Three samples of native or untreated cassava starch were exposed to microwave radiation for periods of 5, 10 or 15 min. The temperature of each sample was measured immediately after each exposure time and the temperature of the samples was around 135 °C. The samples were cooled to room temperature and maintained in a desiccator with anhydrous calcium chloride. All the samples were analysed by thermogravimetry-derivative thermogravimetry, differential scanning calorimetry (DSC), rapid viscoamylographic analysis (RVA), X-ray diffraction powder patterns, non-contact atomic force microscopy and colour characteristics by reflectance spectrophotometry. The thermal behaviour, gelatinisation temperatures, enthalpy and pasting properties were determined. Relative to the time of microwave exposure, the peak viscosity and gelatinisation (RVA and DSC) increased slightly after 5 min, and, after 10 and 15 min, it decreased considerably. The degree of relative crystallinity (%) decreased, while the average roughness increased. The reflectance spectrophotometry showed that microwave action occured quickly and progressively, causing colour changes (mainly with trends to yellow) and very small differences to the starch samples that were heated at controlled temperature in a conventional oven.

The effect of microwave radiation on some thermal, rheological and structural properties of cassava starch

Organic foods and crops are produced throughout the world under strict controls on growing conditions, so that synthetic chemicals, irradiation or genetic modifications are avoided. Organic starch is extracted following the same rules. Heat–moisture treatment (HMT) on starch is a physical method considered to be natural: it consists of heating starch at a temperature above its gelatinisation point with insufficient moisture (<35 %) to cause gelatinisation. Samples of organic cassava starch (with 12.8 % moisture) were dried in an oven with forced air circulation at 50 °C for 48 h and, immediately, distilled water was added to each sample until it reached the ratios of 10, 20, and 30 %, respectively. The samples were transferred into 100 mL pressure flasks, sealed tightly with a cap, and maintained in an autoclave for 60 min at 120 °C. The flasks were opened and the samples were kept in a desiccator containing anhydrous calcium chloride up to constant mass. The effects of HMT were studied using the following techniques: thermogravimetry and derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), rapid viscoamylographic analysis (RVA), reflectance photocolorimetry, atomic force microscopy (NC-AFM) and X-ray diffractometry (XRD). Rheological properties such as the pasting temperature (RVA) and the peak temperature (DSC) increased, while gelatinisation enthalpy ∆H (DSC) decreased. The average diameters of the granules showed no significant changes, while the degree of relative crystallinity decreased.

Effects of heat–moisture treatment on organic cassava starch

The thermal, rheological and structural properties of cassava starch granules modified with hydrochloric acid at different temperatures

The avocado (Persea americana, Miller) is a tree that is native to Central/North America (Mexico) and it is very popular worldwide due to its food applications. Its seeds contain an important amount of starch and there is lack of study and understanding regarding the physico-chemical properties of this biopolymer. In this research, starch granules were extracted from avocado seeds and oxidised with standard sodium hypochlorite solutions at 0.5, 1.0 and 2.0 %. Untreated and modified samples were investigated using the following techniques: simultaneous thermogravimetry–differential thermal analysis, differential scanning calorimetry, non-contact atomic force microscopy, rapid viscoamylographic analysis and X-ray powder patterns diffractometry. The main purpose was to investigate the thermal, structural and rheological behaviour of native and oxidised avocado starch, and it was verified that the treated samples showed a decrease in gelatinisation enthalpy and average roughness as well as in the degree of relative crystallinity and pasting properties.

Thermal, structural and rheological properties of starch from avocado seeds ( Persea americana , Miller ) modified with standard sodium hypochlorite solutions

Characterisation of native starches of seeds of Araucaria angustifolia from four germplasm collections

Starch is one of the most important sources of reserve of carbohydrate in plants and the main source in the human diet due to its abundance in the nature. There no other food ingredient that can be compared with starch in terms of sheer versatility of application in the food industry. Unprocessed native starches are structurally too weak and functionally too restricted for application in today’s advanced food and industrial technologies. The main objective of this study was to compare the thermal behavior of native cassava starch and those treated with hydrogen peroxide, as well as those treated with hydrogen peroxide and ferrous sulfate. The cassava starch was extracted from cassava roots (Manihot esculenta, Crantz) and treated by standardized hydrogen peroxide (H2O2) solutions at 1, 2 and 3% (with or without FeSO4). Investigated by using they are thermoanalytical techniques: thermogravimetry - TG, differential thermal analysis – DTA and differential scanning calorimetry - DSC, as well as optical microscopy and X-ray powder diffractometry. The results showed the steps of thermal decomposition, changes in temperatures and in gelatinization enthalpy and small changes in crystallinity of the granules

Thermoanalytical study of native Cassava starch and treated with hydrogen peroxide

Universidade Estadual Paulista Julio de Mesquita Filho, Departamento de Quimica, Faculdade de Ciencias de Bauru, Bauru, Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, Centro, CEP 17033-360, SP, Brasil

Fernanda Janaina Oliveira Gomes da Costa

Papers

Thermoanalytical study of native Cassava starch and treated with hydrogen peroxide

Thermoanalytical study of cassava starch native and treated with hydrogen peroxide