Flavour generation in food

Abstract

The present invention relates to flavour generation. In particular the invention relates to a method for flavour generation in a heat-treated food product using a prolidase enzyme. The invention also relates to a heat-treated food product prepared according to the method of the invention.

Claims

1. A method for flavor generation, the method comprising: (a) contacting (1) gluten with (2) a prolyl-specific endopeptidase from Aspergillus niger and (3) a prolidase, at a pH from 5.5 to 7.2 to form a hydrolysed preparation, wherein the prolidase comprises the amino acid sequence SEQ ID NO:1; and (b) subjecting a food preparation comprising the hydrolysed preparation to heat treatment to obtain a heat-treated food product, wherein the food preparation comprises a reducing sugar that was present in the hydrolysed preparation or added to the hydrolysed preparation, and the prolidase is obtained from Saccharomyces cerevisiae.

2. The method according to claim 1, wherein the prolidase is obtained by lysis of Saccharomyces cerevisiae.

3. The method according to claim 1, wherein the reducing sugar is rhamnose.

4. The method according to claim 1, wherein the hydrolysed preparation is incorporated into the food preparation in an amount of 0.01 to 5 parts by weight of the food preparation.

5. The method according to claim 1, wherein the heat-treated food product is selected from the group consisting of biscuit, extruded cereal, pizza, beverage powder and caramel.

6. The method according to claim 1, wherein (1) the gluten, (2) the prolyl-specific endopeptidase from Aspergillus niger, and (3) the prolidase are contacted in an aqueous dispersion at a temperature of between 30 and 60° C.

7. The method according to claim 1, wherein (1) the gluten is contacted with (3) the prolidase in an aqueous dispersion at a temperature of 45-55° C.

8. The method according to claim 1, wherein (1) the gluten is contacted with (3) the prolidase in an aqueous dispersion at a pH between 6.3 and 7.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plot of free amino acid quantity (μM) in unreacted wheat gluten (Blank), wheat gluten reacted with prolyl endopeptidase and Saccharomyces cerevisiae prolidase (B) and wheat gluten with prolyl endopeptidase alone (A). The amino acids are Alanine (ala), Arginine (arg), Asparagine (asn), Aspartic acid (asp), Glutamine (gin), Glutamic acid (glu), Glycine (gly), Histidine (his), Isoleucine (ile), Leucine (leu), Lysine (lys), Methionine (met), Ornithine (orn), Phenylalanine (phe), Proline (pro), Serine (ser), Threonine (thr), Tryptophan (trp), Tyrosine (tyr), Valine (val).

(2) FIG. 2 is a plot of free amino acid molar fractions for wheat gluten incubated with prolyl endopeptidase and CPD-Y prolidase (C) or prolyl endopeptidase and S. cerevisiae prolidase (D).

(3) FIG. 3 shows a graph representing the temperature profile during cultivation of S. cerevisiae cells in CP medium as a result of experiments described in Example 3.

(4) FIG. 4 shows the residual glucose during cultivation of S. cerevisiae cells in casein peptone medium as a result of experiments described in Example 3.

(5) FIG. 5 shows the viability of S. cerevisiae cells (cfu/mL) against fermentation time (h) on casein peptone medium as a result of experiments described in Example 3.

(6) FIG. 6 shows the release of selected free amino acids [mM concentration] during S. cerevisiae fermentation in casein peptone medium as a result of experiments described in Example 3.

(7) FIG. 7 shows a graph representing the free amino acid concentration [mM] obtained after 5 days of fermentation as a result of experiments described in Example 3. The amino acids are Alanine (ala), Arginine (arg), Asparagine (asn), Aspartic acid (asp), Cittruline (cit), Glutamine (gin), Glutamic acid (glu), Glycine (gly), Histidine (his), Isoleucine (ile), Leucine (leu), Lysine (lys), Methionine (met), Ornithine (orn), Phenylalanine (phe), Proline (pro), Serine (ser), Threonine (thr), Tryptophan (trp), Tyrosine (tyr), Valine (val).

DETAILED DESCRIPTION OF THE INVENTION

(8) Consequently the present invention relates in part to a method for flavour generation (for example in a heat-treated food product) comprising; a) contacting an edible peptide-containing material with a prolidase to form a hydrolysed preparation, wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1; b) incorporating the hydrolysed preparation obtainable (for example obtained) from step (a) into a food preparation which comprises at least a reducing sugar; or, where the hydrolysed preparation already comprises at least a reducing sugar, the hydrolysed preparation may be the food preparation; and (c) subjecting the food preparation to heat treatment to obtain a heat-treated food product.

(9) The term flavour is used in the present invention to refer to the combination of taste and aroma. Taste refers to the sensation of flavour perceived in the mouth and aroma refers to perception inside the nose. Chemically, a “flavour” may be one or more taste active molecules, one or more aroma molecules, or a mixture of these. Some taste active molecules are also aroma molecules.

(10) Within the context of the present invention, the term “heat treated food product” identifies a food product which has been subject to heat treatment. A food product is a substance that can be used or prepared for use as food. Non-limiting examples of heat treating techniques are: oven baking, roller drying, extrusion, spray drying. Non limiting examples of heat treated food products according to the present invention are:

(11) biscuits, wafers, cereals (breakfast and infant), bread, ice-cream cones, milk powder, non-dairy beverage creamers, pizza and the like.

(12) The term “edible” is used in the context of the present invention to mean substances which can be eaten safely. Whilst the current invention is not limited to substances permitted for consumption in any particular jurisdiction, edible compositions may for example comprise materials approved for human consumption by the U.S. Food and Drug Administration.

(13) The peptide-containing material according to the invention may be comprise a polypeptide. The peptide-containing material according to the invention may comprise proline. The peptide-containing material may comprise a protein. Proteins consist of one or more polypeptides arranged in a biologically functional way. Preferably the peptide-containing material comprises polypeptides which have more than 10 amino acids. The peptide-containing material may be a peptone, a water-soluble mixture of polypeptides and amino acids formed by the partial hydrolysis of protein.

(14) A prolidase is an enzyme that catalyzes the hydrolysis of the peptide bond between an amino acid and proline or hydroxyproline. In the context of the current invention the prolidase may be a proline dipeptidase, but it may also catalyse the hydrolysis of the peptide bond of larger peptides such as tripeptides or tetrapeptides that have proline as the terminal amino acid.

(15) The prolidase may comprise an amino acid sequence having at least 97%, 98% or 99% identity to SEQ ID NO:1. The prolidase may have the amino acid sequence shown in SEQ ID NO:1.

(16) TABLE-US-00001 (SEQ ID NO: 1) MSHSLTSVFQKIDSLKPQFFSRLTKAIQIPAVSSDESLRSKVFDKAKFIS EQLSQSGFHDIKMVDLGIQPPPISTPNLSLPPVILSRFGSDPSKKTVLVY GHYDVQPAQLEDGWDTEPFKLVIDEAKGIMKGRGVTDDTGPLLSWINVVD AFKASGQEFPVNLVTCFEGMEESGSLKLDELIKKEANGYFKGVDAVCISD NYWLGTKKPVLTYGLRGCNYYQTIIEGPSADLHSGIFGGVVAEPMIDLMQ VLGSLVDSKGKILIDGIDEMVAPLTEKEKALYKDIEFSVEELNAATGSKT SLYDKKEDILMHRWRYPSLSIHGVEGAFSAQGAKTVIPAKVFGKFSIRTV PDMDSEKLTSLVQKHCDAKFKSLNSPNKCRTELIHDGAYWVSDPFNAQFT AAKKATKLVYGVDPDFTREGGSIPITLTFQDALNTSVLLLPMGRGDDGAH SINEKLDISNFVGGMKTMAAYLQYYSESPEN

(17) Within the context of the present invention the term “hydrolysed preparation” identifies a composition based on the edible peptide-containing material and comprising any substance generated by the proteolytic action on the edible peptide-containing material of the enzymes present. If the enzymes are generated in-situ, for example by the activities of microorganisms, then the hydrolysed preparation may comprise the microorganisms and/or their residues. Within the context of the present invention, the term “microorganism” identifies a unicellular organism being a bacterium, a filamentous fungi or a yeast. The hydrolysed preparation according to the invention may comprise proline as a free amino acid.

(18) Within the context of the present invention the term “food preparation” identifies a mixture of ingredients which is meant to deliver a “heat treated food product” when subjected to heat treatment. Non limiting examples of “food preparation” are: batters, doughs, mixtures comprising cereals and milk powder, mixtures comprising milk powder and flour, and the like. Within the context of the present invention the terms “dough” or “batter” identify a food ingredient mixture as above defined which is mainly based on cereal flour and water in different ratios. Such dough or batter may also comprise additional ingredients such as for example fats, salts, sugars, eggs, milk and the like.

(19) Within the context of the present invention, the term “reducing sugar” identifies any sugar that either has an aldehyde group or is capable of forming one in solution through isomerisation, such aldehyde group allowing the sugar to act as a reducing agent. The reducing sugar in the current invention may be a mono or oligosaccharide, for example a mono to tetra-saccharide. The reducing sugar may be selected from the group consisting of C5 and C6 monosaccharides. The reducing sugar may be selected from the group consisting of fructose, glucose, xylose, tagatose, rhamnose, maltose, lactose, fucose, arabinose, galactose and mixtures thereof. The reducing sugar may be selected from the group consisting of fructose, glucose or rhamnose. The reducing sugar may be rhamnose.

(20) The prolidase according to the method of the invention may be obtainable (for example obtained) from Saccharomyces cerevisiae. Yeasts have good consumer acceptance in food processing due to their long history of use. The prolidase according to the method of the invention may be comprised within a yeast preparation, for example a yeast preparation comprising lysed cells of Saccharomyces cerevisiae. The prolidase according to the method of the invention may be obtainable (for example obtained) from a modified strain of Saccharomyces cerevisiae. The prolidase according to the method of the invention may be obtainable (for example obtained) from Saccharomyces cerevisiae CNCM I-4003 or CNCM I-4006. The prolidase may be the prolidase from Saccharomyces cerevisiae having the UniProtKB P43616. This enzyme has the amino acid sequence shown in SEQ ID NO:1.

(21) Saccharomyces cerevisiae CNCM I-4003 was deposited with the Collection Nationale de Cultures de Microorganismes (CNCM), Institut Pasteur, 25 rue du Docteur Roux, F-75724 PARIS Cedex 15, France, on 12 Jun. 2008 and given the deposit number I-4003. Saccharomyces cerevisiae CNCM I-4006 was deposited with the Collection Nationale de Cultures de Microorganismes (CNCM), Institut Pasteur, 25 rue du Docteur Roux, F-75724 PARIS Cedex 15, France, on 12 Jun. 2008 and given the deposit number I-4006.

(22) The prolidase according to the method of the invention may be obtainable (for example obtained) by the lysis of Saccharomyces cerevisiae. The lysis may be induced by increasing the temperature of a fermentation broth comprising a temperature sensitive strain of Saccharomyces cerevisiae such as CNCM I-4006, the temperature increase may be accompanied by the addition of a nutrient sugar to the fermentation broth such as glucose. For example, the prolidase may be obtained by growing a temperature sensitive strain of Saccharomyces cerevisiae (for example CNCM I-4006) in a protein containing medium under permissive conditions to reach a concentration of at least 10 million viable cells per mL of protein containing medium and then increasing the temperature of the protein containing medium to a value between 32 to 45° C. for sufficient time to allow the Saccharomyces cerevisiae to at least partially lyse. Within the context of the present invention, the term “permissive conditions” for the growth of a microorganism identifies temperature and atmosphere conditions which are appropriate to allow growth of specific microorganisms, for example without leading to their even partial lysis. For example, for Saccharomyces cerevisiae, permissive conditions may be between 20° C. and 30° C. Where all the components of the protein containing medium are food grade, the medium and the lysed Saccharomyces cerevisiae cells may be incorporated into the hydrolysed preparation of the method of the invention. Indeed, the liberation of prolidase by lysis of Saccharomyces cerevisiae may be directly part of the food product production process, so-called “in-process” generation of enzymes.

(23) In the case of food products it may be beneficial to introduce a yeast into the food production process rather than a pure enzyme. Including a yeast which undergoes lysis when the temperature is increased presents the operational advantage that, in the hydrolysed preparation, prolidase is delivered spontaneously and amino acid flavour precursors are generated without any need for external intervention on the medium. Such hydrolysed preparation can be thus simply incorporated into the food preparation (batter or dough for example) for its standard further processing.

(24) Furthermore, as the structure of the heat-treated food product forms at the same time as the flavour active molecules are generated, the flavour active molecules become trapped within the food matrix and the desirable notes are strong in the finished foodstuff.

(25) Within the context of the present invention, the term “suitable conditions” for the growth of a microorganism identifies temperature and atmosphere conditions which are appropriate to allow growth of specific microorganisms. Within the context of the present invention the term “protein containing medium” identifies a growth medium for microorganisms which comprises, micronutrients, nitrogen sources and carbon sources. If not already provided by the above mentioned nitrogen sources, the medium also incorporates sources of amino acids such as proteins, peptides or protein hydrolysates.

(26) A method for flavour generation may comprise; a) growing at a permissive temperature and in a protein containing medium a temperature sensitive microorganism (for example Saccharomyces cerevisiae) which will at least partially lyse in the temperature range of about 32 to 45° C.; b) after reaching a concentration of at least 10 million viable cells per mL of protein containing medium, increasing the temperature of the protein containing medium to a value comprised between 32 to 45° C. for sufficient time to allow microorganism to at least partially lyse; c) optionally adding while performing step b) any nutrient originally comprised in in the protein containing medium and depleted during step a); d) maintaining the protein containing medium under the same conditions as per step b) for a period ranging from 1 hour to 10 days after temperature has been increased; e) incorporating the fermented preparation obtainable from step d) into a food preparation which comprises at least a reducing sugar; f) subjecting the food preparation to heat treatment to obtain a heat-treated food product.

(27) In one embodiment of the method of the invention, the edible peptide-containing material is contacted with a prolyl endopeptidase in addition to a prolidase. For example, the edible peptide-containing material may be contacted with a prolyl endopeptidase before, or simultaneously with being contacted with the prolidase. The prolyl endopeptidase may be a proline-specific endoprotease that yields a peptide chain with a carboxy-terminal proline residue. The prolyl endopeptidase may be a proline-specific endoprotease from Aspergillus niger, for example the prolyl endopeptidase may be Maxipro PSP or Maxipro XF from DSM.

(28) In one embodiment, the method of the invention generates a hydrolysed preparation comprising a mixture of several free amino acids. For example, the mixture of several free amino acids generated according to the invention may comprise proline, lysine, alanine, glutamine, valine, arginine, phenyl alanine and ornithine. The mixture of several free amino acids generated in the hydrolysed preparation according to the invention may comprise proline, lysine, glutamine, phenyl alanine and ornithine. The mixture of free amino acids generated according to the invention may comprise proline, lysine, glutamine and phenyl alanine, with proline being the free amino acid with the highest molar fraction in such mixture. In an embodiment, in the mixture of free amino acids generated in the hydrolysed preparation according to the invention, asparagine may be substantially absent. In an embodiment, the mixture of free amino acids generated in the hydrolysed preparation according to the invention may comprise a mixture of free amino acids wherein proline, lysine, glutamine and phenylalanine are present at a concentration greater than 1 mM respectively (for example greater than 2 mM respectively). The mixture of free amino acids generated in the hydrolysed preparation according to the invention may comprise a mixture of free amino acids wherein proline is present at a concentration greater than 5 mM.

(29) The food preparation according to the method of the invention may contain flour. In one embodiment, the amount of individual free amino acids in the food preparation according to the method of the invention ranges between 0.001 and 1 parts in weight based on 100 parts of flour. For example, the amount of free amino acids in a food preparation according to the method of the invention may range between 0.005 and 0.1 parts in weight based on 100 parts of flour. The amount of free amino acids in a food preparation according to the method of the invention may range between 0.05 and 0.1 parts in weight based on flour weight.

(30) In an embodiment, the term “heat-treated food product” identifies a product which is dough- or batter-based. The said batter or dough may comprise: Flour: 100 parts Water: from 5 to 200 parts Salts: from 0.1 to 5 parts Fat: from 0.1 to 100 parts Eggs: from 0 to 100 parts Sugar: from 0 to 100 parts

(31) For example, the said batter or dough may comprise: Flour: 100 parts Water: from 100 to 180 parts Salts: from 0 to 5 parts Fat: from 0.5 to 2 parts Sugar: from 0 to 5 parts

(32) Particularly when pure enzymes are used, the hydrolysed preparation according to the method of the invention may contain at least a reducing sugar and be the food preparation. For example, a prolyl endopeptidase and a prolidase comprising an amino acid sequence having at least 95% identity to SEQ ID NO:1 may be added directly to a batter composition as above containing a reducing sugar. When enzymes generated in-situ from microorganisms are used it may be preferable to generate the hydrolysed preparation separately from the main ingredients, for example to better control the growth conditions for the microorganism. In an embodiment, the hydrolysed preparation according to the invention may be incorporated into the food preparation in an amount of from 0.05 to 5 parts in dry weight based on 100 parts of flour. For example, the hydrolysed preparation according to the invention may be incorporated into the food preparation in an amount of from 0.1 to 3 parts in dry weight based on 100 parts of flour.

(33) The hydrolysed preparation according to the method of the invention may be incorporated into the food preparation in an amount of 0.01 to 5 parts by weight of the food preparation. Such levels are appropriate for good flavour generation in the presence of reducing sugars.

(34) In one embodiment, the method of the invention provides a heat-treated food product comprising at least one the of the flavour characteristics: biscuit, buttery, fruity, nutty, caramel, golden syrup, honey, toasted, roasted bread-like and baked. For example, the method of the invention may provide a heat-treated food product comprising a biscuit flavour. In one embodiment, the method of the invention provides a heat-treated food product wherein the heat-treated food product comprises cereal flour (for example wheat flour).

(35) The heat treated food product according to the method of the invention may be selected from the group consisting of biscuit, extruded cereal (for example breakfast cereal), pizza (for example pizza base), beverage powder and caramel.

(36) The biscuit may be a wafer. Wafers are baked products which are made from wafer batter and have crisp, brittle and fragile consistency. They are thin, with an overall thickness usually between <1 and 4 mm and typical product densities range from 0.1 to 0.3 g/cm.sup.3. The surfaces are precisely formed, following the surface shape of the plates between which they were baked. They often carry a pattern on one surface or on both. Wafers may also be produced by extrusion. Two basic types of wafer are described by K. F. Tiefenbacher in “Encyclopaedia of Food Science, Food Technology and Nutrition p 417-420—Academic Press Ltd London—1993”: 1) No- or low-sugar wafers. The finished biscuits contain from zero to a low percentage of sucrose or other sugars. Typical products are flat and hollow wafer sheets, moulded cones or fancy shapes. 2) High-sugar wafers. More than 10% of sucrose or other sugars are responsible for the plasticity of the freshly baked sheets. They can be formed into different shapes before sugar recrystallization occurs. Typical products are moulded and rolled sugar cones, rolled wafer sticks and deep-formed fancy shapes.

(37) The beverage powder may be a heat-treated milk powder, a cocoa or malt beverage powder or a beverage creamer such as a dairy or non-dairy creamer for use with coffee.

(38) Within the context of the present invention, caramel is a confectionery product made by heating a variety of sugars, for example as sugar syrups in water. Milk ingredients such as skimmed milk powder or condensed milk are typically heated together with the sugar syrups. The caramel may be liquid, or it may have undergone a degree of sugar crystallization to form a solid. It is typically brown in colour and is often found as a filling in chocolate confectionery products.

(39) The edible peptide-containing material according to the method of the invention may be selected from the group consisting of flour (for example wheat flour), milk and peptide-containing components of these, for example gluten (a component of wheat flour) or casein (a component of milk). The edible peptide-containing material according to the method of the invention may be a protein hydrolysate such as a casein hydrolysate.

(40) In an embodiment of the method of the invention the edible peptide-containing material, the prolyl endopeptidase and the prolidase may be contacted in an aqueous dispersion at a temperature of between 30 and 60° C., for example between 45 and 55° C. The edible peptide-containing material, the prolyl endopeptidase and the prolidase may be contacted in an aqueous dispersion at a pH between 5.0 and 8.5.

(41) In an embodiment of the method of the invention the edible peptide-containing material may be contacted with the prolyl endopeptidase and the prolidase sequentially or simultaneously. In the embodiment where the edible peptide-containing material is contacted with the prolyl endopeptidase and prolidase sequentially, then the edible peptide-containing material should be contacted with the prolyl endopeptidase before being contacted with the prolidase. The optimum temperature for contacting the edible peptide-containing material with the prolyl endopeptidase in an aqueous dispersion will depend on exact prolyl endopeptidase selected. In the method of the invention the edible peptide-containing material may be contacted with the prolidase in an aqueous dispersion at a temperature of between 45 and 55° C. The edible peptide-containing material may be contacted with the prolidase in an aqueous dispersion at a pH of between 6.3 and 8.2.

(42) The food preparation may be heated to between 60 and 300° C. during the heat treatment according to the method of the invention. The heat treatment may be selected from the group consisting of pasteurization, sterilization, oven baking, roller drying, and extrusion. The heat treatment may be applied during spray drying.

(43) In a second aspect, the invention provides a hydrolysed preparation obtainable by contacting an edible peptide-containing material with a prolidase, wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1. The hydrolysed preparation may be obtainable by contacting an edible peptide-containing material with a prolyl endopeptidase and a prolidase, wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1. For example, the prolyl endopeptidase may be contacted with the edible peptide-containing material before, or simultaneously with the prolidase. The molar fraction of proline as a free amino acid may be at least a factor of 2 times higher than in a hydrolysed preparation with the same composition except that the edible peptide-containing material has been completely hydrolysed to free amino acids.

(44) The invention may provide a food preparation incorporating a hydrolysed preparation according to the second aspect of the invention. In a further aspect, the invention provides a food preparation comprising a prolyl endopeptidase, a prolidase, proline as free amino acid and ornithine as a free amino acid; wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1; and, if methionine is present as a free amino acid, the molar ratio of proline to methionine as free amino acids is greater than 18. Methionine is responsible for savoury/meaty flavours which are undesirable in many baked goods such as confectionery wafers. The prolyl endopeptidase may for example be a proline-specific endoprotease from Aspergillus niger, for example the prolyl endopeptidase may be Maxipro PSP or Maxipro XF from DSM. The invention may provide a heat-treated food product obtainable by heating such a food preparation.

(45) In a still further aspect the invention provides a heat-treated food product obtainable by a method comprising; a) contacting an edible peptide-containing material with a prolidase to form a hydrolysed preparation, wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1; b) incorporating the hydrolysed preparation obtainable from step (a) into a food preparation which comprises at least a reducing sugar; or, where the hydrolysed preparation already comprises at least a reducing sugar, the hydrolysed preparation may be the food preparation; and c) subjecting the food preparation to heat treatment to obtain a heat-treated food product. The heat-treated food product may be obtainable by a method comprising; a) contacting an edible peptide-containing material with a prolyl endopeptidase and a prolidase to form a hydrolysed preparation, wherein the prolidase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1; b) incorporating the hydrolysed preparation obtainable from step (a) into a food preparation which comprises at least a reducing sugar; or, where the hydrolysed preparation already comprises at least a reducing sugar, the hydrolysed preparation may be the food preparation; and c) subjecting the food preparation to heat treatment to obtain a heat-treated food product.

(46) In a still further aspect, the invention provides for the use of a prolidase comprising an amino acid sequence having at least 95% identity to SEQ ID NO:1 to improve the flavour of a heat-treated food product. The prolidase may be used in combination with a prolyl endopeptidase, for example the prolidase may be used after or simultaneously with a prolyl endopeptidase.

(47) Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the method of the present invention may be combined with the product of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined. Where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred to in this specification.

(48) Further advantages and features of the present invention are apparent from the figures and non-limiting examples.

EXAMPLES

Example 1: Generation of Amino Acids with Prolyl Endopeptidase and Saccharomyces Cerevisiae Prolidase

(49) Prolidase enzyme from Saccharomyces cerevisiae having the SEQ ID NO:1 was expressed (Biocatalysts Ltd. UK). A 10% w/v suspension of wheat gluten was incubated for 10 min at 50° C. and pH 5.5 with 0.4%.sub.vs prot. prolyl endopeptidase (Maxipro XF from DSM). Then the pH was increased to 7.2, 1.0%.sub.prot. vs prot. of prolidase from S. cerevisiae was added and the mixture was again incubated for 24 hours at 50° C. For comparison, wheat gluten was treated under the same pH and incubation conditions but only using the prolyl endopeptidase.

(50) The determination of amino acids was performed using a Nucleodur 100-3 HILIC column. Amino acids were eluted with a gradient of water in acetonitrile, both containing 0.5% acetic acid. The detection is perfomed using a Triple Quadropole (QQQ) Mass Spectrometer. Different dilutions of standard solutions were used to determine linear regressions of the ratio between the peak area of each amino acid versus the peak area of the corresponding deuterated amino acid as a function of concentration. The quantities of amino acids obtained are plotted in FIG. 1, the unreacted wheat gluten is also shown (Blank). It can be seen that contacting the wheat gluten with prolyl endopeptidase and the prolidase from S. cerevisiae (B) provides a greater yield of proline than using prolyl endopeptidase alone (A).

Example 2: Comparison with Prolyl Endopeptidase/Carboxypeptidase CPD-Y

(51) The combination prolyl endopeptidase/S. cerevisiae prolidase was compared with using the combination proposed in WO2005/117595; prolyl endopeptidase/carboxypeptidase CPD-Y. Initially a 49% w/v suspension of wheat flour (corresponding to a 10% w/v suspension of wheat gluten) was incubated for 2 hours at 50° C. and pH 5.0 with 0.4%.sub.vs prot. prolyl endopeptidase (Maxipro XF) and 0.1%.sub.prot. vs prot. of either the carboxypeptidase CPD-Y (Sigma), or prolidase from S. cerevisiae as in Example 1. The activity of carboxypeptidase CPD-Y was found not to be the same as prolidase from S. cerevisiae (carboxypeptidase CPD-Y has an overall higher activity) so, to evaluate the selectivity of the enzymes, further experiments were performed with similar extents of conversion, the amount of CPD-Y being reduced compared to the prolidase from S. cerevisiae.

(52) A 10% w/v suspension of wheat gluten was incubated for 10 min at 50° C. and pH 5.5 with 0.4%.sub.vs prot. proline specific endopeptidase (Maxipro XF) before being hydrolysed with either 1.0%.sub.prot. vs prot. of prolidase from S. cerevisiae or 0.1%.sub.prot. vs prot. of CPD-Y. The pH was increased to 7.2 and the mixture was incubated for about 24 hours at 50° C. The free amino acids produced are shown in FIG. 2. The amounts of amino acids are given as molar fractions. The molar fraction represents the proportion of one individual amino acid versus the sum of all free amino acids present after enzymatic hydrolysis. It is a simple way to illustrate the selectivity of the enzyme. It can be seen that prolidase from S. cerevisiae (D) has a much greater specificity for proline production than CPD-Y (C). This is beneficial, as proline generates attractive baked flavours in the Maillard reaction. In addition, prolidase from S. cerevisiae produced less methionine than CPD-Y. Methionine is responsible for savoury/meaty flavours which are undesirable in many baked goods such as confectionery wafers. The ratio of praline to methionine was 13.4 for CPD-Y, but was 22.9 for the S. cerevisiae prolidase.

Example 3: Heat Induced Lysis of S. cerevisiae

(53) Casein peptone (CP) medium was prepared by dissolving 10 g of yeast extract, 20 g of casein peptone and 20 g of dextrose per litre of water. The solution had a pH around 6.5 and was further sterilized by filtration through 0.2 μm filter. S. cerevisiae yeast (temperature sensitive strain CNCM I-4006) was cultivated in the CP medium. An inoculum was prepared from glycerol stock of the yeast strain stored at −80° C. A first culture was carried out inoculating 10 mL of fresh CP medium with 2% of the strain stock. Afterwards, a second culture was performed, inoculating 10 mL of fresh CP medium with 2% of the first culture. The broth was then incubated in a shaker for 24 h at 25° C. and 130 rpm, under aerobic conditions. Fermentation was performed in small fermenter containing CP medium under the following conditions; inoculation 1% v/v, temperature 25° C., aerobic condition controlling the dissolved oxygen at a minimum level of 30%.

(54) Depletion of sugars in the growth medium reflects the depletion of nutrients in the growth medium and indicates the end of microorganism growth. Sugars were determined by HPLC, combining ion exclusion and partition (column Aminex HPX-87H, 300×7.8 mm). Sugars were eluted with 0.6 mL/min 5 mM sulfuric acid and detected using a refractive index detector. Different dilutions of standard solutions were used to determine linear regressions of peak area as a function of the concentration.

(55) Microorganism cell autolysis is indirectly measured on the basis of enumeration of viable microorganism cells in the growth medium. The method used was to count the number of Colony Forming Units per millilitre (cfu/mL) of fermentation broth. Serial dilutions of the sample were used to find the appropriate concentration where every single viable cell is isolated from the others. Diluent was composed of 1 g tryptone and 8.5 g sodium chloride per litre of water. Aliquots of different dilutions (20 μL) were then deposited onto an YPD (Yeast peptone dextrose) agar plate. After drying, the plates were incubated at 30° C. for 48 h. Each of the previous steps was performed in sterile conditions. Finally, the colonies were counted and viable cells count calculated using the equation:
Viable cells count=N×50×D

(56) Where N is the number of colonies in the selected spot and D is the dilution factor.

(57) Initial measured pH for the growth medium during cultivation of S. cerevisiae yeast (temperature sensitive strain CNCM I-4006) was around 6.5. Maximal growth was obtained within 24 h when glucose was completely depleted (see FIG. 4). At 24 h, glucose was added to the medium, up to a concentration of 350 mM within 4 hours. At the same time, temperature was increased from 25 to 37° C. (see FIG. 3)

(58) Glucose was totally consumed during the growth phase and about 250 mM of the added glucose was consumed during the lysis (see FIG. 4).

(59) The viability of S. cerevisiae cells dropped as soon as the cells tried to grow again when sugar was added. Without wishing to be bound by theory, it is believed that the increase in temperature prevents performing a normal division of the cells resulting in their lysis (see FIG. 5).

(60) The amount of free amino acids present in the fermentation medium were measured at different times (determination method as in example 1). Results for selected free amino acids are reported in FIG. 6 (time course of amount developed for Asparagine, Glutamine, Lysine, Ornithine, Phenylalanine and Proline). The measured final concentrations [mM] in the fermentation medium for all the released amino acids is reported in FIG. 7.

(61) Free amino acids that were initially present in CP medium were totally consumed during the growth of strain CNCM I-4006. As soon as the cells lysed and pH was increased to 7 by addition of NaOH aq solution 2M, hydrolysis of proteins and peptides from casein peptone and yeast extract started with associated release of free amino acids (see FIGS. 6 and 7), proline being the second most abundant.

(62) Thanks to the levels of free amino acids developed, the fermented preparation according to the invention may be incorporated into a food preparation comprising at least a reducing sugar to achieve development of appropriate flavours on heat treatment as a consequence of Maillard reactions.

(63) It can be seen that S. cerevisiae lyses upon application of heat and releases prolidase enzymes.