GB2091585A - Process and apparatus for concentrating juices - Google Patents

Abstract

In current practice, fruit and vegetable juices are normally clarified by filtration and/or centrifuging. In addition it is frequently necessary to remove pectin by an enzymatic process. In accordance with the invention, the juice is subjected to a process of ultra-filtration (6) to achieve clarification and depectinization. The juice may be dosed with an enzyme for depectinisation. The juice is then fed to an evaporator (10) to be concentrated. If a cloudy concentrate is required, a controlled proportion of the retentate (9) from the ultra- filtration may be added (22) to the concentrate. The ultra-filtration is preferably carried out prior to aroma stripping, which may take place in a second effect (10) of a multi-effect evaporator (10, 13, 15) in which the juice is concentrated and to which the permeate from the ultra-filtration is fed. <IMAGE>

Description

SPECIFICATION Process and apparatus for concentrating juices This invention relates to process and apparatus for concentrating fruit and vegetable juices.

In the processing of fruit or vegetable to produce liquid beverages, a range of processes are employed to achieve the desired end product. In general, the juice from the extraction stage consists of a cloudy liquid containing suspended solids such as pectin, starch, protein and polyphenols. In order to obtain a clear juice and aid further processing steps such as concentration, it is necessary to depectinise and clarify the juice, usually by means of a combined biological and physical process. It is also usually necessary for certain volatile constituents, known as the aroma, to be recovered or stripped out prior to the principal concentration stage to be recombined with the concentrate at some appropriate time.

Aroma recovery normally takes place before depectinisation and final concentration in order to ensure optimum product quality and prevent high methanol concentrations in the aroma, which can occur if aroma recovery is carried out after enzyme treatment for depectinization. Aroma is recovered by partial evaporation of the juice to boil off the volatile components, from which the aroma constituents are then recovered separately.

Due to the presence of the suspended solids, otherwise known as haze constituents, fouling normally occurs on heat transfer surfaces and extra heat transfer area must be installed to overcome this. In addition the thermal economy of this stage is low.

In order to avoid these difficulties, it is proposed, in accordance with the present invention, to utilize a process of ultra-filtration in the depectinzation and clarification of the juice.

A first aspect of the invention thus consists in a process for the concentration of a fruit or vegetable juice, comprising the steps of subjecting the juice to ultra-filtration by pressurising the juice and passing it past a semi-permeable membrane which retains high molecular weight components but transmits as a permeate the majority of the juice consisting of water and low molecular weight dissolved solids, and concentrating the permeate by thermal evaporation.

A second aspect of the invention consists in apparatus for the concentration of a fruit or vegetable juice comprising an evaporator and, upstream of the evaporator, an ultra-fiítration stage for separating high molecular weight components with suspended solids as retentate, and means for feeding the permeate from the ultra-filtration stage to the evaporator.

It has been found that if the juice is dosed with an enzyme for depectinization, and the dosed fruit is circulated past the membrane, the flux through the membrane is much improved. The retentate is preferably recirculated.

The permeate from the ultra-filtration may be subjected to stripping of the aroma as a preliminary stage of concentration in a multi-effect evaporator. By clarifying and depectinising prior to stripping the aroma, the clogging and fouling of the stripping plant is minimised. Also the stripping may be incorporated in a multi-effect evaporator for concentration so that the overall thermal efficiency is improved.

If a cloudy concentrate is required, a part of the retentate from the ultra-filtration stage may be added back to the concentrate. This enables a much more highly concentrated cloudy concentrate to be obtained without excessive fouling of the evaporator.

The invention will be further described with reference to the accompanying drawing of which: Figures 1 and 2 each illustrate diagrammatically one method and apparatus in accordance with the invention; and Figures 3 and 4 are curves showing the performance under various circumstances.

Turning first to Figure 1, a supply of an appropriate fruit or vegetable, for instance apples, is fed to a series of presses 1 and the juice passes via lines 2 to a coarse screening stage 3 for removal of large particles. A buffer storage stage is shown at 4. From the buffer storage stage, the juice, which at this stage contains suspended solids and also high molecular weight dissolved solids such as protein, pectin, starch and polyphenols, is drawn off by a pump 5 which pressurises it and passes into an ultra-filtration stage 6 wherein it is circulated past a semipermeable membrane, shown diagrammatically at 7, at a controlled temperature and velocity. The bulk of the juice, containing low molecular weight dissolved solids and water, permeates through the membrane and passes out to a buffer storage 8.

This fraction of the juice will subsequently be referred to as the permeate. The remainder of the juice, or retentate, with the suspended solids and high molecular weight components such as the protein, pectin, starch, and polyphenols does not pass through the membrane and leaves the ultrafiltration stage by a line 9. The permeate is thus effectively depectinised and clarified of the suspended solids and is passed from the buffer storage 8 to the second effect 10 of a multi-effect evaporator. In this effect, the permeate undergoes 3 first stage of concentration and with the vapour coming off via a line 11 , certain volatile constituents, known as the aroma, are removed.

These are recovered either as vapour or liquid, via a line 12 with the condensate from the third effect 1 3 of the multi-effect evaporator. The aroma is normally subsequently added back to the concentrate.

The partially concentrated permeate from the second effect 10 is fed via a line 14 to the first effect of the multi-effect evaporator and thence via a line 16 to the third effect 13. The final concentrate comes off via a line 1 7. The first effect 1 5 is heated by fresh steam fed in via a thermocompressor 1 8 which entrains some vapour from the first effect. The vapour from the first effect is fed to a line 1 9 from where part is entrained by the thermocompressor and part is used to heat the second effect 10.

By feeding the juice into the second effect, rather than the first effect, of the evaporator, several advantages accrue. The aroma is recovered at a lower temperature than in the first effect. The aroma is also recovered solely via line 12 and is not split into two streams as would happen if it were evaporated in the first effect and part were entrained by the thermocompressor 1 2.

The concentrate in the line 1 7 is a clear concentrate, e.g. of 72% total solids. This sort of solids concentration is obtainable with depectinised clarified apple juice. If an unclarified apple juice is concentrated, then it is only normally feasible to concentrate to about 54% total solids since the evaporator becomes fouled with the suspended solids.

If a cloudy concentrate is required, then a controlled proportion of the retentate from the ultra-filtration stage 6 may be taken from the line 9 through a valve 21 and fed to a mixing stage 22 wherein it is mixed with the clear concentrate in line 1 7 to produce a cloudy concentrate in a line 23. If the valve 21 is closed, then of course the concentrated line 23 is clear.

By mixing the haze constituents with a highly concentrated clear concentrate, a cloudy concentrate of greater concentration than normally obtainable can be achieved.

In comparison with the conventional clarification using normal filtration and depectinzation by an enzyme process, the use of ultra-filtration offers considerable advantages. The first of these is that the process may be carried out continuously and requires less labour and is simpler to control. Also, the use of enzymes and filter aids and associated capital equipment is avoided. The process as described also enables a greater thermal economy to be achieved in the evaporator together with the reduction in downtime due to reduced fouling. There is also an improved process efficiency by minimising the loss of juice during the enzymatic depectinization stage. it will also be seen that if a cloudy product is required, this can be achieved at a very high concentration by adding back part of the retentate from the art of filtration process to provide a desired and controlled haze level.

In the process described, the optimum operating temperature and pressure would be determined for specific cases, and it is envisaged that the temperature would be normally between 10 and 850C and pressures up to 8 bar may be used.

Figure 2 shows an arrangement which is basically similar to that in Figure 1 and like parts have been indicated with like reference numerals.

The essential difference from Figure 1 is that the depectinization is essentially carried out by an enzyme process within the buffer storage 4. On start-up, the juice in the buffer storage 4 is dosed to the appropriate concentration of enzyme via a line 31. As in the Figure 1 arrangement, the juice, this time with enzyme included, is circulated past the ultra-filtration membrane 7 in the ultrafiltration stage 6 and the permeate is drawn off to the buffer storage 8. The retentate is returned via a line 32 to the buffer storage 4 so that the enzyme is retained within the system. In order to control the level of suspended solids in the circulating system, a small proportion of the material circulating is bled off via a line 33.If it is required to produce a cloudy concentrate, then this line 33 may be used as a source of solids material to be added back via the valve 21 and mixer stage 22.

Since some enzyme may be drawn off via the line 33, make-up quantities of fresh enzyme material may be fed in via the line 31 in order to maintain the required enzyme concentration.

It has been found that the membrane flux under these conditions is markedly higher than when completely undepectinised juice is be;ng used, and the fouling characteristics of the juice are also lower. The flux improvements, as compared with the Figure 1 process of up to 500% had been achieved, which results in lower capital and membrane replacement costs. Although enzyme is still required in this process, the quantities are much reduced from those in conventional processes.

Some examples will now be given of operation of the arrangement shown in Figure 2. In all cases the plant was operated in fed batch mode, i.e. the suspended solids and retentate were retained within the recycling loop formed by the buffer storage 4 and the line 32, while the amount of permeate removed was matched by an equal volume of fresh feed juice added to the buffer storage 4. Thus, the concentration of the material in the loop gradually increased.

EXAMPLE 1 Apple juice of 9 to 9.5 Brix was used as feed at ambient temperature, but the heat input from the circulation pump 5 caused this to rise to a maximum of 500C in the ultra-filtration stage 6 and line 32. The pressure at the inlet of the stage 6 was 4 bar and the outlet pressure 2 bar.

Figure 3 is a plot of membrane flux, measured in litres per square metre per hour against the concentration ratio in the ultra-filtration stage.

Curve 1 of Figure 1 shows the results with undepectinised juice and curve 2 shows the results using juice which has been depectinised by an enzyme at 50 C with a residence time of 1 hour.

It will be seen that (curve 1) while undepectinised juices can be used to get a concentrate ratio of up to 6, i.e. the permeate is 6 times the volume of the retentate, flux rates are low. On the other hand, curve 2 showing results with depectinised juice, shows higher concentration ratios i.e. juice permeation, while in addition, the flux rates are substantially higher.

EXAMPLE 2 Natural lemon juice under the same feed and pressure conditions as in Example 1 was used.

Figure 4 shows a plot of flux rate in litres per square meter per hour against time elapsed in hours. Curve 1 shows the results with unenzymed juice and shows how the flux rate fell off quite sharply during the first hour and then continued to decline, albeit less slightly over about 1.25 hours.

At the point A a batch of depectinised juice was added to the buffer storage 4 and it will be seen that the member flux rose quite sharply to well above the original level, and although it declined from peak xxxxxx it was still, after over 3 hours use, above the level for undepectinised juice.

It is envisaged that although the preferred position for the ultra-filtration stage is between a coarse screen and the multi-effect evaporator, it may be located at different points with advantages. For instance, it may in certain circumstances be appropriate to take the juice from the coarse screening stage 3 and centrifuge it for partial clarification and then submit it to an aroma recovery or stripping stage. Depectinization could then take place in an ultra-filtration stage prior to concentration. Alternatively, the ultrafiltration stage could in fact take place after a partial depectinization by conventional methods and prior to final concentration.

Various other modifications may be made within the scope of the invention.

Claims (1)

1. A process for the concentration of a fruit or vegetable juice, comprising the steps of subjecting the juice to ultra-filtration by pressurising the juice and passing it past a semi-permeable membrane which retains high molecular weight components but transmits as a permeate the majority of the juice consisting of water and low molecular weight dissolved solids, and concentrating the permeate by thermal evaporation.

2. A process as claimed in claim 1, in which the juice is dosed with an enzyme for depectinization and the dosed juice is circulated past the membrane.

3. A process as claimed in claim 2, in which the concentrate is recirculated.

4. A process as claimed in claim 1, 2 or 3, in which aroma is stripped from the permeate in a first stage of concentration.

5. A process as claimed in claim 4, in which the permeate is fed to the second effect of a multieffect evaporator for aroma stripping and thence to the first effect and the or each later effect.

6. A process as claimed in claim 4 or 5, in which the concentrated permeate has a controlled proportion of the retained materials added to it to form a cloudy concentrate.

7. A process for the treatment and concentration of a fruit or vegetable juice substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

8. Apparatus for the concentration of a fruit or vegetable juice comprising an evaporator and, upstream of the evaporator, an ultra-filtration stage for separating high molecular weight components and suspended solids as retentate, and means for feeding the permeate to the evaporator.

9. Apparatus as claimed in claim 8, in which means are provided for recirculating the retentate.

10. Apparatus as claimed in claim 8 or 9, in which the evaporator is a multi-effect evaporator, and in which the permeate is fed to the second effect for stripping volatile aroma constituents from the retentate, the concentrate from the second effect being fed to the first effect for further concentration.

1 Apparatus as claimed in claim 8, 9 or 10, in which means is provided for combining a controlled part of the retentate from the ultrafiltration stage with the concentrate from the evaporaton

12. Apparatus for concentration of fruit or vegetable juice substantially as hereinbefore described with reference to the accompanying drawings.