Location: Food Quality Laboratory
2017 Annual Report
Objectives
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.
Approach
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 microgreen.
Progress Report
Browning reactions are the most important defect that impacts the quality and shelf life of fresh-cut lettuce. To control browning, processors rely on reducing oxygen and increasing carbon dioxide levels inside packages. However, this practice does not fully solve the browning problem; furthermore, these atmospheric conditions result in product spoilage and quality deterioration due to abnormal anaerobic respiration and carbon dioxide injury. Elevated carbon dioxide levels also cause virulence development in human pathogens, increasing food safety risks. Therefore, selecting or breeding lettuce varieties with reduced browning potential for fresh-cut processing could lead to chemical-free and environmentally friendly approaches to address these major food quality and safety problems. In response to stakeholder requests, scientists at the USDA-ARS in Beltsville, Maryland, initiated a research project and worked collaboratively with lettuce breeders and growers in evaluating lettuce varieties for browning potential during fresh-cut processing and storage. Lettuce samples of commercial varieties and new breeding lines were harvested in Salinas, California and shipped to Maryland by fresh-cut processors via in-kind support. The products were processed in our pilot plant and packaged under various atmospheric conditions. Browning potential, quality retention, and sensory attributes were evaluated over time during storage. The evaluated lettuce varieties showed large genetic diversity with significant differences in browning potential. Results to date were shared with industry stakeholders and received very positive feedback. Project completion is expected to enable the growers and processors to utilize new lettuce varieties with improved quality, shelf life, and food safety.
Consumers are becoming increasingly health conscious and are looking to purchase food snack products that are fresh, healthy, and convenient, such as single-serving fresh-cut fruit and vegetables. In the United States, fresh-cut fruit is sold in a variety of simple plastic packages. However, many of these are not ideal for storing fruit and may result in the product having a shorter shelf-life and lower quality. To address these challenges, novel food packages with absorbent materials have recently emerged, but their effectiveness in maintaining quality and shelf life have not been scientifically evaluated. Working with our industry partners, scientists at the USDA-ARS in Beltsville, Maryland, used our unique resources to perform sensory and instrumental analyses of watermelon quality and marketability after storage in novel food packages. Sensory evaluation was conducted to determine the acceptance of snack-sized watermelon packages (novel and traditional packaging methods) during storage using an in-house trained panel, untrained consumer panel, and consumer focus group. Instrumental analysis quantified the watermelon texture, color, and sugar changes during storage in each package type. Results showed that the novel packaging with absorbent materials helped extend the shelf life and improve the overall sensory quality by absorbing excess juice exuded by the watermelon. These results can be used in the design and optimization of absorbent materials for fresh-cut fruit and vegetable packaging to yield higher quality products with a longer shelf life.
Fresh-cut processors have a strong economic incentive to reuse and reduce fresh-cut produce wash water. Environmental benefits from water conservation are also significant. However, sanitizer instability in the presence of high organic load is a major weakness in the current industrial fresh-cut produce washing. Spent processing wash water contains a variety of organic compounds which react with and deplete free chlorine, the most commonly used sanitizer in the fresh produce industry, leading to inadequate disinfection, increased risk of cross-contamination with spoilage microorganisms, and consequent loss of quality and shelf life of the products washed in it. Identifying major chemical compounds responsible for chlorine demand is a major stakeholder need. USDA-ARS scientists at Beltsville, Maryland conducted an in-depth investigation of the chemical mechanisms underlying the rapid depletion of sanitizers. The researchers studied the main types of organic compounds that are released into the water during fresh produce washing; sugars, proteins, phenols, and organic acids and determined the compounds’ reactivity with free chlorine. Results showed that the chlorine consumption was dependent on the abundance and reactivity, both of which varied significantly for different types of organic molecules. Proteins and peptides were both moderately abundant and reactive; these compounds were identified as major reactants with free chlorine in cabbage wash water. These findings provide important guidance for selecting parameters to monitor and maintain chlorine in the wash water and for implementing strategies to treat and reuse the wash water.
Accomplishments
1. A new technology enables on-demand fruit ripening and reduces waste. The United States is losing up to 40% of its food at a cost of $165 billion annually. The main contributors are product spoilage due to varied fruit ripening times, spoilage during shipping, and rapid quality loss when ethylene, a plant hormone, is applied to promote ripening. Ethylene is a highly flammable gas and is only applied by skilled operators using specialized produce shipping or storage containers. In these conventional ethylene applications, large containers of fruits ripen at once and spoilage occurs before it gets to the consumers. To solve this problem, ARS scientists in Beltsville, Maryland, developed a new method to embed the ethylene gas in a plastic coated with copper. This process is being patented. Now ethylene can be applied by anyone when needed, shortening the time between when fruits ripen and when they are consumed. This new technology reduces product waste while maintaining excellent quality, longer shelf life, and better nutrition.
Review Publications
Gao, J., Luo, Y., Turner, E.R., Zhu, Y. 2017. Mild concentration of ethanol in combination with ascorbic acid inhibits browning and maintains quality of fresh-cut lotus root. Postharvest Biology and Technology. 128:169-177.
Yan, S., Luo, Y., Zhou, B., Ingram, D. 2017. Dual effectiveness of ascorbic acid and ethanol combined treatment to inhibit browning and inactivate pathogens on fresh-cut apples. LWT - Food Science and Technology. 80:311-320.
Zhang, B., Luo, Y., Kanyuck, K., Bauchan, G.R., Mowery, J.D., Zavalij, P. 2016. Development of metal-organic framework for gaseous plant hormone encapsulation to manage ripening of climacteric produce. Journal of Agricultural and Food Chemistry. 64(25):5164-5170.
Jiang, X., Huang, H., Xiao, Z., Yu, L., Pham, Q., Yokoyama, W.H., Yu, L., Luo, Y., Wang, T.T. 2016. Red cabbage microgreens lower circulating LDL, liver cholesterol and inflammatory cytokines in mice fed a high fat diet. Journal of Agricultural and Food Chemistry. 64(48):9161-9171.
Gombas, D., Luo, Y., Brennan, J., Shergill, G., Petran, R., Walsh, R., Hau, H., Khurana, K., Zomorodi, B., Rosen, J., Varley, R., Deng, K. 2017. Guidelines to validate control of cross-contamination during washing of fresh-cut leafy vegetables. Journal of Food Protection. 80(2):312-330.
