30D-21 |
Water mobility and textural properties of native and hydroxypropylated wheat starch gels |
S. G. CHOI, Food Science and Technology, University of Georgia, Athens, GA 30602-7610 and W. L. Kerr. Starch is a major food biopolymer used for gelling and viscosity enhancement and as a molding agent. Knowledge about textural properties of starch gels is indispensable for quality control and the development of starchy food. Hydroxypropylation has been used to control the gelling properties by decreasing gelatinization temperature and stabilizing gels. Water is thought to play an important role in controlling the textural properties of gels. Our objective was to investigate the effects of starch concentration and hydroxypropylation on water mobility and textural attributes of wheat starch gels. Wheat starch was hydroxypropylated with propylene oxide (molar substitution (MS) of 0.05, 0.12, and 0.18). Gels were prepared at concentrations between 25 and 40%. Pulsed 1H NMR was used to identify and quantify the molecular motion of water. Transverse proton relaxation (T2) of the systems were analyzed using distributed exponential routine from Carr-Purcel-Meiboom-Gill pulse experiments. Texture profile analysis was done using Instron. All starch gels had two distinct water fractions having different mobility. For the less mobile fraction, T2a ranged from 2~6ms while for the more mobile state, T2b ranged from 20~200ms. Values of both T2a and of T2b increased with increasing moisture content and MS. Control experiments with isolated amylose and granule rich remnant gels indicated that water in the less mobile state was associated with granule remnants. Gel hardness decreased with increasing moisture content, and with increasing MS. Cohesiveness increased with degree of hydroxypropylation. Multi-regression analysis showed that the mobility and amount of water in the less mobile state is a dominant factor for gel hardness. These results suggest that an increase in water content and degree of hydroxypropylation may cause more deformation of swollen granules and prevent aggregation of leached amylose. In addition, the molecular dynamics of water is highly related to textural and structural properties of starch gels.
Session 30D, Food Engineering: Physical and chemical properties
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