| The production of proteins from sweet potato starch wastewater has attracted attention in China due to of its economic benefits and due to environmental concerns. Sweet potato protein (SPP) is one of the major components of starch wastewater generated from the processing of sweet potato starch and has nutritional benefits, a balanced amino acid composition and good functional properties. The study has shown the potential of SPP as a functional additive during food product development. Hence, the appropriate structure modification of an SPP by high hydrostatic pressure (HHPs) might lead to suitable functional properties, which could increase the applications of SPP in the food industry.The influence of high hydrostatic pressure (HHP) treatment on the physicochemical and emulsifying properties of sweet potato protein (SPP) at various concentrations, e.g.2%,4%and6%(w/v, SPP-2, SPP-4and SPP-6), was investigated. Significant differences in the hydrophobicity, enthalpy of denaturation and solubility were observed when the pressure was increased from200to600MPa (P<0.05). The emulsifying activity indexes (EAI) of SPP-2and SPP-6increased at400MPa, whereas the EAI of all SPP significantly decreased at600MPa (P<0.05). Emulsion stability (ESI) was significantly decreased for SPP-2and SPP-6, while increase in ESI was observed for SPP-4above200MPa (P<0.05). SPP-2emulsions showed sharp decrease in apparent viscosity with increase in HHP compared to SPP-4and SPP-6, while pseudo plastic flow behaviour were not changed for all of emulsions produced with HHP treated SPP. Sporamin A and sporamin B were well adsorbed in pressurised SPP emulsion without displacement. These results suggest that HHP treatment could be used to modify the physicochemical and emulsifying properties of SPP, depending on protein concentration and the pressure applied.The effect of high hydrostatic pressure (HHP) treatments on the physicochemical properties of sweet potato protein (SPP) emulsions at three pH values (3,7and8) was investigated. The emulsifying activity index (EAI) and the emulsifying stability index (ESI) of all emulsions at the different pH values were significantly increased by the HHP treatments (P<0.05). The oil droplet sizes were significantly decreased, whereas the volume frequency distribution of the smaller droplets was markedly increased when the pressure was increased from200to600MPa (P<0.05). A significant increase in the interfacial protein concentration in the pH3,7and8emulsions was observed when the pressure was increased from200to600MPa (P<0.05). Under non-reducing conditions, higher molecular weight aggregates formed by disulfide bonds were observed in the pH7emulsions by SDS-PAGE. However, HHPs did not change and/or displace the main electrophoretic bands of SPP. The600MPa HHP decreased the flow indices, which resulted in an increase in aqueous phase viscosity in all the SPP emulsions. The SPP emulsions had shear-thinning behaviors at pH3and7with and without HHP treatment, whereas a Newtonian behavior was observed in the pH8emulsion subjected to the200and400MPa treatments. These results suggest that HHP-treated emulsions stabilized by SPP could have various applications in the food industry. The CD analysis confirmed the modification of SPP secondary structure. Surface hydrophobicity was increased significantly (P<0.05) at pH3and decreased at6and9. Emulsifying activity index (EAI) at pH6was significantly increased with increase in pressure, whereas emulsifying stability index (ESI) values were significantly higher at pH6and9(P<0.05). The oil droplet sizes were significantly decreased, while the volume frequency distribution of the smaller droplets was increased for pH3and6with HHP treatment. Emulsion viscosity of HHP treated SPP were increased at pH6and9and pseudo plastic flow behaviours were not altered for all of emulsions produced with HHP treated SPP. These results suggest that HHP could be applied to modify SPP structure for better emulsifying properties, which will increase the use of SPP emulsion in food industry.SPP in presence of guar gum with HHP treatment increase the stability of emulsions decreased the creaming rate and improve in apparent viscosity compared to the control SPP-hydrocolloids model (0.1MPa). The GMS at another hand showed negative effect on the emulsifying efficiency of SPP and showed poor stability, creaming rate and viscosity of emulsions. These results suggest that HHP is reliable method for modification of emulsifying efficiency of SPP in the presence of guar gum. |
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