Modification patterns in germinating barley—malting II

O’Brien, Ricky; Fowkes, Neville

doi:10.1016/j.jtbi.2004.10.010

Cited by 17 publications

(12 citation statements)

References 10 publications

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“…As a consequence, modification progressively extends throughout the endosperm, which therefore appears divided into a modified mealy region proximal to the embryo, and a unmodified steely region that shrinks to the distal end of the grain (Briggs 1972(Briggs , 1998Aastrup and Erdal 1980). The shape of the modification front depends upon the ratio between its speed of propagation through the endosperm and the speed of the front of enzyme release that propagates in the aleurone layer (Briggs 1972;Oh and Briggs 1989;O'Brien and Fowkes 2005). The typical progress of modification during malting is illustrated in Fig.…”

Section: B-glucan Breakdown During Maltingmentioning

confidence: 99%

“…This represents a minimal fraction of the total grain b-glucan, most of which lies in the unmodified region of the endosperm, beyond the modification front, and then out of the reach of b-glucanase. On the other hand, however, all the secreted b-glucanase is freely permeating the modified region (Jensen 1994;O'Brien and Fowkes 2005). Therefore, all the enzyme is actually available to form ES complexes.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…Since [E] is in excess and only a small fraction of [S] is available at each time, the total amounts of both the enzyme and substrate (b-glucanase activity and b-glucan content, respectively) have only a minor influence on the modification speed (O'Brien and Fowkes 2005). In other words, only strong differences in these two factors can account for relevant diversities in the modification of different genotypes.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

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A theoretical framework for β-glucan degradation during barley malting

Gianinetti¹

2009

Theory Biosci.

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During malting, barley germinates and produces hydrolytic enzymes that de-structure the endosperm, making the grains soft and friable. This process starts close to the embryo and spreads throughout the whole grain. It is leaded by the degradation of cell walls, which are mainly constituted of beta-glucans. Fast and extended breakdown of beta-glucans occurs by means of an expanding reaction front driven by beta-glucanase, and appears to follow pseudo-first-order kinetics. Endosperm permeabilization to macromolecules is closely linked to the dismantling of cell walls, thus that access to beta-glucans by beta-glucanase itself is limited. It is shown that the kinetics of beta-glucan degradation during malting are consequent to this condition, and can be explained according to an anomalous evolution of the reverse quasi-steady-state approximation (rQSSA) for enzymatic reactions. In fact, kinetics based on the rQSSA include a transient phase wherein fast substrate depletion is indeed of pseudo-first-order. In the germinating barley, the conditions in which the physical modification of the endosperm occurs are shown to be suitable for the fast transient to persist in dynamic equilibrium while it progressively expands throughout the grain, depleting most beta-glucans and, then, establishing the overall kinetics of beta-glucan breakdown.

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Section: B-glucan Breakdown During Maltingmentioning

confidence: 99%

Section: Theoretical Considerationsmentioning

confidence: 99%

Section: Theoretical Considerationsmentioning

confidence: 99%

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A theoretical framework for β-glucan degradation during barley malting

Gianinetti¹

2009

Theory Biosci.

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“…We remark that other experimentalists have reported other patterns of modification (e.g. Briggs & MacDonald 1983or Palmer 1983) and these have been discussed elsewhere (O'Brien & Fowkes 2005). Here, our interest is rather with a determination of the front speed and structure in terms of basic physical and chemical parameters.…”

Section: Introductionmentioning

confidence: 74%

“…This is again a consequence of the strongly nonlinear enzymic nature of the process. For further details, see O'Brien & Fowkes (2005). It is possible to change the source geometry by artificially injecting enzymes into the grain; such experiments may be useful for testing the model.…”

Section: Discussionmentioning

confidence: 99%

The application of enzyme reaction, nonlinear diffusion models to the malting process

Fowkes

O’Brien²

2009

Proc. R. Soc. A.

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We extend the classic Michaelis-Menten kinetics model of the enzyme-mediated conversion of substrate to product to situations in which the enzymes need to diffuse through the underlying structure to reach unconverted substrate and in which the diffusivity is greatly increased by the conversion. The work was prompted by the study of the germination and modification of barley grain that occurs during malting, but is broadly applicable. A nonlinear diffusion, enzyme reaction model of the modification process is proposed and some accurate approximate analytic solutions are derived. We find that a sharp modification front is set up between the modified and the unmodified regions of the barley grain. This front propagates with an almost constant speed through the medium and our findings are consistent with the available experimental observations.

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