Influence of microorganisms on retinol isomerization in milk.
In order to have a deeper insight into the retinol isomerization phenomenon, in this work different milk samples have been analysed for their content of trans retinol and its cis-isomers, by means of reliable HPLC techniques. Levels of the different isomers and the degree of retinol isomerization (13-cis/all-trans ratio, %) have been monitored during milk storage at different temperatures and after addition of specific microorganisms. In raw milk stored at 4 degrees C for 96 h the degree of retinol isomerization shifted from 1.1 to 2.3%, while in raw milk stored at 22 degrees C for 24 h it increased from 1.1 to 12.7%. Among microorganisms tested in pasteurized milk, the most active in causing an increment in the 13-cis/all-trans ratio (%), from 3.4 to 33.4% in 8 h, was Streptococcus thermophilus. The results obtained demonstrated a relationship between microbial evolution and retinol isomerization. Therefore, the determination of retinol isomers is of importance not only for a more precise evaluation of vitamin A activity but also for the evaluation of the microbiological quality of milk.
Panfili
Gianfranco
G
DISTAAM, Università degli Studi del Molise, via De Sanctis, 86100 Campobasso, Italy. panfili@unimol.it
Fratianni
Alessandra
A
Di Criscio
Tiziana
T
Gammariello
Daniela
D
Sorrentino
Elena
E
D000818:Animals; D002417:Cattle; D005516:Food Microbiology; D008892:Milk / Q000382:microbiology*; D014801:Vitamin A / Q000737:chemistry*
D014801:Vitamin A