Location: Commodity Protection and Quality Research
2025 Annual Report
Objectives
Objective 1: Develop new preharvest approaches to enhance fruit quality and reduce postharvest diseases.
• Sub-objective 1A: Evaluate the effects of anti-transpiration agents on water loss and fruit quality of blueberries.
• Sub-objective 1B: Evaluate the effects of preharvest applications of plant disease-resistance elicitors on fruit quality and control of postharvest diseases of blueberries.
Objective 2: Develop new postharvest technologies to maintain fruit quality and control postharvest diseases.
• Sub-objective 2A: Evaluate generally-recognized-as-safe products or food additives applied as a postharvest treatment via different application technologies for control of postharvest fruit rot diseases of blueberries.
• Sub-objective 2B: Develop coatings with/without antifungal products for reducing water loss and postharvest fruit rot diseases of blueberries.
• Sub-objective 2C: Evaluate generally-recognized-as-safe products or food additives applied as a postharvest treatment via different application technologies for control of postharvest fruit rot diseases of table grapes.
Approach
The goal of this project is to develop new pre- and postharvest approaches to maintain postharvest quality and control postharvest fruit rots and thus extend storage and shelf life of fresh fruits. Field and laboratory experiments will be conducted to evaluate preharvest use of disease resistance inducers and anti-transpiration agents to increase blueberry fruit tolerance to postharvest diseases and enhance fruit quality. Fruit quality parameters, postharvest disease development, plant chemicals such as flavonoids and phenolic contents, and the activities of known defensive enzymes in the fruit will be analyzed to determine their relationships. Laboratory and cold storage experiments will be conducted to develop new postharvest approaches using generally-recognized-as-safe substances such as peroxyacetic acid and cold plasma-activated hydrogen peroxide and antimicrobial food additives such as natamycin applied via new postharvest application technologies to control postharvest fruit rots and retain fruit quality of blueberries and table grapes. Laboratory and cold storage experiments will also be conducted to develop coatings with/without antifungal products for reducing water loss and postharvest fruit rot diseases of blueberries.
Progress Report
This is the final report for project 2034-43000-041-000D, "New Approaches to Enhance Fresh Fruit Quality and Control Postharvest Diseases”, which was replaced by new project 2034-30600-001-000D, “Innovative Approaches to Control Postharvest Diseases and Expand Market Opportunities of Fresh Fruits”.
Substantial results were realized over the five years of the project. Progress was made on all objectives and sub-objectives.
In support of Sub-objective 1A, progress was made in evaluating Parka, a spray treatment applied in the field that supplements the fruit cuticle, for the ability to improve the postharvest life of blueberries. Multiple sprays over time to two different varieties were applied prior to harvest and the fruit evaluated at various points during cold storage and simulated marketing. All standard measures of postharvest quality were unchanged for both varieties at each evaluation. Due to the lack of effectiveness of Parka, no further research was done with this product. Preliminary work was done with the antitranspirant Vapor Gard, but it was found to severely inhibit ripening of the fruit which was undesirable. No suitable products for blueberries were identified during the project.
Under Sub-objective 1B, ARS researchers in Parlier, California, made significant progress in assessing the effects of plant resistance inducers applied in the field on postharvest fruit rot diseases and fruit quality of blueberries. When benzothiadiazole and potassium silicate, known plant resistance inducers, were applied to blueberry plants four times during the growing season, benzothiadiazole significantly reduced the percentage of naturally occurring decayed fruit compared to the non-treated control in one of the three seasons, and potassium silicate significantly reduced the percentage of decayed fruit compared to the non-treated control in two of the three seasons. A significant increase in soluble solids and reduction in titratable acidity was observed in the fruit treated with benzothiadiazole and potassium silicate for the second and third years of the experiment, indicating that both treatments may have enhanced fruit maturity. ARS results suggest that preharvest use of benzothiadiazole and potassium silicate had limited efficacy in postharvest disease control but may have potential as tools for adjusting fruit maturity of blueberries.
For Sub-objective 2A, ARS researchers in Parlier, California, made significant progress in developing postharvest treatments with natamycin for control of postharvest diseases of blueberries. Natamycin is generally recognized as a safe product and has recently been registered in the United States for postharvest use on certain fresh fruits such as citrus but not yet for blueberries. Natamycin applied as either a spraying or dipping treatment, even at one-fourth of the label rate used for citrus fruit, was highly effective in controlling postharvest diseases of blueberries and had no adverse effect on fruit quality during the storage. ARS results suggest that natamycin is a promising tool for control of postharvest fruit rot diseases of blueberry while maintaining fruit quality. The data from this research is being used to support registration of natamycin for postharvest use on blueberries in the United States.
In support of Sub-objective 2A, significant progress was made to further explore new postharvest application technologies to apply natamycin to control postharvest fruit rot diseases of blueberries. ARS researchers in Parlier, California, evaluated the effectiveness of a postharvest fogging treatment with natamycin to control fruit rots of stored blueberries. Commercially harvested blueberries placed in plastic totes were palletized and fogged with natamycin and then stored for four weeks in a cold storage. Natamycin fogging treatment significantly reduced fruit rots in treated blueberries compared to fruit fogged with water (control). In general, the fruit fogged with natamycin on the top layer had a significantly lower level of fruit rots than those at middle and bottom layers within the pallet, but increasing the volume of natamycin solution and fogging duration enhanced the efficacy of natamycin for control of fruit rots, likely due to improved distribution and coverage of fruit by natamycin within the pallet.
Under Sub-objective 2A, significant progress was made in evaluating the effectiveness of natamycin applied as a postharvest treatment using an electrostatic spray system (ESS) in comparison with a conventional sprayer for control of postharvest fruit rot diseases of blueberries. Natamycin treatments significantly reduced fruit rots compared with the nontreated control, regardless of application method. There were no significant differences in fruit rots between the fruit treated using a hand sprayer and those treated using an electrostatic sprayer, indicating that the electrostatic spraying was equally effective as the conventional spraying but used less water. Electrostatic spray system is a promising technology that can be used as an in-line postharvest treatment during the packing process to control postharvest fruit rot diseases of blueberries.
Also, in support of Sub-objective 2A, significant progress was made in assessing the effectiveness of peroxyacetic acid (PAA) in controlling postharvest fruit rots of blueberries. Two application methods (spraying and dipping) at two various rates of PAA were tested on two cultivars. PAA significantly reduced postharvest fruit rots and disease-control efficacy generally increased as the concentration of PAA increased. In general, PAA did not adversely affect fruit quality and sensory quality of blueberries. The results showed that PAA, generally recognized as a safe substance, is a promising postharvest tool to reduce postharvest fruit rots and maintain fruit quality of fresh blueberries.
Additionally, under Sub-objective 2A, ARS researchers in Parlier, California, evaluated the effectiveness of ionized hydrogen peroxide applied as a fog treatment using specialized equipment based on the Binary Ionization Technology for control of postharvest fruit rot diseases of blueberries. Ionized hydrogen peroxide at a high rate significantly reduced fruit rots of blueberries compared to the nontreated control, but the treatment was phytotoxic to blueberry fruit. Ionized hydrogen peroxide at a low rate did not cause phytotoxic effects on blueberry fruit but was ineffective in reducing fruit rots. ARS findings suggest that ionized hydrogen peroxide applied at the suggested rates had limited benefits in reduction of postharvest rots and maintenance of fruit quality of blueberries.
For Sub-objective 2B, significant progress was made on evaluating the ability of postharvest coatings and reduced vent area of packaging containers to better maintain blueberry quality during storage and marketing. None of the coatings tested, including chitosan, Semperfresh, and sodium caseinate, positively influenced fruit quality parameters except chitosan which was inhibitory to decay. The coatings partially or fully removed the bloom and changed the appearance of the fruit. In an associated sensory testing of blueberries with different degrees of bloom mechanically removed, a large degree of bloom removal negatively affected consumer perception of the fruit. ARS researchers in Parlier, California, also determined that reducing vent area of clamshells (packaging containers) significantly reduced weight loss during storage and simulated marketing with large reductions in shrivel and increases in fruit firmness. Low vent packaging in combination with sulfur dioxide or natamycin applied to the fruit prior to packaging for decay control is an effective means of limiting blueberry weight loss and enhancing postharvest storage and shelf life.
In support of Sub-objective 2C, ARS researchers in Parlier, California, made significant progress in searching for alternatives to sulfur dioxide fumigation for control of postharvest diseases of table grapes. Natamycin is generally recognized as a safe product and has recently been registered in the United States for postharvest use on certain fresh fruits such as citrus but not yet for table grapes. Natamycin at various concentrations applied as either a spraying or dipping treatment was evaluated for effectiveness in controlling postharvest rots of table grapes. ARS researchers in Parlier, California, determined that natamycin, even at one-fourth of the label rate used for citrus fruit, was highly effective in controlling gray mold caused by Botrytis cinerea, a major postharvest disease of table grapes, regardless of application method. ARS results suggest that natamycin is a promising tool to control postharvest fruit rot diseases of stored table grapes while maintaining fruit quality. The data from this research are being used to support registration of natamycin for postharvest use on table grapes in the United States.
Also, in support of Sub-objective 2C, significant progress was made on applying natamycin as a postharvest fogging treatment to control fruit rots of stored table grapes. Organically grown freshly harvested table grapes were palletized, fogged with natamycin, and then kept in cold storage for four weeks. Grapes fogged with natamycin had significantly lower percentage of fruit rots compared to the grapes that were fogged with water as a nontreated control. It appeared that variability in the treatment effect existed within the pallet, depending on the localities of the fruit within the pallet (top, middle, and bottom in the pallet). In general, the natamycin-treated grapes on the top of the pallet had significantly fewer decayed grapes than those grapes in the middle and bottom of the pallet, suggesting that increasing the volume of natamycin solution and fogging duration to enhance the coverage of grapes by natamycin is likely needed to improve its efficacy.
Accomplishments
1. Extra virgin avocado oil from minor varieties characterized to expand market opportunities. Some avocado varieties in the United States, particularly in California, are only used for pollination and have little or no fresh market value. This fruit could be used to produce extra virgin avocado oil and provide additional income for American farmers, but nothing was known about the quality or characteristics of the oil from these varieties. Collaboration between ARS scientists in Parlier, California, and researchers from the University of California, Riverside, involved the extraction of extra virgin avocado oil from ten varieties and characterization of the oils by standard quality parameters, aroma compounds and flavor. Oil from all varieties was of high quality but differed in color, flavor, and aroma compounds. This research will be helpful in enabling the utilization of previously low value avocado fruit and providing information to help in the development of a high-quality boutique extra virgin avocado oil industry in California and elsewhere in the United States.
Review Publications
Asensio, C., Arpaia, M., Obenland, D.M. 2025. The role of fruit surface bloom in consumer preference for blueberries: Sensory evaluation and multisensory interactions. Foods. 14(3). Article 455. https://doi.org/10.3390/foods14030455.
Kulapichitr, F., Cadwallader, K., Obenland, D.M. 2025. Characterization of changes in key odorants in blueberries during simulated commercial storage and marketing by sensory-directed flavor analysis and determination of differences in overall perceived aroma. Foods. 14(7). Article 1244. https://doi.org/10.3390/foods14071244.
Olmedo, G., Plotto, A., Mattia, M.R., Zhao, W., Hunter, W.B., Rosskopf, E.N., Obenland, D.M., Bai, J. Evaluation of modified humidity and controlled-release thymol on the preservation of blueberries and blackberries. Postharvest Biology and Technology. 219:113237. 2024. https://doi.org/10.1016/j.postharvbio.2024.113237.
Saito, S., Wang, F., Xiao, C. 2025. Effects of preharvest application of Acibenzolar-S-methyl and potassium silicate on postharvest diseases and fruit quality of blueberries. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-10-24-0116-R.