Research On Nutritional Properties Of Sweet Potato Leaves And The Bacteriostasis Of Its Polyphenols

58 cultivars sweet potato leaves(SPL)were used as material in this thesis,and the nutritional compositions and functional properties were investigated.Then used the leaves of the most popular starch processing type sweet potato(Shangshu No.19)cultivar as material,microwave-vacuum drying(MVD),hot-air drying(HAD)and vacuum-freeze drying(VFD)with grinding were used to prepare sweet potato leaves powder,and the effect of different drying methods on the nutritional composition,physicochemical and functional properties of sweet potato leaves powder was compared.According to the result,selected an appropriate drying method for sweet potato leaves,and then extracted crude polyphenol.The purify polyphenols from sweet potato leaves obtained from the AB-8 macroporous resins,and the products were analyzed qualitatively and quantitatively by HPLC.Moreover,determined antibacterial activity of sweet potato leaves polyphenols and monomers.The results showed as follow:(1)The nutritional compositions and functional properties of sweet potato leaves from 58 cultivars were investigated.Result showed that sweet potato leaves was good resource contain protein(9.35-38.45g/100g DW),fat(1.36-12.30 g/100g DW),dietary fiber(37.35-45.0 g/100g DW),vitamin C(1.47-131.64mg/100g DW),?-carotene(6.75-59.35 mg/100g DW),vitamin E(0.39-23.30 mg/100g DW).Compared with other cultivars,Zhanshu No.01-2 had higher bioactive compounds(total polyphenol content,antioxidant and PPO activity).The antioxidant activity were highly correlated with the total polyphenol content(TPC;R²=0.748,P<0.0001),indicating that polyphenols are important antioxidant in sweet potato leaves.(2)According to the results of the nutritional compositions of Shangshu No.19 sweet potato leaves,VFD–SPL showed higher total dietary fiber,vitamin C,E,B₁ and B₂,and mineral Mg,P and Zn content than those of MVD–and HAD–SPL.For the physicochemical properties,MVD–SPL showed highest water absorb index,oil absorption capacity,swelling power and solubility.HAD–SPL had smallest particle size(D^[4,3]=56.85?m),which could be further verified by the scanning electron microscopy findings.For the functional properties,total polyphenol content of VFD–SPL was highest(6.30 g CAE/100g DW),followed successively by MVD–and HAD–SPL(6.06 and 4.72 g CAE/100g DW,respectively),and the same order was found for the antioxidant activity(20.58,18.96 and 8.04 g TE/100g DW,respectively).In general,although the nutritional compositions and functional properties of MVD–SPL were intermediate between VFD–and HAD–SPL.The higher physicochemical properties,drying rate and lower cost than VFD–and HAD–SPL suggests that MVD has greater development potential as a new drying technology in SPL powder production.(3)The purify polyphenols from sweet potato leaves obtained from the AB-8 macroporous resins were brown amorphous powder(84.32±3.64%),and the products were analyzed qualitatively and quantitatively by HPLC.HPLC result showed that polyphenols from sweet potato leaves were composed by 9constituents(3-CQA,4-CQA,5-CQA,3,4-CQA,3,5-CQA,4,5-CQA,3,4,5-CQA,rutin and caffeic acid).The contents of di-caffeoylquinic acids were relatively higher than others,and 4,5-CQA had the highest content(40.18%)in sweet potato leaves polyphenols.Used oxford cup method and minimum inhibitory concentration to determine antibacterial activity of sweet potato leaves polyphenols and monomers.The results indicated that the polyphenols were effective in inhibiting bacteria and molds growth.Particularly,it showed strong inhibition on Gram-positive bacteria,and had lower inhibition on Rhizopus oryzae and Aspergillus oryzae.The minimum inhibitory concentration of 3-CQA,4-CQA,5-CQA,3,4-CQA,3,5-CQA,4,5-CQA,3,4,5-CQA,rutin,caffeic acid,polyphenol ranged between 375-1500?375-1500?188-750?375-1500?188-750?188-750?375-750?188-750?47-188 and 94-750?g/m L,respectively.In all tested samples,caffeic acid showed the strongest antibacterial activity.Overall,the polyphenols from sweet potato leaves can be used as a novel source of potential preservative and antimicrobial agent applied in the fields of food and medicine.