Sterilization Of Liquid Foods Research Articles

A new computational technique for the estimation of sterilization time in canned food

Sterilization of liquid food in cans is complicated by the influence of natural convection currents induced by the hot walls of the can. In order to predict the temperature variation of the slowest heating zone (SHZ) with time, it is necessary to use computational fluid dynamics (CFD) analysis, which can be done with the help of a number of available commercial software. However, the required computational time is usually of the order of hours. In this paper, simple method of calculation is developed to predict the SHZ without the requirement of sophisticated computations. A generalized correlation was developed to predict the change of the SHZ with time for different fluids and can sizes.

A computational and experimental study of heating and cooling cycles during thermal sterilization of liquid foods in pouches using CFD

In this study, a theoretical analysis of a heating and cooling cycle during sterilization of a three-dimensional pouch filled with carrot-orange soup was presented and analysed. Transient temperature, the shape of the slowest heating zone (SHZ) during heating and the slowest cooling zone (SCZ) during cooling were presented and studied. The simulation covered the whole heating and cooling cycles of 3600s and 1200s durations, respectively. The computational fluid dynamics (CFD) code PHOENICS was used for this purpose. Saturated steam at 121°C and water at 20°C were assumed to be the heating and cooling media, respectively. The partial differential equations describing the conservation of mass, momentum, and energy were solved numerically using the finite volume method. The liquid food used in the simulation has a temperature-dependent viscosity and density. At the end of heating, the SHZ was found to have settled into a region within 30–40 per cent of the pouch height above the bottom and at a distance approximately 20–30 per cent of the pouch length from its deepest end. In the cooling cycle, the slowest cooling zone (SCZ) was found to develop in the core of the pouch and gradually migrate toward the widest end. The vertical location of this slowest cooling zone was about 60–70 per cent of the pouch height. Experimental validation has been performed by measuring the temperature distribution in the pouch during heating and cooling, using thermocouples fixed at different locations. The predicted results were in good agreement with those obtained from the experiments.

The effect of can rotation on sterilization of liquid food using computational fluid dynamics

In this work, sterilization of a viscous liquid food (carrot–orange soup) in a metal can lying horizontally and rotated axially in a still retort was simulated. The rotating can at 10 rpm was assumed to be heated by steam at 121 °C. The governing equations of mass, momentum and energy conservation for the three-dimensional can were solved using a commercial computational fluid dynamics package (PHOENICS), which is based on a finite volume method of solution. Transient temperature and velocity profiles caused by natural and forced convection heating were presented and compared with those for a stationary can. The results indicated that the combined effect of natural and forced convection splits the slowest heating zone (SHZ) into two distinct regions, unlike what has been previously observed in the stationary can. The volume of the SHZ was found to cover less than 5% of the total volume of the rotated can at the end of heating, which is due to the effect of rotation. The magnitude of the maximum axial velocity of the fluid after 1000 s of heating was found ranging from 2.3×10 −5 to 3.2×10 −4 ms −1, compared with 2.2×10 −7 to 2.1×10 −4 ms −1 for the stationary can. The localized high velocity near the two ends of the can spread gradually throughout the whole length of the can as heating progresses.

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.

High voltage pulse application for the destruction of the Gram-negative bacterium Yersinia enterocolitica

High voltage pulses of peak voltages U = 10–75 kV and rise times t p = 500 −1300 ns were applied with frequency f = 1 Hz in order to cause the irreversible electroporation of the Gram-negative bacterium Yersinia enterocolitica. The bacteria were suspended in a NaCl solution of pH = 7.2 and conductivity γ=0.8–1.3 S m −1. The suspension was placed in a glass tube immersed in the gap of a cylindrical electrode system to which high voltage pulses, generated by a Marx bank, were applied. Such an electrode system will protect the bacteria suspension from the chemical processes at the electrode-liquid interface due to prebreakdown phenomena. A current chopping electrode system was connected in parallel with the sample in order to avoid heat generation from direct discharge of the pulse through the suspension. The maximum temperature rise was only 2–3°C with the application of 70 pulses of 45 kV magnitude. The dependence of the survival ratio s = N N 0 (the number of bacteria per cm 3 after pulse treatment, N, divided by the number of bacteria per cm 3 before treatment, N 0) of Y. enterocolitica on the peak voltage of the pulse, the number of pulses applied and the rise times of the pulses have been measured. A reduction by ∼7 orders of magnitude of Y. enterocolitica viable cells per cm 3 was achieved. The lethal effect on the bacteria strongly depends on the peak voltage and the number of pulses applied; however, the effect of the rise time on the killing of Y. enterocolitica tested was not significant witt in the range of rise times used (500–1300 ns). The results show that a considerable inactivation of the microbes can be achieved by the application of short ( t p <1000 ns) high voltage pulses for the bacteria suspension without directly exposing the suspension to the electrodes. It is therefore possible to use this non-thermal method as a means for sterilization of liquid foods where the effects due to electrolysis must be minimized.

Sterilization of liquid food with silver ion-containing sepiolite

Sterilization of liquid food with silver ion-containing sepiolite

The microbiologically safe continuous-flow thermal sterilization of liquid foods

Thermal sterilization is aimed at eliminating the risk of food poisoning, and may be used to extend product shelf life. Here the guidelines for the microbiologically safe thermal sterilization of liquid food products recommended by the Continuous Heat Treatments subgroup of the European Hygienic Equipment Design Group (EHEDG) are summarized. This paper is the sixth in a series of articles featuring the EHEDG to be published in Trends in Food Science & Technology. The EHEDG is an independent consortium formed to develop guidelines and test methods for the safe and hygienic processing of food. The group includes representatives from research institutes, the food industry, equipment manufacturers and government organizations in Europe.

The effect of pH on continuous high‐temperature/short‐time sterilization of liquid foods

The effect of <i>p</i>H on continuous high‐temperature/short‐time sterilization of liquid foods

Continuous high-temperature/short-time sterilization of liquid foods with steam-injection heating

The continuous high-temperature/short-time sterilization of liquid foods is investigated. A steam-injection, which is frequently used in industrial sterilization processes, is considered. The non-Newtonian power-law model is employed to characterize the liquid food flow and an energy balance to calculate the temperature distribution in the cooling section. Well-established kinetics is adopted to model the microorganism (Cl. botulinum) destruction and nutrient (vitamin B 12) denaturation. The total length of sterilizer is determined for different sterility requirements, process temperatures and pseudoplastic indices.