Location: Citrus and Other Subtropical Products Research
2025 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
This is the final report for Project No 6034-41430-007-000D
Under Objective 1.
Sub-objective 1a. Over fifty citrus genotypes showing various degrees of tolerance to the citrus greening disease (Huanglongbing or HLB) were evaluated over the course of this project cycle. Hybrids including oranges, mandarins and citrus hybrids with Poncirus trifoliata introgressions (a.k.a. ‘poncirus hybrids’) were harvested multiple times and analyzed for volatile and non-volatile (sugars, acids, limonoids, flavonoids) components. Through statistical modeling using volatile and sensory data, we showed that esters were necessary contributors to orange flavor, distinguishing from mandarin flavor.
Further analysis identified a key gene in the ester pathway and its expression was validated in citrus. A DNA marker was developed which could be used in marker-assisted breeding. One mandarin hybrid was released from the ARS lab using data from this project.
Three “forgotten” varieties of oranges, Donaldson, Tresca, and Tobias, planted at the Florida ARS facility 30 years ago appeared to be tolerant to HLB. These varieties as well as two recent ARS releases, SunDragon and SunGlo, were juiced and pasteurized under commercial conditions and compared to the commercially grown but HLB sensitive Hamlin and Valencia. Taste tests revealed that Tresca was indistinguishable from Hamlin when mixed in a 40:60 ratio with Valencia, as is typically done by the juicing industry. Donaldson produced juice that was slightly different from Hamlin. However, when it was cold pasteurized by high pressure processing (HPP), its flavor was very similar to a good Hamlin juice prior to HLB (HLB imparts bitterness and off flavor to juice made from infected oranges). SunDragon and SunGlo juices were cold pasteurized and blended (40:60) and given to attendees of the Ag Outlook event in Virginia with great success.
Lemons and mandarins present potential for Florida citrus growers as they are more tolerant to HLB than oranges and grapefruit. Six ARS mandarin hybrids were harvested and evaluated in the fall of 2023 and 2024. Three hybrids stood out for having easy-peel and seedless fruits with excellent flavor. With respect to lemons, 8 cultivars and two commercial varieties were analyzed for juice content, volatiles and non-volatile compounds. One cultivar, Monachello, had high soluble solids content (SSC) and high ester volatiles. Another cultivar stood out with high alcohol and presence of esters. This study provides information to growers and processors who want to plant lemons and utilize the fruit for juicing potential.
Sub-objective 1b. In a continuing collaboration with the University of Florida strawberry breeder, ARS researchers analyzed soluble solids, titratable acidity and volatile content in strawberry hybrids at an advanced stage of selection and performed sensory evaluation by a trained panel. As a result, two hybrids were released, Florida Pearl® ‘FL 16.78-109’ Pineberry, a white fruited variety with unique appearance and flavor (released in 2022) and Florida Medallion™ ‘FL 16.30-128’ Strawberry, a red early ripening fruit with outstanding flavor (released in 2025).
Avocadoes from the Florida USDA, ARS collection were harvested every 3 to 4 weeks from August 2024 to March 2025 and let ripen at room temperature. Fruit firmness, color and weight loss were measured every other day. When fruit had reached firmness of 15 N, they were transferred to 10 °C for taste panel evaluation and dry matter collection within 2 or 3 days. In general, Hass-like varieties or hybrids were preferred over the West Indian types. Some varieties were more sensitive to postharvest decay, including Day, Ettinger, Gem, Simmonds and Zutano. A couple of selections from the USDA, ARS, appear promising for tree health, fruit quality and fruit set.
The USDA, ARS has a small collection of sugar apples (Annona squamosa). Taste panels and volatile analysis were performed earlier in this project cycle. A consumer taste panel was performed in 2024 to evaluate possible consumer acceptance of this tropical fruit unknown to many consumers. The fruit quality was well received.
Under Objective 2.
Sub-objective 2a. Work continued with CRADA partner to mask undesirable bitterness in orange and other citrus juices using flavor modulators. The partner kept adjusting the modulator quality and concentration using raw ingredients provided by ARS collaborator. The difficulty was to select juice that was not so bitter that nothing could improve its flavor. Work this season identified orange juice that was bitter and to which adding the flavor modulator showed significant improvement.
Sub-objective 2b. Blueberries and blackberries were packed in low-vented (LV) experimental clamshells with an opening ratio 6.43 times lower than in commercial (COM) clamshells and exposed to thymol, an antimicrobial/antifungal essential oil microencapsulated in a pectin-alginate matrix as a controlled-release system. During storage, the relative humidity within LV was higher and less variable than in COM clamshells, which led to a significant reduction in weight loss in both crops. Blueberry firmness, shriveling and marketability were positively impacted by storage in LV clamshells, and adding a microencapsulated thymol sachet in the packaging successfully reduced postharvest decay. Therefore, these two tools combined could be used to extend blueberry shelf life. However, the same strategies were ineffective for blackberry quality. This research underscores the importance of tailoring storage conditions, packaging design and handling methods to each specific fruit type.
Despite being a top commodity in the US, cultivating organic strawberries in Florida presents unique agronomic challenges, such as high disease pressure, subtropical climate and sandy soils. To overcome these hurdles, different agricultural by-products were used to achieve optimal carbon and nitrogen (C:N) ratios in an anaerobically disinfected (ASD) field. Fruit were harvested at commercial ripeness and analyzed for quality and nutritional value. While color and weight remained constant across treatments, metabolomic profiling revealed the effect of soil treatments on biochemical compounds within the fruit. Several amino acids, such as arginine and histidine, were more abundant in fruit grown at low C regardless of N levels. In contrast, arabinose, glutamine and glycine were significantly lower in high-N soil. Flavonoids showed a soil amendment-dependent accumulation, with higher taxifolin in soil with C and N availability, while sinensetin was less accumulated at high C levels. As organic production continues to expand, understanding metabolomic variations is essential for enhancing both environmental sustainability and market competitiveness of Florida grown organic strawberries.
In regards to Objective 3.
Sub-objective 3a. Mandarins or Poncirus-introgressed hybrids were blended with the traditional Valencia:Hamlin juice in proportion of 10% (maximum allowed by FDA rule to maintain an “orange juice” label), 15% and 20%. Trained panelists could detect the presence of mandarin flavor in juices containing 10% mandarin, but untrained panelists could not detect differences between Valencia:Hamlin juice and juice with up to 20% mandarin. These tests are useful as mandarins or Poncirus hybrids tolerant to HLB could complement the deficit volume in oranges processed by the juice industry. The orange juice industry has petitioned the FDA to increase the amount of mandarins in orange juice to 15%.
Sub-objective 3b. 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. Deodorized strawberry puree standardized with 30+ volatile compounds to create an “ideal” strawberry flavor was spiked with methyl anthranilate at 0.1 to 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.
Sub-objective 3c. Previous work by this group reported a correlation between the titer of Candidatus liberibacter asiaticus (Clas) – the presumed agent causing HLB - and sensory quality decline in oranges. This investigation was expanded to 123 samples including sweet oranges, mandarins, grapefruit and their hybrids, some with Poncirus trifoliata introgression - across five consecutive seasons. No direct correlation emerged between CLas titer quantified via qPCR and sensory attributes evaluated by trained panelists across genotypes, likely due to species-specific flavor profiles (e.g., “orange flavor” was higher in oranges, while bitterness and aftertaste were linked to grapefruit flavor). However, principal component analysis revealed that samples with low CLas titer clustered near positive descriptors (e.g., sweetness and orange flavor) and away from negative attributes, suggesting qPCR-based titer quantification could predict fruit quality across species.
Comprehensive metabolic analysis of citrus juice, oranges, mandarins, grapefruit, pummelo and Poncirus hybrids identified the flavonoids rhoifolin, apigenin and tricin in addition to the known limonoids (limonin and nomilin) and the flavonoids neohesperidin, poncirin, naringenin and prunin to be associated with increased bitterness. Rhoifolin was more strongly correlated with bitterness than the previously known bitter compounds. Interestingly, tricin-C-hexoside increased in frozen storage of juices with delayed bitterness. Tricin, a polymethoxylated flavone, is newly identified in citrus. Identifying the compounds that contribute to bitterness in citrus is a crucial first step for future breeding efforts aimed at reducing these compounds.
Accomplishments
1. Rediscovery of the Donaldson tree. While most of the trees in the USDA, ARS experimental citrus field in Groveland, Florida had succumbed to HLB, one 30-year-old tree was standing green and producing oranges – the Donaldson. ARS researchers at Fort Pierce, Florida juiced the fruit under pilot experimental conditions and found it tasted like an early commercial variety, Hamlin. Chemical analysis showed it was very similar to Hamlin. In the era where Huanglongbing has decimated citrus production in Florida, the Donaldson tree is showing promises for the growers. The Florida Department of Citrus estimates 300 acres planted with Donaldson, with over 18,000 propagated scions.
2. Release of USDA, ARS SunGlo mandarin. In the era of endemic Huanglongbing (HLB) citrus disease which has wiped out 90% of the citrus production in Florida, the USDA ARS SunGlo mandarin appears tolerant to HLB. USDA ARS SunGlo is an early-season mandarin that can mature from December to January. Taste panels conducted by ARS researchers at Fort Pierce, Florida have shown that USDA ARS SunGlo is consistently high in sweetness with typical mandarin flavor. It can be marketed as fresh during the peak tourist season in Florida or used in citrus juice. ARS researchers have demonstrated that USDA ARS SunGlo can be blended with orange juice up to 15% without modifying the flavor of Not-From-Concentrate orange juice, yet increasing its sweetness and color, both characteristics of orange juice negatively affected by HLB.
3. Florida Medallion™ ‘FL 16.30-128’ strawberry cultivar release. Currently the main strawberry grown in Florida is ‘Florida Brilliance’ which accounts for ~50% of the acreage. ‘Florida Brilliance’ is a productive variety with early yield and harvest spanning from Thanksgiving to March and bears an attractive glossy fruit. Sweet Sensation™ has followed ‘Florida Brilliance’ in its adoption by the growers because it has an outstanding flavor but has recently decreased in acreage because of lower yields at the beginning of the season in December. ARS researchers at Fort Pierce, Florida, found that Florida Medallion™ had greater sweetness and strawberry flavor than ‘Brilliance’ in most taste panels supported by instrumental data, and at least equal to Sweet Sensation™. Florida Medallion™ fills the gap of an early maturing fruit with eating quality comparable to Sweet Sensation™. It already represents ~20% of the strawberry acreage in 2025.
Review Publications
Olmedo, G., Plotto, A., Mattia, M.R., Zhao, W., Hunter, W.B., Rosskopf, E.N., Obenland, D.M., Bai, J. Evaluation of modified humidity and controlled-release thymol on the preservation of blueberries and blackberries. Postharvest Biology and Technology. 219:113237. 2024. https://doi.org/10.1016/j.postharvbio.2024.113237.
Freitas, T.P., Jeffries, K., Plotto, A., Mattia, M., and Bai, J. Fruit and juice quality of several lemon accessions grown in subtropical Florida. Journal of Horticultural Science and Biotechnology. 100:1. 2024. https://doi.org/10.1080/14620316.2024.2443022
Jeffries, K.A., Fan, Z., Mattia, M.R., Stover, E.W., Baldwin, E.A., Manthey, J.A., Breksa Iii, A.P., Bai, J., Plotto, A. Flavonoid contributors to bitterness in juice from Citrus and Citrus hybrids with/without Poncirus trifoliata in their pedigree. Food Chemistry: X. 26:102289. 2025. https://doi.org/10.1016/j.fochx.2025.102289.
Albrecht, U., Tardivo, C., Moreno, G., De Freitas, J., Singerman, A., Plotto, A., Bai, J. Managing endemic Huanglongbing in commercial citrus production through vascular delivery of oxytetracycline. Crop Protection. 195:107250. 2025. https://doi.org/10.1016/j.cropro.2025.107250.
Jeffries, K.A., Fan, Z., Sun, X.N., Olmedo, G., Zhao, W., Mattia, M.R., Stover, E., Baldwin, E., Manthey, J., Breksa Iii, A.P., Bai, J., Plotto, A. New insights in the flavor and chemistry of Huanglongbing tolerant citrus hybrids with/without Poncirus trifoliata in their pedigree. Frontiers in Horticulture. 3:1425366. 2024. https://doi.org/10.3389/fhort.2024.1425366.
Miranda, M., Bai, J., Pilon, L., Torres, R., Casals, C., Solsona, C., Teixidó, N. Fundamentals of edible coatings and combination with biocontrol agents: A strategy to improve postharvest fruit preservation. Foods. 13(18): 2980. 2024. https://doi.org/10.3390/foods13182980.
Mattia, M.R., Plotto, A., Buzzi, G., Shahid, M., Fan, Z., Jeffries, K.A., Olmedo, G., Freitas, T., Bai, J. The rediscovery of ‘Donaldson’ Sweet Orange, a variety that has potential for use in orange juice. HortScience. 60(3): 362–368. 2025. https://doi.org/10.21273/HORTSCI18351-24.
Trandel-Hayse, M., Bai, J., Jeffries, K.A., Poole, G., Hensley, M.E., Schonborn, W.A., Digioia, F., Rosskopf, E.N. Light source and spectra influence the phytochemical profile of amaranth microgreens. Food Bioscience. 64:105839. 2025. https://doi.org/10.1016/j.fbio.2025.105839.
Dalid, C., Osorio, L.F., Peres, N., Lee, S., Whitaker, V., Plotto, A., Bai, J. Florida Medallion™ ‘FL 16.30-128’ Strawberry. HortScience. 60(7):1032-1036. 2025. https://doi.org/10.21273/HORTSCI18585-25.
Poudel, P., Jeffries, K.A., Bai, J., Dorado, C., Rosskopf, E.N., Di Gioia, F. Light intensity and zinc biofortification differentially impact the metabolomic profile of pea microgreens. Food Chemistry. 490:145146. 2025. https://doi.org/10.1016/j.foodchem.2025.145146.