No abstract

Despite the constant development of novel thermal and nonthermal technologies, knowledge on the mechanisms of microbial inactivation is still very limited. Technologies such as high pressure, ultraviolet light, pulsed light, ozone, power ultrasound and cold plasma (advanced oxidation processes) have shown promising results for inactivation of micro-organisms. The efficacy of inactivation is greatly enhanced by combination of conventional (thermal) with nonthermal, or nonthermal with another nonthermal technique. The key advantages offered by nonthermal processes in combination with sublethal mild temperature (<60°C) can inactivate micro-organisms synergistically. Microbial cells, when subjected to environmental stress, can be either injured or killed. In some cases, cells are believed to be inactivated, but may only be sublethally injured leading to their recovery or, if the injury is lethal, to cell death. It is of major concern when micro-organisms adapt to stress during processing. If the cells adapt to a certain stress, it is associated with enhanced protection against other subsequent stresses. One of the most striking problems during inactivation of micro-organisms is spores. They are the most resistant form of microbial cells and relatively difficult to inactivate by common inactivation techniques, including heat sterilization, radiation, oxidizing agents and various chemicals. Various novel nonthermal processing technologies, alone or in combination, have shown potential for vegetative cells and spores inactivation. Predictive microbiology can be used to focus on the quantitative description of the microbial behaviour in food products, for a given set of environmental conditions.

This study deals with nonthermal food processing techniques and the results and findings present in this study are the root for further prospective studies. The food industry is looking for nonthermal methods that will enable food preservation, reduce deterioration of food compounds and structure and prolong food shelf life.

High power ultrasound (US) and cold gas-phase plasma (CP) are non-thermal processing technologies that maybe used in food processing industry. The main objective of this research was to study the effect of both treatments on selected yeasts (Rhodotorula spp. 74 and Candida spp. 86) in pure culture. Samples were treated by ultrasound with 57.50-, 86.25-or 115-μm amplitude, for 3, 6 or 9 min at 20°C, and 40 or 60°C in the case of thermosonication. For cold gas-phase plasma treatments, samples were treated at a gas flow of 0.75, 1 or 1.25 L min −1 , treatment time of 3, 4 or 5 min, and sample volume of 2, 3 or 4 mL. Each technology has its own advantages and is able to give the best effect on the desired target product. The experiment was designed using central composite design (CCD), and results were analysed and presented using response surface methodology (RSM). The greatest reduction of yeasts was observed after ultrasound treatments at 60°C (thermosonication) and after plasma treatments, after the longest treatment time (5 min) and the lowest sample volume (2 mL). For high power ultrasound treatment, reduction in the number of yeast cells (N) can be attributed to elevated temperature (60°C), cavitation and free radical formation. For plasma treatment, the inactivation can be attributed to UV radiation and plasma reactive oxygen species (ROS).

SummaryThe aim of this study is to determine the adsorption performance of three types of adsorbents for removal of As(V) from water: Bayoxide ® E33 (granular iron(III) oxide), Titansorb ® (granular titanium oxide) and a suspension of precipitated iron(III) hydroxide. Results of As(V) adsorption stoichiometry of two commercial adsorbents and precipitated iron(III) hydroxide in tap and demineralized water were fi tt ed to Freundlich and Langmuir adsorption isotherm equations, from which adsorption constants and adsorption capacity were calculated. The separation factor R L for the three adsorbents ranged from 0.04 to 0.61, indicating eff ective adsorption. Precipitated iron(III) hydroxide had the greatest, while Titansorb had the lowest capacity to adsorb As(V). Comparison of adsorption from tap or demineralized water showed that Bayoxide and precipitated iron(III) hydroxide had higher adsorption capacity in demineralized water, whereas Titansorb showed a slightly higher capacity in tap water. These results provide mechanistic insights into how commonly used adsorbents remove As(V) from water.