Location: Citrus and Other Subtropical Products Research
2022 Annual Report
Objectives
Objective 1: Enable the commercial use of steam explosion fibers from citrus fruit peel for food applications.
Objective 2: Resolve unknown microbial modifications of steam exploded citrus peel flavonoids for conversion into high-value byproducts.
Objective 3: Conduct a novel immunologically-based assessment of citrus pectin for use in raw and processed foods, and industrial products.
Approach
One of the greatest opportunities for reducing waste in the processing of agricultural commodities is the conversion of these materials to high value co-products. At an average proportion of 45% of fresh citrus fruit weight the amount of the fruit biomass (peel) that is directed towards low value side streams is currently (2018-2019) 9.55 · 106 metric tons worldwide and 1.51 · 106 metric tons domestically. The domestic side stream from juice production would contain 1.33 · 105 metric tons of gluten-free fiber, 3.5 · 105 metric tons of pectic hydrocolloids and 6.8 · 104 metric tons of phenolics and flavonoids. We will enable a technology for isolating a gluten free fiber from citrus juice processing side streams that can be used to impart beneficial properties to food when used as an ingredient including improved nutritional value and water retention without negatively impacting color and flavor. Also, we will enable a technology for microbial modifications of the flavonoids in the water washes of steam exploded citrus juice processing side streams (i.e. peel) so that new higher value compounds will be recovered. This will enhance the value of the flavonoids that are already commercialized. But the steam explosion methods will allow easier and more complete recoveries of these flavonoids than currently available. Newly produced compounds will serve as starting points for further products, as well as for further product development. Anticipated products relate to creating a process to convert food waste (fruit peels, pulp, and pomace) into value-added healthful bioactive ingredients. Finally, we will enable a rapid immunological based method to define, measure, and preserve/enhance/reduce factors that impact quality and marketability of the structural/functional properties of pectin. Anticipated products relate to creating a novel methodology to enhance or predict the quality and utilization of agricultural products providing information to assess product quality and to detect factors that diminish quality.
Progress Report
ARS scientists in Fort Pierce, Florida, completed Steam explosion on samples of the citrus juice processing side stream using three temperatures/pressures and four hold times, in order to optimize process conditions. Water holding capacity, color, and particle size analyses have been completed on dried and size reduced steam explosion samples as well as an untreated and a commercial sample as controls. Statistical analysis of the color data, analysis of hydrolyzed sugars and oil holding capacity analysis are underway. Total dietary fiber, viscosity, and surface area measurements are still needed for addition to a draft of the manuscript that is currently in progress.
A conversion of low-value phenylpropanoids and flavonoids into high-value anthocyanidins for food use was initiated. In order to optimize conditions for this conversion we obtained many of the required plasmids to generate mutant bacteria capable of catalyzing the series of needed biosynthetic steps. However, the plasmids needed for the last step are unavailable. An alternate approach using bacterial species that will allow us to proceed has been found. Some bacteria were transformed but few were viable after prolonged storage at -80 degrees Celsius.
In order to fully characterize the nanostructural motifs recognized by anti-pectin antibodies, ARS scientists in Fort Pierce, Florida, have initiated studies to elucidate the epitopes to which the antibodies bind. ARS scientists have focused on the widely used antibody JIM7, and have successfully used it in an Enzyme-Linked Immunosorbent Assay that is required to evaluate the results from epitope protection experiments. JIM7 has been cross-linked to a magnetic bead/Protein L complex to enable the recovery of the protected epitope. ARS scientists have optimized the hydrolysis of unprotected pectin in preparation for removing those portions of the pectin molecules not protected by JIM7 binding. Preliminary trials to recover the protected epitope are under way.
A novel sandwich format lateral flow assay or immunochromatographic assay has been explored for the assessment of pectin’s structural/functional properties. The binding preferences and the sensitivities of anti-pectin homogalacturonan antibodies for pectin in a sandwich lateral flow assay were evaluated. The components and parameters of the lateral flow assay have been optimized for pectin samples. The multiplex lateral flow assay includes three different capture antibodies fixed on a test strip, and two detection antibodies labeled with different colors of Gold NanoParticles/NanoUrchins to flow through the test strip with a pectin sample. The developed lateral flow assay is able to discern pectin’s degree and pattern of methyl-esterification. The method has been validated by testing series of model pectins.
Accomplishments
1. System for rapid assessment of pectin structural/functional properties. Current methods for pectin functionality assessment are time-consuming and laborious. ARS researchers at Fort Pierce, Florida, have submitted a patent application for a novel, easy to use lateral flow assay system to discriminate different functional forms of pectins. Different from any of the previous lateral flow assays that detect one or more targets in a sample, the developed method is a user-friendly, sensitive and robust analytical tool for pectin structural/functional property assessment. Current pectin analysis, such as Degree of Methylesterification or Standard Acid in Glass tests, can take anywhere between 4-24 hours and are very cumbersome and operator dependent. The newly developed lateral flow assay can be used with minimal operator-dependent steps at any point in the pectin production/utilization process chain, and is completed in less than 10 minutes. This technology can provide pectin providers and end users a rapid, easy to use analytical tool to assess pectin structural properties that are related to its functionality.
Review Publications
Dorado, C., Bowman, K.D., Cameron, R.G., Manthey, J.A., Bai, J., Ferguson, K.L. 2021. Steam Explosion (STEX) of citrus x Poncirus hybrids with exceptional tolerance to Candidatus liberibacter asiaticus (CLas) as useful sources of volatiles and other commercial products. Biology. 10:1285. https://doi.org/10.3390/biology10121285.
Sun, X.N., Baldwin, E., Manthey, J.A., Dorado, C., Rivera, T., Bai, J. 2022. Effect of preprocessing storage temperature and time on the physiochemical properties of winter melon juice. Journal of Food Quality. 2022. Article 3237639. https://doi.org/10.1155/2022/3237639.
