Location: Food Quality Laboratory
2017 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 covers year 1 of a 4-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 and calcium. Objective 2 focuses on identification of key genes and/or signaling pathways associated with regulating fruit ripening, nutritional and sensory quality traits in response to effective treatments.
Strawberry is a non-climateric fruit, and the fruit ripening process is not clear. Thus, availability of effective postharvest storage management practices for strawberry are limited. To better understand the fruit development and ripening of strawberry, several novel chemical compounds (derivatives of benzoate) were tested on harvested fruit. These compounds displayed either stimulatory or delayed effects on fruit development and ripening. The effects of these chemicals on gene expression are being studied using RNA Sequence and RT-qPCR so as to identify the key genes affecting strawberry fruit ripening and quality.
In addition to the effects of exogenously applied compounds on regulation of strawberry fruit ripening, fruit ripening and quality are affected by environmental conditions such as light, UV in particular. 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 three films are Clear TIII film (standard clear, STD), TIII TES/IR film (TES), and TempCool™ film (TEM). TEM blocked 40% UV transmittance and TES lowered UV by 5%. The results indicated that strawberry genotype as well as the light composition during plant growth affected fruit quality and shelf life. Film type contributed dominantly for fruit weight loss. Films that block different levels of UV had no significant effect on total anthocyanin content or total phenolic content levels but significantly affected fruit color, total soluble solids and shelf life. For example, Monterey, Portola and Sweet Ann fruits had longer shelf-life under TEM, whereas Albion, San Andrea and Seascape lasted longer under TES. Thus plastic film selection requires consideration of plant genotype differences. In addition, harvested strawberry fruit were treated in the lab with UV-B light for different durations. The preliminary results showed that one time treatment was better than multiple treatments for fruit appearance and shelf life. Detailed analysis of metabolites and other parameters will be performed to determine the optimal treatment protocol.
Broccoli microgreens have been reported to contain abundant glucosinolates (GLS), especially glucoraphanin (GLR) and glucoerucin (GLE), which are associated with many health benefits. To boost the content of GLS in broccoli microgreens, the broccoli seedlings were treated with calcium chloride during the growth period, and with UV-B after harvest. Total aliphatic GLS levels increased significantly after 10 mM CaCl2 treatment, while postharvest UV-B radiation showed a minor effect on GLS contents. In addition, the synergistic study showed that 10 mM CaCl2 spray with UV-B treatments remarkably increased GLE and total aliphatic GLS contents in broccoli microgreens. The greatest proportion of variation for GLE, GLR, and total aliphatic GLS was attributed to calcium chloride. Thus, the enhancement of microgreen stress tolerance and defense by calcium chloride application could be the main factor for the increase in GLS levels. Peharvest CaCl2 and postharvest UVB have positive influence on maintaining the health-beneficial compounds and extending the shelf life of broccoli microgreens.
Accomplishments
1. Determination that the activity of a key enzyme in strawberry involved in fruit anthocyanin biosynthesis is regulated by calcium. Anthocyanins are beneficial to human health. A key enzyme increases the accumulation of anthocyanins in strawberry, however, the activity of this enzyme is inhibited by other compounds in the biosynthetic pathway responsible for anthocyanin production. ARS scientists in Beltsville, Maryland, found that calcium, together with a calcium binding protein, significantly reduced this inhibition. These results provide new fundamental information on regulation of the anthocyanin biosynthetic pathway and are of immediate benefit to researchers working to enhance fruit anthocyanin content. The results will ultimately benefit consumers with commodities that have improved fruit quality and nutritive value.
2. An enzyme for health promoting compounds in a wild eggplant has higher activity than its counterpart in cultivated eggplant. Eggplant produces a variety of phenolic compounds beneficial to human health, however, little is known regarding regulation of the biosynthetic pathway that produces these compounds. ARS scientists at Beltsville, Maryland, identified an enzyme designated as SrSHT in eggplant and one of its wild relatives that is believed to be important in the production of these compounds. Heat-shock/drought treatments stimulated the expression of this enzyme in both leaves and fruits, indicating its involvement in plant stress responses that stimulate production of phenolics. These results were exaggerated in wild eggplant. These results will benefit plant breeders who can breed genes from exotic crop relatives into new cultivars to develop phenolic acid rich fruit for eggplant and other solanaceous crops with improved nutritive value.
3. Genes involved in drought and heat stresses response in strawberry (Fragaria vesca) identified. Strawberry plants are highly susceptible to environmental stress and stress resulting from pathogen attack. ARS scientists teamed up with scientists at the University of Tennessee and identified 50 genes from the woodland strawberry, a relative of the cultivated strawberry. Different genes affected developmental stages of various strawberry tissues and others were important for leaf development and for fruit development. Some genes were more active in response to environmental and biological stress. These results will be used to develop strawberry varieties with improved quality and resistance to stress caused by environmental extremes and pathogens.
Review Publications
Peng, H., Yang, T., Whitaker, B.D., Shangguan, L. 2016. Calcium/calmodulin alleviates substrate inhibition in a strawberry UDP-glucosyltransferase involved in fruit anthocyanin biosynthesis. Biomed Central (BMC) Plant Biology. 16:197. doi:10.1186/s12870-016-0888-z.
Peng, H., Yang, T., Whitaker, B.D., Trouth, F.J., Shangguan, L., Dong, W., Jurick II, W.M. 2016. Characterization of spermidine hydroxycinnamoyl transferases from eggplant (Solanum melongena L.) and its wild relative Solanum richardii Dunal. Horticulture Research. 3:16062. doi: 10.1038/hortres.2016.62.
Lu, Y., Huang, L., Yang, T., Lv, F., Lu, Z. 2017. Optimization of a cryoprotective medium to increase the viability of freeze-dried Streptococcus thermophilus by response surface methodology. LWT - Food Science and Technology. 80:92-97. doi: 10.1016/j.lwt.2017.01.044.
Wang, X., Chen, X., Yang, T., Cheng, Z., Cheng, Q. 2017. Genomic identification of bZIP family genes involved in drought and heat stresses in strawberry (Fragaria vesca). International Journal of Genomics. Available: https://doi.org/10.1155/2017/3981031.
Yan, S., Liu, H., Yang, T., Luo, Y., Chen, P. 2017. Dual effectiveness of ascorbic acid and ethanol combined treatment to inhibit browning and inactivate pathogens on fresh-cut apples. LWT - Food Science and Technology. 80:311-320.
