Inactivation Of Microorganisms And Enzymes By Manothermosonication And The Potential For Soybean Milk Pasteurization

Manothermosonication(MTS)has been studied to become one of the key alternatives to current thermal pasteurization techniques.The treatment involves the combination of mild temperature and pressurized sonication(high power ultrasound),which together establishes another level of destructive cavitation effect.Although MTS could be applied to various applications,the importance of food safety is one of the priority that MTS technology can be tested with.The problem with current ultra-sonication(US),alone,was the lack of cavitation strength to successfully eliminate the unwanted food components such as pathogens and spoilage enzymes.The primary mechanism is the physical disruption from the shear force inflicted by the cavitation’s micro-bubble implosion.This thesis focuses mainly on designing and applying the MTS technology on liquid food as an alternative pasteurization technique to conventional thermal treatment.The study on different aspects were carried out to ensure that this research covered all the critical points of food preservation.1.Approached MTS technology in the engineering aspect by the successful assembling of a stable lab-scale MTS equipment.The effects of heat and external pressure on sonication or cavitation were analyzed whether it was feasible enough to develop the current ultrasound technology.Heating helped to lower the vapor pressure and accelerated chemical reactions,while external pressure created a counter pressure condition;both resulted in more aggressive formation and implosion of micro-bubbles,giving out more disruptive energy.After the step-by-step explanation of system modification,the operation on MTS equipment was evaluated.Overall,the system was able to provide desired treatment conditions and covered the parameter range for food science or other liquid substance projects.The obvious evidence of cavitation being enhanced by the two factors was the immense raise in cavitation noise while operation.Next,COMSOL modeling of heat distribution inside the reaction chamber was included to show how the cavitation occurs at the probe tip and radiated through the liquid sample.Furthermore,the improved sonication was measured using the calorimetric power equation,and found that the temperature increase rate for 400 k Pa was 175% higher than 100 k Pa sonication.Under performance aspect,approximately 28% of input electrical power was converted into thermal power at every pressure level.In addition,the energy consumption of the optimal MTS equipment for milk pasteurization(214.98 KJ/kg/hr),requiring only 1 min treatment time,was predicted to be 27.29% lower than conventional LTLT pasteurization(295.65 KJ/kg/hr).Moreover,the electrical power consumption of the up-scaled MTS equipment(2.92 Watt/L for 514.29 L/hr)was much more efficient than the similar capacity steam batch pasteurization(5.1 Watt/L for 500 L/hr).Finally,this research also provided suggestions on future MTS design for commercial use.2.Established a study on the MTS equipment for pasteurization application by investigating the effectiveness in the inactivation of two opposite gram-stained bacteria.E.coli ATCC 25922 and S.aureus ATCC 25923 samples were treated by mild heat(T,50 °C),sonication(US,100 k Pa),thermosonication(TS,50 °C 100 k Pa),manosonication(MS,400 k Pa),and manothermosonication(MTS,50 °C 400 k Pa)in pulse mode for precise temperature control.After 5 min,the viability of E.coli and S.aureus treated with MTS decreased by 6.25 and 4.55 log CFU/m L and the maximum reduction in non-linear Biphasic decimal reduction(D-value)of the sensitive population were up to 91.35% and 94.24%,respectively.The addition of temperature and pressure improved the number and size of cavitation bubble,releasing much more shear force after exploding to lethally damage bacterial structure or exert protein denaturation.It was confirmed that heat and sonication executed more effectively together as the synergism at 400 k Pa(78.24% and 62.56%)was better than 100 k Pa(3.98% and 0.66%)sonication.Since ultrasound under external pressure generated an impressive amount of excess heat with up to 0.88 °C/sec,an inactivation experiment employing such heat,continuous manosonication(MTSn)was also conducted which resulted in minimal linear D-values of 0.17 min for E.coli and 0.18 min for S.aureus with power intensity of 3.69 Watt/m L thermally or 14.29 Watt/m L electrically.All experiment indicated that gram-positive S.aureus was more resistant to sonication than gramnegative E.coli,but the lethality rate became more comparable with more violent cavitation.Furthermore,the MTS inactivation results were compared to the conventional Low-TemperatureLong-Time and High-Temperature-Short-Time pasteurization in the feasibility aspect.Under the same treatment temperature,the inactivation time could be reduced,or that lower temperature could be used to reach the same inactivation level under fixed treatment time.In addition,results from environmental scanning and transmission electron microscopy also revealed the cellular damages by sonication treatments and further supported the synergism of heat and pressurized sonication.3.Further validated the potential of MTS to be suitable for commercial use by practicing the MTS technique on raw soybean milk which contains high level of bioactivities,starting with the inactivation of spoilage enzymes.The research analyzed the results of changing enzymatic activities after applying a series of heat and sonication treatments on soymilk,which is the source of four major enzymes.Enzymes were subjected through 5 min of mild heat(T,65 °C and 70 °C,100 k Pa),sonication(US,25 °C,100 k Pa),thermosonication(TS,65 °C,100 k Pa),manosonication(MS,25 °C,400 k Pa),and manothermosonication(MTS,65 °C,400 k Pa)in pulse mode.Initially,the result revealed activity reduction in Lipoxygenase(LOX),Peroxidase(POD),Polyphenol Oxidase(PPO),and Trypsin Inhibitor(TI)after treated under mild heat at 65 °C with D-values of 130.09,65.26,261.24,and 52.44 min,respectively.Remarkably,the activity of LOX,POD,PPO,and TI was further reduced significantly(P<0.05)when treated with MTS,with D-values of 12.04,18.34,31.85,and 8.83 min for,respectively.The MTS treatment stimulated both physical and chemical disruptions on enzymes through its aggressive cavitation effect and exerted heat,creating an irreversible unfolding effect on secondary or tertiary enzyme structures.Results also showed a satisfying degree of synergism between heat and pressurized sonication when treated on LOX,POD,and TI,with 115.78%,71.43%,and 68.97% synergism respectively,whereas PPO was found to be immune to both parameters with no synergism detected.Furthermore,continuous pressurized sonication without temperature control was also applied to the soymilk,providing the best Dvalues of 0.64,5.15,17.61,and 3.28 min on LOX,POD,PPO,and TI,respectively.4.Investigated the change in the characteristics and qualities of soymilk after treatment with a series of sonication conditions.No observation was detected in the soymilk texture and appearance directly after treatments.However,the presence of bubble and titanium tip debris occurred with the involvement of higher external pressure.This was because of the more aggressive cavitation and the used of nitrogen gas which can be re-designed in the future.The beneficial side of MTS treatment was the homogenizing effect that broke down the soymilk components and helped to improve overall quality.After 7 days of storage,most treated soymilk samples began to separate as a sign of rancidity,except for 70 °C,MTS and MTSn samples which still remain the same as freshly treated sample.Next,the research on raw soymilk microbial inactivation revealed that MTS(pulse mode 5 min)and MTSn(1.5 min)reduced the initial viable count by 0.22 and 0.27 CFU/m L respectively.The improved MTS cavitation by temperature and pressure confirmed the enhancement of bacterial inactivation mechanism from normal sonication.The 11 days shelf-life study on the treated samples discovered that pressurized sonication could also inflict sub-lethal injuries on the cell,resulting in a further reduction of viable count at the initial storage period.The minimum microbial growth rate per day was 0.02 log CUF/m L obtained by MTS and MTSn.In addition,the protein hydrolysis property was increased by all treatments where the 65 °C sample only increased by 6.01% while MTS sample could boost the detectable protein content up by over 20%.Additionally,the total soluble solid and titratable acidity of all samples remained comparable to the control.The total color difference,however,shift the most by 18.55 with MTS treatment which due to the alteration of fat globule or other soymilk components.As a result,MTS technology was able to preserve or improve food quality even when the cavitation effect became more aggressive from combining with mild temperature and external pressure.Ultimately,a reliable lab-scale manothermosonication system was successfully developed.The addition of temperature and external pressure has synergistically improved the power of ultrasound disruption mechanism in various aspects such as increasing the cavitation bubble number and size,reducing media viscosity,generating more free radical scavenging,and provide chemical disruption by heat.The greater shear force released by MTS bubble implosion was then used to eliminate unwanted microorganisms,enzymes and other unwanted food components that were the main target for pasteurization process.The results also implied that MTS technology could reach the target faster and more delicately than ultra-sonication or conventional thermal pasteurization.After all,MTS could also be used to pasteurization soymilk that contained numerous bioactivities while preserving better food quality than thermal pasteurization.The MTS technology is suitable for implementation into industrial use.