ANNEALING OF WHEAT-STARCH

The moisture, time and temperature dependence of annealing for one com mercial and 10 laboratory extracted starches (from five soft and five hard wheats grown in various places in England in 1994) were investiga ted. Annealing was found to occur at least 15 degrees C below the onse t gelatinisation temperature (T-o), the extent of which was time depen dent, but was much more evident (as indicated by the relative increase in gelatinisation temperatures) the closer to T-o the annealing tempe rature was set. Annealing could be initiated when the starch contained 20% by weight moisture, but the process was restricted unless the moi sture content exceeded 60%. C-13-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, th ereby 'perfecting' starch crystallites rather than promoting the forma tion of additional double helices. This perfection of crystallites is possibly initiated by incipient swelling and the resulting mobility of amorphous cl-glucans which facilitates ordering of double helices and , probably, greater ordering of the amorphous regions themselves. (C) 1998 Academic Press.