Karin Autio

Effects of enzymes in fibre-enriched baking

The aim of the present study was to improve the quality of fibre-enriched wheat breads by enzymic treatment of the fibre fraction. The suitability of different enzymes in fibre-enriched baking and their effects on the dietary fibre content and the ratio of insoluble: soluble fibre content of the breads were studied. The enzyme preparations used were a hemicellulolytic culture filtrate of Trichoderma reesei, a specific (pI 9) xylanase of T reesei and Fermizyme, an α-amylase preparation containing a standardised level of hemicellulase activity. Rye bran was extracted in water (10% (w/w) suspension) to determine the solubilities of the β-glucans and pentosans. Addition of T reesei culture filtrate significantly increased the amount of extractable pentosan obtained from nonautoclaved rye bran. Rye bran supplementation (5%) of wheat flour increased the farinograph absorption and dough development time, but had little or no effect on stability and softening of the dough. The added enzymes decreased dough stability and increased softening. Addition of enzymes caused significant differences in the stickiness of the wheat doughs both with (P<0·003) and without (P<0·001) rye bran. Fermizyme significantly increased the stickiness of wheat doughs both with and without rye bran. The baking results of the fibre-enriched breads were improved by the added enzymes. Addition of T reesei culture filtrate increased the specific volume of the wheat breads both with and without rye bran by almost 20%. Enzyme mixtures were more efficient than individual xylanase in softening the bread crumb and reducing the staling rate of wheat breads both with and without rye bran. Incorporation of enzymes reduced the total dietary fibre content of the breads, but at least doubled the amount of soluble pentosan. The proportions of fluorescent cell walls in the breads were detected by microscopical image analysis. Enzyme addition caused the surface area of insoluble cell walls originating from wheat flours to decrease, suggesting that the enzymes exert more effects on wheat endorsperm cell walls than on bran particles.

EFFECT OF HIGH PRESSURE ON THE PHYSICAL PROPERTIES OF BARLEY STARCH

Abstract The kinetics of the high-pressure gelatinization of barley starch suspensions at two different concentrations (10 and 25%) were studied in the pressure range 400–550 MPa. The pressure-treated samples were examined using rheological methods, microscopy and differential scanning calorimetry (DSC). The rheological properties, the microstructure and loss of birefringence, as well as the melting of amylopectin crystals as determined by DSC, were all both pressure- and time-dependent. For the 10% suspension, only a slight increase in viscosity was observed, while a strong paste with a creamy texture and a maximum storage modulus of approximately 23 kPa was formed during pressurisation of the 25% suspension. The rheological properties and the microstructure of the pressure-treated samples were different from those of the heat-treated samples. The starch granules remained intact after the pressure treatment and no leaching of amylose was observed. The retrogradation of pressure-induced gels was investigated by DSC and was shown to be similar to that of a heat-induced gel.

Effects of Bran Fermentation on Quality and Microstructure of High-Fiber Wheat Bread

ABSTRACT We compared the effects of spontaneous fermentation of the bran fraction and fermentation with added yeast or added yeast and lactic acid bacteria (Lactobacillus brevis) on the quality of wheat bread supplemented with bran. Prefermentation of wheat bran with yeast or with yeast and lactic acid bacteria improved the loaf volume, crumb structure, and shelf life of bread supplemented with bran. The bread also had added flavor and good and homogenous crumb structure. Elasticity of the crumb was excellent. Spontaneous fermentation of the bran fraction did not have the same positive effects on bread quality. The microstructure of the breads was characterized by light microscopy. The positive effect of fermentation of bran on bread quality was evident when comparing the well-developed protein network structure of the breads baked with fermented bran with the control bread. Prefermentation of the bran with yeast and lactic acid bacteria had the greatest effect on the structure of starch. The starch granu...

Influence of oat gum, guar gum and carboxymethyl cellulose on the perception of sweetness and flavour

Abstract The influence of three pseudoplastic hydrocolloids, oat gum, guar gum and carboxymethyl cellulose (CMC) on sensory perception of sweetness and flavour was studied in model systems at two viscosity levels. The sweeteners studied were sucrose, fructose and aspartame, the flavour substances ethyl caproate, a -pinene and cinnamic acid. Sweetness was best perceived from oat gum solutions and most weakly from guar gum solutions. The effect of the composition of the thickener on the perception of sweetness was greater than that of viscosity. Reduction of sweetness by hydrocolloids was weaker for aspartame than for fructose or sucrose. In the perception of flavours, both the total length of perception and the time-intensity pattern were more dependent on the model aroma substance than on the thickener. Possible explanations for the differences are discussed.

Bread quality relationship with rheological measurements of wheat flour dough

ABSTRACT The rheological properties of wheat doughs prepared from different flour types, water contents, and mixing times for a total of 20 dough systems were studied. The results were compared with the results of standard baking tests with the same factors. Water and flour type had a significant effect on storage modulus (G′) or phase angle measured by an oscillatory test both in the linear viscoelastic region and as a function of stress, and on compressional force measured as a function of time. The correlation of maximum force of dough in compression and G′ of dough measured within the linear viscoelastic region was r = 0.80. Correlation between the compression and oscillation test improved when all measuring points of the G′ stress curve were included (r = 0.88). The baking performance of the different doughs varied greatly; loaf volumes ranged from 2.9 to 4.7 mL/g. Although the water content of the dough correlated with the rheological measurements, the correlation of G′measured in the linear viscoel...

Physical properties of (1→3),(1→4)-β-D-glucan preparates isolated from finnish oat varieties

Abstract The β-glucan content in the groats of different Finnish oat varieties cultivated in Finland varied from 3.2 to 5.3% and, in the fibre concentrates obtained by dry milling and a further concentration step including hot ethanol treatment and wet milling, from 11.8 to 18.3%. The viscosities of the isolated crude extracts varied widely between the varieties. Stil, Puhti, Yty and Nasta formed the most viscous solutions and Pol, the typical feed oat, the least viscous solution. The more significant differences in the viscosities between the oat varieties when measured at the same β-glucan concentration could be explained in terms of differences in mean molecular weight. Trypsin decreased the viscosity and the molecular weight of β-glucan of all samples. The viscosity of the β-glucan solutions was independent of pH both before or after enzyme treatment indicating that the protein or peptide is firmly bound to β-glucan.

Evaluation and modelling of rheological properties of high pressure treated waxy maize starch dispersions

Abstract Samples of 10% waxy maize starch dispersions were treated at pressures from 450 to 600 MPa for 0–120 min. The rheological properties of the dispersions were studied by viscosity and low deformation viscoelastic measurements. At 450 MPa, the consistency coefficient did not exceed 7 Pa s n even after a treatment time of 110 min, whereas at 550 MPa a value of 20 Pa s n was reached in about 5–10 min. G ′ measurements as a function of treatment times at different pressures gave almost identical results to viscosity measurement, except that at longer treatment times G ′ decreased, indicating that excessive pressurisation seemed to weaken the gel structure. A sigmoidal type model was found to adequately correlate the consistency coefficient values, obtained at different holding times and processing pressures, with the F value of the process, a value representing an equivalent processing time at specified reference pressure and temperature conditions, defined analogously to the traditional thermal processing terminology.

Effects of laccase and xylanase on the chemical and rheological properties of oat and wheat doughs.

The effects of Trametes hirsuta laccase and Pentopan Mono BG xylanase and their combination on oat, wheat, and mixed oat-wheat doughs and the corresponding breads were investigated. Laccase treatment decreased the content of water-extractable arabinoxylan (WEAX) in oat dough due to oxidative cross-linking of feruloylated arabinoxylans. Laccase treatment also increased the proportion of water-soluble polysaccharides (WSNSP) apparently due to the beta-glucanase side activity present in the laccase preparation. As a result of the laccase treatment, the firmness of fresh oat bread was increased. Xylanase treatment doubled the content of WEAX in oat dough and slightly increased the amount of WSNSP. Increased stiffness of the dough and firmness of the fresh bread were detected, probably because of the increased WEAX content, which decreased the amount of water available for beta-glucan. The combination of laccase and xylanase produced slight hydrolysis of beta-glucan by the beta-glucanase side activity of laccase and enhanced the availability of AX for xylanase with concomitant reduction of the amount and molar mass of WSNSP. Subsequently, the volume of oat bread was increased. Laccase treatment tightened wheat dough, probably due to cross-linking of WEAX to higher molecular weight. In oat-wheat dough, laccase slightly increased the proportion of WSNSP between medium to low molecular weight and increased the specific volume of the bread. Xylanase increased the contents of WEAX and WSNSP between medium to low molecular weight in oat-wheat dough, which increased the softness of the dough, as well as the specific volume and softness of the bread. The results thus indicate that a combination of laccase and xylanase was beneficial for the textures of both oat and oat-wheat breads.

Heterogeneity in a water-extractable rye arabinoxylan with a low degree of disubstitution

From rye grain samples, water extractable arabinoxylan with a low degree of disubstitution (AX I) was isolated by fractionation on a DEAE-cellulose column. AX I of all rye samples had a similar relative composition of un- and monosubstituted xylose residues and with less than 5% disubstitution. It showed a shear thinning behaviour and the viscosity was related to molecular weight. AX I isolated from different rye varieties had different viscosities at the same concentration. One rye sample had a weight average molecular weight of 125[punctuation space]000 (polydispersity 2) according to calculations from both light scattering and viscosity data. Signals from un- and monosubstituted xylose residues in 13C NMR spectra were assigned using 13C-HSQC-DEPT and COSY techniques. AX I probably consisted of blocks or different molecules with sparsely and more densely substituted regions.

Influence of Oat β-Glucan Preparations on the Perception of Mouthfeel and on Rheological Properties in Beverage Prototypes

ABSTRACT The aim was to study the effect of concentration and molecular weight of four different β-glucan preparations on the perceived sensory quality of a beverage prototype. The correlations between sensory and instrumental measures were investigated. Two of the preparations were brantype containing high molecular weight β-glucan, two were more-processed low molecular weight β-glucan preparations. Twelve beverage samples containing 0.25–2% β-glucan and one reference sample thickened with carboxymethyl cellulose (CMC) were profiled by a sensory panel and analyzed by instrumental measurements (viscosity and molecular weight). Sensory profiles of the beverages varied at the same concentration of β-glucan, depending on β-glucan preparation. Beverages made with the bran-type preparations were more viscous and had higher perceived thickness than beverages made with more-processed, low molecular weight preparations. Moderate correlations were obtained between perceived thickness and sliminess and instrumental...