STARCH IDENTIFICATION AND DETERMINATION IN SWEETENED FRUIT PREPARATIONS .2. OPTIMIZATION OF DIALYSIS AND GELATINIZATION STEPS, INFRARED IDENTIFICATION OF STARCH CHEMICAL MODIFICATIONS

Identification and quantification of starch used as thickening and gel ling agent (TGA) in sweetened fruit preparations (SFP) are difficult b ecause of the low levels of concentration and the heterogeneous, gelif ied, and highly sweetened nature of the medium. A method is proposed t hat overcomes those difficulties. In a first step, starches are identi fied by optical microscopy and acetyl and hydroxypropyl modifications are characterized by Fourier transform infrared spectroscopy (FT-IR). Starch quantification requires high purification, achieved by dialysis to remove most of the sucrose. The experimental conditions of this st ep are optimized. A previous gelatinization treatment, the conditions of which are studied here, improves significantly the enzymatic hydrol ysis of starch and the quantification of the released glucose. The met hod proposed, applied to 15 different SFP, allows an accurate and repe atable determination of distarch phosphate, acetylated distarch phosph ate, and acetylated distarch adipate. It provides, furthermore, an app ropriate tool for the special case of a hydroxypropylated distarch pho sphate.