367 Ascorbic Acid, Total Phenolics and Antioxidant Activity of Guava Leaf Extracts K. Iamjud, N. Banyen, U. Boonprakob and K. Thaipong Department of Horticulture, Faculty of Agriculture Kasetsart University, Kamphaeng Saen Campus Nakhon Pathom Thailand Keywords: antioxidant properties, natural antioxidant, ascorbic acid content Abstract Epidemiological studies have indicated that guava leaf extract can act as an anti-free radical reagent, which could reduce the risk of several cancer types. The objective of this research was to investigate ascorbic acid content, total phenolics content and antioxidant activity in guava leaf extracts of 30 cultivars consisting of 10 dessert, 12 processing and 8 local types. The results showed that guava leaf extracts from processing type had the highest level of total phenolic content (gallic acid equivalents) at 5,304±1,485 mg/100 g fresh weight (FW) and antioxidant activity (ascorbic acid equivalents) at 685±135 μmol/g FW. The highest value of ascorbic acid was found in local type at 98±21 mg/100 g FW. Green leaf had higher value of phenolic content (4,584±1,710 mg/100 g FW) and antioxidant activity (559±242 μmol/g FW) than maroon leaf. While, maroon leaves contained higher value of ascorbic acid than green leaves that were 142±52 and 86±29 mg/100 g FW, respectively. Therefore, antioxidants in guava leaf should be extracted from the green processing type in order to get the highest value. INTRODUCTION Psidium guajava L. is an important tropical fruit of Thailand. Guava leaves have been widely used for medicinal proposes as an anti-inflammatory, for diabetes, hypertension, wounds, pain relief and reducing fever in several parts of the world (Gutiérrez et al., 2008). The decoction of guava leaf is an effective antidiarrhoeal reagent (Birdi et al., 2010). Also guava leaf is a good source of natural antioxidants (Qian and Nihorimbere, 2004). The aim of a guava breeding program, initiated in 1998 by the Department of Horticulture, Faculty of Agriculture at Kamphaeng Saen, Kasetsart University, is to develop new cultivars with superior fruit qualities, resistance to biotic/abiotic stresses and high antioxidant contents in fruit/leaf. Several accessions each of dessert, processing and local-type guava were collected. Most published information of antioxidant properties in guava has been reported in fruit (Jimenez-Escrig et al., 2001; Leong and Shui, 2002; Thaipong et al., 2006; Gutiérrez et al., 2008). The aim of this research was to determine antioxidant activity and two important antioxidant compounds: ascorbic acid and total phenolics, in leaves of 30 guava cultivars. MATERIALS AND METHODS Leaves of 30 guava cultivars were collected from the experimental field of the Department of Horticulture, Faculty of Agriculture at Kamphaeng Sanen, Kasetsart University, Nakhon Pathom, Thailand. The samples consisted of 10 dessert, 12 processing and 8 local type cultivars. Two cultivars of the dessert type are maroon leaf and all of the other 28 cultivars are green leaf (Table 1). Extraction One gram of fresh guava leaf was homogenized in 20 ml of methanol using an Ultra-Turrax homogenizer (T25, Ika Works Inc., USA) until uniform consistency. The homogenate was then centrifuged at 15,000 rpm for 20 min at 4°C using a vacuum micro Proc. IS on Tropical and Subtropical Fruits Eds.: N. Chomchalow et al. Acta Hort. 1024, ISHS 2014