Improvements to a method for extracting an active acid extract from agricultural husks and its use to promote plant growth and development under normal conditions or under abiotic stress

A method for extracting an active acid extract from agricultural husks, particularly rice husks, where the active acid extract is obtained through the following phases:

• a) Pentose extraction phase,
• b) Oxidation phase,
• c) Clarification and concentration phase,
• d) Adsorption or retention phase,
• e) Purification phase and
• f) Desorption phase;
• characterized because in the d) adsorption and concentration phase, the filtered or clarified and concentrated product resulting from the classification and concentration phase is circulated through columns packed with 1 to 4 kg, preferably 1.5 to 3 kg of granular activated carbon or a quantity of high specific adsorption capacity resin that can be packed in a volume equivalent to the effective volume of the columns given by an internal diameter of 10.16 cm and an effective height of 85 cm. The selected resins with a high specific adsorption capacity are included in the group of macroporous polystyrene resins functionalized with tertiary amines, such as Purolite® MN-102, or with other hydrophilic molecules, or resins from the amberlite family;
• applying an optimal influent flow rate between 1.0 to 6.0, preferably between 1.5 to 4.5 PBV h−1 (packed bed volumes per hour) for the development and inclusion of an adsorption process so that phenolic compounds and flavonoids contained in low concentrations in the clarified and concentrated product and circulated as influent in the columns, are adsorbed and retained in the adsorbent material;
• while other secondary compounds, such as aliphatic polyhydroxycarboxylic acids, carbohydrates, alcohols and aldehydes, are eliminated in the effluent;
• in the e) purification phase the columns containing the phenolic compounds and flavonoids adsorbed on the activated carbon or high specific adsorption capacity resins are washed in counterflow with 5 to 50 L, preferably with 15 to 30 L of acidified water (pH<4), to eliminate other residual compounds, such as aliphatic polyhydroxycarboxylic acids, carbohydrates, alcohols and aldehydes, absorbed between the pores of the activated carbon or macroporous resins that could act as contaminants during the desorption or elution process. Additionally, and to facilitate the subsequent desorption or elution process, the columns are drained of the washing water and dried by means of counterflow air circulation for 5 to 30 minutes, preferably for 10 to 20 minutes, and in the f) desorption phase 10 to 40 L, preferably 15 to 25 L of 96% (v/v) ethanol or an alkaline aqueous solution of potassium hydroxide 0.05 to 0.2 M, preferably 0.1 to 0.2 M, are circulated in counterflow through the columns packed with the adsorbed polyphenolic compounds, maintaining the pH in a range of 7.0 to 10, preferably between 7.5 to 9.0, to favor the solubility of the adsorbed compounds and facilitate the desorption or elution process to obtain a concentrated active acid extract with polyphenols in a concentration range between 3 to 10 g equivalent of gallic acid/100 mL