Linear and non-linear viscoelastic behaviors of crosslinked tapioca starch/polysaccharide systems

Effects of polysaccharides on both the thickening performance and large deformation behavior of mixtures of various crosslinked tapioca starch and polysaccharide were investigated. It was found that the gelatinized crosslinked tapioca starch at 1-8% w/w in aqueous solutions behaved as swollen granules with the low-shear viscosity described by Krieger & Dougherty equation. To achieve thickening performance, 3.5% w/w starch was cooked with a range of 0.5% w/w polysaccharides, i.e. konjac glucomannan, guar gum, xanthan gum, and their 50:50 mixtures. It was shown that additions of polysaccharides greatly affected the rheological behavior of the suspensions, predominantly in the linear viscoelastic regime. The studied mixtures of starch and polysaccharides exhibited strong synergistic effects as evidenced from the increase in their consistency coefficients and the excess storage moduli calculated from the Palierne equation. Moreover, the mixtures containing xanthan gum showed weak-gel characteristics while the others demonstrated liquid-like behavior. In the non-linear viscoelastic analysis, arrangement of starch granules and specific interfacial interactions evidently affected the deformation behavior of the mixtures of crosslinked tapioca starch and polysaccharide. The mixture of konjac glucomannan and xanthan also largely improved stress susceptibility of the suspension and gave the unique shear stiffening under large amplitude oscillatory shear experiment.     

Effects of cross-linked tapioca starches on batter viscosity and oil absorption in deep-fried breaded chicken strips

In this study, the effectiveness and feasibility of using various degrees of cross-linked tapioca starches in batter and breading formulations to reduce oil absorptions in deep fried chickens were investigated. Shear flow behaviour, water retention capacity (WRC), pick-up as well as cooked yield of the prepared batters were also examined. Flow curves showed that all studied batters were pseudoplastic, i.e. having shear thinning characteristics. In addition, it was found that the substitution of 20% (w/w) cross-linked starches for wheat flour in the batter formulation significantly reduced the consistency index and WRC of the batters. However, batter pick-up and cooked yield values were insignificantly affected. Oil uptake of fried chicken crusts was determined using differential scanning calorimetry due to its specific advantages over the conventional solvent extraction method. In comparison to the control (wheat) formulation, crusts of fried chicken samples obtained from the formulations containing 20% (w/w) cross-linked starch showed significantly lower oil content by at least 17% relative oil reduction. The highest relative oil reduction was found in the batter containing the highly cross-linked tapioca starch. Furthermore, an increase in water content in the batter formulations resulted in a reduction in the batter pick-up, cooked yield and oil absorption. The degree of cross-linking which in turn resulted in the limited starch granule disintegration is the predominant factor in the reduction of oil content for deep-fried battered food.