The effects of thickeners upon the viscous properties of sour cream with a low fat content.

Abstract

Fermented cream is a common and widely used dairy product throughout the world. The structure of sour cream with a low (10 to 15%) fat content is determined by the acid gel of milk proteins, while that of sour cream with a high (≥30%) fat content is determined by the gel formed by fat globules coated with protein. Sour cream with a fat content of about 20% has an intermediate gel structure, which is not characterized with high viscosity. To increase the viscosity of the product, as well as to prevent the separation of whey during storage, thickeners and stabilizers (gelatin, various types of starch, etc.) are added. As these decrease the sensorial characteristics of products, new thickeners (elamin, citrus pectin, flax seed flour, banana puree, and fromase milk-clotting enzyme preparation) are used instead. Sour cream was made by separating whole cow's milk, normalization, homogenization, pasteurization and fermenting by mesophilic lactic acid bacteria. Then thickeners were introduced to the clot: elamin, dry banana, flax seed flour in mass fractions of 0.01%, 0.03% and 0.05%, as well as fromase preparation in the same amount. A control batch of sour cream was made without the use of additives. The ripening process lasted from 8 to 9 hours to obtain a dense consistency. The viscosity of the samples was determined using a rotational viscometer, consisting of two coaxial brass cylinders, between which the test liquid was located. The effective viscosity and its dependence on the shear rate γ in research samples as non-Newtonian fluids were determined. Sour cream is characterized by the presence of a structure quickly destroyed by external forces at shear rates greater than 10 s-1, so exceeding the given value in the production of sour cream is not rational. The dependences of the rheological parameters of sour cream on the content of the additives elamin, flour from flax seeds and dry banana puree, used as thickeners, showed that the greatest strength of intermolecular bonds and the stability of the studied mixtures can be expected with a share of additives ranging from 0.01 to 0.03% (by mass). At the same time, when the said share exceeds 0.05%, the structure of sour cream is weakened - this is especially characteristic in the case of adding dry banana. The research showed that natural thickeners can be chosen to improve the rheological parameters of low fat sour cream without deteriorating its sensorial characteristics. This leads to the conclusion that the studied thickeners can improve the viscosity of sour cream with a low fat content - and dry banana is the best of those studied. Correspondingly, viscous properties are among the principal ones which define customers' perceptions of the product, its low fat content being a possible spoiler of sensorial traits.