Studies on the Optimization and Stability of Low-Fat Biscuit Using Carbohydrate-Based Fat Replacers

Abstract

The objective of this study was to optimize and develop low-fat soft dough biscuits using carbohydrate-based fat replacers (combinations of polydextrose and guar gum). Central composite rotatable design was utilized to optimize the levels of sugar, composite fat (fat, polydextrose, and guar gum), ammonium bicarbonate, and water. The parameters measured were spread ratio, hardness, stress-strain ratio, and sensory properties. Composite fat and sugar were found to be important determinants of biscuit hardness. The principal effect of fat substitutes on biscuits’ attributes was crisper texture but with higher brittleness. The level of water had a significant effect on spread ratio (p < 0.1), hardness (p < 0.1), and stress-strain ratio (p < 0.05). It was also observed that by varying the level of ammonium bicarbonate in the formulation from 0.5 to 2.5 g/100 g flour, the dimensions and texture of the biscuits were affected. The optimum ingredient levels on 100 g flour basis were found to be sugar 24 g, fat 10.5 g, polydextrose 24.2 g, guar gum 0.3 g, ammonium bicarbonate 2 g, and water 24 mL. It was found from the storage study that low-fat biscuit with 70% fat replacement was more oxidative stable than the control sample.

Keywords:

• Physical properties
• Texture
• Storage study
• Fat replacers
• Soft dough biscuits

INTRODUCTION

Reducing fat in the daily diet has become a public health issue and a concern for most consumers. While in some product sectors reduced-fat alternatives are both widespread and acceptable to the consumer, other sectors such as bakeries are generally behind in producing successful reduced-fat alternatives. Increasing evidence indicates that individual fatty acids can affect total cholesterol and low density lipoprotein (LDL) levels and affect the risk of coronary heart disease. The way to influence fatty acid composition in the diet is to decrease certain food groups that are major contributors of certain fatty acids, or substitute certain foods for other foods that are contributors of particular fatty acids. The nutritional awareness amongst the consumers has warranted the production of low calorie food products. Moreover according to the Dietary Guidelines for Americans,^[1] the total fat intake should be 20–35% of your daily calories. Despite these problems, fat and sugar cannot be easily replaced, especially in a complex food system such as biscuits. Cookies especially, are soft-type biscuits whose textural characteristics are mostly provided by their high fat content. It lubricates the structure by being dispersed in the dough or batter during mixing and helps prevent the starch and protein from forming a continuous network. The sensation of a fatty mouthfeel is formed by a combination of several poorly defined or quantitated parameters including viscosity, absorption, cohesiveness, adhesiveness, and waxiness.^[2]

In biscuit-making, the main ingredients are flour, water, sugar, and fat. The quality of the biscuit is governed by the nature and quantity of the ingredients used. Nevertheless, several authors have attempted to describe the effect of ingredients in a dough and formula balance on the final structure of the product.^[3−5] As in the case of flour, water is an essential ingredient in dough formation: It is necessary for solubilizing other ingredients, for hydrating proteins and carbohydrates and for the development of a gluten network. Water has a complex role since it determines the conformational state of biopolymers, affects the nature of interactions between the various constituents of the formula, and contributes to dough structuring.^[6] If the proportion of water is too low, the dough becomes brittle, not consistent, and exhibits a marked “crust” effect due to rapid dehydration at the surface. The effect of sugar on dough behavior is an important factor in biscuit-making. In excess, sugar causes a softening of the dough, due in part to competition between the added sugar and the availability of water in the system.^[7] Fat influences the dough machinability during process, the dough spread after cutting-out, and textural and gustatory qualities of the biscuit after baking.^[8]

Carbohydrate-based fat substitutes have been used to partially or fully replace fat. Carbohydrate-based is the largest group of fat replacers which are plant polysaccharides, e.g., gums, fiber, dextrins, maltodextrins, starch, cellulose, and polydextrose. These short-chain carbohydrate materials mimic the mouthfeel that is provided by fat in foods. Polydextrose has been used in bakery goods and baking mixes, including biscuits, pound cake, yellow cake, brownies, butter cookies, doughnuts, and pastries.^[9,^10] It consists of glucose polymers, sorbitol, and citric acid in a ratio of 89:10:1.^[11,^12] The replacement of shortening by polydextrose in soft dough biscuits showed a significant effect on the sensory characteristics and physicochemical properties of the prepared cookies and also reported that polydextrose appeared to be a suitable replacer for up to 25% of shortening.^[13] Other experiments with polydextrose and several starch based fat replacers showed that the replacement of 35% of fat had the least negative effects on the physical properties of cookies, compared with replacement by 45 or 55%.^[14] However, some reports suggested that higher fat replacement could be used successfully in some bakery products. Hippleheuser et al.^[15] used Amerimaize 2210, a modified, pre-gelatinized starch, in order to produce a low-fat muffin which had sensory and textural properties similar to those of the control.^[16] employed response surface methodology (RSM) to optimize the levels of sugar replacer and Simplesse (protein-based fat replacer) in the production of a functional low-fat and sugar biscuit and studied the effect on thickness and texture of biscuit. Kocer et al.^[17] investigated the effect of polydextrose-substitution on the high-ratio cake in terms of cake batter structure, cake height, average pore size, size uniformity, size and shape distribution of pores, etc. He substituted 25% fat and 22% sugar with polydextrose which resulted in 22% reduction in calorific value based on total sugar and fat content.

The present study was undertaken to optimize and develop low-fat biscuits containing carbohydrate-based fat replacers using RSM. RSM was used to study different response variables as a function of independent variables viz. sugar, composite fat, ammonium bicarbonate, and water. This methodology was employed to minimize the number of baking trials while gathering all information related to ingredient interactions and quality characteristics. The present work also describes the storage stability of the optimized low-fat biscuit.

MATERIALS AND METHODS

Refined wheat flour, whole wheat flour, sugar, skim milk powder, vanilla essence, and hydrogenated fat were procured from local market of Rudrapur, Uttarakhand. Liquid glucose was obtained from Uttarakhand Maize Processing Unit, SIDCUL, Rudrapur. Polydextrose was procured from M/s Ensigns Healthcare Private Ltd., Pune, and guar gum was obtained from M/s Hindustan Gum and Chemicals Ltd., Bhiwani (Haryana).

The formula for the traditional (full-fat) short dough biscuit on a percent flour weight basis was: flour 100 g (refined wheat flour: 63.7 g and whole wheat flour: 36.3 g), sugar 26.5 g, fat 35 g, liquid glucose 3 g, skim milk powder 3 g, sodium bicarbonate 1.18 g, ammonium bicarbonate 1.22 g, water 23 mL, and vanilla essence 0.5 mL. Those are the ingredients commonly used in commercial short dough cookies.^[18] Using a response surface design, carbohydrate-based fat replacers (combination of polydextrose and guar gum) were substituted for 30, 40, 50, 60, or 70% of the fat in the formula in combination with other ingredients viz. sugar, ammonium bicarbonate, and water (Table 1).

TABLE 1 Experimental variables for biscuits, their coded and uncoded (actual) values

	Coded form				Uncoded form
					X1	X2			X3	X4
Expt. No.	X1	X2	X3	X4	Sugar*	Fat*	PD*	GG*	A.B.*	Water*
First order part
1	−1	−1	−1	−1	27	21	13.8	0.2	1	21
2	+1	−1	−1	−1	33	21	13.8	0.2	1	21
3	−1	+1	−1	−1	27	14	20.6	0.4	1	21
4	+1	+1	−1	−1	33	14	20.6	0.4	1	21
5	−1	−1	+1	−1	27	21	13.8	0.2	2	21
6	+1	−1	+1	−1	33	21	13.8	0.2	2	21
7	−1	+1	+1	−1	27	14	20.6	0.4	2	21
8	+1	+1	+1	−1	33	14	20.6	0.4	2	21
9	−1	−1	−1	+1	27	21	13.8	0.2	1	23
10	+1	−1	−1	+1	33	21	13.8	0.2	1	23
11	−1	+1	−1	+1	27	14	20.6	0.4	1	23
12	+1	+1	−1	+1	33	14	20.6	0.4	1	23
13	−1	−1	+1	+1	27	21	13.8	0.2	2	23
14	+1	−1	+1	+1	33	21	13.8	0.2	2	23
15	−1	+1	+1	+1	27	14	20.6	0.4	2	23
16	+1	+1	+1	+1	33	14	20.6	0.4	2	23
Second order part
17	−α	0	0	0	24	17.5	17.2	0.3	1.5	22
18	+ α	0	0	0	36	17.5	17.2	0.3	1.5	22
19	0	−α	0	0	30	24.5	10.4	0.1	1.5	22
20	0	+ α	0	0	30	10.5	24	0.5	1.5	22
21	0	0	−α	0	30	17.5	17.2	0.3	0.5	22
22	0	0	+ α	0	30	17.5	17.2	0.3	2.5	22
23	0	0	0	−α	30	17.5	17.2	0.3	1.5	20
24	0	0	0	+ α	30	17.5	17.2	0.3	1.5	24
Center point
25	0	0	0	0	30	17.5	17.2	0.3	1.5	22
26	0	0	0	0	30	17.5	17.2	0.3	1.5	22
27	0	0	0	0	30	17.5	17.2	0.3	1.5	22
28	0	0	0	0	30	17.5	17.2	0.3	1.5	22
29	0	0	0	0	30	17.5	17.2	0.3	1.5	22
30	0	0	0	0	30	17.5	17.2	0.3	1.5	22
31	0	0	0	0	30	17.5	17.2	0.3	1.5	22
32	0	0	0	0	30	17.5	17.2	0.3	1.5	22

*g/100 g flour;

PD: Polydextrose; GG: Guar gum; A.B.: Ammonium bicarbonate.

Preparation of Soft Dough Biscuit

Fat and sugar powder were creamed in a mixer at speed of 60 rpm for 1 min and continued for creaming for another 3 min. Liquid glucose and skim milk powder were made into suspensions in water, sodium bicarbonate, and ammonium bicarbonate in water were transferred to the above cream and mixed at speed 60 rpm for 2 min. The fat substitute (polydextrose and guar gum) also was incorporated at this stage as gel with its corresponding amount of water at a ratio of 1:2 (fat substitute to water) and further mixed to get smooth cream. Wheat flour was transferred to the above cream and mixed for 2 min at speed 60 rpm to get the biscuit dough. The dough was sheeted to a thickness of 4 mm and cut into round shapes using a dough cutter. The cut dough was transferred to aluminum trays and placed in a baking oven and baked at 190°C for 8 min. Polydextrose and guar gum were added in gel form during fat-sugar creaming whenever included in the formulation. One volume of fat replacer was transferred to 2 volumes of water heated to 40–45°C, cooled, and stirred into smooth gel.

Experimental Design and Statistical Analysis

RSM which involves design of experiments, selection of levels of variables in experimental runs, fitting mathematical models, and finally selecting variables’ levels by optimizing the response^[19] was employed in the study. A central composite rotatable design (CCRD) was used to design the experiments comprising four independent processing parameters (Table 1). Thirty-two experiments were conducted for the present research work. There were eight experiments at center point to calculate the repeatability of the method.^[20] The experimental design and the codes for the processing variables have been reported in Table 1. The present study was carried out to understand the effect of processing parameters—sugar, composite fat (fat, polydextrose, and guar gum), ammonium bicarbonate, and water upon spread ratio, hardness, stress-strain ratio, and overall acceptability (OAA) of biscuits.

The data obtained from the experiment were analyzed for optimization of processing parameters with respect to the responses, viz. spread ratio, hardness, stress-strain ratio, and OAA of the biscuits. Regression analysis and analysis of variance (ANOVA) were conducted for fitting the model (Eq. 1) and to examine the statistical significance of the model terms.

(1)

where, y = responses, X_i, X_j = coded processing parameters, β_0, β_i, β_iii, β_ij = regression coefficients. The adequacy of the models was determined using coefficient of determination (R²), F-value, and adequacy of precision as outlined by Weng et al.^[21] A model is adequate in describing the response if the adequate precision ratio of model is more than four and R² > 70. The effect of variables at linear, quadratic, and interactive level on the response was described using significance at 1 (p < 0.01), 5 (p < 0.05), and 10% (p < 0.1). Numerical optimization technique of the Design-Expert (8.0.6) trial version software (www.statease.com) was used for simultaneous optimization of the multiple responses. The desired goal for each processing parameter and response was chosen. The multiple responses namely, spread ratio, hardness, stress-strain ratio, and OAA were considered for optimization as they represent quality attributes adequately. This software explores 2D contours to identify coordinates and predict responses and critical factors and their interactions can be screened for quickly.

Spread Ratio

The diameter and thickness of biscuits were measured by the methods of the AACC.^[22] To obtain the average, measurements were made by rearranging and restacking the six biscuits. Experiments were performed in triplicate. Spread ratio was determined by dividing the diameter by thickness of each biscuit and the average value was reported.

Texture Analysis

To obtain samples for measuring textural characteristics, the dough was sheeted using a rolling pin over a rectangular platform and frame with a height of 4 mm to get a sheet of uniform thickness. The sheeted and cut cylindrical discs of 4 mm height were used to assess hardness (N). Hardness of the biscuits was measured in a Stable Micro Systems Texture Analyzer (TAXT 2i). The biscuits were placed under sharp-blade cutting probe, 70 mm long and 0.4 mm thick. A speed of 1 mm/s and a distance of 3 mm were used in the studies. The analyzer was set at a “return to start” cycle, a speed of 1 mm/s and a distance of 3 mm, pre-test speed 5 mm/s, post-test speed 10 mm/s and load cell 500 kg. The force required to break six biscuits individually were recorded and the average value reported. Stress was calculated by dividing the maximum force by area of blade and strain was expressed as the maximum distance traveled by probe to break the biscuit. Stress-strain ratio was obtained by dividing stress by strain.

Sensory Evaluation

Ten semi-trained panelists were asked for evaluating sensory attributes. They evaluated each sample for color, texture, taste, flavor, and OAA attributes on 5-point scale, where scores 1, 2, 3, 4, and 5 represented poor, fair, satisfactory, good, and excellent, respectively. Evaluation was done in triplicate and the average value was reported.

Storage and Evaluation

Low-fat soft dough biscuits prepared using optimized level of ingredients were packed in low-density polyethylene bags (200 gauge) bags, heat-sealed, and stored under ambient conditions (15–25°C) for further analysis.

Analysis

Moisture, crude protein, crude fat, and total ash were determined using standard^[23] methods. Crude fiber was estimated as per method given in the AACC.^[24] Carbohydrates were calculated by difference method and calorific value was determined by Swaminathan.^[25]

For determining storage stability, the biscuit samples were stored for three months and drawn after every 15 days. The changes in low-fat biscuits during storage were determined by measuring moisture content, free fatty acids (FFA) content, peroxide value (PV), hardness, and sensory characteristics (taste, flavor, and OAA). Hardness was measured at an interval of one month. Moisture and PV were determined according to the method of Weng et al.^[21] FFA content was determined according to AOCS ^[26] method. Hardness of the biscuit was determined by Stable Micro Systems Texture analyzer (TAXT 2i).

The biscuits were evaluated for different sensory characteristics (taste, flavor, and OAA) on 5-point sensory scale where scores 1, 2, 3, 4, and 5 represented poor, fair, satisfactory, good, and excellent, respectively. All the values were taken in triplicate and average value reported.

Statistical Analysis

The data obtained from experiments mentioned above were processed on a Hewlett Packard Computer and was analyzed statistically according to the methods described by Snedecor and Cochran^[27] and Larmond.^[28] Empirical equations were developed and effect of various parameters on the responses was found. The best fit mathematical models were then developed. This was done using spread sheet Lotus 123, Minitab statistical package, multiple response optimization package, and Surfer. The second order model of the form was fitted to the data using Eq. (1):

(1)

where, y is response, x_i, x_j are variables and β_0, β_i, β_ii, β_ij are regression coefficients. The results of the analysis usually consist of coefficients β_o, β₁, β₂,. … β₁₁, β_22,. … … β₁₂, ANOVA, coefficient of correlation, standard deviation, etc. The adequacy of the model was examined by taking into account coefficient of correlation (R²) and F-value. The effect of individual variables was obtained from the probability values. The response was optimized using second order equation. Various softwares such as Eureka, Matlab, Lotus, Quattro, MS Excel was used for solving a set of linear equations. Multiple optimization (MR) optimization package was used for optimizing the individual response and contour plots were drawn to study the effect of parameters on different responses.

RESULTS AND DISCUSSION

RSM Predictions of Optimum Conditions for Use of Fat Replacers in Soft Dough Biscuits

Response surface analysis was applied to the experimental data and the second order response surface model (Eq. 1) was fitted to all the physical (diameter, thickness, spread ratio), textural (hardness, stress-strain ratio), and sensory characteristics (viz. color, texture, taste, flavor, and OAA). The statistical significance of the model terms were examined with the help of regression analysis and ANOVA. It was observed that the F-values for all the models were insignificant (Fcal < Ftab), implying that the models were accurate enough to predict the responses. The variability explained by all the models was more than 70% (R² > 0.70). And also the adequate precision ratio of all the models was more than four, thus indicative of the fact that the experiments were carried out with adequate precision. All the models exhibited statistically adequacy and were hence used to study the effect of processing parameters on the various responses. The result of the regression analysis for all the models is reported in Table 2.

TABLE 2 Regression coefficients of full second order model and significant terms for different properties of low-fat soft dough biscuits containing polydextrose and guar gum

Factor	Spread ratio	Hardness	Stress-strain ratio	Overall acceptability
Intercept	10.977	32.005	0.939	3.259
X1	0.254***	−1.071	−0.121**	−0.160***
X2	0.064	4.048***	−0.012	−0.249***
X3	0.384***	−5.084***	−0.186***	−0.207***
X4	−0.150*	−2.234*	−0.104**	0.102*
X1 X2	−0.147	−0.782	−0.095	0.138*
X1 X3	−0.014	−0.486	−0.071	0.141**
X1 X4	0.033	1.228	−0.000	−0.079
X2 X3	−0.069	0.371	0.076	0.019
X2 X4	−0.197*	1.765	0.118*	−0.001
X3 X4	0.153	0.557	0.093	0.039
X1^2	0.204**	0.505	0.034	0.056
X2^2	0.005	2.114*	0.013	−0.001
X3^2	0.137*	2.479**	0.063	0.087*
X4^2	0.165**	1.957*	0.010	0.123**
R^2	76.44	73.63	70.53	79.93
F-value	3.94***	3.39***	2.91**	4.83***
Adequate precision	7.34	6.59	7.13	10.03

Significant at ***1%; **5%; *10%;

X₁: Sugar; X₂: Composite fat; X₃: Ammonium bicarbonate; X₄: Water;

X₁, X₂, X₃, and X₄ are in coded form.

Table 2 revealed that sugar significantly (p < 0.01) affected all the responses except hardness, whereas composite fat significantly (p < 0.01) affected hardness and OAA. Ammonium bicarbonate and water significantly affected all the responses at 1 and 10%, respectively. The interactive effect of sugar with composite fat and ammonium bicarbonate was found significant on OAA at 10 and 5%, respectively. There was a decrease in OAA with increase in the level of fat replacer and sugar as shown in Fig. 1a. A similar pattern was also seen in Fig. 1b. It was also noted that interaction between composite fat and water had significant effect on spread ratio and stress-strain ratio. Figure 1c depicts that with spread ratio increased with increase in the level of polydextrose and guar gum. A significant increase in stress-strain ratio was observed with increase in the level of fat replacers and water as shown in Fig. 1d. The stress-strain ratio is related to brittleness of the sample. Higher replacement of fat with polydextrose and guar gum resulted in more brittle biscuits. Similar findings had been reported by Zoulias et al.^[29] Sudha et al.^[30] reported the interactive effect of guar gum and maltodextrin (carbohydrate-based fat replacer) on the physical properties of biscuits. He concluded that guar gum helped in the retention of gas during baking thereby improving the texture of biscuits. He also reported that the addition of guar gum significantly affected the breaking strength of biscuits. At quadratic level, sugar had significant (p < 0.05) effect on spread ratio, whereas fat had affected hardness (p < 0.1). Also, ammonium bicarbonate and water significantly affected all responses, except stress-strain ratio, quadratically. Singh et al.^[31] also observed that the change in water and sugar content in the formulation affected the fracture force of cookies.

FIGURE 1 Contour plot representing the effect of different variables on quality of biscuits (X₁: sugar; X₂: composite fat; X₃: ammonium bicarbonate; X₄: water).

The overall effect of sugar was found significant (p < 0.05) on spread ratio and OAA, whereas composite fat had on hardness at 5% and on OAA at 1%. Ammonium bicarbonate affected all responses significantly at 1% and water overall affected (p < 0.1) the spread ratio, stress-strain ratio, and OAA. The combined effect of all variables on responses was more pronounced at linear level (p < 0.01) than on quadratic level. Design expert (Trial version 8.0.6) of the STAT-EASE software was used for simultaneous numerical optimization of the processing parameters. For the optimization of sugar, composite fat (fat, polydextrose, and guar gum), ammonium bicarbonate, and water, these four responses viz. spread ratio, hardness, stress-strain ratio, and OAA were selected because these responses had direct effect on the quality of low-fat biscuit and the criteria used was that sugar, ammonium bicarbonate, and water were kept in range while composite fat was kept minimum whereas spread ratio and OAA was kept maximum and hardness and stress-strain ratio as minimum. By using the given criterion, the optimum condition for different responses obtained was X₁ = –2 (24 g); X₂ = –2 (fat = 10.5 g, polydextrose = 24.2 g, guar gum = 0.3 g); X₃ = 1.03 (2.0 g); and X₄ = 2 (24 mL). The levels were based on 100 g flour. Low-fat biscuits were made based on this optimum condition and responses were measured. The actual values for different responses viz. spread ratio, hardness, stress-strain ratio and OAA were 11.25 ± 0.07, 48.44 ± 3.21 N, 1.74 ± 0.78, and 4.83 ± 0.41, respectively.

The optimized low-fat soft dough biscuits containing polydextrose and guar gum prepared from above mentioned formulation had more spread ratio than control biscuit as given in Table 3. It was also reported that the biscuits prepared with polydextrose and guar gum were significantly harder than the control owing to higher fat content of the latter. The optimized low-fat biscuit was found more brittle than control due to its higher stress-strain ratio (Table 3). A similar findings were reported by Zoulias et al.^[32] who also observed the effect of fat mimetics namely Litesse (improved polydextrose), C*delight MD 01970 (maltodextrins), Dairytrim (b-glucans), pectin, and Simplesse Dry 100 (whey proteins) on the hardness of soft-type cookies. The composition of optimized low-fat biscuit comprised of moisture: 7.2 ± 0.12%; crude protein: 7.49 ± 0.03%; crude fat: 6.45 ± 0.05%; total ash: 1%; crude fiber: 0.68 ± 0.02%; and carbohydrates: 396.72 ± 0.33 as shown in Table 4. The calorific value of low-fat biscuit calculated from the above composition was found to be 396.72 ± 0.33 Kcal/g as compared to 480.28 ± 0.83 Kcal/g in the control biscuit. The percent reduction in calories in low-fat biscuits containing polydextrose and guar gum was 17.4% and the percent fat reduction was found to be 70%.

TABLE 3 Physical characteristics of different types of biscuits*

Products	Diameter (cm)	Thickness (cm)	Spread ratio	Hardness (N)	Stress-strain ratio
A	5.98 ± 0.01^a	0.62 ± 0.00^a	9.64 ± 0.01^a	32.52 ± 1.53^a	0.73 ± 0.08^a
B	6.51 ± 0.01^b	0.58 ± 0.004^b	11.25 ± 0.07^b	48.44 ± 3.21^b	1.74 ± 0.78^b

*Average of six determinations;

Figures followed by different letters in the same column are significantly different from each other (p < 0.05);

A: Control biscuits;

B: Low-fat biscuit containing carbohydrate based fat replacers (polydextrose and guar gum).

TABLE 4 Chemical characteristics of different types of biscuits*

Products	Moisture (%)	Crude protein (%)	Crude fat (%)	Total ash (%)	Crude fiber (%)	Carbohydrates (by difference) (%)	Calorific value (kcal/100 g)
A	5.21 ± 0.06^a	7.57 ± 0.24^a	21.47 ± 0.2^a	0.99 ± 0.00^a	0.57 ± 0.03^a	64.19 ± 0.41^a	480.28 ± 0.83^a
		(7.99)	(22.65)	(1.04)	(0.60)	(67.72)	(506.68)
B	7.20 ± 0.12^b	7.49 ± 0.03^b	6.45 ± 0.05^b	1.00 ± 0.00^b	0.68 ± 0.02^b	77.18 ± 0.06^b	396.72 ± 0.33^b
		(8.07)	(6.95)	(1.07)	(0.74)	(83.16)	(427.5)

Values given in parenthesis are on dry weight basis;

*Average of six determinations;

Figures followed by different letters in the same column are significantly different from each other (p < 0.05);

A: Control biscuits;

B: Low-fat biscuit containing carbohydrate based fat replacers (polydextrose and guar gum).

Storage Characteristics of Low-Fat Biscuits Containing Polydextrose and Guar Gum

The control and the optimized low-fat biscuit were evaluated at 0, 30, 60, and 90 days of storage by determining the moisture, fat, PV, FFA, hardness, and sensory quality. In general, the use of fat replacers resulted in tougher (greater penetration force gradient) soft dough biscuits with higher moisture content as shown in Tables 5 and 6. Low-fat biscuits were less thicker than control biscuit and hence, had more spreadability. The results (Table 5) showed that there was no significant (p < 0.05) change in the moisture content of biscuits containing polydextrose and guar gum but in control biscuit, a significant (p < 0.05) increase in moisture content was noticed during storage. Similar findings were also reported by Rajiv et al.^[33] who also noted an increase in moisture content of biscuits during 90 days of storage. Hardness of both types of biscuits decreased significantly (p < 0.05) during storage period (Table 6). It was found negatively correlated with moisture content of biscuits. Hardness of biscuits made using polydextrose and guar gum was more or less similar up to one month of storage but decreased significantly (p < 0.05) thereafter. Though the hardness of low-fat biscuits was more than control, these biscuits were found crispier by the panelists. However, there was a significant increase in the PV of the control and low-fat biscuits as shown in Fig. 2. Similar findings have been reported by Rajiv et al.^[33] PV of control biscuits and those containing polydextrose and guar gum ranged from 1.44 to 5.11 and 1.24 to 3.43 meq of O₂/kg of fat, respectively, during 0–90 days of storage. This is mainly due to the lipid oxidation in biscuits. But biscuits made from carbohydrate-based fat replacers were found more oxidative stable than control. A similar trend was seen in case of changes in FFA of biscuits during storage (Fig. 3). This increase in FFA was due to increase in moisture content during storage which promoted lipolysis of fats. Higher increases in FFA content during storage was reported in the control biscuits, more than in biscuits containing polydextrose and guar gum. Also, the fat content was found higher in the control biscuits, more than in biscuits containing carbohydrate-based fat replacers which may be one of the major reasons of higher changes in FFA in control biscuit.

TABLE 5 Changes in moisture content (%) of biscuits during storage*

	Storage period (days)
Products	0	15	30	45	60	75	90	SEM	CD at 5%
A	5.21 ± 0.06	5.22 ± 0.02	5.26 ± 0.02	5.26 ± 0.03	5.31 ± 0.00	5.34 ± 0.03	5.36 ± 0.03	0.01	0.05
B	7.20 ± 0.12	7.21 ± 0.04	7.23 ± 0.02	7.24 ± 0.03	7.24 ± 0.01	7.25 ± 0.03	7.25 ± 0.14	0.03	0.09

*Average of three determinations;

A: Control biscuits;

B: Low-fat biscuit containing carbohydrate based fat replacers (polydextrose and guar gum).

FIGURE 2 Changes in peroxide value (meq of O₂/kg of fat) of biscuits during storage.

FIGURE 3 Changes in free-fatty acid content (%) of biscuits during storage.

TABLE 6 Changes in hardness (N) of biscuits during storage*

	Storage period (in months)
Products	0	1	2	3	SEM	CD at 5%
A	32.52 ± 1.54	31.44 ± 0.69	31.19 ± 0.91	28.74 ± 1.29	0.47	1.39
B	48.44 ± 3.20	45.24 ± 1.31	40.89 ± 1.51	38.21 ± 0.71	0.84	2.47

*Average of three determinations;

A: Control biscuits;

B: Low-fat biscuit containing carbohydrate based fat replacers (polydextrose and guar gum).

Sensory evaluation of biscuits containing polydextrose and guar gum comparing them to control biscuits is shown in Fig. 4. It was noted that there was a significant difference (p < 0.05) in taste score during 90 days of storage in control and low-fat biscuit containing polydextrose and guar gum. The score of low-fat biscuit at the end of storage period was found higher than the control biscuit and thus, was more preferred by the panelists. The control and low-fat biscuits differed significantly (p < 0.05) in taste score up to 30 days of storage but score showed non-significant change during 45 to 75 days storage (Fig. 5). The OAA score was found maximum for biscuits having polydextrose and guar gum, while minimum was seen for control biscuits as shown in Fig. 6. Though the OAA score of both the biscuits decreased significantly (p < 0.05) during storage, the low-fat biscuit was still acceptable by the panelists. It was concluded from the storage study that the replacement of fat with carbohydrate-based fat replacers leads to little changes in sensory parameters of low-fat biscuits than its counterpart.

FIGURE 4 Changes in taste scores of optimized products during storage.

FIGURE 5 Changes in flavor scores of optimized products during storage.

FIGURE 6 Changes in overall acceptability (OAA) scores of biscuits during storage.

CONCLUSIONS

The present study showed that highly acceptable low-fat biscuit was developed by replacing up to 70% of fat in the formulation and resulted in more crispy, brittle, and tasty product than the control biscuit. The study revealed that the texture of biscuit was greatly dependent on the level of the fat and sugar in the formulation. An increase in polydextrose and guar gum level results in harder cookies but found crispier. The brittleness was increased on addition of fat replacers in biscuits and thus resulted in high stress-strain ratio. During storage, the low-fat biscuit containing polydextrose and guar gum was found more oxidative stable due to less increase in PV and FFA content and was also more acceptable.

Acknowledgments

The authors are grateful to Dr. Shruti Sethi, Scientist, and Dr. S.K. Jha, Senior Scientist, at the Division of Postharvest Technology, Indian Agricultural Research Institute, New Delhi for permitting the use of the texture analyzer.