Plant Foods for Human Nutrition

, Volume 65, Issue 3, pp 233–240

Antioxidant Capacity of Alcalase Hydrolysates and Protein Profiles of Two Conventional and Seven Low Glycinin Soybean Cultivars

  • Rudy Darmawan
  • Neal A. Bringe
  • Elvira Gonzalez de Mejia
ORIGINAL PAPER

DOI: 10.1007/s11130-010-0185-1

Cite this article as:
Darmawan, R., Bringe, N.A. & de Mejia, E.G. Plant Foods Hum Nutr (2010) 65: 233. doi:10.1007/s11130-010-0185-1

Abstract

Soy protein hydrolysates are considered a potential dietary source of natural antioxidants with important biological activities. This study was conducted to compare the effect of two conventional and seven low glycinin soybean cultivars on the antioxidant capacity (AC) of soy hydrolysates. Nine cultivars were grown in Bloomington, IL, Findlay, OH and Huxley, IA. The hydrolysates were produced enzymatically using alcalase and analyzed for AC using oxygen radical absorbance capacity (ORAC) assay and soluble protein. Statistical differences were observed in the protein profiles and AC among the different cultivars tested (P < 0.05). The hydrolysate from low glycinin cultivar 3 enriched in β-conglycinin, grown in Bloomington, exhibited the highest AC, compared to the other cultivars across all locations. On average, soy cultivars rich in BC and purified BC hydrolysates (36.2 and 31.8 μM Trolox equivalents (TE)/μg soluble protein, respectively) (P > 0.05) had higher AC than purified glycinin (GL) hydrolysate (28.5 μM TE/μg soluble protein) (P < 0.05). It was possible to select a soybean cultivar that produced a higher antioxidant capacity upon alcalase hydrolysis.

Keywords

Alcalase hydrolysis β-conglycinin Cultivar Growing location ORAC Soy peptide 

Abbreviations

AC

Antioxidant capacity

B

Bloomington IL

BC

β-conglycinin

F

Findlay OH

GL

Glycinin

H

Huxley IA

ORAC

Oxygen Radical Absorbance Capacity

TE

Trolox equivalents

Introduction

Research in bioactive compounds from agricultural products has increased due to a higher demand in natural supplements and functional and/or nutraceutical foods to manage chronic diseases. Soybean, in particular, has been commonly recognized as a natural, functional food ingredient with exceptional nutritional value. Its consumption is associated with lower risk of age-related chronic diseases such as obesity [1], hypertension [2, 3, 4, 5] and cancer [6]. Also, it has become an important agricultural commodity as shown by the growth in sales of soy products from $300 million in 1992 to $4 billion in 2008 [7].

Soy peptides produced from alcalase hydrolysis play a role in regulating body weight [8] and controlling lipid accumulation [9]. The postprandial antioxidant protection imparted by a significant increase in human serum antioxidant capacity was not detectable following acute consumption of 25 g soy protein [10]. However, the antioxidant capacity (AC) of soybean is improved when intact protein is hydrolyzed into peptides [11]. Upon hydrolysis, the amino acid residues are exposed, allowing them to assert strong AC. Several studies have demonstrated the AC of peptides derived from soy protein [11, 12, 13, 14]. Soy peptides have high oxidative inhibitory capacity due to their ability to scavenge free radicals and form a membrane around oil droplets, preventing the penetration of oxidation initiators [15]. Chen et al. [16] concluded that histidine-containing soy peptides could serve as metal-ion chelators, oxygen quenchers and hydroxyradical scavengers. In addition, enzymatic hydrolysis of a major storage soy protein, β-conglycinin (BC), with protease S produced an antioxidant peptide with specific sequence leucine-leucine-proline-histidine-histidine [12].

Cultivar, location and growing conditions play important roles in the production of bioactive compounds in agricultural crops. These parameters have been widely studied to optimize the AC of agricultural products such as berries [17, 18], wheat [19] and spinach [20]. Riedl et al. [21] studied the effect of cultivar and growing location on AC of isoflavone in soybeans. However, there are no studies regarding the effect of cultivars and growing locations on soybean with different protein profiles and AC of their hydrolysates. With the advancement in technology, soybean cultivars with different protein profiles can be selected to improve their biological activities [22, 23]. The objective of this research was to study the effect of conventional and low glycinin (GL) soybean cultivars on AC of peptides generated by alcalase hydrolysis. The cultivars were grown in three locations to identify cultivar (s) that have higher AC across multiple growing regions. In addition, the AC of soy hydrolysates were compared against purified BC and GL hydrolysates to determine if one of the major storage protein types contributes more to AC. The study then identified a specific soybean cultivar that showed high AC upon alcalase hydrolysis.

Materials and methods

Materials

Nine soybean cultivars [Glycine max (L.) Merr.] (two conventional and seven low glycinin) were developed and grown by the Monsanto Company (St. Louis, MO) in 2008 at three different locations: Bloomington, Illinois (B), Findlay, Ohio (F) and Huxley, Iowa (H). The planting dates for B, F and H were June 16th, May 24th and May 17th, respectively. The latitude and longitude global positioning system (GPS) coordinates for B were 40.45 and -89.15; for F 41.02 and -83.73; and for H 41.89 and -93.62, degrees. The plots at each location were two rows 4.5 m long with 76 cm between rows. The seeding rate was 24 seeds m-1. Huxley had fine-loamy, mixed, superactive, mesic Typic Endoaquolls; Findlay had a Hoytville clay (fine, illitic, mesic Mollic Epiaqualf), and Bloomington had Tama silt loam (fine-silty, mixed, superactive, mesic Typic Argiudoll). The seeds from each plot were harvested in bulk with a self-propelled plot combine (ALMACO, Nevada, IA). The numbering of the samples was the same as originally provided by the Monsanto Company and for consistency with other studies the same nomenclature was maintained. Sample number 4 was not available and therefore not provided for this study. A 30 g seed sample was analyzed by near infra-red transmittance with an Infratec 1,221 grain analyzer (Foss, Eden Prairie, MN) to determine protein (AOAC 990.03) [24], lipids (AOAC 2003.06) [24] and moisture (AOCS Ac. 2-41) [25] concentrations based on manufacturer instructions.

Fluorescein [3′,6′-dihydroxyspiro (isobenzofuran-1[3H],9′[9H]-xanthen)-3-one] was purchased from Fisher Scientific (Hanover Park, IL). AAPH [2,2’-azobis(2-amidinopropane) dihydrochloride] was purchased from Aldrich (Milwaukee, WI). Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2 carboxylic acid) and alcalase from Bacillus licheniformis (E.C. 3.4.21.62, 174 units/mg) was purchased from Sigma-Aldrich (St. Louis, MO).

Purification of β-conglycinin and glycinin from defatted soy flour

BC and GL were purified following previously reported protocol by Wang et al. [26].

Preparation of soy protein hydrolysates with alcalase

Defatted soybean flour, pure BC and GL were hydrolyzed with alcalase according to Vaughn et al. [8] with modifications. The pH of the liquid hydrolysates was adjusted to 7.0 before being filtered using stirred ultra-filtration cell (Millipore #5123 with 3 k Dalton (Da) membrane) to remove salts from the mixture.

Measurement of antioxidant capacity by the oxygen radical absorbance capacity (ORAC) assay

The ORAC assay was performed according to published methods by Prior et al. [27] and Davalos et al. [28]. Fluorescein reacted with free radicals generated by AAPH yielding a non-fluorescent product. Loss of fluorescence was measured over time in fluorescent plate reader, FLx800tbi (Bio-Tek, Winooski, VT), at 37 °C and sensitivity 60. Readings were made with excitation 485 nm and emission 528 nm. Then, the area under the curve (AUC) was calculated using the following equation:
$$ \begin{array}{*{20}{c}} {\hbox{AUC}}{ = 0.{5} + {f_1}/{f_0} + {f_{\rm{i}}}/{f_0} + \ldots + 0.{5}\left( {{f_{\rm{n}}}/{f_0}} \right)} \\{\hbox{Net AUC }}{ = {\hbox{AU}}{{\hbox{C}}_{\rm{sample}}} - {\hbox{AU}}{{\hbox{C}}_{\rm{blank}}}} \\\end{array} $$

Where AUC is area under the curve, f1 is fluorescence of first reading (2 min), f0 is fluorescence of reading time zero and fn are n fluorescence readings. The areas under these curves were then compared to a standard antioxidant, Trolox (vitamin E analog). Results were expressed as μM Trolox equivalents (TE), using the standard curve equation y = 0.18x + 0.58, R2 = 0.99.

Peptide mass mapping by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)

Soy protein hydrolysates were freeze dried in a FreeZone freeze dry system (Kansas City, MO). The hydrolysates (1 mg/ml) were analyzed by MALDI-TOF using an Applied Biosystems Voyager-DE STR (Foster City, CA, USA) for molecular mass peptide mapping. The following parameters were used in the analysis: linear mode of operation, positive polarity and 500–20,000 m/z scanning range.

Statistical analysis

The statistical analysis was conducted using SAS version 9.1.3 (SAS Institute Inc., Cary, NC, USA). The statistical difference was tested using two-way analysis of variance using the proc General Linear Models. For significant main effects, means were considered to be different at a significance level of 0.05. Data was expressed as means of at least three replicates. Principle component analysis (PCA) was conducted to detect important factors of variability and describe the relationship between variables and observations. Data were presented in terms of factor loading of the corresponding variables on the observed factors.

Results and discussion

Characterization of soybean cultivars

The major storage proteins present in soybean are trimer BC and hexamer GL which account for 50-70% of total seed proteins [29]. BC has a molecular mass of 150-200 kDa with three major subunits α, α’ and β [30]; whereas the molecular mass of GL is between 320-375 kDa with five major subunits A1aB2, A2B1a, A1bB1b, A5A4B3 and A3B4 [31]. Fig. 1a shows the gel with six major protein bands corresponding to BC subunits (α, α’ and β) ranging from 45 to 67 kDa and GL subunits (A1, 2, 3, 4, and basic chains) ranging from 20.5 to 38.5 kDa. The identities of these protein bands agreed with previously reported studies [9, 24, 32]. Cultivars 1F and 6F showed intense bands on A1,2,4 chain (35 kDa) and basic chain (20.5 kDa) of GL whereas the other cultivars had more intense bands on α chain (60 kDa) and α’ chain (65 kDa) of BC.
Fig. 1

a Protein profiles of soy flours from nine soy cultivars from Findlay (1F -3F and 5F -10F). Each sample was run on a 12% homogeneous Bis-Tris Criterion gel. The molecular mass markers (lane 1) consisted of myosin (139.9 kDa), β-galactosidase (103.6 kDa), bovine serum albumin (59.9 kDa), ovalbumin (41.4 kDa), carbonic anhydrase (27.4 kDa), soybean trypsin inhibitor (20.8 kDa), lysozyme (15.5 kDa), and aprotinin (6.6 kDa). b MALDI-TOF spectrum of cultivar 3F and c cultivar 9F hydrolysates from soybeans grown in Findlay using the following parameters: linear mode of operation, positive polarity and 500-20,000 Da scanning range.

In the present study, the total BC and GL content of all soybean cultivars ranged from 25.9 to 56.8% and 0.4 to 42.8%, respectively (Table 1). Cultivars 1 and 6 from three locations exhibited the highest total GL among the nine soybean cultivars. Growing location did not affect the protein profiles of the soybean samples (P > 0.05). Table 1 also shows the percent distribution of each protein subunit from the nine cultivars and three growing locations. Among different cultivars, GL subunits varied; for example A3 chain ranged between 0.0 and 6.9%; A1,2,4 chains between 0.4 and 19.2%; and basic 0.0 and 20.2% of total protein. Cultivars 2, 3, 7, 8, 9, 10 lacked the GL subunit A3, whereas cultivar 5 had the highest A3 subunit (~6.9%). Cultivar 6 had the highest content in A1,2,4 subunit of GL with approximately 19.2%. Basic GL content was the highest in cultivar 1 and 6 with about 19.3 and 20.2%, respectively. BC subunits also varied among cultivars, the range of α' was between 8.9 and 20.2%, α between 13.3 and 28.2% and β subunit between 3.6 and 13.4%. Cultivar 1, 5 and 6 had the lowest content in α' subunit of BC. The α subunit content was the lowest in cultivar 1, 5 and 6 except for 5B. Cultivars 5H, 9F, 10B and 10H had the highest content in β subunit of BC. These results demonstrated that the cultivars provided a distinct spectrum of subunit composition which allows a potential cultivar selection based on biological activities, such as AC.
Table 1

Protein subunit profiles of nine soybean cultivars grown in three different locations

Cultivar

Locationa

% BCb

% GLb

β-conglycininb

Glycininb

% α’

% α

% β

A3%

A1,2,4

% Basic

1

B

28.2

39.6*

9.7

14.8

3.8

3.1

17.3

19.3*

F

28.8

39.6*

9.3

14.3

5.1

3.6

17.0

19.0*

H

29.3

41.0*

9.5

14.8

5.1

3.4

18.5*

19.2*

2

B

50.4*

3.2

19.6*

25.8*

5.0

0.0

1.4

1.8

F

51.1*

5.0

19.6*

25.2*

6.3

0.0

2.3

2.7

H

52.6*

4.3

19.8*

25.4*

7.5

0.0

2.2

2.1

3

B

48.1*

4.0

18.4*

23.7*

6.0

0.0

1.7

2.3

F

51.4*

5.8

19.7*

24.1*

7.6

0.0

2.9

2.9

H

55.0*

5.5

20.2*

25.9*

9.0

0.0

2.8

2.7

5

B

49.4*

14.2

15.5

22.8*

11.1

6.3*

1.8

6.1

F

47.3*

16.9

15.6

21.1

10.6

6.9*

2.4

7.5

H

47.6*

17.8

15.0

21.0

11.7*

6.7*

2.9

8.3

6

B

25.9

41.6*

8.9

13.4

3.6

3.2

18.4*

20.0*

F

29.0

41.2*

9.6

14.4

5.1

3.7

18.5*

19.0*

H

26.1

42.8*

9.1

13.3

3.7

3.4

19.2*

20.2*

7

B

49.9*

4.3

18.0*

24.2*

7.8

0.0

2.1

2.2

F

56.3*

5.7

18.6*

28.2*

9.5

0.0

2.8

2.9

H

51.0*

5.0

18.1*

24.7*

8.2

0.0

2.3

2.7

8

B

51.8*

3.4

18.3*

24.0*

9.6

0.0

1.5

1.9

F

52.5*

1.5

18.7*

24.5*

9.2

0.0

0.5

1.0

H

53.5*

3.4

19.0*

24.3*

10.1

0.0

1.6

1.8

9

B

53.6*

4.2

19.1*

24.9*

9.7

0.0

2.0

2.2

F

52.8*

8.1

17.1*

23.8*

11.9*

0.0

3.9

4.3

H

54.3*

0.4

19.7*

25.7*

8.9

0.0

0.4

0.0

10

B

56.8*

6.2

18.9*

24.6*

13.4*

0.0

3.2

3.0

F

55.0*

3.5

19.0*

26.3*

9.6

0.0

1.4

2.1

H

52.4*

4.9

17.1*

22.9*

12.5*

0.0

2.7

2.2

* indicates highest values (P < 0.05)

aB Bloomington, F Findlay, H Huxley

bPercentage of total protein

Results are the average of three replications

Besides protein, soybean also contains significant amounts of lipids and fiber which increases its commodity value. The chemical composition of soybean seed depends on varieties and environmental conditions such as water stress and temperature [33]. The nine cultivars used in this study contained protein, moisture and lipid values between 36.4%–42.2%, 6.4%–8.8%, 17.8%–23.6%, respectively, as shown in Table 2. These values are comparable to previous study by Pringle [34] showing the average composition of protein, lipids and moisture to be 40.5%, 20.5% and 6.6%, respectively. BC and GL fractions of soy protein were isolated from different genotypes grown under the same environmental conditions, and it was found that the soy protein fractions were related to more than protein content, such as the amount and type of amino acid in the fraction [35].
Table 2

Effect of cultivar and location on chemical composition of soybean and antioxidant capacity of soy protein hydrolysates

Cultivar

Locationa

Soybeanb

Soy protein hydrolysatesc

% Protein

% Moisture

% Lipids

Soluble Protein

ORAC Value

1

B

37.1

8.0

23.6

18.0 ±1.7a

67.6 ± 4.3d,e,f,g

F

38.5

7.7

22.9

15.0 ± 0.3d,e,f,g,h

60.8 ± 2.1i,j,k

H

39.3

7.8

21.0

14.8 ± 1.0e,f,g,h,i

63.3 ± 2.1f,g,h,i,j,k

2

B

37.1

8.3

21.2

15.2 ± 0.3d,e,f,g

65.8 ± 5.5f,g,h,i,j

F

41.3

7.1

19.4

14.0 ± 0.0i,j,k,l

65.3 ± 0.9f,g,h,i,j

H

40.9

7.6

17.8

14.8 ± 1.2e,f,g,h,i

66.1 ± 3.2f,g,h,i,j

3

B

39.3

8.7

20.2

14.2 ± 0.3h,i,j,k

81.1 ± 0.5a

F

41.6

8.3

19.2

14.4 ± 0.6g,h,i,j,k

74.3 ± 5.1b,c

H

41.7

8.5

17.9

11.8 ± 0.6n

74.5 ± 2.1b,c

5

B

36.8

8.1

23.2

14.4 ± 0.0g,h,i,j,k

63.6 ± 6.8f,g,h,i,j

F

42.0

7.4

20.5

14.6 ± 0.0f,g,h,i,j

60.0 ± 3.5j,k

H

41.7

8.3

19.4

15.8 ± 0.3c,d

66.5 ± 4.3e,f,g,h,i

6

B

40.5

7.2

20.7

16.4 ± 0.3b, c

61.6 ± 7.5g,h,i,j,k

F

41.0

6.4

20.4

15.0 ± 0.7d,e,f,g,h

67.4 ± 0.5d,e,f,g,h

H

40.2

7.2

19.5

14.4 ± 0.3g,h,i,j,k

68.3 ± 3.8c,d,e,f

7

B

39.3

8.2

20.8

16.8 ± 0.6b

66.2 ± 5.1f,g,h,i,j

F

40.7

7.9

20.0

13.2 ± 0.0l,m

61.0 ± 5.2h,i,j,k

H

41.1

8.4

18.5

14.4 ± 0.7g,h,i,j,k

66.8 ± 4.7e,f,g,h,i

8

B

36.4

7.4

22.7

16.4 ± 0.7b, c

64.7 ± 4.8f,g,h,i,j

F

38.7

6.8

21.4

15.4 ± 0.9d,e,f

72.9 ± 3.8b,c,d,e

H

38.6

7.3

20.0

14.8 ± 0.0e,f,g,h,i

75.0 ± 5.9a,b

9

B

37.1

8.7

21.6

15.6 ± 0.6c,d,e

62.8 ± 2.1f,g,h,i,j,k

F

40.4

8.6

20.3

13.2 ± 0.6l,m

57.1 ± 1.6k

H

40.2

8.8

18.8

14.2 ± 0.0h,i,j,k

57.0 ± 2.9k

10

B

40.6

8.6

19.7

13.6 ± 0.3k,l

64.8 ± 4.2f,g,h,i,j

F

42.2

8.2

18.6

13.8 ± 0.0j,k,l

73.5 ± 7.0b,c,d

H

42.0

8.4

17.9

12.6 ± 0.3m,n

68.3 ± 2.7c,d,e,f

aB Bloomington, F Findlay, H Huxley

bResults from non-hydrolyzed soybean

cThe soluble protein and ORAC value of hydrolysate was expressed in μg per μL and μmol Trolox equivalents per gram of flour, respectively

The values mean, followed by the same letter(s) are not significantly different (P > 0.05)

Results are the average of three replications

Antioxidant capacity of soy protein, BC and GL hydrolysates

The benefits of dietary antioxidants have been well documented by the scientific literature [36]. The ORAC assay is widely used to determine AC in vitro by measuring the scavenging activity of peroxyl or hydroxyl radicals [26]. The assay also measures the degree of inhibition and inhibition time (to completion) before combining them into a single quantity using an area-under-the curve calculation [37]. The ability of protein to behave as antioxidants in radical-mediated oxidation reactions was attributed to their ability to trap free radicals [38]. Commercial soy-based foodstuffs were analyzed by peroxyl radical scavenging activity as determined by ORAC FL assay and found that it can be affected as a function of the intensity of the thermal processing [39]. The ORAC values and total soluble protein content of 27 soy protein hydrolysates are shown in Table 2. All hydrolysates showed notable AC which ranged from 57.0 to 81.1 μmol Trolox equivalents (TE)/g flour (P < 0.05). The hydrolysates from cultivar 3B showed the highest AC (81.1 μmol TE/g flour), followed by the cultivar 8H, 3H and 3F (75.0, 74.5 and 74.3 μmol TE/g flour, respectively). Cultivar 3 was then selected as a raw material for soymilk production to be used in a separate, on-going human study. The cultivar with the lowest AC was cultivar 9H and 9F with 57.0 and 57.1 μmol TE/g flour, respectively. As a comparison, Slavin et al. [40] measured the AC of non-hydrolyzed yellow soybean (genotypes MD 05-6073, MD 06-5433-1 and MD 06-5445-5) to have less than 40 μmol TE/g using ORAC assay. In addition, Xu et al. [41] reported the ORAC values of Proto (yellow), Korada (yellow) and Tofuyi (yellow) soybeans to be 36.9, 44.2 and 35.1 μmol TE/g, respectively. These proved that protease digestion of soybean enhanced antioxidant efficacy due to production of antioxidant peptides as supported by previous findings [11, 12, 13, 14]. Previous researches also recorded significant AC of non-soy protein hydrolysates and other dietary peptides [42, 43].

Cultivars 3F and 9F, which represented the cultivars with the most and least AC respectively, were further analyzed using MALDI-TOF-MS (Fig. 1b and c). The peaks were selected by spectrum intensity and cultivar 3F showed a distinct signal (100%) at m/z 3385. Gonzalez de Mejia et al. [44] reported this signal (3385 m/z) as a peptide fragment from BC. On the contrary, cultivar 9F showed a signal at 3385 m/z with only 40% intensity. In the future, isolation of this peptide will be necessary to explore its antioxidant mechanism. Cultivar 3F also presented an antioxidant peptide with a mass of 547 m/z with an intensity of 20%, whereas cultivar 9F did not exhibit any signal for this peptide. Our results are in agreement with Beermann et al. [13] who reported a peptide from BC with that specific signal to exhibit radical scavenging properties.

The average AC for all soybean cultivars and purified BC hydrolysates were not significantly different (36.2 and 31.8 μM Trolox equivalents/μg soluble protein, respectively) (P > 0.05). Purified GL hydrolysate had an AC of 28.5 μM TE/μg soluble protein which was significantly different than soybean hydrolysates (P < 0.05), although statistically similar to purified BC hydrolysate. One possible explanation was that BC was more susceptible to protease hydrolysis, increasing the production of peptides, in comparison to GL [45, 46]. Romagnolo et al. [47] stated that disulfide links, which connected acidic and basic subunits of GL, were buried in the interior part of molecules, decreasing protease hydrolysis reactions. In addition, the hydrophobic association and compactness of GL structure played a role in decreasing the rate of hydrolysis.

The current study showed significant effect of cultivars (P < 0.0001) on the AC of soy protein hydrolysates. Across all locations, the average AC in nine cultivars ranged from 59.0 ± 3.4 to 76.6 ± 3.9 μmol TE/g flour (P < 0.382). Although Huxley was wet all season whereas Findlay and Bloomington started wet and cool and ended dry with normal temperatures, growing location did not show a significant effect on AC. The average AC of hydrolysates from soybeans grown in Huxley, Bloomington and Findlay were 67.3 ± 6.1, 66.5 ± 6.6 and 65.8 ± 7.0 μmol TE/g flour, respectively. This was probably due to the fact that all experimental locations were in mid-western United States where the environmental conditions are not drastically different.

PCA was used to assess the effects of the soybean cultivar and growing location on the AC of alcalase hydrolysates and protein profiles of soybean cultivars. It is known in PCA analysis that an eigenvalue greater than 1 corresponds to a significant effect on a component (PC 1 = 4.8 and PC 2 = 1.2). The highest explained variance, PC 1, was associated to BC and GL subunits which accounted for 68.3% of explained variance, while PC 2 was associated with AC, with an explained variance equaled to 17.4% (Fig. 2). The two PCs accounted for 85.7% of the total variance explained. Cultivars 1 and 6 from all locations showed obvious separation along the positive side of the x-axis, while most of the other cultivars were on the negative side. The two cultivars were separated on the horizontal axis of PC 1 because of their high concentrations of GL subunits in comparison to the other cultivars. Cultivar 5 from all locations was located close to the center on PC 1 axis and did not appear to be dominated by either BC or GL subunits. The dispersion of soybeans along PC 2 axis was a function of AC. Cultivar 3 from all locations was loaded on the upper, positive-half of PC 2, indicating that this cultivar had the highest association with AC.
Fig. 2

PCA of nine soybean cultivars from three different locations. Loadings plots for the first two principal components and its respective percentage of variance. B = Bloomington; F = Findlay and H = Huxley

Conclusions

The study demonstrates the effect of cultivar, but not of growing location, on the soy protein subunit composition and AC of alcalase hydrolysates. The study suggests that it is possible to modify the protein profiles of soybean through breeding programs to produce hydrolysates with improved AC, which can then be used as natural supplements or functional food ingredients.

Acknowledgements

The authors thank personnel at the Monsanto Company for their support.

Conflict of interest

Neal Bringe declares that he works for The Monsanto Company.

Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Rudy Darmawan
    • 1
  • Neal A. Bringe
    • 2
  • Elvira Gonzalez de Mejia
    • 1
  1. 1.Department of Food Science and Human NutritionUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  2. 2.The Monsanto CompanySt. LouisUSA

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