Fermentative conversion of lactose in milk to lactic acid using various microbial cultures

Cilj ovog istraživanja bio je pratiti promjene udjela laktoze i mliječne kiseline, te pH i °SH u mlijeku prije fermentacije te u fermentiranim mliječnim proizvodima koji su čuvani u hladnjaku na 8°C jedan i 28 dana. Istraživanje je obuhvatilo 5 različitih tipova uzoraka: jogurt, jogurt sa povišenom količinom laktoze, bifido mlijeko, kiselo vrhnje i kiselo mlijeko. Udjel laktoze je određivan enzimskom metodom. Rezultati su pokazali da termofilne kulture tijekom fermentacije konvertiraju znatno više laktoze u mliječnu kiselinu (oko 30%), u odnosu na mezofilne kulture (16-20%). Terapijska kultura vrste Bifidobacterium, treba dulje vrijeme prilagodbe za fermentaciju laktoze u mlijeku, pa je stoga konvertirala najmanji udio laktoze (svega 15% nakon prvog dana čuvanja, a nakon 28 dana čuvanja oko 19%). Enzimska metoda, primjenjena u ovom radu, ne daje pouzdane rezultate istraživanja udjela laktoze u proizvodima dobivenim fermentacijom mlijeka mezofilnim kulturama.The purpose of this study was to determine lactose and lactic acid content changes, quantity of pH and °SH in typified milk prior to fermentation and in dairy products on 1st and 28th day of their storage on 8°C in cold environment. In this study 5 different dairy products were observed: yogurt, extra lactose yogurt, bifido milk, sour cream and sour milk. The enzymatic method for determination of lactose has been used. The biggest change in lactose and lactic acid content, according to study results, has happened in proccess of fermentation, as expected. About 16-20% of lactose has been converted by mesophilus, while significantly bigger part (round 30%) of lactose to lactic acid has been converted by thermophilus. The smallest part of lactose conversion was done by Bifidobacterium therapy culture (just 15% after first day and 19% on 28th day of cold storage) and that is due to the greater adjustment period for Bifidobacterium in milk lactose fermentation. The enzymatic method of lactose content determination used in this study doesn't provide reliable results in milk products that were fermented with mesophilus culture