TASER et al.: CHEMICAL PRETREATMENTS ON AIR-DRYING OF BLACK MULBERRY 477 *Address for correspondence Fax: 0-90-356-2521488 E-mail: ftaser@hotmail.com Effects of chemical pretreatments on air-drying process of black mulberry (Morus nigra L.) Omer Faruk Taser*, Sefa Tarhan and Gazanfer Ergunes Department of Farm Machinery, Faculty of Agriculture, Gaziosmanpa_a University 60240, Tokat, Turkey Received 28 September 2006; revised 22 January 2007; accepted 29 January 2007 For drying as the preservation method, black mulberries (Morus nigra L.) placed into sample bags were dipped into one of six different chemical solutions for one minute at room temperature to accelerate the moisture loss. Pretreated black mulberry samples were dehydrated by artificial air-drying, solar drying and open sun drying. The samples treated by 2% ethyl oleate were the fastest ones reaching to the final weight loss percentage (75%) in 22 h by the laboratory tray dryer providing 45.2 °C drying air (artificial air drying) and in 90 h by solar drying. The pretreatment combination caused only slight changes in measured color values of mulberries during all drying trials. Keywords: Air-drying, Black mulberry, Ethyl oleate, Open sun drying, Solar drying IPC Code: A23B Introduction Any drying process to preserve agricultural materials is meant for the retention of product quality, reduction of operational/investment cost and protection of environment 1 . The retention of product quality typically increases the cost of drying process such as in freeze drying 2 . This difficulty has been tried to alleviate by developing new drying strategies such as heat pump drying, microwave drying and radio frequency drying 1-3 or various chemical pretreatment processes 4-7 in both industrial and scientific arenas. On the other hand, solar drying and open sun drying of agricultural materials are extensively practiced all over the world because of their ease of operation and low cost 8-10 . Black mulberry (Morus nigra L.) is used in treatment of type II diabetes mellitus, inflammations of throat, tongue and mouth, and strengthening the solid tissues of teeth 11 . It is good source of phenolic compounds and anthocyanin (2000-2600 mg -1 as juice), which is four times higher than in grapes 11 . Anthocyanin from mulberry may reduce the incidence of heart diseases with its anti-atherosclerotic activity by inhibiting the oxidation of LDL in the arterial wall 12 . Mulberry fruits are normally harvested by handpick or by shaking tree branches and collecting the fruits over a sheet on the ground. Shelf life of fresh mulberries is very short; therefore, they should be processed for preserving as juice, jam, leather, frozen fruit, dried fruit, etc. immediately after harvesting 11 . This research presents appropriate chemical pretreatments for black mulberries dehydrated by three different drying methods (artificial air drying, solar drying and open sun drying). Materials and Methods Black mulberry fruits were handpicked from a local fruit farm in Tokat city located in the Central Black Sea Region of Turkey. Moisture content of fresh fruits was determined according to the vacuum oven method (T=70°C). Fruits (75-80g) were placed into sample bags made of plastic net. Six different pretreatment solutions (T 1 -T 6 ) were prepared as follows (% w/v): T 1 2 % ethyl oleate; T 2 , 1% NaOH; T 3 , 1 % citric acid; T 4 , 1 % ethyl oleate; T 5 , 1 % ethyl oleate + 1 % citric acid; and T 6 , water (control). Dipping temperature corresponded to room temperature (23°C) without heating chemical solution. Sample bags were dipped into each solution for 1 min. at room temperature. Right after rinsing with Journal of Scientific & Industrial Research Vol. 66, June 2007, pp. 477-482