IES64282B2 - A process for the preparation of dried particles and flour of jerusalem artichoke tubers - Google Patents

Abstract

A process for the preparation of flour and dried particles from Jerusalem artichoke tubers comprises reducing the tubers to particle form of average dimensions 10 mm by 10 mm by 2 mm, and shortly thereafter exposing the particles to a first application of a dilute solution of sulphur dioxide to provide a sulphur dioxide residue on the particles of approximately 400 parts per million. The particles are then blanched and the blanched particles are then subjected to a second application of a dilute solution of sulphur dioxide to raise the sulphur dioxide residue on the particles to approximately 500 parts per million. The particles are dried in a six stage air drier to a moisture content of approximately 7.0%. The dried particles are ground to a fine particle powder is a pin mill.

Description

A process for the preparation of dried particles and flour of Jerusalem artichoke tubers The present invention relates to a process for the preparation of dried particles and a flour from tubers of Jerusalem artichoke.

Jerusalem artichoke tubers are a nutritionally valuable food, and its ingestion provides many beneficial health effects. Typically, the promotion of bifidus bacteria, lowering of blood serum cholesterol levels, reduction of dental caries. Additionally, Jerusalem artichokes are high in food fibre, low in calories, rich in nutrients such as, for example, potassium and vitamin C, and are particularly suitable in diabetic diets. Jerusalem artichokes are relatively high in inulin which is a carbohydrate and more specifically a fructosugar/fructosacharide in which the fructose molecules are joined together in a chain ranging in length from 3 to 50, the average chain length being 9. Jerusalem artichoke inulin is relatively indigestible, and thus, is a relatively low calorie product.

However, importantly the inulin of Jerusalem artichokes can be fermented by the naturally occurring microbial flora of the human colon to metabolites which promote the growth of selective bacteria, typically, bifidus. Studies have shown a positive correlation between health and bifidus flora, and it is now believed that as part of healthy normal living moderate levels of bifidus promoting foods should be ingested to exclude potential pathogens, for example, salmonella, Clostridia and listeria from the digestive system.

Because of these considerable health benefits of Jerusalem artichoke tubers, when reduced to particulate form, such as a powder or a fine powder typically, a flour, the flour has significant value as an ingredient for food products. For example, the flour may be used as a thickening agent, for example, in soups. Because of its relatively low calorie content, the use of the flour of Jerusalem artichoke tubers does not significantly increase the calorie content of the soup.

The flour of Jerusalem artichoke tubers is also suitable for use in the preparation of low calorie bifidus enriched bread. The flour may be used as an ingredient, for the stabilisation of bifidus flora in yoghurt, and also for reducing the calorie level and enriching the fibre content of cheese spreads.

While various processes for the preparation of flour from Jerusalem artichokes are known, such processes, in general, suffer from disadvantages. One of the particularly serious difficulties in preparing flour or particulate matter from Jerusalem artichoke tubers is that on being reduced to particle form, the particles rapidly begin to oxidise and turn brown. Where the browning is not inhibited, the flour or particles produced are of quite an objectionable light brown colour. U.S. Patent Specification No. 4,565,705 discloses one process for the preparation of flour from Jerusalem artichoke tubers, and U.S. Patent Specification No. 4,871,574 discloses an alternative process. Both processes attempt to overcome the problem of browning, but both processes suffer from disadvantages. For example, the process disclosed in U.S. Patent Specification No. 4,871,574 is a relatively expensive process in that it requires that the Jerusalem artichoke tubers be macerated to an homogenate. The homogenate must then be heated to a temperature of approximately 150°C, and then spray dried to form a powder. Such macerating, heating and spray drying, are relatively energy intensive, and thus, relatively expensive. Additionally, the texture of the flour is not always acceptable, and in many cases tends to have a relatively brown hue, which in general, is unacceptable.

U.S. Patent Specification No. 4,565,705 on the other hand requires reducing the Jerusalem artichoke tubers to particle form and exposing the particles to an acidified water solution of PH not greater than about 4. The particles are then subjected to a series of pressure steps up to a pressure of approximately 6 atmospheres for removing juice from the particles. The particles are then washed and subsequently dried to a moisture content of 13%, approximately, prior to grinding to form the flour. This process because of the need to subject the particles to a series of pressure steps, is also relatively energy intensive and thus, expensive. Additionally, the flour prepared using this process tends to have a slightly brown hue, which, in general, is unacceptable.

There is therefore a need for a process for the preparation of particles from Jerusalem artichoke tubers, and also for the preparation of flour from Jerusalem artichoke tubers in which the browning effect is substantially inhibited, and the particles or flour produced is a relatively light colour which is approaching white. There is also a need for such a process wherein the process is a relatively low cost process .

The present invention is directed towards providing such a process, and the invention is also directed towards providing dry Jerusalem artichoke particles and Jerusalem artichoke flour.

According to the invention there is provided a process for the preparation of dried particles of Jerusalem artichoke tubers comprising the following steps in the following sequence: (a) reducing the tubers to particle form, (b) exposing the particles to a first application of sulphur dioxide before any substantial oxidation of the particles occurs, (c) subjecting the particles to blanching, (d) exposing the particles to a second application of sulphur dioxide, and (e) drying the particles to a moisture content of not more than 9%.

It is important that the step of exposing the particles to a first application of sulphur dioxide should take place before any significant oxidation of the surface of the particles takes place. Ideally, the particles should be exposed to the first application of sulphur dioxide before any oxidation of the particles takes place. In general, it is advisable that the particles be exposed to the first application of sulphur dioxide within 7 minutes of being reduced to particle form, and preferably, within 6 minutes of being reduced to particle form. Advantageously, the particles are exposed to the first application of sulphur dioxide within 5 minutes of being reduced to particle form, and where possible within 3 minutes of being reduced to particle form, and ideally, within 2 minutes of being reduced to particle form. It will of course be appreciated that if the particles are maintained in an oxygen free environment after being reduced to particle form, and preferably, also during the time the tubers are being reduced to particle form, exposure of the particles to the first application of sulphur dioxide could be deferred while the particles are maintained in the oxygen free environment.

It is preferable that the particles be exposed to the first application of sulphur dioxide prior to blanching so that the residue of sulphur dioxide on the particles after the first application and prior to blanching is at least 100 parts sulphur dioxide per million parts tuber particle. This is has been found prevents or at least significantly minimises oxidation, and in turn, browning of the particles during blanching. It is preferable that the particles be exposed to a second application of sulphur dioxide so that the final residue of sulphur dioxide on the particles after the second application and prior to drying is at least 300 parts sulphur dioxide per million parts tuber particle. This prevents or at least significantly minimises oxidation, and in turn, browning of the particles during drying. It is believed that during blanching some of the sulphur dioxide residue on the particles may be boiled off, and the second application of sulphur dioxide replenishes any sulphur dioxide residue which may have boiled off during blanching, and furthermore, increases the residue of sulphur dioxide prior to drying of the particles. It is believed that by providing a residue of sulphur dioxide of at least 200 parts sulphur dioxide per million parts tuber particle prior to subjecting the particles to blanching further reduces the risk of oxidation, and in turn, browning of the particles during blanching. Better results are achieved by providing a residue of sulphur dioxide on the particles prior to blanching of at least 300 parts sulphur dioxide per million parts tuber particle, and ideal results are produced when the sulphur dioxide residue on the particles is at least 400 parts sulphur dioxide per million parts tuber particle prior to blanching. There is less likelihood of oxidation, and in turn, browning of the particles during drying where the sulphur dioxide residue on the particles is at least 400 parts sulphur dioxide per million parts tuber particle prior to drying. Particularly advantageous results are achieved when the sulphur dioxide residue on the particles prior to drying is at least 500 parts sulphur dioxide per million parts tuber particle. It is preferable that the residue of sulphur dioxide remaining on the particles after drying should not exceed 700 parts sulphur dioxide per million parts tuber particle to prevent detection of the sulphur dioxide by taste.

Ideally, the first and second applications of sulphur dioxide are sprayed on to the particles.

It is desirable that the sulphur dioxide of the first and second application be provided in a dilute solution. Preferably, the sulphur dioxide content of the dilute solution should be in the range of 0.10% to 0.6% by volume of the solution. Advantageously, the sulphur dioxide content of the dilute solution should be in the range of 0.2% to 0.4% by volume of the solution, and ideally, the concentration of sulphur dioxide in the dilute solution should be in the range of 0.25% to 0.4% by volume of the solution. In general, the concentration of sulphur dioxide in the dilute solution should be in the range of 0.3% to 0.35% by volume of the solution.

It is preferable that immediately after the first application of sulphur dioxide the particles should be subjected to the blanching. It is also preferable, and indeed, advisable that the particles be subjected to the second application of sulphur dioxide immediately after blanching. Ideally, the first application of sulphur dioxide, the blanching and the second application of sulphur dioxide is carried out in an inline process, and preferably, on an endless belt conveyor.

The blanching treatment is carried out for the purpose of substantially destroying biological activity, namely, enzymic and bacteriological activity, and the temperature to which the particles are subjected and the residence time of the particles during blanching is dependent on the results of an appropriate peroxidase test. Ideally, the particles are heated by direct steam injection during blanching, and typically, the particles are subjected to a temperature of the order of 94°C to 110°C. Typical residence time of the particles during blanching is in the range of 3 to 6 minutes .

Preferably, the particles should be dried after being exposed to the second application of sulphur dioxide to a moisture content of not greater than 8%, and preferably, to a moisture content not greater than 7.5%, and ideally, to a moisture content not greater than 7%.

The particles are preferably dried after being exposed to the second application of sulphur dioxide in an air drying means. Ideally, the particles are dried in a multi-stage drier, and preferably, in a continuous band multi-stage air drier. Ideally, two multi-stage air driers are provided in sequence, and each air drier comprises three stages, thus providing six drying stages in sequence, namely, stages one to six. The residence time and the temperature ranges to which the particles are subjected in each of the six stages are set out in Table 1.

DRYER 1 STAGE 1 STAGE 2 STAGE 3 Time 20 mins. 25 mins. 50 mins. Temperature 100-122°C 75-90°C 60-75°C DRYER 2 STAGE 4 STAGE 5 STAGE 6 Time 30 mins. 15 mins . 25 mins. Temperature 50-70°C 90-95°C 55-70°C TABLE 1 It is preferable that the particles are subjected to drying in the air drying means for a time period in the range of 120 minutes to 230 minutes, and preferably, for a time period in the range of 150 minutes to 180 minutes. Typically, the total residence time in the air drying means is approximately 165 minutes. Ideally, the product is transferred from the first multi-stage drier to the second multi-stage drier by a bucket elevator and a vibrating feeder.

While the temperatures and residence times in the stages one to six of the driers set forth in Table 1 are preferred temperature ranges and residence times, the invention is not limited to these ranges. It is however desirable that the maximum temperature to which the particles are subjected in the air drying means does not exceed 130°C to avoid cooking of the particles. It has been found that good results are achieved by subjecting the particles to a temperature in the range of 100°C to 122°C for a time period in the range of 15 mins, to 20 mins, in the first stage of the multi-stage drier, and to a temperature in the range of 55°C to 70°C for a time period in the range of 20 mins, to 30 mins, in the final stage of the multi-stage drier means .

Preferably, the temperature to which the particles are subjected in the intermediate stages of the multi-stage drier between the first and final stages should lie in the range 50°C to 95°C and preferably, the residence time of the particles in the intermediate stages of the multi-stage drier between the first and final stages should lie in the range of 165 mins, to 190 mins.

Ideally, the temperature in the second stage of the multi-stage drier is approximately 85°C, the temperature in the third stage of the multi-stage drier is approximately 7 0°C, the temperature in the fourth stage of the multi-stage drier is approximately 60°C, and the temperature in the fifth stage of the multistage drier is approximately 93°C.

Ideally, the Jerusalem artichoke tubers are reduced to particle form in a dicer.

In general, it is preferred that the average maximum dimension of the particles should not exceed 20 mm and preferably, should not exceed 15 mm. Advantageously, the average maximum dimension of the particles should not exceed 12 mm, and ideally, should not exceed 10 mm.

Additionally, it is preferable that the average surface area to volume ratio of the particles is not less than 0.86 mm2 to 1 mm3. Advantageously, the average surface area to volume ratio of the particles should not be less than 0.93 ram2 to 1 ram3, and preferably, should not be less than 1.3 mm2 to 1 mm3. Ideally, the average surface area to volume ratio of the particles should not be less than 1.4 mm2 to 1 mm3. In a preferred aspect of the invention the average particle size is of the order of 10 mm by 10 mm by 2 mm.

Ideally the particle size is of the order of 10 mm by mm by 2 mm. v * The dried particles may be used after being dried. Alternatively, flour may be prepared from the dried particles by milling, and preferably, the particles are milled to form a relatively fine particle powder.

Ideally, the particles are milled in a pin mill.

Preferably, the particle size of the fine powder is in the range of 150 microns to 500 microns.

Additionally, the invention provides dried Jerusalem artichoke particles prepared from Jerusalem artichoke tubers using the process according to the invention.

Further, the invention provides Jerusalem artichoke flour prepared from Jerusalem artichoke tubers using the process according to the invention.

The invention will be more clearly understood from the following description of some examples thereof in which flour is prepared from Jerusalem artichoke tubers.

Before describing the examples the process used in the preparation of the flour in the examples will first be c described with reference to a flow diagram of the process which is illustrated in the accompanying drawing.

In all the examples, the variety of Jerusalem artichoke used is NAHADOKIA. The Jerusalem artichoke tubers are initially washed, see block 1 in the drawing in a tumbler washer to remove soil and other materials from the tubers. After washing the tubers are topped and tailed, see block 2, and then fed into a dicer where they are reduced to particle form of average particle size of 10 mm by 10 mm by 2 mm, see block 3. Within 5 minutes of being reduced to particle form, the particles are delivered onto an endless belt conveyor 4 where sequentially they are exposed to a first application of a dilute solution of sulphur dioxide, block 5 of the drawing, blanching, block 6 of the drawing, and are exposed to a second application of a dilute solution of sulphur dioxide, block 7 of the drawing. The first and second applications of the dilute solution of sulphur dioxide is applied by spraying the dilute solution of sulphur dioxide onto the particles on the belt of the conveyor. In these examples the sulphur dioxide content of the dilute solution used in the first and second applications of sulphur dioxide is identical, and is approximately 0.4% by volume of the solution. A dilute solution of the same sulphur dioxide content is used in all the examples. Immediately, on being delivered onto the continuous belt conveyor 4, the particles are subjected to the first application of the dilute solution of sulphur dioxide, and the particles are then sequentially and immediately conveyed on the continuous < belt conveyor 4 through the blanching process, and then are conveyed immediately to the second application of the dilute solution of sulphur dioxide. The blanching destroys biological activity in the tuber particles and is carried out by subjecting the particles on the conveyor belt to direct steam injection.

The particles after being subjected to the second application of the dilute solution of sulphur dioxide are conveyed to a multi-stage drier, which in these examples comprises two three stage driers, namely, a first drier, block 8 and a second drier block 9 arranged sequentially. Thus, the particles are sequentially subjected to six stages of drying. The particles are conveyed as quickly as possible after being subjected to the second application of the dilute solution of sulphur dioxide to stage one of the first drier block 8. Both first and second driers are continuous band air driers. The particles on leaving the final stage, namely, stage six of the second drier are of moisture content of approximately 7.0%.

After drying the particles may be used without further * processing, or, in the case of the examples which are described below are subjected to milling to form a relatively fine particle powder. Block 10 in the attached drawing represents a mill which in this case is a pin mill which prepares the fine particle powder of average particle size of approximately 200 microns.

The powder is then passed through screens, block 11, and on to a bagging station, block 12 where it is bagged.

In all the examples the respective temperatures in the six stages of the multi-stage first and second driers are relatively constant, and are as set out in Table 2 below. The residence time of the particles in the six stages of the multi-stage first and second driers are also set out in Table 2.

DRYER 1 STAGE 1 STAGE 2 STAGE 3 Time 20 mins. 25 mins. 50 mins. Temperature 120°C 85°C 70°C DRYER 2 STAGE 4 STAGE 5 STAGE 6 Time 30 mins. 15 mins . 25 mins. Temperature 60°C 93°C 60°C TABLE 2 It will of course be appreciated that it is important that both the temperatures to which the particles are subjected in the two driers and the residence times of the particles in the driers are such as to avoid cooking of the particles.

The blanching temperature and time are selected to destroy biological activity in the tuber particles, and are determined by trial and error based on peroxidase test results, which will be well known to those skilled in the art. However, it has been found that by subjecting the particles to a blanching temperature of approximately 102°C for a residence time period of approximately 3¼ minutes provides desired peroxidase test results. It is important, however, that the temperature during blanching should not be too high, since too high a temperature would tend to cook the particles, and likewise, it is important that the temperature of blanching should not be too low, since too low a temperature would not kill off all the bacteria. Likewise, the residence time of the particles through blanching should be not too great in order to avoid cooking of the particles, and not too short to ensure that adequate kill off of the bacteria is achieved.

In the examples the first and second applications of the dilute solution of sulphur dioxide is altered to give varying sulphur dioxide residues on the particles after the first and second applications. These are set out in Table 3 against the various examples. Example S0z residue SO2 residue after first after second application application (parts million) (parts million) 1 200 300 2 150 350 3 250 400 4 300 500 5 220 320 6 200 330 7 180 320 8 190 300 9 250 350 TABLE 3 The flour of Example 4 which had the highest sulphur dioxide residue after the second application of sulphur dioxide was found to have a desirable consistency and was of light colour with virtually no browning. The flour of Examples 1 and 8 which had the lowest residue of sulphur dioxide were also found to be of desirable consistency and of light colour with little browning. However, the flour of these two examples did have a slightly more browny hue than the flour of Examples 4.

The flour of Example 3 in which the particles after the second application of sulphur dioxide had a sulphur dioxide residue of approximately 400 parts per million was found to be substantially similar to the flour of Examples 4 having a substantially similar consistency and of the same light colour with virtually no browning. The flour of Examples 2 and 9 in which the particles had a sulphur dioxide residue of 350 parts per million after the second application of sulphur dioxide were found to have a desirable consistency but had a slightly brownish hue which was less than the brownish hue of the flour of Examples 1 and 8. The flour of Example 6 and 7 were of similar consistency to the flour of the other examples, and in colour lay somewhere between the flour of Examples 2 and 9 and Examples 1 and 8. However, it was noted that the flour of Example 9 had marginly less browning than the flour of Example 2, which would thus indicate that it is important to keep the residue of sulphur dioxide on the particles relatively high after the first application of sulphur dioxide. It will be clear from the examples of Table 3 that the higher the sulphur dioxide residue on the particles after the second application of sulphur dioxide, the lighter will be the colour of the flour subsequently prepared, and likewise of the particles .

Claims (5)

1. A process for the preparation of dried particles of Jerusalem artichoke tubers comprising the following steps in the following sequence: (a) reducing the tubers to particle form, (b) exposing the particles to a first application of sulphur dioxide before any substantial oxidation of the particles occurs, (c) subjecting the particles to blanching, (d) exposing the particles to a second application of sulphur dioxide, and (e) drying the particles to a moisture content of not more than 9%.

2. A process as claimed in Claim 1 in which the 15 particles are exposed to the first application of sulphur dioxide until the residue of sulphur dioxide on the particles is at least 100 parts sulphur dioxide per million parts tuber particle.

3. A process as claimed in Claim 1 or 2 in which the 20 particles are exposed to the second application of sulphur dioxide until the residue of sulphur dioxide on the particles is at least 300 parts sulphur dioxide per million parts tuber particle.

4. A process as claimed in any preceding claim in which the particles are exposed to the first application of sulphur dioxide within a time period not v greater than 7 minutes after being reduced to particle f form.

5. 5. A process as claimed in any preceding claim in which the particles are of size in which the average maximum dimension does not exceed 20 mm.