冻融循环下冷冻非发酵面团品质的变化及机理

Quality changes and mechanism of frozen non-fermented dough upon consecutive freeze-thaw cycles

为了探讨储运销售过程引起的冻融循环对冷冻非发酵面团品质的影响,利用低场核磁共振分析仪(LF-NMR)、质构仪与流变仪等对样品面团水分与蛋白质组分、质构与流变特性进行测定,研究冻融循环下冷冻非发酵面团品质变化。结果表明:5次冻融交替中,失水率显著上升,达至3.14%;总水分中半结合水含量在F1后整体呈下降趋势,表明冻融循环过程中,半结合水不断散失;至第5次冻融时,醇溶蛋白含量显著下降(P<0.05),谷蛋白与谷蛋白大分子聚合物(GMP)含量至第4次冻融后均显著下降(P<0.05),分别降至2.26%与0.70%;生面坯剪切力显著上升,强韧性则与之相反;熟面坯硬度呈上升再下降趋势,黏性基本呈上升,弹性呈下降趋势;弹性模量G'与黏性模量G''均呈下降趋势,且在第4次时,tanδ(tanδ=G'/G'')至最大,表明G'的变化程度比G''大。由此可见,冻融循环致使冷冻非发酵面团品质有所下降。总而言之,冻融循环对冷冻非发酵面团的品质下降产生一定的负面影响。

In order to investigate the effect of consecutive freeze-thaw（FT） cycles on the qualities of frozen non-fermented dough during the process of the storage, transportation and sale, the low-field nuclear magnetic resonance（LF-NMR）, a texture analyzer and a rheometer were used to observe changes of frozen non-fermented dough in quality during five consecutive freeze-thaw cycles. The water loss rate, water distribution and mobility,protein fraction content, textural and rheological properties of the dough samples were evaluated in our experiment. The results showed that： upon five consecutive FT cycles, the water loss rate significantly increased to 3.14%（P0.05）, while the ratio of semi-bound water to the total water declined in general, indicating that the water losing was mainly resulted by the semi-bound water release. The gliadin content significantly decreased（P0.05） at the fifth FT cycles; the glutenin and glutenin macropolymer（GMP） content experienced an obvious drop after the forth FT cycles and down to 2.26% and 0.70%, respectively. 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. The storage moduli and loss moduli（G＇ and G＇＇） both showed a downward trend, and at the forth FT cycles, tan δ（tan δ = G＇ / G＇＇） was up to the maximum, which indicated that G＇ showed a more dramatic drop than G＇＇. From these results, it was thus clear that the consecutive FT cycles led to the decrease in the quality of frozen non-fermented dough. Overall, the consecutive freeze-thaw cycles had certain negative effect on the qualities of frozen non-fermented dough.