Sunday, May 4, 2008
3-21

Protein extraction and enzymatic hydrolysis of ammonia-treated cassava leaves (Manihot esculenta Crantz)

Lauris Urribarrí1, David Chacón1, Orlaidy González1, and Alexis Ferrer2. (1) Química, Universidad del Zulia, Avenida Universidad, Facultad de Ciencias, Maracaibo, Venezuela, (2) Instituto Zuliano de Investigaciones Tecnológicas, Km 15, La Cañada de Urdaneta, Venezuela

Cassava leaves were treated with 0.5 kg ammonia/kg dry matter at 78ºC and 30% moisture content in a 2 kg reactor. Protein extraction was carried out with a calcium hydroxide solution (pH 10) for 30 min at several temperatures (30, 45, 60, 75 and 90ºC) and solid/liquid ratios (1:10 y 1:15) in a thermostatized bath. Soluble protein content of the extracts was determined by the Lowry´s method. Dry substrate concentrations of  5%, 7.5% and 10%, and enzyme doses of 2 IU/g and 5 IU/g dry matter were used for the enzymatic hydrolysis in an orbital incubator at 50ºC and 100 rpm. Both cellulase and xylanase were used. Reducing sugars produced were determined with the DNS method. The highest protein extraction yield for the ammonia-treated leaves was 29.10%, which was 50% higher than with the untreated leaves (20%), and was obtained at 90ºC and with a 1:10 solid/liquid ratio. The highest sugar yield was 54.72% with respect to theoretical, and was obtained with 5% solids and an enzyme dose of 5 IU/g dry matter. This yield was 3.2 times higher than the yield of the untreated leaves (16.72%).
Key words: ammonia treatment, protein, protein extraction, reducing sugars, enzymatic hydrolysis, cassava.

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