Assessing the individual microbial inhibitory capacity of different sugars against pathogens commonly found in food systems

Highly concentrated sugar solutions are known to be effective antimicrobial agents. However, it is unknown whether this effect is solely the result of the collective osmotic effect imparted by a mixture of sugars or whether the type of carbohydrate used also has an individual chemical effect on bacterial responses, that is, inhibition/growth. In view of this, in this work, the antimicrobial properties of four sugars, namely, glucose, fructose, sucrose and maltose against three common food pathogens; Staphylococcus aureus, Escherichia coli and Salmonella enterica, were investigated using a turbidimetric approach. The results obtained indicate that the type of sugar used has a significant effect on the extent of bacterial inhibition which is not solely dependent on the water activity of the individual sugar solution. In addition, while it was shown that high sugar concentrations inhibit bacterial growth, very low concentrations show the opposite effect, that is, they stimulate bacterial growth, indicating that there is a threshold concentration upon which sugars cease to act as antimicrobial agents and become media instead. Significance and Impact of the Study: In this work, an analysis on the antimicrobial properties of glucose, fructose, sucrose and maltose in solution was conducted using a turbidimetric approach. Our findings indicate that while, as expected, all of these sugars exhibit significant antimicrobial effects at high concentrations, at low concentrations they appear to act as substrates for the bacteria which results in enhanced microbial growth instead of inhibition. In addition, the results obtained also suggest that the resultant osmotic stress imparted by the sugar solutions is not the only factor which determines their antimicrobial activity and that other chemical factors may be playing a significant role

Characterization and antimicrobial efficacy against E. coli of a helium/air plasma at atmospheric pressure created in a plastic package

A plasma source, sustained by the application of a floating high voltage (±15 kV) to parallel-plate electrodes at 50 Hz, has been achieved in a helium/air mixture at atmospheric pressure (P = 105 Pa) contained in a zip-locked plastic package placed in the electrode gap. Some of the physical and antimicrobial properties of this apparatus were established with a view to ascertain its performance as a prototype for the disinfection of fresh produce. The current–voltage (I–V) and charge–voltage (Q–V) characteristics of the system were measured as a function of gap distance d, in the range (3 × 103 ≤ Pd ≤ 1.0 × 104 Pa m). The electrical measurements showed this plasma source to exhibit the characteristic behaviour of a dielectric barrier discharge in the filamentary mode and its properties could be accurately interpreted by the two-capacitance in series model. The power consumed by the discharge and the reduced field strength were found to decrease quadratically from 12.0 W to 4.5 W and linearly from 140 Td to 50 Td, respectively, in the range studied. Emission spectra of the discharge were recorded on a relative intensity scale and the dominant spectral features could be assigned to strong vibrational bands in the 2+ and 1− systems of N2 and ${\rm N}_2^+$ , respectively, with other weak signatures from the NO and OH radicals and the N+, He and O atomic species. Absolute spectral intensities were also recorded and interpreted by comparison with the non-equilibrium synthetic spectra generated by the computer code SPECAIR. At an inter-electrode gap of 0.04 m, this comparison yielded typical values for the electron, vibrational and translational (gas) temperatures of (4980 ± 100) K, (2700 ± 200) K and (300 ± 100) K, respectively and an electron density of 1.0 × 1017 m−3. A Boltzmann plot also provided a value of (3200 ± 200 K) for the vibrational temperature. The antimicrobial efficacy was assessed by studying the resistance of both Escherichia coli K12 its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK selected to identify possible cellular responses and targets related with 5 min exposure to the active gas in proximity of, but not directly in, the path of the discharge filaments. Both the parent strain and mutants populations were significantly reduced by more than 1.5 log cycles in these conditions, showing the potential of the system. Post-treatment storage studies showed that some transcription regulators and specific genes related to oxidative stress play an important role in the E. coli repair mechanism and that plasma exposure affects specific cell regulator systems

Citrus juices technology

Citrus fruits are widely grown throughout the world and contain various bioactive compounds with antioxidant activities including vitamin C, carotenoids, and phenolic compounds. These components are very important for human health and provide protection against harmful free radicals. Citrus fruits are mostly consumed as fresh fruits or fruit juices. To obtain high quality and safe citrus juice, certain critical points (oil extraction from peel, juice extraction, pulp removing, pasteurization, evaporation, and aseptic filling) need to be taken into consideration during citrus juice processing. Firstly, oil extraction from the peel is a necessary step to limit the level of peel oil components in the juice. Secondly, selected juice extraction techniques and process conditions are very important for the yield and total quality of the juice. Thirdly, the pulp removal is an important step to remove most of pectinmethylesterase (PME) and its heat resistance isoenzymes. Further inactivation of remaining PME enzymes and pathogenic or spoilage microorganisms is also obtained with the pasteurization step. Finally, equipment used for the juice production and the concentration conditions have various effects on the sensory properties of the citrus juices. As a result, minimal processing would be applied to citrus juices if the processing steps detailed above are optimized. Obtaining clarified citrus juices from the citruses which have lower carotenoid content including lemon and lime juice is a new trend these days. It is needed to be focused on enzymation (depectinization), clarification assistance agents, and filtration conditions during the clarified juices production. Citrus peel (flavedo) and layer of albedo are the main byproducts of the citrus juice industry. Citrus peel oil is obtained from flavedo layer which has a significant commercial value. Recently, promising nonthermal food preservation technologies were developed including pulsed electric fields (PEF), high pressure processing (HPP), and ultrasonication process (US). These technologies are highly appreciated for their ability to extend the shelf life of food products without the application of heat, thus also preserving the quality attributes such as sensory quality and nutritional value, as well as controlling the microbiological safety of food products. © 2014, Springer Science+Business Media New York