Packaging is one of the main driving forces in food marketing in developed countries. It plays an important role in the preservation and extension of the shelf life of both fruits and vegetables from the time of harvest up to consumption by consumers.
Furthermore, packaging helps to reduce the incidence of pest infestation, disease progression and microbial infestation. With the correct packaging and labelling, food can be safely stored, protected and adequately marketed.
One of the best ways to package food is called modified atmosphere packaging (Map), which helps keep food fresh for a longer time compared to other packaging methods.
What is Map, and how does it work?
Modified atmosphere packaging is a packaging technique used to extend the shelf life of fresh produce by changing the air composition around the fresh produce through injecting gases such as nitrogen and carbon dioxide, as seen in Figure 1.
During this process, nitrogen and carbon dioxide are injected into a package container, increasing their levels and reducing that of oxygen.
Since oxygen plays a critical role in lipid oxidation reactions, reduced oxygen helps to slow down the product respiration rate, microbial activity, and ripening, while increased carbon dioxide levels act as an antimicrobial agent to inhibit fungal and bacterial growth.
The goal is to keep food fresh by slowing down its natural decay process, so that it stays fresh and safe to eat for a longer time and maintains the product quality without preservatives.
Maintaining low-temperature or dark storage conditions is crucial to inhibit microbial activities in Map.
Benefits and drawbacks of Map
Modified atmosphere packaging offers several benefits, including extended shelf life, reduced retail waste, minimal or no need for chemical preservation, and overall good food appearance.
Modified atmosphere packaging also has some drawbacks, such as high initial costs for the equipment, environmental concerns related to plastic use, the potential growth of food-borne pathogens due to temperature non-compliance by retailers and consumers, and the loss of Map benefits once the packaging is opened or leaks.
Packaging material is one of the most important considerations in Map. The packaging material must have low gas permeability to prevent leakage. Polymeric films are used to wrap food products in Map to confine the modified gases.
The key characteristics to consider when selecting packaging material for Map foods include resistance to puncture, sealing reliability, antifogging properties, carbon dioxide and oxygen permeability, and water transmission rate.
The common polymeric/plastic films used are polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), biaxially oriented polystyrene (BOPS), polystyrene (PS) shrink film, amongst others.
Costs and shelf-life extension
Modified atmosphere packaging comes with high initial costs due to the expensive equipment and materials required. Additionally, operators need training, and the packaging film is costly due to its high-quality properties.
Maintenance and gas costs also add to the overall expense. However, using Map can help expand one’s market reach, potentially leading to increased sales and profitability.
Modified atmosphere packaging has been successfully applied to various vegetables, including broccoli, cauliflower, carrots, garlic, and mushrooms, with other research also exploring its use for onions, sweet corn, and snow pea pods, using high water vapor permeable films as seen on Figure 2.
The maximum shelf-life extension occurs at the lowest oxygen concentration before anaerobic respiration begins, but this also poses the greatest risk of spoilage.
The majority of products achieve a longer shelf life with Map than with vacuum packaging. On average, Map can extend the shelf life of vegetables from days to weeks. For leafy vegetables, not much significant shelf-life extension can be achieved through Map.
The cabbage lifespan can be extended by 21 days at 4 ± 0.5℃ storage temperature and 90-95% relative humidity (RH), spinach shelf life extended by 7 days at 7℃ and 97% RH, and lettuce life expectance extended by 8 days at 5℃.
The tomatoes’ life expectance can be extended by 21-35 days at 2-10℃, cucumber by 15 days at 4℃, cauliflower by 12-30 days at 1-5℃ and 90-96% RH, broccoli by 21-25 days at 1-10℃ and 90-95% RH, and 27 days for mushrooms at 4 ± 1℃.
As a guideline for atmosphere storage, fruit and vegetables with high moisture content may be stored at 90–99% RH, 0–5℃, whereas fruit and vegetables with lower moisture content may be stored at lower RH of 60–70% and a temperature of 4–9℃.
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