Location: Food Quality Laboratory
2018 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 report documents progress for Project Number 8042-43000-015-00D, "Enhancing Fruit and Vegetable Nutritional Quality with Improved Phenolics Contents.” This report covers Year 2 of a 5-year project aimed at improvement of 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, 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. Progress was made on all objectives and associated subobjectives, all of which fall under National Program 306 “Quality and Utilization of Agricultural Products”, Component 1, Foods.
In regard to Objective 1, this past year strawberry fruits were treated with different dosages of UVB light. We compared the effects of UVB on fruit quality traits and shelf-life at different fruit ripening stages and different storage temperatures. We found that there was little effect of UVB on improving fruit quality of ripened fruit, while the beneficial UVB effect in immature fruit was observed in 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.
Strawberry fruits were also treated with two novel chemical compounds (derivatives of benzoate) which stimulated or delayed fruit development and ripening. The effective dosages of these chemicals were relatively low as compared to abscisic acid, a plant growth regulator for regulating strawberry fruit ripening. Low levels of these novel compounds relative to efficacious levels of the plant hormone abscisic acid were much more effective in regulating fruit ripening. These results are useful for further dissecting the underlying mechanics on controlling fruit ripening and developing new methodology to improve strawberry shelf-life.
In regard to Objective 2, we compared the effects of UVB light 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.
We also studied the effects of the novel benzoate derivatives described for Objective 1 on gene expression using whole genome RNA Sequence in order to understand the mechanisms by which these compounds influence strawberry fruit ripening. The putative key genes affecting strawberry fruit ripening were identified based on bioinformatic analyses and quantitative PCR. Verification of the function of a few selected genes in fruit ripening are under the way.
Accomplishments
1. Preserving broccoli microgreens with preharvest CaCl2 and postharvest UV-B treatments. Glucosinolates (GLS), are a class of phytonutrients which are beneficial to human health. Broccoli flower crowns have been known to be rich in GLS. ARS scientists found that broccoli microgreens, 10-14 day old seedlings, contained four-fold greater total GLS content than that in mature broccoli leaves and broccoli crowns. In addition, preharvest calcium chloride applications significantly increased total GLS levels, while postharvest UV-B light exposure further boosted GLS levels in microgreens. Furthermore, preharvest calcium spray resulted in improved overall visual quality and longer storage life. This research provides valuable information to consumers on nutritive value of broccoli microgreens and provides the microgreen industry a protocol to improve broccoli microgreen nutritional quality.
