Effect of microwave-assisted processing on polyphenol oxidase and peroxidase inactivation kinetics of açai-berry (Euterpe oleracea) pulp.

Microwave heating has been considered a promising technology for continuous flow thermal processing of fluid foods due to better retention of quality. Considering the importance of açai-berry pulp and its perishability, the inactivation kinetics of peroxidase (POD) and polyphenol oxidase (PPO) were investigated under conventional and microwave heating. First-order two-component model was well fitted to the data, indicating the presence of at least two fractions with different resistances. POD was more thermally resistant (90% inactivation for 40 s at 89 °C) and could be considered as a processing target. Inactivation curves dependency on heating technology suggests specific effects of microwaves on the protein structure. Additionally, the dielectric properties of açai-berry pulp were evaluated at 915 and 2,450 MHz for temperatures up to 120 °C. Power penetration depth dropped with temperature at 915 MHz (from 29 to 11 mm), but was less affected at 2,450 MHz (between 8 and 11 mm).

Alternative techniques to improve hydrogen production by dark fermentation.

The production of biofuels as an alternative to the fossil fuels has been mandatory for a cleaner and sustainable process. Hydrogen is seen as the fuel of the future because it has a very high energy density and its use produces only water instead of greenhouse gases and other exhaust pollutants. The biological synthesis of hydrogen by dark fermentation complies with these criteria. In the current work, the use of cheese whey permeate was evaluated aiming hydrogen production by dark fermentation using a microbial consortium in the semi-continuous process, with a reaction volume of 700 mL. The volume of the medium renewal and the frequency of replacements of fresh medium were evaluated to extend the production of H2. It is important to note decreases in the hydrogen production after 84 h. The target-product content became higher particularly when 466 mL of medium were withdrawn, in every 24 h in the first two replacements and, subsequently, in every 12 h. Besides, it was observed lower lactic acid concentration under this condition, suggesting that the shorter removal time of the medium could inhibit lactic acid bacteria, which may secrete bacteriocins that inhibit the hydrogen-producing microorganisms.