title: Acetylation of banana (Musa paradisiaca L.) and corn (Zea mays L.) starches using a microwave heating procedure and iodine as catalyst: II. Rheological and structural studies.
abstract: The effect of iodine concentration on the acetylation of starches with low and moderate degree of substitution (DS<0.5) and its impact on the physicochemical feature and structural features was evaluated. The acetylated starches were prepared with 0.03 mol anhydroglucose unit, 0.12 mol of anhydride acetic, and 0.6, 0.9 or 1.4 mM of molecular iodine as catalyst in a sealed Teflon vessel using microwave heating (600 W/2 min). Pasting profile and rheological properties were obtained under steady flow; dynamic oscillatory test was used. Structural features were obtained by HPSEC-RI. In acetylated starches, DS and acetyl groups increased when the iodine concentration increased, corn starch showed higher values than banana starch. The viscosity of acetylated starches decreased relative to unmodified starches while, acetylated corn starch had lower value than acetylated banana starch. In the flow curves, a non-Newtonian pattern (shear-thinning) was shown in the pastes of native and modified starches. Storage modulus (G') and loss modulus (G") showed low dependence on frequency (G'αω(0.1); G"αω(0.2)) on frequency sweep test, which is characteristic of a viscoelastic gel. Debranched native banana and corn starches presented trimodal chain-length distribution. The pattern was maintained in the acetylated starches, but with different level of short and long chains. The structural differences in native and acetylated samples explain the rheological characteristics in both starches.
authors: Centro de Desarrollo de Productos Bióticos, Instituto Politécnico Nacional, Km 6, Carr. Yautepec - Jojutla, Calle CeProBi No. 8, Col. San Isidro, Yautepec, Morelos, México C.P. 62731, Mexico.
authors: Mirna M
authors: MM
authors: Sánchez-Rivera
authors: Sirlen
authors: S
authors: Almanza-Benitez
authors: Luis A
authors: LA
authors: Bello-Perez
authors: Guadalupe
authors: G
authors: Mendez-Montealvo
authors: María C
authors: MC
authors: Núñez-Santiago
authors: Sandra L
authors: SL
authors: Rodriguez-Ambriz
authors: Felipe
authors: F
authors: Gutierrez-Meráz
mesh_terms: D000107:Acetylation; D002384:Catalysis; D006358:Hot Temperature; D007455:Iodine / Q000737:chemistry*; D008872:Microwaves; D028521:Musa / Q000737:chemistry*; D012212:Rheology; D013213:Starch / Q000737:chemistry*; D003313:Zea mays / Q000737:chemistry*
chemical_list: D013213:Starch; D007455:Iodine