NC State Extension Publications

Introduction

SmartFresh(1-methylcyclopropene, MCP) is a relatively new tool for postharvest management of apples. In 2002, SmartFresh was approved for commercial use on apples by the Environmental Protection Agency under a reduced risk program because of the very low toxicity of the product and the fact that treated fruit have no detectable residue. It is thought to bind irreversibly to the ethylene receptors in plant tissues making the crops insensitive to ethylene and subsequently retarding many ethylene mediated responses such as fruit softening in apples. SmartFresh can maintain apple firmness and acidity, while decreasing scald and greasiness even when stored under less than ideal storage temperatures. However, maximum storage life results from the combination of SmartFresh treatment and recommended storage practices. When using SmartFresh according to the manufacturer’s recommendation, the period between harvest and treatment is cultivar dependent and varies from 3 to 10 days. In addition, the manufacturer (AgroFresh) publishes an annual summary of use recommendations listing a recommended maturity range for most cultivars based upon the starch index and flesh firmness of the fruit at harvest. Being able to determine the flesh firmness and the starch index of the fruit is necessary to use SmartFresh with optimal effectiveness. Apple flesh firmness is determined with a penetrometer (Effegi or Wagner are common brands and can be purchased for $200-300), which is a hand held gauge with a 7/16” probe that is pushed into a peeled patch on opposite sides of an apple. This device can be purchased from several online sources dealing with orchard equipment. The starch level or starch index of the fruit is a very useful tool to determine the maturity of the apple. It reveals the conversion of starch to sugar as the apple matures. Apples are cut in half across the middle of the fruit and one half is placed face down in a shallow pan of a potassium iodide solution and evaluated according to the degree of staining (Figure 1). Laminated copies of the Cornell "Generic Starch-Iodine Index Chart for Apples" (Figure 1) are offered to customers by AgroFresh (contact Heidi Davey, phone 616-745-9379).

Treatment Timing

Treating beyond either the time after harvest or outside of the recommended maturity parameters decreases fruit response, shortens the effective marketing period, and negates the company assurance of increasing the postharvest life of the fruit. According to research and experiences with North Carolina-grown apples, treating the apples as soon after harvest as possible, preferably within 1-3 days, is suggested for optimal effectiveness.

Figure 1 chart taken from: Predicting Harvest Date Windows for Apples.

Starch iodine staining pattern used to determine apple maturity.

Figure 1. Starch iodine staining pattern used to determine apple maturity.

Challenges of using SmartFresh

One of the challenges of using SmartFresh on apples is that the fruit need be sealed in an airtight enclosure during treatment for 24 hrs - exposure to a 1 part per million (ppm) concentration of 1-MCP. After treatment, the fruit can then be held in a regular cold storage room. Controlled atmosphere (CA) rooms are designed to be airtight and have the ability to hold a 1 ppm concentration of 1-MCP in the atmosphere for 24 hrs. However, in many cases growers do not have the capacity to harvest and fill a CA room within the recommended interval following harvest. Many growers selling through retail outlets grow multiple cultivars, need to treat smaller quantities of fruit at varied intervals, but do not have access to CA facilities or an air tight facility for treating apples.

Commercial Use of SmartFresh

At NC State University we have been evaluating the commercial use of SmartFresh for more than 8 years on North Carolina-grown apples (Blankenship, Parker, McArtney, Obermiller and Hoyt). Our studies have shown that if used properly, SmartFresh can maintain the flesh firmness of treated apples over those not receiving the SmartFresh treatment by 3-6+ lbs after 40 days of storage at 32°F and 7 days at room temperature. Figure 2 below illustrates the effect of SmartFresh on three cultivars, ‘Gala,’ ‘Golden Delicious,’ and ‘Rome’. Note the impact of harvest date and postharvest treatment interval treating the fruit at 1, 3, 5 or 7 days after harvest. Fruit not treated the first day were held at 32°F until treatment. SmartFresh was effective at maintaining the firmness of all three cultivars. Earlier harvest dates resulted in greater fruit firmness after 40 days of storage at 32°F and 7 days at room temperature. The first harvest was conducted when the fruit had a starch index of 3-4 based on the Cornell Starch Index 1-8 scale (See Figure 1). It is also important to note that shortening the harvest to treatment interval of ‘Golden Delicious’ and ‘Rome’ greatly increased the flesh firmness response. The resulting firmness benefit increased by up to 40% for fruit treated 1 day after harvest compared to fruit treated 7 days after harvest. In North Carolina, we are recommending that growers treat their fruit as soon after harvest as possible and preferably within 3 days of harvest.

The units of the x–axis are the number of days from harvest to SmartFresh treatment. Fruit were held at 32°F between harvest and treatment. The first harvest is designated by H1 with later harvests numbered accordingly.

SmartFresh is being used commercially in North Carolina. The largest growers using the material have large shells lowered from the ceiling in their cold storage rooms and treat several hundred bins per application. We have also developed applications for effectively using refrigerated tractor trailers for treating approximately 72 bins per application (53 ft trailer). Do not use trailers or facilities with exposed wood on the inside. The active ingredient in SmartFresh is absorbed by wood. Wooden surfaces in treatment enclosures (i.e. plywood walls, wood floors, etc.) should be minimized or sealed with some type of wood sealer with the exception of wooden bins. However, many growers in North Carolina do not have the desire or ability to harvest and treat a large quantity of fruit within 1-3 days of harvest. The goal in North Carolina was to develop protocols and techniques for using SmartFresh to treat smaller quantities of fruit, for growers who primarily sell in retail markets. We conducted three on-farm trials with growers with retail operations and placed treated and untreated fruit (of the cultivars ‘Ginger Gold’, ‘Gala,’ and ‘Golden Delicious’) in their markets. These fruit were held under ambient temperatures in each market. Fruit samples were collected weekly from each retail display area and flesh firmness, soluble solids and starch index were measured on these samples.

Figure 2. Impact of delaying SmartFresh treatment of ‘Gala,’ ‘

Figure 2. Impact of delaying SmartFresh treatment of ‘Gala,’ ‘Golden Delicious,’ and ‘Rome’ apples on the flesh firmness.

SmartFresh Maintains Flesh Firmness

The flesh firmness information from this study is included in Figure 3. The response of the apples was similar at all three retail stands. Untreated fruit of all three cultivars softened very quickly. After 1 week, most of the apples had less than 14 lbs. firmness which we generally considered to be the threshold for high quality fruit. However, SmartFresh treated fruit maintained flesh firmness values similar to the fruit at harvest even after 3-4 weeks at ambient temperature.

Figure 3. Impact of SmartFresh treatment on ‘Ginger Gold’, ‘Gala

Figure 3. Impact of SmartFresh treatment on ‘Ginger Gold’, ‘Gala’ or ‘Golden Delicious’ apple flesh firmness for fruit held at ambient temperatures in commercial retail stand display areas. Solid lines are SmartFresh treated fruit.

Maintaining Fruit Quality

Optimal fruit quality is achieved with most cultivars when the fruit is stored at 32°F. Apples not treated with SmartFresh and stored at 40°F will respire and degrade twice as fast as apples held at 32°F. Fruit held at 60°F degrade six times faster than apples at 32oF. However, many smaller operations maintain storage temperatures above 32°F due to current cooler use patterns and/or limited refrigeration capacity. To deal with these challenges we evaluated the impact of SmartFresh on the quality of fruit held at different storage temperatures. Samples of ‘Ginger Gold’, ‘Gala’ and ‘Golden Delicious’ apples were harvested and either treated with SmartFresh within 1-2 days of harvest or left untreated. The fruit were then stored at 32, 50 or 70°F and sampled at weekly intervals to determine the impact on flesh firmness (Fig. 4). All of the apples without SmartFresh (lines with symbols) had the lowest flesh firmness regardless of temperature for all three cultivars, with the exception of untreated ‘Gala’ fruit stored at 32oF. Also notice that the flesh firmness of SmartFresh treated ‘Ginger Gold’ stored at 70°F was significantly greater than untreated fruit stored at 32°F. There was no difference in flesh firmness of SmartFresh treated ‘Gala’ and ‘Golden Delicious’ apples held at 32 or 50°F after 4 weeks.

As stated earlier, treating apples with SmartFresh needs to be performed in an airtight enclosure. Based upon our data and experiences, our recommendations in North Carolina are to treat fruit within 3 days of harvest to ensure the maximum benefit from SmartFresh treatment. However, obtaining the correct measured amount of SmartFresh and an appropriate facility to treat smaller quantities of fruit (2-12 bins) has been a challenge. In our research trials, we have used SmartFresh SmartTabs and a chamber that holds two stacked bins of apples.

Figure 4. Impact of SmartFresh (SF) treatment on ‘Ginger Gold,’

Figure 4. Impact of SmartFresh (SF) treatment on ‘Ginger Gold,’ ‘Gala,’ or ‘Golden Delicious’ apple flesh firmness for fruit held in at 32, 50, and 70°F. Lines with symbols represent treatments that did not receive SmartFresh.

SmartFresh SmartTabs and Activator Kits Use and Ordering

AgroFresh now sells SmartFresh in a form that can be used for smaller scale use. SmartFresh SmartTabs are packaged in a blister pack of 10 tablets. Each tablet is designed to treat approximately 123 cubic feet (ft3). A packet of 10 tablets comes with an activator kit consisting of a small plastic container, a screw on lid with a small hole in the center, a small quantity of activator solution and 2 activator tablets. When ready for treatment, the lid, with a hole in the center, is removed from the activator kit, a seal is removed and the appropriate number of SmartTabs and activator tabs are placed in the solution. After the lid is replaced, the assembled activator kit is promptly placed inside the treatment chamber and sealed immediately.

The activator kits are designed for a single use regardless of the number of SmartTabs used. Additional activator kits can be ordered at no additional cost when included with the SmartTabs order. The actual volume of fruit treated, and resulting per unit treatment cost, depends upon the size and configuration of the chamber. One bin of apples takes up approximately 50 ft3 of treatment volume. The current cost of the SmartTabs is approximately $320 for a pack of 10. Purchasing the SmartFresh material is also different than most of your other pest management material. You must set up an account and purchase the material directly from the company, AgroFresh. (Note: credit card payment is preferred.) Their contact information is:

AgroFresh, Inc.
Phone: 1-866-206-1001
FAX: 1-888-873-0373
400 Arcola Roiad
Collegeville, PA 19426

Email: FUSAFNA@AgroFresh.com

The AgroFresh sales representative for our area can address additional questions. Contact Ms. Heidi Davey (phone: 616-745-9379; Email: hbdavey@agrofresh.com).

SmartTabs Application

The initial chamber that we used was designed to treat 2 bins of fruit per treatment. It consists of a frame made from 1” PVC pipe (54” wide, 60” long and 65” high) and a 4 mil polyethylene pallet cover (64” x 56” x 108”) (Figure 5). Two bins of apples are stacked and placed centered on a piece of 6’ x 6’ vinyl linoleum (Figure 6). The frame is placed over the two bins of apples and plastic pallet cover was then fitted over the frame and sealed to the linoleum with duct tape. One side is left open until the SmartTabs and activator kit are prepared and placed inside the chamber. For this treatment, one SmartTab was used in one activator kit for each application. The remaining side of the cover is then sealed to the linoleum with duct tape. After 24 hours, the cover is removed from the bins and the apples are handled with the rest of the fruit. If there is enough head room above the top of the bins the plastic cover and frame can be removed as a single unit without having to refit the plastic over the frame for each treatment. Cooling the apples as quickly after harvest is ideal and the SmartFresh application can be made in a cooler. However in all of our grower trials the treatments were made at room temperature with effective results.

Specifications

  • PVC pipe
  • 6 - Ten foot by 1 inch PVC (Schedule 40) pipe
    • Cut PVC
    • 4 - 70 inch
    • 4 – 60 inch
    • 4 – 50 inch
  • 8 -1 inch three way PVC fittings

Cost

  • 6 - Ten foot by 1 inch PVC (Schedule 40) pipe @ 2.35 = $14.10
  • 8 -1 inch three way PVC fittings @ 2.40 = $19.20

Some growers have used plastic sheeting and duct tape to create their own air tight facilities in various sizes and configurations. Company names will be mentioned in the remainder of this paper, however this should not be considered as an endorsement, but rather sources that carry the materials described. The 4 mil pallet covers can be purchased in a roll of 25 at a cost of approximately $200 for the covers and shipping (Clear Shrink Pallet Covers, Flexible Packaging, Houston, TX, toll free (800) 353-9125 (Part number FP14/01/6456108H). Single pallet covers can be purchased from Peach Ridge Orchard Supply, Inc., Sparta, MI (phone: 800-452-6748).

Figure 5.  Diagram for the PVC frame used for creating a treatme

Figure 5. Diagram for the PVC frame used for creating a treatment chamber for treating 2 bins of apples.

Figure 6.  Photo and diagram of the 2-bin treatment chamber usin

Figure 6. Photo and diagram of the 2-bin treatment chamber using a pallet cover.

SmartTabs Grower Trials

In 2010, a grower trial was initiated with 3 retail apple growers. The growers were supplied with a 2-bin treatment frame, pallet covers and SmartTabs (supplied by AgroFresh) for 10 – 2- bin applications. The growers were instructed to harvest the fruit at the stage of maturity normal for their operations. Each bin was sampled before and after treatment. The samples were then held at room temperature (70°F) for 30 days before measuring flesh firmness. Results are presented in Table 1 for some of the cultivars evaluated. Notice that the SmartFresh treatment resulted in significantly greater flesh firmness for all cultivars except ‘Honeycrisp’ and ’Cameo.’ You will also note that many of the SmartFresh applications were made on fruit that were more mature than the AgroFresh recommendations (noted with an asterisk) with successful results after 30 days at room temperature. In retail operations, growers want to harvest fruit at a later stage of maturity with higher fruit quality (and yield), and then treat with SmartFresh and sell within the next 3-4 months. This increase in fruit quality both at harvest and from storage is expected from their clientele. For fruit to be held for a longer period of time, fruit should be harvested within the maturity guidelines described by AgroFresh in their Apple Use Recommendations booklet. AgroFresh also offers a list of modified maturity guidelines for different lengths of storage. Request: "Optimizing Storage of Apples for Various Maturities".

During our trials over the past several years, we recognized the need for an intermediate sized chamber between the 2 bin pallet cover and a 66 bin refrigerated tractor trailer. We were able to work with “The Blimp Works” (Mr. Charles Willard, http://theblimpworks.com/, ph. 704-876-2378) in Statesville, NC to design an adjustable height chamber with a 4 bin square footprint (Adjustable Apple Tent) (Figure 7). The chamber is designed to treat 4, 8 or 12 bins at a time depending upon a stacking height of one to three bins. This chamber can be suspended from a frame as shown in the image below or suspended from overhead ceiling rafters. The chamber itself is constructed of 6 mil polyurethane and is light weight (less than 40 lbs). We added square PVC frames at the top and bottom to maintain a square shape. The shell is lowered over the bins of fruit and a skirt at the bottom is spread out. Water bags or tubes (i.e. lay flat pipe filled with sand) are placed on the skirt to seal the shell to the floor. A two bin capacity chamber designed with a skirt at the bottom to facilitate sealing with a water tube is also available as a “Small Apple Tent”.

Table 1. Harvest maturity and effectiveness of SmartFresh™ application on the flesh firmness for multiple apple cultivars from North Carolina grower trials.
Cultivar Harvest maturity Firmness after 30 d @ 70 °F
Firmness (lb) Starch (1-8) Untreated (lb) Treated (lb) Difference (lb)
Ginger Gold (Grower 1) 9.9 a** 17.5 b + 7.6
Ginger Gold (Grower 2) 8.3** 14.4 + 6.1
Gala (Grower 1) 17.1 5.0 9.1 a** 15.2 b + 6.1
Gala (Grower 2) 14.3* 7.5* 8.4 a** 12.3 b** + 3.9
Honeycrisp (Grower 2) 16.0 6.9 15.3 15.2 - 0.1
Jonagold (Grower 1) 14.8 7.8* 9.3 a** 14.2 b + 4.9
Jonagold (Grower 2) 16.2 5.6 9.0 a** 15.8 b + 6.8
Red Del. (Grower 2) 15.8 6.8* 7.4 a** 13.4 b** + 6.0
Mutsu (Grower 1) 15.4* 5.7* 9.7 a** 15.2 b + 5.5
Golden Del. (Grower 3) 13.9* 6.9* 10.2 a** 14.0 b + 3.8
Golden Del. (Grower 2) 15.6 5.6 11.5 a** 16.1 b + 4.6
Stayman (Grower 3) 14.9 3.0 7.9 a** 14.4 b + 6.5
Fuji (Grower 3) 13.9* 7.1* 13.5 a** 14.6 b + 1.1
Cameo (Grower 3) 15.3* 5.9* 14.3 14.7 + 0.4
Rome (Grower 2 ) 21.0 4.3 12.1 a** 15.3 b + 3.2
Rome (Grower 3) 17.5 6.2 10.3 a** 13.1 b** + 2.8
Empire (Grower 1) 16.4 4.9 8.6 a** 11.9 b** + 3.3
Empire (Grower 3) 15.4 4.4 8.0 a** 12.1 b** + 4.1
Pink Lady (Grower 1) 19.2 6.0 16.8 a 19.5 b + 2.9
* Fruit more advanced in maturity than current AgroFresh recommendations.
** Fruit with unacceptable levels of flesh firmness for optimal fruit quality (<14 lbs).

The Adjustable Apple Tent

Carbon dioxide leak testing was conducted both at the beginning and end of the season to verify the air tight tightness of the Adjustable Apple Tent and the Small Apple Tent. This test, in combination with the flesh firmness response of treated fruit, indicates that the chamber is a very effective treatment facility. These treatment chambers are available commercially from The Blimp Works for approximately $900 for the Adjustable Apple Tent and $500 for the Small Apple Tent. The supply may be limited, so call early for availability.

One of the grower cooperators purchased a unique shipping container that is referred to as a tall cube (produced in China and shipped full of freight to the US) and could treat approximately 24 bins stacked 3 high. Many traditional shipping containers do not allow bins to be stacked in a manner to minimize free headspace. The cost of a “once used” was approximately $4,000. But again, keep in mind that any treatment facility must be airtight and should be designed or have dimensions that allow the efficient stacking of bins in order to reduce the cost of the SmartFresh treatment. In the Adjustable Apple Tent we used 2 SmartTabs for 4 bins, 4 for 8 bins and 5 SmartTabs for 12 bins.

Figure 7.  The Adjustable Apple Tent being used to treat 12 bins

Figure 7. The Adjustable Apple Tent being used to treat 12 bins with diagrams illustrating the treatment of 4 and 8 bins and overall dimensions of the enclosure.

Conclusion

In conclusion, our research has indicated that SmartFresh is a very effective postharvest management tool. It can be used to maintain flesh firmness of the apples for a much longer period of time compared to untreated fruit. Fruit treated with SmartFresh can also be held at higher than optimal temperatures and still maintain acceptable flesh firmness for a longer period of time. In addition to maintaining flesh firmness, SmartFresh also slows the loss of fruit acidity and reduces scald development, even under less than ideal storage conditions. We feel that the use of SmartFresh is a tool that retail operations should consider adopting in order to maintain high quality fruit in storage, during retail display, sales and in the hands and home of the consumer.

Authors:

Extension Horticulture Specialist and Associate Professor (Tree Fruits/Pecans)
Horticultural Science
Former Extension Specialist and Associate Professor, Apples
Horticultural Science
Former Research Technician
Horticultural Science
Agricultural Research Specialist
Horticultural Science

Publication date: Oct. 31, 2014

The use of brand names in this publication does not imply endorsement by the North Carolina Cooperative Extension Service of the products or services named nor discrimination against similar products or services not mentioned.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.