Effects Of Heat Treatment Of Torreya Seed On Phenolics From Torreya Seed Oil And Their Antioxidant Capacities

Torreya grandis‘Merrilli’ is a cultivar of Chinese torreya,a kind of coniferous evergreen plant belongs to the genus Torreya family Taxaceae.Recently,the market demand for Torreya seed as a nut has become increasingly saturated.The kernel of this nut contains 5%to 60%oil,which is riched in nutrients and active ingredients such as β-sitosterol,tocopherol and phenolics,has potential to be developed as a dietary or functional oil to promote the industrialization exploitation of the oil seed.Although roasting is one of an indispensable procedure during Torreya kernel oil(TKO)production,current researches on thermal conditions and endogenous phenolics changes were insufficient.Besides,there was no report about active products interference on contents of total phenolics(TPC)determination during roasting processing.In this paper,TKO was used to investigate the impacts of heat treatment on TPC determination,existing forms and antioxidant activities of phenolics.On the basis of that,anti-oxidation quality of TKO was analyzed comprehensively during roasting to provide support for thermal conditions optimization,plant oil based phenolics research and TPC assays selection.The main research contents showed as follows.1.The browning indices and Maillard reaction products(MRPs)for roasted TKOs were determined.Moreover,the results of Folin-Ciocalteu and FBBB assay adopted to quantify TPC were compared and MRPs disturbances on the methods were studied.The results showed that low-intensity,long-term and high-intensity heat treatment promoted the formation of Maillard intermediates(294 nm),and the end products(420 nm)accumulated during roasting.MRPs of 3-deoxyglucosone(3-DG),methylglyoxal(MGO),glyoxal(GO),5-hydroxymethylfurfural(5-HMF)and furfural(FF)were detected in roasted TKOs,of which the concentrations varied with thermal methods,intensities and time.The diversities between Folin-Ciocalteu and FBBB assays applied to quantify TPC of TKOs were found,and in general,the galic acid equivalent of TPC obtained by the latter was higher.The presence of 3-DG and MGO interfered with the Folin-Ciocalteu assay,of which the former had the greatest effect and the degree of disturbance was concentration-dependent rather than related to TPC of the samples,while GO,5-HMF and FF had hardly effect.By comparison,FBBB assay was not influenced by MRPs obviously,which could reduce the quantitative error of 3-DG and MGO derived from food matrices processing.2.TPC and phenolics profile of different forms phenolics extracts of TKOs were studied,in addition to different behaviors in case of distinct treatments.It is showed that TPC of free phenolics(FP),esterified phenolics(EP)and insoluble-bound phenolics(IBP)extracted from control TKO were 121.13,95.18 and 157.00 μg GAE/g respectively,indicated that IBP is the most stable form of phenolics extracted from cold pressed oil.The sum of TPC of different forms increased by up to 30.40%(150℃,120 min)after roasting,suggested phenolics of Torreya kernel migrated to oil rather than degradated.Phenolic compounds,including hydroxytyrosol,protocatechuic acid,gentisic acid,epigallocatechin,catechin,p-hydroxybenzaldehyde,vanillic acid,ferulic acid and o-vanillin,were detected in different forms phenolic extracts of TKOs,of which protocatechuic acid and o-vanillin were only found in heat-treated TKOs.Catechin was existed in free form,which amount increased or changed in-apparently after roasting.Gentisic acid and ferulic acid were existed in insoluble-bound form,of which the content of the former declined with thermal time.During hot air treated processing,the total content of hydroxytyrosol was dominated by insoluble-bound form,while free form was dominant during microwave treated processing of TKOs.It was observed that content of free hydroxytyrosol decreased and that of the bound form increased under low-intensity roasting(60℃,30 min),while the total amount changed ambiguously.Overall,the concentrations and distribution patterns of TKO phenolics in various forms were influenced by the parameters of roasting temperature,power and time.3.Antioxidant capacity and variation trend in case of distinct treatments of different forms phenolics extracts of TKOs were studied.The correlation between the oxidative stability and quality indicators of TKO was performed,in addition to comprehensive evaluation of heat-treated oil quality adopted by principal component analysis.The results showed that,among the phenolics extracts in different forms from untreated TKO,FP had the highest activity to scavenge DPPH(DRSA)and ABTS radicals(ARSA),while IBP had the strongest capacity to reduce ferric ions(FRAP),in contrast to EP performed worst in the above antioxidant indexes.The result of the accelerated oxidation test showed that the induction time of the unheated sample was 10.33 h,with a maximum increase of 52.68%(560 W,20 min)after heat treatment.The antioxidant activities of FP and IBP could stand for the oxidative stability of oils.Besides,maillard reaction initiation and phenolics concentration changes would influence the anti-oxidation quality of thermal TKOs.The maximum of the comprehensive scores obtained in which oil seeds heated by microwave oven(560 W,20 min)indicated the quality improvement of oils thermal-treated appropriately.