تکنولوژی بسته بندی برای بهبود عمر مفید میوه ها بر اساس پلیمر نانومنفذ کریستالی Packaging technology for improving shelf-life of fruits based on a nanoporous–crystalline polymer

INTRODUCTION Food packaging continues to evolve in response to the advancement of material science and technology, as well as the changing consumers’ demand towards preserved, fresh, tasty and convenient food products with prolonged shelf-life and controlled quality.1–4 In particular active packaging includes oxygen scavengers,5,6 ethylene scavengers, flavor and odor absorber/releaser, antimicrobial, and antioxidant into packaging systems7 with the aim of extending food products quality and shelf-life.8–11 The ability to prolong shelf-life of fruit and vegetables, by active films with a nanoporous crystalline s-PS layer, has been described in an international patent12 as well as in a recent article in which is shown the ability of active s-PS nanoporous–crystalline layer to prolong shelf-life of non-climacteric fruits, like oranges.13 Nanoporous–crystalline forms have been discovered for two industrially relevant polymers: syndiotactic polystyrene (s-PS)14–18 and poly(2,6-dimethyl-1,4-phenylene)oxide (shortly named as PPO).19 As for s-PS the d nanoporous crystalline form presents, inside the crystalline lattice, isolated cavities having a volume close to 0.125 nm3 , whereas the E nanoporous crystalline form presents channels with a diameter of 0.5 nm.20 It is well known the ability of polymeric nanoporous forms to absorb in their crystalline cavities low-molecular-mass molecules, thus forming stable host/guest co-crystalline phases.20–22 Co-crystalline phases, being unstable due to guest release in few minutes or hours, can be also formed with molecules being gaseous at room temperature, like carbon dioxide,23 ethylene,24 and even hydrogen.25,26 Co-crystalline phases, with carvacrol (a relevant natural antimicrobial molecule) being prevailingly (more than 90%) guest of the cocrystalline phase have been prepared, even for high carvacrol content (up to 10–11 wt %). The location of most antimicrobial molecules in the crystalline phase assures a decrease of desorption diffusivity of two to three orders and hence long-term antimicrobial release.