Towards a further biochemistry of silicon

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McLean-Tooke, C., 2002. Towards a further biochemistry of silicon. MPhil, Nottingham Trent University.

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Abstract

Silica plays an important role in the colloidal stabilisation of commercially produced beer, i.e in the treatment to reduce the tendency of a beer to form a visible haze on cooling or extended storage. The aims of this research wre to further the understanding of the mechanisms by which these hazes are formed and to clarify the role of silica in reduction of haze-forming potential of a beer.

Research was carried out to examine whether or not the raw materials used would themselves contribute silica to the brew, resulting in haze formation. Much time was devoted to developing a reliable method for measuring total silica content within fractions of plant cell wall material extracted from the raw materials provided for use during the course of this research. Graphite furnace atomic absorption spectroscopy and inductively coupled plasma atomic emission spectroscopy techniques were employed and after assessment it was shown that the latter is the more reliable technique for silicon analysis due to the problems encountered with the reactions occurring in the furnace tube during analysis using the former technique with these samples. Equisetum telmatia, a heavily silicified plant, was investigated similarly to ascertain whether or not any silica is bound within the pectic & hemicellulosic plant cell wall fractions. It was shown that there was indeed silica bound within these fractions and following specific application of chemical and enzymatic degradation techniques it was possible to release previously bound silica into a form detectable by the molybdenum blue assay. The work suggested that the mechanism of binding for the bound silica mirrored that during colloidal stabilisation of beer.

It became clear following this work that the raw materials of brewing would not contribute a significant amount of silica to the brew, and would be unlikely to contribute to haze formation as a result of contributing silica to the brew. Studies were then carried out to assess the proteinaceous material incorporated into the beer as a result of the brewing process and the interactions with a range of silicas.

Beer proteins can be broadly categorised into two main categories - haze active and foam positive. The foam positive proteins derive largely from globular proteins and their foam-stabilising action has been attributed to interactions between protein side chain amino acids and iso-alpha acids resulting in the formation of nonpolar, surface active compounds which form stable foams. Haze active proteins are typically rich in proline and glutamine and are a major component of beer haze, which also comprises carbohydrate and polyphenolic compounds, largely dimers of catechin and epicatechin.

In order to investigate these materials, model extractions of proteins, carbohydrates and proanthocyanidin materials were carried out under conditions modelling those of the brewhouse. The extracted materials were further investigated by amino acid analysis and by addition to a tris-catecholato silicon (IV) model system to investigate the interaction of these materials with reactive silica. These studies showed that the extracted proteins interacted with the reactive silica, affecting the kinetics of deposition of silica within the system.

Electrophoresis of these extracted materials carried out showed that the molecular weight of protein materials incorporated into solution was broadly similar for a variety of malts and a commercial brew provided for investigation. A number of protein assays were also investigated for their usefulness in assessing protein levels of beer. The several common protein assays were shown to have a limited response to beer proteins and shown to under-represent haze active proteins.

Item Type:

Thesis

Creators:

McLean-Tooke, C.

Date:

2002

ISBN:

9781369317053

Identifiers: