Impacts Of Three Prebiotics On Texture And Viable Numbers Of Lactic Acid Bacteria Of Set-type Skimmed Yoghurt

Inulin,isomalto-oligosaccharides and xylo-oligosaccharides all belong to dietary fibers,and are considered as prebiotics.They can not be digested in the small intestine but fermented by the intestinal flora in the large intestine.The lactic acid bacteria in yoghurt can regulate intestinal flora,and make the protein and minerals easily absorbed by the human.In this study,the three prebiotics were added to skimmed milk at 3 g/kg and 5 g/kg,and then the skimmed milk was inoculated with the starter,followed by fermention at 42 ? for about 5 h until the pH value fell to near 4.5 and storage at 4 ? for 21 d.The influences of prebiotics on the texture,acidity,organic acids and the viable numbers of lactic acid bacteria of yoghurt samples were assayed,to provide theoretical basis for the applications of three prebiotics in yoghurt processing.The main results are listed as below.(1)Based on the analysis results of the main compositions,texture,syneresis and rheological properties of seven set-type skimmed yoghurt samples,inulin,isomalto-oligosaccharides and xylo-oligosaccharides did notsignificantly influence the texture of yoghurt samples.During the storage of 21 d,the texture of yoghurt samples did not change clearly.(2)Based on the detected values of pH,titratable acidity,lactic acid and three organic acid(acetic acid,propionic acid and butyric acid)of yoghurt samples,pH values,titratable acidity and three organic acid contents were not impacted by prebiotics addition,but the content of lactic acid was increased by 10%-20%.During the storage of 21 d,the pH values of yoghurt samples were decreased,while titratable acidityand lactic acid content were increased.(3)By measuring the viable numbers of Streptococcus thermophilus and Lactobacillus bulgaricus in yoghurt samples,it was found that the addition of inulin,isomalto-oligosaccharides and xylo-oligosaccharides could promote the growth of the two strains,in comparison with control yoghurt samples.The number of S.thermophilus was increased by about 10%-38%,while that of L.bulgaricus was increased by about 40%-85%.During the storage of 21 d,the number of S.thermophilus was decreased slightly in yoghurt samples but that of L.bulgaricus was decreased significantly.The results of this study indicated that the three prebiotics(inulin,isomalto-oligosaccharides and xylo-oligosaccharides)could slightly change organic acids contents and the viable numbers of lactic acid bacteria in yoghurt samples,did not affect tyoghurt texture,but conferred higher dietary fiber and more viable lactic acid bacterias.