Controlled processes of drying, storage and hydrothermal treatments for improvement of rice starch quality | |
| Author | Rungarun Hormdok |
| Call Number | AIT Diss. no.FB-07-03 |
| Subject(s) | Rice--Drying Rice--Storage Starch--Drying |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. FB-07-03 |
| Abstract | This study investigated effects of moisture and temperature associated with drying-tempering and storage of rough rice on quality of milled rice, flour and starch. Also, two hydrothermal treatments, annealing and heat-moisture treatment (HMT) were intensively applied to rice starch for modifying their functional properties. The correlations between process parameters and selected functionalities in the form of predictive models were established. Finally, the potential applications of heat-treated rice starch in particular food products were evaluated. In the drying-tempering and storage experiment, two varieties of Thai rice, waxy type (RD6, 3.88 % amylose) and non-waxy type (CNT1, 30.32 % amylose), were evaluated. Results showed that moisture-temperature experience upon drying-tempering, and temperature-time history during storage affected the quality of rice grain and flour more than the starch. Drying of rough rice at 80°C with adiabatic tempering for 2 h showed a pronounced effect compared to drying at 25, 45 and 60°C where no tempering was applied. Upon drying at 80 DC, tempering of grains with high moisture content of 18% (w.b.) resulted in the more apparent changes in rice quality than grains with low moisture content of 13-14% (w.b.). The observed changes were the increase in head rice yield (HRY), water absorption ratio (WA) and volume expansion ratio (VE) for milled rice. Color value, L* (lightness) decreased whereas, b* (yellowness) increased with increasing process temperature. Drying-tempering and storage affected swelling of starch leading to either increase or decrease in paste viscosity as measured by Rapid Visco Analyser (RVA). Pasting temperature (PT) increased, and this was consistent with the increase in gelatinization temperature at onset (To), peak (Tp) and conclusion (Te) measured by Differential Scanning Calorimetry (DSC). Gelatinization temperature range (GR) slightly reduced, however, there was no significant change in gelatinization enthalpy ( Hgel) and retrogradation enthalpy ( Hret). Storage of dried rice grain at high temperature (37°C) accelerated changes in rice quality as compared to storage at low temperature (4 and 25 °C). Some inconsistent observations upon storage indicated complex changes not only in starch but also in non-starch components. Results suggest that care should be taken with drying-tempering of rough rice at 80°C and storage at 37 °c as these temperatures profoundly affected primary quality of rice flour and starch. As a mean to improve rice starch functionalities, two hydrothermal treatments, annealing and heat-moisture treatment (HMT) were applied to two commercial types of rice starch; waxy (3.44% amylose) and non-waxy (27.05% amylose). Annealed rice starch was prepared by incubating starch slurry at 45, 50 and 55 "c for 8, 16 and 24 h. HMT was provided by adjusting starch moisture to 15,20 and 25% (w/w) followed by heating at 100, 105 and 110 °C for 0.5, 1.0 and 1.5 h. Both annealing and HMT noticeably affected functional properties of rice starch which depended upon starch type and treatments conditions. Swelling of starch granules was substantially restricted leading to either increase or decrease in RVA paste viscosities. Gel hardness of non¬waxy rice starch significantly improved. PT increased corresponding to the increased To, Tp and Te after treatments. GR tended to be narrowed after annealing but, broadened after HMT. Hgel increased with increasing moisture (in case of HMT), temperature and duration of treatments. However, starch treated to the maximum extent of annealing (24 °C for 24 h) and HMT (25% moisture 110°C for 1.5 h) showed substantial decrease in Hgel. This contributed to the loss of crystallinity as measured by X-ray diffractometer (XRD). Results with Scanning Electron Microscopic (SEM) showed that some network structures developed among starch granu les of waxy rice starch after anneal ing and non-waxy rice starch after HMT. The predictive models for estimating functional properties were developed successively. When these models were validated, the actual and calculated values showed very good correlation (R²=0.800-0.987). The study explored possibility of producing starch of desired quality from waxy and non-waxy rice starch by using appropriate annealing and HMT. The optimal condition for producing waxy rice starch with high shear stability was annealing at 55°C for 24 h which reduced Breakdown viscosity from 125.75 RVU to 71.88 RVU. The annealed waxy rice starch has low paste viscosity and poor stability to acidic treatment and sterilization. However, freeze-thaw stability was improved as syneresis was reduced from 48.56 to 38.75%. In case of non-waxy rice starch, the optimal condition for producing solid gel with high strength was annealing at 55°C for 24 hand HMT of starch with 20% moisture at 110°C for 1.5 h as the primary gel hardness of 49.82 g raised to 60.38 and 61.23 g, respectively. Substitution of fresh rice flour by 50% annealed rice starch improved the texture quality of noodle closer to the range of commercial noodles. Results showed the practical application of hydrothermal¬treated rice starch in food products. |
| Year | 2007 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. FB-07-03 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Athapol Noomhorm |
| Examination Committee(s) | Rakshit, S. Kumar;Ranamukhaarachchi, S.L.;Pavinee Chinachoti |
| Scholarship Donor(s) | RTG Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2007 |