In vitro starch digestibility and pasting properties of germinated brown rice after hydrothermal treatments

Germinated brown rice (GBR) recently has received renewed attention due to its enhanced nutritional value. Pasting properties and in vitro starch digestibility of GBR were examined before and after hydrothermal treatments. Steeping in water (30 °C, 24 h) raised the moisture content and germination percentage of brown rice. Pasting viscosity was substantially decreased but gelatinization temperatures and enthalpy were decreased only marginally by germination (30 °C, 48 h). However, annealing (50 °C, 24 h) and heat-moisture treatment (100 °C, 1 h at 30% moisture) after germination resulted in increased pasting viscosity and gelatinization temperatures. The hydrothermal treatments, however, induced browning reactions to darken the flour of GBR. The digestibility of starch in brown rice was increased by germination. The contents of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) in the cooked brown rice were 47.3%, 40.8%, and 11.9%, respectively, but changed to 57.7%, 39.1%, and 3.2%, respectively upon germination. The hydrothermal treatments, however, decreased the digestibility of starch in GBR. The heat-moisture treatment decreased the RDS content in GBR near to that of native brown rice. The digestibility and physical properties of brown rice can be controlled by germination and hydrothermal treatments.     

Biochemical and sensory evaluation of wheat bran supplemented sorghum bread

Addition of wheat bran to sorghum flour (Dabar cultivar) at two extraction rates 72% and 80% resulted in lowering reducing sugars. The percent decreasewas 75.6% compared with the control at the end of fermentation period. There was a highly significant (p 0.05) increase in crude fiber content as a result of addition of wheat bran. The increase was from 0.8 to 5.2 and from 0.5 to 5.3% for the 80% S/WB and 72% S/WB blends, respectively. Sorghum bread containing wheat bran was lower in reducing sugars and showed a significant increase (p 0.05) in starch content. Sorghum bread containing wheat bran resulted in a lower in vitro protein and starch digestibilities.     

Enzymatic modification and particle size reduction of wheat bran improves the mechanical properties and structure of bran-enriched expanded extrudates

The aim of this study was to examine enzymatic modification of wheat bran, performed in a low-moisture process, and the reduction of bran particle size as means of improving the technological performance of wheat bran in expanded extrudates. Modification of bran by hydrolytic enzymes increased the crispiness and decreased the hardness and piece density of extrudates containing wheat bran and endosperm rye flour in 20:80 ratio. These improvements correlated (P < 0.01 or 0.05) with an increased content of water extractable arabinoxylan and decreased water holding capacity of the bran, as well as with increased longitudinal expansion of the extrudates. Furthermore, bran with a fine average particle size (84 μm) produced extrudates with improved mechanical properties and higher radial expansion than coarse bran (particle size 702 μm). The impact of bran particle size was also observed in the cellular structure of the extrudates as differences in cell size and homogeneity. The bran drying method, oven or freeze drying after enzymatic modification, did not have a major impact on the properties of the extrudates. The study showed that the functionality of wheat bran in extrusion can be improved by enzymatic modification using a low-water process and by reduction of bran particle size.     

Starch properties, in vitro digestibility and sensory evaluation of fresh egg pasta produced from oat,teff and wheat flour

Specific dietary requirements, e.g. celiac disease, as well as increased consumer demand for products of high nutritional value, makes the production of pasta from alternative cereals interesting. Raw material characterisation showed that the utilisation of oat and teff flour is beneficial as these ingredients contain higher levels of fibre and mineral composition is superior to that of wheat. Starch properties significantly influence pasta quality and therefore damaged starch levels, amylase activity, pasting properties and gelatinisation temperatures of the flours were investigated. Fresh egg pasta based on wheat, oat and teff flour was produced. Sensory properties of oat spaghetti were found to be very close to that of wheat pasta but improvement of smoothness and aroma is necessary, while teff spaghetti showed reduced sensory quality. An in vitro enzymatic digestion was performed using a dialysis system to mimic the behaviour of pasta as eaten and make predictions on the glycemic index (GI). The predicted GI was highest for wheat pasta, followed by teff and oat. Ultra structure was studied using confocal laser scanning microscopy, allowing the visualisation of differences in starch granule size and shape as well as gelatinisation occurring during the cooking process.     

Influence of baking and in vitro digestion on steryl ferulates from wheat

So far, data on absorption and metabolism of steryl ferulates from edible sources is scarce. Therefore, the impact of enzyme-aided baking and in vitro digestion was examined in this study. Wheat flours and wheat breads were subjected to a static in vitro digestion model and changes in the contents of steryl ferulates and free sterols (possible hydrolysis products of steryl ferulates) were monitored. Baking degraded steryl ferulates at a similar rate in all types of breads (43–47%) compared to the corresponding flours, while baking induced changes in free sterols showed no clear pattern. In vitro digestion provoked five folds lower content of steryl ferulates in flours than in breads and it also resulted in significant free sterol accumulation. Interestingly, bioaccessibility (0.01–0.25%) was not influenced by the cereal matrix. The four steryl ferulate species, which were detected in wheat, showed similar hydrolysis rates during digestion. As baking had a significant impact on the steryl ferulate content of wheat, we suggest that both raw and processed sources should be considered further in vitro, animal or human trials, when studying the metabolic fate of steryl ferulates.     

Effects of microfluidization on antioxidant properties of wheat bran

Phenolic compounds present in native wheat bran are majorly bound to polysaccharides and entrapped in the fibre matrix. Recently, it was demonstrated that the microfluidization process could significantly improve physicochemical properties of wheat bran due to particle size reduction and microstructure modification. The current study provides further evidence that the process also significantly increased the contents of surface-reactive, alkaline and acid hydrolysable phenolics by 280%, 60% and 20%, respectively, after a total of 8 passes through the IC₂₀₀ and IC₈₇ chambers. Accordingly, the associated antioxidant capacity increased with increase in the extent of the treatment. However, there was a decrease in solvent extractable phenolic contents due to their dispersion in water and loss during the treatment. It is also worth noting that the residues after alkaline and acid hydrolysis still contained a high content of surface-reactive phenolics, which might indicate a significant underestimation of the total phenolic content and antioxidant capacity of wheat bran when using the conventional method based on solvent extraction and alkaline and/or acid hydrolysis.     

Effect of thermal processing and storage on digestibility of starch in whole wheat grains

Gelatinisation and retrogradation of starch in wheat flour systems and whole wheat grains were studied using DSC and the impact of these events on starch digestibility was investigated. Gelatinisation of starch was possible in wheat flours with more than 60% moisture content (dwb) and gelatinised samples had higher digestibility values. Retrogradation of starch was studied with partially and fully cooked (boiled at 100 °C for 12 min and 32 min, respectively) wheat grains that were subjected to storage at 22 °C for 48 h. Stored samples had lower digestibility values when compared to the freshly cooked counterparts. The effect of moisture on retrogradation was studied with fully cooked wheat grains that were dried to a range of moisture contents (14.6–35.9%, wwb) and stored at 20 °C for 24 h. Retrogradation enthalpy increased with increasing moisture content; however, digestibility values did not reflect the changes in retrogradation enthalpy. The possibility of estimating the degree of retrogradation in fully cooked grains (32 min cooking) was investigated using a wheat flour-water system. The retrogradation enthalpy of fully cooked grains was slightly higher than the wheat flour-water system (at a moisture content of 49%, wwb) during the course of storage at 22 °C.     

Effect of particle size and addition level of wheat bran on quality of dry white Chinese noodles

Wheat bran is one of the major dietary fiber sources widely used in the food industry in order to produce fiber-rich foods. The effects of particle size and addition level of wheat bran on the quality of flour and of dry white Chinese noodles (DWCN) were investigated. Results suggested that increasing wheat bran concentration and particle size decreased midline peak value (MPV). However, the MTxW and MPT increased as particle size increased. Peak viscosity, trough, final viscosity, area of viscosity, breakdown, and setback of blends decreased significantly with increasing bran levels from 5% to 20%, but there were no significant differences in the impact of particle size on pasting properties. For the 5% and 10% addition levels, there was no distinct effect in breaking strength of the noodles when bran size was 0.21 mm and 0.53 mm. Hardness, gumminess and chewiness of cooked DWCN showed a downtrend with increasing addition levels and particle size, while adhesiveness showed uptrend. The total score of DWCN showed a downtrend with increasing of addition level and particle size. For the 5% bran level, the scores of cooked DWCN were more than 83 when wheat bran particle size was 0.21 mm and 0.53 mm. By using 5–10% fine bran or using 5% medium bran in wheat flour, it is possible to satisfactorily produce fiber-rich DWCN.     

Effects of specific domains of high-molecular-weight glutenin subunits on dough properties by an in vitro assay

An in vitro system for incorporating bacterially produced high-molecular-weight glutenin subunits (HMW-GS) into doughs was used to study the effects of specific domains of the HMW-GS. Synergistic effects of incorporating into doughs both the Dx5 and Dy10 subunits are localized to the N-terminal domains. All single and pair-wise combinations of original subunits and hybrid subunits with their N-terminal domains exchanged between Dx5 and Dy10 finds three classes of respondents: the greatest response is when the N-termini of both Dx5 and Dy10 are present, followed by presence of the Dx5 N-terminus alone, and the least response by the presence of the Dy10 N-terminus alone. In addition, studies of Dx5 variants possessing repetitive domains of different length and composition find evidence that the length of the HMW-GS repetitive domain is important for dough properties and that the exact composition of the repeat domain has a detectible, though lesser contribution. Finally, in this experimental system, the Glu-D1 x- and y-subunits function in the mixing experiments as if they were a fused dimer, although the exact molecular basis of the effect is not known.     

Effect of extrusion treatment on enzymatic hydrolysis of wheat bran

Although, wheat bran is a good source of dietary fibre (DF), it has certain disadvantages due relatively lower levels of soluble DF. Therefore, in the current study, the effect of extrusion treatment on microstructure and enzymatic hydrolysis of wheat bran was investigated. Extrusion treatment increased fibre solubility at all process conditions and the screw speed was found to be the most effective parameter. Physicochemical properties of bran were affected from extrusion treatments. While the water-binding capacities of extruded brans were lower than that of non-extruded wheat bran, their water solubilities were higher. Enzymatic hydrolysis increased the soluble DF content of the bran samples as compared to those of respective samples at the beginning of incubation. The results showed that extrusion treatment can be used to disrupt the wheat bran microstructure and thus to increase the soluble fibre content. Enzymatic hydrolysis can also be used for increasing solubility further. The outcomes of this study can be utilized for improving the technological functionality of cereal fibres to develop high fibre ingredients for food applications.     

Effect of solid state fermentation by Enterococcus faecalis M2 on antioxidant and nutritional properties of wheat bran

Wheat bran is the main by-product during wheat flour processing. Although wheat bran is rich in the bioactive compounds and antioxidant capacity, it is not widely utilized in its natural state. To improve the antioxidant and nutritional properties of wheat bran, a dominant strain, Enterococcus faecalis M2, was screened from lactic acid bacteria (LAB) isolated from various foods. Following solid state fermentation, the soluble dietary fiber content of wheat bran nearly quadrupled compared to the raw material. Total proportion of phenols, flavonoids, alkylresorcinols, along with the antioxidant capacity and free radical scavenging rate were significantly improved, particularly the ferulic acid content increased by 5.5 times. Additionally, the free amino acid content increased with degradation of wheat bran protein, whereas the level of anti-nutrient phytic acid decreased. The results of this study could provide an effective method for biological modification of wheat bran, which further enhance the health benefit and utilization of bran.     

Effect of wheat bran and enzyme addition on dough functional performance and phytic acid levels in bread

Effects of bran concentration, bran particle size distribution, and enzyme addition – fungal phytase, fungal alpha-amylase – on the mixing and fermentative behaviour of wheat dough and on the amount of phytic acid remaining in bread have been investigated using a factorial design of samples 2⁴. Bran concentration and bran particle size significantly affected all Farinograph parameters, whereas enzyme effects were particularly observed on both the water absorption of the flour and the parameters characterizing the overmixing. Water absorption was maximized in doughs with higher fine bran addition and/or in doughs with no enzymes, and was minimized in blends containing coarse added bran and alpha-amylase and/or alpha-amylase and phytase. alpha-Amylase addition had a significant positive effect on dough development and gassing power parameters during proofing. At low bran addition, phytate hydrolysis takes place to a greater extent than at high bran addition levels. Combination of bran with amylolytic and phytate-degrading enzymes could be advisable for overcoming the detrimental effect of bran on the mineral availability (phytase) or on the technological performance of doughs (alpha-amylase).     

Changes in bran structure by bioprocessing with enzymes and yeast modifies the in vitro digestibility and fermentability of bran protein and dietary fibre complex

Bran is a good source of dietary fibre, phytochemicals, and also protein, but highly insoluble and recalcitrant structure of bran hinders accessibility of these components for gastrointestinal digestion. In the present work, influence of bioprocessing on the microstructure and chemical properties of rye bran and wheat bread fortified with the rye bran were studied. In vitro protein digestibility, and release of short chain fatty acids (SCFA) and ferulic acid in a gut model were studied. Bioprocessing of rye bran was performed with subsequent treatments with cell-wall hydrolysing enzymes (40 °C, 4 h) and yeast fermentation (20 °C, 20 h). Bioprocessing of rye bran resulted in reduced total dietary fibre content, caused mainly by degradation of fructan and β-glucan, and increased soluble fibre content, caused mainly by solubilisation of arabinoxylans. Microscopic analysis revealed degradation of aleurone cell wall structure of the bioprocessed rye bran. Bioprocessing caused release of protein from aleurone cells, assessed as a larger content of soluble protein in bran and a higher hydrolysis rate in vitro. Bioprocessed bran had also faster SCFA formation and ferulic acid release in the colon fermentation in vitro as compared to native bran.     

Effect of steam explosion on enzymatic hydrolysis and baking quality of wheat bran

In this study, the effect of steam explosion (SE) treatment on microstructure, enzymatic hydrolysis and baking quality of wheat bran was investigated. Coarse and fine bran were treated at different steam temperatures (120–160 °C) and residence times (5 or 10 min) and then hydrolysed with carbohydrase enzymes. The SE treatment increased water extractable arabinoxylan (WEAX) content from 0.75 to 2.06% and reducing sugars from 0.92 to 2.41% for fine bran. The effect was more pronounced with increased SE temperature and residence time. The highest carbohydrate solubilisation was observed in fine bran at SE treatment of 160 °C, 5 min. WEAX content increased to 3.13% when this bran was incubated without enzyme, while WEAX content increased to 9.14% with enzyme addition. Microscopic analysis indicated that cell wall structure of wheat bran was disrupted by severe SE conditions. Supplementation of SE treated (150 °C, 10 min) bran at 20% replacement level decreased the baking quality of bread. However SE followed by enzymatic hydrolysis increased specific volume and decreased crumb hardness (on the day of baking and after three days of storage). Phytic acid content of bread supplemented with SE treated bran was lower than the one supplemented with untreated bran.     

Effect of endosperm starch granule size distribution on milling yield in hard wheat

Increased flour yield in hard wheat is associated with increased endosperm rheology index, calculated from strength and stiffness as measured by the SKCS. A study of the fractured endosperm of hard wheat varieties grouped according to similar rheology index values was performed using environmental scanning electron microscopy (ESEM). Differing microstructures and fracture patterns were observed between each group. Specifically, the group representing high rheology index had a greater concentration of small starch granules in prismatic cells. Samples of diverse wheat germplasm were grown at two sites and subjected to laboratory milling. Starch granule size distribution (SGSD) analysis using a laser diffraction method was undertaken on a subset of samples in triplicate representing a range in flour yield. The results supported an hypothesis for a significant influence of SGSD on flour yield of hard wheat varieties. In addition, a significant part (R²>0.40 (p<0.05) at two sites) of the association appeared to be under genetic control. Results indicate a more even gradation of distributions involving an increase in the sample volume % of small granule (types B and C) and decrease in type A granules. This was associated with increased rheology index values and higher flour yield. The ratio of type A:C starch granules accounted for up to 58% (p<0.05) of the variation in flour yield in the samples studied. Thus, rheological parameters measured using a rapid SKCS screening method can be linked to the genetic regulation of SGSD with implications for the improvement of commercial processing performance of hard wheat.     

Effect of gliadin/glutenin ratio on pasting,thermal, and structural properties of wheat starch

Gluten-starch interactions are of specific importance during the processing of cereal-based products. However, the mechanisms for gluten-starch interactions have not been illuminated. The effects of various gliadin/glutenin (gli-glu) ratios (0:10, 3:7, 5:5, 7:3, and 10:0) on the pasting, thermal, and structural properties of wheat gluten-starch mixtures were investigated. The peak, through, and final viscosities were obviously decreased, and the setback value initially increased and then decreased with increasing gli-glu ratios during the rapid viscosity analysis (RVA). Differential scanning calorimetry showed that the enthalpy changes increased with increasing gli-glu ratios. Thermogravimetric analysis showed a slight increase in the degradation temperature of the mixtures as the gli-glu ratio increased, although it was still lower than that of wheat flour. However, there was no significant difference in the weight loss among different gli-glu ratios. Rheometer-Fourier transform infrared (FTIR) spectroscopy showed that the C-6 peak at 996 cm⁻¹ for all the samples was displaced or disappeared due to the hydrogen bond fracture caused by water molecules entering the starch granules. It was also found that the absorption peak in amide II of gli-starch was more obvious than that of glu-starch. The CLSM obviously described the change structure of mixtures with different gli-glu ratio during starch gelatinizaton. By studying the changes in gluten protein components and how they affected the thermal and structural properties of starch, a simple model was proposed to describe the gelatinization process of the mixtures with different ratios of gli-glu and briefly describe the interactions between starch and wheat gluten components. Optimization of the proportion of protein components in wheat flour will enable greater control over the structural characteristics and elasticity of wheat food products.     

In vitro pullulanase activity of wheat (Triticum aestivum L.) limit-dextrinase type starch debranching enzyme is modulated by redox conditions

Expression of a limit-dextrinase (LD) type starch debranching enzyme (EC 3.2.1.41) was observed in developing wheat (Triticum aestivum L.) endosperm and germinating grains, indicating a role for the enzyme in both biosynthesis and degradation of starch. A full-length cDNA, TaLD1, encoding LD in wheat developing kernels was isolated and predicted to encode a 98.6 kDa mature protein active in amyloplasts. Isolated cDNA was expressed in Escherichia coli to produce a recombinant His-tagged LD, which mainly accumulated in inclusion bodies as an inactive enzyme. Extraction of His-tagged LD from the inclusion bodies followed by dialysis under thiol/disulphide redox conditions allowed partial refolding of the protein and detection of pullulanase specific activities by zymogram analysis and enzyme assays. Several active conformations were demonstrated by the recombinant TaLD1 and pullulanase activity could be modulated by redox conditions in vitro. The results suggest that cellular redox conditions may regulate the level of LD activity in wheat tissues.     

Effects of soaking,cooking and fermentation on composition,in-vitro starch digestibility and nutritive value of common beans

A common bean variety, grown in Burundi, was either fermented, soaked and/or cooked, and then assessed for nutrient composition, in-vitro starch digestibility and protein nutritive value. A decrease in ash, most minerals, vitamins, and some essential amino acids was noted for soaked, cooked and soaked-cooked beans. Compared to untreated beans, soaking decreased soluble sugar (9.8 percent) but increased starch (7.3 percent) and soluble fiber (16.9 percent). In cooked beans, an increase in soluble sugar (1.5 percent), and a decrease in thiamine (81.7 percent), starch (24.6 percent) and soluble fiber (16.6 percent) and nitrogen (2.9 percent) contents were observed. Crude fiber (6.9 percent) and starch (10.0 percent) increased while fat (17.6 percent), fatty acids (linoleic: 10.7 percent; linolenic: 14.3 percent) and soluble sugars (25.4 percent) and nitrogen (14.4 percent) decreased in soaked-cooked beans. Fermentation increased potassium (11.6 percent), soluble fiber (18.9 percent), and some amino acids but decreased fatty acids (linoleic: 13.5 percent; linolenic: 19.9 percent), soluble sugar (75.2 percent) and vitamin (riboflavin: 41.0 percent; niacin: 24.5 percent) contents in common beans. However, the in-vitro starch digestibility was greatly improved (12.3 percent) by cooking while it decreased in soaked beans (29.2 percent). Soaking-cooking and fermentation did not have any significant effect on the digestibility of common bean starch. Finally, among the five treatments applied to common beans, only fermentation showed a significant improvement (8.3 percent) on the protein nutritive value of this legume.     

Effect of the nixtamalization with calcium carbonate on the indigestible carbohydrate content and starch digestibility of corn tortilla

There is a growing interest for an environment-friendly nixtamalization process. Nixtamalization with calcium salts generates a minimum level of polluting residues. The effect of a nixtamalization process with calcium carbonate (NCC) on the indigestible carbohydrate content and starch digestibility of tortillas was evaluated. Traditional and NCC tortillas showed lower moisture content than commercial tortillas. Similar protein, ash, and carbohydrate content were found for the three tortillas, but NCC tortillas showed the highest lipid content. The NCC tortilla had the highest dietary fiber content, with the highest insoluble dietary fiber level. Fresh and stored (96 h) NCC and traditional tortillas showed similar resistant starch content. Fresh traditional tortilla showed the highest slowly digestible starch (SDS), but upon storage the rapidly digestible starch (RDS) content of NCC tortilla decreased. Fresh traditional and NCC tortillas had lower predicted glycemic index (pGI) than commercial tortillas, and upon storage, the three tortillas presented lower pGI values than their fresh counterparts. Consumption of tortillas produced with the NCC can produce positive effects in the human health.