Location: Citrus and Other Subtropical Products Research
2022 Annual Report
Objectives
Objective 1: Establish commercially usable chemical and sensory characteristics of new citrus, strawberry, and avocado genotypes and new crops (microgreens) from subtropical and tropical climates.
Sub-Objective 1a: Develop chemical and sensory profiles of Citrus hybrids tolerant to citrus greening disease or Huanglongbing (HLB).
Sub-Objective 1b: Identify chemical and sensory characteristics for Florida-grown (avocado, strawberry, peach) and new crops (microgreens, tropical fruit) adapted to tropical/subtropical regions.
Objective 2: Enable real-time, commercial pre- and postharvest treatments to optimize shelf life of new genotypes and new crops using packaging, coatings, aqueous treatments, sanitizers, maturity markers and/or addition of flavor modulators.
Sub-Objective 2a: Develop methods to mask undesirable bitterness in orange and other citrus juice using flavor modulators.
Sub-Objective 2b: Develop novel deliveries of antimicrobial volatiles and/or plant essential oils using microencapsulated beads and/or coating technology, combined or not with modified atmosphere packaging to prevent decay in packaged fruit.
Objective 3: Isolate and test biomarkers in fruits (citrus, small fruit) with unique taste, flavor and healthful qualities for better commercial management strategies.
Sub-Objective 3a: Identify the best flavor combinations for an ideal orange or citrus juice.
Sub-Objective 3b: Identify the best flavor combinations for an ideal fresh strawberry.
Sub-Objective 3c: Identify biomarkers in citrus with unique taste, flavor and healthful qualities.
Approach
Fruits from breeding programs will be evaluated for eating quality and storability using sensory evaluations, chemical and texture analyses. For citrus, hybrids tolerant to HLB will be considered for juice quality and blending, in addition to eating quality as fresh fruit. Other fruit will include strawberries, peaches, avocadoes, tropical fruit (papaya, vanilla). A new crop, microgreens, will be included in the evaluations. For citrus and strawberries, sensory and flavor data will be statistically modelled in order to establish either ideal fruit quality markers, or criteria for non-acceptability, that can be used by breeders during the selection process. Furthermore, for citrus, identification of chemical off-flavor/off-taste targets will serve as a basis to test various flavor modulators that could mask undesirable flavors in orange juice. Potential flavor modulators include modified proteins, peptides, or amino acid, and other chemical family molecules will be tested when available. For strawberries, models will be validated by reconstitution experiments. For peaches, samples will consist of a diversity of new and old cultivars, some obsolete while others having withstood a long commercial life. The chemical fingerprint will help breeders understand the differences among genotypes for continuous effort in breeding and selection of new cultivars. For tropical fruit and microgreens, all being new crops, data will be more exploratory and descriptive than hypothesis-driven. Postharvest evaluations will be performed to test new methods of delivery of volatile antimicrobials in the form of spray-dried slow release powder placed in small fruit (strawberries, blueberries) clamshells. Control of postharvest decay as well as residual taste of volatiles will be evaluated. In citrus, Diplodia stem-end rot, due to Lasiodiplodia theobromae, has become more prevalent in citrus infected by HLB. This project will evaluate pre- and post-harvest fungicide treatments to control Diplodia stem-end rot. Finally, this project will evaluate phytochemical biomarkers in orange juice that have biological activity in mammals. Many flavonoids in citrus have been shown to have beneficial effects in human chronic diseases. Metabolites of flavonoids fed to experimental animals were previously extracted and isolated from various organs (liver, kidneys); they remain to be identified and quantified. Furthermore, their bioactivity will be evaluated in in vitro tests with emphasis on inflammation.
Progress Report
ARS scientists at Fort Pierce, Florida, harvested thirty two citrus hybrids from the USDA Whitmore Foundation research farm (Leesburg, Florida), and from the USDA research farm on Picos Rd. (Fort Pierce, Florida). Some hybrids were harvested multiple times. Two projects were covered during the 2021-2022 season: 1) evaluating citrus hybrids tolerant to Huanglongbing for quality as fresh or processed fruit, and 2) phenotyping a population of citrus hybrids to correlate with genotype (collaboration with ARS Breeding Insight). Under project 1), fruit was washed, sanitized per protocol, juiced and the juice was frozen. Frozen juice from the previous season was prepared for sensory evaluation by organizing take-home taste panels during the Covid maximized telework. Taste panels were performed by panelists in their homes after a few virtual “Zoom” sessions were organized to review tasting protocols. Frozen samples from the previous season were chemically analyzed for flavor volatiles, sugars, acids and bitter limonoids content. Initial testing of blending new hybrids with standard cultivars used commercially for juice was performed. Hybrids selected for those blends were based on high sugar and low acid with the goal of improving flavor of standard Valencia or Hamlin juice severely affected by Huanglongbing. Under project 2), fruit were juiced in the field and the juice was analyzed in the lab for soluble solids, titratable acidity and volatiles.
Strawberry selections from the University of Florida breeding program were harvested, juiced and frozen for later analysis of sugars, acids, and volatiles. Fresh fruit could not be evaluated by the trained taste panel because of Covid restrictions (limited number of people being present at the same time in the laboratory in one day).
Avocados from the ARS varietal collection were harvested in the Fall and allowed to ripen at room temperature (20 °C). Fruit was evaluated for ripeness and seeds from the best selection saved for future breeding.
For the analysis of peach volatiles, 43 hybrids or commercial cultivars, from ARS Byron research station were analyzed. The ARS collaborator was sent the raw data for analysis.
Analysis of volatiles of microgreens of 20 plant species was completed. All Brassicaceae species (mustard, arugula, cabbage) were similar in the major volatile components, while species in the Lamiaceae family were discriminated by their volatile profiles. A manuscript is in preparation.
Six sugar apple selections harvested in the previous reporting cycle were analyzed for sugars, acids and volatiles. Fast Pig variety had high fruit and tropical fruit flavor in 2019, which could be explained by higher content of vanillin, benzaldehyde and ethyl butanoate, as well as linalool and hexanal. Gonave also had a peculiar flavor perceived by panelists, likely explained by higher content of terpenes and aldehydes. Gonave also had the highest soluble solids content in comparison with the other five selections.
Several fungicidal materials were tested pre-harvest by University of Florida collaborator on mature grapefruit trees to prevent post-harvest decay due to Diplodia stem-end rot (SER) caused by Lasiodiplodia spp. Two fungicides significantly reduced fruit decay, while an essential oil (thyme oil) had no effect. Post-harvest applications of gaseous chlorine dioxide (ClO2) effectively reduced Diplodia SER on inoculated fruit; however, phytotoxicity was observed as peel injury when ClO2 doses exceeded 1 g per kilo of fruit. In the end, treatments of gaseous fast release CO2 in an enclosed chamber at a rate of 1 g per kilo of fruit and duration of 8 hours effectively controlled Diplodia SER in grapefruit.
Several experiments were performed under Objective 2, “Enable real-time, commercial pre- and postharvest treatments to optimize shelf life of new genotypes and new crops”:
Winter melon is a new crop that can be harvested from May to February in Florida. In this study, a round waxy type winter melon cultivar was grown in the field by ARS collaborator using anaerobic soil disinfestation (ASD) or conventional fertilizer alone as the control treatment. Fruit were harvested in late January and stored at 20 °C for 4 months to cover the gap from February to May. The juice was processed on day 1 and day 120. Storing fruit for 120 d did not change the juice yield or volatile profile. ASD increased fruit yield, juice yield production and cloud stability, and decreased off-odor volatiles.
Jicama, another new crop, cultivars ‘222’ and ‘Marde Ross’, were planted by ARS collaborators. ASD treatment and cultivation technique on trellises were tested for the effects on crop growth and quality. Juice was extracted from the roots harvested after 81, 108 and 150 days of growth. Samples were prepared to analyze sugars, acids, functional nutrients, and volatiles.
Experiments were performed by ARS scientists at Fort Pierce, Florida, to confirm how optimized spectra LED lights in greenhouse improve volatile and nutritional quality of microgreens. The greenhouse work was completed, and samples collected for volatile, nutritional and metabolomics analysis.
Methyl anthranilate is believed to increase fruity flavor in strawberries, and has been the target of breeding programs for some years. However, flavor is complex and the level at which methyl anthranilate improves strawberry flavor is unknown. To test this hypothesis, an experiment was conducted by Texas Woman’s University collaborator. A deodorized strawberry puree was standardized for sweetness and spiked with 30+ volatile compounds to create an “ideal” strawberry flavor. Methyl anthranilate was then added at 0.1, 0.2, 0.4, and 0.8 parts per million. A trained panel found that methyl anthranilate increased fruity, grape-like, floral, candy, and ripe flavor, regardless of methyl anthranilate levels.
In an effort to discover non-limonoid bitter compounds in citrus, orange juice severely affected with Huanglongbing was prepared using several extraction and fractionation techniques. Analytical and semi-preparative HPLC provided three candidate compounds with clean UV spectra and mass spectra. Specialized software will enable us to calculate the chemical compositions of major fragment ion, and thus assist in proposing logical structures of the compounds. The bitterness of these compounds will need to be confirmed by taste, and ultimately enough to be purified for chemical structure verification.
In order to identify off flavor in a newly released apple cultivar, ‘Cosmic Crisp’, a taste panel was trained at collaborator’s site, ARS in the State of Washington. Samples with off flavor were taken and collaborator is analyzing the fruit by gas chromatography and high performance liquid chromatography to identify putative compounds that are responsible for this off flavor.
To further understanding of flavor metabolism in fruit, experiments were designed in collaboration with a professor at Osaka Prefecture University (Japan). Banana pulp was exposed to volatile precursors to demonstrate the role of aldehyde dehydrogenase (ALDH) in fruit volatile metabolism. This enzyme had been found in animals and microbess, and also in some plants. However, to our knowledge, there was no report on the role of ALDH in volatile flavor metabolism in fruits.
Accomplishments
1. A low calorie juice from winter melon fruit. The rise in diabetes and obesity has made some consumers aware of foods with high sugar content, including fruit juices. Winter melon is an annual tropical vine and grows large fruit (10-50 lbs.) with greater than 90% water and less than 2.5% sugar. In collaboration with a CRADA partner, ARS researchers at Fort Pierce, Florida, determined that a round waxy type fruit was providing juice with superior quality, and that acceptability increased with decreasing pulp content. Scientists perfected several methods to remove undesirable sulfur and green/grass volatile compounds that imparted too much off-odor to the juice. Juice processors will now have the option of using winter melon in juice blends with apples, oranges, grape or other fruits to decrease overall sugar and caloric content. This low brix juice will provide an alternative for consumers concerned about juice sugar intake.
Review Publications
Zhong, T., Zhang, J., Sun, X.N., Kou, J., Zhang, Z., Bai, J., Ritenout, M. 2021. The potential of gaseous chlorine dioxide for the control of citrus postharvest stem-end rot caused by Lasiodiplodia theobromae. Plant Disease. 105:3426-3432. https://doi.org/10.1094/PDIS-02-20-0407-RE.
Villavicencio, J.D., Zoffoli, J., Plotto, A., Contreras, C. 2021. Aroma compounds are responsible for an herbaceous off-flavor in the sweet cherry (Prunus avium L.) cv. Regina during fruit development. Agronomy. 11(10):2020. https://doi.org/10.3390/agronomy11102020.
Oliveira Filho, J., Miranda, M., Ferreira, M.D., Plotto, A. 2021. Nanoemulsions as edible coatings: A potential strategy for fresh fruits and vegetables preservation. Foods. 10:2438. https://doi.org/10.3390/foods10102438.
Cruz, M., Neves, C., De Carvalho, D., Colombo, R., Bai, J., Yada, I., Leite Jr., R., Tazima, Z. 2021. Five rootstocks for ‘Emperor’ mandarin under subtropical climate in Southern Brazil. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2021.777871.
Karantzi, A., Kafkaletou, M., Tsaniklidis, G., Bai, J., Christopoulos, M., Fanourakis, D., Tsantili, E. 2021. Preharvest foliar salicylic acid sprays reduce cracking of fig fruit at harvest. Applied Sciences. https://doi.org/10.3390/app112311374.
Miranda, M., Sun, X.N., Marin, A., dos Santos, L., Plotto, A., Bai, J., Garrido Assis, O.B., Ferreira, M.D., Baldwin, E. 2022. Nano- and micro-sized carnauba wax emulsions-based coatings incorporated with ginger essential oil and hydroxypropyl methylcellulose on papaya: Preservation of quality and delay of Post-harvest fruit decay. Food Chemistry. 13. Article 100249. https://doi.org/10.1016/j.fochx.2022.100249.
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.
Christopoulos, ., Gkatzos, D., Kafkaletou, M., Bai, J., Fanourakis, D., Tsaniklidis, G., Tsantili, E. 2022. Edible coatings from Opuntia ficus-indica cladodes alongside chitosan on quality and antioxidants in cherries during storage. Foods. https://doi.org/10.3390/foods11050699.
Bai, J., Jordan, M., Li, J. 2022. Metabolism of fruit volatile organic compounds. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2022.873515.
Ueda, Y., Bai, J., Ihara, H., Imahori, Y., Wendakoon, S., Zhao, W., Tsantili, E., Chamber, A. 2022. Functional characteristics of aldehyde dehydrogenase and its involvement in aromatic volatile biosynthesis in postharvest banana ripening. Foods. 11(3):347. https://doi.org/10.3390/foods11030347.
Sater, H., Ferrao, F., Olmstead, J., Munoz, P., Bai, J., Hopf, A., Plotto, A. 2021. Exploring environmental and storage factors affecting sensory, physical and chemical attributes of six southern highbush blueberry cultivars. Scientia Horticulturae. 289:110468. https://doi.org/10.1016/j.scienta.2021.110468.
Xi, Yu, Y., Li, Q., Yan, J., Baldwin, ., Plotto, A., Rosskopf, E.N., Hong, J.C., Bai, J., Li, J. 2021. Effects of harvest maturity and exposure to refrigeration and blanching of ripe fruit on volatile profiles of ‘Tasti-Lee’ tomatoes. Foods. 10:1727. https://doi.org/10.3390/foods10081727.
