Effects of selected factors on rheological and textural properties of probiotic yoghurt

Svrha ovog istraživanja bila je ispitati utjecaj dodatka inulina, te inulina i bagremovog meda, toplinskih tretmana mlijeka i vremena skladištenja na reološke osobine: viskoznost, sinerezu i teksturu (čvrstoću, konzistenciju, kohezivnost i indeks viskoskoznost) probiotičkog jogurta. Djelomično obrano kravlje mlijeko (1,5 % mliječne masti) nakon dodatka inulina (1 %) toplinski je tretirano pri 85 °C/20 min, odnosno 95 °C/10 min. Nakon hlađenja (do 55 °C) dodan je med (4 %), te je mlijeko nacijepljeno mješovitom probiotičkom kulturom (Bifidobacterium sp., Lactobacillus acidophilus, Streptococcus thermophilus i Lactobacillus delbrueckii ssp. bulgaricus) pri 37 °C. Uzorci su pohranjeni 21 dan u hladnjaku na +5 °C. Svakih 7 dana praćene su: pH vrijednosti, udjeli mliječne kiseline, viskoznost, sinereza, čvrstoća, konzistencija, kohezivnost i indeks viskoznosti. Rezultati rada pokazuju da je dodatak meda, pored inulina, dodatno djelovao na ubrzanje procesa fermentacije u usporedbi s kontrolnim uzorkom, neovisno o primijenjenom toplinskom tretmanu mlijeka. Također, sinergistički efekat inulina i meda rezultirao je znatnim smanjenjem izdvajanja sirutke (p<0,05) tijekom skladištenja, ali nije bitnije utjecao na viskoznost i teksturu. Različiti toplinski tretmani mlijeka nisu značajnije mijenjali reološka i teksturalna svojstava proizvoda.The aim of this work was to study the influence of inulin (1 %), combination of inulin (1 %) and acacia honey (4 %), heat treatment of milk, and storage time on the rheological and textural properties of probiotic yoghurt. Rheological properties were assessed trough viscosity, syneresis and texture (firmness, consistency, cohesiveness and index of viscosity). Yoghurt was prepared from milk (1,5 % fat) with added inulin (1%) before heat treatment at 85 °C for 20 min or 95 °C for 10 min. After cooling to 55 °C honey (4 %) was added. Samples were inoculated using probiotic starter culture (70 % w/w Streptococcus thermophilus, 10 % w/w Lactobacillus bulgaricus, 10 % w/w Lactobacillus acidophilus, 10 % w/w Bifidobacterium ssp.). Yoghurt samples were held on +5 °C during 21 days. Measurements of pH value, lactic acid, viscosity, syneresis, and textural properties were done after 1, 7, 14 and 21 days of storage. The results of this study show that honey addition significantly decreased fermentation time compared to fermentation time of control samples or samples containing inulin. Furthermore, addition of honey and inulin to milk caused significant lower syneresis (p