Abstract:

The aim of this study is to investigate the effects of drying methods and parameters on bioactive compounds and
antioxidant capacity of guava. Different drying methods, including hot air drying (HAD), hot air combined with infrared
radiation drying (HA-IRD), vacuum drying (VD) and vacuum freeze drying (FD), were compared in terms of bioactive
compounds (phenols, flavonoids and ascorbic acids) and antioxidant capacity. The antioxidant capacity was evaluated by
1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt(ABTS)
radical scavenging capacity, ferric ion reducing power (FRAP) and inhibition of linoleic acid peroxidation. The results
showed that, the content of total phenols in guava increased significantly after drying, while the content of flavonoids and
ascorbic acids decreased significantly. VD and FD samples showed higher content of both total phenols and flavonoids, and
higher antioxidant capacity in terms of free radical scavenging capacity and ferric ion reducing power. HAD samples showed
higher inhibition of linoleic acid peroxidation. As the drying temperature increased, the content of flavonoids increased,
whereas the content of ascorbic acids decreased as well as free radical scavenging capacity and ferric ion reducing power
in HAD and HA-IRD samples. Overall, FD and HAD (60 ℃ and 75 ℃) samples represented higher antioxidant capacity.
According to the results of Spearman correlation analysis, high correlation coefficient values were found between either
antioxidant capacity (DPPH, ABTS and FRAP assays) or antioxidant potency composite index (ACI) and total phenolic
content. Furthermore, DPPH radical scavenging capacity and ACI proved to have a significantly positive correlation with
total phenolic content (P < 0.05), which suggested that polyphenols were the major antioxidant compounds in dried guava.

Key words: guava, drying methods, bioactive compounds, antioxidant capacity