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 gelling agent (TGA) in sweetened fruit preparations (SFP) are difficult because of the low levels of concentration and the heterogeneous, gelified, and highly sweetened nature of the medium. A method is proposed that overcomes those difficulties. In a first step, starches are identified 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 step are optimized. A previous gelatinization treatment, the conditions of which are studied here, improves significantly the enzymatic hydrolysis of starch and the quantification of the released glucose. The method proposed, applied to 15 different SFP, allows an accurate and repeatable determination of distarch phosphate, acetylated distarch phosphate, and acetylated distarch adipate. It provides, furthermore, an appropriate tool for the special case of a hydroxypropylated distarch phosphate.