Physical properties of botanical surfactants

Highlights: • Botanical surfactants may be suitable to the organic products sprayings. • Some surfactants properties of Q. brasiliensis and A. angustifolia were studied. • Different methods of preparation and concentration were evaluated. • Dry and grind samples resulted in higher foam column height in both species. • Q. brasiliensis was less able to reduce the superficial tension than neutral soap. Some vegetal species have saponins in their composition with great potential to be used as natural surfactants in organic crops. This work aims to evaluate some surfactants physical properties of Quillaja brasiliensis and Agave angustifolia, based on different methods of preparation and concentration. The vegetal samples were prepared by drying and grinding, frozen and after chopped or used fresh and chopped. The neutral bar soap was used as a positive control. The drying and grinding of samples were the preparation method that resulted in higher foam column height in both species but Q. brasiliensis was superior to A. angustifolia in all comparisons and foam index was 2756 and 1017 respectively. Critical micelle concentration of Q. brasiliensis was 0.39% with the superficial tension of 54.40 mN m^{− 1} while neutral bar soap was 0.15% with 34.96 mN m^{− 1}. Aspects such as genetic characteristics of the species, environmental conditions, and analytical methods make it difficult to compare the results with other studies, but Q. brasiliensis powder has potential to be explored as a natural surfactant in organic farming. Not only the surfactants physical properties of botanical saponins should be taken into account but also its effect on insects and diseases control when decided using them.