Effect Of Different Drying Methods And Blanching Approaches On The Quality And Antioxidant Properties Of Okra

Okra(Abelmoschus esculentus[L.]Moench.)is a kind of vegetable with high nutritional value,which contains large quantities of active ingredients including flavonoids,phenolics and polysaccharides.It is much favored by people in recent years.Present domestic okra planting area is widely used.However,fresh okra fruits are easily wilting in room temperature,serioushy impacting on shelf life.Therefore,it is necessary to prolong okra's shelf life by deep processing.The drying of okra processed into leisure crisp strip products can not only prolong the preservation period,but also increase the added value.In order to choose the best drying method for okra crisp bar,the effects of six drying methods including infrared drying(FID),hot air drying(AD),freezing drying(FD),vacuum microwave drying(MVD),freezing drying coupling vacuum microwave(FD-MVD),and hot air coupling vacuum microwave(AD-MVD)on quality,drying time,energy consumption and antioxidant activity of okra were investigated.Based on this,blanching methods(conventional blanching,ultrasound blanching)were also comprehensively evaluated,so that determine the suitable okra leisure product crisp drying methods and blanching pretreatment.In addition,identification and determination of phenols in okra were conducted,and the correlation between the content of nutrients and antioxidant capacity were also analyzed.The main results and conclusions are as follows:FD samples exhibited the highest retention of flavonoids,total polyphenol polysaccharide and antioxidant potential,but poor hardness and the longest drying time and energy consumption.FID,ADand AD-MVD samples exhibited lower levels of flavonoids,total polyphenol and polysaccharide in order.Moreover,the hardness,color and shrinkage of the samples dried by the three drying methods were worse.FD-MVD and MVD samples showed higher retention of flavonoids,total polyphenol and polysaccharide as well as better hardness and crispness.The texture and nutrient content of MVD and FD-MVD samples were insignificant(P>0.05).The flavonoids,total polyphenol and polysaccharide contents of MVD samples were 14.19 mg/g d.w,10.33 mg/g d.w,60.56 mg/g d.w respectively.Nevertheless,the drying time and energy consumption of FD-MVD are 40 and 5 times higher than MVD samples,respectively.After identification,it was found that the main phenolic substances component in Okra were epigallocatechin gallate(EGCG)and epicatechin gallate(ECG).The polyphenols compounds content of Okra crisp bar produced by different drying methods were significant(P<0.05).The flavonoids,phenolics and polysaccharides content of Okra samples for different blanching methods were significant(P<0.05).The 80? ultrasound blanching sample showed excellent,not only effectively inactivating of POD enzyme activity,the contents of flavonoids,total polyphenol,polysaccharide,EGCG and ECG were also highest in all samples,being 15.24 mg/g d.w,11.83 mg/g d.w,62.10 mg/g d.w,1,251.37 ?g/g,731.07 ?g/g,respectively.Meanwhile,the hardness(2,813 g),crispness(773 g),color and shrinkage(52.52%)of 80 0C ultrasound blanching sample were moderate comparing to control group.Correlation analysis showed that the antioxidant capacity is in accord with the content level trend of total flavonoids,total phenols and polysaccharide,showing a very significant positive correlation.However,the correlation between antioxidant activity and EGCG and ECG content of dried Okra were insignificant(P>0.05).