Good Fruit Grower / Web 2011 / Sustainable cherry packaging

 Email  Print

Sustainable cherry packaging

Researchers test cherries in microperforated bio-based containers

Cherries respire as well as transpire because they are living biological entities. Before harvest, since they are attached to the parental plant, losses due to respiration and transpiration are replaced by water, minerals and others from the plant. After harvest, these losses are not replaced anymore and therefore, deterioration (weight loss, fungal growth, and others) occurs followed by senescence. Altering the gas mixture surrounding the cherries to a composition different from that of air would be an effective tool to prolong the cherry’s quality during distribution and marketing, and this can be achieved by using packaging technologies.

Researchers at MSU School of Packaging, Food Science and Human Nutrition, and Horticulture departments are collaborating in a project led by WSU to develop a sustainable package to prolong the shelf life of fresh sweet stem free cherries during distribution and marketing. The project is supported by a grant from the U.S. Department of Agriculture Specialty Crop Research Initiative.

The goal is to develop a packaging system made from natural resources that creates the optimal environment (humidity and gas balance) necessary mainly to reduce cherry water loss as well as respiration and microbial growth. The idea is that the oxygen depletion and the carbon dioxide enhancement produced in the package headspace by the respiration of the cherry and permeability of the package during storage will be used to reduce or delay the physicochemical and microbiological changes that occur after harvest. In addition, the package will reduce the water loss since it will act as a physical barrier and will also reduce air movement across the fruit surface.

Changes in gas mixture and humidity content inside the package will be achieved by microperforating the material. In a non-microperforated package, the buildup of carbon dioxide and depletion of oxygen caused by the produce respiration is regulated by adjusting the gas transport through the packaging material, which is selected according to its barrier properties to oxygen and caarbon dioxide. Fruits like cherries require the use of film with enhanced permeability to prevent the development of anaerobic atmosphere. The use of microperforated film would allow a more rapid gas exchange through the package than that of a non-microperforated film. In microperforated films, the buildup of carbon dioxide and depletion of oxygen caused by the fruit’s respiration is easily regulated by adjusting the number and/or size of the microperforations.

Plastics are the most successful materials in reaching the needed gas balance and moisture content in the surrounding atmosphere of the fresh produce. Currently, bio-based polymers are a viable alternative to petroleum-based ones for food packaging applications. Among them, polylactic acid (PLA) has many properties that make it attractive as a petroleum plastic substitute. PLA is biodegradable, compostable, made 100% from renewable resources, approved by the U.S. Food and Drug Administration for contact with food, and has physical and mechanical properties similar to those of common petroleum-based plastics like polyethylene terephthalate and oriented polystyrene. In addition, PLA has a transparent and glossy finish.

This research group has conducted different experiments to preliminarily assess the effect of packaging (carbon dioxide/oxygen atmosphere and high relative humidity), temperature, and cherry variety on the shelf life and quality of fresh sweet cherries both with stems and without. Three different packaging systems have been compared:

1. A rigid tray closed with a non-microperforated lidding material, both made from PLA;

2. A rigid tray closed with microperforated lidding material, both made from PLA; and

3. The current commercial package for sweet cherries, a macroperforated flexible bag made from a petroleum-based plastic (polyethylene).

Findings so far include:

- The shelf life of the stem free and stem on cherries is notably affected by the type of package, the surrounding temperature, and the cherry variety;

- An increase of the temperature from 3 to 10 ºC reduced the shelf life of the packaged cherries by one week;

- The proposed microperforated bio-based container reduced the cherry weight loss by about 10% after three weeks of storage; and

- Approximately the same fungal growth was observed in the cherries in the bio-based microperforated packages as in those of the current commercial packages.

During the next cherry season, we will test an improved package and will conduct sensory tests of cherries in the proposed new container.