Successive Reduction Dry Milling of Normal and Waxy Corn: Grain, Grit, and Flour Properties

Abstract

Dry milling of different corn types resulted in varied proportions of germ, pericarp, grit and flour. Grit and flour produced during different reduction stages varied in particle size and chemical constituents, hence applications in food industry. In this study, recovery of different fractions and variation in physicochemical and pasting properties of grit and flour fractions obtained during 3 successive reduction dry millings of 2 normal (African tall, HQPM1) and 1 waxy corn (IC 550353) were evaluated. Waxy corn grains had the highest L*, a*, b*, ash, fat, and protein content and the lowest weight. Waxy and African tall gave the highest recovery of germ and pericarp, respectively. Waxy corn showed lower grit and flour recovery as compared to normal corn. Flour fractions showed higher L* and lower a* and b* values than grit fractions. Particle size of grit and flour fractions ranged from 840 to 982 μm and 330 to 409 μm, respectively. Fractions with larger particle size showed lower L* value. The b* value showed positive correlation with yellow pigment content. Grit and flour from the 1st reduction stage showed higher ash and fat content. Protein content was correlated positively with ash content and negatively with L* value. Grit and flour fractions with higher protein content had lower pasting viscosities. Pasting viscosities were higher for flours than their corresponding grits. Protein profiling of grit and flour fractions from different stages showed quantitative and qualitative differences in medium (22, 28, and 35 kDa) and low molecular weight (16, 17, and 19 kDa) polypeptides and were related to grit and flour yield.

Effect of Extrusion on Physicochemical Properties, Digestibility, and Phenolic Profiles of Grit Fractions Obtained from Dry Milling of Normal and Waxy Corn

“…The grit obtained from 3 successive reduction dry milling stages of 2 normal corn types and 1 waxy corn were used to evaluate their extrusion behavior and product characteristics. The physical (particle size, L * , a * , and b * ), chemical (ash, fat, protein, and yellow pigment contents), pasting properties, and protein profile of grit have been reported in previous research paper (Thakur and others ).…”

“…Francois and Milford () reported that the starches with higher amylose content required higher SME for extrusion. Thakur and others () calculated the blue value of grits, reflecting amylose content, which showed a significantly positive correlation with SME at different extrusion temperatures ( r = 0.831, P ≤ 0.005 at 125 °C, r = 0.770, P ≤ 0.05 at 150 and r = 0.910, P ≤ 0.005 at 175 °C) indicating that the grits with higher blue value had higher viscosity in extruder barrel and hence extruder required more SME consumption. Peak viscosity of grits calculated earlier (Thakur and others ) had a highly significant correlation with SME ( r = 0.827, 0.887, and 0.885, P ≤ 0.005, respectively at 125, 150 and 175 °C) consistent with the results reported earlier (Carvalho and others ).…”

“…Grit fractions from 3 RSs were collected during successive reduction dry milling of African tall, HQPM1 and waxy corn types at Kulwant Nutritions, Batala. The details of the dry milling process have been reported earlier (Thakur and others ). Briefly, cleaned grains of each corn type were passed through the 1st pair of break rolls with 3 mm gap and the material recovered was passed through 14‐mesh sieve and designated as 1st RS grit.…”

“…In a previous study (Thakur and others ), the successive reduction dry milling of corn types gave varied amounts of grit and flour fractions with different characteristics. This study was done as a continuation of previous work to evaluate the (1) physicochemical and phenolic profiling differences among normal and waxy corn extrudates and (2) variation in fried extrudate characteristics as a function of RS, extrusion temperature (ET), and corn type.…”

“…Corn grit is a major constituent of commercial extruded products and is produced by successive reduction stages (RSs) of dry milling. The grit obtained from different corn types varies in composition, particle size, physicochemical characteristics, and end‐use suitability (Singh and others ; Thakur and others ). Robutti and others () observed that the corn grits with hard endosperm gave better expansion and lesser energy consumption than the grits with soft endosperm during extrusion.…”