Application of Modified Atmosphere Packaging of Fruit and Vegetables in China

Min Zhang and Shoujiang Chen

Introduction

Fruits and vegetables are living, respiring and perishable products with active metabolism even after harvest from the parent plant. The storage life and quality of fruits and vegetables can be extended by modifying the atmosphere surrounding products. A modified atmosphere can be defined as one that is created by altering the normal composition of air (21% oxygen and 0.03% carbon dioxide) to provide an optimum atmosphere for increasing the storage length and quality of produce. Modified atmospheres can be achieved by using controlled atmosphere (CA) storage or modified atmosphere packaging (MAP).

CA requires precise control of O₂ and CO₂ concentration around fresh produce and involves large specialised storage buildings and sophisticated operation equipment. CA is more appropriate for long term storage, while MAP is used on smaller quantities of produce and the atmosphere is only initially modified. MAP techniques involves either actively or passively controlling or modifying the atmosphere surrounding the product within a package made of various types of films. Active modification occurs by the displacement of gases in the package, which are then replaced by a desired mixture of gases, while passive modification occurs when the product is packaged using a selected film type, and a desired atmosphere develops naturally as a consequence of the products’ respiration and the diffusion of gases through the film.

In China, passive MAP is extensively used to extend the shelf life of many fresh commodities and fresh cut fruits and vegetables because passive MAP presents a much more economical alternative approach to controlled atmosphere (CA) to extend storage life.

Extending Shelf Life and Maintaining Quality of Fruits and Vegetables by MAP

MAP utilises polymeric films with selective permeability for O₂, CO₂, and H₂O vapor to create an MA around the packaged product due to the respiration of the product and the selective permeability of the packaging material (Guevara et al. 2003). Horticultural products are a main application for MAP, and reduced levels of O₂ and increased levels of CO₂ in the atmosphere surrounding fresh produce seem to have several positive effects: MA reduces respiration rate, ethylene production and sensitivity and texture losses, improves chlorophyll and other pigment retention, delays ripening and senescence and reduces the rate of microbial growth and spoilage ( Rodriguez-Aguilera and Oliveira, 2009).

Fresh fruit and vegetables

MAP is most commonly used for highly perishable commodities and effectively retards deterioration of fresh fruits and vegetables. MAP can prolong the shelf life of mushrooms Pleurotus nebrodensis to 90 days, inhibit the respiration and weight loss, and retard soluble sugars, titratable acidity and anthocyanin decrease of strawberries (Zhang et al. 2003). MAP significantly inhibits the lignification and delay of the ripeness of bamboo shoots. MAP using 0.03 mm PE film could inhibit weight loss and decrease TSS, firmness of fruits and keep an acceptable appearance of mini tomatoes compared with control fruit.

Fresh-cut fruit and vegetables

Modified atmosphere packaging (MAP) is extensively used to extend the shelf life of many fresh cut (minimally processed) fruits and vegetables products. The most suitable packaging material to prolong the shelf life of fresh cut lotus roots has been reported to be 0.04 mm low density polyethylene (LDPE). Fresh cut lotus roots treated by MAP with 100% O₂ could maintain better quality of appearance. Fresh cut celery packaged in MA with three different atmospheres found that 10% O₂, 10% CO₂ and 80% N₂ was the best combination to keep cut celery fresh.

Factors Determining the Effectiveness of MAP
Film type and thickness used in MAP

MAP involves the use of plastic film, with known permeability to gases, for the packaging of products. There is no doubt that MAP materials should be selected appropriately according to their gas permeation properties. Many factors influence film permeability, among which polymer type and film thickness are most important. Many plastic films have been in use for MAP of a variety of produce. Packaging film of correct permeability can create desirable MA of fresh fruit and vegetables. Due to differences in the respiration rates of individual fruits or vegetables, the type of plastic film required to achieve any special equilibrium MA must be defined for each commodity. The MAP industry has an increasing choice of packaging films, yet most packs are still constructed from four basic polymers: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP) and LDPE for packaging of fresh produce (Mangaraj et al., 2009).

Plastic film: LDPE films are among those most commonly used in packaging of fresh produce. that The best packaging material for MAP storage of pioneer cherry has been reported as 0.02 mm LDPE film. Nectarines packed in 0.03 mm LDPE showed significantly less polygalacturonase and cellulase activities, decreased respiration rate and ethylene production, and a slower decrease in flesh firmness and increase in relative membrane permeability than the control.

PP and PVC films are often used to pack fruit and vegetables such as waxberry (0.025mm PVC). Zhang et al. (2003) reported that the composite membrane containing LDPE and PVC was superior to single LDPE and PVC membranes to obtain the optimum gas composition of 2.5% O₂ +16% CO₂ in MAP for strawberry; MAP could inhibit the respiration and weight loss of strawberries and retard soluble sugars, titrable acidity and anthocyanin decrease. The packaging material containing biaxially oriented polypropylene (BOPP): PET: LDPE was reported to be the best choice for keeping bamboo shoots fresh. Fuji apples packed in five types of plastic film bags for seven months showed that apples in MAP film of PVC or LDPE had a fresh-like quality.

Silicon gum film: The effect of silicon gum films as windows for gas exchange on the respiration and quality change of stored edible mushroom Agrocybe chaxingu was evaluated, and showed that silicon gum film windows could extend the shelf life by more than 8 days compared to the control. Packages with the silicon gum film window with initial gas concentrations of 5% O₂ and 10% CO₂ were the most effective for maintaining mushroom quality (Li et al., 2007). Li and Zhang ( 2008) reported that different sizes of silicon gum film windows had a significant effect on quality of Agrocybe chaxingu.

Initial gas composition before packaging

Zhang et al. (2003) reported that the optimum gas composition for MAP of strawberry was 2.5% O₂ and 16% CO₂. The initial gas proportion of 10％ O₂ and 10％ CO₂ at 5oC was effective in maintaining the quality of spinach. The quality of fresh cut onion could be maintained for 17 days at 4oC in a package atmosphere of 80％O₂ and 20％ N₂ combined with 1.5％ citric acid. The optimum initial gas composition for MAP of peas was determined by a comprehensive evaluation model to be 9% O2, 7% CO₂ and 84% N₂.

Conclusion

Current knowledge and use of MAP are mainly empirical, but a systematic approach to designing optimal MAP is being developed. Despite many advantages of MAP, adoption of this technique has been rather slow in countries dependent on machinery to apply it, and the technique has not yet reached its full potential. Possibly, non-availability of fast and reasonably priced equipment and the cost of the film are the main reasons limiting the commercial adoption of MAP. The plastic films used for MAP must be flexible and easy to use, but sufficiently strong to survive normal handling operations. The use of MAP for fresh produce is quite restricted for a number of reasons and no single polymer offers all the properties required for MAP.

References

Guevara, J.C., Yahia, E.M., Brito de la Fuente, E. and Biserka, S.P. (2003) Effects of elevated concentrations of CO2 in modified atmosphere packaging on the quality of prickly pear cactus stems (Opuntia spp.). Postharv. Biol. Technol. 29: 167-176.

Li, T., Zhang, M. and Wang, S. (2007) Effects of modified atmosphere packaging with a silicon gum film as a window for gas exchange on Agrocybe chaxingu storage. Postharv. Biol. Technol. 43: 343–350.

Li, T. and Zhang, M. (2008) Effect of modified atmosphere packaging with various sizes of silicon gum film window on the storage of Agrocybe chaxingu Huang and the modelling of its respiration rate. Packaging Technol. Sci. 21: 13-23.

Mangaraj, S., Goswami, T. K. and Mahajan, P. V. (2009) Applications of plastic films for modified atmosphere packaging of fruits and vegetables: A review. Food Eng. Rev. DOI 10.1007/s12393-009-9007-3. Published online:　15 July 2009 .

Rodriguez-Aguilera, R., and Oliveira, J. C. (2009) Review of design engineering methods and applications of active and modified atmosphere packaging systems. Food Eng. Rev. 1: 66-83.

Zhang, M., Xiao, G., Peng , J. and Salokhe, V. M. (2003) Effects of modified atmosphere package on preservation of strawberries. Inst. Agrophysics 17: 143-148.

Dr Min Zhang (corresponding author) is a Professor in the School of Food Science and Technology, Jiangnan University, Wuxi 214036, Jiangsu, China (E-mail: min@jiangnan.edu.cn), and Dr Shoujiang Chen is an Associate Professor in the Key Laboratory of Food Science and Safety, Jiangnan University, Wuxi 214036, Jiangsu, China.