MODELING USING A NEW THIN‐LAYER DRYING MODEL AND DRYING CHARACTERISTICS OF SWEET BASIL (OCIMUM BASLICUM LINN.) USING TRAY AND HEAT PUMP‐ASSISTED DEHUMIDIFIED DRYING

Abstract

ABSTRACTThe maturity of Thai sweet basil was based on leaf area, % inhibition and total phenolics. Desorption isotherms for sweet basil leaves were performed. It was found that the modified Henderson model showed the best fit to both fresh and blanched sweet basil leaves for Xe = f(Xe,T). Sweet basil leaves were pretreated by blanching prior to drying under three temperatures of 40, 50 and 60C in tray and heat pump‐dehumidified (HPD) dryers. The three‐parameter model was the most effective model in describing sweet basil leaf drying. The drying constant was related to air temperature using the Arrhenius model. Effective moisture diffusivities increased with increasing temperature and blanching treatment, as well as the HPD dryer. Quality evaluation by % inhibition, total phenolics, rehydration ratio and ΔE* showed that the best quality resulted from sweet basil leaves pretreated by blanching and dried at 40C in HPD dryer.PRACTICAL APPLICATIONSTray drying of sweet basil leaves is commonly performed in many industries. Up to now, the exporters have faced the problem of low total phenolics and antioxidant activity in dried sweet basil leaves. The new methods proposed in this study are blanching and heat pump‐dehumidified (HPD) drying. The results revealed that blanching incorporated with HPD drying could reduce drying time and increase total phenolics, antioxidant activity and color values compared with the conventional tray drying.The three‐parameter model proposed in this work was the most effective model to describe the mass transport behavior of dried sweet basil leaves.