To extract protein concentrate from tomato processing wastes, the chemical composition of different parts of tomato processing wastes including tomato processing waste meal, tomato seed meal, and tomato oil extracted seed meal were determined. Protein concentrates were prepared by alkali extraction and acid precipitation. To propose the optimal condition for obtaining the maximum protein yield, we performed alkali extraction by using NaOH in 20-70ċ and 8-12 degrees of pH. Next, acid precipitation was performed with HCl in 3.3-5.5 degrees of pH. After determining the protein concentration and dissolved protein mass in extract, the optimal condition was obtained at the room temperature (25-27 ċ) and pH=12. The maximum protein yield of tomato processing waste, tomato seed, and tomato oil extracted seed was achieved in the pH of 3.9, 4.1, and 4.1, respectively. The effect of heat treatment during acid precipitation on protein yield and two functional properties including water absorption and oil absorption capacities of protein concentrates were studied at the temperature over the range of 25-100ċ. Results showed that the highest protein precipitate is obtained at higher temperatures. Moreover, the most protein percentage of both tomato processing waste and tomato seed is given in the room temperature while that of tomato oil extracted seed is achieved at the temperature over the range of 70-85ċ. In addition, by increasing the temperature in acid precipitation stage, the water and oil absorption of protein concentrates is increased.

Keywords: Tomato processing wastes, Alkali extraction, Acid precipitation, Maximum protein yield, Functional properties