Effect of b-glucan molecular weight on rice flour dough rheology, quality parameters of breads and in vitro starch digestibility

Producción CientíficaThe study aimed at investigating the effects of molecular weight(peak molecular weight, Mp, 83, 192 and 650 kDa) and level (1.3, 2.6 and 3.9 g/100 g flour basis) of enriched in β-glucan (BG) concentrates (from oat and barley) added into rice flour gluten-free (GF) doughs on their viscoelastic and pasting properties, as well as the quality parameters of bread and the in vitro starch digestibility. A purification process of a commercial BG concentrate, followed by an acid hydrolysis step were employed to reduce the content of interfering excipients (e.g. maltodextrins) and obtain preparations with a range of molecular weights. BG-enriched GF breads of improved quality, that can fulfil the EFSA claims (ingest of 3 g of BG per day with a daily bread intake of ∼200 g of bread), were obtained, exhibiting slower starch digestibility (in vitro assay) dependent on the molecular weight and concentration of BG. With the higher Mp BG used, showing the largest impact on dough rheology characteristics and having a greater potential for health benefits, higher specific volume and lower bread crumb hardness were noted among the GF breads. The medium and lowest Mp BG also had an influence on dough rheological behavior and bread quality attributes. The rapidly available glucose of the bread decreased from 81g/100 g to 72g/100 g as result of the 3.9g/100 g addition of the highest Mp BG in the GF formulations

Effect of Microwave Radiation Pretreatment of Rice Flour on Gluten-Free Breadmaking and Molecular Size of β-Glucans in the Fortified Breads

Producción CientíficaCereal β-glucan concentrates can be used in gluten-free breads to improve dough handling properties and quality of final products as well as to enhance their nutritional value; however, the presence of endogenous β-glucanases in rice flour, in combination with prolonged mixing, fermentation and proofing time, can cause a substantial reduction in β-glucan molecular weight, affecting detrimentally their efficacy for bioactivity. In this study, microwave (MIWA) heating was applied to the rice flours before breadmaking at different flour water contents (13-25%) and treatment times (0- 4min) to reduce β-glucanase activity. Gluten-free breads made from the MIWA treated rice flours were fortified with oat β-glucan concentrate to enhance their nutritional profile. The molecular weight of added β-glucan in the final products increased with increasing both flour water content and time of MIWA treatment, reflecting the magnitude of residual β-glucanase activity in the flour. Pretreatment with MIWA radiation for 4 min of the rice flour tempered at 25% moisture resulted in negligible residual β-glucanase activity and preserved to a great extent the molecular weight of β-glucans in the enriched breads. End-product quality was not affected by flour MIWA pretreatment, and even a slightly higher loaf specific volume was noted for breads made from the MIWA -treated flours (4min MIWA at 25% moisture content) compared to that of untreated flour. These findings can contribute to the improvement of nutritional value of rice-based gluten-free breads for celiac consumers as well as of any β-glucan containing yeast-leavened bakery product without altering its sensorial attributes. Additional studies are still required for further evaluation of the effect of more intense microwave treatment on rice flour and its application on breadmaking

Impact of acidification and protein fortification on thermal properties of rice, potato and tapioca starches and rheological behaviour of their gels

Producción CientíficaThe impact of acidification and non-gluten protein fortification (egg-albumin and soy-protein isolate) on thermal transitions of rice, potato and tapioca starches as well as the viscoelastic properties of their gels prepared at two casting temperatures, 90ºC and 120ºC, was investigated. The thermal and rheological behaviour of starches depended on their botanical origin and were significantly influenced by the presence and type of protein added as well as by the pH of the aqueous dispersion. Acidification to pH 4.5 increased the gelatinization temperature of rice starch in the presence of albumin or soy proteins, while reduced it in the case of tapioca starch, regardless of the presence of proteins. Acidification of rice starch dispersions decreased significantly the apparent gelatinization enthalpy; this effect was even greater in the presence of proteins. The addition of proteins brought about a structuring effect on tapioca gels leading to higher viscoelastic moduli and lower tan δ values. In general, acidification led to weaker gel structures, with more pronounced effect for potato starch, most likely related to its higher phosphate content (charge screening). Much weaker gels were obtained at 120ºC compared to those processed at lower temperatures; however, protein incorporation reinforced gel structure, an effect that was not observed in gels formed at 90º, as also revealed by microstructure analysis using confocal scanning laser microscopy. In conclusion, protein addition and pH adjustments of aqueous starch dispersions can provide an effective means to modulate the functional and textural properties of gel-like starch-based gluten-free formulations.Ministerio de Economía, Industria y Competitividad - FEDER (Projects AGL2012-35088 and AGL2015-63849-C2-2-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA072P17

Inactivation of Endogenous Rice Flour β-Glucanase by Microwave Radiation and Impact on Physico-chemical Properties of the Treated Flour

Producción CientíficaThe apparent reduction of β-glucan (BG) molecular weight in rice based gluten-free (GF) breads fortified with cereal BG concentrates reveals the presence of β-glucanase activity in rice flour. Inactivation of endogenous β-glucanase in rice flour thus seems to be necessary step when developing GF breads enriched with BG of high molecular-weight. The aim of this work was to study the thermal inactivation of endogenous β-glucanase in rice flour by means of microwave (MW) processing; rice flours preconditioned at four different moisture levels (13%, 16%, 19%, 25%) were treated by MW radiation at 900 W and five MW treatment times (ranging from 40s to 8 min, applied stepwise at 20s intervals). The effects of microwaves on starch crystallinity, pasting and thermal properties of MW-treated rice flours were also explored. The β-glucanase activity in rice flours was assessed by the rate of decrease in specific viscosity of a dilute solution of a purified β-glucan preparation, upon addition of flour extracts. MW proved to be a useful alternative for thermal inactivation of endogenous β-glucanase in rice flours when applied to moistened samples. The inactivation process followed a first order kinetic response and the apparent rate constant of thermal inactivation increased exponentially with the moisture content of the flour, M, according to the equation 0.0146·exp (0.212·M) (R2 = 0.97). The MW time required for complete β-glucanase inactivation was only 4 min when the initial flour moisture increased to 25%. Following MW treatment, the starch crystallinity was unaffected (p>0.05) and the side effects of the treatment on flour pasting and thermal properties were rather negligible.Ministerio de Economía, Industria y Competitividad - FEDER (Projects AGL2012-35088 and AGL2015-63849-C2-2-R

Mashes to Mashes, Crust to Crust. Presenting a novel microstructural marker for malting in the archaeological record

The detection of direct archaeological remains of alcoholic beverages and their production is still a challenge to archaeological science, as most of the markers known up to now are either not durable or diagnostic enough to be used as secure proof. The current study addresses this question by experimental work reproducing the malting processes and subsequent charring of the resulting products under laboratory conditions in order to simulate their preservation (by charring) in archaeological contexts and to explore the preservation of microstructural alterations of the cereal grains. The experimentally germinated and charred grains showed clearly degraded (thinned) aleurone cell walls. The histological alterations of the cereal grains were observed and quantified using reflected light and scanning electron microscopy and supported using morphometric and statistical analyses. In order to verify the experimental observations of histological alterations, amorphous charred objects (ACO) containing cereal remains originating from five archaeological sites dating to the 4th millennium BCE were considered: two sites were archaeologically recognisable brewing installations from Predynastic Egypt, while the three broadly contemporary central European lakeshore settlements lack specific contexts for their cereal-based food remains. The aleurone cell wall thinning known from food technological research and observed in our own experimental material was indeed also recorded in the archaeological finds. The Egyptian materials derive from beer production with certainty, supported by ample contextual and artefactual data. The Neolithic lakeshore settlement finds currently represent the oldest traces of malting in central Europe, while a bowl-shaped bread-like object from Hornstaad– Ho¨ rnle possibly even points towards early beer production in central Europe. One major further implication of our study is that the cell wall breakdown in the grain’s aleurone layer can be used as a general marker for malting processes with relevance to a wide range of charred archaeological finds of cereal products

Mashes to Mashes, Crust to Crust. Presenting a novel microstructural marker for malting in the archaeological record

The detection of direct archaeological remains of alcoholic beverages and their production is still a challenge to archaeological science, as most of the markers known up to now are either not durable or diagnostic enough to be used as secure proof. The current study addresses this question by experimental work reproducing the malting processes and subsequent charring of the resulting products under laboratory conditions in order to simulate their preservation (by charring) in archaeological contexts and to explore the preservation of microstructural alterations of the cereal grains. The experimentally germinated and charred grains showed clearly degraded (thinned) aleurone cell walls. The histological alterations of the cereal grains were observed and quantified using reflected light and scanning electron microscopy and supported using morphometric and statistical analyses. In order to verify the experimental observations of histological alterations, amorphous charred objects (ACO) containing cereal remains originating from five archaeological sites dating to the 4th millennium BCE were considered: two sites were archaeologically recognisable brewing installations from Predynastic Egypt, while the three broadly contemporary central European lakeshore settlements lack specific contexts for their cereal-based food remains. The aleurone cell wall thinning known from food technological research and observed in our own experimental material was indeed also recorded in the archaeological finds. The Egyptian materials derive from beer production with certainty, supported by ample contextual and artefactual data. The Neolithic lakeshore settlement finds currently represent the oldest traces of malting in central Europe, while a bowl-shaped bread-like object from Hornstaad–Hornle possibly even points towards early beer production in central Europe. One major further implication of our study is that the cell wall breakdown in the grain's aleurone layer can be used as a general marker for malting processes with relevance to a wide range of charred archaeological finds of cereal products

Molecular weight effects on solution rheology of pullulan and mechanical properties of its films

The effects of molecular weight on solution rheology of pullulan, and on thermomechanichal properties of sorbitol and/or water-plasticized pullulan specimens, prepared by either hot pressing or casting of aqueous solutions, were studied. Pullulan samples differing in molecular weight were characterized by 13C NMR spectroscopy and size exclusion chromatography combined with a multiangle laser light scattering and a refractive index detector. For samples with weight average molecular weight (Mw) ranging between 100 and 560×103, the values of limiting viscosity ([η]), critical concentration (c*) and coil overlap parameter (c*[η]) were within the range 0.38–0.70 dl/g, 1.4–3.1 g/dl and 1.0–1.2 dl/g, respectively. The thermomechanical properties of five molecular weight grades of pullulan, either alone or with sorbitol (plasticized at a 10% d.b. level) were examined by dynamic mechanical thermal analysis (DMTA). A large drop in storage modulus E′ (101.5–103 Pa) and a peak in tan δ in the DMTA traces accompanied the glass–rubber transition (Tg) or the α-relaxation (Tα) of pullulan; the magnitude of the drop in E′ and the tan δ peak height increased with increasing water content. The plasticizing action of water and sorbitol was evident in the DMTA curves, and the Tg vs. moisture content data were fitted to the Gordon–Taylor empirical model. Within the range of molecular weights tested there was no effect of polymer molecular weight on Tg. A β-relaxation detected by DMTA was shifted to lower temperature with increasing moisture content and to higher temperature with addition of sorbitol. Apparent activation energies for α-relaxation (Eαα) and β-relaxation (Eαβ) processes, estimated from multifrequency measurements, were within 171–640 and 118–256 kJ/mol, respectively; the values for Eαα and ‘fragility’ parameter decreased with increasing moisture content. Analysis of viscoelasticity data using the time–temperature superposition principle with the Williams–Landel–Ferry equation was successful over the range Tg to Tg+40 °C, provided that the coefficients C1 and C2 are optimized and not allowed to assume their ‘universal’ values. Large deformation mechanical tests demonstrated large decreases in tensile (Young's) modulus (E) and strength (σmax), and an increase in percentage elongation with increasing water content and/or addition of sorbitol in pullulan films. Relationships between the tensile parameters (E and σmax) and water content showed an increase in stiffness of the films from 3 to 7% moisture, and a strong softening effect at higher water contents. The tensile tests revealed some relationships between mechanical properties under uniaxial load and the molecular characteristics of pullulan, e.g. E, σmax, and elongation values increased with increasing molecular weight

Comparative Evaluation of the Nutritional, Antinutritional, Functional, and Bioactivity Attributes of Rice Bran Stabilized by Different Heat Treatments

The objective of this study was to evaluate the effects of different stabilization treatments—namely, dry-heating, infrared-radiation, and microwave-heating—on the nutritional, antinutritional, functional, and bioactivity attributes of rice bran (RB). Among the heating treatments, infrared-radiation exerted the strongest inactivation, resulting in 34.7% residual lipase activity. All the stabilization methods were found to be effective in the reduction of antinutrients, including phytates, oxalate, saponins, and trypsin inhibitors. No adverse effect of stabilization was noted on chemical composition and fatty acid profile of RB. Instead, stabilization by all heat treatments caused a significant decrease of vitamin E and total phenolics content in RB; the same trend was observed for the antioxidant activity as evaluated by the DPPH test. The antioxidant activity, as evaluated by ABTS and FRAP tests, and water absorption capacity were improved by the stabilization of RB, whereas the oil absorption capacity and emulsifying properties decreased. Microwave-heating enhanced the foaming properties, whereas infrared-radiation improved the water solubility index and swelling power of RB. Consequently, treatment of RB with infrared-radiation has a potential for industrialization to inactivate the lipase and improve some functional properties of this material for uses as a nutraceutical ingredient in food and cosmetic products

Rheological characteristics and physicochemical stability of dressing-type emulsions made of oil bodies-egg yolk blends

Two oil body creams, differing in oil volume fraction and surface protein composition, were obtained by applying alkaline aqueous extraction to comminuted maize germ and then recovering the oil bodies from the extract by centrifugation, either in the presence of 0.5 M sucrose (OB-W) or following isoelectric precipitation at pH 5.0 (OB-A). Oil bodies in the former cream are stabilised by natural oil body surface proteins while in the OB-A cream, exogenous proteins, in addition to natural oil body proteins, are also present. The creams were blended with appropriate amounts of water, NaCl and liquid yolk, and the pH was adjusted to 3.8 to obtain 20% or 45% (w/w) in oil OB-W and 20% (w/w) in oil OB-A model dressing-type emulsions. The physical stability of the emulsions, against creaming and coalescence, was monitored upon storage, while the development of emulsion structure during ageing was probed by applying steady shear and small deformation oscillatory rheometry. The adsorbed to oil bodies' surface proteins were analysed by applying SDS-PAGE. Since no yolk protein constituents were detected at the oil body surface layer of the emulsions, it is hypothesised that the presence of unadsorbed yolk particles in the emulsion continuous phase results in the intensification of interdroplet interaction effects, due to depletion events, and may therefore have an indirect but nevertheless strong influence on emulsion structure and physical stability

Stability and rheology of egg-yolk-stabilized concentrated emulsions containing cereal β-glucans of varying molecular size

The effects of barley and oat β-glucans on rheological and creaming behaviour of concentrated egg-yolk-stabilized model emulsions were investigated. Four polysaccharide preparations were used, two from each cereal; one sample with high and one with low molecular weight, i.e. the molecular weights were alike in pairs (110×103 and 40×103, respectively). In order to elucidate the mechanism of action of β-glucans in emulsions, Tween 20-stabilized emulsions were also examined. Tween 20 enhances neither the continuous phase viscosity nor the interactions between the droplets, so the changes could be easily attributed to β-glucans. It appeared that the low Mw β-glucan samples stabilize emulsions against creaming by means of network formation in the continuous phase while their high molecular weight counterparts enhance the viscosity of the continuous phase. Comparison of dynamic rheological tests between a reference emulsion without β-glucans and emulsions containing β-glucans showed that the polysaccharides largely affects the viscoelastic behaviour of the emulsion. Ageing of β-glucan-containing emulsions did not affect significantly the viscoelastic properties except for the emulsions containing low Mw β-glucans extracted from oat. Interestingly, all emulsions containing β-glucans creamed approximately the same after 30 days of storage regardless which preparation was used. The egg yolk constituents seemed to play a dominant role on the viscoelastic and the creaming behaviour of the emulsions, i.e. the viscoelastic behaviour was further enhanced and this could not only be attributed to the presence of the β-glucans but also to the stronger interactions between the oil droplets. Ageing did not affect the viscoelastic properties of β-glucan-containing emulsions while the reference emulsion, prepared only with egg yolk, showed a decrease in the value of storage modulus. The former could be interpreted as a steady consistency of the product during storage independent of the creaming behaviour. The creaming behaviour varied among the samples with the high molecular weight β-glucans from oat showing the highest stabilit