The Study On The Extraction Technology And Functional Properties Of Soluble Protein From Sweet Potato Leaves

Sweet potatoe (Ipomoea batatas) is a member of Convolvulaceae family originated from South Africa. As China is the largest sweet potato producer (accounting for 80% of the world sweet potato production), the yield of sweet potato leaves annually is huge. In the present study, the nutritional composition of sweet potato leaf was evaluated, methods for extracting soluble protein from sweet potato leaves and the functional properties of the extracted protein were investigated, and a mutton sausage incorporated with sweet potato leaves was developed.Sweet potato leaf is highly nutritious and is rich in protein compared to common fruits and vegetables, making it as a potential resource of leaf protein concentration (LPC). Since the sweet potato leaf of Variety 981 is rich in protein with high protein extractability, this variety was used as the raw material for protein extraction in the present study.Results from single factor experiment indicated that, compared to other factors studied, pulping time as well as ratio of sweet potato leaves to extraction solution stronger effected on the extraction of soluble protein from sweet potato leaves. Moreover, acid precipitation is more suitable than heat precipitation to precipitate soluble protein from sweet potato leaves.Extraction of soluble protein from sweet potato leaves depending on alkaline extraction followed by acid precipitation was studied using an orthogonal design. The results showed highest extraction recovery can be achieved using an extraction solution (0.05% NaHSO₃) with pH 8.0, ratio of sweet potato leaves to solution at 1:4 (W/V) , pulping for 3min and acid precipitation at pH 4.5. Under the optimum condition, with an soluble protein recovery rate at 14～18%, soluble protein from sweet potato leaves with 50-65% purity was yieldedUsing soy protein (SP) and Sweet potato leaf extrusion (SPLE) as standards, the effects of pH, NaCl concentration and temperature on the functional properties of soluble protein from sweet potato leaves (SPSPL) were studied. The results showed that pH, NaCl concentration and temperature strongly affected the solubilization and emulsifying capacity (EC) of SPSPL. Compared to SP and SPLE, SPSPL showed higher solubilization and EC at both alkaline condition (pH10) and low NaCl concentration (0.1mol/lNaCl) , while emulsion stability (ES) of SPSPL decreased along with increment in NaCl concentration. Highest SPSPL solubilization was observed at 40℃, while highest EC and ES were found at 60℃. Water holding capacity (WHC) of SPSPL was between those of SPLE and SP. On the other hand, the oil holding capacity (OHC) of SPSPL was close to that of SP, but lower than that of SP. Foaming capacity (FC) and foam stability (FS) of SPSPL was better at pH4.5. FC and FS of SPSPL increased as NaCl concentration rose. Highest FC and FS of SPSPL was observed at 40℃and 20℃, respectively. The values of FC and FS of SPSPL were between those of SP and SPLE.The granularization ability of freeze-dried sweet potato leaves powder was more superior than that of the oven-dried one. Results showed that addition of 0.2% of freeze-dried "Shan 3" improved the unpleasant mutton-odour of mutton sausage.