolic acids,flavonoids and flavonoid glycosides.Phenolic acids were the major compounds,followed by flavonoids.Free phenolic compounds in different areas varied from 52.96 ?g/g to 92.35 ?g/g,while bound phenolic compounds in different areas ranged from20.84 ?g/g to 37.06 ?g/g.(3)Total phenolic compounds were significantly positively correlated with total antioxidant capacities,and bound phenolic fraction showed higher correlation.Bound phenolic compounds possess relatively high antioxidant capacity,and this may be due to the long chain alkyl or various changes in spatial configuration of phenols after binding such as conplane of benzene ring and intramolecular hydrogen bond,which lowered the dissociation energy and molecular ionization potential of functional groups.(4)Physical incubation affected the distribution of bound phenolic compounds in tea seed oil,which maked blank oils with varied oxidative stability after being added with the same amount of exogenous phenolic compounds.Oil with higher distribution of bound phenolic compounds had higher oil oxidative stability.