Cristina M. Rosell

INFLUENCE OF HYDROCOLLOIDS ON DOUGH RHEOLOGY AND BREAD QUALITY

Abstract The effect of different hydrocolloids (sodium alginate, κ-carrageenan, xanthan gum and hydroxypropylmethylcellulose) on the rheological properties of the wheat flour dough and the final quality of breads was investigated. A complete study of the rheological behaviour of the dough containing hydrocolloids was performed by using the following instruments: farinograph, extensograph, alveograph and rheofermentometer. The baking response was also determined by using an oven rise recorder. Xanthan and alginate had the most pronounced effect on dough properties yielding strengthened doughs. A great improvement in dough stability during fermentation was achieved by adding hydrocolloids. Regarding their effect on bread properties, the hydrocolloids increased the specific volume, with the exception of alginate, as well as both moisture retention and water activity. In addition, textural studies revealed that addition of κ-carrageenan or hydroxypropylmethylcellulose reduced the firmness of bread crumb. In conclusion, k-carrageenan and hydroxypropylmethylcellulose could be used as improvers in the bread-making performance.

Effect of the addition of different fibres on wheat dough performance and bread quality

Abstract A good correlation has become evident between fibre consumption and the reduction of coronary heart-related diseases and diabetes incidence. However, fibre intake is commonly lower than recommended. In consequence, the development of foods with high fibre content should be desirable. The potential use of various commercial fibres (carob fibre, inulin and pea fibre), as fibre-enriching agents in breadmaking, is reported. The effects of the addition of these fibres to wheat flour on the viscoelastic properties of dough and both mixing and proofing behaviour is presented. Bread evaluation revealed that carob and pea fibre supplementation, although decreasing specific loaf volume (very slightly in the case of carob fibre), conferred softness to the bread crumbs. In addition, sensory evaluation showed that consumer panellists judged these fibre-enriched breads as acceptable. Therefore, their use, especially carob, allows an increase of the daily intake of fibre without promoting negative effects on the rheological properties of doughs or quality and overall acceptability of the resulting breads. The whole study indicates that these three fibres can be used as additives in breadmaking in order to fortify the diet.

Different hydrocolloids as bread improvers and antistaling agents

Abstract Supplementation of several hydrocolloids with different chemical structure and from diverse origin to the breadmaking process is presented. The effect of hydrocolloids (sodium alginate, xanthan, κ-carrageenan and hydroxypropylmethycellulose) on fresh bread quality and its influence on bread staling were studied. Physical properties (moisture, hardness, volume) and sensory properties of fresh bread and after storage of 24 h were analysed. Hydrocolloids affected in different extent to the fresh bread quality, and concentrations of 0.1% (w/w, flour basis) were sufficient for obtaining the observed effects. Although different improvements were observed associated to specific hydrocolloid, HPMC was the hydrocolloid with an improvement effect on all the parameters tested, specific volume index, width/height ratio, and crumb hardness; in addition good sensory properties for visual appearance, aroma, flavour, crunchiness and overall acceptability was obtained. All hydrocolloids were also able to reduce the loss of moisture content during bread storage, reducing the dehydration rate of crumb. In addition, during storage, alginate and HPMC showed an anti-staling effect, retarding the crumb hardening.

Pasting properties of different wheat flour-hydrocolloid systems

Abstract The effect of several hydrocolloids on the pasting properties and gelling behaviour of wheat flour was investigated. The influence of the selected hydrocolloids (guar gum, pectin, alginate, κ-carrageenan, xanthan and hydroxypropylmethylcellulose (HPMC)) on wheat flour was tested by using two different techniques: amylograph and differential scanning calorimetry (DSC). In order to have a general overview of their effect, hydrocolloids were chosen from different sources implying a broad diversity of chemical structures. Differences among hydrocolloid-wheat flour suspensions were more evident from amylographic analysis than from DSC examination. The hydrocolloid addition largely modified the amylograph parameters of wheat flour—even at the low levels tested [0.5 and 1% (w/w), flour basis], and the extent of their effect depended upon the chemical structure of the added hydrocolloid. The greatest effect on pasting temperature was observed when 1% alginate was added, which produced a decrease of ca 3°C. This reduction is really important since it implies an earlier beginning of starch gelatinization and, in turn, an increase in the availability of starch as enzyme substrate during baking period. Xanthan and pectin increased the cooking stability while κ-carrageenan and alginate did not modify it. Setback was augmented by guar gum and HPMC but alginate, xanthan and κ-carrageenan showed the opposite effect. The bump area related to the formation of amylose–lipid complex, was favoured by κ-carrageenan, alginate and pectin, and slightly affected by xanthan and HPMC. In summary, each tested hydrocolloid affected in a different way the pasting properties of wheat flour. The results obtained are important for the appropriate use of these hydrocolloids as ingredients in the bread making process.

Preparation of activated supports containing low pK amino groups. A new tool for protein immobilization via the carboxyl coupling method

A method for the preparation of new aminated agarose gels containing monoaminoethyl-N-aminoethyl structures, MANA-agarose gels, has been developed. These gels contain primary amino groups with a very low pK value (6.8). In addition to that, we have been able to prepare very highly activated gels (e.g., 10% agarose gels containing up to 200 mu Eq of primary amines per milliliter). These two properties make these activated supports suitable for performing novel and interesting methods for protein immobilizations via very mild carbodiimide activation of carboxy groups. For example, very effective coupling reactions can be performed at pH 5.0-6.0 in the presence of low concentrations of activating agent, e.g., 1 mM. By using a model industrial enzyme, beta-galactosidase from Aspergillus oryzae, we have been able to demonstrate the excellent prospects of these novel activated supports.

Strategies for enzyme stabilization by intramolecular crosslinking with bifunctional reagents

Abstract A original strategy to obtain intramolecular crosslinking is discussed. This strategy consisted of three consecutive steps to direct the reaction to the formation of intramolecular crosslinks: (a) enzyme are partially modified with the bifunctional reagent in a very controlled fashion; (b) the excess of reagent is removed; and (c) the modified enzyme is incubated long-term to allow a crosslinking reaction without the competition of additional single-point modifications. In this way, we were able to obtain interesting stabilizations of immobilized derivatives of penicillin G acylase using glutaraldehyde as a crosslinking reagent under very controlled conditions.

Starch Hydrolyzing Enzymes for Retarding the Staling of Rice Bread

ABSTRACT Previous attempts have been made to obtain gluten-free bread of acceptable quality for bread specific volume and crumb texture. Rice bread is a good alternative to celiac patients, but it has a very rapid staling during storage. Rice starch is more prone to retrograde during storage than wheat starch, and the special hydrophobic nature of the rice proteins requires specific enzymes to be used in the rice bread process. To retard rice bread staling, two different starch hydrolyzing enzymes (α-amylase of intermediate thermostability and cyclodextrin glycoxyl transferase [CGTase]) have been tested and their effect on fresh bread quality and staling during storage has been evaluated. The addition of α-amylase improved bread specific volume and crumb firmness but very sticky textures were obtained. The addition of CGTase produced even higher specific volume and similar crumb firmness with better texture. Both enzymes decreased the ability of amylopectin to retrograde during storage. The firming kineti...

Wheat Flour Proteins as Affected by Transglutaminase and Glucose Oxidase

ABSTRACT Enzymes are good tool to modify wheat proteins by creating new bonds between the protein chains. In this study, the effect of the addition of glucose oxidase (GO) and transglutaminase (TG) on the wheat flour proteins is presented. The modification of wheat proteins was determined by analyzing the changes in gluten quality, alveograph parameters, and protein modifications. The amount of wet gluten increased with the addition of GO and TG, but the gluten quality was not improved in any case. Regarding the alveograph parameters, the effect of GO was readily evident obtaining wheat dough with higher tenacity and lower extensibility than the control, while TG led to doughs with lower tenacity and that were also less extensible. The protein modifications were characterized by free-zone capillary electrophoresis (FZCE). FZCE data indicated that TG polymerizes mainly glutenins and, of those, the high molecular weight glutenin subunits were the most affected.

Rheological Behaviour of Formulated Bread Doughs During Mixing and Heating

During breadmaking different physicochemical phenomena occur producing discernible changes in the rheological properties. Traditionally, these changes have been studied with equipments controlling separately the mixing step and the baking process. The MIXOLAB is a new apparatus which measures torque when bread dough is subjected to a dual mixing and temperature constraint. It was the aim of this study to compare this new tool with other available methodologies in order to explore its use as a suitable technique for determining bread dough rheological properties. A broad range of correlations was found, not only within parameters derived from the MIXOLAB, but also with standard methods as the pasting method performed by the Rapid Visco Analyser, the gluten index and uni- and bi-axial extensional measurements. The use of MIXOLAB has also allowed the identification of the influence of design factors (flour and exogenous enzymes) on the rheological properties. These results confirm MIXOLAB as a promising tool for the rheological assessment of bread dough.

Facile synthesis of artificial enzyme nano-environments via solid-phase chemistry of immobilized derivatives: Dramatic stabilization of penicillin acylase versus organic solvents

Abstract A method to generate a highly hydrophilic nano-environment surrounding immobilized enzymes [penicillin acylase (PGA)] has been developed. The enzyme was firstly multipoint immobilized on a highly activated support having an internal morphology composed by large hydrophilic surfaces (a). After irreversible enzyme immobilization, a high molecular weight polyamine molecule was further immobilized on the same support surface. In this way, all areas of the enzyme next to the support surface may become embedded in a hydrophilic environment (b); or the immobilized enzyme was modified with a high molecular weight poly-aldehydic polymer which also becomes a hydrophilic poly-hydroxyl macromolecule after borohydride reduction (c). The single application of each distinct (b or c) modifications did not promote stabilizing effects on immobilized PGA; however, the combined effect of both consecutive modifications (the chemical modification of the coimmobilized enzyme-polyamine derivative) promoted a dramatic stabilization of PGA versus organic solvents associated with a minimal loss of catalytic activity. The stabilizing effect was higher when the enzyme was incubated with large and hydrophobic organic solvents; thus, the modified derivative retained 80% of activity relative to soluble enzyme, but it was 1,000-fold more stable than the unmodified one in the presence of 90% tetraglyme. A fairly complete embedding of the whole enzyme surface in a highly hydrophilic nano-environment seems to be achieved.