Non-thermal Sterilization Research Articles

Nonthermal sterilization of Listeria monocytogenes in infant foods by intense pulsed-light treatment

The purposes of this study were to determine the inactivation effects of intense pulsed light (IPL) on Listeria monocytogenes and the commercial feasibility of this sterilization method. The inactivation of L. monocytogenes at cultivated plates increased with increasing electric power and treatment time. Approximately 4–5 log reduction of the cell was achieved with IPL treatment for 5000, 600, 300, and 100 μs at 10, 15, 20, and 25 kV of voltage pulse, respectively. In the early stages of IPL treatments at 10, 15, and 20 kV, little inactivation was observed with a critical treatment time ( t c) of 360.6, 95.5, and 32.2 μs, respectively, while an abrupt inactivation without a critical treatment time was observed at 25 kV. The sterilization effects on commercial infant foods inoculated with L. monocytogenes were investigated at 15 kV, which showed higher energy efficiency for the inactivation of L. monocytogenes.

Fatty acid profiling and proteomic analysis of Salmonella enterica serotype Typhimurium inactivated with supercritical carbon dioxide

Non-thermal sterilization and microbial inactivation processes are currently receiving much attention in food and pharmaceutical industries. In particular, since supercritical carbon dioxide (SC-CO 2) treatment, which is conducted at relatively low temperatures, is considered to be a promising alternative method to replace thermal sterilization processes that cannot be safely used in foods and bioactive materials. Although SC-CO 2 has been applied to many microorganisms, the inactivation of microbial cells by SC-CO 2 has only been evaluated by using a conventional viable cell count such as a plating method, by which it is not possible to systematically elucidate the microbial cell inactivation process. Therefore, in this study the physiological status of SC-CO 2 treated Salmonella enterica serotype Typhimurium was analyzed by using GC–MS analysis of fatty acids with principal component analysis and two-dimensional electrophoresis for protein profiling. From the results of these systemic analyses, it was revealed that SC-CO 2 caused significant alterations to the profiles of fatty acids and proteins of the cells.

NONTHERMAL STERILIZATION OF GREEN COCONUT WATER FOR PACKAGING

ABSTRACT A laboratory scale technique for nonthermal sterilization of green coconut water was developed. The process consisted of two‐stage filtrations under constant pressure using different filter media; namely, low ash filter paper (Whatman 42) in the first stage and cellulose nitrate membrane (0.2‐µm pore opening) in the second stage. The quality of the filtered water was evaluated with respect to microbial population, organoleptic characteristics, nutrient contents and physical properties. The water after the second stage of filtration was sterile with no visible growth of microbes on culture plates. The taste of the processed water did not change significantly; however, the flavor and overall acceptability decreased about 9 and 11%, respectively. The water also remained sterile after 1 month in aseptically packed condition, but overall acceptability further decreased by 6%. The filtration reduced different nutrients of the fresh water like fat, ash, total sugar, reducing sugar and protein by 40.0, 43.9, 23.4, 29.2 and 13.3%, respectively; the removal of K, Mg, Ca, Fe and Cu was 10.15, 16.14, 19.04, 20.85 and 22.21%, respectively. The removal of these nutrients increased surface tension and decreased viscosity of the coconut water. PRACTICAL APPLICATIONSPackaging of sterile green coconut water as soft drink has a good global market as it ensures its widespread availability, quantity and reasonable price. Non‐thermal sterilization by membrane filtration has been found to be an alternative to thermal sterilization as the later adversely deteriorates many essential qualities of this delicate coconut water. The present non‐thermal sterilization technique maintained the sterility, nutritional quality and desirable organoleptic profile of the processed water. Thus, this process could be applied for production of green coconut water as packaged soft drink.

Vacuolar H +-ATPase and plasma membrane H +-ATPase contribute to the tolerance against high-pressure carbon dioxide treatment in Saccharomyces cerevisiae

As a non-thermal sterilization process, high-pressure carbon dioxide treatment (HPCT) is considered to be promising. The main sterilizing effect of HPCT is thought to be acidification in cytoplasm of microorganisms. We investigated the tolerance mechanism of Saccharomyces cerevisiae to HPCT with special reference to vacuolar and plasma membrane H +-ATPases. HPCT was imposed at 35 °C, 4 to 10 MPa, for 10 min. slp1 mutant defective in vacuole morphogenesis was more sensitive to HPCT than its isogenic parent. Concanamycin A, a specific inhibitor of vacuolar H +-ATPase (V-ATPase), at 10 μM rendered the parent more HPCT-sensitive to the level of slp1. To confirm further the contribution of V-ATPase to the tolerance against HPCT in S. cerevisiae, we compared vma1 mutant of V-ATPase with its isogenic parent for their HPCT sensitivity. vma1 mutant was more sensitive to HPCT than its parent. Addition of 10 μM vanadate, an inhibitor of plasma membrane H +-ATPase (P-ATPase), to the wild type strains also increased the inactivation ratio. These results clearly show that V- and P-ATPases contribute to the tolerance against HPCT in S. cerevisiae by accumulating excess H + from cytoplasm to vacuole and excluding H + outside of the cell, respectively.

Filtration resistances in non-thermal sterilization of green coconut water

Sterile green coconut water was produced in a developed two stage laboratory scale constant pressure filtration system with a pre-filtration unit by ordinary filter paper (Whatman No. 4) for removal of suspended particles, and a micro-filtration unit by cellulose nitrate membrane (0.2 μm pore opening) for removal of microorganisms. The filtration performances of the systems were tested at three pressure differentials; 5.33, 10.67 and 16.00 kPa. Resistances in both the filtration processes and the cake compressibility factors were investigated. The filter medium resistance ( R m) and the cake resistance ( α) increased with the increase in applied pressure differentials for both the filtration systems. The values of R m varied between 3.497 × 10 9 and 5.042 × 10 9 m −1, and 1.979 × 10 10 and 3.076 × 10 10 m −1 for paper and membrane filter, respectively for the entire range of pressure differentials. The corresponding variations in α were 2.162 × 10 12–4.280 × 10 12 m/kg for paper filter and 2.144 × 10 12–3.942 × 10 12 m/kg for membrane filter. Although the R m values for corresponding pressure differentials were high for membrane filter, the values of α were comparable for both the systems. The deposited cakes were compressible with a compressibility factor of 0.4.

Sterilization of liquid foods by pulsed electric fields

Recent advances in the field of high-voltage pulse power technology have provided scope for the development of nonthermal sterilization methods free from the disadvantages commonly encountered with existing physical, chemical, or radiation sterilization. The flexibility allowed in the application of electrical energy can make high-field sterilization economical, compact, energy efficient, and environmentally acceptable. The main thrust of present research in this field is the application of high-field electric pulse technology to kill microorganisms in a manner consistent with development of industrial scale nonthermal sterilization methods.

The effect of high-dose-rate X-rays on E. coli 0157:H7 in ground beef

The emergence of pathogens in today's world has increased the need for new, portable, nonthermal sterilization technologies. The University of Missouri, Columbia in cooperation with the Institute of Electrophysics, Ekaterinburg, Russia, have built and tested a new accelerator based on solid-state opening switches for the disinfection of pathogens in food. The accelerator utilizes a new solid-state opening switch to generate 40 ns, 2OO-keV electron beam pulses. These pulses were then converted to Bremsstrahlung X-rays using an integral X-ray converter. The efficacy of treating E. coli 0157:H7. In ground beef was tested by irradiating frozen ground beef with the high-dose-rate 10/sup 7-6/ rads/s X-ray pulses. Comparison studies were also done with a Cobalt-60 source located at the Missouri University Research Reactor. The results of the study are presented in this paper.

Planetary Contamination II: Soviet and U.S. Practices and Policies

The accompanying article of Horo witz et al. concluded with the view that the COSPAR recommendations re garding Mars should be adjusted to re flect new environmental information. Specifically, it was concluded that viable terrestrial microorganisms which are transported to Mars inside solid components in sealed spaces have a low probability of being released to the sur face or atmosphere, and that, if any are released, they are not likely to in fect the planet. We suggest, in addition, that both the COSPAR recommenda tions and U.S. planetary quarantine policy should be altered to take into account past and continuing Soviet prac tice regarding the. exploration of Mars and Venus. No amount of analysis by COSPAR, or of costly, self-imposed restrictions by the U.S. on its own planetary exploration program, can reduce the probability of contamination of either Venus or Mars below what the Soviets have already made it, or will make it as they continue their large planetary effort. All that U.S. policy can accomplish is to insure that U.S. efforts do not significantly increase the probability above that level. Any rec ommended policy which would require the U.S. to apply significantly more stringent restrictions is illogical in that, in effect, the U.S. would be asked to increase greatly the cost and complexity of its planetary program without achieving any significant reduction in the probability of actual contamination. There exists some parallelism be tween the problem of planetary quaran tine and that of radioactive fallout from atmospheric nuclear testing, al though the desirable solution to the quarantine problem is not merely to stop all activity. Both are multilateral problems, and individual national policy necessarily must reflect the policy of other nations. Thus, the real questions that must be faced by COSPAR, and by the U.S., are, (i) What is the prob able number of viable terrestrial micro organisms alreadyr transported to Venus and to Mars? and (ii) What is the to tal number to be expected in the next decade or so from foreseeable Soviet efforts alone? Then COSPAR can rec ommend, and the U.S. can decide, that the total U.S. contribution should be equal to some specified fraction of the total present and future Soviet contribu tion. This approach in turn suggests that every effort should be made to induce the Soviets to supply additional de tails on the Zond 2 and Venus 3 mis sion and trajectory and, particularly, on the procedure used for sterilizing the components and assembly of both space craft. With such information, the proba ble number of viable terrestrial microor ganisms deposited on Venus and Mars could be estimated well enough to per mit a. realistic quantitative analysis of what U.S. policy and practice should be. However, if more complete informa tion on Soviet practice cannot be ob tained, then, it seems to us, the U.S. has no logical alternative but to per mit greater engineering freedom in lander delivery technique and to ac cept gaseous and other nonthermal sterilization procedures, where neces sary, in its own program. By relying on the demonstrated U.S. spacecraft reliability to insure that the U.S. con tribution to planetary contamination will remain significantly less than the Soviet contribution, we could reduce significantly the cost and time required to carry out serious scientific investiga tions of the surfaces of Venus and Mars.