Location: Food Quality Laboratory
2019 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” under National Program 306 “Quality and Utilization of Agricultural Products”, Component 1, Foods. Current report covers year 3 of a 4-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, 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 sub-objectives except objective 2B due to critical vacancy.
In terms of Objective 1, four elite strawberry cultivars from different U.S. regions were treated under different UVB dosages and foliar spray of calcium chloride. Fruit were collected at 75% red maturity, and their fruit quality traits and shelf-life were compared. We found that 1.0 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 after heat, microwave and ultrasound treatment. Our results indicate that the simple treatments can significantly boost the phenolics contents. This information will benefit consumers in obtaining more health benefit from these vegetables using these simple treatments.
For Objective 2, we did the transcriptome analysis of strawberry in response to UVB treatment and calcium. We identified 25 putative genes/functional markers related to strawberry fruit ripening and phenolics biosynthesis. We are preparing the constructs containing the selected five genes and verifying the functions of selected five genes by agroinfiltration. This work has been slowed down because of the critical vacancy and government shutdown.
Accomplishments
1. Ultrasound treatment enhances fruit flavor. Free flavor compounds in fruit contribute directly to fruit flavor, not the bound forms that have attached sugars. Bound forms of aroma compounds are odorless and do not enhance flavor. A key enzyme in fruits that removes the bound sugar, enhances the fruit flavor. However, the activity of the enzyme under normal fruit storage condition is low. ARS scientists in Beltsville, Maryland, used low ultrasound intensity and short treatment time to increase the activity of the enzyme (B-D glucosidase), and studied the effects of temperature and ultrasound treatments for improving enzyme activity for potential flavor enhancement. This study shows that ultrasound treatment is an effective approach to stimulate the activity of ß-D-glucosidase and can be used by researchers to develop commercial practices to enhance fruit aroma.
Review Publications
Chen, L., Lu, Y., Yang, T., Lu, Z. 2018. Optimized cultural conditions of functional yogurt for gamma-aminobutyric acid augmentation using response surface methodology. Journal of Dairy Science. 101(12):10685-10693. https://doi.org/10.3168/jds.2018-15391.
Yuan, P., Yang, T., Poovaiah, B.W. 2018. Calcium signaling-mediated plant response to cold stress. International Journal of Molecular Sciences. 19(12):3896. https://doi.org/10.3390/ijms19123896.
