Protein Isolation from Tomato Seed Meal, Extraction Optimization GEORGE N. LIADAKIS, CONSTANTINA TZIA, VASSILIKI OREOPOULOU, and CHRISTOS D. THOMOPOULOS ABSTRACT Water extraction of tomatoseed meal proteins was studied to find op- timal conditions for protein extraction andisolation. A central composite design includingtemperature, pH, time and water/solids was usedand second ordermodels were employed. Optimum conditions were: 5O”C, pH 11.5,20 min and water/solids = 30/l (v/w). Experimental values were:extraction yield (extracted protein to that in raw material) 66.1%, protein contentof product 72.0%, and total protein yield (protein in isolated product to that in raw material) 43.6%.Estimated values were in goodagreement with experimental values. Optimum conditions were confirmed by a largerscale experiment. Key Words: tomato, proteinextraction, seed meal,optimization INTRODUCTION ENVIRONMENTAL POLLUTION causedby food processing wastes could be reduced by appropriate recovery of edible nutrients (Birch et al., 1976; Green and Kramer, 1979; Knorr, 1983). To- mato processing wastes, primarily skins and seeds,comprise 10 to 30% of raw fruit weight (Ben-Gera and Kramer, 1969; Geis- man, 1981). Tomato seeds represent 50-55% of the pomace. Tomato pomace is mainly disposed of as animal feed or fertil- izer (Tsatsaronis and Boskou, 1975; Canella et al., 1979; Can- tarelli et al., 1989). A small fraction of the seedsis used by the oil industry (Canella et al., 1979; Geisman, 1981). About 1 X lo6 metric tons of tomatoes are processed into products annually in Greece (NSSG, 1990), generating F= 100,000 tons of tomato seeds. The potential of tomato seeds as a food source has been re- ported (Ammerman et al., 1963; Drouliskos, 1976; Kramer and Kwee, 1977a,b;Abdel-Rahman, 1982; Al-Wandawi et al., 1985; Lasztity et al., 1986; Rahma et al., 1986). The approximate com- position of tomato seeds(dry basis) is: fat 1l-20%, protein 15- 22% and ash 3-7%. The high unsaturated fatty acid content of tomato seed oil (C,,,, 20%, C,,:, 55-60%, C,,:, 2%) and the nutritive value of the protein compare favorably with soybeans (Rymal, 1973; Rymal et al., 1974; Brodowski and Geisman, 1980; Lazos and Kalathenos, 1988). The high lysine content (8- 10 g/16 g N) of tomato seed protein (Rymal et al., 1974; Cantarelli et al., 1989) makes it suitable for supplementing pro- teins in cereal products (Brodowski and Geisman, 1980; Carlson et al., 1981; Yaseen et al., 1991). In addition the functionality of tomato seed proteins may have many uses in food systems (Kramer and Kwee, 1977a; Moharram et al., 1984; Doxastakis et al., 1988a,b; Doxastakis et al., 1988; Kiosseoglu et al., 1989). Tomato seedslack antinutritional factors or toxic substances of- ten found in other non-conventional protein sources (Rahma et al., 1986). Thus, the recovery and utilization of tomato seed protein for human consumption has been studied (Kwee, 1970; Canella et al., 1979; Doxastakis et al., 1988b; Cantarelli et al., 1989; Kiosseoglu et al., 1989). Protein has been isolated from tomato seeds using a 3-step process: extraction, precipitation and drying of protein precipi- The authors are affiliated with the Laboratory of Food Chemistry & Technology, Dept. of Chemical Engineering, National Technical University of Athens, 5 Heroon Polytechniou St., Zografou, 15780 Athens, Greece. tate (Kramer and Kwee, 1977b; Fazio et al., 1983). Canella and Castriota (1980) examined the effects of several individual fac- tors on protein extraction from tomato seed meal. Latlief and Knorr (1983a,b) studied the protein precipitation step using commercial tomato seeds. Our objective was to determine the optimal conditions for protein extraction from defatted tomato seed meal, examining simultaneously effects of temperature, pH, time and water-to- solids ratio. The effect of extraction conditions on protein yield and on protein content of isolated product was also determined. MATERIALS & METHODS Materials Tomato pomace was obtained from a tomatoprocessing plant (KO- PAIS S.A. Aliartos, Greece). It was sundried (25-3O”C, 3-4 days)and ground in a blender (WaringCommercial Blendor, Dynamics Co., New Hartford, CO). The majorpart of the skinswasremoved usinga 1 mm sieve. The skins remaining on the sieve wereseparated from seeds with a fan blowinganupward airstream. Theseed fraction wasground (Ultra- Centrifugal Mill, TypeZMl, F.K. Retsch GmbH& Co, Haan, Germany) to passa 1 mm sieve.Tomatoseed meal was prepared by defatting ground seeds with n-hexane in a Soxhlet apparatus andgrinding(Ultra- Centrifugal Mill, TypeZMl, F.K. Retsch GmbH& Co, Haan, Germany) to pass a 0.5 mm sieve. Protein isolation from tomato seed Tomato seed meal (10 g) was extracted with deionized water(lO:l- 30: 1 ratio) in a stirred glass vessel. ThepH of the suspension (7.5-l 1 S) waskept constant duringthe extraction by adjusting with OSNNaOH. Temperature (30-50°C) was regulated within -t 0.2”C by a water bath. The slurry was centrifuged at 2600Xg for 20 min, the supernatant was collected and the pH was adjusted to the isoelectric point (3.9) using OSN HCl. The protein precipitate was separatedby centrifugation at 2600Xg for 25 min and freeze dried. The solid residue after protein extraction was dried at 60°C under vacuum and was used for protein determination. Isoelectric point (PI) The pI of tomatoseed proteins was determined as the pH value of maximal precipitation. 20g of tomato seed meal was extracted as de- scribed, under the conditions: water-to-solids ratio 2O:l (v/w), pH 10, 4o”C, 30 min. The p1 was found by titrating aliquots of the collected extract to specific pH values and determining the protein content of the supematantafter centrifugation. The protein content was determined ac- cording to the method of Lowry et al. (1951). Analytical methods Moisture, crude fat, ash, total dietary fiber and crude protein (Nx6.25) were determined according to standard methods (AOAC, 1990). Min- erals were determined by atomic absorption/emissionspectroscopy(Per- kin-Elmer Model 2380, Perkin Elmer Co., Norwalk, CT). Phosphorus was determined photometrically by the ascorbic acid method (Hach Company, 1989), after digestion with concentratedsulfuric acid and hy- drogen peroxide (50%) in a Digesdahl apparatus (Hach Company, Love- land, CO). Total sugars were measuredaccording to the phenol-sulfuric acid method (Dubois et al., 1956) using glucose as standard. Volume SO, No. 3, 1995-JOURNAL OF FOOD SCIENCE477