MXPA98009322A - Method for conservation under pres - Google Patents

Abstract

The present invention relates to a method for substantially decreasing the viability of microorganisms and deactivating enzymes in a contaminated substance by exerting a high pressure on the substance. The substance is conducted in a stable flow through a narrow open tube (6) while the pressure difference between the inlet and outlet of the tube is maintained at 100 MPa or more. The elevation at product temperature during the passage of the tube can be confined to less than 5 ° C. The method allows conservation by PUA completely contin

Description

METHOD FOR PRESERVATION UNDER PRESSURE DESCRIPTION OF THE INVENTION The present invention relates to a method for preservation, particularly preservation under ultra high pressure. The method is used for operation in a continuous mode and is particularly suitable in the food industry.

STATE OF THE ART The industrially prepared food usually has to be subjected to a conservation treatment in order to avoid its decomposition during subsequent storage. Conservation at ultra high pressures (PÚA) is a conservation method that only relatively recently has been developed for industrial application, although the lethal effect of ultra high pressure on microorganisms has been discovered in the previous century by B.H. Hite. A review of the state of the art can be found in New Methods of Food Preservation (1995, ed G.W. Gould). The conservation of PÚA is the subject of many patents: for example US 4,873,094, US 5,228,394, US 4,873,094 and US 5,228,394. NL 102 914 describes driving a spreadable product through a narrow tube under an initial pressure of 40 atmospheres with a beneficial effect on the consistency of the product. However, this pressure is not high enough to have a significant effect on the viability of microorganisms in the product. The substances treated in a homogenizer are also exposed to a very high pressure, but for a very short time (several milliseconds). In said device the forces of shear exerted on the substance during the pressure drop are enormous and often damage the structure of the product. In addition, the energy needed to pass the product through the homogenization space quickly dissipates in a small volume of the shear device resulting in an unacceptably high local temperature rise. Usually this elevation is about 5 ° C per 20 MPa of pressure drop, the elevation also depends on the thermal capacity and heat conductivity of the product.

A major disadvantage of known PUA conservation techniques is that conservation by PÚA applies only in the form of batches. Since most food processing is operated in a continuous mode, a conservation method by PÚA that could be operated as a continuous process and could completely fill this need. Only WO 95/22912 describes a PÚA equipment with which a semi-continuous process can be carried out. The equipment present for processing by PÚA is complicated and is so costly that it prevents an economic use and consequently the general use of the conservation of PÚA.

DECLARATION OF THE INVENTION An unexpectedly feasible combination of two conditions that appear to be contiguous to the system has been found: a condition being the maintenance of a high kinematic pressure in a tube that is relatively narrow and is open at one outlet end, whose kinematic pressure in at least one part of the tube is sufficiently high so that a microbiologically contaminated fluid during its flow through the tube is decontaminates, the other condition being the realization of a flow which is high enough to make the process economically feasible. The invention therefore provides a method for decreasing the viability of microorganisms and / or the activity of enzymes in a contaminated substance by exerting a high pressure on the substance, characterized in that the substance is conducted in a stable flow through a tube, while that the pressure difference between the inlet end and the outlet end of the tube is maintained at 100 MPa or more. The present method allows a process of conservation by PÚA completely continuous.

DESCRIPTION OF THE FIGURE Figure 1 shows a schematic view of the equipment with which the invention can be carried out. c is a tube with a length L and an internal diameter d. a is a storage container connected to the inlet of the tube via a pressure unit b. In d the open hole of the tube is located.

DETAILS OF THE INVENTION The invention is essentially carried out by feeding the substance from the storage container a to the inlet of the tube via a pressure unit b and passing it through the tube to the outlet on the right side. The invention can be applied to all types of fluid substances that need a decontaminating treatment, as long as they have a consistency that allows a sufficiently rapid passage through the necessarily small tubes used with the invention. Said substances comprise pharmaceutical substances, clinical liquids and particularly food products such as spreads, mayonnaise, dressings, milk, tea and even heat sensitive products such as ice cream and soft cheese. The invention is particularly suitable for substances that tolerate only mild treatments. The substance may be a final food product or an ingredient (or a mixture of ingredients) used for the preparation of a food product, including such natural substances as herbs, as long as they can be incorporated into a fluid-carrying substance that can be pumped through the narrow tube. In order to maintain a pressure of at least 100 MPa between the inlet and outlet of the tube, an appropriate balance should be found between one side of the diameter and the length of the tube and on the other side the given viscosity and flow desired of the product that will be treated. The minimum volume V of the tube results from the formula V = t * f, where t is the minimum residence time for effective decontamination and f is the desired flow. The residence time can be adjusted without changing the narrow dimensions of the tube by inserting a chamber at the upstream end of the narrow tube, between the outlet of the pressure device and the entrance of the narrow tube. With said chamber the ultra high pressure volume is increased and consequently the residence time of the fluid. Due to its resistance against high pressures, the chamber preferably also is a tube, whose diameter is greater than the narrow tube diameter so that the pressure and flow drop is not substantially influenced by the presence of the chamber. Preferably said The chamber has a diameter that is at least five times greater than the diameter of the narrow tube. The following description of a tube does not apply to this residence chamber, but to the narrow tube attached. Unless otherwise indicated, the term tube is used for the narrow tube. In the context of the present disclosure, a tube is considered to be a round container with two openings at both ends of the container wherein the length of the container is at least 10 times the width of the container. Generally, the ratio of the average length and diameter of a tube suitable for the invention is at least 1000, preferably at least 10,000. Generally this means a diameter of only several millimeters and a length of at least several meters. The optimal dimensions can easily be found by some calculation and experimentation. Good results can be obtained with a tube that has a length of 200 m and an internal diameter of 10 mm. It is quite surprising that foodstuffs which often have a viscous consistency can be pressed through said tube at a sufficient flow rate for the economical process.

With said open tubes, an output per hour of approximately 50 liters of product can be made having an oil viscosity exerting a pressure of 1000 MPa. The highest flows needed in practice are made by combining large numbers of parallel tube bundles. See also Table I for examples of suitable tube dimensions in relation to the viscosity of the given substance and pressure exerted. It is thought that the combination of pressure in an open tube is possible only with extremely long tubes. Nevertheless, unexpectedly favorable pressure is observed which depends on the viscosity behavior. The pressure inside the tube should be at least 100 MPa, but pressures of at least 300 MPa are preferred. The generally higher pressures allow shorter decontamination times. The ultra high pressures needed to work the invention can be better supported by tubes with relatively narrow diameters: 10 mm or less is preferred. Special reinforcement is not necessary. The conservation device present It does not need very thick walls of the prior art equipment. TABLE 1 Applicable to fluids having a density of approximately 1000 kg / m3 and a heat capacity of 4.2 J / g.K P: pressure drop in Megapascals d: average pipe diameter in meters Flow: flow rate in liters per hour L: tube length in meters Vise. : Viscosity in Pascal seconds The tube can be placed in any position, but preferably a compact shape such as a coil is chosen. Pipes that have a circular intersection are more advantageous for resisting high pressures, but other forms of intersections are not excluded. The preferred tube materials are glass and stainless steel, substances that are compatible with food. For the pressure device or unit a choice can be made of the devices found on the market that are intended to pump fluids under ultra high pressures. In order that the pressure exerted has a sufficient effect on the microorganisms, the residence time of fluid in the tube should be at least 1 second. Generally, longer residence times are required when the pressure is less than 350 MPa. Preferably the residence time is at least 2 minutes, more preferably at least 5 minutes and even more preferably at least 10 minutes.

It is difficult to give general rules since the flow behavior of the substance processed under PUA conditions generally can not be foreseen. Given a particular substance, some experimentation will easily provide the proper combination of dimensions and pressure in the tube. The present device operates with a permanently open orifice at the end of the tube. The effect is a pressure gradient along the entire length of the tube. Consequently, the pressure in the tube is higher in portions upstream than in parts downstream of the tube, with the effect that the decontamination takes place predominantly in the upstream part of the tube. The high pressure energy dissipates uniformly over the entire length of the tube. Within the tube, the shear forces are relatively small. In addition, both the relatively large external surface of the tube in relation to the tube volume, and the relatively thin wall of the tube allow easy control of the temperature of the tube contents if necessary with the aid of additional cooling. The temperature rise of the processed substance during passage of the tube it can be confined to less than 10 ° C, preferably less than 5 ° C. This is adapted in modern concepts to avoid unnecessary heating of the industrially prepared food as soon as possible. Operating the process at a temperature different from room temperature can be advantageous. When the temperature is lowered, the viscosity will increase, which makes it impossible to maintain the pressure at the desired level even when the fluid to be treated is not sufficiently viscous at room temperature. An increase in temperature will cause a decreased viscosity and an advantageous increase in flow will result. Said increase will mean the obvious limitation that the substance to be treated needs a minimum residence time in the area. The present invention provides a method that allows the decontamination of food products, wherein the use of preservative ingredients, a low pH or the use of heating is undesirable. However, the present method of PÚA can be used in combination with one or more methods of different conservation. When the methods are combined, often enough less severe global conditions are given to obtain the degree of decontamination required. A particularly effective combination is the application of pulsating electric or magnetic fields lethal to the substance when it passes through the high-pressure tube. The process of the invention inactivates the vegetative cells. For the inactivation of microbial spores generally a higher pressure and / or a longer exposure time should be applied. Affected microorganisms include bacteria as well as mold and yeast, but also viruses. While full sterilization of the product is possible in principle, a lower degree of decontamination will often suffice, so that less severe process conditions can be applied. The conservation of PÚA has the additional advantage that also the enzymes are completely or partially deactivated. In the context of this specification with a substantial decrease in viability, a reaction in microorganism counting is understood viable with a factor of 1000 or higher. This is often expressed as a log cycle reduction (log (NO / Nt)) that must be 3 or higher. Nt is the count after the process and NOT before the process. The present method is also distinguished from the prior art methods by its surprising simplicity which not only contributes to the economy but also to the reliability of the process. The invention is further illustrated by the following example: Example 1 In 1000 ml of glycerol, they have been dispersed 1000 cells per ml of yeast S a c ch a r omy c e s s e a c e s. The dispersion in which a natural contamination condition was emulated was carried out through a tube with a length of 25 m and a diameter of 1 mm with a pressure of 300 MPa at the inlet of the tube. The residence time in the tube was 60 seconds and the temperature was room temperature, 21 ° C. The substance recovered at the end of the tube was analyzed for contamination, but no detectable amount of yeast cells could be established.

Claims (6)

1. A method for decreasing the viability of microorganisms and / or the activity of enzymes in a contaminated substance by exerting a high pressure on the substance, characterized in that the substance is conducted in a stable flow through a tube, while the pressure difference between the inlet end and the outlet end of the tube is maintained at 100 MPa or more, preferably 300 MPa or more.

2. The method according to any of the preceding indications, characterized in that the residence time of the substance in the tube is at least 1 second, preferably at least 2 minutes, more preferably at least 10 minutes.

3. The method according to any of the preceding claims, characterized in that the substance is a food product or an ingredient for a food product.

4. The method according to any of the preceding claims, characterized in that the ratio of the length and diameter of the tube is at least 1000, preferably 10, 000.

5. The method according to any of the preceding claims, characterized in that the tube contains at its end upstream a chamber, preferably in the form of a tube, of which the diameter is at least 5 times greater than the rest of the tube.

6. The method according to any of the preceding claims, characterized in that the elevation of the temperature of the substance during the passage through the tube is less than 10 ° C, preferably less than 5 ° C.