Abstract
The freezable (FW) and unfreezable water (UFW) contents of wheat and potato starches and their physically modified forms [pregelatinized (PGS) and retrograded (RS)] were analyzed by Differential Scanning Calorimetry (DSC) at various hydration levels (25, 35, 45, 55, 65, 75 and 85%). In all the starch samples, the UFW content increased with increasing hydration level. Potato starch samples (native, pregelatinized and retrograded) had higher UFW contents than wheat starch samples at all hydration levels. Similarly, with the increase of hydration level in all starch samples, onset (To), peak (Tp) and endset (Te) temperatures of the peaks also increased. It was obtained that physical modifications in starches had significant effects (P<0.05) on water absorption index (WAI) and water solubility index (WSI) of starch samples. The highest WAI (10.51) and WSI (2.31) values were determined in pregelatinized potato starches. Rapid Visco Analyzer (RVA) profiles revealed that physically modified starches had higher viscosity values than native starches. The results clearly showed that pregelatinization and retrogradation had positive effects on the physicochemical properties studied.
Highlights
Starch affects texture, viscosity, gel structure, gel formation, adhesion, binding, water holding capacity, film formation and product homogeneity (Kaur et al 2012; Fu et al 2014)
The 8% suspensions (w/w) of wheat and potato starch samples were prepared in Rapid Visco Analyzer (RVA) tubes with distilled water and the samples were loaded into the RVA (RVA 4500, Perten, Sweden)
PGS samples were obtained at viscosity peak from the RVA profile, while RS samples were obtained after being stored for 120 h at 4 °C of the completed RVA samples (Yglesias & Jackson 2005)
Summary
Viscosity, gel structure, gel formation, adhesion, binding, water holding capacity, film formation and product homogeneity (Kaur et al 2012; Fu et al 2014). Because of low shear resistance, thermal resistances, thermal decompositions and high retrogradation tendency, the use of native starches is limited in some industrial food applications. There is a need to make some modifications to enhance the functional properties of starch (Gryszkin et al 2016). The modifications in starches can be carried out in three different ways: chemical (derivatization, acid thinning/hydrolytic depolymerization, dextrinization, oxidation, hydrolysis), physical (pregelatinized and granular cold-water-swelling starches) and genetic (waxy starches, high-amylose starches) (Ashogbon & Akintayo 2014; Kaur & Singh 2015). Physical modifications of the native starch granules involve different temperature/moisture Since starches are not treated with any chemicals in physical modification, these starches are safe for human consumption and, more preferred (Kaur et al 2012; Huang et al 2016).
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