Syed Zakiuddin Ali

Twin-screw extrusion of rice flour without a die : Effect of barrel temperature and screw speed on extrusion and extrudate characteristics

Abstract Rice flour with 14% moisture content was extruded at different barrel temperatures (80–120 °C) and screw speeds (200–400 rpm) through a twinscrew extruder without a die. The system parameters as well as the extrudate attributes were mainly dependent on temperature, whereas the screw speed imparted a lesser effect. Optimum extrusion conditions for obtaining minimum torque, specific mechanical energy (SME) and bulk density were determined. A positive linear (correlation coefficient r = 0.78, significant at a probability level p ≤ 0.01) relationship existed between SME and bulk density, indicating that low-density extrudate is possible to obtain with low SME. Extrusion of rice flour without a die appears to be an alternative approach to produce processed rice flours with high water absorption index and in vitro starch digestibility.

Glycemic response of rice, wheat and finger millet based diabetic food formulations in normoglycemic subjects

Food formulations suitable as dietary supplements to diabetic subjects based on wheat, decorticated finger millet, popped (aralu) and expanded (puri) rice each blended separately with legumes, non-fat dry milk, vegetable oils, spices and a few hypoglycemic ingredients were formulated. The formulations contained 13.0–18.3% protein, 11.3–11.8% fat, 59.9–67.5% starch and 13.2–18.0% dietary fiber. A 50-g equivalent carbohydrate portion of the foods in the form of thick porridge was provided to eight healthy adult subjects and the postprandial blood glucose response was determined. The Glycemic Index (GI) values were 55.4±9, 93.4±7, 105±6 and 109±8 for wheat-based, millet-based, aralu-based and puri-based formulations. The variations in the GI could be attributed to the nature of available as well as non-available (non-starchy polysaccharides) carbohydrates in the foods besides the processing undergone by the cereal ingredients. The higher GI of rice formulations could be due to the easily digestible nature of starches and also their lower dietary fiber contents. The study revealed the suitability of wheat-based formulation as a food supplement or as meal replacer in diabetic subjects but the unsuitability of rice-based formulations.

Screening of variables for extrusion of rice flour employing a Plackett–Burman design

Abstract A screening experiment with ten variables employing a Plackett–Burman experimental design was conducted on extrusion of rice flour. The variables include, hardware variables (mixing disk and reverse pitch screw elements), feed variables (moisture, sugar, salt and amylose contents, and particle size) and operating variables (barrel temperature, feed rate and screw speed). The response functions were extrusion characteristics (torque, specific mechanical energy and residence time), product attributes (water solubility index, water absorption index, and bulk density, peak viscosity, hot paste viscosity and cold paste viscosity). The response functions were highly affected by the hardware variables. A Plackett–Burman experimental design can serve as a useful tool for screening large numbers of variables and reducing the number of experiments.

Properties of Starches Modified by Different Acids

Starches from wheat, maize, finger millet, tapioca, green gram, chick pea, and potato were acid modified using 0.5N HCl, HNO3, H2SO4, and H3PO4 at 50°C for 1.5 h. Alkali Fluidity Number (AFN) for native starches was very low (0.3–2.5) and increased upon modification. HCl and HNO3 produced the highest AFN followed by H2SO4 and H3PO4 . For each acid, cereal and millet starches showed the highest AFN, followed by root, pulse and tuber starches. The extent of hydrolysis was proportional to number average molecular weight ( ), of the native starch in the case of HCl and HNO3 but not in other acids. Intrinsic viscosity [η] of native starches showed positive correlation to their ,. However, the [η] of the modified starches, particularly those produced by HCl and HNO3 , showed no proportionality with their , indicating diverse structural differences in the hydrolsed products. Special behavior of finger millet starch is clear from [η] values of these four acid modified starches. The iodine binding capacity (IBC) of starches, although decreased (2 to 36%) upon modification, did not follow any particular pattern. About 0.01 to 0.94% starch got solubilized during modification—highest being in case of HCl and lowest for H3PO4 . Their and IBC were considerably lower in all cases except potato, which showed same IBC for the solubilized, as well as granular modified starch.

Starch components in hot-water soluble and insoluble fractions of rice flour.

Flour from three varieties of rice containing high, medium and low amounts of amylose-equivalent (AE) was extracted with water at 96 °C. Gel permeation chromatography (GPC) of both the soluble and insoluble components of the rice flour on Sepharose CL-2B gave two fractions (FR I and FR II), as reported for native starch. Nearly one-third of the insoluble matter belonged to FR II and an equal proportion of soluble matter was FR I. The earlier assumed equivalences FR I of native starch ≈ insoluble AE of rice flour amylopectin and FR II of starch ≈ soluble AE of flour amylose, would no longer be valid.

Molecular degradation of rice starch during processing to flakes

Roasting of the soaked paddy (roasting-parboiling) appeared to cause an increase in the proportion of the high-molecular-weight component of starch, separated in Fraction-I, probably due to retrogradation. The solubility of starch also decreased. Flaking of roasted-parboiled paddy in the traditional edge-runner Oaker did not cause any further appreciable change in the proportion of Fraction-I and Fraction-II. Flaking in the roller-Oaker unit, on the other hand, caused a decrease in the proportion of Fraction-I, indicating molecular breakdown of starch. The total starch solubility increased marginally in edge-runner Oakes but substantially in roller-Oaker Oakes. Fractionation of starch that was soluble in hot water showed that the major amount of amylose equivalent resided in this portion as revealed by a higher proportion of Fraction-II and a high lmax of the peak of this fraction. When retrogradation was induced in the Oakes under appropriate conditions of moisture and temperature, the content of the high-molecular-weight Fraction-I of total starch increased slightly in edge-runner Oakes but markedly in roller-Oaker Oakes, indicating an aggregation or reassociation of starch molecules or its fractions.