Studying On The Key Factors Influencing Vermicelli Quality And It's Structure

The vermicelli is a solid product formed by starch being gelatinized,molded,retrogradated and dried.Potato,as one of economic plants cultivated widely in China,has the low price and high nutriments.The potato vermicelli as a unique starch product is deeply loved by consumers.However,the low content of amylose in potato starch leads to the high broken rate and poor boiling resistance of potato vermicelli.Therefore,the study on the key factors influencing the vermicelli quality has to be carried out.The potato amylose was extracted using potato starch as a raw material,sodium hydroxide as a pasting reagent,n-butyl alcohol and isoamyl alcohol as a complexing agent.The amylose content was determined by the measurement of blue value.The effect of technology conditions such as aging time,aging temperature,curing time,soaking time,and amount of paste on the vermicelli quality was investigated by using vermicelli broken rate as a target function.On the basis of single factor test,the process conditions of preparing vermicelli were optimized by the response surface method.The results showed that the best conditions for preparing vermicelli were as follows: aging time 90 min,aging temperature 4 ?,curing time 30 s,amount of paste 10 %,soaking time 90 min.Under the best process conditions,the effect of different additives such as guar gum,amylose,alum,konjac gum,sodium alginate and their addition amount on the vermicelli quality were discussed using potato starch as a raw material.The results showed that the broken rate of vermicelli was lowest,and its quality was best when the dosage of guar gum,alum,konjac gum,sodium alginate was 0.2%,and the dosage of amylose was 12%.The variation of vermicelli made under the different additives and process conditions in surface hydroxyl numbers proved that the broken rate of vermicelli related to the variation in surface hydroxyl numbers on vermicelli.The less the surface hydroxyl numbers were,the lower the broken rate of vermicelli was.It confirmed that the vermicelli structure was one of the key factors influencing the quality of vermicelli.The analysis of the potato vermicelli and potato vermicelli containing additives by a differential scanning calorimeter showed that the absorption peak of vermicelli containing additives became narrow,and its peak temperature decreased,but its intensity obviously increased,compared with the DSC curve of potato vermicelli.In addition,the thermodynamicdata showed that the onset temperature and enthalpy change of vermicelli containing additives rose,but,conclusion temperature decreased.The analysis of the potato vermicelli and potato vermicelli containing additives by means of thermogravimetric analyzer and X-ray diffractometer showed that the onset decomposition temperature and weight loss rate of potato vermicelli containing additives decreased,but the conclusion temperature increased,compared with potato vermicelli.The thermal stability of potato vermicelli containing additives was greater than that of potato vermicelli.Compared with potato vermicelli,the crystallinity structure of potato vermicelli containing additives changed.The crystallinity degree increased owing to the addition of guar gum,amylose,alum,konjac gum and sodium alginate.The fresh vermicelli and vermicelli particles observed by polarizing microscope and scanning electron microscope(SEM)indicated that the surface of potato vermicelli containing additives was more compact than potato vermicelli.And the water distribution of potato vermicelli containing additives was also more uniform than that of potato vermicelli.The voids in vermicelli were reduced by addition of guar gum,amylose,alum,konjac gum and sodium alginate.The vermicelli structure was significantly influenced by additives.The rheological property of potato starch and potato starch containing additives was measured by a rheometer.The experimental results showed the peak viscosity,trough viscosity,final viscosity,setback value and breakdown value of potato starch containing additives decreased,but the pasting temperature increased,compared with potato starch.It proved that the cold and hot viscosity stability of the potato starch was strengthened by addition of addictives.