1a. Objectives (from AD-416):
1. Evaluate the effect of genetics on microbial stability and composition of flavor and healthful compounds - sugars, acids, volatiles, carotenoids, total phenolics, pectin and fiber – in citrus, tomato, and subtropical-bred small fruit breeding lines. 2. Relate chemical composition to sensory flavor and pathogen resistance data from Objective 1 to determine which compounds are important for flavor or have anti-microbial properties. a) Modeling for quality evaluation. b) Modeling for shelf life as limited by decay and identify natural compounds with antimicrobial activity. 3. Develop pre- and postharvest treatment protocols for reducing specific decay pathogens using sanitizers, antimicrobials, such as plant (including citrus) essential oils, with or without coatings and/or other surface treatments and storage atmospheres to minimize postharvest losses and maximize shelf life of the of citrus, tomato, berries and select tropicals for both intact and fresh-cut products. a) Pre-harvest treatments to reduce postharvest pathogens and to enhance postharvest quality. b) Postharvest treatments to prevent decay and transference of fruit surface microbes.
1b. Approach (from AD-416):
Evaluate advanced breeding lines for citrus tomato and small fruits to determine optimal harvest maturity, microbial stability, and overall flavor quality. Evaluate diverse breeding material for citrus, tomato, and strawberry to determine desirable flavor aromas and tastes. Flavor analyses will be done using sensory panels as well as chemical analyses using gas chromatography (GC) mass spectroscopy (MS), GC-olfactometry, and electronic nose for aroma compounds and liquid chromatography (HPLC), HPLC-MS and microplate readers for sugars, acids, vitamin C, carotenoids, phenolic and antioxidant analyses coupled with flame ionization, refractive index and ultraviolet light and photo diode array among other detectors. Sensory panels will consist of consumer or trained descriptive panels to determine preference and fundamental flavor information. Multivariate and other statistics will be used to relate chemical to sensory data. Storage of commodities under study will be done using simulated commercial or abusive conditions for monitoring of quality and decay. Causal decay organisms will be indentified and pre- and postharvest treatments to reduce their population will be tested including pre-harvest deployment of wax-based sprays, sanitizers, and nutrients as well as use of postharvest sanitizers, anti-microbial agents or antagonists with or without coatings. Produce will also be subjected to short-term antimicrobial atmospheres of low oxygen, high carbon dioxide alone or combined with other anti-microbial volatile compounds. Effect of disease (Huanglongbing) on orange juice flavor will also be analyzed and identification and threshold of off-flavor compounds determined.
3. Progress Report:
Objective 1: A second year of data was obtained for new tangerine hybrids on fruit quality in relation to maturation. This will provide information about new cultivars for citrus growers. Collaboration with the University of Florida strawberry and blueberry breeders was continued to evaluate new hybrids by sensory and chemical analysis. Genetic traits were studied for firmness in blueberries and for aroma in strawberry (methyl anthranilate and linalool production, which are two volatile compounds responsible for fruitiness in strawberries). Evaluation of flavor of orange juice made with fruit from trees infected with Huanglongbing (HLB) disease, some of which were receiving nutritional spray treatments in the field, was continued for a second year with two orange cultivars, Hamlin and Valencia. Last year's results showed that nutritional sprays did not improve fruit flavor, however, this year showed some flavor improvement, therefore, studies will continue next year. Objective 2a: Gas chromatography and olfactometry (GC-O) of ‘Fallglo’ tangerines showed that 32% of the identified volatile compounds with aroma activity could be detected by human subjects but not by the instrument detector. Two new aroma-active compounds were found (methional and 1-nonen-3-one), not previously reported in tangerines. A method for detecting DNA from Candidatus Liberibacter asiaticus, the putative bacterium responsible for HLB disease, in orange juice was developed using quantitative polymerase chain reaction. Gene expression of linalool, a potential antimicrobial compound in strawberry fruit, was studied. Objective 2b: Studies are underway that measure plant chemical responses to pathogen attack. Citrus leaves affected by HLB or canker diseases produce different compounds than healthy leaves, hence modifying the microbial population biology on the leaf surface. A soil fungus, Trichoderma viridae, is being studied for its antimicrobial qualities and chemicals are being extracted, identified and tested against Xanthomonas citri, subsp. Citri (Xcc), the bacterium causing citrus canker. Objective 3a: Field applications of a wax formulation on grapefruit trees reduced canker inoculum in the field, and resulted in increased fruit pack out. Field applications of potassium sorbate and “Tree-wash”, a commercial sanitizer (TW) were performed on blueberries during fruit development and before harvest. The TW reduced postharvest decay and increased sweetness but it was not consistent for all varieties. Objective 3b: A combination of field application of wax formulations and postharvest sanitizers such as peroxyacetic acid significantly reduced canker on fruit destined for out-of-State shipping. Fruit inoculated with Xcc had their bacterial count significantly reduced after placing slow release ClO2 sachets (Curoxin®) inside the container of citrus. Curoxin® also extended strawberry and blueberry shelf life by reducing decay and water loss, and maintaining firmness, color and overall quality. Clamshell packaging was developed that extends cherry and blueberry shelf life. Curoxin® was added to soy protein coating and eliminated E. coli from inoculated blueberries.
1. Developed new packaging for small fruit. Small fruit have a short shelf life due to moisture loss and decay. ARS researchers in Fort Pierce, Florida developed new packaging designed with fewer openings resulting in higher relative humidity, to prevent dehydration without increasing decay, thereby extending storage life. Increased storage life results in less postharvest losses which translates into all the resources put into growing, harvesting and processing the fruit, and saves the industry money.
2. Developed antimicrobial sachets for insertion into fresh produce packaging. Decay of fresh produce, especially small fruits, shortens postharvest shelf life. ARS scientists in Fort Pierce, Florida developed in collaboration with CRADA partner, sachets that release chlorine dioxide (Curoxin®), a strong antimicrobial agent,in fresh fruit packaging such as blueberries and strawberries. The Curoxin® was used to treat citrus fruit infected with citrus canker. Canker is a problem for the fresh citrus market, as fruit coming from groves where canker is found is not marketable internationally. Curoxin® in a sachet that was placed inside the containers of citrus significantly reduced bacterial counts. Curoxin® also extended postharvest shelf life of blueberries and strawberries by maintaining fruit firmness, reducing water loss and decay and maintaining color and overall quality. This product is being tested in pilot studies with commercial packing houses and could save the industry the costs incurred by postharvest losses.
Du, X., Plotto, A., Baldwin, E.A., Rouseff, R. 2011. Evaluation of volatiles from two subtropical strawberry cultivars using GC-olfactometry, GC-MS odor activity values, and sensory analysis. Journal of Agricultural and Food Chemistry. 59:12569-12577.