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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Food Quality Laboratory

2013 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 sieversii 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, and rabbiteye blueberry 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. Additional species to be studied include lettuce, tomatoes, strawberries, raspberries, and assorted microgreens.

3. Progress Report:
Studies on the effect of retail store display case design and operation on product quality are progressing well. A multi-dimensional mapping of product temperature, quality and microbial growth profiles for various produce items located in different positions (shelf height, depth) under different operational conditions have been completed. The effect of thermodynamics of the cases, the effect of equipment duty cycles, and retail management practices on product temperature has also been investigated. The discovery that the large temperature differential between the front and back of the case negatively impacted the product quality and shelf life allowed manufacturers to redesign the equipment with improved temperature control features. The redesigned case is currently being tested for the ability to maintain temperature uniformity and shelf life of packaged fresh-cut produce. A significant reduction in operational energy cost is expected from the new design, in addition to benefits on product quality. Although phospholipase D alpha (PLD alpha) hydrolyzing activity is directly associated with softening and senescence in netted and non-netted muskmelons (Cucumis melo), a reproducible and specific enzyme assay has not been found in the literature. Therefore the purpose of this study was to develop a PLD alpha Ca++, pH, reaction time, and temperature specific assay to determine PLD alpha activity in middle- and hypodermal-mesocarp tissues from netted and non-netted honey dew muskmelon (melon) cultivars following simulated retail storage and display. The PLD alpha assay developed provides a reliable assay determining PLD alpha activity in netted and honey dew muskmelon fruits. However, the lack of a significant negative correlation of PLD alpha activity with fruit tissue firmness suggests that other systems may be in play. PLD alpha activity is known to be most active at pH 4.0 to 5.0. The proposed assay produced no PLD alpha activity at this acidic pH range; whereas peak activity in the melon system occurred at the more neutral, pH 5.7. Other PLD enzymes: PLD beta and PLD gamma are most active at neutral pH and will hydrolyze the critical substrate phosphatidylcholine (PC) when in the presence of phosphatidylethanolamine (PE). Melon hypodermal-mesocarp tissue is pH neutral and abundant in PE and PC. This suggests that melon fruit PLD-associated membrane senescence is very likely related to a cocktail of PLD enzymes: PLD alpha, PLD beta and/or PLD gamma rather than just one.

4. Accomplishments
1. Microgreens: the new food that’s a powerhouse of human bionutrients. USDA-ARS scientists at Beltsville, MD are the first to study the nutrient content of microgreens. Microgreens are leafy vegetables that are older than sprouts but much younger than baby greens. The scientists tested 25 commercially available microgreens and discovered that microgreens possess 2 to 4 times higher nutrient content in Vitamin C, Provitamin A, Vitamin K, and Vitamin E than the same plant’s mature leaves. These nutritional data will serve as a reference for health agency recommendations and consumer understanding of fresh microgreen options. In addition, the scientists optimized growing and harvesting conditions, and improved storage life from 3-5 to 14 days. This significant shelf life extension will enable microgreen growers to ship their product by ground transportation instead of air transit, with considerable cost reduction.

2. Moving cool season crops to higher latitudes changes the bionutrient density, but not always for the better. It is an accepted line of thought: that as cool-season crop production moves to higher latitudes (sub-tropics to the sub-arctic), due to global climate change pressures, exposure to longer light duration will provide higher nutritional concentrations. This is plausible as photosynthesis is triggered by light and is functionally dependent upon bio-nutrients (vitamin C, B9, E, K and carotenoids), but no studies exist. Using two different types (flat-leaf and crinkled-leaf) of spinach plants grown in both the sub-tropics and the sub-arctic, scientists at Beltsville, Maryland found that vitamin C was higher in the sub-tropics, whereas folate (B9) was higher in the sub-arctic, and phylloquinone (vitamin K) had a contrasting cultivar response to latitude and day-length. Lutein and total carotenoids were unaffected by latitude; whereas gamma-tocopherol was absent in sub-arctic spinach but was present in subtropical grown spinach. This study is important for other plant physiologists, food scientists, climate researchers, spinach breeders, and growers for an understating of plant bio-nutrient responses to changing environmental conditions.

Review Publications
Kou, L., Luo, Y., Yang, T., Xiao, Z., Turner, E.R., Lester, G.E., Wang, Q. 2013. Postharvest biology, quality and shelf-life of buckwheat microgreens. LWT - Food Science and Technology. 51(1):73-78.

Xiao, Z., Lester, G.E., Luo, Y., Wang, Q. 2012. Assessment of vitamin and carotenoid concentrations of emerging food products: edible microgreens. Journal of Agricultural and Food Chemistry. 60(31):7644-7651.

Lewers, K.S., Luo, Y., Vinyard, B.T. 2012. Strawberry breeding selections for postharvest fruit decay. International Journal of Fruit Science. 13:126-138.

Farnham, M.W., Lester, G.E., Hassell, R. 2012. Collard, mustard and turnip greens: Effects of varieties and leaf position on concentrations of ascorbic acid, folate, B-carotene, lutein and phylloquinone. Journal of Food Composition and Analysis. 27:1-7.

Lester, G.E., Lewers, K.S., Medina, M.B., Saftner, R.A. 2012. Compariative analysis of strawberry total phenolics via fast blue BB vs. folin-ciocalteu: assay interference by ascorbic acid. Journal of Food Composition and Analysis. 27:102-107.

Fernández Trujillo, J.P., Lester, G.E., Dos-Santos, N., Martínez, J.A., Esteva, J., Jifon, J.L., Varó, P. 2013. Pre-harvest muskmelon fruit cracking: causes and potential remedies. HortTechnology. 23:266-275.

Last Modified: 05/28/2017
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