Comparison of different pretreatments on drying characteristics, physical properties, nutritional compounds and antioxidant activity of heat pump‐dried longan pulp

Abstract

SummaryDrying pretreatments are usually considered as effective way to improve the quality of dried fruit products. The results of this research showed that the blanching (BL), ultrasonic (US) and freeze–thaw (FT) pretreatments could significantly shorten the drying time, and improve the rehydration capacity of the dried longan pulp. Compared with the control group (CK, without pretreatment), more irregular inner micropores were formed in the dried longan pulp treated with BL, US and FT. Besides, the brightness and yellowness of dried longan pulp with pretreatments were higher than those of the CK. The higher retention rates of total phenolic content (292.54 mg/100 g d.b.) and ascorbic acid (2.38 mg g−1 d.b.) were observed in the dried longan pulp treated with BL. Meanwhile, a higher chlorogenic acid content was found in the samples treated with FT (3.68 mg/100 g d.b.) and radio frequency (RF) (3.10 mg/100 g d.b.). Furthermore, the highest retention of a total free amino acid (1843.13 mg/100 g d.b) was exhibited by RF‐treated longan pulp. This work guides how pretreatments are applied prior to longan pulp drying.