Relation between the amount of physodes and reducing compounds in some Adriatic brown algae
Abstract
The reducing compounds, present in brown algae are a mixture of different kinds of phenols, probably related to the tannins. These reducing substances are contained in the physodes or fucosan vesicles which represent a special kind of vacuoles. The reducing compounds can be measured by potentiometric titration.
In the investigated Adriatic brown algae were the reducing compounds very low, as compared with the Atlantic species (H a u g, L a r s e n 1958). The highest amount was found in Fucus virsoides and Cystoseira crinita (up to 0,7 mequiv per g dry matter). The seasonal variations of these compounds were observed.
The reducing compounds were determined previously in the dried
material only. In order to find out if the phenols were inactivated during
drying, investigations of the fresh material were carried out. The amount of
the reducing compounds determined in the fresh material was of the same
order of magnitude as in the dried material.
The acid extract of the seaweed meal reacted negatively with the benzidin reagent (H a u g, J e n s e n 1952), while the meal itself gave a positive reaction in all the observed species. Only extracts of Fucus virsoides and Cystoseira crinita gave a weak colour reaction with the mentioned reagent.
To obtain information about the relation of the amount of physodes and the reducing compounds, the total physode volume of the samples (expressed as volume % of the fresh algae) was determined. For these determinations the method introduced by B a a r d s e t h (1958) was used. The mean physode volume was determined and multiplied by the physode number.
The physode volume (as % of the whole tissue volume) was of the same order of magnitude as that in the investigated Atlantic algae B a a r d s e t h (1958), though the reducing power was much lower. Among the Adriatic species investigated, Fucus virsoides showed the highest, and Dictyota dichotoma the lowest physode volume. In this respect there was a correlation with the reducing power. In the Cystoseirae this correlation was less obvious.
In the light of the present observations one could assume that the phenolic compound are present in the Adriatic algae (as indicated by the positive reaction of the meal with the phenolic reagent and relatively high physode volume), but are not extractable (negative reaction of the extract with the phenolic reagent, low reducing power).
The question of the composition of the fucosan vesicles present in Adriatic algae remains thus unsolved. Most probably only phenolic compounds are present, the proteins and carbohydrates being destroyed during the alkali treatment, which proceeded the homogenisation of the tissue.
