Location: Citrus and Other Subtropical Products Research
2024 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
Objective 1.
Sub-objective 1a. ARS researchers at Fort Pierce, Florida develop chemical and sensory profiles of Citrus hybrids tolerant to citrus greening disease or Huanglongbing (HLB). Orange cultivars showing some tolerance to HLB were harvested in early January and early April in 2024. Fruit were processed in a pilot plant and pasteurized, following standard industry practices. Cultivars included Hamlin, US SunDragon, Tresca, Donaldson (Early season) and Valencia and Tobias (late season). Juice was analyzed for Soluble Solids Content (SSC), Titratable Acidity (TA), limonin content and volatiles. Juice was also presented to panelists in blends to see if any of the HLB tolerant varieties could replace HLB-sensitive Hamlin or Valencia. Among those cultivars tested, Tresca could be used in lieu of Hamlin, and late season Tobias improved orange juice flavor.
Some mandarin genotypes express tolerance to HLB, and lemons are very tolerant to HLB. Eight lemon named varieties and two commercial cultivars were harvested and analyzed for SSC, TA, limonoids and volatiles. Juice yield was also measured and was the highest in ‘Malta’ and 9E lemon seedling. SSC ranged from 5.8% to10.1%, and TA varied between 1.8% and 5.8%. Hybrids like 9E Lemon Seedling, ‘Des 4 Saisons’, ‘Malta’, ‘Villafranca’, and ‘Bears’ had well balanced SSC and TA contents. The limonin content, which indicate bitterness, ranged from 7.3 to14.6 ppm. This study offers preliminary information for selecting lemon hybrids suitable for juice production in Florida.
Six mandarin hybrids were harvested in October, November and December, together with two commercial cultivars. Fruit dimensions, peel color, fruit resistance to puncture and internal quality (easiness to peel, number of seeds, SSC, TA, volatiles) were measured. Taste panels were performed with untrained panelists, staff of the USHRL laboratory. Three ARS hybrids were selected for their easiness to peel and seedlessness. Furthermore, they were found to have excellent flavor by the untrained panel. One hybrid had great flavor and texture but was difficult to peel and had many seeds; this hybrid could be used as a parent for further crosses. Finally, one hybrid was difficult to peel, had seeds and had noticeable off flavor, particularly bitterness, and will be eliminated from the breeding observations.
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. Avocadoes were harvested at optimum maturity and ripened at room temperature. They were presented to visitors at several field days. The USHRL selections seemingly tolerant to laurel Wilt and Phytophthora spp. were given high ratings and positive comments for flavor and texture.
Volatile analysis of University of Florida strawberry breeding program adapted to the Florida climate was completed.
In an effort to diversify fruit production under tropical or subtropical climate, native or introduced fruits were analyzed for nutrient content using LC-MSMS. Crops included noni (Morinda citrifolia), java plum (Syzygium cumini), hog plum (Spondias purpurea), beautyberry (Callicarpa americana), cocoplum (Chrysobalanus icaco), golden berry (Physalis peruviana) and Brazilian cherry (Eugenia uniflora).
Artichokes, greatly appreciated for their nutritional properties, are classified as highly perishable products. ‘Green Queen’ (GQ) and ‘Imperial Star’ (IS) are the most promising cultivars to be grown in Florida’s warm and humid climate. A study on the nutritional compounds clearly showed that essential aminoacids, sugars and organic acids accumulation followed the same trend during a 21-day postharvest storage in both cultivars, however, GQ exhibited significant higher concentrations of most compounds than IS. B complex vitamins amounts were similar in both cultivars immediately after harvest, however, after a 7-day storage, GQ accumulated higher levels than IS. Our metabolomic results offer valuable insights into the field of artichokes postharvest storage life, providing data that will be correlated to molecular traits to identify target genes necessary to achieve better storage life and nutritional properties.
Objective 2.
Sub-objective 2a. Develop methods to mask undesirable bitterness in orange and other citrus juice using flavor modulators. In collaboration with CRADA partner, tested several formulations of orange seed proteins added to highly bitter orange or grapefruit juice. Proteins extracted from citrus seeds had inconsistent effect on the perception of bitterness, either no effect or smoothing the harshness from the affected juice. Work is to be continued, perhaps choosing a base juice that is not as bitter as the ones tested so far.
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. Thymol, the main volatile component in thyme essential oil and with proven general antimicrobial activity, was microencapsulated in a pectin-alginate matrix to be released in small doses during blueberry storage. This delivery system reduced decay on blueberries stored in commercial clamshell packaging. More experiments were designed to test the antimicrobial activity of microencapsulated thymol on berries packed in modified humidity clamshells (less vented than commercial packaging). The combination of controlled-release thymol with low-venting packaging effectively controlled decay, reduced weight loss and fruit shrinkage of blueberries. The same treatments had the reverse effect on blackberries where increased decay and shriveling as well as marketability loss were observed.
In an effort to adapt organic strawberry production in Florida, different agricultural by-products were used to achieve optimal carbon and nitrogen (C:N) ratios in a field where soil was anaerobically disinfected (ASD). Commercially ripe fruit were harvested and different quality measurements along with metabolomics studies were performed to detect whether field management had any impact on fruit. While fruit color, weight and taste/flavor remained invariable across treatments, some soil-amendment levels impacted essential aminoacids, sugars and organic acids content in fruit. This study offers useful information for optimizing organic field management for strawberry production.
Objective 3.
Sub-objective 3a. Identify the best flavor combinations for an ideal orange or citrus juice. Volatile and non-volatile data obtained under Objective 1a were compiled from previous years and statistically analyzed. A model using random forest highlighted 26 compounds that were essential for the characteristic orange flavor. Seven esters were identified as key differentiators between orange and mandarin flavors, with six esters showing shared genetic control. Molecular analysis revealed a crucial gene in the ester production pathway, validated through overexpression assays. A SNP-based DNA marker was developed for phenotype prediction. Data, analyzed and published in Science Advances and attracted domestic and international press attention.
Sub-objective 3c. Identify biomarkers in citrus with unique taste, flavor and healthful qualities. Data analyzed in the previous report period were compiled in a manuscript to be submitted. Briefly, comprehensive chemical analysis was performed on a diverse selection of genotypes including orange, grapefruit, pummelo, tangelo, mandarin hybrids with/without P. trifoliata in their pedigree and pure P. trifoliata. The volatile sesquiterpene compounds camphene, trans-alloocimene, ¿-muurolene, and d-elemene were positively correlated with bitterness while esters were negatively correlated with bitterness. LC-MS/MS analysis revealed the flavonoids neohesperidin, poncirin, rhoifolin, apigenin, and tricin were correlated with bitterness, in addition to the well-known limonoids, limonin and nomilin. Determination of the compounds contributing to bitterness in citrus is the first step for future breeding efforts once their biosynthetic pathway is known. These data could also be useful in making debittering technologies more targeted.
Accomplishments
1. Mandarin juice to complement orange juice. Huanglongbing (HLB), or Citrus greening disease, has decimated citrus production in Florida and world-wide. The orange tree (Citrus sinensis) is sensitive to the disease but some mandarin cultivars, or hybrids introgressed with Poncirus trifoliata, a Citrus relative, have shown some tolerance to the disease. Adding mandarin juice to orange juice could complement the current shortage in orange to keep Florida processing plants viable. However, current FDA regulations allow no more than 10% mandarin juice in orange juice in order to maintain the ‘orange juice” label (21 C.F.R. §§146.135, .140; .141, .146 and .151). ARS researchers at Fort Pierce, Florida performed multiple taste panels blending mandarins or mandarin hybrids with orange juice (Valencia and Hamlin, the main varieties used in orange juice). In general, untrained panelists representing general consumers could not detect differences between 100% orange juice and orange juice to which 10, 15 or 20% of mandarin juice was added. The orange juice industry has petitioned the FDA to increase mandarin juice to 15% in orange juice. The ARS results will likely support the petition.
Review Publications
Zhang, J., Yan, J., Bai, J., Hu, C., Pan, T., Carrillo, Y., Cardenas, D., Cano, L., Ritenour, M. 2024. First report of Lasiodiplodia Pseudotheobromae causing postharvest decay of strawberries in Florida. Plant Disease. 108(2):519. https://doi.org/10.1094/PDIS-07-23-1376-PDN.
Fan, Z., Jeffries, K.A., Sun, X.N., Olmedo, G., Zhao, W., Mattia, M.R., Stover, E., Manthey, J., Baldwin, E., Lee, S., Gmitter, F., Plotto, A., Bai, J. 2024. Chemical and genetic basis of orange flavor. Science Advances. 10(9):2051. https://doi.org/10.1126/sciadv.adk2051.
Imahori, Y., Bai, J. 2024. Postharvest management of fruits and vegetables series II. Foods. 13(7):1049. https://doi.org/10.3390/foods13071049.
Olmedo, G., Zhang, J., Zhao, W., Mattia, M.R., Rosskopf, E.N., Ritenour, M., Plotto, A., Bai, J. 2023. Application of thymol vapors to control postharvest decay caused by Penicillium digitatum and Lasiodiplodia theobromae in grapefruit. Foods. 12(19):3637. https://doi.org/10.3390/foods12193637.