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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2020 Oct 15;58(7):2630–2640. doi: 10.1007/s13197-020-04769-9

Effect of fat and sugar replacement on rheological, textural and nutritional characteristics of multigrain cookies

K Ashwath Kumar 1, M L Sudha 1,✉
PMCID: PMC8196185  PMID: 34194098

Abstract

Fat and sugar are responsible for the structure of cookies but make them nutritionally inferior. Therefore, in the present study, cookies with improved nutrition using whole wheat flour (WWF) and incorporation of multigrain mix (MM-oats, peas and fenugreek flours) at 0, 25, 50, 75 and 100% levels was studied. Further, fat was replaced using pumpkin seed (PS) or watermelon seed (WS) at 25, 50 and 75% level and sugar was replaced using dry dates (DD) or raisins (RS) separately at 20, 40 and 60%. MM having protein at 15.13% and dietary fibre at 12.83% significantly decreased the water absorption (68.1–60.6%), stability (2.52–1.35 min), amylograph peak viscosity (665–821 BU), and cookie dough hardness (1737–690.5) at 100% MM. Based on the physico-sensory analysis, 75% replacement of WWF with MM was selected for replacement of fat or sugar. Addition of PS or WS increased the dough hardness (1235–4103 g), whereas the spread ratio of cookies decreased from 6.25 and 6.31 to 5.54 and 4.06 respectively. Replacement of fat with PS at 50%, sugar by DD at 40% along with a combination of sodium stearoyl lactylate (SSL) and glycerol mono stearate (GMS) showed improvement in the cookie texture. The scanning electron microscope (SEM) of cookie showed coating of starch granules and appearance of sheet-like covering of protein network. The mono and polyunsaturated fatty acid profile of cookies improved apart from a two-fold increase in protein and three-fold increase in dietary fibre.

Keywords: Multigrain cookies, Fat replacement, Sugar replacement, Dietary fibre, Fatty acid profile

Introduction

The texture of cookies play an important role in the acceptability of the product and is directly related to the main ingredients such as flour, fat and sugar used in the formulation. Usually starch plays an important role in building a structure in many food products. However, in case of cookies, starch is considered as an inert filler, whereas, fat and sugar play a key role in building the structure of cookies (Mamat and Hill 2014). The consumption of high fat and sugar also lead to major lifestyle disorders like obesity, diabetes, cholesterol, coronary heart disease etc. Reducing the fat and sugar content in cookie formulation is the best way to obtain healthier and lower-calorie products (Drewnowski et al. 1997). Also, there is an increasing customer demand for healthy bakery products with proportionately low fat and sugar ingredients. The complete removal of fat and sugar in complex food system like cookies is difficult; therefore many researchers had suggested limiting to partial replacement to produce good, acceptable quality products (Zoulias et al. 2002).

The fat and sugar replacers are ingredients used in the formulation to mimic the role in the product without affecting the textural and sensorial characteristics. Fat has a shortening effect and also act as a lubricant during mixing, enhancing flavour, mouthfeel and palatability. Sugars, apart from adding sweetness, help to incorporate air inside the shortening during dough development and during baking it contributes to biscuit spread and recrystallization of sucrose provide structure to the product (Hoseney and Rogers 1994; Zoulias et al. 2002).

The fat and sugar replacers are like carbohydrate based (hydrocolloids, starch derivatives, hemicellulose, beta-glucans and soluble bulking agent), protein based and fat based (emulsifiers and synthetic fat substitutes) etc. The most regularly used carbohydrate based fat replacers are inulin, polydextrose, maltodextrin, hydrocolloids and modified starches etc. Serin and Sayar (2016) reported that fat can be replaced using carbohydrate based replacers up to 30% in pogaca formulation without any decrease in the physical, textural and sensory quality of pogaca. Zoulias et al. (2002) studied the effect of Raftiline, Simplesse, C*deLight and polydextrose as fat replacers and polyols namely lactitol, sorbitol and maltitol, for sugar replacement in low-fat, sugar-free cookies. The use of selected carbohydrate based fat replacers derived from pectin; gums and oat bran in fat reduced biscuits were studied by Conforti et al. (1996). The reduction of fat at 33%, 66% and 100% significantly increased the moisture content and crust colour became lighter. Sudha et al. (2007) used polydextrose and maltodextrin in equal quantity as a fat replacer and use of either guar gum or glycerol monostearate along with maltodextrin improved the texture of biscuits significantly.

The above studies clearly show that the fat or sugar mimetics used are synthetic or extracted from natural ingredients in a chemical manner. However, none of the studies so far reported on the use of natural fat and sugar-rich ingredients as mimetic to replace the saturated fat or refined sugar. The use of natural ingredients like WS, PS or DD, RS will improve the nutritional profile of the end products viz. reduced fat, with improved fatty acid profile, mineral profile, dietary fibre etc. Therefore, in the present study, the natural ingredients like PS or WS as fat replacers and DD or RS as sugar replacers on multigrain incorporated whole wheat flour cookies and its effect on rheological, textural, physico-sensorial and nutritional properties were studied.

Materials and methods

Raw materials

The multigrain like oats (Avena sativa), dry peas (Pisum sativum), fenugreek (Trigonella Foenum-Graecum L), WWF and mimetics like WS, PS, RS, DD, butter (Nandini brand), refined sugar powder, skimmed milk powder (Sagar brand), edible salt were procured from the local market, Mysore, India. The baking chemicals such as sodium bicarbonate and ammonium bicarbonate, emulsifiers like sodium stearoyl-2 lactylate (SSL) and glycerol monostearate (GMS) were procured from SD Fine Chemicals, Mumbai, India.

Formulation of MM and replacers

The oats, green peas and fenugreek were milled in a laboratory mill 3100 of Perten instruments (Perkin Elmer), Australia to a particle size of 200 microns. Based on the baking experiment trials to produce multigrain cookies, the oat and green pea flours were mixed in the proportion of 60:40 and 0.5% of fenugreek flour was added to the mix and blended (MM) and was used to replace whole wheat flour at 0, 25, 50, 75 and 100% level. The WS and PS were cleaned and dried at 60 °C for 1 h and further milled coarsely to 400 microns size using a laboratory mill to make grits. RS and DD were also ground similarly.

Chemical composition

The chemical composition like moisture, ash, protein, fat and dietary fibre content of flours were analysed based on AACC (2000) procedures. The experiments were carried out in triplicates and mean values are reported.

Rheological characteristics of wheat flour

The rheological properties of WWF and the effect of MM incorporation on WWF dough was studied using farinograph (Model: E-380, Brabender OHG, Duisburg, Germany) and starch pasting properties using micro-visco amylograph (Model No. 803201, Brabender Measurements and Control Systems, Duisburg, Germany) according to AACC (2000) methods.

Cookie making characteristics

The formulation and methodology followed for experimental baking of cookies were as per Sindhuja et al. (2005) with slight modification. The cookie sheets of 8 mm thick and 75 mm diameter were baked at 200°C for 15 min using an electric oven (APV-ROTEL, Australia). The cookies were prepared from MM at different levels viz. 0, 25, 50, 75 and 100%  replacement of WWF. The replacement of fat at 25, 50 and 75% level using PS and WS separately and sugar replacement at 20, 40 and 60% level using RS and DD were carried out accordingly. The improvement of the texture of optimized cookies using SSL and GMS were also studied.

Physical characteristics of cookie dough and cookie

The hardness of cookie dough and breaking strength of cookies were carried out using a texture analyser (Lloyd Instruments Ltd, Hampshire, England). The maximum compression strength required for compressing to 50% of the cookie dough and force required for breaking the cookie using triple beam snap technique were carried out as per the method of Kumar et al. (2015). The weight of cookies was noted. The spread ratio was calculated by using the formula: diameter divided by the thickness of cookies (Kumar et al. 2016). Colour values of cookie surface were measured using Hunter Lab colour measuring system (Labscan XE, USA) (Kumar et al. 2015).

Sensory characteristics

Quantitative descriptive analysis (QDA) was used to analyse the sensory characteristics of cookies. 20 panellists in the age group of 25 and 50 years, including ten male and ten females, who had earlier experience in quality evaluation of bakery products were selected and further oriented in four sessions, including 2 h of training in each session. The samples were identified with three-digit code numbers and presented in a random order to the panellist as per the method of Kumar et al. (2015).

Scanning electron microscope (SEM) studies of cookies

The SEM of control and optimized cookies were analysed using Leo Scanning electron microscope Model 435 VP (Leo Electronic Systems, Cambridge, UK.) The sample preparation for the study was carried out according to the method of Kumar et al. (2015). The defatted and freeze-dried samples were gold coated and morphological analysis was carried out at high pressure of 9.75 × 10–5 and observed at 15 kV.

Nutritional properties of cookies

The cookies were analysed for moisture, ash, protein, fat and dietary fibre content as per the methods explained earlier. The fatty acid profile of cookies was estimated according to AOCS (1990) methods using Gas chromatograph-mass spectrometry (PerkinElmer TurboMass Gold).

Statistical analysis

The experiments were carried out in triplicates, and the results are expressed as mean ± standard deviation. All the data were analysed for statistical significance by one-way analysis of variance (ANOVA) according to the method described by Steel and Torrie (1960).

Results and discussion

Chemical characteristics of flours

The chemical characteristics of MM and WWF showed that the ash content of MM (3.14%) was three times more than the WWF (1.38%). The protein, fat and dietary fibre in WWF was 10.38%, 1.53% and 11.69% respectively. Whereas the MM had higher protein, fat and dietary fibre content at 15.13% and 5.03% and 12.83% respectively.

Rheological characteristics of flours

Farinograph characteristics

The effect of incorporation of MM on the dough mixing characteristics of WWF showed that the water absorption capacity (WAC) of WWF is 68.1% and incorporation of MM significantly (p ≤ 0.05) decreased the WAC to 60.6% for 100% MM (Fig. 1a). A similar finding was reported by Shimray et al. (2012) in wheat flour-finger millet blend and described that even though finger millet is a fibre rich flour containing a greater number of hydroxyl groups in their fibrous structure, did not increase the WAC when added to wheat flour. Therefore, the decrease in WAC is attributed to the dilution and disruption of the continuity of gluten protein with the incorporation of non-gluten MM (Kumar et al. 2015). The dough development time (DDT) indicating the time required to reach 500 BU consistency, decreased from 4.19 to 3.18 min up to 50% incorporation and at higher levels of 75 and 100% incorporation, it increased. Earlier, Kumar et al. (2015) also reported that there was no drastic change in DDT up to 20% addition of multigrain premixes to wheat flour, however, beyond that level, DDT increased significantly. This increase in DDT at higher levels is attributed to less water availability for gluten development thereby causing a delay in hydration.

Fig. 1.

Fig. 1

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Effect of MM on the rheological characteristics of WWF dough. WWF Whole wheat flour, MM multigrain mix

The dough stability (DS) indicating the dough strength, measured by time in min the dough remains in 500 BU consistency. The incorporation of MM decreased the DS from 2.52 to 1.35 min with the addition of 75% MM. However, only at 100% incorporation, it increased to 4.38 min. Metwal et al. (2011) reported that incorporation of fenugreek and flax seed powder (10–30% level) to wheat flour increased the DDT and DS and this could be due to delayed gluten development. Similarly, in our study, at a 100% level, absence of gluten and slow hydration characteristics of MM increased the DDT and DS. The mixing tolerance index value which is inversely proportional to the strength of the dough significantly increased. Rajiv et al. (2012) the studied the effect of green gram flour incorporation (10–50%) on wheat flour rheology and reported that the DDT, MTI increased and DS decreased, thereby showing the weakening effect of dough with the incorporation of non-wheat flour. The above results show that the incorporation of MM conferred a different mixing characteristics to the dough due to the presence of higher protein, fat and fibre content than WWF.

Amylograph characteristics

With the incorporation of MM to WWF from 0 to 100%, the gelatinization temperature significantly (p ≤ 0.05) decreased from 62°C to 58.5°C. The peak viscosity, the measure of starch’s ability to swell freely before it physically breaks down increased from 665 to 821 BU (Fig. 1b). The above results show that the swelling capacity of starch granules increased with the addition of MM (Rajiv et al. 2012). The hot paste viscosity indicating the stability of broken starch granules at cooking temperature (95°C) increased from 447 to 522 BU. The cold paste viscosity, representing the cooked paste after cooling to 50°C increased from 895 to 1032 BU indicating the strong tendency for starch retrogradation. Breakdown viscosity indicating the ease with which the swollen granules are disintegrated also increased from 208 BU for WWF to 299 BU for 100% MM. The increase in breakdown viscosity shows the increased resistance offered by starch granules to heat treatment and mechanical shearing. The setback viscosity indicating the retrogradation of the cooked starch increased from 448 to 510 BU. Rawat and Darappa (2015) also reported similar findings of increased breakdown and setback viscosity of wheat flour with the addition of fibre-rich ingredients mix. They reported that higher breakdown and setback values confirm that, high fibre in the flour interacts with wheat starch, make the swollen granules more fragile and while cooling convert them to semi-solid paste. Schoch and Maywald (1968) reported that the higher content of other components particularly protein and fat influence the starch swelling power and pasting properties. A similar finding was reported by Indrani et al. (2010) on the incorporation of multigrain mix (0–20%) to wheat flour.

Effect of MM on the cookie quality

Cookie dough texture

The effect of incorporation of MM on the cookie dough hardness are presented in Table 1. As the level of incorporation of MM increased from 0 to 100%, the hardness of the dough decreased. The control dough had 1737 g and it decreased to 690.5 g for 100% MM. As the level of MM incorporation increases, the dough lost its cohesiveness and became sticky. Earlier, Metwal et al. (2011) also reported the decrease in hardness of cookie dough with the incorporation of functional ingredients mix and attributed to the dilution of gluten and also decreased water-binding capacity of gluten due to the presence of high absorption ingredients in the dough system leading to sticky structure.

Table 1.

Physical characteristics of cookie dough and cookies

Sample Weight (g) Spread ratio Cookie surface colour Dough Hardness (g) Breaking Strength (g)
L* a* b*
MM replacement
 MM0 13.23 ± 0.21e 5.65 ± 0.11c 60.75 ± 0.01a 9.05 ± 0.02e 23.80 ± 0.02a 1737.0 ± 34.3a 1046.0 ± 71.6e
 MM25 14.43 ± 0.11d 5.67 ± 0.13c 57.18 ± 0.05b 9.31 ± 0.07d 23.56 ± 0.02b 1505.0 ± 66.9b 1294.3 ± 27.1d
 MM50 14.61 ± 0.12c 5.83 ± 0.11bc 56.91 ± 0.02c 9.64 ± 0.05c 23.25 ± .02c 1340.0 ± 45.2c 1495.3 ± 54.5c
 MM75 14.92 ± 0.17b 6.31 ± 0.22b 55.34 ± 0.03d 9.78 ± 0.04b 22.87 ± 0.03d 1235.0 ±32.4d 1619.8 ± 20.7b
 MM100 16.17 ± 0.09a 6.71 ± 0.15a 54.18 ± 0.02e 9.94 ± 0.02a 22.48 ± 0.01e 690.5 ± 11.7e 2504.3 ± 38.5a
Fat replacement
 MM75 14.92 ± 0.12c 6.31 ± 0.22a 55.34 ± 0.03ef 9.78 ± 0.04a 22.87 ± 0.03b 1235.0 ± 32.4 g 1619.8 ± 20.7g
 WS25 15.23 ± 0.13bc 5.66 ± 0.14c 57.30 ± 0.02c 6.95 ± 0.02e 22.62 ± 0.05c 1956.8 ± 32.5e 1998.5 ± 52.3e
 WS50 15.53 ± 0.08b 4.58 ± 0.15ef 55.43 ± 0.03e 6.92 ± .02e 22.36 ± 0.05d 3560.0 ± 50.9c 3389.0 ± 76.9c
 WS75 16.15 ± 0.11a 4.06 ± 0.11f 59.17 ± 0.05b 5.08 ± 0.02f 22.57 ± 0.05 cd 4103.5 ± 22.5a 4905.0 ± 85.6a
 PS25 15.07 ± 0.15bc 5.85 ± 0.11b 57.27 ± 0.02c 7.40 ± 0.02 cd 22.99 ± 0.03a 1671.5 ± 36.4f 1764.5 ± 43.8f
 PS50 15.31 ± 0.21b 5.49 ± 0.17d 56.57 ± 0.02d 7.49 ± 0.01b 22.62 ± 0.07c 2834.0 ± 43.3d 2994.5 ± 76.9d
 PS75 15.96 ± 0.18a 4.78 ± 0.16e 59.40 ± 0.03a 7.38 ± 0.03c 22.35 ± 0.03d 3741.5 ± 47.6b 4550.05 ± 92.2b
Sugar replacement
 PS50 15.31 ± 0.21d 5.49 ± 0.17a 56.57 ± 0.02a 7.49 ± 0.01e 22.62 ± 0.07a 2834.0 ± 43.3 g 2994.5 ± 76.9f
 DD20 15.42 ± 0.07d 4.92 ± 0.13b 53.52 ± 0.01b 6.61 ± 0.05f 21.66 ± 0.02d 3317.0 ± 38.2f 3479.5 ± 105.4e
 DD40 15.97 ± 0.06c 4.58 ± 0.12 cd 50.13 ± 0.05d 7.94 ± 0.06d 20.82 ± 0.02c 3692.8 ± 58.7d 4022.3 ± 51.1d
 DD60 16.67 ± 0.08b 4.27 ± 0.11e 47.57 ± 0.06f 8.52 ± 0.07c 19.85 ± 0.05f 5665.8 ± 52.4b 5868.5 ± 61.3b
 RS20 16.10 ± 0.13c 4.69 ± 0.09c 52.51 ± 0.06c 8.02 ± 0.02d 21.98 ± 0.03b 3597.5 ± 64.1e 3483.8 ± 90.3e
 RS40 16.33 ± 0.19bc 4.29 ± 0.12e 49.00 ± 0.06e 9.24 ± 0.01b 21.10 ± 0.06e 4198.0 ± 77.7c 4317.3 ± 34.3c
 RS60 16.85 ± 0.09a 3.89 ± 0.11f 44.59 ± 0.02 g 10.45 ± 0.05a 19.55 ± 0.07 g 5878.0 ± 53.9a 5976.0 ± 95.7a
Emulsifiers
 DD40 15.97 ± 0.06a 4.58 ± 0.12d 50.13 ± 0.05c 7.94 ± 0.06a 20.82 ± 0.02c 3692.8 ± 58.7a 4022.3 ± 51.1a
 SSL 15.55 ± 0.21b 4.89 ± 0.17c 53.53 ± 0.05a 7.09 ± 0.03c 21.48 ± 0.06a 3472.5 ± 36.2b 3512.0 ± 74.9b
 GMS 15.28 ± 0.11c 5.06 ± 0.09b 52.07 ± 0.02b 6.98 ± 0.05d 21.17 ± 0.04b 3253.5 ± 53.7c 3285.5 ± 77.9c
 SSL + GMS 14.53 ± 0.14d 5.32 ± 0.19a 49.91 ± 0.02d 7.42 ± 0.02b 20.52 ± 0.03d 2597.0 ± 74.0d 2860.8 ± 36.8d
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Values are mean ± standard deviation of three independent determinations. Mean values in the same column within the experiment group followed by different superscripts differ significantly (P ≤ 0.05). L: lightness/darkness; a: redness/blueness; b: yellowness/greenness

MM multigrain mix, WS watermelon seed; PS pumpkin seed, DD dry dates, RS raisins, SSL sodium steoryl lactylate, GMS glycerol mono stearate

Physical characteristics of cookies

The incorporation of MM significantly affected the cookie physical characteristics like weight, diameter, thickness and spread ratio (Table 1). The weight of the cookies increased from 13.23 g for control to 14.43, 14.61, 14.92 and 16.17 g respectively at 25, 50, 75 and 100% MM. Kumar et al. (2015) reported the similar findings of increased biscuit weight with the addition of multigrain premix at 0–40% level. They attributed the increase in weight of biscuits to increase in density of biscuits by the use of high protein fibre-rich ingredients, which have a higher affinity for water retention even after baking. The spread ratio of cookies increased from 5.65 to 6.71. Lai and Lin (2006) reported that, during baking, melting of fats allows the water molecules to migrate and these water molecules are available for dissolution of sugars thereby helps to increase the spread. The colour of cookie which is a very important parameter for consumer showed that with an increase in MM, a decrease in the lightness value, increase in redness and yellowness values. These results indicate that the cookies are becoming darker in colour as the level of incorporation of MM increased. The lightness of cookies is negatively correlated to the protein content of flour as the Maillard reaction play an important role in the colour formation apart from the caramelization of sugars (Chauhan et al. 2016).

Sensory characteristics

The surface colour of WWF cookie was golden brown colour, with a crunchy texture and eating quality indicates a clean mouthfeel without any residue (Fig. 2a). The cookie surface became rough and darker in colour with the increase in MM. Also, the crumb colour became darker. The breaking strength values increased up to 50% incorporation, however, cookies became brittle due to the reduction in gluten content at 100% MM. Kumar et al. (2015) reported that addition of multigrain at 10–50% level, biscuits became darker and harder and attributed it to the presence of higher protein and fibrous materials in multigrain. The mouthfeel and overall quality score (OQS) indicated that the MM can be incorporated up to 75% without affecting the sensory parameters of the cookies. Hence the cookies with 75% incorporation of MM were selected for further studies.

Fig. 2.

Fig. 2

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Qualitative descriptive analysis of the multigrain cookies. a Effect of MM incorporation; b effect fat replacement, c effect of sugar replacement, d effect of emulsifiers. MM Multigrain mix, WS watermelon seed, PS pumpkin seed, DD dry dates, RS raisins, SSL sodium steoryl lactylate, GMS glycerol mono stearate

Effect of fat and sugar replacement on the cookie quality

Effect of fat replacement

Cookie dough

Fat helps in binding all the raw materials in cookie dough system and was replaced at 25, 50 and 75% level using WS and PS separately. The hardness of the cookie dough increased significantly (p ≤ 0.05) on replacing with either WS or PS. The hardness of the dough increased from 1235 g for 75% MM incorporated dough to 4103 g for dough with WS incorporation at 75% level. This is mainly due to the reduction in saturated fat, which has a major role of air incorporation during mixing and also non-availability of bound fat within the seeds during dough mixing thereby producing stiffer dough. Earlier, Sudha et al. (2007) and Mama and Hill (2014) confirmed the similar finding of increased dough hardness with the reduction in fat content.

Physical characteristics

The weight of the cookies increased from 14.92 g to 16.15 g due to further increase in density. Earlier, Sudha et al. (2007) reported that reduction in saturated fat during mixing increases the density of the dough and biscuit. The spread ratio of cookies decreased from 6.31 to 4.06 at WS 75% level. This may be due to the bound fat present inside the seeds, which are not available for melting while baking as reported by Zoulias et al. (2002). Colour parameters of cookies showed that lightness of cookies decreased and redness increased. It was observed that the hardness of the dough influenced the texture of the cookies. However, the extent of increase in hardness of cookies was less in cookies with PS25 (1764.5 g), WS25 (1998.5 g) followed by PS50 (2994.5 g) when compared to control (1619.8 g). Earlier, Sudha et al. (2007) reported that the fat reduction on the soft dough biscuits increased the dough hardness and the same got reduced when fat was replaced with an equal amount of maltodextrin or polydextrose.

Sensory characteristics

The surface colour of cookies became brighter in colour by replacing fat either with PS or WS as substantiated with the hunter colour values (Fig. 2b). The lightness value increased thereby indicating the improvement in colour parameters (Table 1). The texture of cookies followed a similar increasing trend like breaking strength of the cookies when using either PS or WS to replace fat at different levels. The OQS indicated that there was no significant (p  ≤ 0.05) difference in the sensory score at 25% level of fat replacement using either PS or WS; however, at higher levels of 50 and 75%, PS replacement was more acceptable. Chugh et al. (2013) reported that polydextrose and guar gum can be used as fat replacer at a relatively higher level of 70% level with an increased score for taste, flavour and acceptability. Based on the physico-sensory characteristics of dough and cookies, PS was found to be better fat replacer at any comparable levels when compared to WS and maximum fat replacement can be achieved without affecting the physico-sensory quality were up to 50% level. Therefore, the cookies with 50% fat replacement using PS was selected for further studies.

Effect of sugar replacement

Cookie dough

The hardness of cookie dough increased with the replacement of sugar either with DD or RS. The extent of the increase in hardness was comparatively less when sugar was replaced with DD. The hardness of the cookie dough significantly (p  ≤ 0.05) increased from 2834 g for 50% fat replaced dough (control) to 5665 and 5878 g at 60% replacement of sugar with DD and RS respectively (Table 1). The sugar content in DD or RS was not readily dissolving during dough mixing due to its complex structure. The granulation and solubility nature of the sweetener during the dough mixing stage also affects the dough hardness (Handa et al. 2012).

Physical characteristics

The reduction in sugar content increased the weight of the cookies from 15.31 g for control (50% fat reduced cookies) to 16.85 g for 60% sugar replaced cookie with RS and minimum increase in weight was observed with DD at 20% (15.42 g) and 40% (15.97 g). The RS or DD has more affinity for water during mixing and it retains more moisture even after baking than sugar. The spread ratio of the cookies further reduced while using sugar replacers. The reduction in spread ratio is due to a reduction in sugar content which dissolves during baking thereby allowing greater spread in cookies (Handa et al. 2012). Hunter colour values of cookie showed that replacement of sugar either with DD or RS significantly (p  ≤ 0.05) decreased the lightness and increased the redness and yellowness values. The reduction in sugar content is expected to increase the lightness of cookies due to decreased availability of reducing sugar for Maillard reaction (Kulp et al. 1991a). However, the decrease in the lightness of cookie attributed to the use of dark coloured ingredients as a sugar replacer. The breaking strength of cookies showed a similar increasing trend like cookie dough hardness with the use of increasing level on sugar replacement. Bullock et al. (1992) studied the replacement of sugar with non-nutritive sweeteners acesulfame-K along with bulking agents such a polydextrose, cellulose and soya fibre and observed that, the force required to break the cookies decreased from 582 g for control to 280 g, 270 g and 190 g respectively for replacement of sugar with polydextrose, powdered cellulose and soy fibre cookies. Among the two sugar replacer used at different levels, the DD at 40% replacement showed a minimum adverse effect on the physical characteristics of cookies.

Sensory characteristics

The sensory studies of the cookies showed that score for the surface colour of cookies significantly (p  ≤ 0.05) decreased with the increase in sugar replacement (Fig. 2C). The texture of cookies became harder and the extent of increase in cookie hardness was less with DD at comparable levels of 40% than any other cookies. The OQS of cookies indicated that DD at 20% (7.2) and 40% (7.0) incorporation was almost nearer to control (7.4). Based on the physical and sensory analysis of cookies, it can be concluded that the use of DD to replace sugar at 40% level gave better acceptable cookies than RS at any levels. Savitha et al. (2008) reported that the cookies prepared with 0.05% sucralose to replace 30% of sugar along with 30% of maltodextrin were incomparable with control biscuits.

Effect of emulsifiers

The emulsifiers get adsorbed on to the starch granules to avoid the binding of gelatinized starches to delay the swelling process and helps to forms complex with starch and protein (Forssell et al. 1998). The cookies prepared with 50% fat replacement using PS and 40% sugar replacement using DD were treated with emulsifiers like GMS, SSL and in a combination of both (50:50) to improve the quality characteristics. GMS acts as crumb softener by forming a complex with amylose, which is insoluble in water and will not involve in retrogradation of starch during cooling. SSL acts as both crumb softener and dough strengthening agent (Kumar and Sharma 2018).

Cookie dough

The addition of emulsifier significantly (p  ≤ 0.05) decreased the dough hardness. The hardness of the dough decreased from 3692 g for control (50% fat and 40% sugar reduced) to 3472, 3253 and 2597 g with the use of GMS, SSL and combination of GMS and SSL respectively. Kumar and Sharma (2018) reported the considerable decrease in multigrain biscuit dough hardness with the incorporation of amphoteric (lecithin), non-ionic (GMS) anionic (SSL and DATEM) surfactants. Azizi and Rao (2005) reported that surfactants strengthen the dough by modification of gluten in its state of oxidation or surface tension between its aqueous and fat phases.

Physical characteristics

The addition of GMS, SSL or combination both decreased the weight of cookies and increased spread ratio to varying levels. The decrease in weight of the cookies attributed to decreased density. The increase in the spread ratio of cookies during baking also allows more water evaporation, thereby decreasing the cookie weight. Earlier, Manohar and Rao (1999) also reported decreased weight and increase in the spread ratio of biscuits with lecithin, GMS and SSL. The lightness value of cookie increased and redness, yellowness values decreased with the addition of emulsifiers. Kissell and Yamazaki (1975) observed that the addition of surfactants to the biscuit dough system has the counteractive effect of decreasing dough viscosity and extending the water availability for a longer time during expansion process to increase the spread of biscuit dough during baking and decrease the biscuit density.

Among the two emulsifiers used, GMS showed better improvement effect than SSL for spread ratio and breaking strength of cookies. Tsen et al. (1983) observed the similar findings that GMS helped to improve the spreadability of soy flour incorporated high protein cookies. However, the combination of emulsifiers showed maximum improvement in physical characteristics. The weight of cookies decreased from 15.97 to 14.53 g, cookie dough hardness decreased from 3692.8 to 2597 g; and breaking strength valued decreased from 4022.3 to 2860.8 g. Bansal and Sudha (2011) reported that the combination of GMS and SSL each at 0.25% improved the spread, crispiness and reduction in hardness of wheat germ incorporated biscuits.

Sensory characteristics

The addition of any surfactant individually or in combination significantly (p ≤ 0.05) improved the sensory attributes of the fat and sugar reduced MM cookies (Fig. 2d). The visual appearance of cookies like surface colour and surface character; and mouthfeel, texture and OQS increased with the addition of emulsifiers, however, the highest improvement was observed when using in combination. Based on the above results it can be concluded that fat replaced up to 50% level by using PS, sugar replaced up to 40% level by using DD as replacer and emulsifiers when using a combination of both gave maximum improvement effect.

Scanning electronic microscopic (SEM) studies of cookies

The SEM instrument is most oftenly used to study the changes in the internal structure of cookies like changes in cell size, density, uniformity, which affects the sensory properties of cookies (Mamat and Hill, 2014). SEM images of control cookies (Fig. 3A) showed the presence of partially gelatinized large starch granules enmeshed in the protein matrix. Due to the presence of excess sugar and lack of available water in the cookie dough system, most of the starch granules did not gelatinize during baking (Kulp et al. 1991b). In SEM of fat and sugar reduced multigrain cookies (Fig. 3b), the continuity of the protein matrix was disrupted. The starch granules appear coated and sheet-like covering of protein network appeared. Aranyi and Hawrylewickz (1969) described that the protein component of dough is the network which covers the starch granules. The surface of fat and sugar reduced multigrain cookies showed various sized openings and cavities. These cavities are formed due to the expansion of gas bubbles during baking leading to rupture of the surface of cookies, where the gas escapes. Earlier, Flint et al. (1970) also reported similar openings of various sizes on the surface of sweet, semi-sweet and cream biscuits.

Fig. 3.

Fig. 3

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Scanning electron microscopic images of cookies. a Control cookies, b fat and sugar replaced multigrain cookies

Nutritional evaluation of cookies

Proximate composition

The proximate composition of control and fat and sugar replaced multigrain cookies showed that the moisture content of the cookies significantly increased from 2.23 to 3.56%, however, these values fall under the range prescribed for moisture content (5%) for biscuits and cookies as reported by Pereira et al. (2013) (Fig. 4a). The increase in the moisture content of the cookie could be attributed to high protein content due to the use of MM, which reported to have more affinity for water (Kumar et al. 2018). The ash content of cookies increased with the use of PS and DD. The important finding of the study is that the fat content of the cookies decreased with 50% replacement of fat with PS from 23.93% for control WWF cookie to 18.39% for multigrain cookies. There is a two-fold increase in protein content and a threefold increase in dietary fibre content of MG cookies.

Fig. 4.

Fig. 4

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Nutritional characteristics of cookies. a Control cookies, b fat and sugar replaced multigrain cookies. MM Multigrain mix

Fatty acid profile

The fatty acid profile of fat extracted from control and fat and sugar replaced multigrain cookies are presented in Fig. 4b. Eight peaks for saturated, mono and polyunsaturated fatty acids were detected, but the area under the curve varied according to the concentration of particular fatty acid. In control cookies, the saturated fatty acids like lauric acid, myristic acid, palmitic acid contents were significantly higher than MM cookies. The replacement of fat using WS significantly improved the oleic acid and linoleic acid content from 15.58, 0.86% in control cookies to 27.83, and 11.37% in sugar and fat reduced cookies respectively.

Conclusion

The above investigation indicates that the MM containing oats, dry pea and fenugreek flour can be used to replace WWF at 75% level. The replacement of WWF using MM affected the rheological characteristics by decreasing the water absorption, stability, peak viscosity and breakdown viscosity. The cookie dough became soft and lost its cohesiveness. The cookies prepared also showed an increase in diameter, spread ratio and decrease in thickness and breaking strength. The mouthfeel and overall quality score of sensory studies indicated that the MM can be incorporated up to 75% without affecting much on the sensory parameters of cookies. The replacement of fat using PS and WS affected the cookie dough and cookie at varying levels. Physico-sensory studies indicated that PS at 50% and DD at 40% replacement showed a minimum adverse effect on the physical quality characteristics of cookies. These minimum adverse effects were improved using a combination of emulsifiers. The nutritional profile of cookies indicated that fat content decreased in multigrain cookies and fatty acid profile showed an increase in oleic acid and linoleic acid and decrease in saturated fatty acids.

Footnotes

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