Selected Structural Characteristics of HPMC-Containing Gluten Free Bread: A Response Surface Methodology Study for Optimizing Quality

Figures & data

Table 1 Gluten free bread formulation

Ingredient	Starch/flour base (kg/100 kg)
Maize starch	75
Rice flour	25
Sunflower oil	4
Yeast	2
Sugar	3
Salt	2
HPMC	Variable ^a
Water	Variable ^a
^aAmounts varied according to the experimental design (Table 2).

Table 2 Worksheet of the central composite experimental design

	Independent variables ^a		Dependent variables
Trial	HPMC X1	Water X2	Specific volume (ml/g) Y1	Firmness (N)Y2	Overall acceptability Y3
1	−1	−1	2.35	5.7	4.8
2	+1	−1	2.63	3.1	6
3	−1	+1	2.28	6	4.5
4	+1	+1	2.34	3.4	6.4
5	−1.414	0	2.4	4.5	6
6	+1.414	0	2.18	5	4.9
7	0	−1.414	2.36	6.4	4.4
8	0	+1.414	2.71	3	7
9	0	0	2.92	4.9	6.6
10	0	0	3.12	5	6.8
11	0	0	3	5.1	6.3
12	0	0	3.02	5	6.5
13	0	0	2.95	5.1	6.5
^aVariable levels (starch/flour basis): HPMC: –1.414 = 0.5 kg/100 kg, –1 = 0.79 kg/100 kg, 0 = 1.5 kg/100 kg, +1 = 2.21 kg/100 kg, +1.414 = 2.51 kg/100 kg; Water: –1.414 = 70 kg/100 kg, –1 = 73.66 kg/100 kg, 0 = 82.5 kg/100 kg, +1 = 91.34 kg/100 kg, +1.414 = 2.5 kg/100 kg.

Table 3 Regression equations ^a coefficients and analysis of variance for the different responses. ^b

Coefficient	Specific volume (Y1)	Firmness (Y2)	Acceptability (Y3)
b0	−19.957	−2.177	−43.355
b1	2.032*	1.303**	3.2335*
b11	−0.7168***	−0.3575**	−1.1632**
b2	0.51*	0.2881***	1.059***
b22	−0.003**	−0.0026**	−0.0058**
b12	ns	ns	ns
R^2	0.97	0.99	0.93
Lack of fit	P > 0.05	P > 0.05	P > 0.05
^aYi = b0 + b1X1 + b2X2 + b11X1^2 + b22X2^2 + b12X1X2, X1 = HPMC, X2 = Water. ^bOnly values of significant coefficient are presented (95% confidence level); ns: no significant effect at the 5% level. *Significant at P < 0.05, **Significant at P < 0.01, ***Significant at P < 0.001.

Figure 1 Response surface plot: effect of HPMC and water addition on loaf specific volume. sfb: starch/flour base.

Figure 2 Response surface plot: effect of HPMC and water addition on crumb firmness. sfb: starch/flour base.

Figure 3 Response surface plot: effect of HPMC and water addition on crumb L value. sfb: starch/flour base.

Table 4 Predicted and observed data for the responses at optimum conditions

	Optimum conditions
Independent variables (responses)	Measured value	Predicted value
Specific volume (mL/g)	3.04 ± 0.8	2.96
Firmness (N)	3.5 ± 0.4	4.03
Acceptability	7.0 ± 0.2	6.91

Figure 4 Effect of storage on crumb firmness of the optimized gluten free bread. Mean values ± standard deviation of 3 replicates; Values followed by different letters in the same column are significantly different (P < 0.05).

Figure 5 Effect of storage on crumb moisture of the optimized gluten free bread. Mean values ± standard deviation of 3 replicates; Values followed by different letters in the same column are significantly different (P < 0.05).

Figure 6 Scanning electron micrograms (800×) of the crumb of gluten free bread. (a) Control –non HPMC; and (b) optimized with HPMC.