GB2113247A

GB2113247A - Purifying sugar juice

Info

Publication number: GB2113247A
Application number: GB08201334A
Authority: GB
Inventors: Otto Peter Bent Ginslov; Werner Kofod Nielsen; Rud Frik Madsen
Original assignee: Danske Sukkerfabrikker AS
Current assignee: Danske Sukkerfabrikker AS
Priority date: 1982-01-18
Filing date: 1982-01-18
Publication date: 1983-08-03
Also published as: ZA83105B; SG37485G; EG16452A; MY8600147A; HK57585A; GB2113247B

Abstract

Sugar juice is purified by recovering raw juice from sugar cane and ultrafiltering the raw juice, e.g. through a semi-permeable membrane.

Description

SPECIFICATION Method of making purified sugar juice from sugar cane.

This invention relates to a method of making purified sugar juice from sugar cane.

In a conventional method of making raw sugar juice from sugar cane the sugar cane is passed through a roll mill to squeeze sugar juice out of it.

In some sugar producing countries raw sugar juice is prepared on small sugar cane presses which are placed in the streets and at market places and the juice thus produced is ordinarily consumed on the spot. Such raw juice is cloudy and has a bitter taste. Furthermore, it is ordinarily contaminated with bacteria which may cause serious health problems.

It has now been found that a sparklingly clear sugar juice having no bitter taste and being essentially free from harmful bacteria can be obtained by ultrafiltering the raw sugar juice.

Accordingly, the present invention provides a method of making purified sugar juice from sugar cane, comprising recovering raw sugar juice from the sugar cane, and ultra-filtering the raw sugar juice.

Surprisingly it was found that the ultrafiltration results in the removal of both the components of the raw sugar juice which are responsible for the cloudiness, such as waxes, and those which are responsible for the bitter taste of conventional sugar juice as well as the bacteria without interfering with the desired properties, inter alia the sweetness, flavour and taste of the juice.

The ultrafiltration is preferably carried out at a pressure of from 2 to 10 bars and at a temperature of from 20 to 1 000C. A temperature range of from 60 to 1 000C and specifically a temperature of about 800C is particularly preferred because of the high ultrafiltration capacity and reduced bacteriological contamination of the apparatus used at such high temperatures. Furthermore, the quality of the ultrafiltered juice is high at temperatures below 1000C.

Semipermeable membranes suitably used in the ultra-filtration preferably have a cut off value of about 25,000 in order to effectively reject the undesired high molecular components and to allow the passage of the desired components through the membrane and into the filtrate (permeate). However, in some cases membranes having cut off values of up to 70,000 are also suitable.

The term "cut off value" defines the molecular weight of the smallest compunds which are rejected by the membrane.

Examples of semi-permeable membranes which are suitable for effecting the ultrafiltration of the raw sugar juice in the method of the invention are commercially available under the trade name DDS GR6lPP (sold by DDS RO Division, Nakskov, Denmark).

In cases where the raw juice is strongly coloured, the ultrafiltered juice may be slightly coloured and in such cases it may be preferable to adjust the pH of the ultrafiltered juice to a value within the acid range in order to further reduce the colour of the juice.

The ultrafiltered juice obtained by the method of the invention and which ordinarily contains 12~15% by weight of sugar can be used directly as a beverage. Thus, it may be packed in cartons or be bottled as such. However, in order to increase the stability of the ultrafiltered juice, it is preferably sterilized by conventional methods or by the UHT-method (ultra high temperature method) before it is packed in cartons or is bottled.

The ultrafiltered sugar juice is also suitable as a sweetener in the conventional production of beverages in which crystalline (white) sugar or sugar syrups (liquid sugar) ordinarily are used as sweeteners. Thus, it is customary to add crystalline or liquid sugar to beverages in an amount to provide a sugar concentration within the range of 10~20% by weight.

The production of crystalline or liquid sugar is an energy consuming process in which the major proportion of the engery is used for the evaporation of purified sugar juice and for the crystallisation of the concentrated juice.

When using ultrafiltered sugar juice obtained by the method of the invention as a sweetener, the energy consuming evaporation and crystallization steps are avoided and the natural taste and flavour are retained and are transferred to the beverages to be sweetened.

By using ultrafiltered sugar juice obtained by the method of the invention as a sweetener instead of the conventional white sugar, the sugar contained in the raw sugar juice can be more efficiently utilized. Thus, in the conventional production of white sugar part of the sugar, i.e.

12-1 5%, is lost in the molasses.

In the method of the invention less than 5% of the sugar of the raw sugar juice is lost in the concentrate formed.

When the ultrafiltered sugar juice obtained by the method of the invention is to be used as a sweetener, it may be desirable to adjust its sugar concentration and/or dry solids content as well as its pH at predetermined values. Such adjustment of the sugar concentration and/or dry solids content (standardization) may be effected by methods which are well known per se. Thus, the standardization may be effected by evaporation or by filtration through semipermeable membranes which only permit the passage of water molecules.

The concentrate obtained by the method of the invention contains small amounts of sugar, i.e.

about 5% by weight of the sugar present in the raw juice. This concentrate which additionally contains high molecular compounds rejected by the semipermeable membrane typically has a dry substance content of 15~20% by weight. This liquid product is preferably evaporated and dried to form a dry solid which is suitable as an animal feed or an animal feed component.

The raw juice used in the method of the invention may be prepared by milling sugar cane by conventional methods. However, it may also be obtained by cutting sugar cane into small pieces and by extracting the product thus obtained with water or an aqueous solution. Such an extraction is preferably effected in an extractor of the type comprising an inclined trough having mounted therein one or more screw conveyors capable of moving the pieces of sugar cane introduced at the lower end of the trough towards its upper end counter-currently with water or aqueous solution introduced at its upper end. After having passed through the sugar cane being moved from the lower end of the trough towards its upper end, the sugar containing water or aqueous solution is discharged from the lower end of the trough in the form of a sugar juice.

If the raw sugar juice contains substantial amounts of suspended particles, it is preferable to remove such particles therefrom, e.g., by conventional filtration techniques or by decantation in a clarifier before the juice is ultrafiltered.

When removing the suspended particles in a clarifier, the settling of such particles in the form of a sludge may be accelerated by neutralizing the juice with lime and/or by heating the juice, e.g. to a temperature of about 10000.

In case the raw juice is recovered by extraction, the settled sludge may be separated and introduced into the extractor.

It is well known to subject purified sugar juice obtained from raw sugar cane juice to ultrafiltration in order to remove therefrom high molecular weight compounds, such as pectins and proteins, cf. US patent specification No.

3 799 806. However, hitherto it has been considered impossible to ultrafilter raw sugar cane juice because of its content of undissolved contaminants. Thus, it was assumed that these contaminants would black the pores of the semipermeable ultrafiltration membranes and thus reduce the filtration capacity to such a degree that the ultrafiltration would be uneconomical.

The invention will be further described with reference to the following illustrative Example.

Example Unburnt sugar cane was introduced into a roller crusher, so as to produce 400 litres of juice. The juice thus obtained had a pale orange colour and a high content of suspended solid particles. In order to remove these suspended particles the juice was sieved through two wire gauges with openings of 5 mm2 and 2 mm2, respectively. Finer particles were removed by filtration through a fine nylon filter bag.

In order to reduce oxidation and fermentation during the following steps, the pH of the juice was lowered from 5.1 to 4.7 by the addition of a 50% citric acid solution. The juice was then processed in an ultrafiltration apparatus (type DDS UF35-2.25) equipped with DDS GR61PP membranes at a temperature of 8000 and at a pressure of 4.4 bars.

The ultrafiltration resulted in 320 litres of permeate and 80 litres of concentrate. The permeate was immediately cooled to below 50C under sterile conditions. The concentrate was discharged. The Brix value (i.e. the content of dry matter) of the permeate was 21% by weight. This juice was too sweet and heavy to be used directly as a beverage and therefore water was added in an amount to provide a more suitable Brix value of 13%. Ascorbic acid (vitamin C) was added in an amount of 0.1 5 g/litre.

After pasteurization at a temperature of 9500 the product was bottled in ordinary disposable bottles which could be stored at 5000 for more than one month without spoilage. The juice thus obtained was fully satisfactory as a beverage.

Claims

1. A method of making purified sugar juice from sugar cane, comprising recovering raw sugar juice from the sugar cane, and ultrafiltering the raw sugar juice.

2. A method as claimed in Claim 1, wherein the ultra-filtration is effected at a pressure of from 2 to 10 bars.

3. A method as claimed in Claim 1 or 2, wherein the ultrafiltration is effected at a temperature of from 20 to 1 0000.

4. A method as claimed in Claim 3, wherein the ultrafiltration is effected at a temperature of from 60 to 10000.

5. A method as claimed in any of Claims 1 to 4, using an ultrafiltration membrane having a cut off value of about 25,000.

6. A method as claimed in any of Claims 1 to 5, wherein the pH of the ultrafiltered juice is adjusted to a value of below 7.

7. A method as claimed in any of Claims 1 to 6, wherein the raw sugar juice has been obtained by extraction of sugar cane.

8. A method as claimed in any of Claims 1 to 7, further comprising removing suspended particles from the raw sugar juice prior to the ultrafiltration.

9. A method as claimed in Claim 8, wherein the suspended particles are removed by filtration or by decantation in a clarifier.

10. A method according to Claim 1 of making purified sugar juice, substantially as herein described in the foregoing Example.

11. A purified sugar juice prepared by the method as claimed in any of Claims 1 to 10 for use as a beverage.

12. A purified sugar juice prepared by the method as claimed in any of Claims 1 to 10 for use as a sweetener for beverages.