Moisture Sorption Isotherm and Isosteric Heat of Butterfly-pea Flowers (Clitoria ternatea)

Abstract Butterfly-pea (Clitoria ternatea) flowers are containing various active compounds such as flavonoids, myricetin, quercetin, flavonols, and anthocyanins which have potential as antioxidants. Dried butterfly-pea flower is often used as an ingredient of herbal tea drinks. The drying procedure for the butterfly-pea flower is important to maintain the shelf-life. However, during the drying process, anthocyanins are easily be degraded before reaching the balance of water content. Therefore, a study focus on moisture sorption isotherm of fresh butterfly-pea flowers is needed. This present study aims to determine the balance of water content and isosteric heat of butterfly-pea flowers using a static gravimetric method. Water activities were conditioned using chemical solutions of KOH, MgCl2, K2CO3, NaCl, KCl, and BaCl2 with a water activity range of 0.06-0.90. The hysteresis curve was determined using desorption and adsorption samples with various temperature variations of 30, 40, and 50°C. The isothermal behavior of butterfly-pea flowers was determined based on GAB, BET, Halsey, Oswin, and Peleg models. As a result, the Peleg model was found to be the most suitable model to represent the moisture sorption isotherm of butterfly-pea flowers and based on Brunauer classification including the Type II-sigmoid curve in which has been statistically analyzed using determination coefficient (R 2), mean relative modulus (P), and root mean square error (RMSE). The hysteresis curve indicated that the balance of water content of the desorption sample is higher than the adsorption sample on the same water activity level. The net isosteric heat in the desorption and adsorption samples were 48.529 exp (−xe/0.0734) and 53.591 exp (−xe/−0 0797), respectively.