Annealing of wheat starch
1998
Tester, R.F. | Debon, S.J.J. | Karkalas, J.
The moisture, time and temperature dependence of annealing for one commercial and 10 laboratory extracted starches (from five soft and five hard wheats grown in various places in England in 1994) were investigated. Annealing was found to occur at least 15 degrees C below the onset gelatinisation temperature (To), the extent of which was time dependent, but was much more evident (as indicated by the relative increase in gelatinisation temperatures) the closer to To the annealing temperature was set. Annealing could be initiated when the starch contained 20% by weight moisture, but the process was restricted unless the moisture content exceeded 60%. 13C-CP/MAS-NMR indicated that the number of double helices remained constant post-annealing and it is proposed that annealing improves the crystalline register of double helices, thereby 'perfecting' starch crystallites rather than promoting the formation of additional double helices. This perfection of crystallites is possibly initiated by incipient swelling and the resulting mobility of amorphous alpha-glucans which facilitates ordering of double helices and, probably, greater ordering of the amorphous regions themselves.
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