Effect Of Modified Starches On The Freeze-Thaw Stability Of Fruit Paste

Fruit paste, one kind of fruit sauce, replace the fresh fruit used in cake surface for decoration, piping or writing. It can also be directly smeared on the fruit surface to add luster, or used as pastry fillings, endowing the product with rich fruit aroma, sweet and sour taste and bright appearance. As high-grade pastry essential raw material, there is broad application prospects for fruit paste in the baking industry. However, after repeated freezing and thawing, dehydration shrinkage phenomenon in varying degrees and sponge structure could be found on the fruit paste, resulting in poor water retentivity and cracking phenomenon for the product, furthermore, seriously affecting the product sensory quality.As known, stability of fruit paste system is maintained by hydrophilic and water holding capacity of the starch. Therefore, it is serious necessary to modify starch to improve its freeze-thaw stability, so that the fruit paste can still maintain a good quality after repeated freezing and thawing. Modified starch with good freeze-thaw stability was screened and the fruit paste processing was optimized, in order to improve its freeze-thaw stability.Meanwhile, viscosity, transparency, retrogradation, spreadability and other properties of modified starches as well as the application effect of the frost resistant fruit paste were explored. Conclusions were drawn as follows:(1) It is meaningful for production to modified corn starch so that to improve its freeze-thaw stability and other processing characteristics. Among four kinds of grain starches including corn starch, waxy corn starch, potato starch and cassava starch, there was the lowest amylose content for waxy corn starch, only 0.8%, while the highest one, 26%for corn starch. Freeze-thaw stability, transparency and anti-aging ability could be poor for starch with high amylose content. So, this kind of starch is lack of advantages in processing and it would be with great significance for production to modified this starch.(2) Hydroxypropyl distarch phosphate with the highest peak viscosity, the best thermal stability, the strongest gel property, the lowest retrogradation and the best freeze-thaw stability was chose to prepare for frost resistant fruit paste. Among 3 kinds of modifiedstarches modified from corn strach including Carboxymethyl Starch Sodium(CR20),Phosphated Starch(CR30) and Hydroxypropyl distarch phosphate(Per), CR20 was the most easy one to gelatinization and accompanied with poor thermal stability and gel property. While, there was the highest viscosity, the best thermal stability and the strongest gel property, but low transparency for Per. Retrogradation comparison: CR30 > CR20 > Per.Comparison for freeze-thaw stability: Per > CR30 > CR20.(3) The optimal process conditions for frost resistance fruit paste preparation by Per modified from corn starch were as follows: gelatinization temperature of 80 o C, p H value of4.0, gelatinization time of 15 min and sugar adding content of 25%. Under these conditions,the average volume of water released after 5 freeze-thaw cycles for fruit paste was only5.81%.(4) Compared with the original formula, the spreadability could be improved and the volume of water released could be decreased by the improved fruit paste when applicating to fresh fruit and cakes, while no changes on the color and transparency of the products.