An toàn thực phẩm và an ninh lương thực lần 3 năm 2019 - Kỷ yếu hội nghị khoa học

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An toàn thực phẩm và an ninh lương thực lần 3 năm 2019 - Kỷ yếu hội nghị khoa học An toàn thực phẩm và An ninh lƣơng thực lần 3 năm 2019 EVALUATION OF IN-VITRO ANTIOXIDANT CAPACITY OF DRIED TURMERIC (CURCUMA LONGA L.) LEAVES Nguyen Ai Thach*, Pham Thi Thuy An, Phan Thi Nhe Faculty of Agriculture and Food Technology, Tien Giang University, Viet Nam * Corresponding author, Email: nguyenaithach2001@gmail.com ABSTRACT Present study evaluated the antioxidant activity of turmeric leaves which dried at 50, 60, and 70oC for 30, 60, and 90 minutes in a constant temperature oven for DPPH radical scavenging activity, FRAP, and iron chelating ability assay. DPPH radical scavenging activity of dried turmeric leaves was not affected by the drying time (p>0.05); the dried temperature, however, had has a significant impact on antioxidant activity (pAn toàn thực phẩm và An ninh lƣơng thực lần 3 năm 2019 Parkinson's disease, and brain tumors (Goel et al., 2008; Košťálová et al., 2013; Lee et al., 2013; Villegas et al., 2008). Dehydration is a method of food preserving that includes in the removal of free water from food, leading to a decrease in water activity (Yang et al., 2016). Dehydration of turmeric leaves is an effective processing method, because it not only increases the shelf-life of the product but also reduces the cost of storage. Oven drying is one of the most popular, simple and inexpensive dehydration methods which have been implemented, but can cause great sensory changes in the food products (Zielinska and Markowski, 2016). The investigation of other preservation methods is a common engineering process to avoid quality loss in food products (Najafabadi et al., 2017). Some dehydration methods may increase less sensory changes, including microwave drying that use a short time when compared to oven drying although high working temperatures, and freeze-drying which causes smaller changes besides being a time- consuming technique (Therdthai and Zhou, 2009; Zielinska and Markowski, 2016). Some studies have confirmed that the drying process also preserves nutritional quality, such as the content of phenol compounds in Curcuma longa leaves studied by Chan et al. (2009) and peppermint leaves (Mentha piperita L.) which were studied by Uribe et al. (2016). Dhaouadi et al. (2015) also found high antioxidant activity and phenolic compounds content in Lawsonia inermis L. dried leaves. Recently, there has been increasing interest in using naturally occurring compounds, especially bioactive compounds, to treat disease. The turmeric rhizomes of the plant are the most relevant part and are harvested for various products. In commercial operations, however, leaves are considered as waste. Thus, the objective of the present study is to evaluate the in-vitro antioxidant capacity of Curcuma longa L. leaves which dried in different temperature and duration conditions. 2 MATERIALS AND METHODS 2.1 Preparation of dried leaves Turmeric leaves were cut and harvested (March 2019) from the ground up three centimeter after planting about six months at Binh Tan Commune, Go Cong Tay District, Tien Giang Province, Viet Nam. The leaves were washed for removal of surface soil. The stems of leaves were removed and leaves cut into two cm squares which dried at 50, 60 and 70oC for 30, 60 and 90 minutes in a constant temperature oven (DKN412C, Yamato Scientific Co., Ltd., USA) with temperature distribution accuracy ±2.5 oC. Dried turmeric leaves were stored in PA packaging at 5 oC until using (Figure 1). The final moisture content for treatments were confirmed. The moisture content of fresh and dried leaves were determined by a MX-50 moisture analyzer. The dried materials were finely ground into powder and used to prepare extract aliquots. 12 An toàn thực phẩm và An ninh lƣơng thực lần 3 năm 2019 One gram dried turmeric leaves and 100 mL ethanol, which was stirred for 15 minutes and then, rested for 30 minutes. The extracts were filtered by Whatman @ cellulose filter paper from Sigma-Aldrich and stored at -5oC which avoid exposure to light and oxygen until analysis. 2.2 In-vitro antioxidant capacity 2.2.1 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity The antioxidant capacity was determined by the DPPH radical scavenging activity method according to Blois (1958) with modifications. A 0.3 mL aliquot of leaf extracts were mixed with 4.7 mL DPPH (Sigma Aldrich, Singapore) solution (0.2 mM), and allowed to react in the dark place for 60 minutes (A1). After, the absorbance was read in a spectrophotometer (UV-Visible UH5300, Hitachi, Japan), at 517 nm, using ethanol- aliquot extracts solution as a blank sample (A2) and control sample (A3). Percentage of antioxidant activity (AA%) = 100 – [(A1 - A2)x100/ A3]. 2.2.2 Ferric reducing antioxidant power (FRAP) The FRAP assay was done according to Chan et al. (2009) with some modifications. One mL different extract dilutions were mixed to 2.5 mL phosphate buffer (0.17 M, pH 6.8) and 2.5 mL K3Fe(CN)6 (1%) which incubated at 50°C for 30 minutes. After, 2.5 mL trichloroacetic acid (10%) was added in it. Then, 2.5 mL aliquots were diluted with 2.5 mL distilled water, and 0.5 mL FeCl3 (0.15%) was added to aliquots. After 30 minutes, readings were performed in a spectrophotometer (UV-Visible UH5300, Hitachi, Japan) at 700 nm. The FRAP value was calculated based on a gallic acid standard curve (y = 0.051x + 1.1716, R2 = 0.9893) and expressed in mg of gallic acid per gram of dry weight sample (mg GA/g DW). 2.2.3 Iron chelating ability According to Chan et al. (2008) with some modifications, solutions of 2.5 mM FeSO 4 and 4.5 mM ferrozine (Sigma Aldrich, Singapore) were diluted twenty times. Then, o ...