influence of acidity regulators on the stability of a

copy 2017 Japan Society for Food Engineering

Influence of Acidity Regulators on the Stability of a Soymilk Colloidal Dispersion System

Kanako SATO1 Shiori IDOGAWA12dagger Tomoyuki FUJII2

1 Taishi Food Inc 51-1 Shinden Furukawashimizu Osaki Miyagi 989-6228 Japan2 Graduate School of Agricultural Science Tohoku University

468-1 Aramaki Aza Aoba Aoba-ku Sendai Miyagi 980-0845 Japan

To elucidate the influence of acidity regulators on stability using a soymilk colloidal dispersion system a viscous model was constructed and its effectiveness was verified When the pH of soymilk was reduced using ascorbic acid the apparent viscosity of all soymilk increased significantly at approximately pH 58-59 this was found to be a universal phenomenon in the soymilk colloidal dispersion system When the pH decreased after addition of six types of acidity regulators to soymilk the apparent viscosity behaviors of the samples were similar Assuming that the bulkiness of the aggregate was proportional to the hydrogen ion concentration in the high pH range calculations were made by applying the extended equation obtained from the viscosity equation of Einstein and the Krieger-Dougherty equation A negative correlation was confirmed with the parameter hc representing the degree of bulkiness of the aggregate and the parameter Kc representing the degree of filling state of the gigantic aggregate Moreover the macroscopic aggregation behavior was similar even if the internal structure of the isolated aggregates dif fered depending on dif ferences in the crosslinking mechanism Because of the correlations between parameters this system for soymilk processing may have industrial applicationsKeywords soymilk pH colloidal dispersion system stability aggregation

Original Paper

1Introduction

Soymilk is a colloidal dispersion system in which pro-

tein particles and lipids are dispersed in a dissolved pro-

tein solution [1] Lipids exist as oil bodies consisting of

triacylglycerols whose surface is covered with phospho-

lipids and oleosin [2-4] The oil body extracted by grind-

ing the swollen soybean has proteins and cell wall com-

ponents adhering to surface of the oil body Then depos-

its such as protein are dissociated by heating and the oil

bodies are dispersed in soymilk as colloidal particles of

several hundreds of nanometers [5] The oil bodies in

soymilk are thought to prevent coalescence of oil bodies

due to the presence of oleosin as a result soymilk

becomes a stable colloidal dispersion system [6-8]

Thus it is necessary to elucidate the colloidal character-

istics of soymilk whose consumption is increasing in

Japan to improve and stabilize soymilk production and

develop novel soymilk processed products

In soymilk acids are generally used for food process-

ing based on their induction of gel-like coagulation by

addition to soymilk However the stability of colloids var-

ies depending on multiple factors such as pH heat elec-

trolytes and organic matter content [9-11] By evaluat-

ing the viscosity it thus becomes possible to quantita-

tively observe and evaluate the stability of colloids such

that it can be used as an indicator of the variation of daily

production and the quality control of the product at the

manufacturing site In a previous paper we evaluated pH

as a factor controlling stability and found that the appar-

ent viscosity and colloidal stability of soymilk were rap-

idly altered as the pH decreased due to addition of ascor-

bic acid solution [12] Thus the component composition

in soymilk was thought to affect the pH at which a rapid

viscosity increase occurred however the mechanisms

through which aggregation involving oil bodies and pro-

teins occurs have not yet been determined To clarify the

characteristics of soymilk colloid aggregation accompa-

nying a decrease in pH it is necessary to elucidate the

mechanism from the stage at which the soymilk particles

exist in an isolated state until the particles gather and

produce gigantic aggregates with a filled state or gel

The characteristics of acrylamide and agarose have been

studied extensively during gelation [13-15] and cross-

linking aggregation and coagulation are often observed

(Received 5 Apr 2017 accepted 17 Sep 2017)

daggerFax 0229-36-1702 E-mail s-itonotaishi-foodcojp

J-STAGE Published online on 17 Nov 2017

Japan Journal of Food Engineering Vol 18 No 4 pp 177 - 184 Dec 2017 DOI 1011301jsfe17491

Kanako SATO Shiori IDOGAWA Tomoyuki FUJII178


in many food manufacturing processes [16 17]

However few models have been developed to quantita-

tively describe the changes in viscosity accompanying

aggregation in foods characterized as multicomponent

dispersions

In soymilk oil bodies can be regarded as spheres cov-

ered with oleosin and if the size is sufficiently small the

oil bodies behave like rigid spheres in the dispersion

phase [18] Most of the proteins present in the continu-

ous phase in soymilk are globulin proteins mainly 11S

globulin (glycinin) and 7S globulin (β-conglycinin)

Each globulin is an association of subunits and the iso-

electric points of the proteins differ depending on the

subunits or polypeptides [19] Therefore depending on

the pH the surface potential of the protein changes and

the amount of protein participating in aggregation may

increase or decrease

In this study we hypothesized that aggregates were

formed because of the decrease in protein solubility as

the pH of soymilk decreased and approached the isoelec-

tric point of protein contained in soymilk Thus we con-

structed a viscous model combined with the extended

Einstein equation and the Krieger-Dougherty equation

and experimentally investigated the validity of the model

2Theory

A viscosity model combining Einsteinrsquos viscosity equa-

tion and Krieger-Doughertyrsquos viscosity equation was pre-

viously developed to analyze the viscous behavior of the

process of colloidal coagulation with a crosslinking agent

[20] In a system in which the rigid spheres are dis-

persed if the relative viscosity in the diluted state is ηr

and the volume fraction of the dispersed phase is φ the

following Einsteinrsquos viscosity equation [21 22] can be

established

ηr＝1＋25φ (1)

Einsteinrsquos viscosity theory is limited to the case in

which φ is suf ficiently small because hydrodynamic

interactions between dispersoids are not considered

Given that bulky aggregates are formed by adding an

acidity regulator under conditions of low pH and assum-

ing that the increase in the effective volume fraction

from the formation of aggregates is proportional to the

hydrogen ion concentration Einsteinrsquos viscosity equation

can be extended as follows

ηd＝1＋25timeshctimesC (2)

where hc denotes the bulkiness of the colloidal aggre-

gates and C denotes the hydrogen ion concentration

Furthermore under conditions of high pH assuming

that the bulkiness of the aggregates is proportional to

the hydrogen ion concentration the Krieger-Dougherty

equation [23] is expanded as a viscous model applicable

to the concentrated dispersion system and the following

equation is obtained

ηd＝(1－KctimeshctimesC )-25Kc (3)

where Kc is the reciprocal of the closest packing ratio of

the disperse phase and is a parameter of the bulkiness of

the gigantic aggregate in the closest packed state

3MaterialsandMethods

31 Materials

The soybeans used in this study were produced in

America Canada Hokkaido Aomori Iwate and Miyagi

Soymilk was provided by Taishi Food Inc (Aomori

Japan) The moisture content was determined by micro-

wave drying (SMART TURBO CEM Japan KK Tokyo

Japan) and the protein content was determined by the

improved Dumarsquos method using a nitrogen analyzer

(SUMIGRAPH NC-220F Sumika Analysis Chemical

Service Ltd Tokyo Japan) The lipid content was deter-

mined by nuclear magnetic resonance (NMR SMART

TRAC CEM Japan KK) [24] The results are shown in

Table 1

Lactic acid malic acid hydrochloric acid ascorbic

acid citric acid and phytic acid (Wako Pure Chemical

Industries Ltd Osaka Japan) were used as acidity regu-

lators The concentration of each acidity regulator was

028 M

32 Measurementofviscosity

Soymilk heated to 25 was adjusted to pH 56-62 by

adding an acidity regulator The apparent viscosity η of

Table 1 Water protein and lipid contents of soymilk samples

Water[]

Protein[]

Lipid[] Harvest area

A 884 49 29 Miyagi Japan

B 890 51 30 USA

C 880 55 35 Canada

D 876 53 30 Hokkaido Japan

E 891 51 26 Aomori Japan

F 886 53 26 Iwate Japan

Soymilk stability 179


soymilk was measured with a cone plate viscometer

(TPE-100 Toki Sangyo Co Tokyo Japan) at 25 using

a 1deg34primetimesR24 rotating cone at a shear rate of 1915 s-1

Soymilk was applied to the viscometer 30 seconds after

the addition of an acidity regulator and the value after 30

seconds from the start of measurement at a shear rate of

1915 s-1 was adopted The dimensionless viscosity

ηd was defined as the value obtained by dividing the

apparent viscosity η by the viscosityηc0 of the soymilk

before adding the acidity regulator

33 Calculationoftheviscosityparameter

The concentration of hydrogen ions contained in soy-

milk was calculated from the pH of soymilk Viscosity

parameters were obtained by applying a viscosity equa-

tion to measured values of the hydrogen ion concentra-

tion and dimensionless viscosityηd and fitting by a least

squares method (Office Excel 2002 Microsoft Co)

4ResultsandDiscussion

41 Changesinviscosityofsoymilkwith

decreasedpH

The change in the apparent viscosity of the six types of

soymilk when the pH was reduced with ascorbic acid is

shown in Fig 1 As the pH decreased the apparent vis-

cosity increased slightly up to approximately pH 60

When the pH was lower than 60 the apparent viscosity

increased gradually and when the pH was lower than 59

the apparent viscosity increased exponentially The soy-

milk from Miyagi prefecture (Soymilk A) showed an

acidic shift of 01 in pH Thus the apparent viscosity was

increased slightly to approximately pH 59 and a sharp

increase was confirmed when the pH was lower than pH

58 Although there was a difference in the degree of

change in viscosity depending on the type of soymilk the

increase in apparent viscosity when adding ascorbic acid

was a universal phenomenon in the soymilk colloidal dis-

persion system regardless of the variety of soymilk In

particular regarding the point of pH deviation in the vis-

cosity change in Soymilk A the possibility that the com-

ponent content influenced the viscosity (Table 1) was

examined based on a report showing that the lipid and

protein contents of soymilk affected the pH at which the

viscosity change was observed when ascorbic acid was

added to soymilk [12] and another report showing that

the solid concentration influenced the viscosity of the liq-

uid food [25] However no correlation between ingredi-

ents and viscosity was observed before the ascorbic acid

solution was added Proteins in soybeans have been

shown to differ in terms of the proportions of globulin-

containing protein in soymilk composed of different vari-

eties of soybean [26] As the pH decreases to near the

isoelectric point of the protein the structure of the pro-

tein can change and the protein may become insoluble

[19] Therefore differences in isoelectric point between

globulin proteins may affect changes in viscosity in dif-

ferent types of soymilk Because ash phosphorus and

potassium have been reported as soymilk components

[27] the pH decrease may also be affected

42 Analysisofchangesinviscosity

accompanyingthedecreaseinpHusing

differentacidityregulatorsandevaluation

ofviscositybehaviorsofpH-dependent

aggregationsystemsbytheextended

Krieger-Doughertyequation

Changes in viscosity with decreases in pH following

addition of six types of acidity regulators in soymilk pre-

pared from American whole soybeans (Soymilk B) are

shown in Fig 2 As observed following addition of ascor-

bic acid to the six types of soymilk the apparent viscosity

increased slightly as the pH decreased until reaching a

pH of approximately 60 and the viscosity increased

sharply when the pH was lower than 59 When lactic

acid was added the viscosity increased rapidly after the

pH was below 59 In the system in which other acidity

regulators were added the pH at which the apparent vis-

cosity exceeded 50 mPas was approximately pH 57 or

less however in the case of lactic acid this value was

slightly higher at pH 58 In addition the change in

apparent viscosity was slightly lower when phytic acid Fig 1 Apparent viscosities of the six types of soymilk

after addition of ascorbic acid



solution and citric acid solution were added At approxi-

mately pH 59 there was almost no increase compared

with the apparent viscosity before addition of phytic acid

or citric acid and a rapid viscosity increase was observed

beginning at approximately pH 57 These results may be

explained by the chelating action of phytic acid and citric

acid [28] Aggregation of soymilk was caused not only by

the pH decrease but also by divalent cations [29] In

addition soybeans contained many minerals and soy-

milk also contained magnesium ions and calcium ions

[30] In particular phytic acid combined with calcium

and magnesium has been shown to affect the onset of

aggregation [31] The chelation of magnesium ions by

phytic acid and citric acid may suppress the onset of

aggregate formation as a result the apparent viscosity

may gradually increase

For each of the six types of acidity regulator the rela-

tionship between the concentration of hydrogen ions

contained in soymilk and the measured value of dimen-

sionless viscosityηd is shown in the plot in Fig 3 From

these results the viscosity parameter was calculated by

fitting to the extended Einstein equation and Krieger-

Dougherty equation (Eqs 2 3) When analyzing the vis-

cosity change accompanied by the pH decrease we con-

sidered that the charge state of the protein changed as

the soymilk pH decreased ie as the hydrogen ion con-

centration increased and bulky aggregates were formed

to increase the viscosity Therefore we attempted to ana-

lyze the viscosity change using the variable C of the

extended Krieger-Dougherty equation as the hydrogen

ion concentration First in the range in which the hydro-

gen ion concentration was low fitting was performed on

the first equation of the extended Einstein equation (Eq

2) and measured values to find hc Next for all measured

values including the range with high hydrogen ion con-

centrations we fitted the second equation (Eq 3) of the

extended Krieger-Dougherty equation to obtain Kc The

obtained parameters hc and Kc are shown in Table 2 hc

was within the range of approximately 32times103 to 105times

103 M-1 for each type of acidity regulator and Kc was

within the range of approximately 4 to 18 The values

described from the extended Krieger-Dougherty equa-

tion using the hc and Kc values in the system of each pH-

adjusting agent are shown by solid lines in Fig 3 As a

result the solid line was almost near the plot of the mea-

sured value and the measured value could be described

well hc represents the bulkiness of the aggregate larger

hc values were associated with bulkier aggregates Kc

indicates the filling state of the gigantic aggregate

formed by agglomerates gathering and the reciprocal of

the maximum particle packing ratio As the value of Kc

increased the agglomerates were not densely packed

ie the bulkiness of the gigantic aggregate was high

Because the hc of citric acid was the largest of the six

acidity regulators citric acid was thought to significantly

enhance the aggregation in soymilk The molecular

weight and acid dissociation constant of the acidity regu-

lator are also shown in Table 2 but correlation with the

hc value was not found As the soymilk pH decreased the

charge state of the protein changed to form aggregates

However because the proteins contained in soymilk dif-

fered in their isoelectric points proteins participating in

aggregation seemed to change as the pH changed

However we found that one equation (Eq 3) could

describe the viscous behaviors of the soymilk aggrega-

tion system quite well due to the continuous pH decrease

accompanying the addition of the acidity regulators

Furthermore the system assumed that aggregate forma-

tion would progress with an increase in viscosity

Fig 2 Apparent viscosities of Soymilk B after addition of each acidity regulator

Table 2 The viscosity parameters hc and Kc and molecular weight (MW) and acid dissociation constant (pKa) for each acidity regulator

Acidity regulators hc

[times103 M-1]Kc

[-]MW[-]

pKa[-]

Lactic acid 775 79 901 39 [32]

Malic acid 829 70 1341 34 [32]

Hydrochloric acid 712 79 55 -80 [33]

Ascorbic acid 328 182 1761 41 [32]

Citric acid 1052 45 2101 31 [32]

Phytic acid 740 62 6600 19 [34]



43 Relationshipbetweenparametersh cand

Kcintheaggregate-formingsystemdueto

thepHdecrease

The relationship between the viscosity parameters hc

and Kc obtained from the viscosity measured using six

types of soymilk and six acidity regulators is shown in

Fig 4 A negative correlation was found and the coeffi-

cient of determination (R2) was as high as 097

Fig 3 Dimensionless viscosities (ηd) of soymilk plotted against the concentration of hydrogen ions after addition of lactic acid (a) malic acid (b) hydrochloric acid (c) ascorbic acid (d) citric acid (e) and phytic acid (f) The solid line shows the viscous model combining the extended Krieger-Dougherty equation



Therefore these data suggested that as the size of the

aggregate produced in the high pH range above approxi-

mately pH 60 increased the agglomerates became

denser and the bulk became smaller In contrast as the

size of the aggregate decreased bulky aggregates

became more bulky Additionally because the data were

plotted on the same curve regardless of the type of acid-

ity regulators even if the internal structure of the iso-

lated aggregate differed depending on the difference in

crosslinking mechanism the macroscopic aggregation

behaviors were thought to be similar

Even when coagulating with a crosslinking agent such

as magnesium chloride a negative correlation between

hc and Kc is obtained in previous work [20] In crosslink-

ing aggregation the interaction between colloidal parti-

cles is electrostatic interaction On the other hand in

acid aggregation physical interaction such as hydropho-

bic interaction is mainly The interactions acting between

colloidal particles in both are different As shown in Fig

4 the same tendency was observed even when acid

aggregation with hydrogen ion concentration as a vari-

able strongly suggesting that macroscopic aggregation

mechanism is similar in both acid aggregation and cross-

linking aggregation

Because there was a correlation between hc and Kc

viscosity could be predicted at low pH range below about

pH 59 by measuring changes in viscosity at a high pH

Accordingly it may be possible to predict aggregation

behaviors due to decreased pH in soymilk in the high pH

range and these results may be applied to control the

viscous quality of soymilk

5Conclusion

In this study when the pH of soymilk with different

primary producing areas was reduced using ascorbic

acid the apparent viscosity of all soymilk increased sig-

nificantly at approximately pH 58-59 this was found to

be a universal phenomenon in the soymilk colloidal dis-

persion system Even when the pH decreased following

the addition of six types of acidity regulators to soymilk

prepared from American whole soybeans the apparent

viscosity increased sharply when the pH was lower than

59 However because the apparent viscosity increase

was relatively moderate when phytic acid and citric acid

were added the chelating actions of phytic acid and citric

acid suppressed the initial formation of aggregates

Assuming that the bulkiness of the aggregate was pro-

portional to the hydrogen ion concentration in the high

pH range calculations were made by applying the

extended Krieger-Dougherty equation obtained from

Einsteinrsquos viscosity equation and the Krieger-Dougherty

equation a negative correlation was confirmed with the

parameter hc representing the degree of bulkiness of the

aggregate and the parameter Kc representing the degree

of filling of the gigantic aggregate Moreover the macro-

scopic aggregation behaviors were similar even if the

internal structure of the isolated aggregates dif fered

depending on the difference in crosslinking mechanism

Because of the correlation between hc and Kc viscosity in

the low pH range can be predicted by observing changes

in viscosity in the high pH range Based on these fea-

tures this process may have industrial applications In

future studies we will evaluate the rheological character-

istics of soymilk and assess the applications of these find-

ings in other systems with aggregation Furthermore

additional studies are needed to examine the aggregation

of soymilk particles and structure in greater detail

NOMENCLATURE

C hydrogen ion concentration M-1

Kc reciprocal of closest packing ratio -

hc parameter of bulkiness M-1

φ volume fraction -

η apparent viscosity mPas ηc0 initial viscosity mPas ηd dimensionless viscosity -

ηr relative viscosity -

Fig 4 Relationship between the viscosity parameters hc and Kc obtained from the viscosity measured using six types of soymilk and six acidity regulators



Acknowledgements

This research was supported by a grant from the

Project of NARO Bio-oriented Technology Research

Advancement Institution (Project for Development of

New Practical Technology)

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(2009)

3) A H C Huang Oil bodies and oleosins in seeds Annu Rev

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5) S T Guo T Ono M Mikami Interaction between protein

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6) D Iwanaga D A Gray I D Fisk E A Decker J Weiss D

J McClements Extraction and characterization of oil bod-

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7) M A Schmidt E M Herman Suppression of soybean oleo-

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8) C C Peng V S Lee M Y Lin H Y Huang J T Tzen

Minimizing the central hydrophobic domain in oleosin

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the stability of colloidal montmorillonite particles at differ-

ent pH and ionic strength Appl Clay Sci 43 21-26 (2009)

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12) K Oizumi S Idogawa Y Iwamoto K Ito T Fujii Influence

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(2000)

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18) K Ito S Idogawa Elastic behavior of tofu emulsion gel (in

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19) Y Morita ldquoSoybean Protein (Daizu Tanpakushitu)rdquo Korin

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20) S Idogawa T Fujii Rheological analysis of the aggregation

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豆乳コロイド分散系の安定性に及ぼす pH調整剤添加の影響

佐藤加奈子 1井戸川詩織 12dagger藤井智幸 2

1太子食品工業株式会社2東北大学大学院農学研究科

豆乳はタンパク質溶液にタンパク質粒子と脂質が分散したコロイド分散系である豆乳中に含まれる脂質はオイルボディとして存在しており表面を覆うオレオシンによって合一が抑制され安定なコロイド分散系を形成していると考えられている豆乳の製造管理および豆乳加工品の開発のためには豆乳のコロイド特性の把握が重要と考えられるコロイドの安定性は pHや熱電解質有機物の添加などの要因で変動することが知られている筆者らはアスコルビン酸溶液の添加による pHの低下に伴って豆乳の見かけ粘度が急激に変化する挙動を確認しているオイルボディとタンパク質が関わる凝集体の生成により見かけ粘度が上昇すると考えられるが凝集の詳細は明らかになっていないpH低下に伴う豆乳コロイドの凝集挙動の詳細を明らかにするためには豆乳の粒子が孤立状態で存在している段階から粒子が集まり充填状態やゲル構造を伴う巨大凝集体を生成するまでのメカニズムに関する理解が求められる本研究では豆乳の pH低下によって豆乳中に含まれるタンパク質の等電点に近づくことでタンパク質溶解度が低下し凝集体が形成されると仮説を立て拡張アインシュタイン型の式とKrieger-Dougherty型の式とを組み合わせた粘性モデルを構築してその有効性を実験的に調べた原料産地が異なる 6種類の豆乳にアスコルビン酸溶液を添加してpH 56-62の pH調整豆乳とし円錐平板型回転粘度計を用いて見かけ粘度を測定したpHが低下するにしたがいおよそ pH 60までは見かけ粘度はやや微増するにとどまったがpHが 60より低くなると徐々に見かけ粘度が上昇しpHが 59より低くなると指数関数的に見かけ粘度が上昇したまた宮城県産大豆から調製した豆乳Soymilk AではpHがおよそ 01低い条件で同様の挙動がみられ品種の違いによるグロブリンタンパク質の含有割合の変化や灰分などの他成分による影響が考えられた6種類の pH調整剤をアメリカ産大豆から調製した豆乳Soymilk Bへ添加して見かけ粘度を測定したところ先述の実験と同様

におよそ pH 60までは pH低下に伴って微増しpHが59より低くなると急激に粘度が上昇する挙動を示したただしフィチン酸溶液およびクエン酸溶液の場合は粘度が顕著に変化する pHが低くこれはキレート作用によるものと示唆された

6種類の pH調整剤によるそれぞれの結果について豆乳に含まれる水素イオンの濃度を豆乳の pHから算出し無次元粘度ηdの実測値との関係を示したこのプロットに対し拡張 Krieger-Dougherty型の式に当てはめて粘性パラメータ hcKcを算出したhcは凝集体のかさ高さを表しhcの値が大きいほど凝集体がかさ高いことを示すKcは分散相の最密充填率の逆数であり巨大凝集体のかさ高さを示すつまり Kcの値が大きいほど凝集体が密ではなく巨大凝集体がかさ高いことを表す各 pH 調整剤の系において拡張 Krieger-Dougherty

式の適用妥当性を検討したところpH調整剤の添加に伴う連続した pH低下による豆乳の凝集形成系について1つの式で良好に記述できることがわかった

6種類の豆乳および 6種類の pH調整剤を用いて測定した粘度データから得られた粘性パラメータ hcと Kc

に負の相関が認められたつまりpH低下によって進行する凝集過程において高 pH領域にて生成される凝集体の大きさが大きいほど巨大凝集体が密に充填してかさが小さくなり逆に凝集体の大きさが小さいほど巨大凝集体はかさ高くなることが示唆されたまたpH調整剤の種類によらず同一の曲線上にプロットされたことから孤立状態にある凝集体の内部構造が架橋機構の違いにより異なっていてもマクロな凝集挙動は同様であることが示唆されたさらにhcと Kcに相関関係があるために高い pH領域で粘度変化を測定することによって低い pH領域での粘度が予測できることが示されたこのことは豆乳における pH低下による凝集挙動を高 pH領域で予想可能であることを表し豆乳の品質管理に応用できる可能性が期待される本研究は生研センター「革新的技術創造促進事業（事業化促進）」の支援を受けて行った

（受付 2017年 4月 5日受理 2017年 9月 17日）

1 989-6228　宮城県大崎市古川清水字新田 51-1

2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約

「日本食品工学会誌」 Vol 18 No 4 p 185 Dec 2017



in many food manufacturing processes [16 17]

However few models have been developed to quantita-

tively describe the changes in viscosity accompanying

aggregation in foods characterized as multicomponent

dispersions

In soymilk oil bodies can be regarded as spheres cov-

ered with oleosin and if the size is sufficiently small the

oil bodies behave like rigid spheres in the dispersion

phase [18] Most of the proteins present in the continu-

ous phase in soymilk are globulin proteins mainly 11S

globulin (glycinin) and 7S globulin (β-conglycinin)

Each globulin is an association of subunits and the iso-

electric points of the proteins differ depending on the

subunits or polypeptides [19] Therefore depending on

the pH the surface potential of the protein changes and

the amount of protein participating in aggregation may

increase or decrease

In this study we hypothesized that aggregates were

formed because of the decrease in protein solubility as

the pH of soymilk decreased and approached the isoelec-

tric point of protein contained in soymilk Thus we con-

structed a viscous model combined with the extended

Einstein equation and the Krieger-Dougherty equation

and experimentally investigated the validity of the model

2Theory

A viscosity model combining Einsteinrsquos viscosity equa-

tion and Krieger-Doughertyrsquos viscosity equation was pre-

viously developed to analyze the viscous behavior of the

process of colloidal coagulation with a crosslinking agent

[20] In a system in which the rigid spheres are dis-

persed if the relative viscosity in the diluted state is ηr

and the volume fraction of the dispersed phase is φ the

following Einsteinrsquos viscosity equation [21 22] can be

established

ηr＝1＋25φ (1)

Einsteinrsquos viscosity theory is limited to the case in

which φ is suf ficiently small because hydrodynamic

interactions between dispersoids are not considered

Given that bulky aggregates are formed by adding an

acidity regulator under conditions of low pH and assum-

ing that the increase in the effective volume fraction

from the formation of aggregates is proportional to the

hydrogen ion concentration Einsteinrsquos viscosity equation

can be extended as follows

ηd＝1＋25timeshctimesC (2)

where hc denotes the bulkiness of the colloidal aggre-

gates and C denotes the hydrogen ion concentration

Furthermore under conditions of high pH assuming

that the bulkiness of the aggregates is proportional to

the hydrogen ion concentration the Krieger-Dougherty

equation [23] is expanded as a viscous model applicable

to the concentrated dispersion system and the following

equation is obtained

ηd＝(1－KctimeshctimesC )-25Kc (3)

where Kc is the reciprocal of the closest packing ratio of

the disperse phase and is a parameter of the bulkiness of

the gigantic aggregate in the closest packed state

3MaterialsandMethods

31 Materials

The soybeans used in this study were produced in

America Canada Hokkaido Aomori Iwate and Miyagi

Soymilk was provided by Taishi Food Inc (Aomori

Japan) The moisture content was determined by micro-

wave drying (SMART TURBO CEM Japan KK Tokyo

Japan) and the protein content was determined by the

improved Dumarsquos method using a nitrogen analyzer

(SUMIGRAPH NC-220F Sumika Analysis Chemical

Service Ltd Tokyo Japan) The lipid content was deter-

mined by nuclear magnetic resonance (NMR SMART

TRAC CEM Japan KK) [24] The results are shown in

Table 1

Lactic acid malic acid hydrochloric acid ascorbic

acid citric acid and phytic acid (Wako Pure Chemical

Industries Ltd Osaka Japan) were used as acidity regu-

lators The concentration of each acidity regulator was

028 M

32 Measurementofviscosity

Soymilk heated to 25 was adjusted to pH 56-62 by

adding an acidity regulator The apparent viscosity η of

Table 1 Water protein and lipid contents of soymilk samples

Water[]

Protein[]

Lipid[] Harvest area

A 884 49 29 Miyagi Japan

B 890 51 30 USA

C 880 55 35 Canada

D 876 53 30 Hokkaido Japan

E 891 51 26 Aomori Japan

F 886 53 26 Iwate Japan






















decreasedpH






































































































































[times103 M-1]Kc

[-]MW[-]

pKa[-]

Lactic acid 775 79 901 39 [32]

Malic acid 829 70 1341 34 [32]


Ascorbic acid 328 182 1761 41 [32]

Citric acid 1052 45 2101 31 [32]

Phytic acid 740 62 6600 19 [34]





thepHdecrease
































linking aggregation








5Conclusion



































NOMENCLATURE










Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約























decreasedpH






































































































































[times103 M-1]Kc

[-]MW[-]

pKa[-]

Lactic acid 775 79 901 39 [32]

Malic acid 829 70 1341 34 [32]


Ascorbic acid 328 182 1761 41 [32]

Citric acid 1052 45 2101 31 [32]

Phytic acid 740 62 6600 19 [34]





thepHdecrease
































linking aggregation








5Conclusion



































NOMENCLATURE










Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約












































































[times103 M-1]Kc

[-]MW[-]

pKa[-]

Lactic acid 775 79 901 39 [32]

Malic acid 829 70 1341 34 [32]


Ascorbic acid 328 182 1761 41 [32]

Citric acid 1052 45 2101 31 [32]

Phytic acid 740 62 6600 19 [34]





thepHdecrease
































linking aggregation








5Conclusion



































NOMENCLATURE










Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約






thepHdecrease
































linking aggregation








5Conclusion



































NOMENCLATURE










Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約



























linking aggregation








5Conclusion



































NOMENCLATURE










Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約




Acknowledgements





References







(2009)





(1992)



Food Chem 45 4601-4605 (1997)











Chem 55 5604-5610 (2007)









73 89-102 (1993)








(2000)




1756-1760 (1975)








Technol 47 587-597 (2010)







Res 21 479-487 (2015)




(1905)



591-592 (1911)



Rheol 3 137-152 (1959)











(2003)





39 586-595 (1992)






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約






170 (2003)



Biochem 57 24-28 (1993)




Res Int 30 659-668 (1997)



1200 (1967)



Res Bull 36 511-519 (2001)



1981 pp 1577-1578



(1982)











（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約












（受付 2017年 4月 5日受理 2017年 9月 17日）


2 980-0845　仙台市青葉区荒巻字青葉 468-1


和文要約


influence of acidity regulators on the stability of a

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