Food or edible material: processes – compositions – and products – Processes – Treatment of liquid with nongaseous material other than...
Reexamination Certificate
2001-02-26
2003-11-25
Weier, Anthony J. (Department: 1761)
Food or edible material: processes, compositions, and products
Processes
Treatment of liquid with nongaseous material other than...
C426S522000, C426S583000
Reexamination Certificate
active
06652898
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the manufacture of a milk product having a reduced spores and bacteria content, especially a process for treating milk to produce standardized milk for consumption or cheese making, or skim milk powder or whole milk powder as well as a plant for carrying out the process, and also a process for the manufacture of whey or pre-concentrated whey having a reduced spores and bacteria content, and to a plant for performing the process
In the production of standardized milk for consumption or cheese making or milk powder the starting material, viz. the milk, is conventionally separated into a cream fraction and a skim milk fraction before the subsequent processing. The cream fraction which has a high content of spores and bacteria (microorganisms) is subjected to a heat treatment suitable to obtain a maximum killing of these microorganisms (sterilization). In parallel to the treatment of the cream fraction, the skim milk fraction which also contains spores and bacteria (microorganisms) and fat is subjected to a microfiltration resulting in a separation into a retentate carrying an increased content of microorganisms and fat and a permeate consisting of skim milk having reduced microorganism and fat content. The sterilized cream fraction and the permeate consisting of skim milk of reduced microorganism and fat content is brought together and mixed in a defined ratio to produce the desired milk products.
It is an advantage of the prior art processing method that only a minor portion of the milk product, viz. the cream fraction, has to be sterilized to obtain a standardized milk for human consumption or cheese making having a reduced content of microorganisms. Thus, the permeate consisting of skim milk having a reduced content of microorganisms and fat needs not to be heated when the content of such micro biological contaminations are sufficiently low. By omitting this heating, a more or less pronounced conversion of the proteins in the permeate due to denaturation is avoided and also the complete or partial destruction of enzymes in the permeate is prevented.
It is well-known that such changes of the milk inter alia influence the curdling ability of the milk when used in cheese making. This may for instance result in liberation of moisture during the subsequent curing of the cheese, or if the milk has been subjected to intensive heating it may become completely unsuitable for the manufacture of cheese.
The possibility of omitting a heat treatment or at least to use only a lenient heat treatment of the permeate due to the low content therein of the microorganisms influencing the shelf-life of the milk product (bacteria, yeasts, moulds, virus, and bacteriophages) is advantageous in connection with the production of standardized milk for human consumption. Hereby the desired organoleptic and nutritional characteristics of the milk are maintained at least in this component of the mixture.
Besides, the reduction of the microfiltration to the skim milk fraction alone involves a considerably increased capacity of the microfilter.
STATE OF THE ART
It is an object of the invention to provide a process according to the preamble of claim
1
. A process of this type is known from EP 0 194 286 B1 or U.S. Pat. No. 4,876,100. However, this process is restricted as far as the recovering of the cream fraction and the skim milk fraction is concerned to the use of a preliminary centrifugal separation of the milk in spatial vicinity to the subsequent treatment. By said process the microfiltration of the skim milk is especially important. The skim milk is during the microfiltration recycled in a loop including a microfilter arranged so that the skim milk flows parallel to the surface of the filter membrane (crossflow filtration). The microfilter is provided with pipes and connected in a conventional manner, i.e. the microfiltration unit consisting of the microfilter and the pipe connections belonging thereto is supplied with the skim milk to be filtered through a feed conduit, and the permeate passing through the microfiltration membrane as well as the concentrate (the retentate) which builds up in the flow loop is recovered from the microfiltration unit through conduits connected thereto. Subsequently, the retentate is sterilized. In one embodiment of the plant, a recycling loop is connected to the permeate exit from the microfilter and a pump is used for recycling permeate from the microfilter to the inlet of the circulation loop. It is not described in which ratio any permeate is recycled to the circulation loop of the one-step microfiltration unit, and for which purpose such a recycling is performed and which result is obtained thereby.
A further process of the type in question is known from EP 0 697 816 B1. Also in this process, the cream fraction and the skim milk fraction are recovered by a centrifugal separation of the milk in spatial vicinity to the subsequent treatment. By this process, the concentrate containing spores and bacteria (microorganisms) which leaves the microfiltration unit as retentate is recycled to the centrifugation and mixed with the milk fed to the centrifugal separator.
The process of EP 0 697 816 B1 can only be used when the cream and skim milk fractions are recovered from a milk centrifugal separator connected prior to the plant for their further treatment and spatially near said plant. Thus, it cannot be used when for instance the two fractions are provided from feed vessels connected upstream of the equipment for further treatment spatially near thereto.
WO 91/09667 discloses a process for performing tangential microfiltration, reverse osmosis or ultra-filtration using a two-stage plant. No information is given on the envisaged field of application. In this process, a retentate formed in a first step is used as feed for a second step. It is not specified how the permeates from the two steps are used or handled. A process of this type, and in which the two permeates are pooled, is depicted in
FIG. 3
on the drawing attached hereto.
The amount of germs in the final products of prior art processes using microfiltration within the dairy industry is unsatisfactory due to the skim milk component available for mixing with the cream fraction. For the above-mentioned reasons (complete omission of a heat treatment or only a lenient heat treatment) it is desired and attempted to reduce the content of microorganisms in the available skim milk as far as possible since these microorganisms have a decisive influence on the shelf-life of the milk product.
From WO 00/74495 and U.S. Pat. No. 5,685,990 it is known to perform filtration, incl. microfiltration, using two or more steps. The permeate from one step is conducted to one or more steps, meaning that it passes through at least two membranes. Thereby an efficient and safe purification is obtained but at the cost of capacity/required filter area. Another drawback is the repeated recircling of the fraction having the highest bacteria content.
The drawbacks of the above briefly described known processes for producing standardized consumer or cheese milk also exists when skim milk powder or whole milk powder is the final milk product. An object of the present invention is to provide a process of the type dealt with by which it is possible to produce the desired milk product via a skim milk having a reduced content of microorganisms (germs and bacteria) compared to the microoganism content in prior art processes. Moreover, the invention makes it possible to produce whey or pre-concentrated whey having a reduced spores and bacteria content by using characteristic features thereof.
SUMMARY OF THE INVENTION
The object of the invention is achieved by a process having the characteristics defined in claim
1
. Preferred embodiments of the proposed process are subject of the sub-claims. Independent claim
1
characterizes a process for producing a whey product or having a reduced spores and bacteria content.
According to the invention, the process is carried out using a two-steps micro
Niro Holding A/S
Weier Anthony J.
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