Sorption isotherms and physical properties of three quinoa varieties grown at two altitudes

Abstract Quinoa seeds grown in the high Andean regions are susceptible to adulteration with seeds grown in other regions due to the increasing global demand. Therefore, characterising quinoa will help to develop a process for certifying origin. The aim was to determine the physical properties, sorption isotherms, and microstructural characteristics of three quinoa varieties grown at 2600 m and 3818 m above sea level. Samples were taken at both altitudes and their shape, size, colour, density, and adsorption isotherms were determined using the standard static gravimetric method. The results were fitted to six models and their microstructure was analysed using Scanning Electron Microscopy (SEM). The size varies from 1.30 – 1.83 mm, the density is 966 - 1097 kg/m3. The isothermal curves show a type II behaviour according to the Brunauer-Emmett-Teller classification, the water in the monolayer ranges between 0.038 and 0.047 g H2O/g d.b. The water uptake was higher in seeds grown at 2600 m above sea level than at 3818 m. The starches have spherical and oval shapes with 25 μm and 30 μm diameter, respectively. The study demonstrated the feasibility of establishing physical differentiation criteria for altitude-adapted varieties to determine storage conditions, quality control, traceability, and denomination of origin.