Addition of Reducing Agents, Vitamin C and Citric Acid during Wheat Conditioning and their Effects on the Quality Characteristics of the Corresponding Flour and Dough

The most important component of wheat proteins is gluten, and the most prominent bonds in gluten are disulfide bonds, which bind glutenin subunits. Therefore, oxidizing and reducing agents with great effects on the thiol-disulfide system of the dough can change the mechanical and rheological properties of the dough. Due to the positive effects of ascorbic acid on the properties of the dough, it is used as a flour improver. To weaken the structure of the dough, reducing agents such as cysteine-L can be used, and by adding organic acids, increasing the specific volume and decreasing the moisture, the pH and hardness are observed in comparison with the control. This study is performed to evaluate the effect of adding reducing compounds, vitamin C and organic acids during the conditioning of wheat and their effect on the yield of the resulting pulp.

First, Physical properties of wheat include: specific density, colorimetry, estimation of grain length, width and thickness, grain hardness, hectoliters, 1000-grain weight, grain moisture, degree of extraction were measured for the tested wheat. Moisture, pH, ash, particle size, fat, protein and zeal number tests were performed on wheat flour. From elementary cleaned and weighed wheat, 13 samples of 240 g each were weighed separately and poured into plastic bottles. One sample was conditioned with only 30 ml of distilled water and the other 12 samples were conditioned with the following solutions, respectively:1- Cysteine solution at three levels of 0.25, 0.5 and 0.75% by weight 2- Citric acid solution in three levels of 0.3, 0.4 and 0.5% by weight Vitamin C solution in three levels of 100, 150 and 200 ppm 4- solution of 80 ppm vitamin C and 0.1% cysteine, solution of 100 ppm vitamin C and 0.2% cysteine, solution of 120 ppm vitamin C and 0.3% cysteine After 24 hours, the conditioned wheat samples were milled by a laboratory waltz mill, and then subsequent tests including gluten, sulfhydryl-disulfide, glutathione, and solvent retention capacity (SRC) were performed on the samples. Statistical analysis was performed using SAS statistical software in a randomized complete block design. Each measurement was performed in at least three replications and the means were compared at 95% confidence level with the least significant difference in LSD.

The results of physical tests on wheat grain and chemical tests on flour obtained by milling  the wheat samples without adding additives during conditioning are presented in tables. The results  of gluten, glutathione, sulfhydryl-disulfide and solvent storage capacity tests on samples of conditioned wheat flours are also presented. Based on the results of gluten and glutathione test, it was shown that ascorbic acid is oxidizing and strengthening the dough, but cysteine is reducing and weakening the dough. Simultaneous addition of cysteine and ascorbic acid strengthened the dough, adding citric acid to certain level strengthened the dough as exhibited in the gluten test. However, byond that level, weakened the dough, but in the glutathione test it was almost ineffective. The results of sulfhydryl-disulfide test showed that increasing the amount of vitamin C at three levels of 100, 150 and 200 ppm increases the number of disulfide bonds, although this increase was not in linear trend, which can be due to the limited number of groups of sulfhydryl with a suitable spatial arrangement for oxidation. Accordingly, the number of sulfhydryl groups is significantly reduced, although it does not reach zero. With the addition of reducing cysteine, the opposite trend was the case, as the number of thiol groups increased, the number of disulfide bonds and bridges decreased. The addition of organic acid had no significant effect on both parameters and showed that the performance of these two variables is independent. By adding both reducing and oxidizing compounds, it was found that the oxidizing effect of vitamin C is far greater than the reducing effect of cysteine. Regarding the solvent retention capacity test performed with 4 solvents of deionized water, 50% sucrose, 5% sodium carbonate and 5% lactic acid, the expected results are that the addition of cysteine has a reducing and weakening effect on the dough, adding vitamin C and cysteine + vitamin C strengthens the dough and the addition of citric acid initially strengthens the dough, but by increasing its level weakens the dough, but this effect is small and can beneglected . The results obtained by comparing the samples conditioned with cysteine, vitamin C, citric acid and cysteine + vitamin C, with the sample conditioned with distilled water in some additive levels matched the expected results, but in some cases did not.