Catalyzed sulfur dioxide release system for controlled fumigation of postharvest crops and related methods

Abstract

A moisture-activated sulfur dioxide (SO.sub.2) release system is disclosed for postharvest preservation of fruits, vegetables, and other fresh plant products. The system comprises a composition including sodium metabisulfite (SMBS) and citric acid that, upon exposure to humidity, rapidly generates SO.sub.2 gas to suppress fungal growth. Various deployment systems enable immediate or sustained release based on packaging conditions and crop type. The system provides a safer alternative to traditional SO.sub.2 fumigation, and provides improved decay control and extended shelf life.

Claims

1. A system for deploying a sulfur dioxide (SO.sub.2)-generating composition in harvesting containers, storage containers, and shipping containers, comprising: a. a dry composition comprising sodium metabisulfite (SMBS) and citric acid configured to react upon exposure to moisture to release SO.sub.2 gas; and b. a deployment mechanism that houses or incorporates the dry composition, wherein the deployment mechanism is configured for placement in a container for transporting fresh produce to control the release of SO.sub.2 gas over time within the container.

2. The system of claim 1, wherein the deployment mechanism comprises a sachet containing a measured amount of the composition enclosed in a moisture-permeable material.

3. The system of claim 1, wherein the deployment mechanism comprises a microencapsulated formulation embedded within a moisture-sensitive coating selected from hydroxypropyl methylcellulose, alginate, or starch-based materials.

4. The system of claim 1, wherein the deployment mechanism comprises a tablet or pellet, wherein the SMBS and citric acid are compressed together and covered in a hydrophilic coating.

5. The system of claim 1, wherein the deployment mechanism includes a moisture-activated release barrier to prevent premature activation.

6. The system of claim 1, wherein said pre-determined ratio of SMBS and citric acid is in a range from about 1:1 to about 3:2 SMBS:citric acid.

7. The system of claim 1, wherein the SMBS is present in an amount ranging from about 10% to about 70% by weight of the composition and the citric acid is present in an amount ranging from about 8% to about 50% by weight of the composition.

8. A system for controlling mold and rot in postharvest produce, comprising: a. a container for housing harvested whole produce; and b. a sulfur dioxide (SO.sub.2)-generating composition in a deployment mechanism having a moisture permeable outer surface in proximity to said harvested whole produce, wherein the composition comprises sodium metabisulfite (SMBS) and citric acid.

9. The system of claim 8, wherein the deployment mechanism is a sachet.

10. The system of claim 8, wherein the deployment mechanism is a sheet or pad, wherein said composition is applied to a surface of said sheet or pad.

11. A system for deploying a sulfur dioxide (SO2)-generating composition in harvesting containers, storage containers, and shipping containers, comprising: a. a composition comprising sodium metabisulfite (SMBS) and citric acid configured to react upon exposure to moisture to release SO.sub.2 gas, wherein the composition comprises a ratio of SMBS to citric acid that is no higher than about 3:2; and b. a deployment mechanism that houses or incorporates the composition, wherein the deployment mechanism is configured to control the release of SO.sub.2 gas over time within a container for holding whole fresh produce.

12. The system of claim 11, wherein the deployment mechanism comprises a sachet containing a measured amount of the composition enclosed in a moisture-permeable material.

13. The system of claim 11, wherein the deployment mechanism comprises a sheet or pad impregnated with the composition and enclosed within a composite material consisting of plastic and paper.

14. The system of claim 11, wherein the deployment mechanism comprises a microencapsulated formulation embedded within a moisture-sensitive coating selected from hydroxypropyl methylcellulose, alginate, or starch-based materials.

15. The system of claim 11, wherein the deployment mechanism comprises a tablet or pellet, wherein the SMBS and citric acid are compressed together and covered in a hydrophilic coating.

16. The system of claim 11, wherein the deployment mechanism is positioned in the upper portion of the container to facilitate downward dispersion of SO.sub.2 gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 provides photographs of exemplary sachets according to an embodiment of the present invention, as used in the experimental examples.

(2) FIG. 2 provides an image of a sealed plastic container system, as used in the experiment or test examples.

(3) FIG. 3 provides a graph of the accumulated sulfur dioxide emission during a laboratory test after applying 0.5 g sodium metabisulfite (SMBS)+0.4 g citric acid in a table grape container.

(4) FIG. 4 provides a graph of the accumulated sulfur dioxide emission during a laboratory test applying 0.25 g SMBS+0.2 g citric acid in a table grape container.

(5) FIG. 5 provides a graph of the accumulated sulfur dioxide emission during a laboratory test applying 0.125 g SMBS+0.10 g citric acid in a table grape container.

(6) FIG. 6 provides a graph of the accumulated sulfur dioxide emission during a laboratory test applying 0.0625 g SMBS+0.05 g citric acid in a table grape container.

(7) FIG. 7 provides photographs of packing boxes used for table grapes for field experiments only. They are not table grape boxes used for packing and shipping.

(8) FIG. 8 presents a table of data on the natural decay incidence in Stella Bella table grapes affected by different postharvest treatments, including 0.5 g SMBS+0.4 g citric acid, 1 g SMBS alone, and an untreated control.

(9) FIG. 9 presents a table of data from field trials evaluating gray mold incidence across seven table grape cultivars, comparing 0.5 g SMBS+0.4 g citric acid to an untreated control.

DETAILED DESCRIPTION

(10) References will now be made in detail to certain embodiments of the invention, and example compositions and applications of such embodiments. While the invention will be described in reference to these embodiments, it will be understood that they are not intended to limit the invention. On the contrary, the invention is intended to cover alternatives, modifications, and equivalents that are included within the spirit and scope of the invention as defined by the claims. In the following disclosure, specific details are given to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details.

Example 1Lab Tests

(11) The lab studies aimed to evaluate the controlled release of sulfur dioxide (SO.sub.2) from sodium metabisulfite (SMBS) combined with citric acid in sachet-based applications for postharvest grape storage. FIG. 1 shows the sachets used in the experiment, which were disposable NEPAK tea bags (sachet 100) having dimensions 3.153.94W3.15H. The primary goal was to determine how different doses of SMBS and citric acid affect SO.sub.2 emission rates, with a focus on fungal suppression (Botrytis cinerea) and rachis preservation under high-humidity conditions.

(12) The experiment was conducted in a controlled 20-liter volume sealed plastic box system, simulating commercial table grape storage conditions. The 20-liter box system is shown in FIG. 2. The sealed plastic containers were designed with a sampling inlet and outlet circuit using surgery tubing, from which air was running constantly throughout for CO.sub.2 and SO.sub.2 detection without depleting the gas composition inside the container. SO.sub.2 concentrations were measured using a Porta Sens III gas analyzer, while CO.sub.2 levels were assessed with a Horiba VIA-510 infrared gas analyzer. Sachets containing varying doses of SMBS and citric acid were placed inside the sealed system, and gas emission data were collected over time.

(13) The SO.sub.2 release profiles for different SMBS-citric acid dosages were analyzed over the first hour following application, with each treatment replicated three times to ensure statistical accuracy and reproducibility. The results demonstrated a clear dose-dependent emission pattern, where higher SMBS-citric acid concentrations produced greater and more immediate SO.sub.2 release, while lower doses resulted in a slower, more sustained release.

(14) As shown in FIG. 3, the highest SO.sub.2 release was observed in the 0.50 g SMBS+0.40 g citric acid treatment, which exhibited a rapid peak concentration within 20 minutes of exposure, followed by gradual stabilization. This formulation is expected to be most effective for rapid fungal suppression, particularly in high-humidity storage conditions.

(15) As shown in FIG. 4, the sachets containing 0.250 g SMBS+0.200 g citric acid treatment showed a moderate but sustained SO.sub.2 release, with a slower buildup compared to the highest dose but still reaching levels sufficient for mold prevention. This dosage may be better suited for medium-term storage applications where a gradual emission is preferable.

(16) As shown in FIG. 5, the 0.125 g SMBS+0.10 g citric acid treatment exhibited a lower SO.sub.2 emission profile, characterized by delayed release and a reduced peak concentration. While this formulation may be less effective for immediate fungal suppression, it could be advantageous for long-term storage scenarios where sustained exposure to SO.sub.2 is needed.

(17) As shown in FIG. 6, the lowest tested dose, 0.0625 g SMBS+0.05 g citric acid, produced the least cumulative SO.sub.2 emission and may be insufficient for effective fungal control. However, it could be beneficial for sensitive fruits requiring ultra-low SO.sub.2 exposure to avoid quality degradation.

(18) The SO.sub.2 release rate directly correlated with SMBS-citric acid dosage, demonstrating a dose-dependent emission pattern. Higher doses produced immediate and elevated SO.sub.2 peaks, whereas lower doses provided a more gradual and extended release. These findings show that SO.sub.2 concentration can be precisely adjusted based on storage duration, fruit sensitivity, and fungal suppression needs, allowing for customized postharvest protection strategies across different fruit storage and transport conditions.

(19) Field Trials

(20) Field experiments evaluating SO.sub.2 emissions from sodium metabisulfite (SMBS) and citric acid sachets, were also conducted to evaluate the effectiveness of these formulations in commercial postharvest table grape storage. The field trials were conducted across two seasons, focusing on red, green, and black table grape cultivars. The primary objective was to determine the impact of SMBS with and without a citric acid catalyzer on gray mold (Botrytis cinerea) incidence and overall rachis condition during cold storage.

(21) The field trials tested the application of sulfur dioxide (SO.sub.2) from sodium metabisulfite (SMBS) combined with citric acid in sachet-based applications applied immediately after harvest, during standard field packaging in plastic grape boxes (13.019.05.0, or about 20 liters), as shown in FIG. 7. The boxes were then transferred to cold storage (32 F.) within 8 hours. Unlike conventional postharvest treatments that involve weekly sulfur dioxide fumigation, no additional SO.sub.2 applications were made in the cold room, providing an uncontaminated SO.sub.2 free environment to assess the efficacy of the sachet application. The experimental setup included four randomized replications per treatment, with sachets containing a pre-measured dry chemical combination of sodium metabisulfite (SMBS) and citric acid sealed in disposable tea bags (3.15L3.94W3.15H), as shown in FIG. 1.

Example 2Natural Decay in Stella Bella Table Grape

(22) Decay incidence was evaluated at four weeks of cold storage, based on visible mycelial growth or slip-skin symptoms, with results expressed as decay incidence by weight. Statistical significance was assessed using Tukey's test at a 5% probability level to determine treatment differences.

(23) FIG. 8 presents the natural decay incidence in Stella Bella grapes from the 2022 season, comparing SMBS alone (1 g), SMBS+citric acid (0.5 g+0.4 g), and an untreated control. The SMBS+citric acid treatment significantly reduced gray mold incidence (0.9%), equating to an 88% reduction relative to the untreated control (3.3%). The 1 g SMBS-only treatment showed a moderate reduction (2.4%), but was still significantly less effective than the SMBS+citric acid combination. These results indicate that citric acid plays a crucial role as a catalyzer, enhancing the efficacy of SMBS by promoting faster and sustained SO.sub.2 release.

(24) Regarding rachis condition, the SMBS+citric acid treatment received a score of 2-3, indicating moderate rachis preservation compared to 3-4 showing severe damage in the untreated and SMBS-only treatments. This suggests that SO.sub.2 exposure from SMBS+citric acid may slow rachis desiccation, likely by reducing oxidative stress and fungal colonization.

Example 3Gray Mold in Seven Table Grapes

(25) FIG. 9 provides field trial data on gray mold incidence in seven different table grape cultivars from the 2023 season, comparing 0.5 g SMBS+0.4 g citric acid to an untreated control after four weeks of storage. Across all cultivars, the SMBS+citric acid treatment significantly reduced gray mold, with relative reductions ranging from 29% to 50%. The greatest effect was observed in Flame Seedless (50% reduction), followed by Thompson Seedless (39%) and Stella Bella (34%). Even in cultivars with lower baseline gray mold incidence, such as Allison and Red Globe, the treatment still resulted in a significant reduction (33%).

(26) These findings reinforce the broad efficacy of SMBS+citric acid sachets across multiple grape varieties, suggesting that SO.sub.2 release mechanisms are effective regardless of cultivar-specific susceptibility to Botrytis cinerea. The statistical significance of these reductions was confirmed by Tukey's test (p<0.05), indicating that the observed differences were not due to random variation.

(27) The dose-response relationship observed across both seasons confirms that SMBS combined with citric acid is a superior postharvest treatment compared to SMBS alone. The catalyzing effect of citric acid enhances SO.sub.2 production, leading to greater fungal suppression and improved rachis preservation. The consistent reductions in gray mold incidence across multiple grape cultivars demonstrate the broad-spectrum effectiveness of this approach in postharvest table grape management.

(28) From a commercial perspective, these findings suggest that integrating SMBS+citric acid sachets or in other delivery mechanisms into standard packaging could provide a viable alternative to weekly SO.sub.2 fumigation, particularly in organic cold storage systems where conventional fumigation is restricted. The treatment's proven efficacy in reducing gray mold makes it an attractive option for long-distance fruit shipments, ensuring fungal suppression and prolonged fruit quality during extended storage and transport. Additionally, the positive impact on rachis condition suggests that this formulation may enhance the visual appeal of fruit.

(29) It is to be understood that variations, modifications, and permutations of embodiments of the present invention, and uses thereof, may be made without departing from the scope of the invention. It is also to be understood that the present invention is not limited by the specific embodiments, descriptions, or illustrations or combinations of either components or steps disclosed herein. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. Although reference has been made to the accompanying figures, it is to be appreciated that these figures are exemplary and are not meant to limit the scope of the invention. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.