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United States Department of Agriculture

Agricultural Research Service

Research Project: Enhanced Utilization of Carbohydrates and Polysaccharides from Citrus Processing Waste Streams

Location: Citrus and Other Subtropical Products Research

2011 Annual Report


1a.Objectives (from AD-416)
1. Develop green and scalable integrated processes which improve production economics to obtain modified pectins, ethanol or other biofuels, and other co-products such as limonene and flavonoids from citrus process waste streams. 2. Develop new commercially viable industrial bioproducts made from pectin. a) Enzymatic modification of citrus pectin nanostructure to tailor functionality. b) Determine ion exchange properties of enzyme modified pectin and peel particles. c) Determine rheological and water holding properties of chemically modified pectin and peel particles.


1b.Approach (from AD-416)
Commercial success for development and recovery of byproducts from citrus waste streams depends on the ability to economically recover sufficient quantities to meet market demands, favorable recovery costs and market value. Integration of processes to separate and recover limonene, fermentable sugars, pectin and other polysaccharides, flavonoids and other components to produce multiple high value co-products will be investigated. Recovery of pectin or modified pectin along with other polysaccharides after water extraction of fermentable sugars will be investigated for utilization in industrial applications and integrated with a steam stripping treatment for recovery of volatile terpenes. Hydrolysis of citrus peel waste utilizing commercial enzyme products and subsequent fermentation of released sugars will be evaluated for efficacy in liquefaction, conversion of cellulose to glucose, ethanol production, and cost. This will be compared to extraction, concentration and utilization of isolated sugar and pectin/polysaccharide fractions. Separation, concentration and recovery schemes to separate fermentable sugars from non-fermentable components will include residue hydrolysis, use of ion-exchange and absorbent resins, ultrafiltration, nanofiltration, reverse osmosis, water/solvent extractions and selective precipitation. Mass balances and extraction efficiencies will be determined for major byproduct components

Pectin is a major component of citrus peel with extensive functionality and the degree of methylesterification has a very strong influence on functionality. Techniques to reliably produce novel, non-random patterns of methylesterification in pectin molecules and accurately characterize their distribution will be investigated. Fractions containing pectin or other polysaccharides from citrus processing waste will be characterized for macromolecular and nanostructural properties. They will then be treated with pectin modifying enzymes at varying pH, temperature, and salt concentrations and the resulting changes in functionality and nanostructure determined. Chemical modifications will be performed using nucleophilic reagents to modify functionality alone or in combination with enzymatic treatments. Materials generated will be tested for biosorption properties as amorphous powdered materials and after conversion via chemical crosslinking. In addition, water holding capacity, viscosity, and other rheological functional properties such as yield point will be determined along with changes in fragmentation size, molecular weight distribution, degree of polymerization, degree of substitution of added groups, as well as thermal and pH tolerance. Materials with appropriate properties will then be tested in applications such as drilling fluids, dry strength additives for paper, cement additives, and absorbents for spill applications.

The economics of producing newly developed by-products will be evaluated and compared with those products currently utilized for targeted applications. Economic information will include raw materials, consumable, and energy costs, fixed capitol investment cost, and a breakdown of operating and capital cost estimates.


3.Progress Report
A patent to pretreat of citrus processing waste to produce fuel ethanol was granted. Two new commercial cellulose degrading enzymes were tested for improvements on the simultaneous enzymatic hydrolysis and fermentation of citrus processing waste to liquify, convert available cellulose to fermentable sugars, and convert fermentable sugars to ethanol for use as a biofuel. Both enzymes are much less expensive than previously available food grade products and showed much higher activity to produce glucose which is easily fermentable from cellulose. One enzyme tested also was able to produce a relatively low viscosity fermented mixture and was much easier to strip the ethanol off than previous fermentation mixtures have viscosities over 10,000 centipoise. These new available enzymes lower the enzymes cost for citrus waste treatment to approximately $0.50/gallon ethanol produced.

Multiple pressings of citrus processing waste with minimal water addition showed that greater than 80% of the soluble sugars could be removed from the nonsoluble residues, yielding a 5-6% sugar wash and residue that is suitable for pectin extraction. Non-thermal concentration of the water sugar wash is being pursued to overcome fouling issues in order to produce a 20-25% fermentable sugar substrate for improved ethanol production for use as a biofuel.

A method for rapid pectin analysis for determining free acid groups based on conductivity. Determination of these functional groups is important for development of suspension aid products.

Analyzed fractions from high temperature extraction of citrus peel for molecular weight and other important properties, which is important for understanding separation pectin fraction before peel fermentation takes place.

It has been found that not all pectin is involved in the formation of gels. Preliminary testing and data suggests that only a subfraction of the pectin molecules are modified by enzymatic deesterification and that the potential properties of pectin may not be fully realized without further improvements to the enzymatic the modification procedure.

This project replaced project 6621-41000-013-00D which was a bridging project for project 6621-41000-011-00D.


Review Publications
Widmer, W.W. 2011. Analysis of biomass sugars and galacturonic acid by gradient anion exchange chromatography and pulsed amperonmetric detection without post-column addition. Biotechnology Letters. 33:365-368.

Cancalon, P.F., Barros, S.M., Haun, C., Widmer, W.W. 2011. Effect of maturity, processing, and storage on the furanocoumarin composition of grapefruit and grapefruit juice. Journal of Food Science. 76(4):C543-548.

Widmer, W., Zhou, W., Grohmann, K. 2010. Pretreatment effects on orange processing waste for making ethanol by simultaneous saccharification and fermentation. Bioresource Technology. 101:5242-5249.

Hanley, M.J., Cancalon, P., Widmer, W.W., Greenblatt, D.J. 2011. The effect of grapefruit juice on drug disposition. Expert Opinion on Drug Metabolism & Toxicology. 7(3):267-286.

Last Modified: 10/20/2014
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