Evaluation of a Low-Glucose Gluten-Free Bread Made from Hydrolyzed Cassava Starch and Lupine Flour ^†

Abstract

Currently, there is an increase in diabetes cases and people sensitive to gluten. However, there are few foods in commerce with good quality and that serve to appease, in synergy, these diseases. The aim of this work was to evaluate a low-glucose gluten-free bread made from hydrolyzed cassava starch and lupine flour. The starch of the cassava variety INIAP 651 (CM1335–4 genotype), cultivated in Ecuador, as well as the debittered flour of lupine (Lupinus mutabilis Sweet) from Ecuador were used. A cassava starch/water dilution was gelatinized, lyophilized, ground, and sieved. Then, it was hydrolyzed with pancreatic α-amylase prepared at 100 U/g, for 0, 1, 2, and 3 h. In addition, breads were made from gels without the addition of yeast. The gels showed significant differences for the hydrolysis times 0 and 1 h, in hydrolysis level, consistency, cohesiveness, firmness and viscosity level. No significant differences were found in those parameters for 1, 2 and 3 h. In the bread, significant differences were found for 0 and 1 h in specific volume, firmness, springiness, cohesiveness, adhesiveness, and resilience. There were no significant differences between 0 to 3 h of hydrolysis for those parameters. Up to 10% partial substitution of hydrolyzed cassava starch by lupine flour, there were no significant differences in rheological properties.

1. Introduction

The mechanism that confers the expansion in sour cassava starch bread, without the use of leavening agents, is given by supramolecular and molecular degradations which come from traditional starch processes of spontaneous fermentation (30 days) and solar drying (12 h), respectively. These treatments are irregular and as a result, bread-making products of different quality are obtained. Previous studies have tried to mimic these processes with treatments that make it possible to control starch granule degradation (addition of organic acids) and/or oxidation at the molecular level (using UV-Vis lamp, sodium hypochlorite, ozone) [1]. However, the effect of degradation at the granular level by α-amylase to achieve a bread-making product with good properties has not been investigated. α-amylase hydrolyzes the alpha-1-4 bonds of starch, depolymerizing it. On the other hand, in the starch granule, the degradations required to achieve this expansion could be minimal, of the order of 1%, according to a single existing reference [2]. This would produce a minimum amount of reducing sugars, ideal for making bread low in simple sugars. However, the minimum level of hydrolysis necessary to achieve adequate breadmaking has not been precisely determined.

Likewise, proteins of vegetal origin such as lupine from Ecuador (Lupinus mutabilis Sweet) have been used in order to improve the nutritional content of the bread due to its high protein (40–45%), fiber (25–30%), calcium, etc. In addition, lupin intake helps to increase satiety and reduces energy intake and LDL-cholesterol level in the blood [3].

Also, certain studies have explained that the mechanisms of action of lupine proteins, including a strange protein called gamma conglutin, inhibit the enzyme DPP-4 (dipeptidyl peptidase-4), which favors glucose control in patients with type 2 diabetes; increase glucose uptake in insulin-dependent cells; and they also inhibit gluconeogenesis (glucose production in the liver), as does metformin [4].

The aim of this contribution was to study a gluten-free low-in-free-sugar bread made from modified cassava starch with alpha-amylase and lupine flour.

2. Materials and Methods

For this work, the starch of the cassava variety (Manihot esculenta Crantz) INIAP 651, from the CM1335–4 genotype, cultivated in Manabí-Ecuador, was used. A starch/water (1:20) dispersion was gelled, lyophilized, ground and sieved (106 µm). Then, it was hydrolyzed with pancreatic α-amylase (A 6255, Sigma-Aldrich, St. Louis, MO, USA), prepared at 500 U/g, for 0, 1, 2, and 3 h. Hydrolysates were analyzed for enzymatic digestibility using the Megazyme D-glucose kit (Megazyme International Ireland Ltd., Bray, Ireland) by UV-Vis to determine enzymatic hydrolysis level. For the analysis of rheological parameters, the same gel preparation procedure mentioned above was carried out except for lyophilization. A Perten TVT 6700 texturometer ((Perten Instruments, Hägersten, Sweden) coupled to a probe of 45 mm diameter compression plate and a 120 mL container was used to analyze the hydrolyzed gels. The 24-01.02 Curdled Consistency-Back extrusion test from TexCal 5 software of the texturometer was used to analyze the rheological properties of the obtained gel and bread. On the other hand, breads without the addition of yeast made from the described gels were elaborated, and the specific volume and textural properties were evaluated. In addition, a bread partial substitution of modified cassava starch with lupin flour (0, 5, 10, 15 and 20%) was performed to determine the loaf volume of bread. To determine statistically significant differences, an ANOVA (analysis of variance) followed by LSD (Fisher´s least significant differences) test were performed (p < 5%; n = 3).

3. Results and Discussion

Table 1. Results from gel and bread made from alpha-amylase cassava starch.

Parameter/Time	0 min	60 min	120 min	180 min
Gel-amylase cassava starch
Consistency (gf mm)	158.67 ± 9.29 a	350.01 ± 9.54 b	341.67 ± 25.54 b	329.00 ± 8.00 b
Cohesiveness (g)	−26.33 ± 0.58 a	0.00 ± 0.00 b	0.00 ± 0.00 b	0.00 ± 0.00 b
Firmness (g)	32.33 ± 0.58 b	14.67 ± 0.58 a	14.67 ± 0.58 a	14.00 ± 0.00 a
Enzymatic hydrolysis (%)	10.01 ± 5.51 a	63.09 ± 0.52 b	56.21 ± 7.45 b	60.70 ± 1.87 b
Bread-amylase cassava starch
Loaf volume (g/mL)	0.91 ± 0.04 a	0.87 ± 0.03 a	0.91 ± 0.05 a	0.94 ± 0.00 a
Resilience	0.63 ± 0.00 a	0.70 ± 0.10 a	0.725 ± 0.00 a	0.69 ± 0.00 a
Springiness	0.90 ± 0.00 a	0.93 ± 0.00 a	0.91 ± 0.00 a	0.90 ± 0.00 a
Adhesiveness (g f mm)	−88 ± 17 a	77 ± 15 a	−60 ± 28 a	−114 ± 28 a
Firmness (g)	477 ± 23 a	410 ± 13 a	455 ± 20 a	436 ± 26 a
Cohesiveness	0.83 ± 0.00 a	0.90 ± 0.00 a	0.90 ± 0.10 a	0.88 ± 0.10 a

^a,b Different letters, within row, indicate significant differences at p < 0.05 (Fisher). n = 3.

shows results from alpha-amylase cassava starch gel and bread. The gels showed significant differences for the hydrolysis times 0 and 1 h, in hydrolysis level (10 and 63% w/w), consistency (158 and 350 gf.mm), cohesiveness (−26.6 and 0 gf), firmness (32.2 and 14.7 gf) and viscosity level (158 and 0 gf.mm). No significant differences were found in those parameters for 1, 2 and 3 h. In the bread, significant differences were found for 0 and 1 h in specific volume (1.93–2.47 mL/g) [1], firmness (4106–4774 gf), springiness (80–93%), cohesiveness (0.83–0.97), adhesiveness (−60.5–−114.3 gf.mm) and resilience (0.63–0.925). There were no significant differences between 0 to 3h of hydrolysis for those parameters. These results suggest that only 1 h of amylase hydrolysis, or perhaps less, is enough to significantly modify the level of hydrolysis and the rheological properties of gelatinized starch. However, when evaluating the finished product with the different hydrolysis times, there are no differences between the treatments. An additional modification with UV-Vis to the hydrolyzed starch could cause positive degradations at the molecular level and contribute to improving the functional properties of the bread that can be correlated with the other results obtained.

On the other hand, specific volumes of bread with partial substitution of modified cassava starch with lupin flour at 0, 5, 10, 15 and 20% were, respectively, 2.47; 2.39; 2.40; 2.07; and 1.91 mL/g. There were no significant differences for 0, 5 and 10% of bread partial substitution in loaf volume and textural properties (resilience, springiness, adhesiveness, firmness, and cohesiveness) [5].

4. Conclusions

Gel and bread made from cassava starch modified with α-amylase did not change rheological properties from 1 h of amylase hydrolysis. It would be necessary to explore different hydrolysis times between 0 and 1 h to determine changes in properties. Up to 10% partial substitution of hydrolyzed cassava starch by lupine flour, there are significant differences in breadmaking properties.