Effect of Microwave Radiation on the Physicochemical Properties of Normal Maize, Waxy Maize and Amylomaize V Starches

Abstract

Normal maize, waxy maize and amylomaize V starches were treated at a moisture content of 30% by microwave radiation. The results showed that the surface was porous and a cavity could be clearly observed at the center of the three starches. Microwave treatment increased the X‐ray intensities of the major d‐spacings of all starches and changed the X‐ray pattern of amylomaize V from B to A+B. The swelling power (amylomaize V < normal maize < waxy maize) and solubility (amylomaize V < normal maize < waxy maize), syneresis (waxy maize > normal maize > amylomaize V) and the enthalpy of gelatinization (amylomaize V (B‐type)> normal maize waxy maize (A‐type)) decreased on this treatment. Microwave treatment increased the gelatinization transition temperatures (amylomaize V > waxy maize > normal maize) and the gelatinization temperature range (amylomaize V > normal maize ¡Ö waxy maize) of all starches. A rise in pasting temperature and a drop in viscosity of the three starches were observed after microwave irradiation. The viscosity patterns of waxy and normal starches remained unchanged, while that of amylomaize V starches changed from C to D on microwave treatment. The data showed that rearrangements restricted to sections of the starch molecules resulted in the formation of new crystallites of different stabilities and led to a more ordered crystalline array.

Functional Properties of Some Non-Conventional Treated Starches

“…Microwave treatment on starch were carried out especially on samples with high water content, over 20%, and less on samples with low (1 -5%) or limited (7 -15%) moisture content. The results showed that microwaves may determine the rearrangement of intermolecular structure indicating that the starch granule structure is disintegrated and, consequently, they lead to slight reduction of the water absorption ability, of solubility and swelling power as well as changes of the gelatinization temperature, syneresis or paste viscosity (Lewandowicz et al, 1997;Lewandowicz et al, 2000;Gonzalez & Perez, 2002;Gonzalez Parada & Perez Sira, 2003;Szepes et al, 2005;Luo et al, 2006;Lares & Perez, 2006) strongly correlated with experimental treatment parameters. Starch exposed to electrical discharges (plasma) may suffer either crosslinking phenomenon (Zou et al, 2004 or depolymerization to dextrins with different molecular weights (Lii et al, 2002a;Lii et al, 2002b) …”

Effect of extrusion treatment on the thermal stability and structure of corn starch with different emulsifiers

“…A total weight of 3.0 mg of starch samples (db) and distilled water (1 : 2, w/w) added with a microsyringe to corn starch in pre-weighed aluminium sample pans. The pan was hermetically sealed and allowed to equilibrate for 12 h before analysis (Luo et al 2006;Klein et al 2013). The time was enough for the hydration of corn starch examples.…”

“…Extrusion weakened the crystalline structure within starch particles and the double helix unwinding after extrusion processing . Emulsifier combined the unwinding of the double helix formed a different type of amylose emulsifier complexes and then reaggregation occurred, which caused a different rise in gelatinisation temperature (Bhatnagar & Hanna 1994;Luo et al 2006;. The increased gelatinisation temperature was attributed to structural changes within the starch particles, which involved amylose-amylose and amylase-lipid interactions (Da Rosa Zavareze & Dias 2011).…”

“…The lower gelatinisation enthalpy showed that the internal crystalline and amorphous regions of starch were destroyed and some portion of the internal double helical structure disappeared (Hu et al 2014). Luo et al (2006) showed that ΔH values of gelatinisation primarily reflect the loss of the ordered double helices. Hence, the starch extrudate particles would be more mobile and more prone to disruption than native corn starch.…”

Sago Palm

“…This can be observed in the loss of birefringent properties and in the swelling of the starch granules. Luo et al (2006) conducted a study to investigate changes in crystallinity, swelling power and solubility, gelatinization parameters, retrogradation characteristics, and pasting properties of corn starches at 30% moisture after being subjected to microwave heating at 1 W/g microwave energy for 20 min. Microwave heating could convert starch directly to glucose in a relatively short time.…”