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The influence of a range of additives on the change in the viscosity of cassava starch pastes on ageing following gelatinisation has been investigated. The inclusion of sulfite with pasted starch markedly decreases the viscosity of the paste with time and this is prevented by the addition of propyl gallate. Intrinsic viscosity measurements strongly support the view that sulfite addition promotes polysaccharide degradation. Ascorbate has a greater degradative effect than sulfite, whereas only limited degradation is observed with glutathione. Salts such as sodium chloride and sodium sulfate show no effect on viscosity. If the chelating agent EDTA is added as well as sulfite, the reduction in viscosity is smaller, although the effect is not cancelled out completely. Interestingly, the degradative effect of sulfite and ascorbate can be shown at 30, 60 and 80° C. The results presented uphold the previous suggestion that sulfite addition promotes oxidative reductive depolymerisation (ORD) and largely rule out any residual enzyme activity as the cause. It is suggested that the strong degradative action of ascorbate on starch could be one of the explanations for its action in baked products.

Addition of sulphite at levels between 0.004 and 1% helps to protect the water soluble neutral polysaccharide guar gum from thermal degradation. The greater the amount of sulphite incorporated the more viscous the guar is post-retorting. Starch granules, from a wide range of sources, swell when heated in excess water. The amount of polysaccharide released from the swollen granule after pasting for 60 min at 95 °C is increased by the inclusion of low levels (~0.01%) of sulphite. For cassava starch, a pronounced minimum in swelling volume is observed at this sulphite level. This minimum has been related to the pro-oxidant activity of the sulphite in contrast to the antioxidant activity shown for the guar. Intrinsic viscosity data indicates that the action of the sulphite is to degrade the polysaccharides within the starch granule and this can be reduced by scavenging oxygen from the system or by the addition of propyl gallate. It therefore appears that low levels of sulphite protect guar gum from degradation but can cause degradation of the starch polysaccharides.

The influence of low levels of sodium sulfite on the viscosity of 0.90 g/100 mL dispersions of wheat and potato starch pasted at 95 °C has been studied. It is shown that, if pasting is carried out in 0.01 g/100 mL sulfite, the viscosity of the starch following solubilisation in 0.5 M KOH is lower than a control pasted in the absence of sulfite. The starch intrinsic viscosity is also reduced after pasting in sulfite, indicating that some polysaccharide degradation has occurred. It is suggested that this is the reason for the increased release of polysaccharide from the starch granule when pasted in the presence of sulfite. For both starches the intrinsic viscosities show that there is a reduction in degradation when the sulfite level is increased or when the polar antioxidant propyl gallate is included in addition to sulfite indicating that the mechanism is oxidative reductive depolymerisation of the starch polysaccharides. It is also suggested that oxidative degradation may have an important influence on the integrity of the starch granule following pasting and may be a factor in the functional behaviour of oxidising agents in baked products. Low levels of sodium sulfite and sodium chloride both dramatically reduce the viscosity of potato starch as a result of a non-specific ionic effect.

Recent research has revealed that low levels of sodium sulphite (0.01%) induce degradation of cassava starch granules when pasted at 95°C for 1 h. The degradation is evidenced by a decrease in swelling volume and is accompanied by an increase in solubility. A greater range of botanical sources of starch has now been investigated and it is evident that this effect is common to all the types of starch examined. The non cereal starches are particularly susceptible. These ‘fragile’ granules are affected by low levels of sulphite after pasting at 95°C and exhibit the typical decrease in swelling volume and concomitant increase in solubility associated with cassava starch. The cereal starches, however, appear more resistant and require a temperature of 121°C in order to show a similar effect. The fact that, with the exception of potato starch, the sulphite effect can be prevented by the addition of low levels of the antioxidant propyl gallate suggests that the sulphite promotes oxidative degradation of the starch polysaccharides.

The effect of low levels of sulphite on the swelling volume and release of polysaccharide from a range of starches pasted at 95°C and 121°C has been investigated. In all cases the addition of 0.01% sulphite enhanced the release of polysaccharide on heating at 95°C and for potato, cassava and sago starches the measured volume showed a marked reduction. In the case of rice and wheat starches, sulphite only had a large effect on the swollen volume at pasting temperatures of 121°C, whereas, even at this temperature, maize was little affected. The addition of the polar antioxidant propyl gallate completely nullified the sulphite effect, with the exception of potato starch, suggesting that sulphite could act by promoting oxidative reductive de-polymerisation of the polysaccharide. The effect of 0.01% sodium chloride was also investigated. It was found to have a similar effect to sulphite in the case of potato starch but did not influence the swelling volume or solubility of the other starches. Die Wirkung geringer Anteile von Sulfit auf die Quellung und die Loslichkeit von Starken. Es wurde der Effekt eines geringen Anteils von Sulfit auf das Quellungsvolumen und die Freisetzung von Polysacchariden an einer Reihe von Starken, die bei 95°C und 121°C verkleistert wurden, untersucht. In allen Fallen erhohte die Zugabe von 0.01% Sulfit die Freisetzung von Polysacchariden beim Erhitzen auf 95°C, und fur Kartoffel-, Cassava- und Sagostarken zeigte das gemessene Volumen eine deutliche Verringerung. Im Falle von Reis- und Weizenstarke hatte Sulfit nur einen bedeutenden Effekt auf das Quellungsvolumen bei Verkleisterungstemperaturen von 121°C, wahrend Mais auch bei dieser Temperatur kaum einen Effekt zeigte. Die Zugabe des polaren Antioxidationsmittels Propylgallat hob den Sulfiteffekt, auser fur Kartoffelstarke, total auf, was andeutete, das das Sulfit die oxidative/reduktive Depolymerisation der Polysaccharide fordern konnte. Der Effekt von 0.01% Natriumchlorid wurde ebenso untersucht. Es hatte einen ahnlichen Effekt wie Sulfit auf Kartoffelstarke, aber keinen Einflus auf das Quellungsvolumen oder die Loslichkeit der anderen Starken.

A Q-switched alexandrite laser (180 ns at 755 nm) was used to irradiate samples of agar embedded with red, black and green tattoo dyes. The acoustic waves generated in the samples were detected using a PVDF membrane hydrophone and compared to theoretical expectations. The laser pulses were found to generate acoustic waves in the black and green samples but not in the red pigment. Pressures of up to 1.4 MPa were produced with irradiances of up to 96 MWcm-2 which is comparable to the irradiances used to clear pigment embedded in skin. The pressure gradient generated across pigment particles was approximately 1.09 X 1010 Pam-1 giving a pressure difference of 1.09 +/- 0.17 MPa over a particle with mean diameter 100 micrometers . This is not sufficient to permanently damage skin which has a tensile strength of 7.4 MPa.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An alexandrite laser has been used in the fixed-Q and Q-switched modes, at the fundamental and frequency doubled wavelengths on a selection of hard and soft tissue. In an investigation into the potential use of the laser for the removal of deep lying lesions such as cutaneous vascular lesions and tatoos, studies have been carried out to characterize the depth and extent of the laser/tissue interaction in samples of tissue which greatly absorb the 750 nm radiation. The interaction of the laser radiation with extracted teeth was investigated looking at healthy enamel and dentine, and caries. Surface profile measurements of the enamel and dentine before and after irradiation show little physical effect of the laser irradiation, whereas caries appear to be ablated.