Location: Citrus and Other Subtropical Products Research2019 Annual Report
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.
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.
Under Objective 1. Citrus hybrids showing tolerance to Huanglongbing (HLB) were obtained from an ARS collaborator for the third year, evaluated by a trained sensory panel, and chemically analyzed for flavor volatiles, sugars, acids and bitter limonoids. Ultimately, HLB-tolerant hybrids with acceptable eating quality (i.e. optimal sugar acid balance, orange-like or pleasant aroma and minimal bitterness) will be further assessed for juice quality. Strawberry selections from the University of Florida breeding program were evaluated each month (January to March) by a trained taste panel, and fruit were analyzed for firmness, sugars, acids and volatiles. This data helps the breeder select fruit for eating quality. A sensory panel trained by a collaborator at Texas Woman’s University found that methyl anthranilate at 0.01 and 0.02 ppm increased strawberry, fresh and fruity flavor in a strawberry flavored puree, while at levels above 0.04 ppm, it created a perfumey and soapy flavor. This study determined the effect of methyl anthranilate on fruity flavor in strawberries. Twelve tomato selections, including both round and plum tomato types, from the University of Florida tomato breeding program, were analyzed for sensory flavor and chemically 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 for a second season and contained fruity floral aromas. Peaches from a breeding collection at ARS in Byron, Georgia, were collected for a third season and analyzed for flavor volatiles. 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 provides fundamental information to link with genetic markers to ultimately develop marker-assisted selection (MAS) in future peach breeding. A study was initiated with University of Florida tropical fruit breeder investigating volatiles in a population of papayas. The objective of the study is to identify which volatiles contribute to the musty odor that some, but not all, papayas express. Under Objective 2. A study applying micro- and nano-emulsion carnauba wax coatings on fresh tangerines was completed. Carnauba coatings, both micro- and nano-emulsions, resulted in better flavor, with more internal oxygen and less carbon dioxide than did the shellac coating. The shellac coatings exhibited more shine initially, but not after removal from cold storage. In addition, ginger essential oil showed antimicrobial activity against citrus pathogens in vivo, but not when added to the nano-emulsion coating, which showed antimicrobial activity on its own. A new formulation of controlled-released chlorine dioxide was applied on strawberry fruit to extend fruit shelf-life and prevent decay. Furthermore, microencapsulation technology was tested with carvacrol and thymol, the two main components of oregano and thyme essential oils, respectively, both being natural antioxidant compounds with strong antimicrobial activity. Thymol was microencapsulated in a pectin-alginate matrix. The powder was placed in a pouch (sachet) attached to the lid of a clamshell commercially used to pack strawberries. That setup provided slow release of the thymol in the clamshell atmosphere. The thymol sachets were compared with thymol incorporated into an edible coating of whey protein isolate. Strawberries were tasted by a non-trained panel. Thymol flavor could be perceived up to 8 days after application and described as “off flavor” or “medicinal” in the two highest dose coatings. Conversely, thymol was not perceived in the fruit packaged with thymol powder in sachets at any time in storage. This proof of concept study will lead to development of more packaging with slow-release active materials, and will be tested for decay control with inoculated fruit. Mango is a fruit that has become popular for its delicious tropical fruit flavor. In an effort to increase mango availability to consumers, the National Mango Board is promoting consumption of ready-to-eat (fresh cut) mangoes as well as whole fruit. The challenge for processors of fresh cut mangoes is the ripeness stage at which the fruit should be cut. Several experiments were undertaken, and for the two most common cultivars, ‘Kent’ and ‘Tommy Atkins’, cutting the fruit at 6.7-7.9 lb-f (30-35N) firmness levels provided a good eating quality product with a 10-day shelf life. Another cultivar, ‘Keitt’, required cutting at a firmer stage (8.9 lb-f = 40 N). Post-cutting dips with several edible coatings were tested, and the most beneficial post-cutting dip was with citric acid at 0.8%, which delayed oxidative browning of the slices. This study was performed in collaboration with the University of Florida in Gainesville. 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 maintaining the “100% fruit juice” label. Experiments in previous years identified cultivars and processing methods that produce acceptable juice quality. However, a sulfury/vegetable-like flavor was still noticeable. In collaboration with a partner, two methods were tested to remove undesirable volatile compounds: a resin column absorbing the volatiles, and rotary evaporation under vacuum and low temperature. Both methods resulted in an acceptable product. Plans were to test both methods on a larger scale and confirm instrumental volatile data with taste panels. The experiment was not completed due to the Government Shutdown. Under 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 and flavonoids resulting in higher nutritional value but slight 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. A good quality juice will depend on the raw material as well as methods of processing. Under Objective 3b. Orange juice from HLB affected fruit, slightly bitter and off flavored, was tasted with added whey or pea protein as a proof of concept for the masking effect of bitterness by proteins. Pea and whey protein isolates increased sweetness and decreased bitterness of the HLB-affected orange juice. This proof of concept will be extended to other protein sources. Under Objective 3c. Two antibiotics, streptomycin and tetraoxycyclin, were approved for use in orange groves to combat Huanglongbing (HLB) infection, and three more antibiotics are currently under evaluation. Analytical methods were developed to detect these antibiotics in orange juice, and results showed that they are undetectable. Data will be confirmed by an outside laboratory.
1. ‘Florida Brilliance’ strawberry cultivar release. ‘Florida Radiance’ is currently the leading strawberry cultivar grown in Florida, followed by Sweet Sensation® ‘Florida 127’. ‘Florida Brilliance’ fills an ever increasing demand for early ripening fruit, with harvest spanning from Thanksgiving to late March. Its yield at that time is comparable to ‘Radiance’ but it produces more consistent and greater quality fruit early in the season. ARS researchers in Fort Pierce, Florida, found its eating quality to be equivalent to ‘Florida 127’ and greater than ‘Florida Radiance’ in most taste panels, supported by instrumental data (soluble solids and titratable acidity). This cultivar has already been planted in small acreage and is expected to represent 40% to 50% of the Florida acreage in the 2019-2020 season.
2. A new packaging to maintain freshness of stored fruit. A clamshell packaging that maintains optimum humidity, hence preventing fruit to lose weight in storage, but does not induce modified atmosphere, was designed by ARS scientists in Ft. Pierce, Florida. The new clamshell has an opening/surface ratio of 0.44% in comparison with commercial clamshells with an opening/surface ration of 2.83%. The opening is large enough so the atmosphere in the clamshell is only minimally modified. The new clamshell, initially designed to maintain turgor and freshness in the stem of sweet cherries, was tested with litchis, strawberries, blueberries, Chinese bayberries, apricots, loquats and cherry tomatoes over a period of 11 years in 37 experiments. Quality attributes of the packaged fruits could generally be better maintained in the ARS-designed clamshells, especially for those attributes susceptible to water deficit, such as shriveling, desiccation-induced browning and/or drying of pedicels in cherries, calyx of strawberries, pericarp of litchis, peel shriveling of cherry tomatoes and softening of blueberries and strawberries.
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