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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Research Project #429418

Research Project: Enhancing Utilization of Citrus Processing Co-products

Location: Citrus and Other Subtropical Products Research

2016 Annual Report

1. Enable, from a technological standpoint, new commercial products from pectic hydrocolloids derived from citrus processing. 2. Characterize and quantify bioactive flavonoid compounds from byproducts of citrus processing, determine their in vivo pharmacokinetics and bioavailability; and enable a new commercial delivery of bioactive flavonoids in food and feed by encapsulation with pectic hydrocolloids. 2A. Characterize and quantify bioactive flavonoid compounds from byproducts of citrus processing, determine their in vivo pharmacokinetics and bioavailability. 2B. Enable a new commercial delivery of bioactive flavonoids in food and feed by encapsulation with pectic hydrocolloids. 3. Enable a novel immunologically-based assessment of structural quality and functional properties of citrus pectin in raw and processed foods and industrial products.

Experimentation is required to determine the necessary time, temperature and concentration conditions to enable pilot-scale functionalization of the released pectic hydrocolloids from steam explosion of peel material. Response surface methodology will be used to determine these parameters using analytical methods. Consequently, the variables of temperature, time and concentration of steamed peel waste will be manipulated to determine optimal conditions for functionalizing the released pectic hydrocolloids. Functionality will be assessed by measuring resulting calcium induced viscosity using a concentric cylinder viscometer and/or oscillatory measurements using a stress controlled rheometer and related to final degree of methylation, charge distribution and molecular weight (MW) of the modified pectic hydrocolloids. Compositional analysis and structural properties will be characterized by Size Exclusion Chromatography (SEC) coupled to Multi Angle Laser Light Scattering (MALLS), Refractive Index (RI) or Conductivity Detectors; High Performance Anion Exchange Chromatography (HPAEC) coupled to an Evaporative Light Scattering Detector (ELSD) or Pulsed Amperometric Detector (PAD) and enzymatic/chemical methods. Composition of the polysaccharides present in peel wash after steam explosion will be determined by enzymatic hydrolysis and liquid chromatography with electrochemical detection. Use of polysaccharide specific enzymes (arabinase, arabinofuranosidase, etc.) will allow for determination of the contribution of individual polysaccharides. Pectin populations will be examined via interaction with antibodies that bind to specific structural epitopes on individual pectin molecules. Pectin populations will be produced by enzymatic and/or chemical methods that contain various sizes of ionically-charged or neutral, methyl-protected domains. Elucidation of the modes of anti-inflammatory actions of the health promoting compounds in citrus byproducts will be accomplished by characterizing their metabolites and pharmacokinetics, and elucidating their biochemical actions at the cellular level using in vitro assay microplate technologies. These biochemical actions subsequently will be investigated in animal trials conducted through collaborations with other research laboratories or through commercial contract research laboratories. The research will first require the isolation and chemical characterization of mammalian metabolites of the test citrus byproduct compounds, and these isolations will be achieved through established chromatographic and HPLC-MS techniques.

Progress Report
Citrus and many other agricultural waste biomasses contain a variety of potentially value added components. Citrus juice processing wastes contain relatively large amounts of both pectic and phenolic (flavonoids) materials. Pectic materials possess inherent functionality as a viscosity modifier, gelling agent, hydration control agent or ion capture agent while phenolic compounds represent numerous bioactive compounds. A constraint limiting their wider application has been the ease of recovery from their cellular entrapment. We have explored “Green”, low cost methods to recover these valuable components from citrus peel and other agricultural biomass. During the reporting year a continuous, pilot scale, steam explosion process capable of releasing pectic hydrocolloids and phenolics from citrus processing waste and even whole Huanglongbing-related culled or dropped citrus fruit was demonstrated. Preliminary trials also showed that this continuous steam explosion process could be used to process other agricultural crops. Sugar beets were resized and steam explosion was used to liquefy the biomass, releasing both fermentable sugars and pectic materials. Preliminary fermentations demonstrated nearly equivalent ethanol yields from steam-exploded sugar beet biomass as compared to homogenized, enzyme hydrolyzed sugar beet biomass. As with citrus biomass, sugar beet pectin was recovered from the steam exploded tissue using a simple water wash. Additionally, the pectic material released from citrus biomass was characterized in regard to its structural and functional properties. Results indicate some molecular fragmentation that is likely due to the pressure and temperatures used. It was demonstrated that in-situ chemical functionalization of the pectic material was possible using calcium capturing alkaline reagents. Following functionalization the steam-exploded biomass could be dried and milled. Conversely the pectic material could be isolated from the steam-exploded biomass using a simple water wash and subsequently chemically functionalized using enzymatic or alkaline reagents. This material could be precipitated and freeze dried. Structural and functional properties of pectic material from steam exploded citrus fruit tissue were compared to those from pectin obtained using conventional hot acid extraction. An increased number of subpopulations was evident in steam exploded pectin and the majority of the molecules were of a smaller size. Functional properties associated with molecular size, i.e. rheological and viscosity, were reduced in steam exploded tissue. Even so, especially for pectic material isolated from the remaining steam exploded solids, significant functionality could be introduced by chemical modification. Production and characterization of structurally and functionally distinct model pectin populations for immunological screening was initiated. A series of pectins with differing degrees of methylesterification are being characterized for nanostructural properties related to charge distribution.

1. Release and recovery of pectic hydrocolloids and phenolics from HLB-related preharvest dropped citrus fruit. Making use of prematurely dropped fruit from huanglongbing disease-affected trees. Huanglongbing is a bacterial disease spread by sucking insects that is devastating U.S. citrus production. Trees die prematurely and yields are decreased. Additionally, the preharvest dropping of maturing fruit has greatly increased. No value is gained from this dropped fruit. ARS scientists at Fort Pierce, Florida, demonstrated that valuable chemicals could be recovered from these fruit using a pilot scale, continuous, steam-explosion process. This process could potentially recover lost value to both citrus growers and juice processors as well as providing very large amounts of valuable coproducts from a wasted resource.


Review Publications
Cameron, R.G., Chau, H.K., Manthey, J.A. 2016. Continuous process for enhanced release and recovery of pectic hydrocolloids and phenolics from citrus biomass. Journal of Chemical Technology & Biotechnology. 91:2597-2606. doi: 10.1002/jctb.4854.