Physical and Mechanical Pretreatment of the Raw Material for the Extraction of Health-Promoting Components

Abstract

Phytochemicals are naturally occurring plant-derived compounds and they are believed to have curative, preventative or nutritive values. They are present in many fruits and vegetables, but extracting them from these plant matrices and purifying them is quite challenging. In order to improve the yield and quality of the extracted phytochemicals, a pretreatment of the raw material is essential. Cell disruption is the most important pretreatment and this procedure can be divided into four classes: mechanical, ultrasonic, high-pulsed electronic field pulse, and nonmechanical treatments. High-pressure homogenization is the most widely used method for large-scale cell disruption. The reduction of plant material into fine particles can also be accomplished with a hammer mill or bead mill. With the bead mill, the grinding action is provided by glass beads that impact and apply shear force against the cell wall. The French Press is generally used for small operations, but it can be scaled up. The liquid cell suspension is subjected to a pressure differential causing the cell wall and membrane to burst. Ultrasonic disruption is a new method that is based on sound waves and a phenomenon known as cavitation. A major problem with sonication is the buildup of heat in the samples. Pulsed electric field treatment is a nonthermal method used to permeabilize the cell membrane of the plant material. Short pulses of high-voltage electricity can rupture the cell while maintaining the fresh physical, chemical and nutritional characteristics of the foods. Nonmechanical disruption processes include osmotic shock and freeze-thaw. The supercritical fluid treatments show great promise, especially for material of high-value health-promoting ingredients.