Zein and Spent Coffee Grounds Extract as a Green Combination for Sustainable Food Active Packaging Production: An Investigation on the Effects of the Production Processes

In this work, the effect of different production techniques was evaluated on the physical and antioxidant properties of bio-based packaging intended to prevent the premature oxidation of packaged foods. Spent coffee ground extract, rich in antioxidant molecules, obtained through high pressure and temperature extraction, was loaded on zein polymeric matrices. The techniques adopted in this work are particularly suitable due to their mild conditions to produce active packaging completely based on natural compounds: electrospinning, solvent casting, and spin coating. The novelty of this work lay in the investigation of the dependance of the properties of active packaging on the adopted production techniques; the results clearly indicated a strong dependence of the features of the films obtained by different production processes. Indeed, spin coated samples exhibited the best oxygen barrier properties, while a higher tensile strength was obtained for the casted samples, and the fastest release of active compounds was provided by electrospun mats. The films produced with different methods had different physical properties and the release of extract bioactive compounds can be tunable by varying the production technique, dependent on the variable to be considered. The products developed offer an alternative to traditional packaging solutions, being more eco-sustainable and promoting waste valorization

Diffusive transport and self-consistent dynamics in coupled maps

The study of diffusion in Hamiltonian systems has been a problem of interest for a number of years. In this paper we explore the influence of self-consistency on the diffusion properties of systems described by coupled symplectic maps. Self-consistency, i.e. the back-influence of the transported quantity on the velocity field of the driving flow, despite of its critical importance, is usually overlooked in the description of realistic systems, for example in plasma physics. We propose a class of self-consistent models consisting of an ensemble of maps globally coupled through a mean field. Depending on the kind of coupling, two different general types of self-consistent maps are considered: maps coupled to the field only through the phase, and fully coupled maps, i.e. through the phase and the amplitude of the external field. The analogies and differences of the diffusion properties of these two kinds of maps are discussed in detail.Comment: 13 pages, 14 figure

The Role of Surfaces in Gas Transport Through Polymer Membranes

This paper describes a procedure to measure the permeability P, diffusivity D, and rate of adsorption k1, thus determining the solubility S and rate of desorption k2 of He, N2, O2, CH4, and CO2 on a polydimethylsiloxane (PDMS) membrane. The described procedure is able to determine experimentally all the physical quantities that characterize the gas transport process through a thin rubber polymer membrane. The experiments were carried out at room temperature and at a transmembrane pressure of 1 atm. The results are in good agreement with the available data in the literature and offer an evaluation of k1 and k2

Easy method enhancing the sensitivity of a helium mass-spectrometer leak detector

Commercial He mass spectrometer leak detectors usually do not provide sufficient sensitivity to perform accurate measurements of the permeation rate of He through glass. Ultrasensitive dedicated systems have adeguate sensitivity but involve high costs and complex procedures. However, both cryogenics and photomultiplier technology routinely demand this goal. Here, we propose a novel method to increase the sensitivity of commercial devices to easily measure accurate permeation rate. We modified a commercial leak detector by reducing the pumping speed at the inlet of the rotary pump, thus increasing its sensitivity by one order of magnitude. The modified detector was used to measure the leak rate of the permeation of He through the glass walls of a photomultiplier. Further improvements made to decrease the minimum detectable signal were limited by the high ultimate pressure in the spectrometer tube

Potential Use of PLA-Based Films Loaded with Antioxidant Agents from Spent Coffee Grounds for Preservation of Refrigerated Foods

: The aim of this work concerned the production of an active food packaging suitable for refrigerated foods. Polylactic-acid-based films were produced by optimizing the solvent casting technique and testing different loadings of extracts obtained from spent coffee grounds. Indeed, an extract obtained by high-pressure and -temperature extraction (HPTE) and a further purified extract by liquid-liquid extraction (LLE) were separately used as active agents, and the effects on packaging features and active compounds migration were analyzed. The selected active agents showed antioxidant and lipid peroxidation inhibition effects on food simulants (peroxide values of 9.2 ÷ 12.0 meqO2/kg extra virgin olive oil), demonstrating the possibility of enhancing food shelf life. In addition, significant effects on the packaging structure due to the presence of the extract were observed, since it can enhance gas barrier properties of the polymer (O2 permeability of 1.6 ÷ 1.3 × 10-9 cm2/s) and confer better processability. In general, the HPTE extract exhibited better performances than the further purified extract, which was due to the presence of a complex pool of antioxidants and the browning effect on the film but a limited loading capacity on the polymer (840 μg caffeine/g PLA), while higher loading capabilities were enabled using LLE extract

Permeability thickness dependence of polydimethylsiloxane (PDMS) Membranes

The paper describes a reliable technique to prepare PDMS membrane used to determine the permeability to CO2 and He. SEM controls morphology of surface membrane and SEM/FIB measures the membrane thickness. The data show that permeability becomes thickness dependent below some tens of micrometers. The Islam\u5f3s model, based on the non-equilibrium sorption\u2013desorption process at the interface, fits quite well with the experimental data. The comparison shows that flux models based on interface reaction could apply to describe quantitatively the thickness-dependence of the permeability. The model allows to determine the surface reactions rate constants for CO2 and He on PDMS. The introduction of a specific characteristic thickness Lc provides a functional form, which describes very accurately the results of the present paper and other experiments on polymers. By reducing the membrane thickness below 200 nm, both permeability and selectivity change, indicating Knudsen diffusion as flux mechanisms responsible for permeation. In this range of thickness, SEM images reveal membrane defects