Changes In Molecular Size Research Articles

Astringency of Fruits and Fruit Products in Relation to Phenolic Content

Publisher Summary This chapter briefly discusses the nature of the constituents responsible for the sensation of astringency and the physiology of the astringency sensation and the factors influencing it. Variety, maturity, and climate are known to influence the astringency of fruit. The chapter presents extensive data on the effect of seasonal conditions on the astringency of American grape juices, and also on apple juices. Certain fruits are astringent when they are unripe. During ripening on the tree or in storage, this astringency disappears. This loss in astringency may be accompanied by a change in the tannin fraction. The actual change in tannins, determined chemically, are small and may either increase or decrease. In astringent fruits, the main phenolic compounds found are flavanols. Both the flavanols and the flavan diols occur. Other major constituents of the phenolic fraction consist of the flavanols, kaempferol, quercetin, myricetin, chlorogenic acid, and the cinnarnic acids such as caffeic acid. Apart from environmental factors such as locality, season, stage of development, and mineral nutrition, which are known to affect the level of phenolic compounds in fruits, and hence astringency, various secondary treatments can decrease the degree of astringency in fruits, for example, treatment with carbon dioxide, ethylene; precipitation of the tannin with acetic acid, formaldehyde; and oxidation with ozone. Astringency may also be reduced by air drying, particularly in persimmons. If the fruit is chilled, astringency may increase. The various theories proposed to explain loss in astringency have been classified into three groups: binding, change in molecular size of the tannins, and a change in the hydroxylatzon pattern of the Phenolic Compound.

Carboxymethylated soybean protein

SummarySoybean protein in aqueous alkaline dispersions at pH 10–11 reacts readily with sodium chloroacetate at temperatures of 50–70°C. to give a protein derivative containing 7–9% carboxymethyl groups. Ultracentrifugal measurements indicate no change in molecular size of the protein when the reaction is carried out at 50°C. but lowered molecular weight at 70°C. The reaction with sodium chloroacetate lowers the pH of minimum solubility from pH 4.5–3.1 and renders the protein more soluble at a neutral pH. Dispersions of carboxymethylated proteins exhibit resistance to putrefaction and do not gel on the addition of formaldehyde.

AN ULTRACENTRIFUGAL ANALYSIS OF CONCENTRATED STAPHYLOCOCCUS BACTERIOPHAGE PREPARATIONS

Analytical observations have been made with the air ultracentrifuge on concentrated staphylococcus bacteriophage solutions and on these solutions inactivated by alkali, chymo-trypsin, and heat. All active solutions contain a homogeneous heavy component that sediments with a constant of s(20 degrees ) = ca. 650 x 10(-13) cm. sec.(-1) dynes(-1), has an apparent density of ca. 1.20, and a molecular weight probably not less than 200 millions. There is also present some very light ultraviolet-absorbing material which is not a carrier of bacteriophage activity. The amount of the heavy component is not strictly proportional to the bacteriophage activity so that if the activity resides in it, as appears to be the case, inactivation may occur without measurable change in molecular size and shape. When the bacteriophage solutions are inactivated by chymo-trypsin, the heavy component is not disrupted but the sedimenting boundaries have always been fairly diffuse. As the activity gradually disappears from alkaline solutions, the heavy component is replaced by unsedimentable material. When a solution is inactivated by heating, a dilute gel is produced which sediments with an exceptionally sharp boundary in a relatively intense centrifugal field.