Analysis of the Thermal Energy Requirements for the Extraction of Leaf Protein Concentrate from some Green Plants

Abstract

Extraction of protein from the leaves of green plants is very important because of the high cost of conventional forms of protein such as meat, milk and fish. In order to design machinery for this extraction, and also to embark on leaf protein concentrate extraction, it is necessary to measure and analyse the energy requirements to carry out each process involved in the extraction, using different plant species. Experiments were carried out to determine the amount of crude protein, and the thermal energy required to extract leaf protein concentrate, from juices obtained from the leaves of some plant species. Leaves from the following plants were selected: cassava ( Manihot esculanta), Siam weed (Chromolaena odorata), bitter leaf ( Vernonia amygdalina), gliricidia ( Gliricidia maculata) and thorny tree ( Hura crepetans). The leaves from the plant species were macerated in a laboratory pulper. Juice was obtained from the samples using perforated cylinders and a hydraulic press. The specific heat capacity of the juices was determined using the cooling curve method. The values of the heat capacities were used to calculate the amount of thermal energy required to raise the temperature of each juice from its normal temperature of about 25°C to a total protein coagulation temperature of about 80°C. The crude protein content of the extract was determined using the Kjeldal method. Results indicate that the green coagulum extracted from all the juices all have a protein content of at least 37%. The thermal energy required to coagulate protein from the juices ranges from 1·59 kJ kg −1 for Hura crepetans to 2·7 kJ kg −1 for Vernonia amygdalina. The energy requirement to obtain crude protein (CP) ranges from 8 kJ kg −1 [CP] with Hura crepetans to 182 kJ kg −1 [CP] with Vernonia amygdalina. Both results are statistically significant at the 0·01 confidence interval. It is concluded that the choice of plant species can significantly lower the thermal energy requirement for the extraction of leaf protein concentrate.