Some Functional Properties of Rapeseed Protein Isolates and Concentrates

Some Functional Properties of Rapeseed Protein Isolates and Concentrates L. P. Kodagoda, S. Nakai and VV. D. Powrie Department of Food Science University of British Columbia Vancouver 8, B.C.

Abstract Protein isolates and concentrates obtained from rapeseed flour by a successive water, HCI, and NaOH extraction process were subjected to baking, emulsification, and whipping tests. In baking, a 5% replacement of wheat flour with rapeseed protein isolates and concentrates decreased loaf volume by 10 t:J 15% and 20%, respectively. Addition of .5% emulsifier (Atmul 124) restored loaf volume to most breads: 10 to 15% larger loaf volume for the water and HCl extracted isolate breads than the all-wheat control; 8% inferior loaf volume for the protein concentrate breads except for the NaOH extraded concentrate (12% larger loaf volume). Whipping tests with 3% replacement of egg white protein by isolates or concentrates generally resulted in a decreased specific volume compared to the all-egg white control. An exception was the HCl extracted isolate with a 10% larger specific volume than the control. All fractions improved foam stability; particularly, meringues containing the water extracted isolate showed no sign of drip for 1.5 h. The water extracts displayed highest emulsification capacity; 45 ml of corn oil per 100 mg of protein in the isolate compared to approximately 35 ml for other fractions. Emulsions containing the HCl extract showed remarkable stability: 200 min compared to 3 min for the control. No significant correlation was observed between the solubility of rapeseed protein nroducts and their functional properties.

Resume Les isolats et concentres de proteines obtenus de la farine de colza par un procede d'extraction en trois etapes successives a l'eau, a l'acide hydrochlorique et a l'hydroxyde de sodium ont ete soumis a des epreuves de cuisson, d'emulsification et de fouettement. A la cuisson, une substitution de 5% de la farine de bIe avec des isolats et concentres de proteine de colza ont diminue le volume du pain par 10 a 15% et 20%, respectivement. L'addition de 0.5% d'emulsif (Atmul 124) a restitue le volume de la plupart des pains. Les volume~ des pains contenant des isolats de farine de colza extraits a l'eau et a l'acide hydrochlorique ont ete 10 a 15% plus forts que celui des pains faits entierement de farine de bIe. Ceux des pains contenant des concentres de proteines extraits a l'eau et a l'acide ont ete 8% plus faibles, tandis qu'avec le concentre extrait a la soude, le volume des pains a ete 12% plus fort. Les epreuves de fouettement ont demontre qu'en remplal;ant 3% des prott§ines de blanc d'oeuf par des isolats ou concentres le volume specifique a ete moindre, sauf dans le cas de l'isolat extrait a l'acide aui a produit un volume specifique 10% plus fort que celui du temoin. Toutes les fractions ont ameliore la stabilite de I'ecume, particulierement pour les meringues contenant de l'isolat extrait a l'eau lesquelles n'ont montre aucun indice de degouttement pendant 1.5 h. Les extraits a I'eau ont montre la capacite d'emulsification la plus elevee soit 45 ml d'huile de mals par 100 mg de proteine dans l'isolat comparee it 35 ml pour les autres fractions. Les emulsions contenant de I'extrait acide ont montre une stabilite remarquable soit 200 min. comparee a 30 min. pour le temoin. Aucune correlation significative n'a ete observee entre la solubilite des produits de proteine de colza et leurs proprietes fonctionnelles.

Introduction Compared to soybean proteins, rapeseed proteins have not been extensively utilized for food supplementation. Before such application be made, thorough Can. Inst. Food Sel. Teehnol. J. Vol. 6, No. 4, 1973

investigation of functional properties of rapeseed protein fractions must be conducted in comparison to studies with soy protein products. Alcohol-washed soy proteins produced stable lowdensity foams similar to egg white (Eldridge et al.) 1963). In baking, adding up to 1% of unheated soy flour to dough increased loaf volume as reported by Pollock and Geddes (1960). Sroybean protein supplementation of bread improved the nutritional value in terms of amino acid balance (Ehle and Jansen, 1965) . Pearson et al. (1965) found that sodium soy proteinate did not improve meat emulsions in the usual pH range. Swift et al. (1961) stated that the participation of water soluble protein in emulsion formation is dependent on added sodium chloride and that the amount of oil emulsifier per mg of salt soluble protein increased as the total amount of protein in solution decreased. Sheikh et al. (1970) used rapeseed protein concentrates for preparation of enriched bread containing higher protein, calcium and iron. However, no reference was made to physical properties of this rapeseed-protein containing bread. In this paper we report results of laboratory scale experiments to determine functional properties of different rapeseed protein concentrates and isolates separated by the three stage extraction process reported earlier by Kodagoda et al. (1973) . The abbreviations, PW, PA, PB, and PS, are for the protein isolates from the first stage water extract, the second stage HCI extract, the third stage NaOH extract and from the single stage NaOH extract, respectively. The letter C replaces P for the corresponding protein concentrates. PAl and PA2 were precipitated at pH 3.6 and subsequently at pH 7.0.

Experimental Preparation of microloaves (the ten-gram baking method) Bread was prepared according to the method of Shogren et nl. (1969) with modifications. Rapeseed protein isolates or concentrates were incorporated into wheat dough at a level of 5% with .5% Atmul 124 (A mono- and diglyceride mixture containing 52 to 56% alpha-mono- and 61 to 66% total monoglycerides. Atlas Chemical Industries) and the dough was mixed Ly hand for 2.5 min. After fermentation, the dough was punched and proofed before baking at 210°C for 10 min. The baked microloaves were removed immediately from the metal pans and cooled on a wire mesh. One hour after baking, the microloaves were weighed and the loaf volumes measured by dwarf rapeseed displacement. 266

Crust colour was determined by the method of Ehle and J ansen (1965). Dry crust was removed by scraping, ground, and extracted with 50% ethanol by mechanical shaking for 4 h. Absorbance of the supernatant was determined at 460 nm after centrifugation. Determination of emulsifying capacity The method of Swift et al. (1961) was used with modifications. Samples (100 mg) of isolates or concentrates in 30 ml of IN NaCl were heated at 80°C for 5 min and blended in an Omni-mixer (Ivan Sorvall, Inc., Norwalk, Conn.) at 1,000 rpm for 2 min. After adding 20 ml of corn oil, cutting and mixing at 13,000 rpm was repeated for 30 sec. Further addition of oil was continued at a rate of .8 ml per sec until the emulsion broke and the phase transition occurred. Emulsifying capacity was reported as ml oil added to 100 mg protein isolate or concentrate. Stability test for emulsions The procedure was similar to that of Pearson et al. (1965). The optimum level of oil (5% less than the emulsifying capacity) was added to 100 mg of protein isolate or concentrate in 30 ml of IN NaCl and blended at 13,000 rpm for 2 min. The emulsions were then transferred to 15-ml graduated cylinders and filled to the 12-ml mark. The destabilization time was reported when phase separation occurred.

Determination of whippability Performed as described by Garibaldi et al. (1968). Sixty grams of fresh egg albumen were whipped at a [Speed setting of 10 in a Sunbeam Mixmaster for 40 sec. Rapeseed protein isolates or concentrates (.25 g diluted with 46 g of sucrose) were added to the mixer in three equal portions and whipped for 4 sec at a setting of 6 after each addition. The control was treated in the same manner without rapeseed proteins. Specific volume as a measure of expansion of the whip was calculated from the weight of the meringue in a funnel of known volume. Drip was reported for 1.5 h at a 30 min interval. Solubility Forty milligrams of protein isolates or concentrates in 30 ml of water were stirred manually with a glass rod or by blending under the same conditions as the emulsifying capacity test except that no corn oil was added. Kjeldahl N was determined in the supernatant after centrifugation at 27,000 x g for 30 min. Nitrogen solubility index (NSI) as defined by Paulsen et al. (1960) was also determined. A Lourdes Model MM-lA Multimixer set at the 100 mark was used for this test to blend 30 mg of isolates in 20 ml of water for 10 min. Kjeldahl N of the supernatant was then analyzed after centrifugation at 1,400 x g for 10 min.

Results and Discussion Baking tests Preliminary baking experiments revealed that bread containing 5% rapeseed protein isolates and concentrates decreased loaf volume by 10 to 15% and by approximately 20%, respectively. Atmul 124 at .5% level restored loaf volume to isolate containing breads hut not to those containing concentrates. ::67

Table 1. Loaf volume of bread and the colour of bread crust containing 5% rapeseed protein isolates. 1 Protein isolate

Loaf volume (ml) 56 58 50 50 51

F\V

PAl PB PS Control

b

a c c c

Absorbance at 460 nm .04 .04 .07 .04 .03

'a' 'b' and 'c' are three groups significantly different at the co~fidence limit of 99% (Duncan's multiple range test). 1 Atmul 124, .5% was added to doughs except the control.

As shown in Table 1, breads containing 5% protein isolates of either water- or HCl-extracts with a supplementation of Atmul 124 yielded a 10 to 14% larger loaf volume than the control. The large loaf volume obtained for the HCl extracted isolate (PAl) may be due to the basic nature of the protein fraction, which increases electrostatic interactions in dough protein (Jones and Carnegie, 1971). Loaf volume of breads from the NaOH isolates (PB and PS) was not significantly different from that of the control. Whole and cut micro}oaves containing isolate fractions are illustrated in Figures la and b. Loaf volume of concentrate containing breads was 8% inferior even after Atmul 124 supplementation except for a 12% superior loaf volume of concentrate CB containing bread (Table 2). This increase could be due to the presence of lipid material including glycolipids (Pomeranz et al., 1969). The solubility of concentrates CW, CA, and CB was 77, 80 and 71%, respectively, indicating no correlation with loaf volume. Figures 2a and b illustrate the whole and cut microloaves containing rapeseed protein concentrates. The effect of protein concentration on loaf volume and crumb 0010ur is shown in Figures 3a and b. The microloaf containing 1 % protein isolate PS had the largest loaf volume. At supplementation levels higher than 6% darkening of the crumb was observed. Crust colour of isolate or concentrate containing bread was slightly darker than that of the control. The values obtained from isolate PB and concentrate CB were about three times greater than that of the control ('rabIes 1 and 2). Emulsification As shown in Table 3, isolate PW revealed an «pproximately 28% higher emulsifying capacity than other isolates. Emulsifying capacity of concentrates was approximately 25% lower than that of their corresponding isolates. Emulsions containing isolate PA Table 2. Loaf volume of bread and the colour of bread crust containing 5% rapeseed protein concentrates.! Protein concentrate CW

CA CB CS Control

Loaf volume (ml) 48 47 57 47 51

c c a c b

Absorbance at 460 nm .03 .035 .06 .04 .C25

a, 'b', and 'c' are three groups significantly different at the confidence limit of 99% (Duncan's multiple range test). 1 Atmul 124, .5% was added to doughs except the control. J. Inst. Can. Sci. Technol. Aliment. Vol. 6, No 4. 1973

Fig. la and b. Microloaves baked from rapeseed protein isolates. From left to right, bread containing W: isolate PW, A: isolate PAl, B: isolate PB, S: isolate PS and C: the control. 5% of wheat flour was replaced with each protein isolate. Atmul 124 (.5%) was added to doughs except the control. Top row, whole loaves; bottom row, cut loaves.

Fig. 2a and b. Microloaves baked froIr. rapeseed protein concentrates. From left to right, bread containing W: concentrate CW, A: concentrate CA, B: concentrate CB, S: concentrate CS and C: the control. Top row, whole loaves; bottom row, cut loaves. Atmul 124 (.5%) was added to doughs except the control.

and concentrate CA were most stable (200 min). Emulsions from the rest of the protein fractions collapsed in 6 to 10 min compared to 3 min for the control. Addition of is'olate PAl increased specific volume of whipping egg albumen by 10% while othee isolates decreased it by approximately 16%. This property of FA may again be due to the basic nature of its protein. Concentrates decreased specific volume from 2 to 19% when compared to the control (Table 4). During the first 30 minutes drip was negligible for all is'olates and concentrates except CS and PS. Ninety minutes after whipping all fractions except PW showed drip volume of ~ to 3.? ml.. Isolate PW showed no sign of drip durmg this perIOd, whereas the drip volume of the

control was 4.5 ml. In general, concentrate containing meringues showed higher drip volumes than did those containing isolates. Solubility of rapeseed protein isolates and concentrates was determined (Table 5). For soy flour and grits correlations have been reported between functional characteristics and the nitrogen solubility index (J ohnson, 1970). However, in the case of rapeseed protein isolates, solubility cannot explain all of the functional differences observed in this study such as largest loaf volume for isolate PAl (Table 1), highest emulsi,fying capacity of PW along with highest stability by PAl (Table 3), and lowest drip of PW containing whipped meringue. The loaf volume improvement, the emulsion stabilizing ability and the whipping capacity of the

Table 3. Emulsifying capacity and stability of the protein isolates and concentrates (the average of duplicate runs).

Table 4. Whipping property of the protein isolates and concentrates (the average of duplicate runs).

Whippability

Sample PW PAl PB PS CW CA CB CS Control

Emulsifying capacity (ml ccrn oil/WO mg)

Emulsion stability (min)

45.3 36.3 32.4 37.3 33.2 27.5 25.1 29.5

Can. Inst. Food Se!. Teehno!. J. Vo!. 6, No. 4, 1973

10 200 8

e.5

7.5 200 7 6.5

3

D:ip (m1) Samp:e PW

PAl

PB PS

CW CA CB CS Control

Specific volume 2.94 3.75 2.82 2.89 2.76 3.33 3.17 3.31 3.39

0.5h

1.0h

1.5 h

0 0 .3 1.0 0 .2 0 1.0 1.0

0

0 1.0 1.8 2.7 2.6 3.5 1.6 3.2 4.5

.6 1.0 1.8 1.5 2.1 1.0 2.0 2.1

268

HCI extracted isolate PAl may be due to the charac_ teristic basic properties of this protein fraction. Solubility improvement of other protein isolate in the same fraction (P A2) remains for future studies.

Acknowledgement 'We are grateful for the technical assistance of Miss H. Berekoff in the establishment of the baking procedure.

References

Fig. 3a and b. Microloaves baked from single stage NaOH-extracted isolate (PS). From left to right, bread containing 1, 2, 4, 6, 8, and 10% protein isolate and the control. Top row, whole loaves; bottom row, cut loaves. Tab!e 5.

Solubility (%) of the protein isolates and concentrates (the average of duplicate runs). Manual stirring

Blending

NSI

PW PAl PA2

59 49

47 46

PS

42 43

49 34

95 87 <12 98

CW CA CB CS

77 80 71 48

50 91 47 53

Sample

PB

2G9

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J. Inst. Can. Sc!. Technol. Aliment. Vo!. 6, No 4, 1973