Ingredient |
Gluten-free mixture base |
Gluten-free mixture |
70 |
Blueberry pomace |
30 |
Sugar |
35 |
Glucose syrup |
16 |
Vegetable fat |
18 |
Powdered egg |
2 |
Water |
36 |
Cookie |
Temperature |
Time (min) |
1 |
170 |
10 |
2 |
170 |
13 |
3 |
170 |
14 |
4 |
170 |
16 |
5 |
160 |
16 |
6 |
160 |
17 |
Cookies weight (m0 and mt) was determined as average value of 8 independent measurements.
Baking is a complex process which results in a series of physical, chemical and biochemical changes in the product (Sablani et al., 1998). Physically, it is a process involving the simultaneous heat and mass transfer phenomena, and both baking time and temperature are industrially important process considerations affecting the final quality (Fahloul et al., 1994; Sablani et al., 1998). Dimensions and moisture content changes of cookies are considered to be important parameters of cookie quality, since the large variability in these parameters may cause breakdown (cracking, checking, etc) problems (Cronin and Preis, 2000). Typical baking temperatures for fibre enriched cookies are in the range of 160-180 ºC (depending on the type of oven) with a baking time between 7 and 16 minutes (Manley, 1998).
In our experiment, two temperatures (160 and 170 °C) were chosen on the basis of previous experience in baking of gluten free cookies using the experimental oven. Baking quality results of the cookies are summarized in Table 3. Cookies 1-4 obtained at the baking temperature of 170 °C and different baking times had diameter values which were not significantly different (p < 0.05). Similar results were obtained for the cookies produced at the baking temperature of 160 °C (cookies 5 and 6), indicating that the baking time did not affect the width of the cookies. Referring to the experiment as a whole, the difference in baking conditions caused variation between the diameters of less than 1%.
However, in regard to the S/L at the temperature of 170 °C, significant differences existed between the samples baked for 10 min and those baked for 13, 14 and 16 min, which pointed out that more oval cookies (higher S/L value) were obtained when baking time was shorter. The S/L values of cookies baked at 160 °C were not significantly different (p < 0.05) from those obtained at 170 °C for 16 min.
Spread factor (W/T) was significantly higher for cookies baked at 160 °C in comparison to those baked at 170 °C. Since diameter values for all cookies were similar, changes in spread factor between cookies were caused by the differences in cookies’ thickness (T). The lowest value of thickness and the highest W/T ratio was obtained for cookies baked for 17 minutes, probably due to the highest vapour and gas loss, which caused cookie spreading and deformation (the lowest S/L).
Cookie |
W (mm) |
T (mm) |
W/T |
S/L |
1 |
51.31 ± 0.06a |
8.04 ± 0.05a |
6.38 ± 0.03a |
0.983 ± 0.00c |
2 |
51.29 ± 0.14a |
8.05 ± 0.03a |
6.38 ± 0.03a |
0.966 ± 0.01b |
3 |
51.30 ± 0.10a |
8.05 ± 0.03a |
6.41 ± 0.03a |
0.962 ± 0.00b |
4 |
51.29 ± 0.08a |
8.16 ± 0.02d |
6.29 ± 0.02b |
0.937± 0.01a |
5 |
51.41 ± 0.05a,b |
7.67 ± 0.03c |
6.71 ± 0.04c |
0.942± 0.01a |
6 |
51.60 ± 0.16b |
7.55 ± 0.06b |
6.84 ± 0.07d |
0.932± 0.01a |
Different letters in the same column indicate significant differences (p < 0.05) between mean values according to the Duncan’s range test
The overall quality of bakery products is dependent on chemical, biochemical, physical, rheological and structural changes (volume expansion, evaporation of water, starch gelatinization, protein denaturation, aroma compound formation) which occur during baking (Thorvaldson and Janestad, 1999), which are highly influenced by changes of moisture content as a function of process parameters (time and temperature). Therefore, another important factor that affects the quality of cookies is the moisture content (Manley, 1998). Equilibrium moisture of cookies is usually ranged from 3 to 5% while cookies of a special type may contain up to 7% moisture (Manley, 2000). Although the most uniform shape of cookies was obtained for the shortest baking time (10 min), these baking conditions could not be chosen as optimal since the obtained cookies had moisture content of 10.03 ± 0.04 %.
Water activity is a measure of food dryness and susceptibility of a product to microbial spoilage. The components of blueberry pomace (sugar and pectin) as well as guar gum from gluten free mixture bind the water making it less available for microbial growth (Einhorn-Stoll et al., 2012).
Cookie |
aw |
Moisture (%) |
Baking weight loss (%) |
Hardness (g) |
1 |
0.60 ± 0.00e |
10.03 ± 0.04e |
10.26 ± 0.36d |
894.4 ± 104.2b |
2 |
0.43 ± 0.00a |
6.68 ± 0.01a |
14.36 ± 0.22e |
3265.5 ± 140.8a |
3 |
0.43 ± 0.00a |
6.64 ± 0.04a |
15.44 ± 0.20a |
3465.1 ± 409.5a |
4 |
0.36 ± 0.00c |
5.76 ± 0.02c |
15.88 ± 0.03b,c |
4824.1 ± 232.3c |
5 |
0.41 ± 0.00d |
6.15 ± 0.02d |
15.63 ± 0.31a,b |
3522.8 ± 222.1a |
6 |
0.32 ± 0.00b |
5.12 ± 0.01b |
16.15 ± 0.10c |
5378.9 ± 410.3d |
Different letters in the same column indicate significant differences (p < 0.05) between mean values according to the Duncan’s range test
The results of aw and moisture content in cookies baked at different conditions indicate the significant influence of baking temperature and time on these parameters (Table 4). The lowest aw value and moisture content were obtained in cookies baked for 17 minutes at 160 °C and cookies baked 16 minutes at 170 °C. These results are highly correlated with the results of cookies weight loss during baking. However, cookies obtained at the temperature of 170 °C baked for 10 min were susceptible to yeasts and moulds growth due to their high aw value. Although correlation between the total moisture content and aw of a food is often reported (as in this study) this correlation does not occur at all times (Zamora et al., 2006).
Instrumentally measured, the hardness of cookies was expressed as a maximum force necessary to break them. When it is sensory estimated, the hardness is a force required to bite the cookie. Textural characteristics of cookies are one of the most important quality parameters governing consumers’ acceptance. The highest value of this parameter was obtained in cookies characterized by the longest baking time while cookies baked 10 minutes at 170 °C had the lowest value of hardness. Textural properties of cookies baked at the following baking conditions: 13 min at 170 °C, 14 min at 170 °C and 16 min at 160 °C were not significantly different (p < 0.05).
Hardness of cookies is highly correlated with the moisture content, aw, baking loss and S/L values (Table 5). Apart from the baking conditions, the type and quantity of the ingredients used for the product manufacture have been known to highly influence its hardness and other textural characteristics. According to Pyler (1988), ingredient used can be categorized by its functional role, for example shortening is a tenderizer, flour is a toughener and egg proteins help build a stable cell structure.
Significant positive correlation existed between following parameters: moisture/aw; moisture/S/L ratio; aw/S/L ratio as well as a negative correlation between baking loss and moisture/aw.
|
S/L |
H (g) |
BWL (%) |
M (%) |
aw |
T (mm) |
W/T |
H (g) |
-0.8680* |
|
|
|
|
|
|
BWL (%) |
-0.8208* |
0.9095* |
|
|
|
|
|
M (%) |
0.8019* |
-0.9501* |
-0.9714* |
|
|
|
|
aw |
0.8656* |
-0.9728* |
-0.9551* |
0.9811* |
|
|
|
T (mm) |
0.5125* |
-0.3868 |
-0.3590 |
0.3302 |
0.4270 |
|
|
W/T |
-0.5333* |
0.4120 |
0.3810 |
-0.3581 |
-0.4467 |
-0.9962* |
|
W (mm) |
-0.4027 |
0.3735 |
0.3817 |
-0.4063 |
-0.3619 |
-0.5182* |
0.5889* |
Correlations between cookies parameters obtained at different baking time and temperatures
Marked correlations (*) are significant at p < 0.05
S/L – short/long ratio; H (g) - hardness; BWL (%) – baking weight loss; M (%) – moisture; aw – water activity; T (mm) – thickness; W/T - cookie spread factor; W (mm) – width
Top surface |
Bottom surface |
|||||
|
L* |
a* |
b* |
L* |
a* |
b* |
1 |
30.45 ± 0.46a |
17.42 ± 0.38a |
2.47 ± 0.09c |
25.77 ± 1.40a |
15.19 ± 0.25b |
2.63 ± 0.17a |
2 |
31.16 ± 0.83a |
17.41 ± 0.32a |
2.18 ± 0.07a |
25.60 ± 0.40b |
14.48 ± 0.32a |
3.46 ± 0.47b |
3 |
32.58 ± 0.33b |
17.46 ± 0.36a,b |
2.23 ± 0.11a |
24.72 ± 0.78a |
14.49 ± 0.68a |
2.56 ± 0.23a |
4 |
32.51 ± 0.34b |
17.99 ± 0.62b,c |
2.03 ± 0.08b |
27.35 ± 0.65b |
13.96 ± 0.62a |
3.32 ± 0.63b,c |
5 |
31.17 ± 0.43a |
17.58 ± 0.20a,b |
2.20 ± 0.09a |
25.65 ± 1.03a |
14.23 ± 0.29a |
2.89 ± 0.23a,c |
6 |
32.82 ± 0.63b |
18.14 ± 0.32c |
2.28 ± 0.02a |
27.31 ± 0.97b |
14.20 ± 0.39a |
3.47 ± 0.24b |
Different letters in the same column indicate significant differences (p < 0.05) between mean values according to the Duncan’s range test
The colour characteristics (L*, a* and b*) of cookies' top surfaces were dependant on baking conditions (Table 6). Increase in the temperature and duration of the thermal treatment led to increase in redness (a*) and lightness (L*). With the increase in baking time L* value increased, probably due to higher vapour loss during baking, which indicated that cookies were not over baked and that Maillard reaction and caramelization did not occur to extend to negatively influence the colour formation (Chung et al., 2014). Colour characteristics (L*, a* and b*) of the top and bottom surface of cookies were significantly different (p < 0.05). The bottom surface is characterized by lower L* and a* values and higher b* values. However colour evaluation of cookies during their sensory evaluation indicate that cookies' bottom surfaces were not over baked.
The mean values of overall sensory quality are shown in Fig 2. As the expert panel had a well-defined concept of cookies' quality in their evaluation, the samples were sorted into two groups (p < 0.05). Sample 4, obtained by baking at 170 °C was found to be of the best acceptability. However, regarding the fact that sample 3 had more regular shape (S/T value) and hardness, and that it was similarly scored by the panel, baking time of 14 min at 170 °C could be considered optimal for the blueberry pomace enriched gluten-free cookies in the previously mentioned type of oven.