The textural properties of the skin moisturizer samples were measured using a Texture Analyzer TA.XT Plus (Stable Micro Systems Ltd., Godalming, U.K.). The unit had a load cell of 30 kg, with an A/BE back extrusion rig, which included a locating base plate, sample containers (50mm internal diameter), and compression discs (35mm diameter). After penetrating the sample (25 mm deep) at a rate of 2.0 mm/s, the probe returned to the initial position. Following this procedure, the firmness, consistency (related to hardness), cohesiveness, and index of viscosity (related to adhesiveness) of the samples were measured in duplicate and average values were calculated for all parameters (all expressed as positive values). All the measurements were taken at room temperature of 20 ± 0.2°C.
Microscopy: Emulsions were observed using a portable microscope Dino-Lite® Edge AM7515MT8A (Taipei, Taiwan), with a magnification of 900x, and images were captured with the in-built camera 5Mpixels (2592x1944). For this, a small amount of sample was mounted on a glass slide along with a drop of distilled water under a coverslip. All samples were examined two months after preparation to assure long term stability.
Evaluation of white residues after product application on skin: An adaptation to the descriptive skin-feel analysis method described by ASTM E1490-0365 was implemented here to establish a qualitative comparison of the white residues left by two products during rub-out. In this case, 0.1 g of each product was spread on the mid-section of the forearm, using the index finger for one product and the middle finger for the other product, both from the opposite hand. The white residues of both samples were compared after 15 circular rubs at a rate of two strokes per second.