| Quick frozen dumplings were prone to cracking, browning and retrogradationduring freezing and transporting, losing of liquid after thawing, noddle soup getturbidity, and these reduced the quality of the dumplings. Modified starch as a modifiercan improve these problems of frozen dumplings, in particular, can reduce the crackingrate of dumpling wrapper. But there is no report focused on the mechanism of modifiedstarch on frozen dumplings. The main purpose of this paper is to study how themodified starch reduced the cracking rate of frozen dumplings, and what themechanism is.As this research target, we determined parts of the physicochemical properties ofacetylated potato starch, and prepared six types of frozen dumplings. These sampleswere:0%,5%,7.5%,10%,12.5%and15%of acetylated potato starch added frozendumplings. And abbreviated as control, APS-5, APS-7.5, APS-10, APS-12.5, APS-15.The color measurement was carried out on the surface of dumpling wrapper usinga colorimeter. Addition of acetylated potato starch can improve the lightness ofdumplings, samples with15%acetylated potato starch caused a significant increase oflightness. In contrast, yellowness of the samples decreased significantly with theincreasing of APS substitution. However, redness of the dumpling wrappers has nochange with the addition of APS. This result indicated that the acetylated potato starchcan improve the color and effectively enhance the sensory properties of dumplings.Through the water holding capacity test we found that acetylated potato starch hasa significant impact on the water holding capacity of flour, along with the addition ofacetylated potato starch increased, WHC value of the flour increased correspondingly.A differential scanning calorimetry was used to test the thermodynamic propertiesof different quick-frozen dumplings wrappers. The melting enthalpy of dumplingwrapper added acetylated potato starch was significantly lower compared to the samplewithout added starch. Melting enthalpy reduced with the content of acetylated potatostarch increased, which means acetylated potato starch can reduce the frozen water indumpling wrapper, made an effective role on reducing the cracking rate of dumpling.The molecular mobility of different dumpling wrappers was analyzed by T2assays with a Pulse NMR. The results showed that the dumpling wrappers withacetylated potato starch had bigger T2(1) relative area than the control. Meanwhile, the relaxation time T2(1) found an obvious decrease after addition of APS. Sincespecies with shorter relaxation times have lower activity than those with higherrelaxation times. This means that this portion of water in APS substituted samples hadlower activity and harder to frozen than control, that is APS addition led to the freewater content reduced and harder to frozen, which in turn create less damage todumplings during freezing.The SEM and FM microscopes results showed that addition of12.5%acetylatedpotato starch had a large amount of void among starch granules and the gluten networkshowed less dense than the control. These voids among starch granules could be aroom for crystals during refrigeration, and then reduce the destruction to the dumplingwrapper caused by growing of ice crystals.Due to the hydrophily, water-holding capacity of hydrophilic groups in acetylatedpotato starch, it made the frozen water content decreased and effectively prevented theamount of ice crystals formed during the freezing process. Furthermore, a more loosestructure provided a room for crystals during refrigeration and finally reduced thedamage to dumpling wrapper caused by the growth of ice crystals during freezing. |
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