Abstract

GLORIO PAULET, Patricia; BELLO-PEREZ, Luis Arturo; SALAS, Francisco  and  BULEJE, Evelyn. Viscoelastic behavior and molar mass estimations of oca (Oxalis tuberosum) starch. Rev. Soc. Quím. Perú [online]. 2009, vol.75, n.2, pp.266-276. ISSN 1810-634X.

Oxalis tuberosum starch was obtained by water extraction and sedimentation. Part of the starch was treated with 95% dimethyl sulphoxide for being used in the study of macromolecular features by multi-angle laser light scattering techniques. The apparent weight - average molar mass (Mw) and weight-average root-mean square radius of gyration (Rg) were estimated as follows for peruvian oca starches: from Ancash Collecting Number AMM5144 = 7,17 x 10⁶g/mol and 114,2 nm respectively; yellow oca mawuay from Cajamarca, Chota: Collecting Number AGM 5093 = 9,35 x 10⁶ g/mol, 123,2 nm; and reddish oca from Junin: Collecting Number AVM5543= 8,38 x 10⁶ g/mol, 108,3 nm. Viscoelastic properties of oca native starches (10% solids) were studied using an AR 2000 Rheometer (cone and plate geometry). It was observed after 150 seconds during the heating period and for all oca collection numbers starches studied, that storage G' and loss moduli G" adopted a linear behavior of small slope, being G' (modulus of elasticity) > G" (modulus of viscosity). When temperature was kept constant at 95°C, G' and G" showed a linear increase and for G" the slope was higher. As time passed by during cooling up to 25°C, G' > G" showing a parallel increase in their value which turned mostly stable after 300 seconds. Following a period of aging of 12 minutes at 25°C it was observed that G' increases slowly meanwhile G" showed a steeper slope increase. All the results suggest that oca starch gels are soft enough for important gastronomic applications.

Keywords : oca; starch; MALLS; G', G".

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