Carbohydrate Polymers 111 (2014) 592–597 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me pa g e: www.elsevier.com/locate/carbpol Structural and physicochemical characteristics of starch from sugar cane and sweet sorghum stalks Fernanda Viginotti Alves a , Luís Fernando Polesi b , Cláudio Lima Aguiar a , Silene Bruder Silveira Sarmento a,∗ a Departamento de Agroindústria, Alimentos e Nutric ¸ ão, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Av. Pádua Dias 11, CP 9, 13418-900 Piracicaba, SP, Brazil b Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Av. Centenário, 303, 13416-903 Piracicaba, SP, Brazil a r t i c l e i n f o Article history: Received 25 June 2013 Received in revised form 25 April 2014 Accepted 16 May 2014 Available online 26 May 2014 Keywords: Starch Saccharum officinarum L. Sorghum bicolor (L.) Moench a b s t r a c t The starch present in sugar cane and sorghum juice has been considered a problem to the sugar industry. The objective of this work was to study the structural and physicochemical characteristics of the starch present in sugar cane and sweet sorghum. Sugar cane and sweet sorghum starches presented small granules (maximum 5.9 and 7.9 m), A-type diffraction pattern, high degree of relative crystallinity (44.4 and 42.0%), and low amylose content (17.5 and 16.4%), respectively. Sugar cane starch presented more uniformity in granule shape and size, more homogeneity in amylose chain length, higher number of long lateral chains of amylopectin, and higher susceptibility to enzymatic digestion. Besides being in higher amount in the juice, sweet sorghum starch presented lower values for thermal properties of gelatinization, as well as higher swelling factor, which can cause more problems during processing. Additional studies are needed to evaluate the variety and maturity influence on these properties. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The sugar (sucrose) and alcohol (ethanol) industry has become an important part of the agro-industrial sector in certain parts of the world. Although sugar cane is widely utilized as raw material for sugar and alcohol production, the use of alternative feedstocks has been tried experimentally. Sweet sorghum can be employed as a complementary option during sugar cane off-season. Starch is one of the main products of photosynthesis in supe- rior plants, stored in chloroplasts, in the form of granules, as energy storage reserves when photosynthesis is not occurring (Bello-Pérez, Montealvo, & Acevedo, 2006). Starch content in sugar cane juice stalk ranges from 1.6 to 2.6 g/kg (Figueira, Car- valho, & Sato, 2011), depending on season of the year, plant variety, diseases, maturity, processing, method of analysis (Imrie & Tilbury, 1972), climatic conditions, stress, and type of soil (Eggleston, Montes, Monge, & Guidry, 2007b). In recent years higher concentra- tions of starch in sugar cane have been delivered to factories, mainly because of the processing of unburned sugar cane, environmental conditions, and the use of new varieties with higher amounts of this polymer (Eggleston et al., 2013; Zhou et al., 2008). ∗ Corresponding author. Tel.: +55 19 3429 4150; fax: +55 19 3429 4288. E-mail address: sbssarme@usp.br (S.B.S. Sarmento). The presence of starch in sugar cane poses a great problem, since it affects negatively the quantity and quality of sugar pro- cesses and products (Zhou et al., 2008). The increased use of sweet sorghum in agro-industries may aggravate these problems, because this plant species has even higher starch content than sugar cane. In sweet sorghum juice starch content ranges from 76 to 154 g/kg, depending on plant variety, harvest period, and maturity (Zhao, Steinberger, Shi, Han, & Xie, 2012). Starch is a polysaccharide composed of two macromolecules: amylose, which has a linear chain structure made up of glucose units linked through -1,4 bonds, and amylopectin, which has a branched chain structure made up of glucose units linked through (1–4) and (1–6) bonds. The morphology, chemical composition, and molecular structure of starches are unique for each particular plant species (Bello-Pérez et al., 2006). The adverse effects of starch in sugar cane and sweet sorghum processing are mainly related to the behavior of starch granules during their hydration and heating (Zhou et al., 2008). Even in small amounts in the juice, the presence of starch can cause problems due to viscosity increase in sugar cane and sorghum mills and refineries. The starch in juice is not soluble, but with the heat applied during clarification and evaporation, starch granules progressively swell, and rupture releasing amylose and amylopectin, which results in an amorphous viscous solution. On cooling, the amylose chains association, a phenomenon known as http://dx.doi.org/10.1016/j.carbpol.2014.05.034 0144-8617/© 2014 Elsevier Ltd. All rights reserved.