In this study, we extensively describe experimental models, with correlating experimental conditions, which were used to investigate the enzymatic hydrolysis of bacterial cellulose (BC) to obtain nanocrystals. Cellulase from Trichoderma reesei was used in five enzyme/BC ratios over a period of h. The turbidity data was modeled using both logistic regression and empirical regression to determine the fractal kinetics, resulting in unique kinetic patterns for the mixtures that were richest in BC and in enzymes. The evolution of the yield was inversely related to the turbidity, as confirmed through a semi-empirical approach that was adopted to model the experimental data. The yield values after 74 h of hydrolysis were higher for the substrate-rich mixtures (~20%) than for the enzyme-rich mixtures (~5%), as corroborated by cellobiose and glucose quantification. Transmission electron microscopy and atomic force microscopy analyses revealed a shift from a fibril network to a needlelike morphology (i.e., aggregated nanocrystals or individual nanocrystals ~6 nm width and 200-800 nm in length) as the enzyme/BC ratios went from lower to higher. These results were explained in terms of the heterogeneous substrate model and the erosion model. This work initiated a promising, environmental-friendly method that could serve as an alternative to the commonly used chemical hydrolysis routes.
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Applying a circular economy approach, this research explores the use of cheese whey permeate (CWP), by-product of whey ultrafiltration, as cheap substrate for the production of bacterial cellulose (BC) and Sakacin-A, to be used in an antimicrobial packaging material. BC from the acetic acid bacterium Komagataeibacter xylinus was boosted up to 6.77 g/L by supplementing CWP with β-galactosidase. BC was then reduced to nanocrystals (BCNCs, 70% conversion yield), which were then conjugated with Sakacin-A, an anti-Listeria bacteriocin produced by Lactobacillus sakei in a CWP based broth. Active conjugates (75 Activity Units (AU)/mg), an innovative solution for bacteriocin delivery, were then included in a coating mixture applied onto paper sheets at 25 AU/cm2. The obtained antimicrobial food package was found effective in reducing Listeria population in storage trials carried out on a fresh Italian soft cheese (named “stracchino”) intentionally inoculated with Listeria. Production costs of the active material have been mainly found to be associated (90%) to the purification steps. Setting a maximum prudential 50% cost reduction during process up-scaling, conjugates coating formulation would cost around 0.89 €/A4 sheet. Results represent a practical example of a circular economy production procedure by using a food industry by-product to produce antimicrobials for food preservation.
In this study, cinnamon essential oil (CEO) nanocapsules were stabilized by means of bacterial cellulose nanocrystals (BCNCs) and encapsulated using fish gelatin as the main polymer phase. Emulsions were prepared at pH 5 using different CEO concentrations (0.03, 0.06, 0.12, 0.24, 0.36, and 0.48% v/w) and a fixed amount of fish gelatin (3% w/w) and BCNCs (0.06% w/w). The controlled release of the essential oil was assessed by release studies, which revealed that the higher the CEO concentration, the lower the release rate of CEO. In addition, modelling of experimental data using five different equations showed that the best fitting was obtained for the Korsmeyer-Peppas model, according to which the CEO release obeyed a non-Fickian behavior. Films obtained from the same formulations were characterized in terms of optical properties (light transmittance and haze), surface wettability, barrier (oxygen, carbon dioxide, and water vapor transmission rates) and mechanical properties. It was observed that an increased amount of CEO in the films did not significantly affect both transparency and haze, while it yielded an increase in surface hydrophobicity (~ 120% increase in water contact angle over the control) and elongation. Finally, the barrier performances of films against O2, CO2, and water vapor suggest a potential application of CEO/GelA-BCNC matrices as antimicrobial layers (in the form of coatings deposited on plastic films or directly on food) in living foods that have a respiratory metabolism, such as modified atmosphere-packaged crustaceans and mollusks as well as fruits and vegetables.
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