Effects Of Different Pretreated Sweet Potato Flour On Dough Rheological Properties And Characteristics Of Sweet Potato-wheat Bread

Sweet potato(Ipomea batatas[L.]Lam)is the sixth most important food crop in the world,which is an important source of starch,protein,dietary fiber,vitamins and minerals,etc.White-fleshed sweet potato is a good source of starch,orange-fleshed one is rich in?-carotene,whereas purple-fleshed one is enriched with anthocyanins.Sweet potatoes with different flesh are considered to be good sources for staple products.However,limited information about production of high-quality sweet potato flour(SPF)is currently available,as well as their effects on dough properties and characteristics of staple products.In this study,effects of high hydrostatic pressure(HHP)and soaking solution on proximate composition,polyphenols,anthocyanins,?-carotene and antioxidant activity of white,orange and purple fleshed SPF were studied.The effects of particle size distribution on proximate composition,physicochemical and antioxidant properties of SPF were evaluated,as well as dough rheological properties and quality of sweet potato-wheat bread(SPWB).In addition,effects of different proteins and hydrocolloids on dough rheological properties and characteristics of SPWB were investigated.Effects of HHP(100,200 and 400 MPa)and soaking solution(citric acid,calcium chloride,ascorbic acid and distilled water)on proximate composition,polyphenols,anthocyanins,?-carotene and antioxidant activity of white,orange and purple-fleshed SPF were investigated.Total polyphenol content(TPC)were increased in SPF of Jishu 98(white)at 200 MPa with ascorbic acid and Pushu 32(orange)at0.1 MPa with ascorbic acid treatment(0.51 and 0.83 mg GAE/g DW respectively)but was decreased in Xuzishu No.3(purple).Decreases in total anthocyanin content(TAC)were observed in all treated SPF.HHP with citric acid,calcium chloride,and distilled water significantly increased?-carotene content in Pushu 32.Correlation analysis between TPC,TAC and antioxidant activity suggested that polyphenols are the most important antioxidant in SPF.HHP and soaking solution treated SPF could be potentially utilized in food with acceptable nutritional values.Effects of particle size distribution on proximate composition,physicochemical and antioxidant properties of orange and purple-fleshed SPF with particle sizes 75-355?m were investigated.With particle size decreasing from 355 to 75?m,protein content,water absorption capacity and water solubility index decreased,whereas starch,reducing sugar and crude fat increased in both orange and purple-fleshed SPF.TPC in purple-fleshed SPF(8.25 to 9.27 mg GAE/g DW)were higher than orange ones(0.22 to 0.28mg GAE/g DW),whereas vitamin C content in orange-fleshed SPF(23.59 to 29.26 mg/100g DW)were higher than purple ones(4.24 to 4.89 mg/100g DW).Antioxidant capacities of both SPF were gradually increased with the decrease of particle size(from 355 to 75)due to the contribution of higher content of TPC and vitamin C.All SPF fractions exhibited irregular-shaped surface,and with no morphological difference between both SPF.SPF sieved with different particle size might be used to produce novel food products with certain nutrients,texture and functional properties.Dough rheological properties and characteristics of SPWB affected by particle size distribution(45-355?m)of orange-fleshed SPF were investigated.Dough produced from SPF through particle size 45?m showed improved network structure with fused starch granule and branched protein,exhibited the highest ability to elongate due to accumulation of stronger elasticity,and presented the largest maximum height(H_m,19.70 mm).SPWB from SPF through particle size 45?m showed larger specific volume(1.81ml/g)and lower hardness(8612.3 N)compared to those through other particle sizes.After in vitro digestibility,SPWB from SPF through particle size 106 and 75?m showed higher?-carotene content,followed by that through 45?m,and the bread from SPF through particle size 45?m showed higher polyphenols content.Thus,SPF through particle size 45?m might be used to produce novel bread with desired nutritional and textural properties.To improve the quality of SPWB,effects of proteins and hydrocolloids on dough rheological properties and characteristics of SPWB were investigated.On the basis of higher specific volume and lower hardness of SPWB,egg white protein(EWP)and xanthan gum gum XG was further studied.XG1.5%incorporation significantly increased the water absorption(58.3 to 61.20%)of sweet potato-wheat flour.Sweet potato-wheat flour with XG 1.5%presented higher peak viscosity(1300.67 RVU),final viscosity(248)and increased setback(77.33).SPWB with the incorporation of XG 1.5%exhibited higher specific volume,lower hardness,higher viscosity and elasticity.XG incorporation significantly decreased the expected glycemic index and rapid digestible starch in SPWB as compare to other samples.XG 1.5%with SPF particle size 45?m might be used to produce novel SPWB with better texture and functional properties.In conclusion,freeze-dried white-fleshed SPF(Jishu98),orange-fleshed SPF(Pushu32)treated with0.1 MPa+calcium chloride and freeze dried purple-fleshed SPF(Xuzishu No.3)showed best quality.SPF sieved through particle size 45?m incorporated with XG 1.5%exhibited higher potential application value in SPWB.