Determination of the efficacy of ultrasound combined with essential oils on the decontamination of Salmonella inoculated lettuce leaves

Salmonella is one of main pathogenic bacteria present in fresh produce. Ultrasound has been reported to be effective at inactivating food-borne pathogens. Moreover, ultrasound can be combined with essential oils to enhance its efficacy. This study evaluates the reduction and inactivation of Salmonella enterica Abony inoculated on lettuce leaves by the application of continuous and pulsed ultrasound as well as ultrasound combined with the essential oil of oregano and thyme. The physicochemical properties of these essential oil nanoemulsions are characterised while the structural damage of treated leaves is determined by the electrolyte leakage. Ultrasound combined with essential oils enhanced the microbial reduction on lettuce leaves and inactivation on the treated water, resulting on significant differences at concentrations higher than 0.018% (v/v) compared to control. Particle size, zeta potential and pH varied between 35 and 133 nm, −26 to −36 mV and 5.67 to 5.38, respectively. Electrolyte leakage was similar for both the control and the treated samples, increasing when essential oils were applied.peer-reviewe

Bioproduction of the Recombinant Sweet Protein Thaumatin: Current State of the Art and Perspectives

There is currently a worldwide trend to reduce sugar consumption. This trend is mostly met by the use of artificial non-nutritive sweeteners. However, these sweeteners have also been proven to have adverse health effects such as dizziness, headaches, gastrointestinal issues, and mood changes for aspartame. One of the solutions lies in the commercialization of sweet proteins, which are not associated with adverse health effects. Of these proteins, thaumatin is one of the most studied and most promising alternatives for sugars and artificial sweeteners. Since the natural production of these proteins is often too expensive, biochemical production methods are currently under investigation. With these methods, recombinant DNA technology is used for the production of sweet proteins in a host organism. The most promising host known today is the methylotrophic yeast, Pichia pastoris. This yeast has a tightly regulated methanol-induced promotor, allowing a good control over the recombinant protein production. Great efforts have been undertaken for improving the yields and purities of thaumatin productions, but a further optimization is still desired. This review focuses on (i) the motivation for using and producing sweet proteins, (ii) the properties and history of thaumatin, (iii) the production of recombinant sweet proteins, and (iv) future possibilities for process optimization based on a systems biology approach

Effect of food microstructure on growth dynamics of Listeria monocytogenes in fish-based model systems

Traditionally, predictive growth models for food pathogens are developed based on experiments in broth media, resulting in models which do not incorporate the influence of food microstructure. The use of model systems with various microstructures is a promising concept to get more insight into the influence of food microstructure on microbial dynamics. By means of minimal variation of compositional and physicochemical factors, these model systems can be used to study the isolated effect of certain microstructural aspects on microbial growth, survival and inactivation. In this study, the isolated effect on microbial growth dynamics of Listeria monocytogenes of two food microstructural aspects and one aspect influenced by food microstructure were investigated, i.e., the nature of the food matrix, the presence of fat droplets, and microorganism growth morphology, respectively. To this extent, fish-based model systems with various microstructures were used, i.e., a liquid, a second more viscous liquid system containing xanthan gum, an emulsion, an aqueous gel, and a gelled emulsion. Growth experiments were conducted at 4 and 10 °C, both using homogeneous and surface inoculation (only for the gelled systems). Results regarding the influence of the growth morphology indicated that the lag phase of planktonic cells in the liquid system was similar to the lag phase of submerged colonies in the xanthan system. The lag phase of submerged colonies in each gelled system was considerably longer than the lag phase of surface colonies on these respective systems. The maximum specific growth rate of planktonic cells in the liquid system was significantly lower than for submerged colonies in the xanthan system at 10 °C, while no significant differences were observed at 4 °C. The maximum cell density was higher for submerged colonies than for surface colonies. The nature of the food matrix only exerted an influence on the maximum specific growth rate, which was significantly higher in the viscous systems than in the gelled systems. The presence of a small amount of fat droplets improved the growth of L. monocytogenes at 4 °C, resulting in a shorter lag phase and a higher maximum specific growth rate. The obtained results could be useful in the determination of a set of suitable microstructural parameters for future predictive models that incorporate the influence of food microstructure on microbial dynamics

Isolating the effect of fat content on Listeria monocytogenes growth dynamics in fish-based emulsion and gelled emulsion systems

The influence of food matrix fat content on growth kinetics of bacteria is quite complex and, thus far, not fully elucidated, with different studies reporting contradictory results. Since results in studies involving real food products are possibly influenced by variations in compositional and physicochemical properties, there is a need for systematic studies in artificial food model systems among which the influence of fat content is effectively isolated. In this study, the isolated effect of a gradual increase in fat content, in the range of 1–20% (w/w), on the growth dynamics of Listeria monocytogenes in fish-based emulsion and gelled emulsion model systems was investigated at 4, 7 and 10 °C. Growth parameters estimated by the Baranyi and Roberts model were compared among the different model systems. Overall, an increase from 1 to 5% fat resulted in a significant reduction of the lag phase duration λ in both model systems at all studied temperatures, while a further increase in fat content did not significantly affect λ. The relationship between the fat content (%) and the maximum specific growth rate μmax was more complex, following the same trends for both emulsions and gelled emulsions and tested temperatures, i.e., (i) μmax was higher at 5% than at 1% fat, (ii) μmax was lower at 10% than at 5% fat, (iii) μmax at 20% fat was higher than or equal to μmax at 10% fat, and (iv) μmax was the highest at 5% fat. Based on these experiments, fundamental knowledge was provided which could lead to the development of food matrix-related factors describing the influence of fat content in future predictive modeling tools which include food microstructural elements. Such models could increase the accuracy of the shelf-life estimation for fat-containing foods, in turn resulting in improved food safety

Heat adaptation of Escherichia coli K12: Effect of acid and glucose

AbstractThe objective of this work is to investigate the effect of the (possible) acid adaptation during growth in a glucose rich environment on the heat resistance of Escherichia coli K12 MG1655. E. coli cells were grown in TSB and/or TSB dextrose free broth until they reached the stationary phase. Afterwards, the stationary phase cells were added in TSB and/or TSB dextrose free broth and inactivation took place at 54oC and 58oC. It was observed that growth in a glucose rich environment leads to an increased heat resistance, most likely due to a certain level of acid and further heat adaptation via cross protection

Exploring the Effect of Ultrafiltration/Diafiltration Processing Conditions on the Lactoferrin and Immunoglobulin G Content of Feta Whey Protein Concentrates

In this paper, the production of powder enriched in lactoferrin (Lf) and immunoglobulin G (IgG) from untreated feta cheese whey is studied. More specifically, the influence of transmembrane pressure (Δp) and temperature on flux and separation ability during ultrafiltration combined with continuous diafiltration is investigated. Two different types of membranes were used, a spiral polyvinylidene fluoride (PVDF) (molecular weight cut-off [MWCO 75 kDa) and a set of 18 cylindrical PVDF membranes (MWCO 100 kDa). For the production of the whey powder, two drying methods were compared: spray and freeze drying. All combinations lead to powder with high total protein content and with a notable content in these two bioactive proteins. However, cylindrical membranes (at a temperature of 20C and a transmembrane pressure of 4 bar) in combination with freeze drying resulted in the highest yield from whey into Lf and IgG and excellent sensory characteristics. Practical Applications Whey powder enriched in the multifunctional proteins lactoferrin and immunoglobulin G have very large potential both as nutrition additives and for pharmaceutical purposes. The systematic study of the parameters affecting all unit operations involved leads to the most efficient and cheapest production. In order to achieve this, the methodology was kept as simple and low cost as possible. This way, a strong tool could be created for the utilization of the cheese-making by-product whey, which still causes large environmental problems

Artificial neural networks as a tool for incorporating microbial stress adaptations in the quantification of microbial inactivation

Quantifying microbial adapted responses due to thermal stresses by an accurate methodology is imperative for assessing the efficacy of a heat process. Two different artificial neural network (ANN) models are constructed for studying the increased induction of the heat resistance of Escherichia coli K12 under a treatment of decreasing heating rates. In the first model structure there are two input vectors, namely, time t and temperature rate dT=dt, whereas in the second case is also added a third one, namely, the microbial load delayed with one time unit Nk¡1. For both models a minimal fully-connected feedforward architecture is used consisting of one hidden neuron and one output neuron. Results as based on the prediction capability of the model structures demonstrate the comparative advantage when an ANN architecture with a delay in its inputs is employed. Incorporation of past events seems to be an essential input for taking into account the observed induced microbial heat resistance.peer-reviewe

GASDS: A kinetic-based package for biomass and coal gasification

In this paper, a simulation package called GASDS is introduced. It is particularly suited to evaluate the pyrolysis, gasification and combustion of biomass and coal feedstocks. The aim of this work is to describe the package from a numerical point of view and its interface. Additionally, experimental results for a countercurrent fixed-bed biomass gasification reactor are reproduced. The influence of reactor and particle discretizations are investigated with respect to accuracy and computational time. Some differences are present between experimental and simulation results. In order to improve the agreement between simulation and experimental results it is suggested to improve the kinetic scheme of the solid phase and gas-solid reactions. The negligible differences in terms of predictions, instead, do not justify the adoption of finer discretizations for the particle and reactor, which imply longer computational times

Novel methods to monitor the biodegradation of polylactic acid (PLA) by Amycolatopsis orientalis and Amycolatopsis thailandensis

Plastics are essential in modern life, but their conventional production is problematic due to environmental pollution and waste management issues. Polylactic acid (PLA) is a widely used bioplastic that is bio-based and biodegradable, making it a key player in the bioeconomy. PLA has been proven to be degradable in various settings, including aqueous, soil, and compost environments. However, monitoring and optimizing PLA biodegradation remains challenging. This study proposes methods to improve the quantification of PLA biodegradation by Amycolatopsis spp. Ultrasound treatments (10 s) significantly improved the enumeration of viable Amycolatopsis cells by breaking the pellets into quantifiable individual cells. A separation technique combining ultrasound (120 s) and 40 μm cell strainers effectively isolated PLA particles from biomass to quantify PLA weight loss. This enabled the monitoring of PLA biofragmentation. Finally, CO2 production was measured according to ISO 14852 to quantify mineralization. Integrating these methods provides an improved quantification for PLA biodegradation along its different stages. In a case study, this led to the construction of a carbon balance where 85.1% of initial carbon content was successfully tracked. The developed techniques for monitoring of PLA biodegradation are essential to design future waste management strategies for biodegradable plastics