Analysis of the influence and optimization of concentration of organic acids on chemical and physical properties of wheat dough using a response surface methodology and desirability function/ Analiza efekata i optimizacija koncentracije organskih kiselina na hemijske i fizicke osobine psenicnog testa primenom metode odzivne povrsine i funkcije pozeljnosti

In order to improve physical and chemical properties of dough produced from wheat flour of suboptimal quality (protein content 10.7% dry basis, dough energy 4.0 [cm.sup.2]), optimal doses of ascorbic and citric acid were evaluated using a response surface methodology and desirability function. The paper brings the analysis of the main effects as well as their interactions. The effect of organic acids was evident in relation to pH lowering and decrease in free thiol groups, which consequently changed the physical properties of dough (increased dough energy, extensibility and resistance). The well known oxidative effect of ascorbic acid which is manifested as increase in dough energy and resistance, was enhanced by the addition of citric acid, i.e., their synergistic action. Contribution of citric acid was the donation of hydrogen ions which changed the pH, lowered the content of free -SH groups and increased protein aggregation. Ascorbic acid individually significantly increased energy (linear regression coefficient [b.sub.1] = 4.0 X [10.sup.-4]) but higher effect was exerted by the addition of ascorbic and citric acid mixture as seen through higher interaction regression coefficient ([b.sub.12] = 0.076). Dough resistance was significantly affected only by ascorbic acid due to its oxidizing action whereas dough extensibility was affected by both acids (main effects) at all applied doses and their mixtures. The effect on dough extensibility depends on the dose of acids but resistance decreased with quadratic increase of acid doses. Second-orderpolynomials were used in modeling of responses (dough energy, resistance and extensibility) which showed a good fit with experimental data as shown by high values of the coefficients of determination [R.sup.2] for energy, resistance and extensibility (0.953, 0.976 and 0.996, respectively). Based on F value, it could be concluded that the model gave good prediction of experimental data while p-values for all responses showed that the models were significant at significance of 90%. The obtained models were used to optimize the doses of ascorbic and citric acid in order to maximize dough energy and extensibility. Significant increase of dough energy by 4.7 times and extensibility by 1.5 times was achieved by the set of optimum conditions of 97 mg/kg citric and 100 mg/kg ascorbic acid. The obtained results are applicable in semi-industrial and industrial facilities for flour processing. Keywords: Ascorbic acid * Citric aci