Location: Commodity Protection and Quality Research
2024 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 report documents progress for project 2034-43000-041-000D, titled, “New Approaches to Enhance Fresh Fruit Quality and Control Postharvest Diseases”, which started in May 2020.
In support of Sub-objective 1B, ARS researchers in Parlier, California, evaluated the effects of plant resistance inducers applied in the field on postharvest fruit rot diseases and fruit quality of blueberries. Benzothiadiazole (Actigard), potassium silicate (Sil-MATRIX), and a nontreated control (water) were applied to blueberry plants (Jewel variety) under field conditions four times during the growing season. Blueberry fruit were harvested at commercial maturity. Part of the fruit was used to test its quality. Another part of the fruit was used to assess development of postharvest diseases during cold storage. After completion of cold storage at 1 degree C for four weeks, fruit were evaluated for decay development, and fruit quality attributes were measured. Both benzothiadiazole and potassium silicate treatments significantly reduced postharvest fruit rots by about 22% compared to the nontreated control. There were no significant differences in fruit quality attributes between the treated and nontreated fruit.
For Objective 2, preliminary experimentation was initiated on characterizing extra virgin avocado oil from avocados that have little or no fresh market value. The results from this research will provide information useful to utilizing these varieties and providing more income to avocado growers. The flesh of four varieties was individually ground, mixed, and the oil centrifuged out of the paste to conform with extra virgin oil requirements. Varieties differed greatly in how much oil could be extracted, providing information useful for future research with these varieties. Work on characterizing the oil for quality, aroma volatiles, and sensory quality is underway.
In support of Sub-objective 2A, ARS researchers continued to evaluate the effectiveness of postharvest treatment with natamycin applied using an electrostatic spray system (ESS) in comparison with a conventional sprayer for control of postharvest fruit rot diseases of blueberries. Four concentrations of natamycin were used for the ESS application in comparison with a conventional spray method at two different concentrations. Two non-treated controls (water applied by a conventional sprayer and an ESS) were also included. The experiment was conducted on the blueberry varieties, Jewel and San Joaquin. Upon completion of storage at 0 degrees C for four weeks, decay development was evaluated in the treated and nontreated fruit. Natamycin treatments significantly reduced fruit rots compared with the nontreated control, regardless of application methods. 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. There were no significant differences in fruit quality attributes between the treated and nontreated fruit, except acidity in the Jewel variety, but there was no evident trend associated with natamycin treatments or application methods.
Also, in support of Sub-objective 2A, research continued in 2023 and 2024 seasons to evaluate the effectiveness of natamycin as a postharvest fogging treatment to control postharvest fruit rots of blueberries. Commercially harvested blueberry fruit were used for this experiment. Natamycin and a nontreated control (water) were applied using a fogger in a temperature-controlled environment room at 15 degrees C. Blueberry fruit were placed in plastic totes with five totes per layer for a total of 65 totes that were palletized. In 2023, the palletized blueberries were fogged with six gallons of natamycin solution for 70 min, followed by 20 min of waiting time for fogged droplets to settle down. In 2024, the fruit were fogged with 10 gallons of natamycin solution for 120 min with 20 min of waiting time. The control treatment was fogged with water. Fruit was then packed into 6-oz clamshells and stored at 1 degree C for four weeks. Fruit rots were evaluated after the cold storage period. In 2023, natamycin fogging treatment significantly reduced fruit rots from 56% in the nontreated control to 42.8% in the treated fruit. For the palletized blueberries fogged with water (control), there were no significant differences in incidence of fruit rots among the fruit samples taken from top, middle and bottom layers of the pallet. For the palletized blueberries fogged with natamycin, the fruit on the top layer had a significantly lower level of fruit rots than those at middle and bottom layers within the pallet. In 2024, natamycin fogging treatment significantly reduced fruit rots from 13.3% in the nontreated control to 5.5% in the treated fruit. For the fruit fogged with water (control), the fruit on the top layer had significantly more fruit rots than those at middle and bottom layers within the pallet. However, for the palletized blueberries fogged with natamycin, there were no significant differences in incidence of fruit rots among the fruit from top, middle, and bottom layers of the pallet. The results indicated that increasing the volume of natamycin solution and fogging duration improved the efficacy of natamycin for control of fruit rots in palletized blueberry fruit.
Under Sub-objective 2B, further efforts were conducted this year to find a coating for blueberries to experiment with that both reduces weight loss and maintains appearance. Unfortunately, this was not successful.
Also for Sub-objective 2B, research found that reducing blueberry clamshell vent area from 4.8% (commercial) to either 0.27% or 0.81% reduced blueberry weight loss by 40% following four weeks of cold storage and two days at room temperature. Coinciding with the weight loss was a significant decrease in berry shrivel and an increase in firmness relative to the commercial clamshells. Decay was not enhanced by reducing clamshell vent area but fumigating the blueberries with sulfur dioxide or dipping in natamycin prior to placing the fruit in the final clamshells was effective in reducing the natural decay in all vent areas to very low levels.
Additionally, in support of Sub-objective 2B, research was conducted to understand the influence of storage for three weeks at 1 degree C, followed by a period of simulated marketing of 1 week at 10 degrees C and two days at 20 degrees C on blueberry flavor. Soluble solids were unaffected by storage but both firmness and acidity declined. Sensory analysis of the blueberry aroma indicated that aroma declined during storage at 1 degree C relative to that at harvest but then recovered when the storage temperature warmed. Changes in key aroma volatiles concurred with the sensory result with Z-3-hexenal, 1-octen-3-ol, 1-octen-3-one, Z-3-hexenal, cinnamyl alcohol, decalactone, nerol, eucalyptol, geraniol, citronellol and linalool being the volatiles most impacted by storage.
In support of Sub-objective 2C, ARS researchers continued to evaluate the effectiveness of natamycin as a postharvest fogging treatment to control postharvest fruit rots of table grapes. Organically grown, freshly harvested Scarlet Royal variety table grapes were used in this experiment. Four 4-lb clamshells of table grapes were placed in a plastic fruit tote. Totes were placed on a wooden pallet. One tote layer consisted of six totes. A total of 10 tote layers were placed on the pallet. Two pallets of fruit were prepared for the experiment, one pallet for the nontreated water control and the other for natamycin treatment. Grapes in the pellet were fogged with six gallons of natamycin solution for about 70 min, followed by a 20-min of waiting time for fogged droplets to settle down. Six gallons of water containing surfactant was used as control. After the treatment, grapes were packed into 4-lbs clamshells. Two sets of samples were prepared: one set of samples was stored for four weeks at 1 degree C, and the other set was stored for four weeks at 1 degree C, followed by a two-day storage at 20 degrees C to simulate retail conditions. After the four-week cold storage, grapes fogged with natamycin had significantly lower percentage of fruit rots compared to the grapes that were fogged with water, with incidence of fruit rots reduced from 73% in the nontreated control to 19% in the natamycin fog-treated fruit. 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). After the 4-week cold storage, followed by a two-day storage at 20 degrees C, the natamycin-treated top layer had significantly fewer decayed berries, and the differences in the percentages of decayed fruit between the two treatments among the layers became more evident.
Accomplishments
1. Storage temperature influences blueberry aroma. Blueberries are often stored for long periods of time at 0-1 degree C followed by warmer temperatures as the blueberries move from storage to the consumer, but the influence of different storage conditions on aroma, which is important to flavor, remained to be fully determined. ARS researchers in Parlier, California, evaluated sensory aroma and identified important volatiles in blueberries at three stages of storage: 1) fresh blueberries for three weeks at 1 degree C, 2) stage 1 followed by one week at 10 degree C, and 3) stage 1 and 2 followed by two days at 20 degrees C. The two later stages simulated distribution and marketing conditions. Blueberry aroma declined during storage at 1 degree C but recovered during subsequent storage at warmer temperatures. These variations coincided with alterations in aroma active volatiles that were responsible for the changes. This research enhanced understanding of how temperature and storage time affects blueberry flavor to help maintain optimum blueberry quality for consumers.
2. Postharvest application of natamycin has potential to control fruit rots in table grapes. Postharvest fruit rot diseases are a key factor limiting the storage and shelf life of table grapes. Control of postharvest diseases is important to the domestic and international marketing of table grapes, but no products are registered in the United States specifically for control of postharvest diseases of organic table grapes. ARS researchers in Parlier, California, evaluated natamycin as a postharvest dipping or spraying treatment for control of postharvest fruit rots of table grapes. Natamycin was highly effective in controlling fruit rots. Natamycin is commonly used as an antimicrobial food additive in the food industry and is considered a biofungicide. Thus, Natamycin is a promising postharvest tool to control postharvest fruit rots and maintain fruit quality of table grapes. Once registered in the United States, it could be used on both conventional and organic table grapes.
3. Electrostatic spray's potential to control postharvest fruit rot diseases of blueberries. Postharvest fruit rot diseases affect the storability and shelf life of blueberries. Developing postharvest technologies to control fruit rots is critical to retain/expand domestic and export markets of blueberries. Natamycin is a natural food preservative commonly used in the food industry and has been shown to be effective in controlling major fruit rot diseases of blueberries when it was applied as a spraying treatment. ARS scientists in Parlier, California, compared the effectiveness of electrostatic and conventional sprayings of natamycin for control of postharvest fruit rots of blueberries. Electronic spraying of natamycin provided a similar level of control of fruit rots in blueberries but used only approximately 40% of the water compared to the conventional spraying. Thus, electrostatic spraying is a promising tool to apply natamycin for control of postharvest diseases of blueberries.
Review Publications
Ismail, A., Pervaiz, T., Comstock, S., Bodaghi, S., Rezk, A., Vidalakis, G., El-Sharkawy, I., Obenland, D.M., El-kereamy, A. 2023. Unraveling the occasional occurrence of berry astringency in table grape cv. Scarlet Royal: A physiological and transcriptomic analysis. Frontiers in Plant Science. 14. Article 1271251. https://doi.org/10.3389/fpls.2023.1271251.
Rezk, A., Pervaiz, T., Douhan, G., Obenland, D.M., Arpaia, M.L., El-kereamy, A. 2024. Postharvest mandarin rind disorder: Insights into varietal differences and preharvest treatments effects on postharvest quality. Plants. 13(8). Article 1040. https://doi.org/10.3390/plants13081040.
Saito, S., Wang, F., Xiao, C. 2023. Sensitivity of Mucor piriformis to natamycin and efficacy of natamycin alone and with salt and heat treatments against Mucor rot of stored mandarin fruit. Plant Disease. 107(11):3602-3607. https://doi.org/10.1094/PDIS-04-23-0796-RE.
Wang, F., Saito, S., Xiao, C. 2024. Postharvest application of natamycin to control gray mold in table grapes. Postharvest Biology and Technology. 210. Article 112777. https://doi.org/10.1016/j.postharvbio.2024.112777.
Pervaiz, T., Park, S., Rezk, A., Hur, M., Obenland, D.M., Arpaia, M., El-kereamy, A. 2023. Metabolomic analyses provide insights into the preharvest rind disorder in Satsuma Owari mandarin. Frontiers in Plant Science. 14. Article 1263354. https://doi.org/10.3389/fpls.2023.1263354.
Kulapichitr, F., Asensio, C., Arpaia, M., Walse, S.S., Obenland, D.M. 2024. Effect of controlled atmosphere storage on key volatiles and sensory perception of Muscat grapes. ACS Food Science and Technology. 4(3):766-772. https://doi.org/10.1021/acsfoodscitech.3c00661.
Yang, W.Q., Takeda, F., Zhang, M., Li, C., Sargent, S.A., DeVetter, L., Beaudry, R., Obenland, D.M., Saito, S., Xiao, C. 2024. Internal bruise damage in machine-harvested blueberries. Acta Horticulturae. 1381:392-400. https://doi.org/10.17660/ActaHortic.2023.1381.50.