ABSTRACT

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The influence of sodium metabisulphite (SMS) on the performance of single wheat varieties in the production of semi-sweet biscuits has been studied. In general doughs produced with SMS required a shorter mixing time, produced shorter dough extrusion times and lower elastic and viscous moduli than doughs produced at the same water level without SMS. Doughs were also produced at a higher water level in the absence of SMS to give similar rheological properties to the corresponding doughs containing SMS. However, dough pieces from doughs containing SMS showed less contraction on processing than dough pieces from all doughs without SMS, including those with similar rheological characteristics to doughs containing SMS. It is believed that this is due to the rheological properties of the dough being achieved through different mechanisms. In the presence of SMS the gluten proteins undergo chemical modification whereas the increased water in the absence of SMS causes a reduction in the magnitude of the rheological parameters through a dilution process. The inclusion of SMS, or increasing water content, caused a reduction in the hardness of biscuits from the varieties Galahad and Riband. The hardness of biscuits from other varieties studied was not affected by a reduction in dough strength. Measurements of flour protein quality were able to rank varieties in order of their likelihood to exhibit dough contraction on processing. However, the measurement of the rheological parameters of dough gave a better prediction of the dimensions of the baked biscuit.

From experience of the use of both lithium metaborate and tetraborate as fluxes for a wide variety of minerals and refractories, it is postulated that when the sample contains a preponderance of acidic oxides (e.g., silica), lithium metaborate has considerable advantages. The melts from metaborate are much more fluid and decomposition can be carried out by heating over gas burners. For samples that contain high contents of basic oxides

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