Biosystems Engineering (2006) 94 (1), 67–73 doi:10.1016/j.biosystemseng.2006.02.004 PH—Postharvest Technology Effect of Temperature, Alkali Concentration, Mixing Time and Meal/Solvent Ratio on the Extraction of Watermelon Seed Proteins—a Response Surface Approach Ali Abas Wani 1 ; D.S. Sogi 1 ; L. Grover 2 ; D.C. Saxena 3 1 Department of Food Science and Technology, Guru Nanak Dev University, Amritsar 143 005, India; e-mail of corresponding author: dsogi@yahoo.com 2 Department of Mathematics, Guru Nanak Dev University, Amritsar 143 005, India 3 Department of Food Technology, Sant Longowal Institute of Engineering & Technology, Longowal, India (Received 14 January 2006; accepted in revised form 1 February 2006; Published online 3 April 2006) Watermelon seeds are a byproduct of juice manufacture and contain good-quality extractable proteins. The effect of temperature, alkali concentration, mixing time and solvent/meal ratio was studied on the extraction of watermelon (Citrullus lanatus Cv Mateera) seed protein. A central composite design was used with four variables: temperature (40, 45, 50, 55 and 60 1C); alkali concentration (03, 06, 09, 12, and 15% w/v); extraction time (5, 10, 15, 20 and 25 min); and solvent/meal ratio (30:1, 40:1, 50:1, 60:1 and 70:1). The experimental values of protein yield ranged between 7549% and 8608%. The second-order model obtained for protein yield revealed coefficient of determination of 0.846. Protein yield was primarily affected by alkali concentration and solvent/meal ratio. Maximum yield was obtained when alkali concentration, solvent/meal ratio, temperature and extraction time were 12% w/v, 70:1, 40 1C and 15 min, respectively. These results help in designing the process of optimal protein extraction from watermelon seeds. r 2006 IAgrE. All rights reserved Published by Elsevier Ltd 1. Introduction Watermelon is one of the major under-utilised fruits grown in the warmer part of the world. The juice or pulp from watermelon is used for human consumption while rind and seeds are major solid wastes (Bawa & Bains, 1977; Hour et al., 1980; Ahmed, 1996). The rind is utilised for products such as pickles and preserves as well as for extraction of pectin (Hasan, 1993; Godawa & Jalali, 1995), whereas seeds are a potential source of protein (Oyenga & Fetuga, 1975; Teotia & Ramakrish- na, 1984; Kamel et al., 1985; Sharma et al., 1986; Lasztity, 1986) and lipids (Lazos, 1986; Melo et al., 2000; El-Adaway & Taha 2001). The amino acid composition of watermelon seeds indicated good quality protein with predominant amounts of arginine, glumatic acid, aspartic acid and leucine (Nwokolo & Sim, 1987; Lasztity et al., 1986; El-Adawy & Taha, 2001). Various parameters such pH, temperature, ionic strength, solvent type, extraction time and solid–liquid ratio affect protein solubility (Liu, 1997). The extrac- tion, isolation and fractionating procedures differ depending on the end use. For food application the extraction of protein-rich material in alkaline solution followed by isoelectric precipitation is commonly followed (Sathe et al., 1984). Response surface methodology (RSM) is a sta- tistical technique used to design experiments that yield the relevant information in the shortest time with the least cost. The basic principle of RSM is to relate product properties to regression equations that describe inter-relations between input para- meters and product properties (Giovanni, 1983; Mon- tgomery, 1984). Its use leads to the rapid and efficient development of new and improved products and processes. In the present study, RSM was employed to standardise the parameters (temperature, alkali con- centration, extraction time and solvent/meal ratio) for maximum protein extraction from watermelon seed meal. ARTICLE IN PRESS 1537-5110/$32.00 67 r 2006 IAgrE. All rights reserved Published by Elsevier Ltd