Effect of Different Types of Surfactants on Cassava Starch Properties

Subramony N. Moorthy

The effect of anionic, neutral, and cationic surfactants in three different concentrations on cassava starch properties was studied. The iodine affinity of total amylose was reduced by 20 -40% by all surfactants, with highest reduction being observed for cetyltrimethylammonium bromide. The iodine affinity of soluble amylase was suppressed by all reagents except cetyltrimethylammonium bromide, which lowered the value to almost zero. There was no significant difference between the concentrations 0.04 and 0.06 mol of surfactant per 100 g of starch. Viscosity was stabilized by potassium stearate and potassium palmitate without greatly affecting the peak viscosity of 660 BU of pure starch, but sodium lauryl sulphate and cetyltrimethylammonium bromide increased the peak of viscosity to 900 and 780 BU respectively at 0.06-mol concentration and did not show stable viscocity during the holding period. Defatted and raw starch showed similar viscosity patterns on incorporation of surfactants. Pasting temperature as increased to over900C by potassium sateratte, palmitate and glyceryl monosterate, while the increase was only by 3.150C over control (650C) by the other two reagents. The swelling volume of starch was reduced to nearly half the original value by potassium palmitate and stearate, glyceryl monostrate did not change it noticeably. Sodium lauryl sulfate and cetyltrimethylammonium bromide increased the value by nearly 50%. Sol stability was improved considerably by all the reagents. The results are discussed in relation to structure of the surfactants.

Introduction

Surfactants have been in use in food industry since 1920s mainly as dough conditioners, as crumb softeners in breads buns and rolls, and as amylase complexing agents in starch based foods. The crumb-softening effect of the surfactants is based on the formation surfactants amylase complexing index of various surfactants and their crumb softening effect has been found (Krog and Nyobojenson, 1970; Lagendijk and pennings, 1970; Krog, 1981.

Similarly, use of monoglycerides in the production of dehydrated mashed potato is aimed at binding free amylase to control the stickness or gluiness of the product. Here also the role of the surfactant as amylase complexing agent has been established (Hoover and Hadziyev, 1981 a,1981 b, 1982.)

The structure of the amylose-surfacant complex has been investigated in detail. It has been observed early that iodine affinity of starch is reduced drastically by addition of fats and surfactants. Butanol precipitated corn amilose showed reduction of iodine affinity from 18.7% to 0 % by addition of 10% palmitic acid (Schoch and williams1944.) osman et al(1961), however found that though the iodine of affinity of corn starch amylase was reduced by addition of surfacatants, it never reached zero value. On the basis of iodine affinity studies, it has been proposed that amylase forms a helical structure that is stabilized by the hydro carbon part of the surfacatant, which full fills the hydro phobic salvation requirements of the helix (Krog,1981.) Carlson et al.(1979) have used X-ray and Raman spectroscopies to study the complexes, and their result also confirm a helical inclusion complex.

The effect of surfacatants on the siscosity of starch pastes has been studied by Osman and Dix (1960) and Krog(1973). The former group observed that the pasting temperature of corn starch was increased in the case of nonionic surfacatants. The effects was related to length of hydro carbon chain in the surfacatants. Krog used monoglycerides, steroyl 2-lactylates, and diacetylated tartaric acid easters of monoglycerides (DATE) at 0.5% concentrations in his study of their effects on various starches including cassava starch. The peak viscosity of cassava was slightly reduced by all the emusifiers. The viscosity during the holding period was stabilized by glyserylmonosterate (GMS) while it was destabilized by DATE. The pasting temperature was increased by GMS and sodium steroylactylate while calcium steroylactylate and DATE had no effect.

Hoover and Hadziyev ( 1981 a,1981b,1982) have studies in detail the poto amylosic monoglyceride complex and the effect of this complexing on starch properties like swelling power, water binding capacity, solubility and blue value index. They found that swelling power and solubility were reduced by both monoglycerides and the potassium salts of fatty acids and the reduction was dependent on the chain length of the fatty acid portion of the surfactants. Both water binding capacity and blue value index were suppressed.

Apart from the study on the bra bender viscosity pattern and pasting behavior of cassava starch in the presents of various surfactants by Krog (1973), there has been no systematic investigation on the effects of different surfactants on the properties of cassava starch. Hence the present study was undertaken using cationic,anionic, and neural surfactants in three concentrations each (0.02,0.04,and 0.06 mol per 100 g of starch). In addition to the total and soluble amylase binding capacity, the 2% solution viscosity and 6% paste viscosity of cassava starch in the presents of surfactants, the effect of swelling power and sol stability have been examined, since cassava starch has a high swelling power and low retrogradation tendency compared to cereal starches. Cassava starch find extensive use in food and industry, and the result can prove useful to find out ways to improve its undesirable properties like unstable viscosity and long cohesive texture of its paste.

Materials and Methods

Commercial grade cassava starch obtained from Lakshmi Starch Factory, Kundara, kerala,India, was used as such or after defatting by hot extraction with petroleum ether (60-800C). The five surfactants used for the study include three anionicand one each of neutral and cationic surfactants. The anionic ones were potassium stearate and potassium palmitate with 16 and 18 carbon chains in the hydrophobic portion and sodium lauryl sulfate with a 12-carbon chain. The neutral surfactant was glyceryl monostearate (18 carbon chain) while the cationic one was cetyltrimethylammonium bromide (with chain length of 16 carbons in the hydrophobic portion). Analar grade reagents were used for the preparation of the complex with starch. Three concentrations of each of the surfactants were tried, viz 0.02,0.04,and 0.06mol per 100 g of starch. The concentration factor was fixed as moles/100 g of starch to eliminate the effect of the large difference in molecular weights between the surfactants.

The starch-surfactant complex was prepared by the procedure described by Hoover and Hadziyev (1981 a). the surfactant was dispersed in 50 ml of distilled water pre-heated to 650C and stirred for 30 min. The temperature was brought down to 450C,50 g of dry starch in 100 ml of water was added, and the slurry was heated at 450C for 6hwith continuous slow stirring. The suspension was filtered, washed thoroughly, and dried at room temperature.

Blue values for total amylase and soluble amylase were determined by the colorimetric procedure described Sowbhagya and Bhattacharya(1971) and Shanty et al (1980), respectively using pure amylase (SIGMA) as standard. Three replications were used for determination of blue values.

Viscosity of the starch and starch and starch surfactant, complex solutions (2%)was determined by the ISI procedure using Redwood viscometer no.1,(ISI, 1970). A 4-gsample of material was dissolved in 200g of hot distilled water, heated at 100 0C for 30 min., filtered through cheese cloth, and cooled to 75 0C, and viscosity was taken as the time taken in seconds for 50ml. of the solutions to pass through the office of the viscometer. Three readings were taken for each sample.

Paste viscocity of a 6% paste of starch and its complexes were monitored on a brabender viscomylograph (Model 801020) provided with automatic heating and stirring systems ( 75 rpm, 1.5 0C /min).27 g of the material (dry weight basis) was suspended in 450 ml of distilled water in the amylograph cup and heated with stirring at 75 rpm at 1.5 0C/min.At 97 0C , the temperature was maintained constant for 20 min. The pasting temperature range was maintained constant for 20 min. The pasting temperature range was obtained as the range between the temperature at the start of increase of viscosity and that at which it remains constant.

The swelling volume was obtained by Schoch’s method (Schoch, 1964). A 0.5 -g portion of dry material in 5o mL of distilled water was heated with stirring to 80 0C in a water bath, maintained at 85 0C for 15 min, cooled, and centrifuged at 2200 rpm for 15 min, and the swelling volume was expressed as the volume of gelatinous sediment per 1g of dry starch. The sol stablility was taken as the time taken by the starch gel to start settling on keeping undisturbed (with a little amount of toluene added to prevent microbial damage).

Results and Discussions

The total iodine affinity and the iodine affinity of soluble amylase are given in Table 1 in terms of the blue values. The maximum reduction in iodine affinity of total amlose is observed in the case of cetyltrimethylammonium bromide. All the other reagents show an almost equal reduction in affinity. Since reduction in iodine affinity value can be taken as a measure of the complex formation, it can be concluded that cetyltrimethylammonium bromide complexes to the maximum extent and potassium stearate and sodium lauryl sulfate the least.

It is also seen from Table 1 that the difference in blue values at concentrations of 0.04and 0.06 mol are nonsignificant. The reduction in blue value of amylase with addition of increasing amounts of fatty acids or surfactantsis reported by many others, but the present study indicates that blue value of cassava starch tend to taper off on increase in concentration above 0.04 mol of surfactant per 100 g of starch. Similar results have been obtained for potato starch by Hoover and Hadziyev(1982) who found that the blue value remain constant above a concentration of 0.3 glyceryl monosterate. Hence at higher concentrations the surfactant may not be forming an effective complex. The amylopeetin molucles may be offering resistence to the surfactant to complex with the amylase molucles, and hence all the amylose is not bound by the surfactants.

The blue values of the soluble amylase in the treated samples give an indication of the preference of the reagents to add to free amylase. The results (Table 1) indicates that all the surfactants reduce the value considerably and that the ratio of blue values of total to soluble amylase is in the range 2-2.5 for all reagents except in the case of cetyltrimethylammonium bromide which imparts a very low blue value for soluble amylase. Here also there is no significant difference between the concentrations 0.04 and 0.06 mol. Though all the treatments are significantly different the values with cetyltrimethylammonium bromide point out that this surfactant has a very high affinity for soluble amylase. At a 0.06-mol concentration, the blue value nearby reaches zero, indicating that this reagent is binding almost all the soluble amylose. Such high tendency of surfactantto complex with soluble amylase is reported for the first time.

Figure 1. Effect of potassium palmiate on the Brabender viscosity curve of cassava starch., cassava starch (raw defatted);?.., cassava starch + 0.02 mol of potassium palmitate (per 100 g of starch) cassava starch+0.04 mol;on cassava starch +0.06 mol.

Figure 2. Effect of potassium palmitate Brabender viscosity curve of cassava starch(raw defatted ) cassava starch +0.02 mol of potassium palmitate (per 100 g of starch)? cassava starch+0.04 mol -.-, cassava starch + 0.06 mol.

Figure 3. Effect of glyceryl monostearate on the Brabender viscosity curve of cassava starch(raw defatted ) cassava starch +0.02 mol of of GMS (per 100 g of starch);–.–, cassava starch+0.04 mol –.–, cassava starch + 0.06 mol.

Figure 4. effect of sodium lauryl sulfate on the Brabender viscosity curve of cassava starch(raw defatted ) cassava starch +0.02 mol of sodium lauryl sulfate (per 100 g of starch);–.–, cassava starch+0.04 mol –.–, cassava starch + 0.06 mol.

Figure 5. effect of cetyltrimethylamonium bromide on the Brabender viscosity curve of cassava starch., cassava starch (raw defatted);?.., cassava starch + 0.02 mol of cetyltrimethylamonium bromide (per 100 g of starch);–.–, cassava starch+0.04 mol –.–, cassava starch + 0.06 mol.

The velocity of 2 % solution of starch and surfactant-incorporated starch is given in table II. Treatment with surfactants at all concentrations increase the viscosity, especially with sodium lauryl surfate and cetyltrimethylammonium bromide. All the treatment and concentrations show significance difference in viscosity. However no direct relation between the increasing concentration and an increase in viscosity could be observed. In the case of potassium setearate, potassium palmitate, and sodium lauryl sulfate, there is only a slight increase in viscosity at 0.06 -mol concentrationcompared to that of 0.02 -mol concentration. Cetyltrimethylammonium bromide, however exhibits a regular increase in viscosity with increasing concentration. The absence of regular increase in viscosity with increase in concentration in the case of treatment with GMS may be due to incomplete gelatinization of starch granules, as observed by congo red staining experiments that showed that 20-25% of the granules in the solution remained ungelatinzed.

The Brabender viscosity curves for the samples are given in figures 1-5. The results indicate that different surfactants show different patterns. Potassium palmitate and setearate suppress the peak viscosity slightly, but the viscosity remains almost steady during the holding period. Thus, a slight reduction in swelling with a good strengthening of the starch granules against shear and temperature is imparted by the these reagents. The peak viscosity does not show an increase with increasing concentration of the reagent. The results point out that these regions can be useful in stabilizing the viscosity of cassava starch. The increased resistance to break down under shear and temperature can be useful to prevent the long cohesive nature of the starch paste. The stabilization is achieved even at the lowest concentration(0.02 mol), and the production of the surfactant -starch complex is easier compared to cross linking by chemical reactions (Srivastava and Patel, 1973; knight, 1974) or physical treatment (Moorthy, 1980).

Table II : Viscosity and Pasting temperature of Surfactant – Incorporated Starch

  2% Visc, s Peak visc, pasting 6% paste, temp0C
Starch 50 660 65-77
Starch (100g) +0.02 mol of potassium stearate 57 600 95-97
Starch (100g) +0.04 mol of potassium stearate 55 620 95-97
Starch (100g) +0.06 mol of potassium stearate 62 600 97
Starch (100g) +0.02 mol of potassium palmitate 64 640 95-97
Starch (100g) +0.04 mol of potassium palmitate 72 680 96-97
Starch (100g) +0.06 mol of potassium palmitate 70 660 97
Starch (100g) +0.02 mol of GMS 95 680 90-97
Starch (100g) +0.04 mol of GMS 55 420 88-94
Starch (100g) +0.06 mol of GMS 70 420 94-97
Starch (100g) +0.02 mol of sodium lauryl sulfate 84 800 78-94
Starch (100g) +0.4 mol of sodium lauryl sulfate 90 880 78-92
Starch (100g) +0.06 mol of sodium lauryl sulfate 87 900 77-88
Starch (100 g) +0.02 mol of acetyltrimethylammonium bromide 69 680 78-85
Starch (100g) +0.04 mol of acetyltrimethylammonium bromide 90 740 68-83
Starch (100g) +0.06 mol of acetyltrimethylammonium bromide 96 780 68-80
CD (5%) for interaction 2.41    
CD (5%) for concn 1.08    
CD (5%) for reagents 1.40    

Sodium lauryl sulfate increase the peak viscosity considerably, and at a 0.06-mol concentration, it reaches 900 BU. However, during the holding period, the viscosity drops rapidly and reaches the value of pure starch. This results shows that sodium lauryl sulphate binds with starch molecules and allows them to swell considerably but under shear and temperature, the complex breaks down down to release the swollen starch granules that starts fragmenting.

Glyceryl monostearate increase peak viscosity slightly at a0.02-mol concentration, but at higher concentrations, the values fall. These results, as also the 2% viscosity values, shows that gelatinization is not complete at 97 0C . the viscosity is maintained during the holding period, and hence this reagent can also be used at 0.02-mol concentration for viscosity stabilization of cassava starch. Krog (1973) in his study has also found that GMS at 0.5% concentration stabilizes cassava starch viscosity. However, he found, a slight decrease in peak viscosity with the reagent at 0.5% concentration.

Cetyltrimethylammonium bromide leads to a steady increase in peak viscosity with increasing concentration, reaching 780 BU at 0.06 mol concentration. However, the viscosity breaks down during the holding period, similar to the case of sodium lauryl sulfate incorporated starch, indicating that the complex is unstable on heating and stirring.

In order to compare the effects of surfactants on defatted and non defatted cassava starch, the Brabender viscosity pattern of surfactant incorporated starch prepared from non defeated (raw) starch was obtained. It was found that there is practically no difference in the viscosity pattern, peak viscosity, or pasting temperature, between defatted or starch treated with surfactants. This can be explained by the low fat content of cassava starch compared to cereal starches.

Taylor and Nelson (1920) reported values of 0.61% and 0.11 % fat content, respectively, for maize and cassava starches. Compared to the high lipid content, in maize starch (0.87%; Morrison,1976) or rice starch (0.4% Maninget and Juliano, 1980). The mirror amount of lipid in cassava starch may not be existing as a complex with amylase molecules to be affected by addition of surfactants. The gelatinization temperature is lowered by extraction of lipids from corn, wheat (Melvin, 1979), or rice (Ohashi et al.1980) starches, but no such effects is observed in cassava starch.

The pasting temperature as observed from the Brabender viscosity curves are given in table II. Invariably all the reagents increase the pasting temperature, but to different extents. In the case of potassium palmitate and stearate, the pasting temperature initiation is increased by around 30 0C and the pasting temperature range is narrowed to 2 0C . At higher concentrations, the rise in visocosity appears only at 97 0C . It was also found by congo red staining that all the granules do not gelatinize at 97 0C , but only during the holding period. The high pasting temperature indicates the resistence offered by the surfactants that fit into the amylase helix to entry of water molecules. With GMS also, the pasting temperature is enhanced to over 90 0C , but the range is comparatively more than with potassium palmitate or stearate. At higher concentrations, incomplete gelatinization becomes prominent.

Sodium lauryl sulfate and cetyltrimethylammonium bromide increase the pasting temperature to a lower extent. At higher concentration of the reagents, there is even a drop in the pasting temperature. The results pasting temperature show that reagents with small hydrophilic groups impart a higher increase in pasting temperature. This may be due to the closer paking these reagents can achieve with the starch molucles. As carbon has pointed out (1979), part of the hydro carbon chain lies outside the amylase helix and this length may be dependent on the bulk of the hydrophilic group. Sodium lauryl sulfate and cetyltrimethylammonium bromide having big hydrophilic groups do not fit so closely as the other reagents into the starch molecules, when compared to the surfactants with smaller hydrophilic groups. The reduction in pasting temperature with a higher concentration of the reagents is also indicative of mutual crowding of the surfactant molecules.

The effect of the size of the hydrophilic portion of the surfactant in comparison to the hydrophobic chain has been discussed by Osman and Dix (1960) as well as Krog (1973). The results obtained also confirm the importance of close packing of the hydrophobic group into the amylose helix to render it stable.

Table III : Swelling volume and Sol Stability of surfactants Incorporated Starch

  Swelling Vol (mL) Sol Stability (days)
Starch 40.0 2
Starch (100g) +0.02 mol of potassium stearate 21.0 7
Starch (100g) +0.04 mol of potassium stearate 19.5 9
Starch (100g) +0.06 mol of potassium stearate 19.0 9
Starch (100g) +0.02 mol of potassium palmitate 24.0 8
Starch (100g) +0.04 mol of potassium palmitate 23.0 7
Starch (100g) +0.06 mol of potassium palmitate 22.5 8
Starch (100g) +0.02 mol of GMS 37.0 10
Starch (100g) +0.04 mol of GMS 40.0 8
Starch (100g) +0.06 mol of GMS 37.0 9
Starch (100g) +0.02 mol of sodium lauryl sulfate 64.5 12
Starch (100g) +0.04 mol of sodium lauryl sulfate 64.0 14
Starch (100g) +0.06 mol of sodium lauryl sulfate 63.5 14
Starch (100g) +0.02 mol of acetyltrimethylammonium bromide 57.0 11
Starch (100g) +0.04 mol of acetyltrimethylammonium bromide 64.5 12
Starch (100g) +0.06 mol of acetyltrimethylammonium bromide 66.5 11
CD (5%) for interaction 0.94  
CD (5%) for concen 0.42  
CD (5%) for reagents 0.54  

The very slight increase observed in the pasting temperatures in the case of cetyltrimethylammonium bromide in contrast to the notable decrease in bluevalue with the same reagent indicates that this reagent is able to block the entry of bulky 1­3 ion and not the much smaller water molecule.

Swelling volume is important characteristic of starch, especially for cassava starch, which exhibits high swelling property. A large swelling can lead to reduction in associative forces, resulting in breakdown of granules and simultaneous cohesive texture. The swelling volume of treated samples are given in Table III. The treatments and concentrations show significant variations. It is seen that potassium stearate and palmitate reduce the swelling volume to almost half its original value, even at lowest concentrations. GMS also reduce s the swelling volume, but only to a very small extent. Sodium lauryl sulphate on the other hand increase the value considerably. A similar result is also obtained with cetyltrimethylammonium bromide.

GMS has been reported to reduce the swelling power of potato starch by 10%, but the value tapers off above 0.3% concentration of GMS (Iloover and Hadziyey, 1982). Such, high reduction in swelling volume in the case of potassium stearate and palmitate and increase by over 50% by sodium lauryl sulphate and cetyltrimethylammonium bromide have not been reported so far.

The swelling of starch is determined by the strength of associative forces between molecules and also contributes to the viscosity of the paste. The high paste viscosity obtained for starch incorporated with cetyltrimethylammonium bromide and sodium lauryl sulfate and the swelling volume of these starch complexes. GMS exhibits almost the same swelling volume and viscosity as pure starch, but potassium stearate and palmitate reduce the swelling volume without reducing the viscosityof starch. Associative forces between starch molecules in the starch granules may be playing a role in determining these properties.

The sol stability of starch paste was found to be increased by all the reagents (Table III). Among the reagents, sodium lauryl sulfate exhibited highest stability (10 days) while there was not much difference between the reagents. The reagents act by inhibiting parallel association of linear amylase chains or the outer chains of amylopection molecules that would otherwise lead to settling of the starch gel.

Thus, study points out that different types of surfactants modify the properties of cassava starch differently. Cetyltrimethylammonium bromide shows high affinity for soluble amylase compared to other surfactants. Potassium stearate and potassium palmitate stabilize the past viscosity of cassava starch without affecting the peak viscosity but do not stabilize the viscosity. The instability of the complexes of amylase with these reagents may be explained as due to the relatively bulky hydrophilic group in them as suggested by Krog (1973). The lack of difference between viscosity properties of defatted and non defatted starch non surfactant incorporation may be due to relatively low lipid content of cassava starch. The wide variations in swelling volume of starch imparted by different types of surfactants and the improvement in sol stability are reported for the first time. The study also shows that concentrations above0.04mol/100g of starch do not have much effecton most of the properties.

Acknowledgment is due to Dr. S.P.Ghosh, Director of CTCRI, and Dr. C.Balagopalan, Head of Division of Technology, CTCRI, for facilities provided and encouragement.

Registery No.GMS, 31566-31-1; starch,9005-25-8 amylose, 9005-82-7;seaterate, 57-11-4 potassium palmitate, 2624-31-9; sodium lauryl sulfate, 151-21-3; CH 3 (CH2)N (ME)3Br.57-09-0

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