The use of Tetrahymena themophila mutant cell line for removal of cholesterol from milk. Improvement of food´s sensorial properties

GENTILI HERNÁN; NOSEDA DIEGO GABRIEL; NUDEL CLARA; FLORÍN-CHRISTENSEN JORGE

Cordoba

Congreso; Congreso Internacional de Ciencia y Tecnología de los Alimentos; 2006

Asociacion Argentina de Tecnologos de Alimentos

The non-pathogenic ciliate Tetrahymena thermophila can sequester sterols from milk at very high rates, it converts cholesterol into provitamin D compounds and then it accumulates them as steryl esters inside intra cellular lipid droplets. Removal of cholesterol is a desirable trait. However, prolonged incubation with wild type strain CU-399 at high densities results in a final deterioration of milk properties, possibly as a result of secreted hydrolases. Here we attempted to solve this problem using MS-1 Tetrahymena strain, a stable mutant with low rate of hydrolases secretion A specific examination of two hydrolases, protease and lipase was carried out since they are likely lo play a key role in milk alteration. Protease activity of wild type CU-399 and MS-1 mutant was tested in culture supernatants using azocasein as substrate. Higher extracellular protease activity was found in CU-399, and this difference was reflected on milk casein degradation, as shown by SDS-PAGE. Striking, hydrolysis with CU-399 turns milk caseins almost undetectable in a short period. By contrast, these proteins were largely conserved upon treatment with MS-1. Lipolytic activity was measured by p-nitrophenylpalmilate breakdown in culture supernatants. About half of the activity present in CU-399 is observed in the case of MS-1. Again this is reflected in a differential hydrolysis of the natural lipids present in milk, like triacylglycerol and diacylglycerol as shown by TLC analysis. It is evident that these lipids are degraded to a higher extent in CU-399, a feature that may explain the better flavor displayed by MS-1 treated milk. This may influence the sensorial properties of the milk, particularly regarding the rancid smell that milk treated with CU-399, which can be accounted for by the released for free butyrate. We suggest that the different activities of both hydrolases can substantiate the differential effects on milk coagulation of each strain. These findings point out how relevant hydrolases are when Tetrahymena is applied to food treatment. We further compared cholesterol removal from supernatants of the milk suspensions. Cholesterol is removed to similar extent by both Tetrahymena strains, indicating that mutation in MS-1 does not affect cholesterol uptake. In conclusion, Tetrahymena shows particularly interesting properties for cholesterol removal from food. They are enhanced by the generation of MS-1, which prevents milk spoilage despite high cell density incubation periods. We therefore propose the use of this organism as a new possibility for microbiological improvement of some of the most often used food sources.