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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

2012 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 capital investment cost, and a breakdown of operating and capital cost estimates.


3.Progress Report:
Objective 1: All pilot scale equipment (pretreatment system, fermentation tank, distillation tower, boiler, and associated control systems) and analytical equipment was moved, reinstalled, and tested to be in satisfactory working condition at the new Fort Pierce facility. Additionally, tests were performed on extraction and recovery of pectic fragments from citrus waste as a possible co-product with ethanol production. Effective extraction of pectin and/or pectic fragments significantly diluted fractions containing fermentable sugars and requires a concentration step of the sugar fraction prior to fermention to ethanol.

Objective 2: Progress was made pertaining to value-added research into the polysaccharide structures of citrus byproducts. Pectin methylesterase present in a commercial papaya enzyme extract was used to demethylate a model pectin molecule. The resulting modifications to the pectin nanostructure have been characterized. The results indicate that reaction conditions (i.e., pH and enzyme/substrate ratios)affect the introduced nanostructural motifs.


4.Accomplishments
1. A predictive model for the relationship between pectin nanostructure and rheological properties was developed. Pectin functionality is dependent on the distribution of charges along its polymeric backbone. Random versus ordered distribution affects its functionality and variations in the degree or order within the polymer chain also affect rheology. Pectin charge distributions were modified using enzymes or chemical processes and technology was developed to statistically describe the nanostructural modifications introduced. Rheological testing of the engineered pectins enabled us to develop a predictive model relating the nanostructural parameters to rheological properties. This accomplishment has the potential to allow producers of hydrocolloids greater control over texture, gel formation and viscosity of pectin in formulations targeted for industrial applications.


Review Publications
Milokva, V., Kamburova, K., Cameron, R.G., Radeva, T. 2011. Complexation of ferric oxide particles with pectins of ordered and random distribution of charged units. Biomacromolecules. 13:138-145.

Grohmann, K., Cameron, R.G., Kim, Y., Widmer, W.W., Luzio, G.A. 2012. Extraction and recovery of pectic fragments from citrus processing waste for co-production with ethanol. Journal of Chemical Technology & Biotechnology. DOI: 10.1002/jctb.3859.

Last Modified: 7/28/2014
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