Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2002-04-18
2004-09-14
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S016000
Reexamination Certificate
active
06790288
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the recovery of lactose from liquids formed as by-products in the dairy industry and related industries.
More specificly, the invention relates to a process and a plant for converting lactose-containing liquids into easy to handle particulate products having non-caking and free-flowing characteristics.
In the present specification and the attached claims the term “lactose-containing liquids” is used as comprising solutions, wherein all lactose is in a dissolved state, as well as slurries of lactose crystals in lactose solutions.
BACKGROUND OF THE INVENTION AND PRIOR ART
Lactose is a disaccharide, which in solid state exists in at least three forms, viz. &agr;-lactose, crystallizing as the monohydrate from aqueous solutions at temperatures below 93.5° C., &bgr;-lactose, and amorphous lactose.
Of these three forms, the &agr;-lactose monohydrate is preferred since it when relatively pure forms stable, hard, and non-hygroscopic crystals.
In contrast thereto, especially the amorphous form of lactose is hygroscopic, and the presence of even minor amounts of the amorphous form on crystals of &agr;-lactose monohydrate may impair the non-caking and free-flowing characteristics of the latter.
Lactose is present in a concentration of approximately 5% in cow milk, which is the dominating source therefore.
Nearly all cheese-making processes have a by-product, whey, which is an aqueous solution, which, besides nearly all the lactose originally present in the milk, contains some fat, protein, and inorganic salts. The term “whey” is here applied in a broad sense, comprising cheese whey, rennet casein whey, acid whey, and salty whey.
With the primary purpose of recovering protein values from the whey or from milk, this is often subjected to an ultra-filtration, whereby the proteins are obtained as retentate, whereas the lactose and most of the minerals remain dissolved in the water passing through the filter membrane. This aqueous solution of lactose with highly reduced protein consent is simply termed “permeate”. This is the lactose source preferred in connection with the present invention although other whey-related products come into consideration.
Before used as starting material in the exploitation of the present invention, such permeate or related whey products may be subjected to a purification, e.g. a demineralization, and it is, preferably by means of vacuum evaporation, concentrated to a dry solids content of 40-75% by weight.
The main applications for lactose are as sweetener for ice cream mixes, for baking applications, and as component of animal feed but substantial amounts are also used as nutrient in culture media for micro-organisms in the bio-technical industries. For the baking industry it is, inter alia used with the purpose of obtaining a desired brown colour of the bread crust.
Although these various fields of application have different requirements as to purity and visual appearance of the lactose, it is for all applications desired to use the lactose as a particulate non-sticking, non-hygroscopic, and non-caking free-flowing product.
Several processes have been suggested and used for converting lactose in whey or whey-derive products into a particulate material.
However, a relatively fast drying process as obtained by spray drying results in particles, in which only a part of the lactose is present as &agr;-lactose monohydrate, whereas the remaining part thereof is present in a form which makes the particles sticky and hygroscopic.
Thus, a certain rest time is necessary before the cooled product resulting from the drying process can form free-flowing particles.
However, even after such treatment the resulting particles show tendency of hygroscopicity and caking.
This principle of fast drying combined with a subsequent rest is utilized in the FILTERMAT® process (Niro A/S) disclosed in U.S. Pat. No. 4,351,849 and also in the process disclosed in U.S. Pat. No. 5,006,204 (Assignee: A/S Niro Atomizer). In this last-mentioned process, a pre-crystallization is used before the spray drying, and the spray dried material rests on a rotating disc before after-drying in a fluidized bed.
A different concept is used in U.S. Pat. No. 6,335,045, according to which the lactose-containing concentrate is heated to a temperature above the crystallization temperature and thereafter subjected to a flash process resulting in a concentrate of higher dry solids content than the starting concentrate, which concentrate is subsequently cooled to induce crystallization. Afterwards, the crystallized concentrate can be dried in a spin-flash dryer. However, even with this rather complicated process, the results are not always satisfactory in terms of caking properties.
In the considerations preceding the present invention, we assumed that if a higher percentage of the lactose in the particulate product were present as the &agr;-lactose monohydrate form, the properties in the above-mentioned respects would be improved, and this turned out to be correct.
Highly concentrated aqueous lactose solutions have high viscosity, and we assumed that this could be an important reason why the crystallization of &agr;-lactose monohydrate in the prior art processes has been incomplete.
The invention is based on the recognition that it is possible by intensive agitation of the concentrate while it is being further concentrated by evaporation, due to the pseudo-plastic and thixotropic properties of the concentrate, to reduce the viscosity thereof to an extent, which highly promotes crystallization. The beneficial effect of this decrease of viscosity on crystallization more than compensates for any negative effect on the crystallization process caused by the intensive agitation. Thereby it is achieved that formation and growth of crystals occur simultaneously with the evaporation of the concentrate. Thereby, the viscosity is lowered, not only due to the pseudo-plastic and thixotropic characteristics of the concentrate mentioned but also because an excessive viscosity increasing super-saturation would be prevented.
It should be observed that generally the effect of mechanical agitation on the crystallization process is somewhat unpredictable. Reference is made to Mullin and Raven: “Influence of mechanical agitation on the nucleation of some aqueous salt solutions”, Nature, Vol. 195, page 35-38 (1962). According to said paper, nucleation, which is a prerequisite for crystallization, is generally higher in a moderately agitated liquid than under quiescent conditions but with increasing intensity of agitation, nucleation decreased and at still further intensities increased again and finally some decrease was observed. In said paper it is proposed that this unpredictable effect is a combined result of the influence of the agitation on the diffusion and the attrition.
In most commercial crystallization processes where relatively large crystals are desired, such as in the sugar industry, crystallization is performed at rather gentle agitation of the crystallizing medium, e.g. by using so-called crystallization cradles. An intensive agitation is regarded as harmful, not only due to attrition but also because it may result in the formation of too many crystallization embryos causing too small and uneven crystals.
However, as mentioned above, it has turned out that due to the pseudo-plastic and thixotropic properties of the lactose concentrates under evaporation an improved crystallization result is obtained by using a mechanical agitation of high shear rate.
SUMMARY OF THE INVENTION
The present invention thus relates to a method for evaporative concentration and crystallization of a viscous lactose-containing aqueous liquid, comprising:
(a) introducing the lactose-containing aqueous liquid having a dry solids content of 40-75% by weight into a zone and therein subjecting it to the following simultaneous measures:
i) progressive heating at a temperature above 40° C. but below the maximum temperature for crystallization of &agr;-lactose monohydrate from the liquid;
(ii) remov
Dinesen Richard Andrew
Henningfield Thomas David
Brunsman David
Niro A/S
Sughrue & Mion, PLLC
LandOfFree
Process and plant for evaporative concentration and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and plant for evaporative concentration and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and plant for evaporative concentration and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3220902