EFFECT OF ACETIC ACID AND CMC ON RHEOLOGICAL AND BAKING PROPERTIES OF FLOUR

KULWMDER KAUR and NARPINDER SINGH'

Department ofFood Science and Technology Guru Nanak Dev University

Amrisar- 143 005. India

Accepted for Publication May 19, 1998

ABSTRACT

The effects of addition of acetic acid (0.05, 0.1, 0.2 and 0.4%) and carboxymethyl cellulose (0.25, 0.5, 1 .O, 2,0%) on rheological, gas release and bread making properties of flour were examined. Water absorption, dough stability, dough development time, loaf volume and overall acceptability scores decreased, while degree of softening and breadfirmness increased with an increase in acetic acid concentration. Addition of CMC showed similar effects on dough stability, dough development time and degree of softening. Maximum dough height (H,,,), maximum height of CO, production (H, ), gas formation and retention decreased with the increase in acetic acid and CMC levels. Addition of 0.05% of acetic acid in combination with 0.25% CMC was most effective in improving dough characteristics, and overall acceptability scores.

INTRODUCTION

Different optional ingredients such as hydrocolloids, fat, acids, and gluten are included in bread formulation to improve nutritional, shelf-life and organoleptic properties (Sultan 1980; Chug and Pomeranz 1983; Singh et al. 199 1; Mettler and Seibel 1993; Sekhon et al. 1995). Hydrocolloids are used in bakery products to improve shelf stability by retaining more moisture and retarding staling (Twillman and White 1988; Bell 1990). The addition of hydrocolloids has been reported to significantly affect processing and product quality (Glicksman 1982). A balance between improved shelf stability, good processing efficiency and product quality is always desired; Skarra and Evans (1988) and Mettler and Seibel (1993) suggested that emulsifiers and hydrocolloids can be combined to improve baking characteristics and to contribute to optimum functional properties of whole grain bread.

'To whom to correspond with.

Journal of Food Quality 22 (1999) 317-327. All Rights Reserved. 'Copyright I999 by Food & Nutrition Press, Inc.. Tnunbull, Connecticut. 317

318 K. KAUR and N. SINGH

Acetic acid is used in bread formulation to improve the shelf-life of bread. Treatment of flour with acetic acid has been suggested as an alternative to bromate and ascorbic acid in bread making (Seguchi et al. 1997). In a mixographic study, Hoseney and Brown (1983) reported that decreasing the pH of flour-water dough gave mixograms with decreased mixing stability. Bayfield and Young (1964) reported dough lost its cohesiveness and became sticky at pH 4.6, but they did not observe weakening of farinograms in contrast to the observations made by Galal et al. (1978). Bennett and Ewart (1962) reported that acids react strongly with the protein of dough. They reported a marked reduction in dough extensibility as a result of acid addition and attributed the effect to addition of hydrogen ion to the dough. Galal et al. (1978) stated that lowering the pH resulted in an increase in net positive charge on the proteins. A combination of lowering the pH, increasing the salt concentration and adding L-cystine HC1 was observed by Ranhotra et al. (1977) to be effective in producing acceptable quality bread from high maltose flours. Sekhon er al. (1995) described the beneficial effect of lowering pH and addmg vital gluten in the production of bread from highly sprouted wheat flour. In the present study, we describe the effect of acetic acid and carboxymethyl cellulose on farinograph, gas formation and retention, and bread making properties of flour using response surface methodology.

MATERIALS AND METHODS

Analysis

Moisture (44-15A), protein (46-lo), ash (08-lo), gluten (38-lo), and Falling Number (56-81B) were determined according to AACC (1990) methods. The gluten strength was determined using an SDS-sedimentation method (Axford el al. 1979).

Materials

Acetic acid of analpcal grade and sodium salt of carboxymethyl cellulose (CMC) were obtained from CDH Bombay, Inha. Bakers compressed yeast (Tower Brand, Calcutta) was used. Commercial flour milled from HD-2329 variety was supplied by Jawala Flour Mill. A homogenous gel was prepared every day by mixing known quantity of CMC and water which was used for studying farinographic, gaseous release and bread making properties. CMC and acetic acid was added along with other ingredients during dough mixing.

ACETIC ACID AND CMC EFFECTS ON BREAD FLOUR 319

Farinographic Properties

of acetic acid and CMC on farinographic properties. The constant flour method of the AACC ( 1990) was followed to study the effect

Dough Development and Gaseous Release Characteristics

The Rheofermentometer (Chopin, Tripette & Renaud, France) as described earlier (Czuchajowska and Pomeranz 1993) was used to study the effect of acetic acid and CMC at different levels on dough development, gas formation and gas retention properties of flours. Weighed quantities of compressed yeast (7g) and salt (5g) were dissolved in small quantity of distilled water separately. Flour (250 g), water (optimum), yeast and optional additives were mixed optimally in a laboratory mixer (National Manufacturing Company, Lincoln, NE) using water absorption and dough development time determined using a farinograph. The salt solution was added to the dough during the last minute of mixing. The kneading was finished at 30C into a smooth dough by stretching and folding manually. A portion of the dough (350 g) was placed in the removable basket of the gasometer and a resistance weight (762 g, equivalent to 7.62 g/cm’) was placed directly on the dough. The cover of the vat was fitted with an optical sensor and the test was run for 3 h at 29.5C. Maximum dough height (H,,,), development height of the dough at the end of the test (h), maximum height of gaseous release (H.,,,), CO, production and retention were measured.

Bread Making

Wheat flour (200 g), compressed yeast (5 g), sugar (4g), salt (3.0g) and water absorption according to farinograph absorption at 500 BU were used. All the ingredients were mixed to optimum development in a mixing bowl with the laboratory mixer. The kneading was finished at 30C into smooth dough by stretching and folding manually and fermented for 75 min in a fermentation cabinet (National Manufacturing Company, Lincoln, NE) maintained at 30C and 85% RH. The dough was remixed for 30 s in the same mixer and molded on a National molder after which it was proofed for 60 min and then baked at 235C for 25 min in a reel type oven (National Manufacturing Company, Lincoln, NE). Loaf volume of breads prepared in triplicate was measured by rapeseed displacement method and were organoleptically evaluated by a panel of six panelists as described earlier (Singh et al. 1990). The firmness of bread was studied with the help of an Instron Universal Testing Machine (Model, 4464) using the following settings: bread slices (two), 23mm (thickness); cross head speed, IOmm/min; compression, 5 mm and plunger diameter 35 mm. The firmness of bread slices was measured in triplicate in ‘kN’ force required for 5 mm compression at the center. Average force is reported.

320 K. KAUR and N. SlNGH

Statistical Analysis

The second order polynomials were computed using two variables at five levels by stepwise regression using Minitab Statistical Software (Minitab Inc., USA). Acetic acid and CMC levels were used as independent variables having values of X, (acetic acid levels), 0, 0.05, 0.1,0.2 and 0.4% and X, (CMC levels), 0,0.25,0.5, 1 .O and 2%. The polynomials were fitted to measure the dependent variables, water absorption, dough stability, dough development time, degree of softening, H,, bread firmness, bread volume and overall acceptability scores of bread.

RESULTS AND DISCUSSION

The flour used had protein, ash, wet gluten, SDS-Sedimentation Value and Falling number value of 9.6%, 0.45%, 29%, 53 mL and 350 s, respectively. The pH of dough decreased from 5.7 to 4.6,4.14, 3.8 and 3.56 with the addition of 0.05, 0.1, 0.2 and 0.4 % of acetic acid. Second order polynomials were computed. The statistical data and regression models tabulated are reported in Tables 1-2. All the models correlate well with the measured data and are statistically significant. R2 values for different models ranged between 82.5-92.8 which represents the proportion of variability of data accounted for by the model (Gardiner 1997). The standard error of estimates also are shown in Table 2.

TABLE I . T-RATIOS FOR RHEOLOGICAL AND BREAD PROPERTIES IN SURFACE REGRESSION

Term Water DDT Dough Degreeof & Bread Absomtion Stabilitv Softening Volume

Acetic acid - 6141**** -4.305**** - 3.27*** 4.584**** -0.875 -3.6..

CMC 1.737. -4.298b*** -6.17"** 0.346 -0.092 -0.838

Acetic acid x 3.436*** 1.869. 2.07. -3.237.. - 1.88. 0.898 Acetic acid

CMC XCMC -3.709*** 2.471*. 3.840,. 1.984' -1.687 -1.156

Acetic Acid x 0.934 2.331'. 2.57'' -1.37 2.14.. 0.532 CMC

****p L 0.0005. ***p 6 0.005. **p s 0.05, *p< 0.1 DDT= Dough development time

ACETIC ACID AND CMC EFFECTS ON BREAD FLOUR 321

TABLE 2. COEFFICIENTS OF REGRESSION MODELS FOR RHEOLOGICAL AND BREAD PROPERTIES IN

RESPONSE SURFACE REGRESSION

Term Water DDT Dough Degmeof H, Bread Absorption Stability Soflening Volume

Constant 58.47 1.74 6.81 106 55 890

Acetic Acid -20.31 -2.582 - 16.21 1048 -43.7 -1119

CMC 1.15 -0.515 -6.10 16 - 0.9 - 52

Acetic Acid x Acetic 25.61 2.526 23.10 -1667 -211.5 630 Acid

CMC x CMC -1.11 0. I34 1.71 41 - 7.6 - 32

Acetic Acid x CMC 1-11 0.50 4.55 -1 12 38.2 59

R’ 90. I 84.5 82.5 82.7 83.3 89.3

s 0.59 0.107 0.88 40.88 8.93 55.6

DDT = Dough development time s = standard error of estimate

Farinographic Properties

Table 1 reveals that both acetic acid and CMC had significant effects on water absorption, dough development time and dough stability of flour, however, the effect of acetic acid on water absorption was more pronounced. Acetic acid showed significant effect both in linear and quadratic terms on water absorption and, in linear terms only, on dough development time, dough stability and degree of softening. Water absorption, dough stability and dough development time decreased and degree of softening increased with the increase in acetic acid concentration. Figure 1 illustrates the effect of acetic acid and CMC on water absorption of dough. Similar effects of reducing pH to 4.2 with diluted HCl on farinographic characteristics of dough have been reported earlier (Singh et al. 1995). Hoseney and Brown (1983) also reported a decrease in pH resulted in a decrease in dough stability. They attributed the changes in dough characteristics brought by the change in pH to the change in charge on the protein. Increased levels of CMC showed similar effects on dough stability, dough development time and degree of softening as observed for acetic acid. CMC showed highly significant effect on dough development time and dough stability, both in linear and quadratic terms while the effect on water absorption was significant in quadratic terns only. Water absorption increased with the addition of CMC up to the 1% level and decreased at the 2% level. Addition of CMC at 2% level and acetic acid at 0.4%

322 K. KAUR and N. SlNGH

0 1 2 CMC ( * l o )

FIG. 1. CONTOUR PLOT SHOWING THE EFFECT OF ACETIC ACID AND CMC ON WATER ABSORPTION (%) OF DOUGH

level resulted in a sticky dough which was difficult to handle. An improvement in water absorption of dough with the addition of CMC has also been reported by Friend et al. (1993).

Gas Formation and Gas Retention Properties

Maximum dough height (H,), height after 3 h of fermentation (h) and maximum height to CO, production (H.,,,) decreased with the increase in acetic acid and CMC levels (Table 3). Acetic acid along with CMC showed beneficial effect on dough behavior and gaseous release characteristics. Addition of 0.05% of acetic acid and 0.25-0.5% CMC resulted in higher H,, H-,, total CO, production and retention as compared with the control. Retention volume improved with the addition of 0.05-0.1% of acetic acid while the CO, retention progressively decreased with the increase in CMC. Acetic acid showed significant effect on H, value both in linear and quadratic terms whereas CMC showed significant effect in quadratic t e r n only. The acetic acid and CMC interacted significantly in affecting the H, value. The decrease in C Q retention with the addition of CMC may be attributed to the decrease in dough strength as indicated by a decrease in dough stability and an increase in degree of softening. Total C02 production progressively decreased with the increase in acetic acid. Total C02 production decreased fiom 2195 mL to 2150, 1760,574 and 153 mL with the addition of 0.05, 0.1,0.2 and 0.4%, respectively, of acetic acid. The decrease in CO, production with the increase in acetic acid may be attributed to inhibition of yeast fermentation. Acetic acid has a low dissociation constant and its addition results in denaturation of protein, inhibition of metabolic enzymes, mhibition of incorporation of amino acids into yeast cells fiom outside and a decrease in pH (Yamamoto et al. 1989).

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324 K. KAUR and N. SINGH

Bread Characteristics

Bread volume progressively decreased with the increase in level of acetic acid. The statistical analysis showed that acetic acid had the most pronounced effect on bread volume followed by CMC (Table 1). A reduction of 3.5, 9.4 and 21.17% respectively, in bread volume with the addition of 0.1, 0.2 and 0.4% of acetic acid was observed. A contour plot of bread volume as a function of acetic acid and CMC levels is shown in Fig. 2. Bread firmness increased with the increase in acetic acid concentration and decreased with CMC (Fig. 3). The effect of acetic acid on bread firmness was observed to be statistically significant both in linear and quadratic terms. In Fig. 4 overall acceptability scores are displayed as a function of both acetic acid and CMC levels. Overall acceptability scores decreased significantly with the addition of acetic acid and CMC beyond 0.1 and 0.25% levels, respectively. The effect of both was found significant in linear as well as quadratic terms; however, the acetic acid showed greater deteriorative effect on overall acceptability scores. Overall acceptability scores of breads prepared using 0.25% CMC and 0.05% acetic acid were higher than those of control samples. Thus, CMC and acetic acid together could be added to improve the quality of bread. The decrease in loaf volume with the increase in acetic acid may be attributed to the reduction in dough stability and activity of yeast cells as revealed by deteriorated gas formation properties measured using the Rheofermentometer F,. Wolt and D'Appolonia (1984) reported a damaging effect of glutathione released by dead yeast cells on bread making. Therefore, the contribution of glutathione released by dead yeast cells at higher acetic acid concentration in deteriorating bread quality can not be ignored. The improvement in loaf volume with CMC may be attributed to the improvement in water absorption of flour.

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FIG. 2. CONTOUR PLOT SHOWING THE EFFECT OF ACETIC ACID AND CMC ON BREAD VOLUME (ML)

ACETIC ACID AND CMC EFFECTS ON BREAD FLOUR 325

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FIG. 4. CONTOUR PLOT SHOWING THE EFFECT OF ACETIC ACID AND CMC ON OVERALL ACCEPTABILITY SCORES (100)

Acceptability limits can be assigned to the dependent variables and area of acceptable performance of dough and bread determined. The limits were water absorption above 58, H, value above 60, loaf volume above 800 mL, bread firmness below 0.03 kN and overall acceptability scores above 90. Figures 1-4 show that these values come under the limits of 0.05% acetic acid and 0.25% CMC. Thus, 0.05% acetic acid and 0.25% CMC can be used in bread making in order to have their beneficial effects.

326 K KAUR and N. SlNGH

Second order polynomials can be a useful tool to study the effects of the addition of acetic acid and CMC on dough rheology and bread characteristics. In summary, addition of 0.05% of acetic acid along with 0.25% CMC showed beneficial effects on gas formation and retention properties of dough studied using Rheofementometer F2 and firmness and overall acceptability scores of bread.

ACKNOWLEDGMENT

The authors gratefilly acknowledge Jawala Flour Mill, Amritsar for providing the flour for carrying out this study.

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