Manisha Guha

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.

Effect of processing methods on the nutraceutical and antioxidant properties of little millet (Panicum sumatrense) extracts.

The effect of germination, steaming and roasting on the nutraceutical and antioxidant properties of little millet (Panicum sumatrense) was investigated. The nutraceutical properties were determined by evaluating the total phenolic, flavonoid and tannin contents while the antioxidant properties were studied by the DPPH free radical scavenging activity and the iron reducing power assay. The results showed that the total phenolic, flavonoid and tannin contents of processed little millet increased by 21.2, 25.5 and 18.9mg/100g, respectively, compared to native sample. The DPPH radical scavenging activity and the iron reducing power of roasted millet extract were the highest compared to the other processed millet. Fractionation of phenolic extracts by HPLC showed that the analytes were derivatives of benzoic acid (gallic acid, proto-catechuic acid and vanillic acid), aromatic carboxylic acid (gentisic acid) and cinnamic acid (syringic acid and ferulic acid). The results indicate that processing has significant effects on the nutraceutical and antioxidant properties of little millet phenolic extracts.

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.

MOLECULAR DEGRADATION OF STARCH DURING EXTRUSION COOKING OF RICE

ABSTRACT Effect of barrel temperature (80°–100°C) and amylose content (28.6 gkg−1, 22.3 gkg−1 and 5.0 gkg−1) of rice upon extrusion cooking on macromolecular profile of starch was studied by gel permeation chromatography (GPC) of the rice flour on Sepharose CL-2B. Starch in all rice samples was separated into two main fractions, viz. Fraction-I, a high molecular weight, was excluded by gel, amylopectin, and Fraction-II, a low molecular weight, that entered the gel, amylose. Extrusion cooking of rice led to the degradation of high molecular weight fraction of the starch, the extent of degradation increasing with increasing severity of extrusion conditions. The absorption maxima (λ max) of iodine complex of the fraction-I showed an increase after extrusion cooking and this increase was more in the non-waxy variety of rice than in waxy.

Optimization of infrared heating conditions of sorghum flour using central composite design

Storage stability parameters like free fatty acid (FFA) content and lipase activity were evaluated for infrared heated sorghum flour. Infrared heating conditions (temperature and duration) were optimized using a central composite design. Processing at a temperature of 120°C for 8.5 min was optimum to provide the lowest FFA content (0.03%), lipase activity (15 µeq·mg/h), and peak viscosity (318 BU). Correlation coefficient values (R2) for responses of FFA content (96.24%), lipase activity (97.74%), and peak viscosity (90.87%), derived using experimental data, indicated that the model was a good fit. Infrared heating at 120°C for 8.5 min can be useful for development of shelf stable sorghum flour.