GB1569339A - Decolouring of pea flour - Google Patents

Description

(54) DECOLOURING OF PEA FLOUR (71) We, THE GRIFFITH LABORATORIES LIMITED. a Canadian Corporation, of 757 Pharmacy Avenue, Scarborough. Ontario. MIL 3J8. do hereby declare the invention. for which we pray that a patent may be granted to us. and the method bv which it is to be performed to be particularly described in and bv the following statement: This invention relates to the decolouring of yellow pea flours. including those that have had their percent protein increased by removal of some of the non-protein components.

Dried pea protein flours are an excellent source of vegetable protein. They are made by grinding dried peas. The protein content can be increased by separating starchy components to leave a flour that is high in protein content. Fhey tend. however. to have a bitter taste and a characteristic pea flavour which restricts their use in food products. As described in co-pending United States Patent 4.(L2.)lY issued Mav 10. 1977. the bitter taste can be removed by heat treatment and the pea flavours can be removed with steam to give products useful in food systems.

Yellow dried pea flours contain yellow pigments characteristic of mellow peas which dominate their appearance in contrast to green peas in which the chiorophyll pigments dominate. Heat treatment under moist conditions can produce orange-brown pigments which then dominate the product appearance. The pigments in yellow pea flours. especially the orange-brown pigments which develop on heat treatment. are objectionable in certain food products.

The chemical nature of the orange-brown pigments in yellow peas which develop on heat treatment is not known. They differ from the yellow pigments present in raw. untreated pea flours in that they are not removed by conventional flour bleaching agents, e.g. dibenzoyl peroxide and chlorine dioxide, whereas the yellow pigments are. It has, however, been found that they are soluble in certain organic solvents under the extraction conditions described in this invention.

The constituents of yellow pea flour that cause the orange-brown colour on heat treatment are not apparent in raw pea flour before heat treatment. They are. however, present and it has been found that they can be removed bv organic solvents in accordance with this invention either before heat treatment when they are not visablv apparent or after heat treatment when they are apparent bv their orange-brown colour. The yellow pigments apparent in the raw untreated flour are also removed bv the solvents in accordance with the invention.

The method of removing orange-brown colour causing constituents from yellow pea flour in the manufacture of high protein pea flour wherein the flour is heat treated according to this invention, includes the steps of extracting the flour with a solvent comprising an unsubstituted Cl. C2 or C3 monohydric alcohol at a temperature above 40 C and not more than 30% water bv volume to remove the brown colour causing constituents, and then removing the residual solvent from the flour.

The use of aqueous organic solvents for improving the flavour of vegetable protein concentrates, e.g. soy protein concentrates, is well known. However, vegetable proteins such as soy are very sensitive to protein denaturation by alcohol solvents and the extractions must be carried out at low. ambient temperatures to prevent extensive protein denaturation. Protein denaturation is accompanied hv a lt)ss of protein solubilitv in water.

In many cases of colour extraction with this invention there is little or no protein denaturation. For example. it has been found that yellow pea flours previously treated with moist heat to remove the bitter flavour and the pea flavour can be decoloured in accordance with this invention with little or no further protein denaturation.

As indicated. protein denaturation is accompanied by a loss of protein solubility in water and a generally accepted method for the determination of protein solubility is to measure nitrogen solubilitv index (N.S.I.) bv the method of the American Association of Cereal Chemists (AACC Method 46/23). For many applications vegetable protein products with low N.S.I., e.g. below 25%. tend to lack the functional properties of undenatured. high N.S.I. vegetable protein products in the sense that they have relativelv poor emulsification properties in food systems. As will be apparent from the results of experiments set forth in this specification. it is not at all difficult with the method of this invention to decolour yellow pea flours and maintain a high N.S.I. value.

At the same time, lower values of N.S.I. in the order of 10 to 25 may be satisfactory for use in many food systems if they have a relatively high hydration capacity. Some colour removal in accordance with this invention results in a lowering of the N.S.I. value of yellow pea flour to the order of 10 to 25 but at the same time there is an increase in hydration capacity. The combination of reduction in N.S.I. and increase in hydration capacity gives an acceptance water binding capacity for many end products. In every instance the principal object of decolouring the yellow pea protein flour by removing the orange-brown pigments and/or colour causing constituents that result in orange-brown pigments on heat treatment to obtain white or off-white end product is achieved.

Yellow pea flours debittered and deflavoured with moist steam were extracted with the solvents in accordance with the conditions of Table I and the solution colour and product examined. The flour had an orange-brown colour. The desired result was in each case to achieve a white or off-white result.

The soluble fraction of the extracted moist heat treated pea flour subjected to an extraction process is an indication of the efficiencv of an extraction in reducing colour. For example. if the colour of the solution is orange. it is an indication that the colour extraction has been efficient. If. on the other hand. it is a light yellow or pale orange. it is an indication that it is inefficient and that too much colour has remained in the pea concentrate.

Moreover. if the yield of solid content in the soluble raction in hitch. it Is an indication that substances other than colour have been removed. In many cases. it is protein that is removed. It can also be an indication of denaturing. The tolioxninq table illustrates the 3() minute extractions of moist heat treated pea flour of concentrated protein content with pure solvents at temperatures indicated. The starting flour had an orange-brown colour caused bv its heat treatment which was contacted with steam to cuase its temperature to reach about llO"C for a time duration to debitter it and remove volatiles.

TABLE I Moist-Heat Treated Pea Flour Organic Solvent Extraction (1:10 solvent ratio) Extrac- Extraction tion Prod. AACC time temp. Solution Prod. Prod. Protein NSI Solvent (min.) ( C) Colour Colour Yield % S nil - - - tan - 62 60 isopropanol 30 22 yellow tan 96.5 64.7 58 isopropanol 30 82 yellow tan 94.5 66.5 60 ethanol 30 22 yellow tan 94.8 65.6 60 ethanol 30 60 pale tan 93.0 67.0 60 orange ethanol 30 78 orange white 90.5 69.5 28 methanol 30 22 yellow tan 93.6 66.5 60 methanol 30 40 pale tan 91.5 68.0 60 orange methanol 30 50 light off- 90.0 68.6 60 orange white methanol 30 60 orange white 88.9 70.0 40 methanol 30 60 orange white 88.9 70.0 40 methanol 180 60 orange white 88.9 70.0 35 The colour of the product resulting from the extraction should be white or off-white and on the basis of the foregoing results it is apparent that onlv ethanol and methanol at or near reflux temperatures had sufficient extractive power to give a satisfactory product.

Water was added to the solvents to increase their extractive power and extractions were carried out at room temperatures. Following are the results: TABLE II Moist-Heat Treated Pea Flour Aqueous Organic Solvent Extraction at 22 C. (30 min: 1:10 solvent ratio) Hydration Capacity Prod. Prod. AACC By AACC Water Solution Product Yield Protein NSI Method 56-20 Solvent % (v/v) Colour Colour % % % % Methanol 0 yellow tan 93.6 62.6 60 264 10 yellow tan 91.1 63.2 60 279 20 pale orange tan 84.6 66.8 60 294 30 pale orange tan 81.7 68.4 60 306 50 pale orange tan 76.1 71.4 56 333 ethanol 0 yellow tan 94.8 62.6 60 10 yellow tan 91.7 65.4 60 248 20 pale orange tan 88.1 67.0 62 279 50 pale orange tan 75.4 70.5 57 303 isopropanol 0 yellow tan 96.5 60.7 58 253 10 yellow tan 93.1 65.3 60 228 20 pale orange tan 90.9 66.9 59 259 30 pale orange tan 87.5 69.3 59 276 50 pale orange tan 76.8 70.1 54 346 It is apparent that extraction at room temperatures | (22 C) with these aqueous organic solvents, with or without their extractive power increased with water, does not result in a satisfactory product colour. The temperature of the solvents was raised to 60 C and following are results of tests carried out on colour removal of pea protein concentrate debittered as explained.

TABLE III Moist-Heat Treated Pea Flour Aqueous Organic Solvent Extraction at 60 C (30 min: 1:10 solvent ratio) Hydration Capacity Water Solution Product Prod. Prod. AACC By AACC Solvent % (v/v) Colour Colour Yield Protein NSI Method 56-20 methanol 0 orange white 88.9 70.0 40 252 10 orange white 85.2 72.9 21 315 20 orange white 80.9 75.6 16 328 30 light offorange white 78.4 76.3 16 337 50 pale orange tan 74.2 74.2 10 408 ethanol 0 pale orange tan 93.0 67.0 60 270 10 orange white 88.6 70.8 52 275 20 orange white 84.1 73.5 24 348 30 light offorange white 79.3 74.6 15 365 50 pale orange tan 72.1 73.4 9 427 isopropanol 0 pale orange tan 94.5 66.5 62 211 10 light offorange white 92.6 67.9 59 237 20 orange white 90.5 69.2 55 262 30 light offorange white 86.2 70.4 28 351 50 pale orange tan 71.4 71.8 12 427 There is effective colour removal as indicated bv the white and off-white product colour. and a decrease in product yields. Colour extraction efficicncv varies with the general extraction power of the solvent with methanol being more effective than ethanol and isopropanol being the least effective. However, bv increasing the general extraction power of ethanol and isopropanol by the addition of small amounts of water colour, extraction is increased but extraction with water levels in excess of 30% does not produce efficient colour removal.

Following is a result sheet of experiments using isopropanol with its extraction power increased by addition of water in different amounts and at different temperatures.

TABLE IV Moist-Heat Treated Pea Flour Aqueous Isopropanol Extraction (30 min: 1:10 solvent ratio) Hydration Capacity Product Product AACC By AACC Water Temp. Solution Product Yield Protein NSI Method 56-20 % (V/V) ( C) Colour Colour % % % % 0 82 yellow tan 94.5 66.5 60 211 10 80 orange white 91.8 68.8 59 318 10 70 orange white 92.3 69.3 60 304 10 60 yellow tan 92.6 67.9 59 237 10 40 yellow tan 92.7 68.9 59 232 10 22 yellow tan 93.1 68.3 61 218 15 80 orange white 98.6 69.7 43 250 15 70 orange white 98.8 69.9 58 299 15 60 light offorange white 98.9 67.7 60 278 20 80 orange white 89.7 70.2 21 304 20 60 light offorange white 90.5 69.2 55 262 20 40 pale orange tan 90.8 70.1 57 262 20 22 pale orange tan 90.9 69.9 59 259 30 80 light offorange white 85.7 71.3 14 369 30 60 light offorange white 86.2 70.4 28 351 30 40 pale orange tan 86.8 73.1 55 296 30 22 pale orange tan 87.5 72.3 59 276 50 80 pale orange tan 63.7 69.2 9 467 50 60 pale orange tan 71.4 68.8 12 427 50 40 pale orange tan 74.5 70.9 27 401 50 22 pale orange tan 76.8 70.1 45 339 Colour extraction was increased by raising the temperature, but high temperature extractions with aqueous organic solvents of increasing general extraction power mav lead to greater protein denaturation or lowered N.S.I. The N.S.I. of the starting pea protein flours for all of the foregoing extractions was about 6() and it is apparent that by arranging extraction conditions, pea protein flours debittered bv moist heat treatment can be decoloured without any significant further reduction in N.S.I.

A further sample of steam treated yellow pea flour containing 57' protein. having an N.S.I. value of 56 and a hydration capacity of 225% was solvent extracted for one half of an hour as in the cases of the above noted tests and the residual solvent removed. The results thereof are summarized in Tables V and VI which follow. In every case the end product was white or off-white, an acceptable colour.

TABLE V Moist-Heat Treated Pea Flour Aqueous n-propanol Extraction (30 min: 1:10 solvent ratio) Hydration Capacity Product Product AACC Bv AACC Water Temp. Yield Protein NSl Method 56-20 % (v/v) ( C) % % % % 10 60 92.6 6().X 56 315 15 60 91.4 61.4 54 328 20 60 89.8 62.4 44 323 10 70 92.2 60.6 56 324 15 70 91.1 61.4 39 342 20 70 89.6 62.6 20 341 20 80 89.1 63.0 15 345 TABLE VI Moist-Heat Treated Pea Flour Extractions with solvent mixtures (30 min: 1:10 solvent ratio) Hydration Solvent % Temp. Product Product AACC Capacity Composi- ( C) Yield Protein NSI By AACC tion % % % Method 56-20 % ethanol 100 70 91.3 61.6 54 324 ethanol/hexane 90/10 66 92.3 61.2 56 302 ethanol/toluene 90/10 70 91.9 61.0 56 325 ethanol/chloroform 90/10 70 91.9 62.2 51 334 ethanol/water 90/10 60 88.4 63.8 47 350 ethanol/hexane/water 80/10/10 60 89.4 61.8 50 320 ethanol/toluene/water 80/10/10 60 89.0 62.6 45 336 ethanol/chloroform/water 80/10/10 60 89.4 61.6 37 315 ethanol/water 80/10 60 87.9 62.4 44 309 ethanol/water 90/10 70 87.5 64.8 27 344 ethanol/hexane/water 80/10/10 62 89.1 63.0 40 292 ethanol/toluene/water 80/10/10 70 88.6 63.6 28 339 ethanol/toluene/water 70/20/10 70 89.6 63.6 22 325 ethanol/chloroform/water 80/10/10 70 88.5 64.0 21 354 ethanol/chloroform/water 70/20/10 65 89.8 61.6 20 334 ethanol/chloroform/water 60/20/20 65 86.7 65.0 13 358 ethanol/toluene/water 65/20/15 70 88.1 64.8 14 326 ethanol/methanol/water 80/10/10 70 87.2 64.6 26 330 ethanol/isopropanol/water 80/10/10 70 88.7 64.0 38 317 ethanol/acetone/water 80/10/10 70 88.2 65.2 32 322 ethanol/acetone/water 60/30/10 70 89.8 64.2 48 296 ethanol/acetone/water 45/45/10 66 90.9 62.2 56 310 ethanol/isopropanol/water 45/45/10 70 90.5 62.6 50 317 ethanol/n-butanol/water 45/45/10 70 91.3 61.0 40 303 ethanol/acetone/water 40/40/20 70 87.4 63.4 34 342 orange-brown colour when extracted with the solvents ol this invention did not develop an orange-brown colour upon subsequent heat treatment that would have developed an orange-brown colour had they not been colour extracted in accordance with this invention.

As indicated, extraction times are empirical. Sufficient contact time with the solvent and product is necessary to achieve the colour extraction. In most cases with agitation a time of about five minutes was found satisfactorv. While in most cases protein denaturation is rather insensitive to extraction time it is aiwavs best to avoid an extended extraction time.

It was also noted that the extraction processes according to this invention tended to remove bitter and pea flavours in raw flour and in flour that had been previously heat treated to remove bitter flavour.

In each case the residual solvent was removed from the product by a suitable method and in most cases heat and/or vacuum techniques were used. It has been found that the residual alcohol can be removed without reductions in N.S.l. and that it can be done at low temperatures (below 5() C) under vacuum. It can also be done at higher temperatures with similar effect. A particularly effective method of removing residual alcohol solvent is to use steam. It has been found that the N.S.l. of the alcohol extractive products of this invention are relatively insensitive to steam treatment. Steam treatment followinlr extraction does not result in the development of further orange-brown pigments and it is evident that the chemical precursors of the orange-brown pigments which develop on nonprocessed moist heat treatment have been removed by the alcohol extraction process described in this invention.

The class of alcohols found to be effectve is the C1, C2 or C3 monohydric alcohols, i.e. methanol, ethanol, isopropanol and n-propanol.

Claims (8)

WHAT WE CLAIM IS:

1. A method of removing orange-hrown colour causing constituents from yellow pea flour in the manufacture of a high protein pea flour wherein the flour is heat treated including the steps of extracting the flour with a solvent comprising an unsubstituted CI, C2 or C3 monohydric alcohol at a temperature above A()'C and not more than 3)C( water by volume to remove the brown colour causing constituents. and then removine the residual solvent from the flour.

2. A method of removing colour causing c)nstituent.s from yellow pea flour as claimed in Claim 1 in which the monohydric alcohol of said solvent comprises a mixture of two or more C1, C2 or C3 monohydric alcohols

3. A method of removing colour causing constituents from yellow pea flour as claimed in Claim 1. wherein the pea flour has previously been heit treated to cause it to have an orange-brown colour.

4. A method of removing colour causing constituents trom yellow pea flour as claimed in Claim 1. wherein the pea flour has not been previouslv heat treated to cause change of colour.

5. A method of removing colour causing constituents from yellow pea flour as claimed in Claim 2 wherein the pea flour has not been previ()uslx heat treated to cause change of colour.

6. A method of removing colour causing constituents from yellow pea flour as claimed in Claim 2 wherein the pea flour has previously been heat treated to cause it to have an orange-brown colour.

7. A method of removing orange-brown colour causing constituents from yellow pea flour, as hereinbefore described.

8. Pea flour produced in accordance with the method ot any of the foregoing claims.