Study On Physicochemical Characteristics Of Waxy Wheat Flour And Effect Of Its Blends On Quality Of Bread, Dry White Chinese Noodle And Chinese Steamed Bread

Strarch is the major component in the wheat kernel, which is mainly composed by the amylose and the amylopectin. The wheat without amylose in its endosperm was called "waxy wheat". There is no natural waxy wheat in the world, so it has been investigated in many countries. There is extremely few or no amylose in waxy wheat endosperm. Amylopectin structure of waxy wheat is similar to nonwaxy and partial-waxy wheat. Its branch number or the polymerization extent has no difference to the other two wheats, and its amylopectin has the maximum molecular weight but no special length branched chain has been examined. Some researches indicated the waxy wheat has low setback, pasting temperature and the peak temperature, and higher breakdown, peak viscosity, gelation temperature, water absorption, SDS- sedimentation, damaged starch content, swelling power, alkaline water retention capacity (AWRC), as well as greater degree of crystallization, absence of amylose-lipid complex, and shorter peak time compared with nonwaxy wheat. In addition, it could adjust the amylose content, improve the wheaten food quality, such as improving noodles sensory quality, extending bread shelf-life and so on by adding of waxy wheat flour to nonwaxy ones. Former studies paid great attention to the adding proportions but neglected physicochemical properties of waxy wheat flour blends when making bread, so the results maybe deviated the truth. Furthermore, the researches emphasized on white salted noodle, but few on dry white Chinese noodle or Chinese steamed bread which consumed the most wheat flour in China. This article measured physicochemical characteristics, and added the waxy wheat line Wx5 to Yangmai 17 and Yangmai 158 which come from Gaoyou and Yangzhou (noted 1 and 2 in bracket) to investigate the effect of waxy wheat flour proportions on dry white Chinese noodle and Chinese steamed bread quality; adding Wx5 to the imported Canadian spring wheat, the physicochemical characteristics of waxy flour blends were adjusted by Yangmai 158 flour for according to breadmaking and evaluated the effect of waxy wheat flour proportions on bread qualities and staling. Furtherly it analyzed the effect of waxy wheat flour blends physicochemical characteristics on these wheaten food qualities. The following were results of the investigation:1. Waxy wheat has not been able to synthesize amylose as a result of absence three Wx genes, waxy wheat flour has higher water absorption, simultaneously has the higher tolerance index and lower four quality number, therefore the rheology characteristic is wickly. The starch content does not have the remarkable difference with nonwaxy and partial-waxy wheats, which indicated the waxy mutation has not affected starch biosynthesis. The peak temperature and the pasting temperature are lower than the nonwaxy and partial-waxy ones, and has the high breakdown and setback.2. By adding the different proportion of waxy wheat to nonwaxy, most of the flour physicochemical characteristics were changed more or less. The waxy wheat flour blends exhibited obvious "two-peak" curve measured by micro-visco-amylograph; the temperature of the first peak was similar to waxy wheat flour, and the second peak was similar to nonwaxy wheat flour, these showed that the two kinds pasted independently after mixed, and the result was not altered after six months later, but the partial-waxy wheat flour with the same amylose content was similar to nonwaxy in pasting properties, it indicated that structure differences should be presented in the waxy and nonwaxy wheat starches.3. Amylopectin content was increased in wheat flour blends by adding of waxy wheat flour, and amylose content in total starch decreased, so it should extend the bread shelf life to a certain extent, but excessive waxy flour cause the bread internal structure poor, appears many big air bubbles, the coherency also increase along with it, resulted the bread total score decreased. Although the proportions of waxy wheat flour are lower than 15% the influence was not remarkable to the bread quality, adding of excessive waxy wheat flour to nonwaxy resulted the bread quality decreased, so adding of excessive waxy wheat flour not only had no function to improve but also decreased the fresh bread quality. Adding of waxy wheat flour obviously reduced the firmness and loss of weight and volume during storing. Adding of 10～15% waxy wheat flour to nonwaxy should be possible to maintain bread freshness without decreasing bread qualities.4. Although the protein, starch, amylose, damage starch content, Farinograph and Extensograph properties are extremely important to dry white Chinese noodles sensory qualities, they do not have the remarkable influence on total score actually. Starch pasting properties not only affect the dry white Chinese noodle sensory scores, but also has the important influence on total score, such as lower peak viscosity and setback, and higher peak temperature would improve the dry white Chinese noodle quality. Peak viscosity and peak temperature are the primary factors of influencing the dry white Chinese noodle total score, so we can improve the dry white Chinese noodle qualities by increasing the peak temperature and reducing the peak viscosity. Waxy wheat flour has the low peak viscosity and setback, but simultaneously has the low peak temperature, so we cannot simply add of waxy wheat flour to the nonwaxy to improve the dry white Chinese noodle quality, therefore adding of lower proportions (about 35%) of waxy wheat flour to nonwaxy will achieve better pasting properties, and then the production of the high quality dry white Chinese noodle should be considered.5. Adding of waxy wheat flour to nonwaxy resulted the change of Chinese steamed bread qualities, and the relationship of Chinese steamed bread qualities and flour physicochemical characteristics also changed. The peak viscosity, water absorption, total starch, amylose content, and the extensibility (135min) were the most important factors influencing Chinese steamed bread sensory scores. Though Chinese steamed bread quality has no difference to nonwaxy wheat flour (0%, control) when waxy wheat flour proportion was lower than 20%, it decreased all sensory scores but specific volume. Waxy wheat flour possessed high water absorption, extensibility, and low peak viscosity characteristics, these were suitable for Chinese steamed bread quality improving, but adding of waxy wheat flour should decreased the increase Chinese steamed bread quality for decreasing of amylose, so the application of waxy wheat was limited on Chinese steamed bread for these characteristics should be adjusted to appropriate level. Although Chinese steamed bread qualities decreased after storing at -18℃for three days, adding of appropriate proportion (10～15%) could decrease the firmness after re-steamed.