| During refrigerated and frozen storage or transportation, a major issue for frozen dough or products is the loss of quality in a number of ways. mainly including the weak antifreeze ability, the increase in liquid loss, the decrease in steamed quality for frozen dough and so on. For solving or relieving such issue, changes of non-fermented dough in quality during freeze-thaw cycle (FT) were investigated. Then, upon the forth consecutive FT cycle (F4), effects of flour’s main components on the quality of non-fermented dough were studied by the method of separation and recombination. Furthmore, the effects of additives (enzymes and modified starches) on anti- FT quality of non-fermented dough were explored. Main results were as the following:1. Effect of FT cycle times on the qualities of non-fermented dough. Results showed that: upon five consecutive FT cycles, the water loss rate significantly increased (P<0.05) while the ratio of semi-bound water to the total water declined in general The gliadin content significantly decreased at F5 (P< 0.05). The contents of glutenin and glutenin macropolymer (GMP) both experienced an obvious drop after F4. For uncooked samples, firmness obviously increased and toughness was on the contrary. For cooked samples, hardness increased at first and then decreased, adhesiveness presented ascendant trend basically and springiness declined. G’and G" both showed a downward trend, and at F4, tan 8 was up to the maximum. So, it was clear that the FT cycles led to the decrease in the quality of non-fermented dough.2. Effect of flour’s main components on the qualities of non-fermented dough at F4. Results showed that:It appeared that the structure of starch and gluten suffered different degrees of damage. After recombination, with the decline in the ratio of protein and starch content from the recombined dough, the water loss rate increased; the relative content of deep-bound water decreased; firmness and toughness both decreased gradually. TPA indexes all had significant changes (P< 0.05) in samples with higher protein; G’and G" both decreased. Therefore, protein and starch both have certain influences on the freeze-thaw qualities of non-fermented dough, but protein has greater impact on it.3. Comparing the transglutaminase’s (TGase) and xylanase’s effects on the qualities of FT and non-fermented dough. They both changed the protein fractions’ content:the former reduced the gliadin and glutenin content, and raised GMP, and the latter increased the gliadin. Xylanase effectively reduced the water loss rate, but TGase improved its inner water distribution, especially the effect was more obvious at 1%; for improving the firmnness and toughness,0.03‰ and 0.06‰ of xylanase were appropriate and its improvement surpassed TGase’s; The two enzyme both improved the different aspects of TPA. To optimize the rheological properties, TGase’s improvement was better than xylanase’s. Therefore, TGase and xylanase both played a role in their different aspects to improve the freeze-thaw quality of non-fermented dough.4. Differences in the effect of hydroxy propyl distarch phosphate (HPDSP), tapioca acetate starch (TAS), hydroxy propyl starch (HPS) and PAS (potato acetate starch) on the FT qualities of non-fermented dough. Results showed that:The addition of modified starches didn’t inhibit the water loss, but increased the ratio of deep-bound water; the gelation both fell behind. To improve the textural properties, the dosage should not be too high (less than 5%) and 5% HPS was best; TAS was not conducive to the rheological properties. So, adding a small dosage has some improvements to the FT qualities.5. Based on the above results, we verified the effect on the quality change of dumplings during frozen storage by adding a certain amount of gluten-starch (15%:35%), xylanase (0.03%o) and HPS (5%). Results showed that:With the frozen time increased, three treatments all can effectively alleviate the quality of frozen dumplings’ deterioration to some extent. |
PDF Full Text Request