Research Project: Quality, Shelf-life and Health Benefits for Fresh, Fresh-cut and Processed Products for Citrus and Other Tropical/Subtropical-grown Fruits and Vegetables

Location: Citrus and Other Subtropical Products Research

2020 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
This is the final report for Project No. 6034-41430-006-00D. Objective 1. Citrus hybrids showing tolerance to Huanglongbing (HLB) were obtained from an ARS collaborator for four consecutive years. Fruit were evaluated by a trained sensory panel, and chemically analyzed for flavor volatiles, sugars, acids and bitter limonoids. On the fourth year, plans were made to initiate blends with juices from promising selections to achieve optimum taste. However, the restriction of research due to Covid 19 only allowed for harvest and freezing of samples. No analyses were performed in 2020. Strawberry selections from the University of Florida (UF) breeding program were evaluated each year for three or four months (December to March) by a trained taste panel, and fruit were analyzed for firmness, sugars, acids and volatiles. These data help the breeder selecting hybrids with high quality, discarding those with negative sensory attributes. Two cultivars were released during the Plan period resulting from the collaboration with UF. Analysis of the five-year data show that genotypes, followed by season, strongly effect sensory perception. Statistical models revealed which volatiles increased perception of sweetness and strawberry flavor. Genetic studies of target volatiles are underway to facilitate the selection of strawberry cultivars with higher sweetness and flavor through marker-assisted selection. Volatile production in different tissue (structure) of the tomato fruit was measured in four commercial cultivars. In general, the pericarp tissue showed the highest volatile concentration, with the highest aldehydes and herbaceous-like compounds. Compounds with floral and fruity characters were more abundant in the inner fruit tissue, i.e. septa and columella, and locular gel and seeds. Distinct volatile profiles were found in different cultivars. Peaches from a breeding collection at ARS (Byron, Georgia) were collected for three seasons and flavor volatiles were analyzed. The objective is to compare aroma volatile profiles in peach and nectarine genotypes with different melting/non-melting and yellow/white flesh. A subset of samples including 15 cultivars/hybrids with different degrees of skin hair were assessed for their volatile profile. The only volatile which was detected in the nectarines but not in peaches was hexanol, indicating alcohol hedydrogenase (ADH) and hexanol are potential markers for peach-to-nectarine mutants. However, overall peach-to-nectarine mutants showed broad pleiotropic effects for fruit size, taste, and aroma, in addition to hairlessness. Twenty one papaya accessions from the UF tropical fruit breeding program were evaluated for aroma volatiles by gas chromatography-mass spectrometry (GC-MS), revealing a large variation among samples. A subset of samples were evaluated by GC-olfactometry to pinpoint which volatile compounds may potentially contribute to aroma and flavor. These results provides the breeder potential to select hybrids with high eating quality. Avocadoes from the ARS varietal collection were harvested monthly or bi-monthly, and let ripened at room temperature (20 C). Once ripe, fruit were tasted by expert panels. This study establishes maturity windows for unknown cultivars or hybrids. Some hybrids seemed to show tolerance to laurel wilt and phytophthora root rot. A collection of photos was taken for future use. Objective 2.Thyme oil, thymol, carvacrol and Thyme Guard (a commercial formulation containing thyme oil) were most effective at controlling decay of Florida strawberries, on both inoculated or naturally infected fruit. Formulations with microencapsulated slow release volatiles applied to sachet in clamshells and fruit stored at low temperatures (i.e. 5 C) controlled Botrytis gray mold and Rhizopus soft rot without affecting fruit quality. Likewise, a new formulation of chlorine dioxide vapor was effective at controlling strawberry decay. Covid 19 restrictions did not allow commercially simulated tests. Experiments on fresh-cut mangoes and winter melon quality were finalized in the previous period. Objective 3a. ‘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, flavonoids and carotenoids resulting in higher nutritional value but slight bitter taste. Juice processed with a reamer had more peel oil, specifically because food service/juice stand type was used where peel oil was not removed prior to juicing. A good quality juice will depend on the raw material as well as methods of processing. Grapefruits free from HLB (grown in a “Citrus Under Protective Screen” (CUPS) production system) were compared with grapefruits infected with HLB for the chemical profile in different fruit structures, flavedo, albedo, peel oil, and flesh. Fresh samples were prepared and frozen. Instrument analysis were not completed due to Covid 19 restrictions of research. Citrus hybrids showing tolerance to HLB were evaluated for volatiles, limonin and nomilin (the two bitter limonoids), sugars, acids and flavor by sensory evaluation. Juice is also analyzed by qPCR to evaluate the infection status of each tree. In the long term, biological and chemical markers of citrus sensory attributes (sweetness, sourness, bitterness, citrus flavor, tropical flavor, etc) will be well defined from a large range of genetically diverse material. Objective 3b. ARS collaborator extracted proteins from orange seeds, and those were added to orange juice from HLB affected fruit, and tasted in comparison with other commercial protein sources. The citrus seed proteins added citrus flavor, while whey or pea protein isolates increased sweetness and decreased bitterness of the HLB-affected orange juice. A CRADA was implemented with commercial partner to explore this concept. Spiking HLB-affected orange juice with the combination of volatiles and non-volatile compounds was not further explored due to Covid 19 restrictions of research.

Accomplishments
1. Processing fresh cut mangoes for a better quality product. A 2017-2018 retail store survey by ARS researchers at Fort Pierce, Florida, and collaborators found that fresh-cut mangoes on the retail market were of low quality due to improper monitoring of fruit ripeness before processing. ARS researchers at Fort Pierce and collaborators determined that mangoes can be cut at a riper stage and still maintain acceptable shelf life of 10 days. Furthermore, a treatment with citric acid helped maintain quality of stored mangoes without affecting taste. Citric acid is a cheap ingredient for food processors and it additionally reduces microbial growth. As a result of this research, fresh-cut mango processors are now monitoring mango ripeness before cutting. This study was sponsored by the National Mango Board, who is promoting mango consumption in all aspects and helps producers and processors market a high quality product.

Review Publications
Plotto, A., Bai, J., Baldwin, E.A. 2020. Effect of CA/MA on sensory quality. Book Chapter. https://doi.org/10.1016/B978-0-12-804599-2.00007-7.
Ali, S., Plotto, A., Scully, B.T., Wood, D.R., Stover, E.W., Owens, N.D., Pisani, C., Ritenour, M., Anjum, M., Nawaz, A., Naz, A., Bai, J. 2020. Fatty acid and volatile organic compound profiling of avocado germplasm grown under East-Central Florida conditions. Scientia Horticulturae. 261. https://doi.org/10.1016/j.scienta.2019.109008.
Sun, X.N., Cameron, R.G., Bai, J. 2020. Effect of spray-drying temperature on physicochemical, antioxidant and antimicrobial properties of pectin/sodium alginate microencapsulated carvacrol. Food Hydrocolloids. 100:105420. https://doi.org/10.1016/j.foodhyd.2019.105420.
Raithore, S., Kiefl, J., Manthey, J.A., Plotto, A., Bai, J., Zhao, W., Baldwin, E.A. 2020. Mitigation of off-flavor in Huanglongbing-affected orange juice using natural citrus non-volatile compounds. Journal of Agricultural and Food Chemistry. 68:1038-1050. https://doi.org/10.1021/acs.jafc.9b07756.
Hijaz, F., Al-Rimawl, F., Manthey, J.A., Killiny, N. 2020. Phenolics, flavonoids and antioxidant capacities in citrus species with different degree of tolerance to Huanglongbing. Plant Signaling and Behavior. https://doi.org/10.1080/15592324.2020.1752447.
Bai, J., Baldwin, E.A., Tsantili, E., Plotto, A., Sun, X.N., Wang, L., Kafkaletou, M., Wang, Z., Narciso, J., Zhao, W., Xu, S., Seavert, C., Yang, W. 2019. Modified humidity clamshells to reduce moisture loss and extend storage life of small fruits. Journal of Food Packaging and Shelf Life. 22:100376. 10.1016/j.fpsl.2019.100376.
Bowman, K.D., McCollum, T.G., Plotto, A., Bai, J. 2019. Minnie finger lime: A new novelty citrus cultivar. HortScience. 54(8):1425-1428. https://doi.org/10.21273/HORTSCI13622-18.
Loayza, F., Brecht, J., Simonne, A., Plotto, A., Baldwin, E.A., Bai, J., Lon-Kan, E. 2019. Enhancement of the antioxidant capacity of ripe tomatoes by the application of a hot water treatment at the mature-green stage. Postharvest Biology and Technology. 61:111054. https://doi.org/10.1016/j.postharvbio.2019.111054.
Hijaz, F., Gmitter, F., Bai, J., Baldwin, E.A., Biotteau, A., Leclair, C., Mccollum, T.G., Plotto, A. 2020. Effect of fruit maturity on volatiles and sensory descriptors of four mandarin hybrids. Journal of Food Science. 85/1548-1564. https://doi.org/10.1111/1750-3841.15116.
Ribeiro, C.B., Ramos, F.M., Manthey, J.A., Cesar, T.B. 2019. Effectiveness of Eriomin® in managing hyperglycemia and reversal of prediabetes condition: A double-blind, randomized, controlled study. Phytotherapy Research. pg. 1-13. https://doi.org/10.1002/ptr.6386.
Ference, C.M., Manthey, J.A., Narciso, J.A., Jones, J.B., Baldwin, E.A. 2020. Detection of phenylpropenoids in citrus leaves produced in response to Xanthomonas citri subsp citri. Phytopathology. 110:287-296. https://doi.org/10.1094/phyto-06-19-0219-R.
Ference, C.M., Baldwin, E.A., Manthey, J.A., Jones, J. 2019. Inhibitory extracts of calamondin leaves associated with precipitous decline of Xanthomonas citri subsp. citri populations. European Journal of Plant Pathology. 156:451-461. https://doi.org/10.1007/s10658-019-01894-w.
Li, J., Di, T., Bai, J. 2019. Distribution of volatile compounds in different fruit structures in four tomato cultivars. Molecules. 24, 2594. 10.3390/molecules24142594.
Zhang, J., Kou, J., Ozbudak, E., Zhong, T., Pan, T., Bai, J., Cano, L., Ritenour, M. 2020. First report of Gilbertella persicaria causing postharvest soft rot of strawberry fruit in Florida. Plant Disease. online. https://doi.org/10.1094/PDIS-10-19-2081-PDN.
Whitaker, V., Peres, N., Osorio, L., Fan, Z., Nunes, C., Plotto, A., Sims, C. 2019. 'Florida Brilliance' strawberry. HortScience. 54(11):2073-2077. https://doi.org/10.21273/HORTSCI14327-19.