Pine Needles as a Biomass Resource for Phenolic Compounds: Trade-Off between Efficiency and Sustainability of the Extraction Methods by Life Cycle Assessment

Polyphenols are natural organic compounds with many possible applications because of their unique biological activities. They can be extracted from a wide variety of waste biomasses, and a great deal of interest exists in identifying extraction processes optimized in terms of both yield and environmental impact. In this framework, we have compared three techniques, namely, maceration and extraction assisted by either ultrasounds or microwaves, for the extraction of phenolic compounds from dry pine needles, largely available and under-exploited biomass. The yields in terms of total phenolic compounds and condensed tannins were assessed as a function of the extraction time, and a life cycle assessment (LCA) approach was adopted for quantifying the environmental impacts of the three techniques. Despite being time-consuming, maceration is the least-impact method, immediately followed by (much faster) ultrasound-assisted extraction. The energy intensity is mainly responsible for the overall eco-profile of the three techniques, whose hotspot resulted to be electricity consumption. Short processing time is hence crucial, as the gains in terms of yield achievable by prolonging the extraction processes bring about energy burdens that nullify the environmental advantages. Even the choice of "greener" solvents (e.g., ethanol instead of acetone) appeared questionable, as the extraction yield has an impact greater than the "greenness " of the raw materials.