Influence of Added Enzymes on the Rheological Properties of a Wheat Flour Dough

Cereal Chem. 69(5):542-546 The changes in rheological properties of a wheat flour dough due to the wheat flour dough were clearly influenced both by the type of the addition of enzymes were measured. The dough, made of flour of a-amylase and by mixing protease with the a-amylase. The presence of standard baking quality, was characterized by oscillatory measurements a-amylases caused a decrease in G' after a shorter period of time, and at room temperature and after storage at 400C. Different commercially lower G' values were obtained. A time and temperature dependency of available a-amylases and mixtures of a-amylases and proteases were G' was evident. The change in G' related to the amount of damaged added. The elastic modulus, G', increased slowly with time at room temstarch was also studied, and it was found that G' increased as the level perature, whereas during the same time (2 hr) at 400 C, a maximum value of starch damage increased. This increase in G' could be compensated followed by a continuous decrease in G' was observed. The phase angle, for by addition of more water. 6, increased slightly with time at 400C. The rheological properties of Wheat flour contains enzymes, including aand /3-amylases, proteases, lipases, phosphatases, and oxidases (Reed and Thorn 1971). If the wheat is ungerminated, the enzymes are present in low level, and they remain inactive during storage if moisture and temperature are kept low. The characterization of enzymes in wheat is dependent on the source from which the enzymes derive. Three groups of enzymes can be distinguished: the indigenous enzymes (normal constituents of food material at harvest), e.g., amylases; the endogenous enzymes produced in situ by microorganisms either present as contaminants or added as cultures; and the exogenous or added enzymes (Fox and Mulvihill 1982). Whether the enzymes are normal constituents or added, the amylases in wheat flour are very important during baking. a-Amylase has been intensely studied, since small amounts of a-amylases caused by preharvest sprouting can lower bread quality. This can be avoided by harvesting when amylase activity is low (Hill and MacGregor 1988). Supplementation of a-amylase can therefore be necessary, providing benefits such as improved gas retention and increased loaf volume (Cauvain and Chamberlain 1988). This makes optimizing the amount of amylase valuable to produce a high-quality end-product (Kruger and Reed 1988). Most of the added amylases used in bakeries are from bacterial or fungal sources. These exogenous enzymes have different physical properties, such as thermal stability. Bacterial a-amylase has a higher degree of heat tolerance than cereal a-amylase, whereas fungal amylase has a lower tolerance. The proteases in wheat flour are mainly of the endogenous type and are thought to be of little importance to the flour proteins during baking (Ewart 1977). Addition of proteases to obtain weaker and more flexible doughs from strong wheats is normally not necessary in breadmaking, but proteases can be used in flours for cookies or wafers. The aim of the present investigation was to study the effect of added enzyme preparations (principally a-amylases) on rheological properties of dough. A second objective was to investigate whether the enzymes commercially available to the baker affect the rheological properties of dough in the same way. The study concentrated on rheological changes occurring during a time and temperature protocol corresponding to fermentation. The high proportion of starch in a wheat flour and the amount of water present, together with amylases, indicate the possibility of rheological changes with time in a wheat dough. The results from such studies might be expected to depend on the enzymes present and their properties. Enzymes from different microbial sources vary depending on type and strain of the microorganism, growth conditions, and purification methods (Himmelstein 1984). The enzyme preparations used in this study were all of commercial 'Department of Food Technology, University of Lund, Lund, Sweden. t 1992 American Association of Cereal Chemists, Inc. 542 CEREAL CHEMISTRY quality, and the purity in such enzyme batches may differ from one preparation to another. Thus, it is valuable to know the actual behavior of the commercial enzyme preparation on a pure substrate. The activity of the added enzyme preparations was therefore studied on a gelatinized starch suspension in a viscometric test. The rheological properties of the wheat flour doughs were characterized by oscillatory measurements. Oscillation tests were chosen because it is possible to work with small deformations and small shear rates without any orientation effects, since direction of deformation changes. In oscillatory measurements, viscoelastic properties of a wheat dough can be divided into two components, the dynamic shear storage modulus, G', and the dynamic shear loss modulus, G". G' is the dominating factor when small strains are applied, i.e., at strains below 0.1 (Funt Bar-David and Lerchenthal 1975). A more complete study of dynamic shear moduli in wheat flour doughs and their dependence on amplitude and frequency was published by Smith et al (1970). MATERIALS AND METHODS Flour The wheat flour used was of standard baking quality provided by Skanemollan, Tagarp, Sweden. The composition was, on a 15% moisture basis, 10.5% protein, 1.5% lipids, and 73% carbohydrates. The damaged starch content was 9.3% (also on a 15% moisture basis). The flour was treated in dry-milling equipment, consisting of a stainless steel tube with three stainless steel balls, to obtain higher values of damaged starch. The damaged starch was analyzed according to AACC Method 76-30A (AACC 1983). The falling number of the wheat flour was 270. Enzymes The amylase preparations used were of commercial quality from Rohm GmbH, Darmstadt, Germany, and available under the trade name Veron (Table I). They contain a-amylase from fungal sources, and some of the batches also have protease activity. Fungal amylases also were supplied by Grindsted Products A/ S, Brabrand, Denmark. These amylase preparations are available under the trade name Grindamyl (Table I). All of the doughs and starch gels in this study were made with tap water containing 1.5 mM Ca2+ ions, which is a sufficient quantity for maintaining the stability of the a-amylase (Marchylo et al 1976). Starch Gel A wheat starch of commercial quality (AB Juvel, Stockholm, Sweden) was used. The starch gels were made at a concentration of 4% dry weight. The starch suspension was gelatinized while it was gently stirred in a water bath at 950C for 60 min. The starch gel then was equilibrated for 30 min in a water bath at 25° C before use. All of the analyses were performed on a mixture of gelatinized starch solution (25 ml) and enzyme preparation. The enzyme preparations were added after gelatinization of the TABLE I Commercial Enzyme Preparations Used Recommended Dosage Used Dosage Activity Trade Name Type of Enzyme (mg/10 g of flour) (mg/10 g of flour) SKB/g Rohm Veron AV a-Amylase 0.9-1.5 1.3 1,500 Veron AC' a-Amylase 0.3-0.5 0.4 4,500 Veron AF a-Amylase + protease 1.0-2.0 1.9 1,500 Veron APb a-Amylase + protease 1.0-2.0 1.9 1,500 Grindsted Grindamyl A 1000 a-Amylase 0.60 0.65 NMC Grindamyl S 100 a-Amylase 2.0 2.2 NM a Veron AC has a threefold greater a-amylase activity compared with the other Rohm enzymes. bVeron AP has greater protease activity than Veron AF. cNot measured. starch as powder, and the enzymatic activity was followed as a decreasing viscosity during a constant shear rate of 146.7 sec-1