Packaging and Shelf Life of Perishables
Perishable products degrade due to spoilage mechanisms such as respiration, water gain or loss, lipid oxidation, photo oxidation, enzymatic browning, non-enzymatic browning, ethylene production, autolysis, and microbiological growth. Specific packaging technologies can delay the degradation processes resulting from the aforementioned spoilage mechanisms, thus diminishing the loss of quality and safety, and maximizing freshness and shelf life of perishable products.
Among these technologies, modified atmosphere packaging (MAP) is most common. MAP is based on the replacement of the ambient air (78.09% nitrogen (N2), 20.95% oxygen (O2), 0.03% carbon dioxide (CO2), and 0.93% Argon (Ar) plus others) inside the package with a single gas or a mixture of gases that can lead to shelf-life extension of perishable products.
Depending on how that replacement occurs, MAP is classified into two types: active MAP (AMAP) and passive MAP (PMAP).
In AMAP, the ambient air in the package is replaced with a desired mixture of gases or a single gas by direct flushing prior to package sealing. The most adequate gas or mixture of gases is selected based on the type of perishable to be packaged. Furthermore, the packaging material is tailored in order to maintain a quite constant gas composition over time.
In PMAP, which is only used in produce packaging, air free of contaminants, such as medical air, replaces the ambient air inside a package by direct flushing and after package sealing the composition of that air is modified due to the interplay between produce respiration, which consumes O2 and replaces it with CO2, packaging characteristics, and the storage conditions (Almenar and Wilson, 2016). Both continuous and microperforated films can be used in PMAP to control gas exchange. Microperforated films perform better than continuous films since they allow a faster entrance of O2 into the package that mitigates the high/low concentrations of CO2/O2, respectively, developed in continuous film packages containing produce. A desired gas composition can easily be obtained with microperforated films by varying the number, area, and length of the microperforations (Koutsimanis, Harte, and Almenar, 2015).
More recently, packaging technologies such as active packaging, in-package cold plasma, and coatings have been created to extend the shelf life of perishable products. Active packaging can be defined as the packaging technology where certain additives, known as “active compounds,” are incorporated into the packaging material or placed within the packaging container in order to interact directly with the perishable product and/or its environment to extend its quality and/or safety (Almenar, 2018). Active compounds can be grouped into three types depending on how they interact with the perishable product: (1) scavenging compounds (e.g., O2 scavengers, ethylene absorbers, moisture absorbers); (2) active-release compounds (e.g., CO2 emitters, ethanol generators); and (3) controlled-release compounds (e.g., antimicrobials). They can be placed inside the package along with the product to be packed (e.g., in sachets or labels) or can be part of the materials that form the package itself (e.g., blended in the bulk polymer matrix, applied to the package as a coating, integrated in the ink used for printing) (Almenar, 2006).
Other packaging technology that allows a non-thermal killing of microorganism after the food is packaged is in-package cold plasma. This packaging technology consists of the generation of highly reactive species like ions, free radicals, and photons inside a sealed package to inactivate the foodborne pathogens of the packaged product (Almenar, 2018). Unlike the previously described packaging technologies, coatings are not primary packages since they do not provide many of the benefits of packaging, including protection from mechanical damage. However, they can be coupled with the primary packaging to enhance quality, safety, and nutritional content. A coating can be defined as an edible continuous matrix applied directly on the food product. This matrix can be prepared by mixing food components such as polysaccharides, proteins, and lipids with water or ethanol, which evaporates. Plasticizers and other additives can be added to improve the matrix properties (Almenar, 2018).
New market needs including tracking, monitoring of product and environment changes during storage, antitheft prevention, identification, and communication with consumers, among others, are not possible using the previously described packaging technologies. As an alternative, intelligent packaging has been conceived to fulfill these new market requirements for perishables (Almenar, 2018).
More details on packaging technologies that can extend the shelf life of perishable products as well as packaging-related topics (i.e., cold chain, sanitation techniques, packaging materials, shelf-life protocols and predictions) are offered by Professor Almenar in two courses at the School of Packaging, Michigan State University. Food Packaging (PKG 455; on campus) is offered in the spring and Packaging and Shelf Life of Perishables (PKG 456; online) is offered in the fall.
Almenar, 2018. Innovations in packaging technologies. In: Beaudry, RM, Gil, MI, editors. Controlled and Modified Atmosphere Use for Fresh and Fresh-cut Produce. Elsevier (In press).
Almenar, E.; Hernández-Muñoz, P., Lagarón, J.M., Catalá, R., Gavara, R. 2006. Advances in packaging technologies for fresh fruit and vegetables. In: Advances in Postharvest Technologies of Horticultural Crops. Benkeblia Noureddine and Shiomi Norio, Eds. Editorial: Research Signpost Publisher, Kerala (India). Pp. 87-112.
Almenar, E.; Wilson, C. 2016. Advances in packaging fresh produce. Food Science & Technology, 30 (3): 38-40 http://www.fstjournal.org/features/30-3/packaging-fresh-produce
Koutsimanis, G.; Harte, J.; Almenar, E. 2015. Freshness maintenance of cherries ready for consumption using convenient, microperforated bio-based packaging. Journal of the Science of Food and Agriculture, 95(5): 972-982.
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