Study On Factors Influcing Flour And Products Color And Analysis Of PPO Activity

In this paper, first we studied the main factors influencing the color of flour and wheat-based products, followedly we studied the PPO activity influencing the color of flour and wheat-based products. We contrasted different assays of PPO activity and the influence of SDS on extraction and activation of PPO in wheat. Lastly we studied the correlations between PPO activity and quality traits. The results are as follows:1 The correlations between color traits and quality traitsWe use recombinant inbred populations and this can clear up the affect of genetic background to some content and reflect the correlations between color traits and main quality traits exactly.Results showed that there are four clusters of quality traits influencing flour and flour based products.The first cluster contains hardness, water absorption, wet gluten, dry gluten and protein with main reflection of protein quantity. These traits had negative correlations with flour whiteness, flour and fresh sheet L* value most at 1% level and positive correlations with a* value and b* value at 1% or 5% level. The second cluster contains flour yield, dough development time, yellow pigment, PPO activity, and sedimentation value. These quality traits had negative correlations with flour and fresh sheet L* value, positive correlations with b* value at 1% or 5% level and no significant correlation with a* value. The third cluster contains gluten index, dough stability time and setback. Gluten index and dough stability time are main reflection of protein quality and had significant positive correlations with flour whiteness and fresh sheet L* value. The forth cluster contain parameters of starch pasting properties. These traits had positive correlations with flour whiteness, flour and fresh sheet L* value at 1% level, and negative correlations with flour and fresh sheet a* value at 1% level.2 The color advantage of Chinese wheat with high whiteness and analysis of affecting factors for color formationIn this test, we chose Aobaimai imported from Australia and Jimai 21 in course of spreading in Shandong province as contrasts. Firstly, we studied the color advantage of Chinese wheat cultivars (line) Youmai3hao, Shannong12, Shannong8355 and 62008 which have good appearance to investigate, and followedly analyzed the main factors influencing the formation of the color. Results showed that the brightness of the four wheat cultivars(line) was lower than Aobaimai, but the yellowness was also lower than Aobaimai, especially the appearance of steamed bread of 62008 and Shannong12 were better than Aobaimai. The changes of flour color after added with BPO in the four wheat genotypes were smaller than Aobaimai. Through the analysis of the affecting factors for the color formation, we found that the main affecting factors of color formation were low PPO activity and yellow pigment content for high-protein content cultivars and low protein content and high starch content for low-protein content cultivars. In the breeding selection of wheat color, we can choose wheat lines with low PPO activity and yellow pigment content in wheat materials with high protein content. We can also choose wheat lines with low PPO activity and yellow pigment content in wheat materials with low protein content and high starch content. Moreover, we can choose wheat lines with low PPO activity and high yellow pigment content in wheat lines with low protein content and high starch content .3 The comparison of different assays of wheat polyphenol oxidase activityPolyphenol oxidase(PPO) is highly related to undesirable brown discoloration of wheat-based end products. At present, there are several different assays of wheat polyphenol oxidase activity based on relative reports, including the difference in absorption wavelength,reaction time,substrates and the choice of samples. With catechol as substrate, there was an broad,symmetrical absorption peak at 401nm and a sharp peak at 301nm. With tyrosine as substrate, there was a strongest absorption at approximately 322nm. The nature of the reaction products responsible for 301nm with catechol as substrate and 322nm with tyrosine as substrate should be further studied prior to using this wavelength. So in this test, we still assayed at this wavelength. The best reaction time was 30 min after mixed with substrate. There was significant correlation between the two assays with catechol and tyrosine as substrate respectively. The PPO activity with catechol as substrate were higher, however the variation coefficient of the PPO activity was larger in different cultivars when used tyrosine as substrate. 4 The influence of SDS on extraction and activation of Polyphenol Oxidase in wheatIn this paper, we mainly studied the influence of detergent SDS on wheat PPO activity using 29 wheat samples.We investigated that SDS could enhance wheat PPO activity and 50mmol/LSDS were most effective. PPO activities were quite stable in presence of SDS because there were no significant changes in PPO activity with different extraction time. SDS not only enhanced the extraction efficiency of wheat PPO, but also activated the PPO from high PPO lines and inhibited the PPO from low-PPO lines by inducing conformational change. The PPO activities assayed after extraction in presence of SDS showed significant negative correlations with dough sheet brightness (L*) at 24 hours and high significant positive correlations with decrease (0-24 hr) in dough sheet brightness. So PPO activities assayed after extraction in presence of SDS is more reliable for screening wheat germplasms with different PPO activities, especially low PPO activity wheat. Moreover, the biochemical properties present in the process can offer theoretic evidences for the integrity of PPO physiological mechanism in wheat.5 Correlations between flour PPO activity and quality traitsWhen we used different wheat cultivars and RIL populations, there were same correlations between PPO activity and following traits. PPO activity had significant positive correlations with protein content, significant negative correlations with starch content at 1% level, and had negative correlations with flour whiteness, flour and fresh sheet L* value at 1% level.There were still different correlations between PPO activity and quality traits when we used different materials. In different wheat cultivars, PPO activity had significant positive correlations with sedimentation value, hardness, crude lipid, falling number, flour and fresh sheet a*value, no significant correlations with parameters of starch pasting properties. In RIL populations, PPO activity had no significant correlations with sedimentation value, hardness, and flour and fresh sheet a*value, significant negative correlations with falling number and parameters of starch pasting properties, and significant correlations with b* value. So we can improve PPO activity through the selection of other traits indirectly, and at the same time we should also consider other quality traits comprehensively in the process of wheat PPO activity improvement.