Stiasny polyphenol number

The pilot plant-scale extract used in this study was made from bark obtained from old trees decked at a plywood plant. When 4.0% sodium sulfite and 0.4% sodium carbonate (on dry bark weight basis) were used to extract this finely ground bark for 2 hours at 100 °C, extract yields were only 18% of dry bark weight. The extract had a Stiasny polyphenol number of only 0.52 it gave a total of 18% sugars after hydrolysis, and contained 5.8% sodium and 3.8% sulfur. When bark from pulpwood-aged trees is extracted under similar conditions, extract yields typically vary between 20 and 24% and Stiasny polyphenol numbers are typically 0.60 to 0.75. The extract used for this work was also dried by a hot-pan evaporation method rather than being spray dried. So, the extract used represented a near worst-case example. 

Gravimetric Method 25 ml of extract were acidified with HCl to pH=l and a molar excess of formaldehyde was added. This excess was calculated assuming that catechin and formaldehyde react in a 1 1 proportion. The suspension was refluxed during 30 min. The reaction products were filtrated, washed several times with hot water and dried to constant weight at 100 X. The polyphenol content is expressed in absolute terms by the Stiasny precipitation number with formaldehyde , %, defined by ... 

Formaldehyde reactive polyphenolic compounds (Stiasny number). 2Extract modified with 2% phenol (ovendry weight). 

The Stiasny number is usefiil as an absolute measure for the condensable polyphenols in the extract but does not represent itself the content of this phenolic material. Therefore, it can not be used directly as a quantification method for this type of materials. Additionally, it is a laborious, slow and messy ocedure that demands large quantities of extract solution. 

The Stiasny number method was used to determine the polyphenol content of the extracts [24]. Fifty ml of 0.4% w/w tannin solution was pipetted into a 150 ml flask. Aqueous formaldehyde (37%, 5 ml) and hydrochloric acid solution (10 N, 5 ml) were then added and the mixture was heated under reflux for 30 min. The reaction mixture was filtered through a sintered glass filter (40-100 pm) while it was still hot. After that the precipitate was dried in an oven at 105°C to constant weight. The Stiasny number is the ratio of the oven dried weight of the precipitate to the total dissolved solids content of the tannin extract, expressed as a percentage. 

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See also in sourсe #XX -- [ ]

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