RESEARCH ARTICLE Effect of acid treatment on the physicochemical and structural characteristics of starches from different botanical sources Heidi M. Palma-Rodriguez 1 , Edith Agama-Acevedo 1 , Guadalupe Mendez-Montealvo 1 , Rosalia A. Gonzalez-Soto 1 , E. Jaime Vernon-Carter 2 and Luis A. Bello-Pe ´ rez 1 1 Centro de Desarrollo de Productos Bio ´ticos (CEPROBI) del Instituto Polite ´cnico Nacional, Yautepec, Morelos, Me ´ xico 2 Departamento de Ingenierı ´a de Procesos e Hidra ´ulica, Universidad Auto ´noma Metropolitana-Iztapalapa, Mexico City, Me ´ xico Starch and starch derivatives (maltodextrins) are used as encapsulating materials. Starch for use as encapsulating material could be subjected to mild acid treatment. However, the granule size and organization of starch components (AM and AP) play an important role in the acid treatment. The aim of this research was to produce modified starch that might be used as encapsulate material, applying moderate acid-treatment with 3 N sulphuric acid in a ratio 1:5 w/v for 3 h at 608C, in starches from different granule size, evaluating their morpho- logical, physicochemical, and structural features. Acid treatment has an effect in the AM content and the outcome was higher in starch with larger granule size. Bimodal granule size distribution was found in acid-treated rice and maize starches. Erosion and exo-corrosion were observed in acid-treated starches with SEM. The XRD pattern did not change with the acid treatment, the native and acid-treated samples showed similar crystallinity values, except rice starch. The branching degree was higher for modified potato starch, showing higher branching points, modified starches had shorter chains with increased A-chains, and decreased B3þ chains, and the effect was higher in cereal starches; modified starches had a higher degree of retrogradation and they did not show pasting properties. The internal organization given by the granule size is an important parameter in the acid treatment of starches as it affected their physicochemical and structural features, and in the end, their functionality as encapsulate agent. Received: May 31, 2011 Revised: August 2, 2011 Accepted: August 2, 2011 Keywords: Acid treatment / Granule size / Modified starch / Morphology / Physicochemical properties / Structural characteristics 1 Introduction Starch granules show wide variation in size and shape depending on their botanical source (e.g., potato starch 40–100 mm and oval shape; maize 15–20 mm and polyg- onal shape; rice 3–5 mm and spherical shape). The morphology of starch granules is due to the AM/AP ratio as well as the organization of both molecules in concentric rings that produce the amorphous and crystalline regions. Potato [1] and maize [2] starch granules possess inhomo- geneous internal structures, as AM is concentrated in the periphery of the granules, while long chain of AP are in the hilum. Furthermore, AM content is highly dependent on the botanical source of the starch, e.g., AM from normal potato starch ranges between 20 and 31% [3, 4], from normal maize between 22 and 32% [5, 6] and from rice between 5 and 28% [7, 8]. For this reason native starches Colour online: See the article online to view Fig. 2 in colour Correspondence: Dr. Rosalia A. Gonzalez-Soto, Centro de Desarrollo de Productos Bio ´ ticos (CEPROBI) del Instituto Polite ´cnico Nacional, Yautepec, Morelos, Me ´ xico E-mail: rsoto@ipn.mx Fax: þ52 735 3941896 DOI 10.1002/star.201100081 Starch/Sta ¨ rke 2012, 64, 115–125 115 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com