2007 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.
Analysis and optimization of citrus waste to ethanol fermentation: Determined flow characteristics of the hydrolyzed and fermented citrus waste treated under low enzyme loads and designed and ordered a stripper to remove ethanol from the fermented product which resists fouling and has a flexible configuration for testing and optimization of ethanol removal from fermented citrus waste. This was necessary because although pretreatment and fermentation steps for citrus processing waste to produce ethanol in a commercially scalable process for use as a biofuel has been demonstrated, to reduce enzyme costs, the final fermented product is too viscous to be handled by distillation equipment used by the corn ethanol industry. Preliminary analysis of economics of the process to convert citrus waste to ethanol resulted in an estimated production cost of $1.25 per gallon of ethanol when limonene is recovered and sold as a co-product. Without limonene recovery the estimated cost per gallon of ethanol from citrus waste increases to $1.79 per gallon. This accomplishment is relevant to NP 306, "Quality and Utilization of Agricultural Products", Component 2b, "New Uses for Agricultural By-products".
Separation, purification and characterization of pectin oligomers for industrial use: Affinity chromatography columns were made and are being used to separate and purify the four pectin methylesterase enzymes from citrus processing waste. The four citrus methylesterase enzymes are being collected, accumulated and used in pectin structure modification and functional characterization studies. Using one of the thermally labile pectin methylesterase enzymes, a series of enzymatically modified model pectins with varying amounts of demethylation were produced and structure-functional analysis of the series performed to determine yield stress, modulus, viscosity, block size and block number of demethylation, and how these properties related to gelation and suspension ability characteristics useful for design of industrial pectin products. Optimum calcium concentration needed to maximize suspension aid properties was also determined for new product development. These properties of the thermally labile pectin methylesterase are being used to probe and define the enzyme mode of action for comparison with other citrus pectin methylesterases. Enzymatically modified pectins with varying amounts of demethylation were also produced using the thermally tolerant pectin methylesterase citrus enzyme and their structure-functional properties are being examined for comparison. This accomplishment is relevant to NP 306, "Quality and Utilization of Agricultural Products", Component 2b, "New Uses for Agricultural By-products".
5.Significant Activities that Support Special Target Populations
Development of high value co-products from the waste produced by the citrus juice processing and fresh cut fruit industry will improve crop value and increase profits processors and growers of these specialty crops. Producing a renewable bio-fuel from fruit processing waste will also help reduce US dependence on foreign energy.
|Number of active CRADAs and MTAs||1|
|Number of invention disclosures submitted||1|
|Number of patent applications filed||2|
|Number of non-peer reviewed presentations and proceedings||9|
|Number of newspaper articles and other presentations for non-science audiences||4|
Wilkins, M.R., Widmer, W.W., Grohmann, K., Cameron, R.G. 2006. Hydrolysis of grapefruit peel waste with cellulase and pectinase enzymes. Bioresource Technology. 98:1596-1601.
Hunt, J.J., Cameron, R., Williams, M.A.K. 2006. On the simulation of enzymatic digest patterns: The fragmentation of oligomeric and polymeric galacturonides by endo-polygalacturonase II. Biochimica et Biophysica Acta. 1760:1669-1703.