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United States Department of Agriculture

Agricultural Research Service



2009 Annual Report

1a.Objectives (from AD-416)
Characterize the structure and functional properties of the polysaccharides present in the citrus processing waste stream. Develop new and use existing procedures including chemical, physical or enzymatic processes to modify and produce new polysaccharide materials, value added polymers, or resins with unique functional properties. Develop new industrial uses for new products produced either isolated or while still contained in the bulk waste stream residue for use as ion-exchange, building and construction materials, paper products, and other non-food related materials. Develop economically viable method for enzymatic and chemically catalyzed depolymerization of polysaccharides in citrus waste streams to monomeric sugars with subsequent fermentation of hydrolysates to value added products such as ethanol, citric and other organic acids, and similar products.

1b.Approach (from AD-416)
Reactions initiated by acid, base, enzymes, and/or thermal treatments will be performed to modify polysaccharides in bulk citrus processing waste or minimally separated citrus waste stream components. Pectinmethyesterase enzymes from citrus will be characterized for their response to temperature, pH, salt, and modifications made to pectin substrates. The effect of modifications on chemical changes such as degree of esterification, fragmentation size and polymerization will be determined along with how these modifications improve water holding capacity, increase ion-exchange capacity, decrease or increase viscosity and other rheological properties. Polysaccharides in citrus residue products and pectin extracts will also be further modified using nucleophilic reagents such as amines and sulfhydryl compounds to produce substituted polymers with new functionality. New grinding, separation and/or filtration process technologies will also be evaluated for economic and environmental advantages for production of more economically attractive carbohydrate and polysaccharide products from citrus waste streams. Products with desirable properties will be produced on a pilot scale and supplied to industrial partners for testing in specific applications. Modified polysaccharides will be tested in applications such as dry strength additives for paper and building materials, metal chelation and ion exchange applications such as industrial wastewater treatment, and water binding capacity for superabsorbant applications. Commercial enzyme systems for efficient hydrolysis of polysaccharides from citrus waste will be evaluated to optimize enzyme loading, temperature and pH of reactions, ability to recycle enzymes, and degree of mixing necessary in pilot scale-up from lab scale experiments. Efficient separation of hydrolysed citrus waste will then be investigated using centrifugation, rotary and flat bed filters to allow fermentation to produce fuel ethanol and organic acids.

3.Progress Report
Release of pectin from peel in a cost effective manner prior to enzyme or chemical modifications is a challenge and optimization with regard to pH and heating conditions were achieved to minimize cost and optimize molecular disaggregation. A challenge has been to release the pectin from the peel in a cost effective manner prior to enzyme or chemical modification. High yields of pectin were observed by adjusting pH values using microwave heating as compared to using longer times by resistance heating. Data suggest that by careful selection of pH and temperature, acceptable yields of pectin can be obtained while preserving a significant portion of the molecular properties needed for applications. Results indicate acceptable yields can be obtained under relatively mild pH conditions with short reaction times, which will aid in developing a scalable and cost effective process. These extraction conditions are now applied for rapid analysis of pectin in peel for applications work and evaluation of effects of tropical diseases on citrus peel and juice quality. Several new analytical procedures have been developed which permit faster and much better property characterization of pectin and modified pectin components. To facilitate mapping of pectin structures and modifications made to pectin after treatment with enzymes and chemicals, methodology was developed and improved making it possible to separate individual pectic fragments containing more than 70 galacturonic acid units, important for determination of functional properties and how they relate to structural changes introduced through enzyme modifications. Three of the 4 pectin methylesterase enzymes (PME) present in citrus fruit peel have been isolated utilizing a method developed in this lab which uses ultra filtration followed by affinity and ion exchange chromatography separations. Two of the 4 PME forms are present in low amounts. One of these has been isolated in sufficient amounts and is undergoing characterization while work continues to isolate the fourth citrus PME in sufficient quantities. Enzymatically modified model pectins with varying amounts of demethylation were produced and structure-functional analysis performed to determine yield stress, modulus, viscosity, block size and block number of demethylation, and how these properties relate to gelation and suspension characteristics and ion exchange properties. A commercially scalable process was developed and optimized to steam strip and recover limonene from citrus processing waste followed by simultaneous enzymatic hydrolysis and fermentation for biofuel ethanol production. Incorporation of simultaneous saccharification and fermentation to produce ethanol from citrus peel waste has allowed a dramatic decrease in the amount of enzymes required and a preliminary economic analysis suggests the process is close to being economically feasible. Further development of co-products from non-fermentable components in citrus waste are still needed. Saccharomyces cerevisiae and Kluyveromyces marxianus were evaluated as fermentation organisms, S. cerevisiae giving slightly better ethanol yield. Replaced by bridging project 6621-41000-010-00D.

6.Technology Transfer

Number of Active CRADAs1

Review Publications
Zhou, W., Widmer, W., Grohmann, K. 2008. Developments in ethanol production from citrus peel waste. Proceedings of Florida State Horticultural Society. 121:307-310.

Cameron, R.G., Luzio, G.A., Widmer, W.W., Iqbal, M. 2008. Biosorption properties of citrus peel derived oligogalacturonides, enzyme-modified pectin and peel hydrolysis residues. Proceedings of Florida State Horticultural Society. 121:311-314.

Luzio, G.A. 2008. Microwave release of pectin from orange peel albedo using a closed vessel reactor system. Proceedings of Florida State Horticultural Society. 121:315-319.

Cameron, R.G., Goodner, K.L., Luzio, G.A., Williams, M.K. 2008. Demethylation of a model homogalacturonan with the salt-independent pectin methylesterase from citrus: I. Effect of pH on demethylated block size and distribution. Carbohydrate Polymers. 70:287-299.

Last Modified: 4/17/2014
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