Valorisation des coproduits issus des industries d’agrumes : extraction des molécules bioactives par des technologies innovantes

Abstract : This work consists of the valorization of citrus by-products with innovative technologies. Citrus pressing produces millions of tons of waste per year worldwide. This waste (peels, pulps and seeds) is generally dedicated to animal feed or eliminated by composting or incineration. However its content in bioactive molecules leads to several ways of valorization. Since peels present about half of the citrus waste mass, studies have been focused on the valorization of citrus peels by the extraction of bioactive compounds. Conventional methods generally used for the extraction of bioactive compounds (solid-liquid extraction, hydrodistillation) have several disadvantages such as the use of expensive and toxic solvents, long extraction times and high energy consumption. For this reason, several innovative non-thermal technologies such as Pulsed Electric Fields (PEF), High Voltage Electrical Discharges (HVED) and Ultrasounds (US) and thermal treatments such as microwaves (MO) and infrared (IR) have been tested for the valorization of citrus by-products. Whole citrus fruits (oranges, pomelos, lemons) were PEF treated at an intensity of 3 kV/cm, then citrus juice and polyphenols were extracted by pressing. The study of the PEF-induced cell permeabilization was conducted by several methods and showed that the degree of damage varied according to the type of the treated fruit. The electroporation of the cells induced by the PEF, allowed an increase the juice yields after pressing and improved the liberation of the polyphenols from the citrus peels into the juice. This explains the possibility of obtaining a juice rich in polyphenols by treating the whole fruits with PEF before pressing. Among the solvents tested for the extraction of polyphenols from citrus peels, water is the least effective. The addition of 20% glycerol to water changed the polarity of the medium and improved the extraction of the polyphenols. The use of an enzyme mixture enhanced the release of the polyphenols related to the polysaccharides. Deep eutectic solvents have been as effective as hydroethanolic mixtures. To improve the yields and the kinetics of extractions in the different green solvents and in the enzyme mixture, citrus peels were pretreated with HVED in water. The mechanical effect of HVED, based on the fragmentation of the peels has improved the extraction of polyphenols in the various solvents. The intensification of polyphenols extraction was also conducted by IR and US. The extraction of polyphenols by IR was optimized using the surface response methodology. IR heating did not alter the extracted polyphenols which have significant antifungal and anti-mycotoxinogenic activities. The pretreatment of citrus peels with IR weakened the cell structures, increasing thus the diffusion of polyphenols during US treatment.
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Sally El Kantar. Valorisation des coproduits issus des industries d’agrumes : extraction des molécules bioactives par des technologies innovantes. Génie des procédés. Université de Technologie de Compiègne; Université Saint-Joseph (Beyrouth). Faculté des Sciences, 2018. Français. ⟨NNT : 2018COMP2440⟩. ⟨tel-02139105⟩

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