2 results for Alkhafaji, S

  • Determination of an effective treatment temperature of chemical and biological reactions

    Farid, Mohammed; Alkhafaji, S (2012)

    Journal article
    The University of Auckland Library

    Thermal microbial inactivation kinetics can be influenced significantly by the non-isothermal condition of the sample tested. In many instances, it is practically difficult to maintain the temperature constant during chemical and biological reactions. To minimise error caused by such non-isothermal condition, an effective treatment temperature was derived based on fundamental principles of reaction kinetics. This effective temperature was significantly different from the arithmetic mean temperature due to the exponential effect of temperature on reaction rate. In order to validate the developed concept, Escherichia coli ATCC 25922 suspended in simulated milk ultra filtrate was thermally inactivated using test tubes of different diameters. As expected, the D value was accurately related to the water bath temperature only when small capillary tube was used for the measurements. As the tube diameter increased, the D value increased and was found not to be related to the water bath temperature. On the other hand, the measured D values using different tube diameters correlated very well with the calculated effective treatment temperature. Our calculations show that the effective temperature can be calculated with reasonable degree of accuracy even if there is some uncertainty in the value of the activation energy of the reaction. A number of important applications are addressed in this paper to show the importance of using such a concept. The use of effective temperature will allow accurate comparison of reaction kinetics reported in the literatures on chemical and biological reactions.

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  • Pulsed Electric Field continuous pasteurization of different types of beers

    Alami Milani, Elham; Alkhafaji, S; Oliveira, Maria (2015-04)

    Journal article
    The University of Auckland Library

    Thermal pasteurization of bottled beer is used to extend its shelf life. However, the thermal process negatively affects the beer sensory. In this research, beer was processed using Pulsed Electric Fields (PEF), a non-thermal continuous preservation technology that has the potential to be implemented at a commercial scale by the brewing industry. The main goal of this work was to investigate the feasibility of PEF for yeast inactivation and its impact on beer sensory. First, the effect of a PEF process (temperature below 43 °C, 45 kV/cm electrical field intensity, 46 pulses, 70 μs) on Saccharomyces cerevisiae ascospores inactivation in nine different beers comprising ale, lager, dark, low alcohol, and no alcohol, was investigated. Log reductions of 0.2 and 2.2 were registered for 0 and 7% alc/vol beers, respectively, which indicated that the alcohol content is the major beer constituent driving the microbial inactivation. Then, 0, 4, and 7% alc/vol beers containing S. cerevisiae ascospores were submitted to PEF combined with thermal processing up to 53 °C. An increase in the PEF treatment temperature from 43 to 53 °C caused at least an additional 0.7, 2.1 and 1.8 log reductions in the yeast spore population for 0, 4, and 7% alc/vol beers, respectively. Results of another experiment carried out with 4 and 7% alc/vol beers, showed the huge advantage of using PEF compared with thermal processing. Additionally, lightstruck attribute sensory tests revealed six (aroma) and three (flavour) PEF beers did not develop the lightstruck character, being acceptable in terms of sensory. The results of this study can be helpful for designing appropriate PEF conditions to pasteurize beers with different alcohol contents.

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