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United States Department of Agriculture

Agricultural Research Service

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Research Project: Innovative Ultraviolet-B Processing to Enhance Health Promoting Bioactive Components in Specialty Crops

Location: Healthy Processed Foods Research

2012 Annual Report

1a. Objectives (from AD-416):
(1) Establish which specialty crops respond best to UV-B treatment for the enhancement of their health-promoting properties (e.g. phenolics, antioxidants) and determine dose-response. (2) Establish the localized and distal effects of UV-B treatment on plant tissues (e.g. skin vs. interior). (3) Determine the effect of postharvest conditions on the synthesis of phenolic compounds with and without UV-B treatment and analyze the stability of these compounds during normal storage. Determine the effects of these treatments on sensory quality and nutritional value. (4) Verify enhanced bioavailability of phenolic compounds following UV-B treatment using in-vitro and in-vivo methods.

1b. Approach (from AD-416):
Recently harvested produce, including whole and precut fruits and vegetables such as whole grapes, whole berries, cherry tomatoes, baby carrots, broccoli florets, and apples will be exposed to UV-B treatments at different doses. Effectiveness of the treatments will be evaluated and subsequently optimized based on increased phenolic compound concentrations, antioxidant capacity, and PAL activity. Increases in specific compounds, such as trans-resveratrol, anthocyanins, quercetin glycosides, tocopherols, and carotenoids will be determined through HPLC analysis. The potential impact or improvement resulting from UV-treatment on quality factors (color, firmness, acidity/sweetness ratio, ascorbic acid, etc.), sensory attributes, respiration rate (under controlled atmosphere, temperature, and %RH) and shelf-life will also be evaluated for the most promising samples. Changes in the bioavailability of phenolic compounds from UV-B treated fruits and vegetables will be verified using both in-vitro and in-vivo methods.

3. Progress Report:
In order to investigate the hypothesis that crops are naturally protected from UV exposure, may be more UV- B responsive than fruits and vegetables typical exposed to natural sunlight during growth, we screened white sweet corn and a number of root crops, including sweet potatoes, six varieties of colored potatoes, and sliced sweet potatoes, radish and daikon. In addition, we conducted a depth analysis on carrot responsiveness to UV-B treatment focused on three areas: 1) the synergistic response resulting from the combination of wounding and UV-B treatment, 2) the influence of genotype on responsiveness, and 3) processing conditions that yielded maximal enhancement of antioxidant activity without reducing product quality. Research efforts consisted of nearly 900 samples, including whole and precut root crops and vegetables evaluated under multiple conditions, and confirmed that among the crops tested, carrot is the most responsive to UV-B treatment. Samples of whole sweet potatoes, colored potatoes, and white sweet corn, and sliced sweet potatoes, radish and daikon did not show a measurable response to UV-B treatment. We evaluated five commercial pre-cut carrot products possessing increasingly greater area/weight ratios and found that UV-B responsiveness, as measured in terms of TSP, antioxidant content, chlorogenic acid content, and PAL activity, increased directly as the area/weight ratio increased. We also found that UV-B light exposure only slightly increased the surface temperature of the carrot samples and did not stimulate the accumulation of carotenoids. Analysis of the 21 varieties of UV treated carrots revealed that response and the level of responsiveness was dependent upon the color of the carrot, suggesting that genotype and phenotype plays a role in determining responsiveness. The effect of post-UV treatment conditions and cold storage on the synthesis and stability of phenolic compounds in carrots with and without UV-B treatment was examined. We found that increases in the TSP content of UV treated carrot products were dose and temperature dependent. We were able to identify optimal treatment, handling, and packaging conditions that produced a 2-fold increase in antioxidant content in baby carrots while maintaining product quality that was shelf-stable for 21 days. Bench sensory tests indicated that there were no differences in flavor, odor, appearance and texture between UV-treated and control baby carrots. This project relates to objectives 1 though 3 from the parent project, in which the objectives were addressed.

4. Accomplishments

Last Modified: 10/19/2017
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