Leaching behavior of water-soluble carbohydrates from almond hulls

Abstract

Over 58% of the dry matter content of the hulls from the commercial almond (Prunus dulcis (Miller) D.A. Webb) is soluble in warm water (50–70°C) extraction. The water-soluble extractables include useful amounts of fermentable sugars (glucose, fructose, sucrose), sugar alcohols (inositol and sorbitol), polysaccharides, and other components. Extraction rate data were taken over a range of temperatures and particle sizes (including whole hulls). Equilibrium concentrations and liquid retention data were taken over a wide solubles concentration range, enabling use of a standard leaching model for the calculation of stage-to-stage concentrations and flows in an ideal countercurrent extractor. The relations between recovery, product concentration, number of ideal stages, and ratio of solvent-to-feed were determined using the model. The data indicate that a solutes concentration of 18–20% dry matter in the concentrate liquid is attainable. Due to the nature of the native hulls to preferentially absorb water from dilute solutions, initial contact of hulls with the overhead liquid concentrate (if well below ∼18% solutes) may result in a significant enhancement of overhead concentration.