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United States Department of Agriculture

Agricultural Research Service

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Research Project: Evaluation and Maintenance of Flavor, Nutritional and Other Quality Attributes of Fresh and Fresh-Cut Produce

Location: Food Quality Laboratory

2012 Annual Report


1a.Objectives (from AD-416):
1. Evaluate the effects of pre-harvest production and post-harvest processing and storage treatments on fruit flavor, maintenance and/or enhancement in diverse accessions and breeding lines of Capsicum pepper, Malus serversii apple and blueberries; determine underlying molecular mechanisms controlling flavor quality. 2. Evaluate technologies to maintain the quality and marketability of fresh and fresh-cut produce through integrated microbiological and physiological approaches and innovations in post harvest handling, sanitation, and modified atmosphere packaging technology.


1b.Approach (from AD-416):
Mature produce from 30 to 240 accessions of non-cultivated and/or cultivated accessions of Capsicum peppers, Malus sieversii apple, lettuce and assorted microgreens, rabbiteye blueberry, raspberry, strawberry and tomato will be evaluated for flavor and nutritional quality-related substances using established gas chromatography, liquid chromatography and sensory methods and for shelf stability and overall marketability. Substances evaluated analytically will include aromatic volatiles, free sugars, organic acids, capsaicinoids and their analogs (pepper only), antioxidants (e.g., anthocyanidins, carotenoids, phenolic acids), vitamins (provitamin A, B9, C, E, K1) and radical scavenging/antioxidant enzymatic activities. Fresh and fresh-cut produce from accessions identified as having high flavor and/or associated nutritional quality attributes will be further evaluated for sensory quality using consumer (untrained) and trained panelists and for efficacy of pre- and post-harvest processing treatments to further enhance their quality. Pre-harvest treatments will primarily focus on emerging foliar potassium fertilization protocols that enhance nutritional quality and post-harvest treatments will emphasize modified atmosphere and light storage treatments (microgreens only), novel fresh-cut wash operations (primarily fresh-cut lettuce) and new technologies for improved cold chain integrity. Since these pre- and post-harvest treatments can affect overall quality, quality attributes of color, texture, visual appearance, electrolyte leakage, decay and microbial (aerobic, psychotropic, lactic acid bacteria, yeast and molds) growth will be determined as appropriate. If laboratory studies indicate that an intermediate rinse step between cutting and washing lettuce reduces accumulation or organic matter in the rinse water and improves sanitation, pilot plant evaluations will be conducted using specially designed processing equipment supplied by industry partners. In addition, intraspecific crosses will be made between peppers with high flavor/nutritional quality and commercial bell pepper breeding lines. Resulting F1 families will be selfed to create F2 mapping populations and segregating F2 populations will be selfed to create F3 populations. Fruit from F3 plants and parental lines will be phenotyped for flavor/nutritional quality and segregating F2 populations will be genotyped using SNP marker technology: quantitative trait loci (QTL) for flavor/nutritional quality attributes will be identified. In cooperation with collaborators, these QTLs will be introgressed into elite bell pepper breeding lines.


3.Progress Report:
Microgreens, (seedlings of edible green vegetables and herbs) have gained popularity as a new culinary trend over the past few years. Although small in size, microgreens can provide surprisingly intense flavor, vivid color and crisp texture and can be served as edible garnishes or new salad ingredients. However, the nutritional content of microgreens has yet to be evaluated. ARS researchers at Beltsville, MD, determined the concentrations of ascorbic acid (vit. C), carotenoids (provit. A), phylloquinone (vit. K) and tocopherols (vit. E) in 25 commercially available microgreens. Among the microgreens assayed, red cabbage, cilantro, garnet amaranth and green daikon radish had the highest concentrations of assayed nutrients. In comparison with fully mature leaves, the nutritional concentrations of corresponding microgreen cotyledonary leaves generally possessed 2- to 4-fold higher nutritional densities for all vitamins and carotenes. These data provide a scientific basis for further evaluating the nutritional values of microgreens, the results of which will serve as a reference for health agencies’ recommendations and consumers’ choices of fresh microgreens. Microgreens have delicate tissues that are susceptible to damage, dehydration and decay which limit their shelf life (3-5 days) and often require costly air transportation to reach their destination while still fresh. Studies were conducted to develop technologies and practical approaches to maintain quality and extend shelf life of microgreens. Results indicate that the shelf life of microgreens can be significantly extended by optimizing postharvest handling conditions, storage temperature, package atmosphere, sanitizing wash and dewatering. Under optimized packaging and storage conditions, acceptable quality of daikon radish and buckwheat microgreens can be maintained for over 14 days storage, enabling economic ground transportation, expansion of the microgreen market, and broader availability of these highly nutritious fresh foods to consumers. Fruit of green bell pepper (Capsicum annuum) often lack the unique flavor qualities of chili peppers. As a result, worldwide production of green bell peppers has stagnated while production of chili peppers has more than doubled over the past decade. While less cultivated than bell peppers, ají chili peppers (C. baccatum) are well known for their fruity flavor qualities. Based on analytical and sensory screenings of flavor quality-related attributes in fruit from 224 C. baccatum accessions, we have selected those accessions with the most fragrant and tasty fruit, hybridized them with each other and/or with a commercial C. annuum breeding line. Generations of pepper families have been created and three third generation families have been screened for fruit flavor quality. Identifications of a previously unknown flavor-related metabolic pathway for fruity flavor and of gene sets for other flavor quality attributes have been made. This on-going characterization in hybrid peppers is the first step towards development of improved C. baccatum cultivars with novel flavors and the introgression of those desirable attributes into bell pepper breeding lines.


4.Accomplishments
1. A new assay directly detects total phenolics in fruit and vegetable tissues. Folin-Ciocalteu (F-C), a universally used indirect measure of total phenolics in fruits and vegetables, is an assay which suffers from interfering substances, specifically ascorbic acid (AsA) and sugars. ARS researchers at Beltsville, MD, separated phenolics in strawberry fruit, which are naturally abundant in phenolics, AsA and sugars, by HPLC and determined their concentrations by F-C and by a recently developed assay, Fast Blue BB (FBBB), which detects phenolics directly. FBBB reported an average 2.9 fold greater concentration of total phenolics versus F-C, had a significant correlation (r=0.80; P=0.001) with total phenolics and did not interact with AsA or sugars. In contrast, the F-C assay appeared to under report total phenolic concentrations, had no significant correlation (r=0.20) with total phenolics or with sugars, but did have a significant correlation (r=0.64; P=0.05) with total AsA. Results from this study indicated that previous studies of strawberry fruit, using the standard indirect F-C assay, had greatly underestimated the total phenolics concentration and that this assay should be replaced in future studies by the direct and more accurate FBBB assay.


Review Publications
Albrecht, E., Saftner, R.A., Stommel, J.R., Zhang, D. 2011. Genetic diversity and population structure of Capsicum baccatum genetic resources. Genetic Resources and Crop Evolution. 59:517-538.

Hodges, D., Lester, G.E. 2011. Cucurbits [Cucumber, melon, pumpkin and squash]. In: Terry, L., editor. Health-Promoting Properties of Fruit and Vegetables. Wallingford, UK: CABI Publishing. p. 118-134.

Kausch, K.D., Sobolev, A.P., Goyal, R.K., Fatima, T., Laila-Beevi, R., Saftner, R.A., Handa, A.K., Mattoo, A.K. 2011. Methyl jasmonate deficiency alters cellular metabolome including the aminome of tomato (Solanum lycopersicum L.) fruit. Amino Acids. 42:843-856.

Kou, L., Turner, E.R., Luo, Y. 2012. Maintaining Quality of Edible Flowers with Controlled Release of 1-Methylcyclopropene and Modified Atmosphere Packaging. Journal of Food Science. 77(5):S188-S193.

Lester, G.E., Saftner, R.A. 2011. Organically versus conventionally grown produce: Common production inputs, nutritional quality, and nitrogen delivery between the two systems. Journal of Agricultural and Food Chemistry. 59:10401-10406.

Lewers, K.S., Luo, Y., Vinyard, B.T. 2012. Evaluating strawberry breeding selections for post-harvest fruit decay. Euphytica. 186:539-555.

Wu, Y., Luo, Y., Wang, Q. 2012. Antioxidant and antimicrobial properties of essential oil constituents encapsulated in zein nanoparticles prepared by liquid-liquid dispersion method. Journal of Food Science. 48:283-290.

Xiao, Z., Luo, Y., Luo, Y., Wang, Q. 2011. Combined effects of sodium chlorite dip treatment and chitosan coatings on the quality of fresh-cut d’Anjou pears. Postharvest Biology and Technology. 62:319-326.

Last Modified: 9/29/2014
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