Sorghum and millets have considerable potential in foods and beverages. As they are gluten-free they are suitable for coeliacs. Sorghum is also a potentially important source of nutraceuticals such ...antioxidant phenolics and cholesterol-lowering waxes. Cakes, cookies, pasta, a parboiled rice-like product and snack foods have been successfully produced from sorghum and, in some cases, millets. Wheat-free sorghum or millet bread remains the main challenge. Additives such as native and pre-gelatinised starches, hydrocolloids, fat, egg and rye pentosans improve bread quality. However, specific volumes are lower than those for wheat bread or gluten-free breads based on pure starches, and in many cases, breads tend to stale faster. Lager and stout beers with sorghum are brewed commercially. Sorghum's high-starch gelatinisation temperature and low
beta-amylase activity remain problems with regard to complete substitution of barley malt with sorghum malt . The role of the sorghum endosperm matrix protein and cell wall components in limiting extract is a research focus. Brewing with millets is still at an experimental stage. Sorghum could be important for bioethanol and other bio-industrial products. Bioethanol research has focused on improving the economics of the process through cultivar selection, method development for low-quality grain and pre-processing to recover valuable by-products. Potential by-products such as the kafirin prolamin proteins and the pericarp wax have potential as bioplastic films and coatings for foods, primarily due to their hydrophobicity.
This study was conducted to improve the quality and theoretical understanding of gluten-free sorghum bread. The addition of 2% hydroxypropyl methylcellulose improved bread based on 105% water, 70% ...sorghum flour, and 30% potato starch. Nevertheless, a flat top and tendency toward a hole in the crumb remained. Sourdough fermentation of the total sorghum flour eliminated these problems. Size-exclusion high-performance liquid chromatography demonstrated that during sourdough fermentation, proteins from the dough liquid were degraded to peptides smaller than kafirin monomers (<19 kDa). Laser scanning confocal microscopy showed aggregated protein in bread crumb without sourdough fermentation, whereas with sourdough fermentation, only small isolated patches of protein bodies embedded in matrix protein remained. In oscillatory temperature sweeps, sourdough fermentation caused a significantly higher resistance to deformation (|G*|) after gelatinization of the above batter relative to batters without sourdough. Results suggest that a strong starch gel, without interference of aggregated protein, is desirable for this type of bread. Keywords: Sorghum; gluten-free bread; sourdough; size-exclusion-HPLC (SE-HPLC, SEC); rheology; laser scanning confocal microscopy (LSCM)
Gluten-free breadmaking quality of 10 sorghum flours was compared using (relative basis) decorticated sorghum flour (70), corn starch (30), water (105), salt (1.75), sugar (1), and dried yeast (2). ...Batter consistency was standardized by varying water levels to achieve the same force during extrusion. Crumb properties were evaluated by digital image analysis and texture profile analysis (TPA). Significant differences (P < 0.001) in crumb grain were found among the hybrids with mean cell area ranging from 1.3 to 3.3 mm2 and total number of cells ranging from 13.5 to 27.8/cm2. TPA hardness values of the crumb also varied significantly (P < 0.001). Based on significant correlations (P < 0.01), starch damage, influenced by kernel hardness, was identified as a key element for these differences. Breads differed little in volume, height, bake loss, and water activity. Investigation of added ingredients on bread quality was conducted using response surface methodology (RSM) with two sorghum hybrids of opposite quality. Addition of xanthan gum (0.3-1.2% flour weight basis fwb) and skim milk powder (1.2-4.8% fwb) and varying water levels (100-115% fwb) were tested using a central composite design. Increasing water levels increased loaf specific volume, while increasing xanthan gum levels decreased the volume. As skim milk powder levels increased, loaf height decreased. Quality differences between the hybrids were maintained throughout the RSM.
Studies were conducted with two newly developed gluten-free bread recipes. One was based on corn starch (relative amount 54), brown rice (25), soya (12.5), and buckwheat flour (8.5), while the other ...contained brown rice flour (50), skim milk powder (37.5), whole egg (30), potato (25), and corn starch (12.5), and soya flour (12.5). The hydrocolloids used were xanthan gum (1.25) and xanthan (0.9) plus konjac gum (1.5), respectively. Wheat bread and gluten-free bread made from commercial flour mix were included for comparison. Baking tests showed that wheat and the bread made from the commercial flour mix yielded significantly higher loaf volumes (P < 0.01). All the gluten-free breads were brittle after two days of storage, detectable by the occurrence of fracture, and the decrease in springiness (P < 0.01), cohesiveness (P < 0.01), and resilience (P < 0.01) derived from texture profile analysis. However, these changes were generally less pronounced for the dairy-based gluten-free bread, indicating a better keeping quality. Confocal laser-scanning microscopy showed that the dairy-based gluten-free bread crumb contained network-like structures resembling the gluten network in wheat bread crumb. It was concluded that the formation of a continuous protein phase is critical for an improved keeping quality of gluten-free bread.
Gluten-free bread was prepared from commercial zein (20
g), maize starch (80
g), water (75
g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (
T
g) at 40°C. ...Addition of hydroxypropyl methylcellulose (HPMC, 2
g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2
ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its
T
g softer (i.e. |
G*| was significantly lower). LSCM revealed that cooling below
T
g alone did not destroy the zein strands; however, upon mechanical impact below
T
g, they shattered into small pieces. When such dough was heated above
T
g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below
T
g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below
T
g resulting in structural weakness.
Commercial corn prolamin (zein) aggregates in water at elevated temperatures into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production ...of gluten-free bread from true dough systems and not from batters. The present study examined laboratory-scale isolation of such functional zein from dry milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure α-zeins, with a maximum ratio of (β + γ)/α-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (β + γ)/α-zeins. Isolation of the analogous prolamin (kafirin) from dry milled sorghum required a more hydrophobic extractant such as 83% isopropanol to achieve partial functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added; however, it quickly became firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide bonds are the key to gluten-like functionality of zein and kafirin.
► We studied how extraction of zein and kafirin impacts their ability to form dough. ► Not all extraction methods produced functional proteins. ► Dough formation in maize and sorghum proteins is driven by non-covalent bonds.
Maize prolamin (zein), together with starch, hydroxypropyl methylcellulose, sugar, salt, yeast and water can form wheat-like cohesive, extensible, viscoelastic dough when mixed above room temperature ...(e.g. 40
°C). This dough is capable of holding gas. However, it is excessively extensible, and when used for hearth-type rolls, it tends to become flat. Bench-scale defatting of zein with chloroform at room temperature significantly (
P
<
0.05) improved specific volume (4.5
ml/g vs. 3.3
ml/g) and shape of the rolls (width-to-height 2.0 vs. 3.9). The total lipid content determined by accelerated solvent extraction (100
°C, 69
bar, chloroform), however, only decreased from 8.0 to 6.6% due to this bench-scale defatting. Staining experiments with Naphthol Blue Black suggested that bench-scale defatting removed surface lipids from the zein particles, and thus facilitated their aggregation. Aggregation experiments with zein and water at 40
°C, and laser scanning confocal microscopy with zein-starch dough confirmed that zein particles aggregated more easily when surface-defatted. Dynamic oscillatory temperature sweeps demonstrated that surface-defatting lowered the temperature at which protein cross-linking occurred by 2
°C. This research can help to produce superior gluten-free bread and could also possibly contribute to the better understanding of wheat dough.
Biochemical properties of carob germ proteins were analyzed using a combination of selective extraction, reversed-phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography ...(SEC) coupled with multiangle laser light scattering (SEC-MALS), and electrophoretic analysis. Using a modified Osborne extraction procedure, carob germ flour proteins were found to contain ∼32% albumin and globulin and ∼68% glutelin with no prolamins detected. The albumin and globulin fraction was found to contain low amounts of disulfide-bonded polymers with relatively low M w ranging up to 5 × 106 Da. The glutelin fraction, however, was found to contain large amounts of high molecular weight disulfide-bonded polymers with M w up to 8 × 107 Da. When extracted under nonreducing conditions and divided into soluble and insoluble proteins as typically done for wheat gluten, carob germ proteins were found to be almost entirely (∼95%) in the soluble fraction with only (∼5%) in the insoluble fraction. As in wheat, SEC-MALS analysis showed that the insoluble proteins had a greater M w than the soluble proteins and ranged up to 8 × 107 Da. The lower M w distribution of the polymeric proteins of carob germ flour may account for differences in functionality between wheat and carob germ flour.
The aim of this study was to understand the chemistry of spelt (
Triticum aestivum ssp.
spelta) gluten in relation to its quality, to classify European spelt cultivars based on gluten quality, and to ...compare their protein compositions with those of modern wheats. Gluten quality of two sets of 25 spelt cultivars was studied using dynamic oscillatory and creep tests, an SDS sedimentation test, moisture content of the wet gluten and wet gluten content. These data were compared with the results of size-exclusion HPLC analyses of the spelt proteins. Significant correlations indicated that insoluble polymeric proteins (IPP) contributed resistance to deformation in creep tests, elasticity in oscillatory and creep tests, and swelling capacity of the gluten. Gliadins had the opposite effects, whereas the contribution of soluble polymeric proteins (SPP) depended on the type of test. In creep tests (strain 0.3–1.5) SPP behaved similarly to gliadins, in oscillation (strain 0.001) they tended to increase elasticity. In comparison to hard red winter wheats, spelt was characterized by lower IPP, but higher gliadins and SPP, resulting in softer and less elastic glutens. A wide variation in gluten quality was found among the spelts. Three groups could be identified by cluster analysis (one closer to modern wheat, a second typical spelt group and a third a poor quality group).
The fundamental rheological characteristics of a biologically acidified, a chemically acidified, and a neutral preferment (sourdough) were monitored over the course of a 24-hr fermentation period ...using a split-plot design. Three doughs were subsequently prepared in which 20% of the flour was in the form of the respective preferment. A control dough containing no fermented material was also prepared. The fundamental rheological properties of both the dough and its isolated wet gluten were determined. Laser-scanning confocal microscopy was used to capture images of selected preferments and doughs. Results from the preferment showed that there was a decrease in elasticity (phase angle data from oscillatory measurements and relative recovery values from creep tests) and viscosity with fermentation time for all three preferments, all of which reached similar end values for these parameters. The microscopy images illustrated that the gluten strands were dissolved to a more amorphous structure during the fermentation period. Changes in the nature of the preferments were reflected in the rheological characteristics of the respective doughs and their wet glutens, which were significantly less elastic (phase angle and relative recovery data) and softer (maximum creep compliance) than the control treatment. It is concluded that degrading processes over time are key to the sourdough process.
