The analysis of different processes of extraction: yield of extracts obtained from Aloe vera (Aloe barbadensis Miller) and sweet bay (Laurus nobilis L.) and the exergy analysis of applied processes

The present study was aimed to investigate and compare the efficiency of different methods for the isolation extract from a plant material. Extracts from dried leaves of Aloe vera (A. barbadensis Mill.) and Sweet Bay (Laurus nobilis L.) were obtained applying the following techniques: supercritical carbon dioxide (SC CO2) extraction at 30 MPa and 100°C, a combined ultrasonic extraction and pre-treatment using SC CO2 (US-SCCO2), and a conventional ultrasonic extraction (US) with 96% ethanol. US-SCCO2 resulted in much higher yields of extracts of aloe and bay compared to SC CO2 extraction. Determined extract's yield was used for calculating the maximum useful work and exergy loss as a measure of irreversibility of the extraction process. Calculated maximum useful work per 1 kg of the extract was ranged from 0.7 to 226 kJ while estimated values of the exergy loss were from 48 to 416 kJ per 1 kg of the extract. The maximum useful work and exergy loss have the largest value for SCE much more than for other processes of extraction (US and US-SCCO2). The pre-treatment of the plant material with SC CO2 before an ultrasound-assisted extraction or the decrease of a particle size used for ultrasound-assisted extraction of Aloe vera has led to the decrease of maximum useful work and exergy loss. Unlike, pre-treatment with SC CO2 followed by ultrasound-assisted extraction increased the exergy loss when bay was used as the plant material.