A compositional study on two current types of salep in Iran and their rheological properties as a function of concentration and temperature

Major compositional components and rheological behavior as a function of concentration and temperature for two current types of salep (palmate- and rounded-tuber) in Iran were investigated. Palmate-tuber salep (PTS) was richer in glucomannan content (58.22% versus 22.13% w/w) but lower in starch content (1.67% versus 6.15% w/w) than the rounded-tuber salep (RTS). A clearly pseudoplastic behavior was observed at all concentrations (2%, 3%, 4%, 5% for PTS, and 4%, 5%, 6%, 7% for RTS) and temperatures (5, 25, 45 and 65 °C) for each two salep types. The power law model well described the rheological behavior of the salep solutions with high determination coefficients, r2. An increase in concentration was accompanied with an increase in pseudoplasticity, n, and consistency index, k. As temperature increased, the salep solutions showed a lower consistency and were tending to be closer to Newtonian flow (the n-values nearer to 1). At similar concentrations and temperatures, the PTSs created solutions with more pseudoplasticity and consistency than the RTSs. This was attributed to their different chemical composition, mainly glucomannan and starch contents. Temperature dependency of the consistency index for the salep solutions was successfully described by the Arrhenius model with high r2 values. The activation energy, Ea, for the PTS decreased from 36.356 kJ/mole at 2% concentration to 22.746 kJ/mole at 5% concentration. For the RTS, the activation energy decreased from 29.628 kJ/mole at 4% concentration to 25.430 kJ/mole at 7% concentration. In contrast, the frequency factors, A, increased as the concentration increased.