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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

2020 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
ARS 2015 – 2020 project plan in Ft. Pierce, Florida, terminated in June 2020. ARS researchers at Ft. Pierce, Florida, made advances on the recovery of value added co-products from various forms of biomass, with an emphasis on citrus juice processing side streams (Objective 1). The focus was on using a pilot scale, continuous steam explosion system to release sugars, pectic hydrocolloids, phenolic compounds, essential oils, and volatile aromas and flavors from their intracellular entrapment. Recoveries of these compounds was accomplished using a simple water wash of the steam exploded biomass, or trapping volatiles by directing released steam to a water cooled condenser. In addition to citrus biomass, several other types of biomass were treated by steam explosion for the recovery of value added co-products. They include sugar beets, banana residues and olive leaves. Recovered pectic hydrocolloids from juice extracted citrus fruit peel were utilized as encapsulating agents (Objective 2B) for an antimicrobial essential oil used as a controlled-release decontaminator in food and nutraceutical processing industries. Additionally, the recovered pectic hydrocolloids were used to encapsulate tangeretin, a bioactive polymethoxylated flavone. The effect of processing conditions of temperature and time-at-temperature on the release and recovery of co-products were explored using a batch steam explosion system. These conditions were tested on fresh sweet orange and grapefruit peel, as well as stabilized lime pectin peel. A subordinate project on the effect of fruit maturity on the recovery of value added co-products from citrus processing biomass has completed its second season for fresh peel, and peel has been dried for comparison of the recovery of pectin, sugar and flavonoids from both. This is related to Objective 1 in that it provides baseline data on pectin quality and yields from US orange varieties. ARS researchers at Ft. Pierce, Florida, conducted an additional study on the effects of citrus greening disease (HLB) on the macrostructural properties of pectin from HLB infected and healthy grapefruit peel. This also provides baseline data on the quality properties of pectin from US citrus. A research agreement with an industry collaborator has been established for testing gelling and water holding capacity of fibers from steam exploded orange juice processing residues (Objective 1). Equipment for fiber analysis is currently being procured and will be used to test for total, dietary and insoluble fiber in steam exploded orange juice processing residues. Conversations with an international collaborator on life cycle analysis have been initiated and we are currently developing a survey for local orange juice processors to complete. This will contribute to the life cycle and economic analysis of conventional orange juice processing feed mill operations compared to using steam explosion. Preliminary studies on the use of immunological methods to easily and rapidly characterize pectin structure and functional properties have been initiated (Objective 3). Using an immunochromatographic method we have been able to discriminate between pectins having different amounts and distribution of charge.

1. Production of gluten-free fiber from citrus juice-extracted fruit peel. When citrus fruits are processed into juice the material that remains is converted into low monetary value animal feed and molasses, in a process that uses the most energy at the processing plant, and is quite costly. This process destroys compounds within the residues that, if recovered, can be used to make high value products such as gluten-free fiber. Steam explosion systems have been used in the past by ARS scientists in Fort Pierce, Florida, to recover valuable compounds from orange juicing residues but never from grapefruit juicing residues, and fibers have not been recovered previously either. As part of a research agreement with an industry partner, ARS scientists in Fort Pierce, Florida, conducted steam explosion on grapefruit juice processing residues and successfully recovered fiber, pectin, phytonutrients, and essential oils. Scientist continue to interact with stakeholders interested in using steam explosion on an industrial level for processing grapefruit juice processing residues at their facilities for the production of fiber.

2. Effect of citrus greening disease on citrus pectin. Citrus pectin, from citrus fruit peel, comprises approximately 85% of the commercial pectin market used for foods, pharmaceuticals and personal care products (greater than one billion USD per year). Citrus greening disease is known to affect citrus fruit development and quality. It was unknown if citrus greening disease had any effect on citrus pectin structure or functionality. Using field grown citrus (infected with greening disease) and citrus grown under protective screen (healthy), ARS researchers at Ft. Pierce, Florida, extracted and characterized pectin from both types of fruit using commercial pectin extraction methods. The structural and functional properties of these pectins were compared, and it was found that greening disease did affect the properties of citrus pectin, potentially necessitating formulary modifications to maintain desired functionalities.

Review Publications
Pitino, M., Sturgeon, K., Dorado, C., Shatters, R.G., Cano, L.M., Manthey, J.A., Rossi, L. 2020. Quercus leaf extract contains and suppresses HLB disease. Nature Plants. 148:70-79.