WO1998052423A2

WO1998052423A2 - A method for fruit processing

Info

Publication number: WO1998052423A2
Application number: PCT/EP1998/003227
Authority: WO
Inventors: Yves André Gérard COUTEL; Rodney Hugh Sharpe Dale
Original assignee: Dsm N.V.
Priority date: 1997-05-23
Filing date: 1998-05-25
Publication date: 1998-11-26
Also published as: NZ501237A; WO1998052423A3; AU8334898A; AU730898B2; EP0987953A2

Abstract

The present invention relates to a method for heat-treating an entire fruit or vegetable or fruit or vegetable pieces in the presence of calcium ions, and preferably also pectin esterase. The fruit or vegetable pieces survive such heat-treatment, such as sterilisation or pasteurisation, with only minimal damage to their texture and firmness.

Description

A method for fruit processing

Technical field

The present invention provides a process to improve fruit or vegetable texture, firmness and integrity in fruit or vegetable preparations.

Background of the invention

The texture of plant foods is attributed to the structural integrity of the primary cell wall and the middle lamella. The primary cell wall model consists of cellulose micro-fibrils aligned in parallel. Cellulosic microfibrils are cross linked with hemicellulosic xyloglucan polymers. This domain is embedded in pectin matrix which form junctions with arabinogalacturonan and arabinogalactan side chains. (J.P. Vincken, Thesis ageningen Agricultural University, Ref ISBN 90-5485-510-X, 1996) . The middle lamella is mainly composed of pectic substances partially esterified and cross linked with Ca²⁺ divalent cation. The middle lamella acts like adhesives between adjacent cells. Ripened fruit tissue contains a higher degree of esterified pectin making it less cross-linked by Ca²⁺ and consequently more heat labile (D.T. Huber, Food Sci . , 49: 1310 - 1315, 1988), (R.L. Jackman and D.W. Standley, Trends Food Sci. and Technol. 6: 187-194, 1995).

The manufacturing of food compositions comprising entire fruit or fruit pieces is conventionally performed by mixing fruit, sucrose and other ingredients and heating the mix to prevent the possibility of microbiological contamination (sterilisation) .

Unfortunately, the heating needed for sterilisation has a negative effect on fruit texture and firmness and typically results in fruit with a fluffy appearance and mouthfeel . EP 0 624 062 describes a method for making food from

Jiruit and vegetables with improved mouthfeel by in si tu demethoxylation of the pectin backbone and allowing the thus treated fruit and vegetable pulp to form a gel.

Summary of the invention

The present invention relates to a method for heat- treating an entire fruit or vegetable or fruit or vegetable pieces in the presence of calcium ions, and preferably also pectin esterase. The fruit or vegetable pieces survive such heat -treatment , such as sterilisation or pasteurisation, with only minimal damage to their texture and firmness .

Description of the invention

The present invention relates to a method for preserving firmness and good mouthfeel of an entire fruit or vegetable or of fruit or vegetable pieces which are subjected to a heat-treatment . More specifically, the present invention relates to a method in which an entire fruit or vegetable or fruit or vegetable pieces are subjected to a heat-treatment in the presence of calcium ions, more preferably also in the presence of pectin esterase .

The major advantage of the method of the invention is that damage and desintegration of the heat-treated fruit is minimised. This effect is markedly strong where a combination of pectin esterase and calcium ions is used. Neither the pectin esterase nor the calcium ions gives by itself the same postive effect which is experienced when a combination of both is used. The amount of pectin esterase needed exceeds the amounts disclosed in EP 0 624 062.

Another advantage is that the integrity and firmness and the texture of the fruit is preserved as much as possible. Many types of fruit may be used in the method of the present invention, ^'including strawberries, apples, pears, raspberries, rhubarb and so on. The method of the invention may be used on fruit, whether it is in one piece or in pieces, such as sliced or diced fruit; whether it is fresh, frozen or thawed. However, if the fruit is in pieces, these pieces are preferably not smaller than 5 mm³.

Although the method of the invention may be used for subjecting fruit to any kind of heat treatment, such as for example blanching, cooking, baking, it is especially advantageous for the sterilisation or pasteurisation of fruit .

Any pectin esterase (EC 3.1.1.11) which is suitable for the de-esterification of pectin, may be used in the method of the invention. Such pectin esterases are obtainable from plants, bacteria or fungi. The pectin esterase is preferably from fungal origin. More preferably, the pectin esterase is obtainable from Aspergilli , especially preferred is the use of a pectin esterase obtainable from Aspergillus niger .

Although both randomly and blockwise de-esterifying pectin esterases may be used, blockwise de-esterifying pectin esterases are preferred.

The pectin esterase may be partially or completely purified from other enzyme activities, provided that pectin depolymerising activites, such as pectin/pectate .lyase or polygalacturonase activity are kept at levels which leave the pectin backbone intact. In a preferred embodiment, a pectin esterase preparation from Aspergillus niger is used.

The calcium ions which are present in the method of the invention, may be added in any form. In a preferred embodiment of the invention, CaCl₂.2H₂0 is used to supply the calcium ions.

The pectin esterase and the calcium ions should be present in sufficient amounts. Therefore, at least 560 pectin esterase units per kg fruit (PE U/kg) are present and preferably, at least 2000 PE u/kg fruit. One PE unit is as defined in EP 0 624 062. The minimum amount of Ca²⁺ which should be present is 0.6 mmol Ca²⁺ per kg fruit. Preferably, at least 1.0 mmol Ca²⁺ per kg fruit is present.

The invention also relates to a method for preparing a food composition which comprises an entire fruit or vegetable or fruit or vegetable pieces that are heat-treated according to the method of the invention, and to food compositions thus obtained.

The method of the invention is particularly suitable for the preparation of dairy and bakery food compositions, which need a heat treatment (for sterilisation and baking, respectively) .

Examples of such food compositions according to the invention include but are not limited to yogurt fruit preparations, bakery fruit preparations, such as oven stable conserves and canned fruits in syrups.

The amounts of calcium ions and pectin esterase may be varied as long as at least 560 pectin esterase units per kg fruit (PE U/kg) are present and at least 0.6 mmol Ca²⁺ per kg fruit. The person skilled in the art will understand that the effect of the pectin esterase and the calcium ions will not only depend on the amount of these compounds present, but also on the time of incubation and the presence of other compounds. One such compound which will have a negative effect is citrate, or its derivatives. In one preferred embodiment it is shown how the effect of citrate/citric acid may be neutralised by the addition of extra calcium ions.

The person skilled in the art will understand that the method of the invention is also applicable to plants, especially to dicots, which have similar cell wall structure. Therefore, the method of the invention may also be used to minimise heat damage during sterilisation of vegetables .

The invention will be illustrated by the following examples .

Examples

Fruits texture analysis Texture analysis were made on a TA.HD 50 kg F Texture Analyser (Stable Micro Systems, Vienna Court. Lammas Road, Godalming, Surrey, England) using the OTTAWA Cell system. We have used two tests:

The first, Maximum Extrusion Force measurement is realised to evaluate fruit firmness. For that 240 g of fruits are extruded with a constant velocity displacement through an extrusion plate located in the base of the cell . The maximum extrusion force is calculated by average of forces registered at the constant part of the curve.

The second, springiness measurement is realised in a range of forces situated in the viscoelastic deformation phenomenous domain. A constant force is applied on fruit sample to obtain a planned regular surface. On a second time a stress at constant displacement is applied on the sample. The forces ratio between stress maximum force and the lowest force value registered at the end of the relaxation time gives us an estimated value of fruits springiness properties .

The value of Max Extrusion Force (Firmness) is calculated by average of 5 measurements . Springiness value is calculated by average of 3 measurements.

Example 1 Pectin esterase and calcium treatment effect on strawberries firmness

Washed frozen graded Turkish strawberries were used (size between 18-22 mm) and the process is presented in Scheme 1. Treatments were carried out in distilled water (30 % w/w ) and in agitated vessel at 20 rpm. 600 g of strawberries were treated with pectin esterase activity from 0 up to 8600 PE U/kg treated fruits. The pH of the reaction mixture was not regulated but is estimated at 3.47 ± 0.05 pH unit after average calculation. The added calcium level was fixed at 0.05% (w/w) of CaCl₂- 2H₂0 except for the control. The enzyme is inactivated by heat treatment at 85°C for 20 mn. All the trials were duplicated. The results summarised in Table 1 show the effect of enzyme dosage combined with calcium at constant concentration on strawberries firmness.

PE in combination with calcium increase the firmness of strawberries and significantly preserve the firmness of fruits during cooking.

Table 1: The effect of pectin esterase on the firmness of heat treated strawberries

It is possible to determine an optimum enzyme effect at a dosage of 2240 PE Unit/kg of fruit.

Example 2 Calcium dosage effect on PE treated strawberries.

Using the same material and process as in Example (1) we have studied calcium dosage effect from 680 up to 6800 meq Ca++/ kg of treated fruits at a constant PE activity. The Pectin esterase activity is fixed at 2240 PE U/ kg of fruit except for the control. The firmness measurements of such treated strawberries is summarized in Table II. They indicate an optimum calcium level located around 0.05% w/w CaCl₂- 2H₂0 per kg reaction mixture. This optimum corresponds to 136 mg of CaCl₂ or to 3400 μmole Ca²⁺ per kg treated strawberries . Table 2 The effect of calcium on the firmness of PE treated strawberries

Example 3 Citrate buffering agent effect on fruit firmness treatment

Strawberries are treated in the same way as in Examples 1 and 2, except higher PE activities up to 2250 and 2700 U/kg of treated fruit were used to reduce the holding time during fruit cooking. Firmness values measured on such treated fruits according to conditions summarised in Table 3 show us a negative effect of Citrate buffering agent on texture improvement (Trials 1 to 3) .

Table 3 The effect of citrate levels on the firmness of PE treated strawberries

This effect may be eliminated by addition of a sufficient amount of calcium chloride for complete citrate anion saturation (Trials 5 to 7) .

Example 4 Use of the invention for processing strawberries conserves for use with yogurts and dairy desserts

Many trials have been made at pilot and industrial scale. We describe in the following examples a few of them to illustrate each point which constitute key points for the present invention.

Enzyme preparation We have used to perform the following trials a pectin esterase preparation from Aspergillus niger at 950 PEUnit/g.

Texture analysis

The texture analysis was performed in the same manner as described previously.

For fruit piece texture measurement we used a retroextrusion cell (50 mm Internal diameter ) with a 45 mm compression disc. With this kind of probe it is not possible to measure the fruit pieces springiness.

Pilot scale process descriptions

The two processes we used at pilot scale for strawberries yogurt preparation with entire fruits are described briefly in Schemes 2 and 3.

The enzyme level needed was calculated according to our previous work ( Examples 1, 2, 3) as was other biochemical data in regard of the amount of fruit, the pH, the temperature and the incubation time used in the trials.

The calcium chloride level was also calculated according to our previous work.

We used two kinds of frozen entire strawberries. The first one was the same as in previous example (Turkish origin, graded between 18 and 22 mm) the second one consisted of Polish strawberries (graded 15 mm - 22 mm) . The Turkish strawberry batch was used to produce the diced fruit pieces .

First experiment: Trials on entire Turkish and Polish strawberries using process I (scheme 2) and II (scheme 3) .

Trial details and texture analysis measurements are summarised in Table 4.

Table 4 The effect of PE and calcium on the firmness of whole strawberries

Trials 1 and 2 demonstrate the improved firmness obtained by the use of calcium addition alone. However, trials 3, 4 and 5 show the synergistic effect of PE and calcium. Trials 3 and 5 show that the effect is reproducible for different strawberry varieties sourced from different countries . Scheme 1 Laboratory combined pectin esterase and calcium treatment on crude entire calibrated strawberries .

Frozed Strawberries, 600 g weighted into the reactor

Thawed at 5°C, one night

Water (with CaCl₂- 2H₂0 according the experiment)

Heated at 50 °C

Enzyme solution (50 mil

Incubation at 50 °C 60 mn at 20 tr/mn.

Heated to 85 "C (20 min)

Transferred in boxes (H20 of 900 g )

Stored 48 h in cold chamber

Texture analysis measurements Scheme 2 PROCESS I (BATCH)

WATER + PE (5700/11400 PE Unit/kg Fruits) + CaCl₂- 2H₂0

4.46 g/kg Fruits)

(20°C) Agitation 8 rpm

FRUIT + SUGAR (20°C)

BRING TO 50 °C HOLD 20mn

THICKENING AGENT

BRING TO 85 "C

ADD

CITRIC ACID SODIUM CITRATE

FILL 80 C

Φ

COOL Scheme 3 PROCESS II (Continuous)

WATER + PE (4885 U/kg Fruits) + CaCl₂- 2H₂0 4.46 g/kg Fruits!

(20°C) Agitation 8rpm

FRUIT + SUGAR + THICKENING AGENT (20°C)

BRING TO 25 °C HOLD 60mn

BRING TO 85 'C

CITRIC ACID SODIUM CITRATE

FILL 80°C

COOL Second experiment : Trials on diced Turkish strawberries using process (I) .

Table 5 The effect of PE and calcium on the firmness of fruit pieces

Results of those trials clearly demonstrate improvement to firmness and fruit piece integrity (Table 5) .

Third experiment: Scaling up of the process

Table 6 The effect of scale-up on the firmness of strawberries treated with PE and calcium

*) continuous process

Scaling up does not reveal negative effect on fruit texture and identity improvement in the two processes studied for both batch and continuous production systems. Example 5 Treated fruit texture stability during prolonged storage of the fruit preparation

Preparations made in Example 4 (first experiment) were stored in a dark room at 15 ° C for 14 weeks. Texture measurements were performed after 1, 8 and 14 weeks storage. The texture measurement results are summarised in Table 7.

The positive effect on fruit texture between first and 8th weeks measurements on trials 3 and 4 may be caused by non achieved equilibrium between the processed fruits and their medium.

A longer storage time does not alter fruits texture properties . Consequently we can expect to apply the treatment described in the present invention to fruits and vegetables long shelf life products sterilised by heat treatment like canned fruits.

Table 7 Strawberry texture stability during storage

nd: Not determined.

Example 6 Treated fruit texture stability mixed in yogurt

PE treated strawberry preparation as described in Example 4, first experiment, was mixed with yogurt at an inclusion level of 17%. The mix and the original sample were stored under refridgerated condition. Texture analysis was performed after one and three weeks storage time on washed fruits .

The texture analysis measurement summarised in the following table show good fruit stability in such conditions . The fruit firmness seems to increase slightly in yogurt which may be due to calcium equilibria within the system.

Table 8 The firmess of PE/calcium treated strawberries throughout the shelf-life of yogurt

Example 7 Effect of pectin esterase treatment on fruit pectin

Pectin esterase effect on processed pectin has been studied using the following methods on samples issued from trials 1, 2, 3, 6 and 7 example 4 (Use of the invention for processing strawberries conserves for use with yoghurts and dairy desserts) .

Strawberries Insoluble Alcohol Material (I.A.M.) were extracted according to the method described by D.J. Huber et al . , (D.J. Huber, Food Sci., 4_9: 1310-1315, 1988).

Pectin breakdown according to pectin solubility properties were estimated using the method AFNOR NF 05-128 (Nov.1984) .

Esterification Degree (ED) of extracted IAM were determined after saponification using High Performance Liquid Chromatography (HPLC) method according to A.G.J. Voragen et al (Food Hydrocolloϊds, Vol. 1, (1) : 65- 70, 1986) .

According to the results summarized in Table 9, pectin esterase decreases the methylation degree of strawberry IAM, whereby fruit firmness is improved. Especially if we compare the fruits processed with the same physical parameters (Trials 1, 2, 3 and 4 process I and trials 4 and 6 for process II) .

Table 9 Pectin esterase and calcium effect on strawberry pectin

Pectin esterase treatment decreases fruit pectin Methylation Degree (MD) with a concommittant effect on fruit firmness improvement.

The pectate ratio increases and water soluble pectin ratio decreases due to pectin esterase treatment and calcium chloride addition. The use of calcium salt alone as additive did not affect IAM methylation degree. However, it has an effect on pectin breakdown and improves fruit textural properties, but not to such a significant level as when used in combination with pectin esterase.

Firmness measurement values of those processed fruits revealed a correlation between pectate and soluble pectin ratios and fruit textural properties.

This shows that the ratio of soluble polyuronides on total polyuronides, which is known to be a good indicator of fruit softening during maturation, can be modified using pectin esterase and calcium treatment during processing.

Example 8 Pectin esterase and Calcium process adaptability

First Experiment: Process regulation using physico chemical enzyme properties .

It is well known that enzymatic process can be regulated according to an enzyme's physico-chemical properties which influence enzyme kinetics. The following experiments illustrate this point.

Experiments were carried out according to an experimental design in order to determine the role of each factor which has an effect on enzyme activity in regard to strawberries firmness improvement. The pectin esterase preparation is the same as previously. All trials and firmness measurements are presented in Table 10. Table 10 Experimental design and results,

From the results of trials 1 to 4 the effects of each factor on firmness may be determined.

Factors Effect on firmness improvement

Holding temperature from 40 to 50°C + 6 kg

Pectin esterase dosage from 6650 to 13300 UPE/kg + 4.5 kg

Hold time 5-15 min. + 2.2 kg

The temperature increase has the strongest effect on firmness improvement which is shown by statistics. The enzyme amount cannot be considered as significant and holding time has also little effect in our process.

Second Experiment: Enzyme preparation from Genetically Modified Aspergillus niger origin

To perfom this experiment, we compared strawberries from Example 8, first experiment trials 5,6 and 7 which were treated with pectin esterase from the classical organism Aspergillus niger, with strawberries treated with pectin esterase obtained from a genetically modified Aspergillus niger strain in which the homologous gene has been amplified. The results reported in Table 11 illustrate the similarity between fruit identity texture improvement obtained with those two enzyme preparations .

Table 11 The effect of the source of pectin esterase on the firmness of strawberries

Third Experiment: Combined PE/Calcium treatment on other frui ts We have optimised the process I (Scheme 2; Example 4) to apply it to different kinds of fruits for fruit preparation manufacturing. The first trial was performed on diced apple pieces . The results reported in Table 12 demonstrate the beneficial effects of the combined PE and calcium on the fruit texture.

The second was performed on entire thawed raspberries . Raspberries texture measurements were performed on full fruit preparation using retro extrusion cell, 50 mm Internal diameter with a 45 mm compression disc. The value of Max extrusion Force is calculated by average of 15 measurements. The results reported respectively in Tables 12 and 13 demonstrate the beneficial effects of combined PE and calcium on fruit texture. Table 12 The ef fect of PE and calcium on apple pieces

Table 13 . PE and calcium ef fect on entire thawed raspberries .

Example 9 Pectin esterase and calcium treatment effect on tomato pieces texture

This example was performed with canned diced peeled tomatoes as raw material . Trials have been done using the process described in scheme 4. Tomato pieces were washed with distilled water before treatment to remove tomato sauce. The citric acid content in washed tomato pieces was checked using the enzymatic method according to the procedure described by AFNOR, Controle de la qualite des produits alimentaires, produits derives de fruits et legumes, p300-303, (1990 ), AFNOR., Paris.

Calcium chloride in mono hydrated form was used as calcium salt. We added a sufficient amount of calcium to improve tomato pieces firmness and to counterbalance the citrate complexation effect as described respectively in examples (2, 8 and 3) .

Pectin esterase activity was as high as 6000 U /kg of fruits, using the same enzymatic preparation as previously. Enzymatic incubation has been done between 20 and 48 °C during 50 min. The pH of the reaction mixture was not regulated and was found to be 4.3.

The agitation mixture was agitated only every ten minutes during 20 sec at 20 rpm to reduce mechanical effect on tomato pieces integrity. The enzyme was inactivated at the end of the reaction time by heating the reaction mixture to 90 °C during 20 °C using a microwave oven.

Texture measurement were done for 20 h after processing with the same tests as previously. Texture measurement values summarised in Table 14 are in line with our previous results.

Scheme 4 Laboratory pectin esterase and calcium treatment on canned- tomato pieces .

Canned tomato pieces

Washed with distilled water

600 g

Φ Water with CaCl₂.2(H₂0) according to the experiment

200 ml

Enzyme solution or water (50 ml)

Heated up to 48°C during 50 min.

Heated to 90°C (20 min)

Transferred in boxes

Stored one night in cold chamber

Texture analysis measurements.

Table 14 Effect of PE and calcium on tomato pieces texture .

Pectin esterase reaction combined with calcium addition increase tomato pieces firmness and springiness significantly. Trials 3 and 4 demonstrate that texture improvement obtained by calcium addition alone is not as such significant as the combined treatment.

Claims

1. A method for treating an entire fruit or vegetable or fruit or vegetable pieces, which is characterised in that the fruit or vegetable or fruit or vegetable pieces are subjected to a heat-treatment in the presence of pectin esterase and calcium ions.

2. A method according to claim 1 wherein the pectin esterase is present in a concentration of at least 560 units per kg fruit or vegetable or fruit or vegetable pieces .

3. A method according to claim 1 or 2 wherein the calcium ions are present in a concentration of at least 0.6 mmol per kg fruit or vegetable or fruit or vegetable pieces .

4. A method according to claims 1-3 wherein 1,000-10,000, preferably 2,000-5,000 units pectin esterase and 1-30 mmol Ca++ are present per kg fruit or vegetable or fruit or vegetable pieces.

5. A method for preparing a fruit or vegetable composition comprising an entire fruit or vegetable or fruit or vegetable pieces, which is characterised in that the entire fruit or vegetable or fruit or vegetable pieces are treated according to any one of the methods of claims 1-4.

6. A fruit or vegetable composition comprising an entire fruit or vegetable or fruit or vegetable pieces which is obtainable by a method according to claim 5.

7. A fruit or vegetable composition according to claim 6 wherein the fruit is a strawberry, apple, raspberry or a tomato .

8. The use of a fruit or vegetable composition according to claim 6 or 7 in a dairy, bakery or canned product.

9. A vegetable or fruit composition comprising an entire heat-treated fruit or vegetable or fruit or vegetable pieces, wherein the heat-treated fruit or vegetable or fruit or vegetable pieces have improved firmness .

10. A vegetable or fruit composition according to claim 9 wherein the fruit or vegetable or fruit or vegetable pieces have a firmness which is at least 50% improved.

11. A method for treating an entire fruit or vegetable or fruit or vegetable pieces, which is characterised in that the fruit or vegetable or fruit or vegetable pieces is subjected to a heat-treatment in the presence of calcium ions .

12. A method for sterilising or preserving an entire fruit or vegetable or fruit or vegetable pieces, which is characterised in that the fruit or vegetable or fruit or vegetable pieces are subjected to a heat-treatment in the presence of pectin esterase and calcium ions.