Elsevier

Journal of Cereal Science

Volume 56, Issue 3, November 2012, Pages 644-651
Journal of Cereal Science

Effects of fungal α-amylase on chemically leavened wheat flour doughs

https://doi.org/10.1016/j.jcs.2012.08.002Get rights and content

Abstract

Chemical leaveners are used in doughs to generate carbon dioxide, as an alternative to yeast, in making a range of bakery products. In this study, the effects of fungal α-amylase and ascorbic acid on chemically leavened doughs were followed by measuring dough extensibility, true rheological properties, the amount of free liquid in doughs following ultracentrifugation and the quality of baked products. As with yeasted doughs, the bake qualities of chemically leavened doughs also improved in the presence of fungal α-amylases. The bake qualities were not affected when the equivalent amount of ascorbic acid was added. The differences in dough formulations were detected from measurements of true rheological properties, not from extensibilities of doughs. The amount of free liquid was larger and of lower viscosity in doughs containing α-amylases. The properties of the continuous liquid phase were found to be important in defining the rheological and baking qualities of doughs.

Highlights

► Fungal α-amylase positively impacts baking qualities of chemically leavened doughs. ► α-amylase affects the physical properties of the suspending phase in doughs. ► Strain hardening characteristics capture differences between dough formulations.

Introduction

Chemical leaveners are used in frozen doughs, refrigerated doughs as well as fresh doughs for making a wide range of bakery products ranging from breads and pizza crusts to cakes and muffins (Holcomb and Rayas-Duarte, 2012; Kulp et al., 1995). These leaveners are mixtures of certain acidic and alkaline carbonate compounds that react readily to produce carbon dioxide, the same gas as produced by yeast during proofing of doughs. The alkaline component is almost always sodium bicarbonate (baking soda). The leavening acids include sodium pyrophosphate (SAPP), sodium aluminium phosphate (SALP), glucono-deltalactone (GDL) and citric acid. Rapid production of carbon dioxide from the leavening reaction helps to reduce and/or eliminate proofing time and thereby reduce product preparation time (Heidolph et al., 2000).

Due to this unique method of production of gas, chemical leaveners have gained popularity for use with frozen doughs as with yeasted frozen doughs, bake qualities are compromised when yeast dies during freezing (Miller, 2006). Refrigerated yeasted doughs require special packaging as continued production of gas from yeast fermentation can lead to bursting of packages during storage. The convenience of ‘ready to bake’ frozen and refrigerated doughs is also popular with consumers as well as food service organisations and have promoted the use of chemical leaveners in the baking industry. Note that although product quality is acceptable, the loaf volumes, texture and eating qualities are not as high as commonly obtained with yeasted fresh doughs. Further research is required in this area (Heidolph et al., 2000) for developing chemically leavened doughs with superior finished product qualities.

Dough improvers are a class of additives that are also widely used in the baking industry due to their beneficial effects on dough handling and end product quality even when added in minute amounts. Examples of dough improvers include ascorbic acid (added also as a nutritional supplement), mono-and di-glycerides, enzymes like fungal and bacterial alpha (α)-amylases, and calcium salts such as calcium iodate. Whilst many of these improvers have been used in chemically leavened doughs (Domingues and Lonergan, 2007), there is little information about the use of α-amylases in these doughs despite their widespread use for yeasted doughs. Understanding of the functionalities of these improvers, especially ascorbic acid and amylases, has been gained by studying yeasted doughs only.

Loaf volumes increase when doughs contain ascorbic acid. It is acknowledged that ascorbic acid strengthens the gluten matrix by increasing the density of di-sulphide bonds in gluten (Aamodt et al., 2003; Koehler, 2003) and stronger gluten leads to higher loaf volumes. In line with this, higher shear moduli for doughs containing ascorbic acid have been reported (Larsson and Eliasson, 1996). They also report that doughs containing ascorbic acid had less free liquid (dough liquor). There are no set rules for the dosage of these improvers. Increases of up to 20% in baked specific volume of yeasted breads have been reported with ascorbic acid added at as low concentration as 30 mg/kg flour (Grosch and Wieser, 1999; Joye et al., 2009). In chemically leavened doughs, addition of ascorbic acid in the range of 100 ppm to 10,000 ppm has been reported by Domingues and Lonergan (2007).

Larger loaves with softer texture are obtained when dough contains either fungal or bacterial α-amylases. Fungal α-amylases facilitate proofing under ambient conditions while bacterial α-amylases act at higher temperatures and enhance loaf expansion during baking. The fungal α-amylases have been used in amounts of ∼300-400 mg per 100 g flour (Kim et al., 2006; Sahlstrom and Brathen, 1997). Due to the ease of use and benefits observed on finished product qualities, mixtures of ascorbic acid and fungal α-amylases are widely used in bakeries in Australia as a way to boost the bread-making qualities of local flours (discussion with Mr. Robert Millard, Bakery Training Instructor, Polytechnic West, Perth, Australia).

It is thought that fungal α-amylases depolymerise damaged starch and reduce its ability to bind moisture, thus allowing more moisture to be available for gluten hydration (Martinez-Anaya and Jimenez, 1997). Microscopic observation has shown that starch granules disintegrate in doughs mixed with α-amylase, possibly due to extensive hydration and swelling (Blaszczak et al., 2004). Depolymerisation also facilitates the production of dextrin or fermentable sugars, which in turn facilitates the production of carbon dioxide by yeast (Kragh, 2003; Linko et al., 1997). Thus, more gas is produced and the loaves are larger. Beneficial effects of α-amylases on quality (texture) have also been reported for chapattis (Hemalatha et al., 2010). However, this cannot be explained by greater gas production as chapattis are not made with yeast. Hence it is not clear if the observed improvement in finished product qualities arising from addition of α-amylases occurs due to production of excess gas during fermentation or from changes in dough strength resulting from improved gluten hydration. It is not simple to design studies incorporating yeasted doughs that decouple these two potential mechanisms. Such an opportunity is available when analysing the effects of fungal α-amylases on chemically leavened doughs, since the gas production is independent of production of simple sugars resulting from degradation of starch by α-amylases.

This study was carried out to determine the effects of fungal α-amylase and ascorbic acid on chemically leavened doughs and thereby to gain a better understanding of their mechanisms of action on doughs and breads. Doughs were mixed with either each improver individually or commercially available dough improver, which is a mix of α-amylase and ascorbic acid. Control doughs were also mixed with no improver. Baked products were analysed for baked specific volume and crumb strength. Doughs were ultracentrifuged to extract dough liquor and the liquor volumes were measured. Dough elasticity and strain-hardening properties were measured using lubricated compression tests (Chakrabarti-Bell et al., 2010). The amounts of simple sugars and damaged starches in doughs were also measured. Results are presented.

Section snippets

Sample preparation

Commercial bakers' flour was sourced from Western Australia. The protein content, damaged starch content and optimal water absorption was 12.3% at a 14% moisture basis, 7.4% by flour weight, and 65.2%, respectively. However, all doughs were mixed at 62.5% moisture as used in commercial bakeries for this particular flour.

The chemical leavener was a mixture of sodium bicarbonate (supplied by IMCD Australia) added at 32.3% w/w dry leavener, GDL (IMCD Australia) added at 47.7%, and SALP (also known

Mixing energies

The mixing energy of the doughs varied with formulation (Table 1). The doughs containing ascorbic acid (D + DI and D + Am + As) had slightly higher mixing energies than the other doughs, although this difference was not statistically significant.

A high level of reproducibility in rheological data was observed both within and between batches, which confirms that the dough mixing protocol used here (constant temperature ingredients and constant mixing energy target) produces dough batches of

Acknowledgements

The authors would like the thank Dr. Marcus Newbury (CSIRO) and Dr. Crispin Howitt (CSIRO) for helpful discussions, Mr. Michael Watson (Deltagen Australia Pty Ltd.) for measuring enzyme activities, Dr. Ken Dods (Chemistry Centre, Perth, Western Australia) for measuring free sugars and damaged starches and Mr. Stephen Brown (State Agricultural Biotechnology Centre, Murdoch University, Australia) for assistance with the ultracentrifuge tests.

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