Comparison of different methodological choices in functional unit selection and results implication when assessing food-packaging environmental impact

As defined by ISO standards 14040 and 14044:2021, Functional Unit (F.U.) is a quantifiable function of a product and is the reference basis for system modelling in environmental assessment. For this reason, F.U. definition is one of the most critical and controversial methodological aspects of LCA methodology. Literature search showed that two different F.U. are indistinctly used for shelf-life inclusion in food packaging LCAs. Inherent F.U., or attribute driven approach, includes shelf-life as an inherent characteristic of packaging solutions. An example would be “the conservation of X grams of packaged food until the end of its shelf-life”, On the other hand, Explicit F.U., or decision driven approach, explicitly requires a target timespan to be fulfilled such as “the conservation of X grams of packaged food over a Y-days timespan”. Still, the two are implemented without actual knowledge of their conceptual differences, resulting in inconsistency among practitioners. This paper aims at clarifying the impact of the two F.U. on comparative food packaging LCAs with the scope of harmonising future methodology for shelf-life inclusion into impact assessment methodology. The case of packaged fresh raspberries was used for this purpose. Three packaging solutions were compared by means of both the Inherent and Explicit functional units. Impact assessment results demonstrated that the two F.U. call for different scopes, modelling as well as providing different outcomes. For Inherent F.U., the overall best packaging solution was the one that successfully balanced food protection with packaging production and disposal impacts. On the contrary, the packaging system that most successfully fulfilled the targeted timespan resulted as the best available choice for the Explicit functional unit. Based on LCA outcomes, it was suggested that an Inherent approach should be used to discriminate packaging solutions based on their attributes and to critically analyse them. On the other hand, Explicit F.U. a packaging system to is best implemented when a predefined time requirement needs to be met. This decision-driven approach compares packaging solutions in respect to their goodness to fulfil a required shelf-life and to guide future eco-design decisions. Nevertheless, hot-spot analysis uniquely showed that food production, with food waste probability, was the most impactful factor, highlighting the relevance of shelf-life inclusion in LCA studies. Eventually, the study provided suggestions on the best use of the two F.U. for food packaging environmental assessment.