Location: Citrus and Other Subtropical Products Research
2018 Annual Report
Objectives
Objective 1: Establish bioactive and sensory characteristics of new marketable genotypes (citrus, tomato, strawberry) and new Florida crops (avocado, blueberry, peach).
Objective 2: Enable real-time, commercial pre- and postharvest treatments to optimize shelf life of new genotypes and new Florida crops using packaging, coatings, and maturity markers.
Objective 3: Identify new sensory targets, enable new sensors, processing methods and management strategies to predict and mitigate HLB disease effects on citrus juice nutritional and flavor quality.
Sub-Objective 3a: Identify chemical and biological markers that characterize the effect of HLB on fruit/juice quality.
Sub-Objective 3b: Develop methods to mitigate the effect of HLB on citrus juice quality.
Sub-Objective 3c: Develop methods to mitigate the effect of HLB on citrus fruit quality.
Approach
Phenotypes for fruit quality in citrus, tomatoes, strawberry, peaches and avocados will be screened for flavor markers: volatiles, sugars and acids, and sensory characteristics by gathering chemical and sensory data on a wide range of genetically variable breeding lines (or hybrids). In the long term, plant breeders will identify genes associated with fruit quality traits and map them on the genome to aid in marker-assisted selection. For advanced selections or commercial cultivars of peach and avocado, fruit will be harvested multiple times during maturation and ethylene and respiration rate will be measured at harvest and in stored fruit. For the effect of citrus greening or Huanglongbing (HLB) disease on orange fruit/juice flavor, fruit or juice will be obtained from collaborators, or from groves undergoing various field treatments (pesticides, growth regulators, antibiotics or thermotherapy), or from trees grown on different rootstocks to study a wide range of HLB flavor symptoms. Juices will be tested for CLas infection by qPCR and for levels of sugars, acids, volatiles, flavonoids, limonoids and for flavor perception using sensory evaluation. Taste panels will serve as the biosensors for compounds isolated from HLB-affected orange juice to determine compounds responsible for these putative off-flavor taste attributes. The electronic nose and electronic tongue will be used to screen for HLB-induced off-odor or flavor. The effect of HLB on the flavor quality of grapefruit and tangerines will be investigated. HLB-induced off-flavor can be managed by blending, by modifying juice processes or by adding citrus-derived natural compounds (volatiles or non-volatiles) to mask or bind off-flavor compounds. Studies will be conducted on several citrus types using fungicide sprays (strobulorins, Topsin) targeting D. natalensis to determine if the HLB-induced fruit drop and postharvest stem end rot can be reduced.
Progress Report
Flavor volatiles, sugars and acids were analyzed for citrus at Ft. Pierce, Florida, and peach at Byron, Georgia, breeding collections for a third season. For citrus, the objective is to identify hybrids that show tolerance to huanglongbing (HLB) and that might show potential for the fresh or processed market. Flavonoids and limonoids were also analyzed for citrus hybrids. The objective for peaches is to compare aroma volatile profiles in peach and nectarine genotypes with different melting/non-melting and yellow/white flesh. The aroma volatile profiles and interrelationships among volatile compounds will provide fundamental information to link with genetic markers and develop marker-assisted selection (MAS) in future peach breeding.
A new finger lime (Microcitrus sp.) cultivar was released by an ARS collaborator, with sensory and quality data that described the fruit as light and fresh, with lime and lemon flavor, sour, with vesicles that “pop in the mouth”. This fruit is intended for the “gourmet” food market as it can be used as garnish and flavoring in seafood, avocado, deserts and beverages.
Strawberry selections from the University of Florida breeding program were evaluated each month (December to March) by a trained taste panel, and fruit were analyzed for color, firmness, sugars and acids. Volatiles will be analyzed at a later time. These data help the breeder select fruit for eating quality. Another set of strawberries from a breeding population were analyzed for mesifuran and gamma-decalactone, two volatiles that are important contributors to the perception of sweetness and strawberry flavor. A list of strawberry volatiles was built to create the “ideal” strawberry flavor, which was made in a model solution by a collaborator at Texas Women University. Those volatiles will be added to a strawberry deodorized puree in chosen combinations and amounts, and evaluated by the trained panel, as well as analyzed by gas chromatography (GC). The dynamics of volatiles in a fruit puree is different than it would be in a model solution, and by using this system, the contribution of key volatiles will be determined.
Ten tomato selections, including both round and plum tomato types, from the University of Florida tomato breeding program, were analyzed for sugars, acids and volatiles. These tests are part of a continuing collaboration with the University of Florida breeder. Chemical data are compared with taste panel data to model flavor quality. One plum-type tomato with green vascular tissue was rated highest in flavor and contained fruity floral aromas.
A survey of flavor profile of selected microgreens was initiated in order to establish a flavor “lexicon” that could be used to describe the large array of species that can be grown as microgreens. Species tested were basil, beet, daikon radish, red mustard, Russian kale and arugula. ARS collaborators are studying the growth characteristics: time between seeding and sprouting, time to reach the first 2 leaves, which is the stage at which the microgreens are commercialized.
Experiments to extend fruit shelf-life and prevent decay were continued with controlled release of chlorine dioxide gas to measure its dynamics in clamshell packaging with grape/cherry tomatoes. A new approach to develop microencapsulation of a natural antimicrobial agent with controlled release properties was also tested. The antimicrobial agent was carvacrol, a volatile essential oil from oregano, and it was microencapsulated in pectin-alginate, a food grade polymers, using a spray drier. The physical properties, encapsulation efficiency, stability, and the microstructure of the microcapsules were analyzed as well as the product antimicrobial and antioxidant properties.
Clamshell packaging and edible coatings were applied post-harvest to peaches from a commercial farm in Fort Pierce, Florida. The edible coating delayed fruit ripening but did not prevent water loss, while clamshell packaging with reduced ventilation prevented water loss. Decay in closed clamshells was controlled with a postharvest fungicide. Coated fruit remained firm after 14 days shelf life; however, some off flavor developed after 8-14 days. Off flavor was less when the coating was diluted down to 25%. Work will continue to optimize coating formulation, amount applied and clamshell packaging.
Tangerines from a local grower were used to test a new nano-emulsion carnauba wax coating compared to a micro-emulsion carnauba wax coating, a commercial shellac coating and an uncoated control. Then nan-emulsion coating had slightly more shine than the micro-emulsion carnauba coating, and both retarded water loss better than shellac. Although shellac exhibited more gloss/shine initially, both carnauba coatings were shinier after removal form cold storage and during storage at the warmer marketing temperature. Both carnauba coatings resulted in more internal oxygen and less carbon dioxide than did the shellac coating, thus producing less ethanol, which can affect flavor. The new nano-emulsional coating with and without an anti-microbial ginger essential oil, extracted from ‘Gigante’ ginger rhyzomes, was tested on tangerines for decay control and compared to a commercial ginger essential oil product. The ginger essential oil had shown activity against fruit fungal pathogens in vitro. Results showed that the nano-emulsion coating was effective against decay on its own, with no added advantage due to the ginger essential oil.
Winter melon (Benincasa hispida) is a new Florida crop that is of interest to the juice industry because it has potential for blending with other juices to reduce sugars while still preserving qualification for the “100% fruit juice” label. Last year’s research showed that a waxy commercial cultivar had superior processing properties in comparison with a non-waxy cultivar. The same waxy cultivar was further evaluated to measure effects of harvest season, maturity and storage regime on juice flavor and nutritional qualities. Traditionally, fresh market winter melon is harvested at a fully mature stage, and harvested starting in June. At the end of the growing season in December, the vine dries out, fruit that are left in the field and still can be harvested until the following season starts in May. This research is to understand traditional systems while exploring new agricultural practices to improve winter melon juice quality.
Last year’s survey of fresh-cut mango quality on supermarket shelves showed that mangoes were generally processed at an unripe stage, resulting in poor eating quality. Experiments were initiated to identify the optimum ripeness stage at which mangoes should be processed for good quality while maintaining an acceptable shelf-life of 2 weeks. The cultivars ‘Kent’ and ‘Tommy Atkins’ were processed at three firmness stages, and for both cultivars, the firmer fruit had a longer shelf-life. The firmer fruit in this experiment is still softer than industry practice. Another experiment was performed where mango slices were coated with edible films and antioxidants, which showed promising results. The maturity study and coating experiment will be repeated with more cultivars. This study is performed in collaboration between ARS Researchers in Ft. Pierce, Florida and University of Florida in Gainesville.
Citrus greening disease or Huanglongbing (HLB)-affected ‘Valencia’ oranges were juiced using two types of commercial extractors, a reamer and a squeezer type. The physical and chemical properties of the juices were compared. Juice processed by squeezing the fruit contained higher limonoids and flavonoids resulting in higher nutritional value but bitter taste. Juice processed with a reamer had more peel oil, specifically because in this pilot experiment, peel oil was not removed prior to juicing.
In collaboration with a flavor company and in individual research, non-volatile compounds were isolated from healthy and HLB-affected orange juice that were tested by a sensory panel and found to enhance or mitigate HLB-induced off-flavor for which the data has been analyzed and published or in draft manuscript form.
Accomplishments
1. Natural food colors were developed for the fresh fruit citrus industry. The fresh fruit citrus industry has traditionally used “Citrus Red No2” as a postharvest color added to fruit before waxing to increase color of oranges when harvested early, before orange color development. Citrus Red No2 has been listed as a group 2B carcinogen by the European Union. ARS researchers at Fort Pierce, Florida, tested five oil-soluble natural colorants that could be added to citrus waxes to improve citrus color. Annato and paprika were identified to have similar color characteristics (lightness, hue), provided an attractive color to the fruit, and were compatible with fruit waxes, but only annatto was stable in storage and under simulated marketing conditions. Annato and paprika are now used by a commercial manufacturer of citrus waxes as natural colorants. The potential use of this color add is for fresh oranges (US 2016-17 production at 4.9 million metric tons) and mandarins (US 2016-17 production at 899,000 metric tons).
2. Citrus greening disease or huanglongbing (HLB) has resulted in orange juice with less sugar, higher acids, and higher flavonoids and limonoids which renders the juice less sweet and more sour, bitter and astringent. Added flavor moderators “from the named fruit” (FTNF) can legally be used to mitigate off-flavor, while still retaining the 100% fruit juice label. ARS researchers at Fort Pierce, Florida, fractionated orange juice to obtain compounds to test as off-flavor moderators, discovering several in collaboration with a flavor company. A flavor panel reported these moderators to reduce bitterness in HLB-affected orange juice.
Review Publications
Yu, Y., Bai, J., Chen, C., Plotto, A., Baldwin, E.A., Gmitter, F.G. 2018. Comparative analysis of juice volatiles in selected mandarins, mandarin relatives and other citrus genotypes. Journal of the Science of Food and Agriculture. 98:1124-1131.
Wang, L., Bai, J., Yu, Z. 2017. Responses of volatile compounds in inner tissues on refrigeration in full ripe tomatoes. Journal of Food Processing and Preservation. 41:e13272. https://doi.org/10.1111/jfpp.13272.
Wang, L., Li, X., Bai, J., Luo, H., Jin, C., Hui, J., Yu, Z. 2017. Residual impact of methyl salicylate fumigation at the breaker stage on C6 volatile biopathway in red tomato fruit. Journal of Food Processing and Preservation. 41:e13285. https://doi.org/10.1111/jfpp.13285.
Xu, S., Li, J., Baldwin, E.A., Plotto, A., Rosskopf, E.N., Hong, J.C., Bai, J. 2018. Electronic tongue discrimination of four tomato cultivars harvested at six maturities and exposed to blanching and refrigeration treatments. Postharvest Biology and Technology. 136:42-49. https://doi.org/10.1016/j.postharvbio.2017.10.004.
Whitaker, V.M., Osorio, L.F., Peres, N.A., Fan, Z., Herrington, M., Do Nascimento Nunes, C.M., Plotto, A., Sims, C.A. 2017. 'Florida Beauty' strawberry. HortScience. 52(10):1443-1447. https://doi.org/10.21273/hortsci12281-17.
Dala Paula, B., Raithore, S., Manthey, J.A., Baldwin, E.A., Bai, J., Zhao, W., Gloria, M., Plotto, A. 2018. Active taste compounds in juice from oranges symptomatic for Huanglongbing (HLB) citrus greening disease. LWT - Food Science and Technology. 91:518-525.
Goncalves, D.R., Ferreira, P.S., Baldwin, E.A., Cesar, T.B. 2017. Health benefits of orange juice and citrus flavonoids. In: Ye, X., editor. Phytochemicals in Citrus: Applications in Functional Foods. Cleveland, OH:CRC Press. p. 299-323
Baldwin, E.A., Plotto, A., Bai, J., Manthey, J.A., Zhao, W., Raithore, S., Irey, M. 2018. Effect of abscission zone formation on orange (Citrus sinensis) fruit/juice quality for trees affected by Huanglongbing (HLB). Journal of Agricultural and Food Chemistry. doi:10.1021/acs.jafc.7b05635.
Wang, L., Chunlu, Q., Bai, J., Luo, W., Jin, C., Yu, Z. 2018. Difference in volatile composition between the pericarp tissue and inner tissue of tomato (Solanum lycopersicum) fruit. Journal of Food Processing and Preservation. 42(1):e13387. https://doi.org/10.1111/jfpp.13387.
Moon, P., Fu, Y., Bai, J., Plotto, A., Crane, J., Chambers, A. 2018. Assessment of fruit aroma for twenty-seven guava (Psidium guajava) accessions through three fruit developmental stages. Scientia Horticulturae. 238:375-383.
Pillett, J., Chambers, A.H., Barbey, C., Boa, Z., Plotto, A., Bai, J., Schwieterman, M., Johnson, T., Harrison, B., Whitaker, V., Colquhoun, T., Folta, K. 2017. Identification of a methyltransferase catalyzing the final step of methyl anthranilate synthesis in cultivated strawberry. Biomed Central (BMC) Plant Biology. 17:147-159. https://doi.10.1186/s12870-017-1088-1.
Sun, X.N., Baldwin, E.A., Plotto, A., Cameron, R.G., Manthey, J.A., Dorado, C., Bai, J. 2018. The effect of cultivar and processing method on the stability, flavor, and nutritional properties of winter melon juice. LWT - Food Science and Technology. 97:223-230. https://doi.org/10.1016/j.lwt.2018.06.059.
