Location: Food Quality Laboratory
2020 Annual Report
Objectives
The overall goal of this project is to identify effective treatments that lead to improved product quality and nutritional value, and to identify the associated genetic elements responsible for fruit ripening and stress responses. Specific objectives are listed as follows:
Objective 1: Evaluate and characterize changes in fruit ripening, postharvest nutritional and sensory quality parameters of strawberries due to pre- and post- harvest treatments with selected compounds, UV and calcium.
Sub-objective 1.A. Identify effective treatment strategies that delay fruit ripening, improve postharvest nutritional and sensory quality parameters, and extend shelf-life.
Sub-objective 1.B. Apply selected effective treatments to commercially harvested varieties of strawberries from different geographical regions, and validate efficacy and applicability of treatment(s) for industry.
Objective 2: Identify key genes and signaling pathways regulating fruit ripening and biosynthesis of sugars, acids, volatile compounds and phenolics in response to effective treatments.
Sub-objective 2.A. Conduct bioinformatic analyses of global gene expression profiles and correlate results with those obtained for physiological, metabolomic and sensory evaluations and identify candidate genes and signaling pathways that regulate the nutritional and sensory quality parameters.
Sub-objective 2.B. Produce transgenic plants/fruits with the increased or reduced expression of selected candidate genes. Determine whether the up- and down- regulation of a single gene may mimic the improved quality traits that were observed in wild-type fruits following treatments.
Approach
Locally grown strawberry fruit will be subjected to pre- and postharvest treatments with selective compounds, ultraviolet irradiation and calcium. Selective compounds are synthesized organic compounds, for example, the derivatives of benzoate, which have shown effect on fruit ripening and color. Fruit quality traits including firmness, soluble solid content, total titrable acid content, color and decay, as well as sensory parameters, such as taste, flavor and appearance, will be evaluated. Treatments that enhance nutritional and sensory quality will be further tested on diverse strawberry varieties produced by commercial strawberry growers throughout the United States. The metabolome profiles of targeted fruit phenolics and volatile compounds correlated to nutrition and flavor/aroma in selected treatments will be analyzed by HPLC and GC-MS to determine which metabolites and pathways are altered. Global gene expression profiles in treated fruit will be analyzed by RNA sequence and bioinformatics analysis. The analyses will focus on genes involved in oxidative signaling, calcium signaling, and ABA signaling, as well as on the phenylpropanoid pathways and genes affecting biosynthesis of sugars, acids, volatile compounds. Stable or transient transformation with silencing or over-expression gene constructs driven by constitutive or fruit-specific promoters will be used to assess the function of specific genes in various aspects of fruit physiology and metabolism, including ripening, sensory parameters, responses to stresses, and accumulation and/or retention of health-beneficial secondary metabolites from the phenylpropanoid pathway. Quality traits including flavor, color, firmness, stress tolerance, and phytonutrient content will be analyzed in the transgenic lines.
Progress Report
This is the final report for Project Number 8042-43000-015-00D “Enhancing Fruit and Vegetable Nutritional Quality with Improved Phenolics Contents” under National Program 306 “Quality and Utilization of Agricultural Products”, Component 1, Foods. It covers the four year project with the aim to improve fresh produce quality, including appearance, texture, flavor, and nutrition. Objective 1 is to evaluate and characterize changes in fruit ripening, post-harvest nutritional and sensory quality traits, and shelf-life of strawberries due to pre- and post-harvest treatments with selected compounds, ultraviolet (UV) light and calcium. Objective 2 focuses on identification of key genes and/or signaling pathways associated with regulating fruit ripening, and nutritional and sensory quality traits in response to exogenous treatments.
In terms of Objective 1, fruit and vegetables were treated with UVB, calcium, ultrasound and microwave during growth stage (preharvest) and after harvest (postharvest).
Preharvest UV treatment was done for six strawberry cultivars grown in low tunnels covered with three plastic films which can differentially block the UV transmittance. The results indicated that strawberry genotype was the main factor affecting fruit quality and shelf life. Film type contributed dominantly for fruit weight loss. Films that block different levels of UV significantly affected fruit color, total soluble solids and shelf life. Thus plastic film selection requires consideration of plant genotype differences.
We compared the effects of UVB on fruit quality traits and shelf-life at different fruit ripening stages and different storage temperatures. There was little effect of UVB on improving fruit quality of ripened fruit, while the beneficial UVB effect in immature fruit was observed for postharvest quality. Temperature significantly affected the effectiveness of UVB treatments. Higher temperature could facilitate the UVB effect. This information is important for industry how to use UVB to treat strawberry fruits for better fruit quality and longer shelf-life.
Four elite strawberry cultivars from different U.S. regions were treated under different UVB dosages and foliar spray of calcium chloride. We found that one mM calcium spray significantly increased fruit total soluble solids, phenolics content, and shelf life as compared with no calcium control. In particular, when UV dosage was over 0.15 W/m2 (UV index 6 or more), 1-5 mM CaCl2 spray demonstrated highest fruit quality benefit for all the cultivars. The UV index for strawberry fruiting season are usually between 5 to 9. Thus this information is important for growers to use calcium spray for increasing the fruit quality and shelf life.
We also studied the phenolics changes in broccoli and eggplant in response to temperature, microwave and ultrasound treatment. For example, glucosinolate levels of broccoli microgreens increased significantly after preharvest 10 mM CaCl2 and UVB treatments, while postharvest UV-B radiation showed a minor effect. Ultrasound treatment is effective to activate ß-D-glucosidase with potentially aroma enhancing capability. Our results indicate that the simple treatments can significantly boost the phenolics contents. This information will benefit all the consumers to obtain more health benefit using the simple treatments before cook the vegetables.
In support of Objective 2, we compared the effects of UVB on the expression of UVB responsive genes and the key genes in the phenylpropanoid pathway and related branch pathways under different temperatures. The gene expression results agreed with the Objective 1 observations of fruit quality traits after UVB treatments. The UVB responsive genes of ripened fruits were less responsive to UVB than the developing fruits.
In order to identify new method to control fruit development and ripening, a collection of 10,000 compounds were used to screen their effect on strawberry growth. About twenty compounds showed stimulatory or inhibitory effect on fruit development and ripening. One compound showing clear stimulatory effect was selected for analyzing gene expression changes during fruit development. RNA Sequence analysis indicated that over one hundred genes responded to the chemical treatment. Those genes were related to stress responses, such as abscisic acid action genes, auxin action genes. They can be used as functional markers for industry management and breeding program.
Further, two genes affected by the novel compound were used for transgenic studies to confirm their function in plants. It was observed that increased expression of ABI5B or reduced expression of IAA27 promoted strawberry fruit ripening, whereas decreased expression of ABI5B or increased expression of IAA27 inhibited fruit ripening. Analysis of the transgenic fruits at red stage showed that there were no significant differences on fruit quality traits, including total soluble solids, total phenolics and anthocyanins. The results indicate that ABI5B and IAA27 are positive and negative regulator of fruit ripening respectively. They could be used for further genome editing to produce possible new cultivars with reduced fruit ripening and long shelf-life.
Accomplishments
1. Microwave cooking increases anticancer compounds in broccoli. Broccoli cooked in a microwave oven produces an anticancer compound, sulforaphane. ARS scientists in Beltsville, Maryland, investigated and found that microwave and low-temperature cooking increases sulforaphane contents in broccoli by about 80%. Using a high-power microwave with a short time was better than low-power microwave cooking. With this information, consumers receive the most benefit from cooked broccoli.
Review Publications
Lu, Y., Pang, X., Yang, T. 2020. Microwave cooking increases sulforaphane level in broccoli
. Food Science and Nutrition. 8(4):2052-2058. https://doi.org/10.1002/fsn3.1493.
Jurick II, W.M., Peng, H., Beard, H.S., Garrett, W.M., Macarisin, O., Peter, K., Gaskins, V.L., Yang, T., Lu, Y., Mowery, J.D., Bauchan, G.R., Cooper, B. 2019. Blistering1 modulates Penicillium expansum virulence via vesicle-mediated protein secretion. Molecular and Cellular Proteomics. https://doi.org/10.1074/mcp.RA119.001831.
Sun, Y., Zeng, L., Xue, Y., Yang, T., Cheng, Z., Sun, P. 2019. Effects of power ultrasound on the activity and structure of ß-D-glucosidase with potentially aroma-enhancing capability. Journal of Food Science and Nutrition. 7:2043-2049. https://doi.org/10.1002/fsn3.1035.
