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United States Department of Agriculture

Agricultural Research Service

Research Project: Metabolomic and Microbial Profiling of Tropical/subtropical Fruits and Small Fruits for Quality Factors and Microbial Stability

Location: Citrus and Other Subtropical Products Research

2013 Annual Report


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: Study of the effect of field nutritional sprays on Huanglongbing was continued for a third season. Four harvests were performed, with two harvests for each ‘Hamlin’ and ‘Valencia’, the two main industry cultivars grown for processing. Samples are being analyzed for chemical components as well as sensory evaluation. Poncirus x Citrus hybrids, with potential for Huanglongbing (HLB) tolerance, were evaluated for eating quality. Hybrids with 25% poncirus in their background (second generation) had a peculiar taste and flavor. They were very high in volatile esters, monoterpenes and sesquiterpenes (number and quantity). However, there was no clear pattern of inheritance for non-volatile compounds. These hybrids with a long term potential interest for dealing with HLB will continue to be evaluated. Collaboration with the University of Florida strawberry and blueberry breeders was continued to evaluate new hybrids by sensory and chemical analysis. A feasibility study was performed to evaluate the crispness trait in processed blueberries. Ten years of tomato flavor data on University of Florida breeding lines has been compiled for publication.

Objective 2: Detection of DNA from Candidatus liberibacter asiaticus, the bacterium responsible for HLB disease, in orange juice was optimized. Preliminary observations seem to indicate a correlation between the amount of DNA present in the juice and off flavor. Further correlations are sought using the electronic tongue and chemical analyses. Sensory evaluation of Citrus x Poncirus hybrids and tangerine hybrids further revealed the importance of certain volatile compounds for tangerine flavor, such as aldehydes with citrus aroma, and carvone. Off flavor in orange pulp was determined to be caused by para-vinyl guaiacol (PVG). It is hypothesized that high levels of PVG are produced by a heat tolerant yeast, Rhodotorula rubra; this hypothesis is being tested by inoculating R. rubra in sterile pulp. Several plant essential oils were tested against E. coli, Penicillium digitatum and the citrus black spot organism, Guignardia citricarpa. Some oils, including carvacrol, trans-cinnamaldehyde and cinnamaldehyde, had strong activity against Guignardia, Penicillium and E. coli. In vivo studies are being conducted. Trichoderma viridae extracts were tested as antimicrobial agents against the citrus canker organism (Xanthomonas citri subsp. citri) and E. coli ,with positive results with E. coli. Objective 3: The effect of storage temperature, packaging and postharvest decay control with ClO2 (Curoxin®) was evaluated on strawberries, blueberries, grape, lychee and cut cantaloupe. Curoxin® significantly reduced postharvest decay, as well as maintained firmness for whole berries such as strawberries, blueberries and grapes. For the most part, fruit color was maintained in storage. Furthermore, Curoxin® may have a beneficial effect on strawberry weight loss through regulation of stomata opening.


4.Accomplishments
1. Detection of Candidatus liberibacter DNA in orange juice. ARS researchers from Fort Pierce, Florida optimized a polymerase chain reaction (PCR) technique that allowed isolation and quantification of DNA from Candidatus liberibacter asiaticus, the bacteria responsible for Huanglongbing (HLB) or greening disease in citrus, in orange juice. The citrus industry needs a fast method to determine the amount of HLB juice in juice blends to control the quality of orange juice. Orange juice made with fruit from trees severely affected by the HLB disease have a distinct off flavor. Detecting and quantifying the DNA in juice is one of the many methods that will be available to orange juice processors for quality control.

2. Strawberry variety release. The University of Florida released a new strawberry cultivar, FL 09-127, with the help of ARS researchers from Fort Pierce, Florida for sensory quality evaluation, sugars and acids. This cultivar is adapted to climates with mild winters, and has consistently produced fruit with outstanding eating quality, being sweeter and with higher sugar levels than other cultivars in the trial most of the time. A name has been submitted to the patent office. New cultivars with improved market potential benefit Florida strawberry growers.


Review Publications
Dea, S., Brecht, J.K., Nunes, M.N., Baldwin, E.A. 2013. Optimal Ripeness Stage for Processing ‘Kent’ Mangoes into Fresh-cut Slices. HortTechnology. 23:12-23.

Imahori, Y., Yamamoto, K., Tanaka, H., Bai, J. 2013. Residual effects of low oxygen storage of mature green fruit on ripening processes and ester biosynthesis during ripening in bananas. Postharvest Biology and Technology. 77:19-27.

Bai, J., Ford, B.L., Manthey, J.A., Luzio, G.A., Cameron, R.G., Narciso, J.A., Baldwin, E.A. 2013. Effect of Extraction, Pasteurization and Cold Storage on Flavonoids and other Secondary Metabolites in Fresh Orange Juice. Journal of the Science of Food and Agriculture. 93:2771-2781.

Last Modified: 8/19/2014
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