Mannans determination

The use of quantitative, paper chromatography is discussed in this Section, since one of the most important factors in its application to wood-cellulose analysis is that it permits a satisfactory determination of mannan. Reasonably reliable methods for the determination of xylan have been available for some time, but mannan determinations, for the reasons discussed above, have been less satisfactory. The fact that (on chromatograms) xylose, as well as other carbohydrates, can be determined simultaneously with mannose is an added attraction in the use of this technique. 

A very different structure has been found for the mannan that is present in yeast. Methylation and hydrolysis67 showed this to be a highly branched molecule. The methylated material was inhomogeneous, the intrinsic viscosity of different fractions varying between 0.062 and 0.212, with corresponding molecular weights (determined by osmotic pressure measurements) between 18,000 and 76,000 (90-830 hexose units). 

The main structural constituents of Saccharomyces cerevisiae yeast cell wall are glucans and mannans with a minor proportion of chitin (Walker 1998). Manno-proteins are located in the outer layer of the yeast cell wall and determine most of the surface properties of the wall. Vasserot et al. (1997) studied the capacity of yeast lees to adsorb anthocyanins in an attempt to reduce the detrimental effects of charcoal on the color of red musts and wines. Experiments based on model wine solutions revealed that yeast lees possess a greater affinity for anthocyanins than... 

To determine sonophoretic transport route(s) at the ultrastructural level, Bom-mannan and co-workers [72] visualized guinea pig skin with transmission electron microscopy (TEM) after the application of colloidal lanthanum hydroxide (an electron dense tracer) and treatment in vivo with 10- or 16-MHz ultrasound (0.2 W/cm ). In control samples, the tracer did not appear to penetrate into the stratum comeum. But in samples exposed to sonophoresis, the tracer was found in localized areas of the intercellular space, which may correspond to the lacunae (polar head-group domains) described by Hou and co-workers [73] as polar or head-group domains. In addition, sonophoresis for 5 minutes (at both 10 and 16 MHz) did not appear to alter the morphology of the epidermal cells, whereas damage to cells was observed after 20 minutes of treatment (16 MHz). Thus, sonophoresis appears to cause the permeation of the tracers via the intercellular route within the stratum comeum. 

The degree of polymerization of permethylated mannan, obtained from measurements of osmotic pressure, is 200— 400 units. Values of 350 for bakers yeast mannan and of 450 units for brewers yeast mannan were obtained on the basis of sedimentation and diffusion determinations. 

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