Location: Food Quality Laboratory2019 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 microgreen.
3. Progress Report:
The quality and shelf-life of fresh-cut lettuce, strawberry, and whole grain products are important to breeders, growers, processors, and consumers. Working with our breeder and grower partners, scientists at the USDA-ARS in Beltsville, Maryland, used unique resources to perform sensory and instrumental analyses of several commodities to determine their quality and marketability from the consumer perspective. An untrained consumer panel was used to assess the quality of six varieties of fresh-cut romaine lettuce. Results showed differences in the quality and browning potential between lettuce varieties that had greater genetic diversity. Trained sensory panels were used to quantify the eating quality of ten strawberry cultivars and whole grain products (steam buns, pancakes) that were made with wheat processed using six different pre-treatments. Sensorial attributes that best described the appearance, flavor, and texture of strawberry fruit or whole grain products were developed using descriptive analysis. Sensory techniques were augmented with instrumental analyses like color and size quantification using image analysis, texture assessment, and physiochemical composition, such as pH, soluble solids content, and electrolyte leakage. Results showed significant differences in overall acceptability and quality among the strawberry cultivars, and among wheat pre-treatment methods. These results can be used in the development and selection of lettuce and strawberry cultivars with improved quality and the optimization of wheat bran processing to obtain whole wheat products that meet consumers’ expectations. NASA has recently started trials to grow microgreens in space due to the desirable flavors and nutrients. One challenge encountered is microgravity in space, which impacts fluid and gas distribution and greatly reduces the binding between seeds and soil particles, creating difficulties for fixating, germinating, and nourishing seeds. A research program was initiated at the Food Quality Lab at USDA-ARS to develop a convenient and reliable solution for growing microgreens in space. The concepts tested include (1) a durable substrate with patterned growth chambers and channels for nutrients, (2) a hydrophilic, biodegradable matrix with porous filling materials (e.g., wood or hemp fiber) that fixes the seeds and retains water and nutrient, (3) a reservoir for water and fertilizer, and (4) a control system that analyzes the status of the plant and delivers nutrients at desirable doses and mixing ratios. In the preliminary trials, two commercially available water absorbents were employed as the matrix and compared against soil for their support on mizuna microgreens at varied water/polymer ratios. While these polymers showed good water-holding capacity, they did not provide adequate water and air for seed germination. Future studies will focus on modifying the polymer and soil mix to balance the needs for seed- and water-holding and water and air availability. Project team continued and expanded the water composition and chemical analysis to include lettuce, carrots, and onions. Results obtained so far showed both similarities and uniqueness among the wash water samples. Sugars are the predominant contributor to chemical oxygen demand (COD) in all wash water samples, followed by proteins, organic acids, and phenolic compounds. Among the produce types, carrot, cabbage, and onion wash water carry far higher COD than that of lettuce wash water. However, while cabbage and onion wash water exhibited higher chlorine demand (CLD) than lettuce water, the CLD for lettuce water was greater than that for carrot water. Proteins were found to be the most significant contributor to CLD in iceberg lettuce (50% contribution), romaine lettuce (51% contribution), cabbage (50% contribution), and onion (36%) wash water, while its contribution in carrot wash water was relatively small at 17% contribution. Sugars contributed to less than 15% of the total CLD in lettuce, cabbage, and onion, despite their predominant presence; however, they accounted for over 32% of the CLD in carrot wash water. Approximately 20% of the CLD for all water samples comprised phenolic compounds in the first five minutes, but that percentage decreased substantially as chlorination progressed. Water fractionation was further performed to investigate the distribution of COD and CLD among different classes of compounds. Results showed that low molecular weight (3 kDa or less), polar, and negatively charged fractions contributed to over 90%, 50 to 70%, and 5 to 30%, respectively, of the total COD in different types of wash water samples. Follow-up studies will be performed to establish the CLD distribution among the fraction of wash water, as well as potential treatment plans to mitigate COD and CLD during produce washing. This continuing study expands knowledge on the source of COD and CLD in various fresh produce wash water and provides essential information for produce processors to develop safe, effective, and economical wash water treatment/reuse and chlorine replenishment strategies. Kale is known as one of the most nutritious vegetables and is well liked by consumers. Microgreens are generally known to be nutrient dense. However, the nutrition profile of microgreen vs mature kale is unknown. USDA food scientists and nutritionists have teamed up in a study to compare the health benefits of microgreen kale to those of mature kale, in rats fed a diet incorporating the vegetable at the two different maturities. Darkibor kale seeds, the main cultivar of kale sold as a mature vegetable in grocery stores were cultivated in nested trays, filled ¾ full with a peat based potting soil watered to saturation. Seeds were spread evenly over the soil surface and kept in the dark for 3½ days. On the fourth day microgreens were exposed to LED light from fixtures comprising several wavelengths optimized for general plant growth, for a 12-hour photoperiod. A clear plastic cover over the tray limited moisture evaporation and plants were watered as needed by lifting the top tray, with holes and pouring water into the bottom tray. Plants were harvested between day 10 and day 12, freeze dried, and incorporated into the rats’ diet. Diet studies are on-going. Rats will be monitored for several key indicators of health such as cholesterol and triglyceride levels. Results will help elucidate the health effects of microgreen and mature kale vs controls.
1. Romaine lettuce varieties with reduced browning potential. Pinking and browning discoloration is a major quality defect that significantly impacts the fresh-cut produce industry. Current technology to curtail such a problem via initial nitrogen gas flush and the use of packaging films with low oxygen transmission rate is costly. ARS researchers in Beltsville, Maryland, identified several romaine lettuce varieties that are resistant to this browning defect. The use of resistant varieties identified by the researchers will significantly improve product quality and shelf life, and decrease the operational cost. Findings from this study also provides important information for breeders to develop new lettuce varieties with improved quality and shelf-life traits.
2. A novel patented fresh wash system removes organic materials and conserves water. In commercial production facilities the accumulation of organic materials in the wash system reacts with chlorine and helps bacteria survive when chlorine is depleted. ARS scientists in Beltsville, Maryland, invented a novel “in-flight” wash system that removes organic materials early in the process without damaging plant tissues. The new process exposes all surfaces of the produce to the solution, resulting in effective removal of organic matter from cut produce and improved process control and wash efficacy. This system also allows exceptionally efficient use of the vertical space in the processing plant. The fresh produce industry is scaling up this technology for commercialization.
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