Study On Drying Of Vaccinium Braeteatum Thunb. Leaves And Pigment Extraction,Stability Evaluation And Pigmentation Design

Vaccinium braeteatum Thunb.(VBT)leaves have been used as herbs and foods in China for a long history,which possess many physiological activities,such as anti-diabetes,anti-cancer,anti-depression,and anti-neurodegenerative activities.The extracts of VBT leaves can dye glutinous rices with deep blue or black color to make traditional food "Wu mi".In this thesis,the effects of freezing and thermal pretreatments on drying of VBT leaves were studied and the changes in physicochemical properties were evaluated.Then,iridoids were extracted by ultrasound from dried leaves and subsequently purified by macroporous resin.In addition,the stability of iridoid in VBT leaf extarct was assesed.Finally,the pigmentation process was optimized.The results are shown as follows:1.The effects of freezing(-18?,8h),water blanching(100?,1min)and steam blanching(100?,2min)pretreatments on drying of VBT leaves at 60?,and its physicochemical properties before and after drying was studied.The results indicated 8-h freezing,1-min water blanching and 2-min steam blanching pretreatments all improved the De and k(fitting parameters from mass transfer model),internal water transfer and surface water diffusion,and drying efficiency of VBT leaves during drying.And combined treatment of freezing and blanching showed further promotion for above index.The 8-h freezing pretreatment led to the decrease of PPO and ?-glucosidase activities,while water or steam blanching pretreatments directly inactivated the enzymes.And the two enzymes were inactivated completely after drying.1-min water blanching and 2-min steam blanching both siginificantly retained polyphonel and iridoid,ABTS+radical cation scavenging activity and ferric reducing antioxidant power(FRAP),and "Wu mi" dyeing ability(requiring additional ?-glucosidase precatalysis),while 8-h freezing treatment showed adverse effect for above index.Combined treatment of freezing and blanching showed certain retention effect,and no additional ?-glucosidase was needed to dye "Wu mi"using the extracts from leaves with freezing treatment.2.The effects of extraction scale and ultrasonic power on extraction kinetic of iridois from VBT leaves were studied.At a lab-scale,the increasement of ultrasonic power from 3.53 to 10.12W and decreasement of extraction volume from 50 to 200mL both promoted F,k1,k2(kinetic model fitted parameters)and De(mass transfer model fitted parameters),inernel and surface mass transfer of iridoids,and extraction rate and equilibrium yield of iridoids,where 50mL-10.12W group showed highest iridoids yield(227.52mg/g DW).At pilot-scale(ultrasonic power 281.26W),no influence was observed with the increasement of extraction volume(0.8,2,3L).The average iridoid yield of 0.8,2 and 3L group was 224.22mg/g DW,which wasn't significantly different from the 50mL-10.12W group.Above results indicated that there was a limit on extraction enhancement by extraction scale and ultrasonic power.The predictive model about extraction scale,ultrasonic power,and De can predict the mass transfer of iridoids within the experimental range,that will provide effective guidance of actual production.In addition,methanol was more a suitable extraction solvent for iridoids in VBT leaves compared to enthanol.The extraction efficiency of iridoids by ultrasonic(50mL-10.12W)was higer than water bath shaking method(50mL-120rpm),indicating the rationality of ultrasound technology.3.The purification of iridoid in VBT extract by macroporous resin,and stability of iridoids in purified product was studied.After phase separation of VBT leaf water extract by ethyl acetate,the color difference of "Wu mi" dyed by upper phases(blue purple color)and lower phases(brown color)indicated there were auxiliary dyeing ingredients in VBT leaves together with iridoids.Among the three resins considered(polyamide,AB-8 and D101),D101 showed the highest adsorption and desorption rate of both iridoid and pheniloc compounds in VBT leaves extract,and the adsorption rate,desorption rate,recovery and final purity improvement rate by D101 were 89.87±0.24,82.03±2.03,73.72±1.77 and 64.82%for polyphenols,and 89.87 ± 0.24,82.03±2.03,73.72±1.77 and 64.82%for iridoids.The stability of iridoids in VBT leaf extracts was high.No significant change in total iridoid content was observed at various storage(including condition of 25 and 4?,with and without light),temperature(70-100? for 12h),and pH(3.0-4.0)conditions.Besides,the presence of Fe3+,Fe2+ and Cu2+ led to the degradation problem,while Mg2+,Ca2+,Na+ and K+ had no effect.The degradation was thought due to acid environment formed by metal ions.4.The feasibility of color enhancement of "Wu mi" by the addition of edible metal salts(Ca2+,Mg2+,Fe2+and Zn2+)or phenolics(rutin,caffeic acid,trans-p-hydroxycinnamic acid,tannin and luteolin)was tested.And the optimization of "Wu mi" dyeing process were studied.The additions of Fe2+,rutin and luteolin significantly enhanced the color of "Wu mi".And rutin was choiced as a color enhaner for the subsequent study.Response surface method with central experimental design was used to optimize "Wu mi" dyeing process.The optimized factors included iridoids concentration(mg/mL),rutin added amount(mg/mL),?-glucosidase added amount(mg/mL),and enzymatic reaction time(h).Responces were color of "Wu mi".Model variance and response surface analysis indicated that iridoids concentration and rutin added amount are the main factors.The optimized conditions were iridoids concentration:5(mg/mL),rutin added amount:1.28(mg/mL),?-glucosidase added amount:2.5(mg/mL)and enzymatic reaction time:4.42(h).Under this condition,the experiemntal color of "Wu mi" was close to the precdicted value.