Joint water and salinity stresses increase the bioactive compounds of Aloe vera (Aloe barbadensis Miller) gel enhancing its related functional properties

The Aloe vera plant is an important source of bioactive compounds. Its growing conditions may have a considerable effect on both its physiological and chemical characteristics. Thus, the objective of this study was to evaluate the effect of joint water and salinity stresses (water + salinity) on the main bioactive compounds of the Aloe vera gel, the colorless inner parenchymatous tissue (also known as inner leaf juice), and their related functional properties. Aloe vera plants were treated with two levels of available soil moisture (high and low) and five levels of salinity (0, 20, 40, 60 and 80 mM NaCl). Plants grown at high available soil moisture without salt concentration were taken as a control (HASM-0). Total phenolic compounds, aloin, cell wall polysaccharides and water-soluble polymers were the bioactive compounds analyzed along with the antioxidant activity, radical scavenging, swelling, water retention and fat adsorption capacities. In general, the water + salinity stress negatively affected the development and growing process of the plants. However, it did cause a considerable increase in the total amount of dry matter, from 1.0 to 2.1 g/100 g of fresh Aloe vera gel. This increase was mainly due to the synthesis of new polysaccharides, and in particular of water-soluble mannose-rich polymers composed of mannose, galactose and glucose which increased from 194.4 to 345.8 mg/g of water-soluble material as water + salinity stress increased. Further, there was a significant increase in the aloin content, from 10.7 to 19.6 mg/g of total solid contents from Aloe vera gel. These changes in the bioactive compounds were reflected in the functional properties studied. Hydration properties of Aloe vera gel, such as swelling and water retention capacity, exhibited higher values for those plants treated with water deficit and salinity. The antioxidant capacity, determined by FRAP and DPPH methods, was also higher in the gel from stressed plants. Overall, these results show that water + salinity stress could be an agricultural strategy for increasing not only the content of bioactive compounds present in the Aloe vera gel but also for improving their related functional properties.