Bacteria are flocculated with high molecular weight cationic synthetic flocculants and chitosan. High charge density polymers are the most effective of the synthetic flocculants. Only chitosan is effective in flocculating the E. coliand B. subtilis cultures in complex broth. The difference in effectiveness between the synthetic flocculants and chitosan for flocculating E. coli, B. subtifisand Z. mobilismay be attributed to hydrogen bonding between the polysaccharide flocculant and cell surface polymers in addition to electrostatic interactions, and, in complex media, complexation of synthetic polymers with anionic polyelectrolytes.
In experiments where the interaction of starch and cell size were kept to a minimum by taking identical material for each experiment (disks from the same tuber), the loss of compressive strength of potato tissue on cooking was found to be related to the release of pectic substances into the cooking liquor. This relationship was found to hold true whether large differences in compressive strength were produced by cooking the disks in water for varying lengths of time or by cooking disks in solutions of calcium or potassium chloride for fixed times. The release of starch into the cooking liquor was not related to loss of compressive strength when the results of a number of experiments from disks from the same tuber were compared.Increased cooking time, or the presence of potassium chloride in the cooking solution, reduced compressive strength and increased the amount of pectic substances released. The presence of calcium chloride had the reverse effect. It was not clear whether the effects of calcium chloride were due to calciumper se or the pH of the solutions after cooking, which were inversely related to calcium chloride concentration.
It was shown from experiments on disks cooked in solutions of calcium chloride and calcium acetate, and in buffered solutions of calcium chloride at various pHs (sodium concentration constant) and from experiments where the ratios of disks to calcium chloride were varied, that the effect of calcium in increasing the compressive strength of the disks was small compared to the effect of reduced pH. The interaction of sodium and calcium was investigated at pH 6 (z the pH of cooked potato tissue). The effect of sodium in reducing compressive strength of the disks outweighed the effect of calcium in increasing compressive strength. Sodium and potassium chloride had a similar effect on loss of compressive strength on cooking. Increased compressive strength due to pH or the presence of calcium was overcome by extending the length of cooking. It is suggested that transelimination, ion exchange and hydrogen bond breakage may be more important factors than the chelation of calcium by naturally occurring phytin, in the breakdown of pectic substances and loss of intercellular adhesion during normal cooking of potatoes.
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