Effect Of Different Oligosaccharides On The Gelatinization And Retrogradation Properties Of Sweet Potato Starch

In this paper,the effects of different oligosaccharides(sucrose,raffinose,stachyose)on the properties of sweet potato starch(SPS)under different conditions(process,freeze,refrigeration)were studied,and the interaction mechanism between oligosaccharides and starch were also investigated.Firstly,the effects of different oligosaccharides on the gelatinizatoin properties of SPS were studied.RVA and DSC results indicated that the pasting and gelatinization temperature of SPS increased with increasing sugar concentration in the order of stachyose > raffinose = sucrose.Addition of sugars significantly decreased the peak,trough and final viscosities as well as setback value of SPS.Gelatinization enthalpy only increased when sugar was added at high concentration compared with the native starch.Sugars addition increased the yield stress and consistency coefficient of SPS-sugar mixed paste.The SPS-sugar mixed pastes exhibited a pseudoplastic and shear-thinning behavior under yield stress condition.Moreover,storage moduli(G′)of SPS-sugar mixed pastes decreased with addition of sugars.The results also showed that sugars addition promoted liquid-like characteristics of SPS-sugar mixed pastes.Secondly,the effects of different oligosaccharides on the freeze-thaw(FT)stability of SPS were investigated.The results showed that addition of sugar changed the value of syneresis,and the FT stability of SPS gels was improved or declined by sugar addition.And the improvement of FT stability followed the order: sucrose > raffinose.SEM results indicated that sucrose and raffinose stabilized the gel matrix surrounding pore,the smaller cavity size or thicker fibrillar network could be observed on the sponge-like structure.DSC data showed that transition temperatures of SPS decreased with the repeated FT cycles,and declined by addition of sugars at the same FT cycles compared to native starch.The retrogradation enthalpy of starch was decreased in the presence of sucrose or raffinose,which more effective than stachyose.The relative crystallinity increased with FT cycles and was inhibited by addition of sucrose or raffinose for each FT cycle.However,stachyose increased enthalpy and relative crystallinity of starch gels compared to the native starch during FT cycles,suggesting that stachyose accelerates retrogradation process of sweet potato starch during FT cycles.Lastly,during 28-day storage at 4 oC,the effects of oligosaccharides on the short-term and long-term retrogradation of SPS were studied.Transparency of starch pastes decreased with increasing storage time,addition of sucrose or raffinose significantly improved the transparency,but addition of stachyose changed transparency depended on storage time.DSC results indicated that melting temperature increased and retrogradation enthalpy decreased with increasing sugar concentration in the order of sucrose > raffinose.Stachyose increased enthalpy of retrogradation compared to the control during entire storage time.TPA tests showed that the hardness of starch gel increased and the springiness decreased with storage time.All sugars increased the hardness during short storage time caused by change of solid-to-liquid ratio,but sucrose and raffinose decreased the hardness at a later stage.At short-term retrogradation stage,the retrogradation was inhibited by sugars in the order of stachyose > raffinose >sucrose,which was consistent with the setback value from RVA experiment.