Abstract
With attractive flower colours ranging from dark green to purple, Butterfly pea (Clitoria ternatea L.) is grown year-round in Vietnam. The purpose of this study is to determine the effect of air temperature on drying time and antioxidant compounds of Butterfly pea flowers, fitting the drying curves and testing the goodness of fit. In this study, air drying characteristics of the Butterfly pea flowers were determined using drying air temperature from 55oC to 70oC at a constant air velocity of 1 m/s. The data of experimental moisture loss were fitted to selected seven thin-layer drying models. The effect of drying conditions on the anthocyanin and total phenolic compound changes of Butterfly pea flower were compared. The effect of temperature on the diffusivity was described using the Arrhenius equation with an activation energy of 71.63 kJ.mol- ¹. At increasing temperature, the effective moisture diffusivity values ranged from 2.39×10-12 and 7.76×10-12 m²s - ¹. The mathematical models were compared according to the three statistical parameters such as the coefficient of determination (R2 ), reduced chi-square (χ 2 ) and root mean square error (RMSE) between the observed and predicted moisture ratios. The highest value of R2 (99.8%) and the lowest values of χ 2 (0.0004) and RMSE (0.0178) were observed for drying air temperature of 70oC. Among the seven mathematical models tested with experimental data, the Page model could sufficiently be described the drying characteristics of the Butterfly pea flower.
Highlights
The total phenolic compound (TPC) was determined based on the method by Wong et al (2006) with total content was quantified using the standard curve of gallic acid as a standard phenolic compound (0.2 to 1 mg/mL), which was dissolved in deionised water and expressed as mg gallic acid equivalent (GAE) per gram plant material
The effect of temperature used for the thin layer drying process of butterfly pea flower was remarkable with moisture ratios that have decreased continuously in increasing temperature and time (Figure 1)
Thin layer drying characteristics of butterfly pea flowers were investigated at four drying temperatures
Summary
Natural colourings are extracted from vegetables, fruits, and tubers, which are available in nature. They do offer attractive appearances, but they have been recognized to increase the nutritional value of the foods. Butterfly pea species (Clitoria ternatea L.) possesses beautiful flowers with dark blue to purple petals that can bloom almost year-round in Vietnam. Recent concerns about the use of synthetic food colours and their effects on human health have increased, natural colourants such as butterfly pea flowers extract have become alternatives commonly in food processing. The butterfly pea flowers mostly contain alkaloids, flavonoids, taraxerols, taraxerones, triterpenoids and anthocyanins as active chemicals that bring about its biological effects (Kosai et al, 2015). Its extracts possess a wide range of pharmacological activities including antibacterial, antidiabetic, antidiarrheal, antifungal, anthelmintic, antiinflammatory, antimicrobial, antioxidant, antidepressant, and antipyretic activities, hypolipidemia, immunomodulatory, and wound healing (Kosai et al, 2015)
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