دکتر فاطمه حبیبی

Nowadays, gums are used in cereal and flour products to replace gluten by optimizing physicochemical and rheological properties. In this study, with the aim of improving the rheological properties of the dough compared to the control sample, the effect of different concentrations of guar gum, xanthan and pectin gums (0.3, 0.6 and 0.9%) in terms of weight / weight percentage based on rice flour of Nemat  and Neda cultivars was examined. Based on the results of the viscosity properties, the highest Peak viscosity is in Nemat and Neda cultivars with the addition of guar (0.9%) and the lowest Peak viscosity is in Nemat cultivar without adding gum or control sample. The results show that with increasing guar and increasing the concentration of added guar, the tendency to absorb water increases and the volumetric expansion of the dough will increase. The greatest effect on the rate of breakdown viscosity was observed in Nemat cultivar with the addition of xanthan gum and the highest rate of breakdown viscosity was observed in Neda cultivar with increasing guar (0.9%). Due to the decreasing trend on the rate of breakdown, we find that xanthan is not a suitable hydrocolloid to improve the rheological properties of rice flour paste of Nemat cultivar. The highest rate of setback viscosity was observed in both Nemat and Neda cultivars with an increase of 0.3% and the lowest rate was in the control sample. Comparison of the average of statistical data shows that the highest final viscosity in both Nemat and Neda cultivars with an increase in guar 0.9% and the lowest in the control sample. It can be concluded that increasing the gums used in this study increases the tendency of the final product or product to dry after cooling.

Rice is the staple food of the Iranian people and its pollution with heavy metals has irreparable dangers for consumers. The aim of this study is to find a way to reduce the absorption of heavy metals from rice. To study the effect of nitrogen fertilizer and parboiling process on heavy metals, a factorial experiment was conducted in a randomized complete block design with three replications. In this study, nitrogen fertilizer at three levels (N1: 60, N2: 80 and N3:100 KgN /Ha) and parboiling at two levels of soaking temperature (C1:50 and C2:80 °C) and two levels of steaming time (T1:10 And T2:15 min) were applied. Induced plasma mass spectrometry (ICP-MS) was used to determine heavy metals. Increasing the soaking temperature and steaming time reduced all heavy metals, but changes in fertilizer levels had no significant effect on heavy metals. The interaction effects of the treatments showed that N3C1T1 treatment had the highest percentage of weekly allowance for Cr and Ni (99% and 58%, respectively) and N2C1T1 treatment had the highest percentage of weekly allowance for Mg and Cd (11% and 9.5%, respectively). Increasing the soaking temperature and steaming time minimizes the weekly intake of all heavy metals so that the N2C2T2 treatment shows the lowest weekly intake of all heavy metals. In less heat and time, the remaining heavy metals cannot be ignored, so parboiling at higher temperatures and times is recommended to maintain consumer safety and health.

Viscosity is used as the most important indicator in evaluating the cooking quality of rice. In order to investigate the best irrigation method and nitrogen application and their interaction effects on viscosity or cooking quality in Guilaneh rice cultivar, this experiment was conducted as a factorial experiment in a CRBD with 3 replications. Irrigation managements was considered in 3 levels(full irrigation, 7 and 14 day interval irrigation) and nitrogen fertilizer as the second factor in 3 levels(50, 75 and 100 kg/ha). It will achieve better cooking quality with higher peak viscosity, lower trough viscosity and lower final viscosity. In the study of the interaction effects of nitrogen fertilizer application and irrigation, the highest peak viscosity was observed in the treatment with 14-day interval irrigation and 75 kg nitrogen fertilizer per hectare (2707 Centipoise). The lowest trough viscosity was obtained in the treatment of 75 kg fertilizer and irrigation under flooding (1767 Centipoise). The lowest final viscosity was obtained with 7-day interval irrigation and 75 kg nitrogen fertilizer per hectare (3648 Centipoise). In the study of viscosity, the higher breakdown and lower setback indicate better cooking quality. The highest breakdown (881Centipoise), the lowest setback (957 Centipoise) and the lowest pasting temperature (84.54°C) were related to the treatment of nitrogen fertilizer 75 kg/ha and 7-day interval irrigation. Therefore, according to environmental conditions and recommendations to reduce fertilizer and water consumption, if there is no effect on yield, treatment with 7-day interval irrigation and nitrogen fertilizer 75 kg/ha to achieve the best cooking quality for Gilaneh cultivar is recommended.

This study investigated the influence of type and structure of starch components on the cooking quality of Iranian rice varieties. Six traditional Iranian rice cultivars were harvested, their drying and moisture contents were adjusted, they were milled and their white grains and flour were evaluated in a completely randomized design. The starch properties of amylose content, gelatinization temperature and gel consistency were measured. Characterization of polymeric structure of amylose and amylopectin was evaluated using chromatographic methods. Although there was little difference in amylose content, gelatinization temperature and gel consistency, the results showed significant differences at the 1% level for amylose and amylopectin hot water-soluble components and degree of polymerization. The rice varieties of good quality were Hasansaraee, Tarom and Domsiah; these showed higher hot water-soluble amylose content in results of size exclusion chromatography. The chain length distribution of amylopectin chains and the degree of polymerization were determined by capillary electrophoresis. Selected varieties showed significant differences for A, B1, B2, B3 and longer chains at the 1% level. The results showed that good quality cultivars, such as Domsiah, had more short chains (A) with less polymerization. There was no difference between the B1 and B2 chains by cultivar. The greatest difference was found between short chains (A), B3 and long chains. Differences in the polymeric structure of rice grains also should be considered to obtain more accurate analysis and new insights into quality.

In order to understand rice quality well، there is requirement for knowing all components of its seed and investigating their interaction. In this research، to investigate the effect of proteins on the viscosity properties، some of Iranian rice varieties including Hasan Sarai، Khazar، Dorfak، Binam، Hashemi were selected. Using extraction by dilute alkali، protein content deleted and then viscosity of extracted starch was compared with its properties before extraction. The result showed viscosity properties that changes in cooking temperature including Peak (maximum viscosity during heating the sample)، Trough، Final viscosity، Breakdown، Setback، Pasting temperature and pasting time. With rising the temperature due to absorption of water by the starch granules and protein، viscosity properties will increase. The effect of protein on all characteristics was significant at the 1% level except the maximum viscosity however the combined effects of protein and genotype was significant for all traits. The greatest impact of protein on the minimum viscosity was observed in Binam (+119. 16) and the lowest was observed in Khazar (+14. 64). When the sample is cooled during a period time، final viscosity again increases and at the end of test، final viscosity is recorded. Protein Removal from sample decreased the amount of final viscosity and the most influence was observed in Hashemi (+ 99. 25). The rate of setback is changes which occur upon cooling or of gelatinized starch. Effect of protein on setback of obtained gel was significant in all varieties and the most and the lowest effect recorded respectively in Khazar (+ 95. 15) and Hasan Sarai (+23. 87). Also، the effect of protein on the trough was negative in all varieties. With protein removal، viscosity curve will rise in less time. Actually، protein in rice grain، postpones emergence of gelatinization properties and subsequently increases required time for cooking. Different pasting rates for every variety with the same amylose content، implies involvement of proteins in this case. So، although starch has been known as the most important factor in rice quality، protein can also be considered as a measure of influence.

Rice cooking and eating quality are the most important factors for accepting a variety by consumers. To determine the accurate gelatinization properties of rice starch with Little and Differential Scanning Calorimeter (DSC) methods, this research was carried out on 10Iranian rice varieties. All varieties were similar in amylose content and gelatinization score with Little method. The starch properties such as gelatinization enthalpy (ΔH), onest temperature (T0), peak temperature (Tp), conclusion temperature (Tc) were measured by using of the curve derived from DSC. Analysis of variance showed significant differences between studied varieties for gelatinization parameters obtained from DSC method, but there weren’t the significant differences between varieties for gelatinization scores derived from Little’s method. The maximum and minimum enthalpy (ΔH) was observed in Domsorkh (11.48 j/g) and Hasssansaraee varieties (6.44 j/g), respectively, but Domsorkh and Hassansaraee varieties had similar scores for alkali spreading values from the Little’s method. In varieties with the same amylose content, lipid-amylose complex increase crystalline structure of starch so enthalpy for gelatinization will be increased. Data analysis showed that there was significant correlation between lipid content and enthalpy at 5% probability level. In mean comparisons between varieties, the minimum and maximum onest temperature (T0) were observed in Domsefid (64.82 oC) and Domsiah (67.7 oC) varieties, respectively. Also, there was the significant correlation between onest temperature and lipid content. Results from current research showed that the Little’s method is a rapid and economical method for selecting lines and varieties with suitable gelatinization properties (3-5 score), but DSC method can explain more details of cooking differences between varieties where Little’s method is unable to explain them.