FR2700245A1 - Prodn. of apple or pear puree by inhibiting polygalacturonase activity of crushed fruit - Google Patents

Abstract

A puree of apples or pears is prepd. by (a) placing the crushed fruit in conditions such as to inhibit the polygalacturonase activity and to give an inhibited pulp, and (b) contacting the inhibited pulp with a pectinesterase at 10-60 deg C for 0.25-12 hr. Pref. the polygalacturonase activity is inhibited at at least 80 (90-95) deg C for at least 2 (3-4) mins. The inhibited pulp is contacted with pectinesterase at pH 3-4.5, with addn. of 0-50 wt.% of fruit juice or nectar, and opt. of 0.5-2 g of a Ca salt, w.r.t. kg of pulp, before or after contact with a pectinesterase.

Description

Puree of apple or pear and its process of preparation
The present invention relates to a process for improving the texture of apple or pear puree, as well as the products obtained by said process (thickened, gelled, sweetened pulps, etc.) and their applications in the food industry.

 Pectins are parietal polysaccharides used in the composition of many plants in varying proportions depending on their origin. Their major structural feature is the presence of a backbone of partially methylated galacturonic acids, that is to say in which the carboxylic acid functions are partially esterified with methanol.

 These polysaccharides can be used in pure form as a gelling agent or thickener of food preparations. The possibility and conditions of gel formation depend on the degree of pectin methylation which is itself a function of the plant from which it is extracted and the extraction process. They are usually naturally highly methylated, but this degree of methylation (DM) can change during fruit ripening.

Highly methylated pectins (HM = High
Methoxyl), that is to say those in which more than 50% of the carboxylic functions of galacturonic acids are methylated, can form gels in the presence of sugars (in concentration greater than 55 t) and in acidic medium (pH = 2, 5 to 3). This process is commonly used in making jellies, jams ...

 Activation tests for the natural pectinesterase activity of plants have been carried out with the aim of improving the firmness of the pieces of plants (apples (Wiley RC and Lee YS, 1970), tomatoes (Hsu et al., 1965). carrots (Lee CY et al., 1979) These tests have been conducted to show the influence of calcium in maintaining the firmness of the fruit, and the endogenous pectinesterases are only really active relatively high pH (pH> 6).

 Currently, the production of fruit puree texture particular requires either the addition of thickening agents or gelling agents as texturizing additives, or the application of heat treatment and / or mechanical pushed, such as dewatering and the evaporation. These are intended to increase the viscosity by concentration of the pulp. However, these treatments cause a loss of aromas, juices and sometimes a change in the color of the pulp.

 The invention compensates for this by a process for the preparation of an apple or pear puree, which consists of putting ground fruit under conditions which inhibit the polygalacturonase activity to obtain inhibited pulp and to put the pulp inhibited into contact with a pectinesterase at a temperature of 10 to 600C for 15 minutes to 12 hours.

 The in situ demethylation of pectins by the action of exogenous pectinesterases makes it possible to obtain products that can have a range of textures, ranging from thickened pulp to complete gelation. The enzymatic reaction makes the pectins sensitive to the presence of calcium ions, and if present, a three-dimensional network is formed within the mash, which leads to a profound change in texture.

 The method according to the invention makes it possible to extend the possibilities of gelling high-methylated pectin-rich purees in sugar-reduced systems, without the addition of a gelling agent or thickener. The process is therefore of great economic and nutritional interest, since it makes it possible to diversify the use of the purées thus modified in lighter foodstuffs, because it makes it possible to obtain new products that can have various textures and because it allows recovery of juice.

 The process of the invention does not require the addition of exogenous pectins, or even any thickening or gelling agent, to obtain new textures. It uses purified pectinesterases that are not found in the fruit puree obtained. This exogenous enzymatic action is different from the natural one of the products, the endogenous polygalacturonase and possibly pectinesterase activity must even be inhibited, for example by the firing prior to the enzymatic treatment. This inhibition of natural enzymes is necessary to prevent the degradation of fruit pectins by endogenous polygalacturonases.

 The products studied by WILEY and LEE (1970) are pieces of fruit, that is to say that a certain tissue integrity must be maintained for the calcium and possibly the pectinesterase to have an action. On the contrary, according to the invention, the integrity of the fruit is not necessary and a fruit puree is preferred to ensure a good distribution of pectinesterase and calcium. If one grinds apples slices having undergone the treatment as described by WILEY and LEE, one does not obtain the textures obtained according to the invention. The application of a calcium bath (and pectinesterase) is not feasible on an apple puree. Moreover the addition of calcium alone to the apple pulp does not lead to an increase in viscosity as great as by the method of the invention. The two methods differ fundamentally, by the mechanism of action of pectin methylesterase and calcium. For apple pieces, WILEY and LEE showed that the effect of pectin methylesterase had little effect compared to that of calcium on cell tissues. In the invention, the role of the enzyme is preponderant, calcium playing only an additional role in the development of the viscosity of the pulp. Finally, the working conditions (pH range, implementation of the process) are entirely different and require different technologies.

 The invention also relates to an apple or pear puree, substantially free of texturizing additives, which has a pectin demethylation rate of less than 70%, a calcium content by weight greater than 300 parts per million and a consistency index Bostwick at 25 "C less than 2. This index reflects the thickened texture of the product.

 The product obtained by the process of the invention is therefore characterized by: - a thick texture achieved thanks to the action of a technological aid, pectinesterase, and without the addition of a thickening or gelling agent, such as alginates, gum guar, gum tragacanth, gum arabic, carrageenans, agar-agar, microcrystalline celluloses, and their derivatives, and more particularly pectins, of any degree of methylation whatsoever. The product is, however, not incompatible with other food additives such as, for example, dyes, preservatives, antioxidants, or flavors, as far as the use rates, they do not interfere with the development of the viscosity of the product, and if they are introduced at the beginning of the enzymatic reaction, they do not inhibit the activity of pectinesterase, - an average degree of methylation of the pectins present in the mash of apples and lower pears at 70%, this parameter being determined by the method of SCHULTZ TH

(1965), - a calcium concentration, determined by atomic absorption spectrometry, greater than 300 ppm, - an improvement of the texture relative to the starting material. The Bostwick index can reach all values lower than the baseline (up to an index of 0 units), depending on the reaction time, the calcium concentration and the acidity of the product. It is especially less than 2.

 In order for the enzymatic reaction with pectinesterase to be perfectly controlled, it is necessary to inhibit the enzyme activity intrinsic to apple and pear, and in particular the polygalacturonase activity. This is achieved according to the invention by methods known in themselves, and, for example, by baking a crushed previously washed apple. At the outlet of the mill, the particles may have an overall size of 1 cm by 2 cm. The cooking itself can be carried out in various ways, whether discontinuous or continuous. For example, the crushed apples can be heated by direct injection of steam at low pressure (0.3 bar), in a cooker where the advancement of the product is provided by an Archimedean screw. The rise in temperature to 950C is achieved in 6 to 7 minutes.

Until the exit of the cooker, the product is chambered and it leaves at 90OC approximately. Baking can also be achieved by heating in a tubular exchanger at 920C for 3-4 minutes. Juice extraction (up to 10%) can optionally be performed by draining. The marc is extracted by refining, that is to say by passing on sieves.

The refiner can, for example, be provided with 2 sieves mounted in series, with mesh sizes (in mm) of 15/10 and (8/10 or 12/10) for apples, and 15/10 and 4 / 10 for pears. The pulp obtained is capable of undergoing the enzymatic treatment, after cooling to the desired temperature and after possible addition of fruit juice or nectar.

The product can be diluted up to 50% by weight of juice.

 The enzymatic hydrolysis of the pulp thus prepared is carried out in the presence or absence of calcium salts (in any form but preferably in the form of calcium carbonate). The use of calcium carbonate makes it possible to adjust the pH to higher values and accelerates the enzymatic process. The calcium salts can be used at concentrations of between 0.5 and 2 g / kg of pulp, the acidity of the mixture and the concentration of calcium determining the final gelling rate, the latter being measured by the Bostwick number. The acidity of the product is preferably less than 7 g of malic acid equivalent per kg of pulp, a too strong acidity retarding or even preventing the gelling of the pectins.

 The refractometric index of the product can also be adjusted to different values (up to 400brix) by sweeteners, by concentrated juice during or after enzymatic treatment, or by any other ingredient which does not inhibit the enzymatic activity. it is introduced before the reaction.

 The pH of the product can be between 3 and 4.5.

It is chosen so that the enzyme can function and, as far as possible, approach the pH where the activity of pectinesterase is greatest. Although the pH can be further adjusted, it will be preferred to be within the pH range at which the modified pectins can gel. For apple pulp, care should be taken to maintain pH values slightly higher than 4. Thus, the release of acids during demethylation will bring the pH back to values fully compatible with the hygienic quality of the product (pH < 4).

 The temperature of the reaction is set by the optimum temperature of action of the enzyme. It will be lower than the inactivation temperature of the enzyme (<700C). Temperatures ranging from 10 to 600C can be applied, it will be advantageous to use temperatures of 40 to 500C.

 All ingredients are thoroughly homogenized before adding the enzyme. The pectinesterase concentration determines the reaction rate, the reaction times can be from 15 minutes to 12 hours, and preferably from 1 to 3 hours. Any purified pectinesterase (that is to say free of polygalacturonase activity) can be used, advantageously used pectinesterase RAPIDASE CPE, sold by Gist-Brocades (France), at concentrations of between 0.1 and 10 ml / kg of pulp, and preferably 0.3 to 1.0 ml / kg of pulp.

Depending on the desired texture and the packaging of the products, the action of pectinesterase can be carried out according to two distinct processes
10. In the absence of agitation: After homogenization of the pulp and ingredients, the whole is enzymed and transferred into the conditioning jars (cup-type). These are then taken to an incubation chamber at the desired temperature. When the texture is correct (ie when the gel point is reached or when the pulp is considered sufficiently thickened), the enzymatic activity is inhibited by pasteurization of the pots.

 In stirred system: The action of the pectinesterase is carried out in the mixing vat with stirring After hydrolysis, the product is taken to the pasteurization system and is then conditioned.

 After enzymatic reaction and pasteurization, the product can be consumed as is or be incorporated into any food preparation, and especially mixed with fruit purées of too low consistency.

 According to another embodiment of the invention, the enzymatic demethylation is carried out without calcium salt and with or without sugaring. The introduction of calcium and possibly sweetening materials is then performed either before or after pasteurization. Calcium salts are however more effective in increasing the viscosity of the product when introduced before pasteurization.

This method has the advantage of only increasing the viscosity of the product after cooling in the packaging containers and thus limits the power of the material necessary to handle and circulate the product.

However, the calcium salts must be perfectly distributed in the product so that the latter is homogeneous and there is a slight loss of efficiency of the system under these conditions.

 The following examples illustrate the invention. The characteristics indicated in these examples are determined in the following manner.

- Brix
Brix (or refractometric dry matter content) is determined by refractometry at 250C.

- Acidity
The acidity of the pulps is determined by titration of 5 g of sample up to pH 8.2 by the addition of 0.05 N sodium hydroxide. The acidity is expressed in g of malic acid equivalent per kg of pulp is obtained by the following equation
Acidity = (NaOH x 1000P / ChI)
P being the exact weight of the sample
Pech being the weight of the sample in the oven
- Calcium content
2 g of fresh material are weighed in a previously weighed platinum crucible. The whole is placed in an oven at 600C overnight, then 2 hours at 1020C and then 6 hours oven at 5500C. The ashes are taken up with 2 to 3 ml of 0.5N HNO3. The dissolution is carried out by heating under a watch glass, the whole is filtered and brought to 20 ml. The calcium is determined by atomic absorption spectrometry with
LaCl3 as a spectral buffer.

- Degree of esterification of pectins
The degree of esterification of the pectins (which corresponds to their methylation rate) is determined by the method of SCHULTZE TH, described in "Methods in
Carbohydrate Chemistry, RL WHISTLER ed., 1965, 5, 189,
Acad. Press.

- Flow of the pulp:
The texture of the pulp is assessed by the consistometer
Bostwick at 250C. The reservoir is carefully filled with pulp and the barrier is lifted at time 0, so as to allow the flow of the product. 1 minute later, the length of the flow is read (in Bostwick index). The test is carried out using the Bostwick Consistometer which is available from CSC Scientific Company inc. The apparatus comprises a trough divided into two parts by a barrier. One of the parts serves as a reservoir. The bottom of the other is graduated, which makes it possible to measure the distance covered by a product in a given time when the barrier is raised.

Example 1: Production of a sweetened gelled apple pulp in cups.

 The apples are grinded to a particle size of 1 cm × 2 cm and the mash is ground by steam injection at 0.3 bar. The temperature rise up to 95 ° C. is carried out in six minutes, 10% of the juice is drained off and the residue is then removed by refining it successively on a sieve having a mesh size of 15 mm, then 10 mm 3500 kg of dried pulp at a price of 350 kg of apple juice at 120brix are added and cooled to 500 ° C. Then 605 kg of crystallized sugar and 3.5 kg of calcium carbonate are added. 1.75 l of pectinesterase rapidase CPE and 0.5 kg of ascorbic acid are added. The resulting product is put into cups and incubated at 50 ° C. for 4 hours, followed by pasteurization to obtain perfectly gelled apple puree (bostwick index = 0) with a brix of 24.5 and an acidity of 3 g of malic acid equivalent / kg of pulp. The final pH is 3.8. The calcium concentration is 292 mg / kg of fresh material, ie 1192 mg / kg of dry matter, and the degree of esterification of the pectins is 26%.

Example 2: Production of a thickened sweet apple puree
The procedure is as in Example 1, except that it is not packaged in cups after enzyming. Conditioning is done after pasteurization. During contacting of the inhibited pulp with the pectinesterase, the mixture is stirred at 100 rpm.

 The results obtained are recorded in Table I.

Table I
Time Brix pH Bostwick acidity (in hours) (g of ac / kg)
0 25.1 4.01 2.66 6.25
1 25.1 3.92 2.82 6.2
2 25.3 3.87 3.03 4.75
3 25.1 3.84 3.00 2.5
4 25.3 3.81 2.66 0.25
After 4 hours of enzymatic reaction, the pulp obtained is perfectly gelled. It can be used as is or mixed with pulp of less consistency (see Example 3). Its Ca2 + content is 1241 mg / kg of dry matter and the degree of esterification is 32 t.

EXAMPLE 3 Production of a Diversified Textural Range by Mixing Textured Pulp According to the Method, and Pulp of Too Low Consistency as Table II
Table II
Normal pulp rate Bostwick Concentration Degree of in the final gelled pulp in Ca (ppm) methylat ion
0% 0.00 1280 32
10% 0.25 1053 39
30% 1.00 828 49
50% 2,75 705 61
100% 4,75 217 89
The incorporation of gelled pulp pulp of lower consistency improves the texture of the latter. The taste and color of the product are not changed.

Claims (7)

 1. Process for the preparation of a puree of apple or pear, characterized in that it consists in putting ground fruit under conditions which inhibit the polygalacturonase activity to obtain inhibited pulp and to put the pulp inhibited into contact with a pectinesterase at a temperature of 10 to 600C for 15 minutes to 12 hours.  2. Method according to claim 1, characterized in that it consists in putting the inhibited pulp in contact with a pectinesterase at a pH between 3 and 4.5.  3. A method according to claim 1 or 2, characterized in that it consists in adding the inhibited pulp of 0.5 to 2 g of calcium salt per kg of pulp, before or after it is brought into contact with a pectinesterase.  4. Method according to one of claims 1 to 3, characterized in that it consists in adding the inhibited pulp from 0 to 50% by weight of fruit juice or nectar.  5. Method according to one of claims 2 to 4, characterized in that it consists in inhibiting the polygalacturonase activity by bringing the crushed fruit at a temperature of at least 800C for at least two minutes.  6. A method according to claim 5, characterized in that it consists in inhibiting the polygalacturonase activity by bringing the crushed fruit at a temperature between 90 and 950C for 3 to 4 minutes.  7. Apple or pear puree, substantially free of texturizing additives, characterized by a degree of methylation of the pectins of less than 70%, a calcium content by weight of more than 300 parts per million and a Bostwick consistency index at 250C less than 2.