Ana Niurka Hernández- Lauzardo Guadalupe Méndez-Montealvo Miguel Gerardo Velázquez del Valle Javier Solorza-Feria Luis Arturo Bello-Pérez Centro de Desarrollo de Productos Bióticos del IPN, Yautepec, Morelos, México Isolation and Partial Characterization of Mexican Oxalis tuberosa Starch The chemical, physicochemical and rheological characteristics of Oxalis tuberosa starch were investigated. Oxalis starch presented an apparent amylose content of 33%, similar to maize starch used as control, with a granule size between 25–50 mm with oval and elliptical shapes and A-type X-ray diffraction pattern. The gelatinization temperature of oxalis starch was 64.07C, that was lower than the one determined in maize starch (73.07C), with an enthalpy value of 12.2 J/g, which was similar to that of maize starch. Both oxalis and maize starch pastes behaved as weak viscoelastic systems with the elastic character (G 0 ) predominating over the viscous character (G 00 ). An increase in the level of solids in the pastes increased the values of the moduli. The results suggest that heating the systems (gelatinization), causes a more pronounced enhancement in the structure of the maize starch pastes than in that of oxalis starch pastes. Overall, it was concluded that due to its physicochemical, functional and rheological properties, Oxalis starch could be suitable for testing its use in the cosmetic and in the food industry. Keywords: Oxalis tuberosa starch; Microscopy; X-ray diffraction; Rheology 1 Introduction Starch is the major dietary component in all human popu- lations. It is a reserve polysaccharide present in the endo- sperm of the grain of maize (Zea mays L.), banana pulp (Musa paradisiaca) and yuca (Manihot esculenta), to name only a few [1]. Starch is extracted and used in the food industry to impart functional properties, modify food texture and consistency and so on. Not only is the amount of starch important for the texture of a given product, but also the starch type is critical [2]. Starch owes much of its functionality to its main components amylose and amylo- pectin and the physical organization of these macromole- cules in the granular structure [3]. Native starches have been used since ancient times as a raw material to prepare different products. They are employed in foodstuffs because of their good thickening and gelling properties. Starches are also good texture stabilizers and regulators in food systems [4]. In recent years, substantial progress has been made in obtaining starches from non-conventional sources and studying their functional, rheological and physicochemical proper- ties [5]. In the Andean region diverse tubers and roots exist, that can be used as starch sources. Some studies report size and form of the granules, starch gelatiniza- tion, chain length distribution of amylopectin [6–9] and recently, physicochemical and rheological characteriza- tion [10, 11]. The rheological properties of starches are important from a number of standpoints; rheological stud- ies may help in the understanding of the microstructure of starch and may be particularly helpful in following the changes which occur during gelatinization [11]. Oca (Oxalis tuberosa) is an endemic crop of the Andes. It seems to have been domesticated in Central Peru and Northern Bolivia, where the major diversity of wild and cultivated forms are found. About two hundred years ago, culture of oca was introduced in Mexico [6], but with no reports so far dealing with its starch isolation and characterization. The aim of this work was to isolate the starch from Oxalis tuberosa and to evaluate its chemical composition, along with some morphology, physicochemical and rheological characteristics. 2 Materials and Methods 2.1 Starch isolation The tubers of Oxalis tuberosa were purchased in the local market in Yautepec, Morelos, Mexico. Starch was isolated using a modification of the procedure of Adkins Correspondence: Luis Arturo Bello-Pérez, Centro de Desarrollo de Productos Bióticos del IPN, Apartado postal 24 C.P., 62731, Yautepec, Morelos, México. E-mail: labellop@ipn.mx. Starch/Stärke 56 (2004) 357–363 357  2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.de Research Paper DOI 10.1002/star.200300235