CytroCell: Valued Cellulose from Citrus Processing Waste

Abstract

Isolating cellulose from citrus processing waste without employing chemicals has so far been an unfulfilled goal of chemical research applied to the valorization of a widely available biowaste, annually totaling >100 million tonnes. We have applied hydrodynamic cavitation using a Venturi-type reactor for the extraction of all valued bioproducts of industrial citrus processing waste in water only, directly on a semi-industrial scale. After reporting the discovery of IntegroPectin in the soluble fraction of the aqueous extract, we now report the isolation of a cellulosic material in the water-insoluble fraction of cavitated lemon and grapefruit processing waste. Named “CytroCell”, the material is cellulose of low crystallinity, high porosity, good water holding capacity and good dispersibility in water. These properties open the route to mass-scale production of a useful functional material from a cheap and abundant biowaste.

Nanocellulose from citrus processing waste using water and electricity only

“…We brie y remind that these nanocelluloses adsorb and retain 8 g water /g cell in the case of lemon CytroCell and 5 g water /g cell for grapefruit CytroCell. 20 In general, for powdered an dhighly puri ed wood cellulose used as dietary ber, the WHC increases with increasing ber length. 25 The fact that the water holding capacity (WHC) of lemon nanocellulose of signi cantly shorter ber length is higher than that of grapefruit nanocellulose suggests a different chemical composition of lemon CytroCell nanocellulose.…”

“…Repeated at Khalifa University of Science and Technology, the XRD measurements (plots not shown) con rmed previous XRD analysis showing that both CytroCell materials consist of cellulose of low crystallinity index (0.33 for lemon and 0.36 for grapefruit CytroCell). 20 Again, the grapefruit-derived cellulose was found to contain more abundant calcium oxalate crystals (with diffraction peaks at about 14.6°, 24.4° and 29.3°), abundant in both the lemon and grapefruit fruit peel, 23 and particularly abundant in plants grown in dry climates such as that of southern Sicily where both citrus fruits used to produce CytroCell originate (under drought conditions oxalate releases CO 2 and water molecules). 24 The SEM images of both lemon abd grapefruit CytroCell in Figure 3 show a compact and relatively convoluted surface for both lemon nanocellulose nanorods and grapefruit nanocellulose micro brils.…”

“…Based on the IR analysis, this difference has been ascribed to the partial esteri cation of lemon CytroCell and the primary alcohol groups with citric acid residual in the wet lemon processing biowaste during the HC-assisted extraction. 20 Highly hydrophilic free and esteri ed carboxyl groups of the esteri ed cellulose enhance the WHC.…”

“…The higher amount of carboxylate groups in lemon-derived CytroCell (visible in the IR spectra) 20 is re ected in the additional weight loss slope variation in the TGA and peak in the DTA pro le for the lemon-derived nanocellulose at around 500 °C, which likely corresponds to the decomposition of the glycosyl-units resulting from the previous decomposition of the citric acid-esteri ed groups, followed by the formation of a carbonaceous residue.…”

“…18 Now, we report that the insoluble fraction resulting from the hydrodynamic cavitation (HC) of citrus processing biowaste carried out on a semi-industrial scale in water consists of a new nanocellulose of high quality. Dubbed "CytroCell", 20 this citrus nanocellulose is readily obtained in large amounts through a one-pot process requiring no prior or subsequent chemical or mechanical treatment.…”