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Effect of Lactic Acid Bacteria Extrapolysaccharide on the Texture of Set Yogurt

Author: WeiXiaoYing
Tutor: QiaoXuGuang
School: Shandong Agricultural University
Course: Of Food Science
Keywords: Exopolysaccharide Yogurt Physical and Chemical Properties Texture
CLC: TS252.1
Type: Master's thesis
Year: 2010
Downloads: 154
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Abstract


Lactic acid bacteria exopolysaccharide secretion of lactic acid bacteria in the process of growth and metabolism to cell wall permeability often outside the class of carbohydrate compounds in the medium has to keep the yogurt gel structure to prevent syneresis, increase the role of viscosity and curd strength . The exopolysaccharide separation and purification systems, mainly nature and under different conditions of solidification type yoghurt impact on yoghurt production has important guiding value. In this study Lactobacillus bulgaricus extracellular polysaccharide separation and purification systems, mainly the nature and impact of solidification type yoghurt, designed to provide theoretical support for yoghurt production practices. The main results are as follows: optimized the the exopolysaccharide separation system, when the supernatant was concentrated in multiples of 1:6 ethanol concentration of 70%, the TCA concentration of 20%, the maximum extraction rate of 67.8%. DEAE ion exchange chromatography comparison, determine the choice of the the The Sephacryl gel column chromatography crude purified extracellular polysaccharide. After purification the two main components, named as the of LBZ-1 and LBZ-2. UV spectra and biuret reaction test, to prove its purity. Study of the physical and chemical properties of the extracellular polysaccharide, infrared spectroscopy detection prove the LBZ-1 and LBZ-2 are of polysaccharides, there is the characteristic absorption peak of uronic acid and rhamnose. Determined by high performance liquid chromatography (HPLC), and its monosaccharide composition were rhamnose: fructose: glucose = 1:3.12:4.67 and 1:3.64:7.65. Extracellular polysaccharide content, average molecular weight, determination of uronic acid content exopolysaccharide content were 47.67mg / L and 342.64 mg / L, the average molecular weight of 2.1 × 106Da and 1.7 × 103Da uronic acid contents were 2.61% and 1.88% respectively. Studied factors affect exopolysaccharide viscosity results show that: increasing concentrations, pH, ionic strength and the addition of metal ions can increase the viscosity of the extracellular polysaccharide, while the temperature increases its viscosity is reduced. Further, the viscosity of the extracellular polysaccharide by MW affect most cases the high molecular weight the LBZ-1 viscosity than LBZ-2, 4 within the extracellular polysaccharide source, exogenous (added directly in the raw milk) and external source 2 (dissolved raw milk) is added to the raw milk fermentation, yoghurt indicators measured results show that: the endogenous and exogenous added fermented yoghurt indicators better. Both add a way that yogurt elevated water holding capacity, the syneresis reduce viscosity, sticky the cohesion and Reply improved hardness appropriate to reduce. 5. Yoghurt at 37 ° C, 40 ° C and 43 ℃ fermentation produces different proportions of extracellular polysaccharide, i.e. LBZ-H, LBZ-M and LBZ-L, the content ratio of its components were 1:6.26,1:3.05 and 1:2.37, the order of the average molecular weight as LBZ-M lt; LBZ-H lt; LBZ-L. Yoghurt index measurement results show that the the LBZ-H and LBZ-L syneresis less, better water holding capacity, viscosity, cohesiveness and resilience high, moderate decrease in hardness, yoghurt texture by extracellular polysaccharide content and molecular weight influence. 6. Study the interaction of the extracellular polysaccharides and casein protein, whey protein, and milk fat, the results showed that: With the increase in the proportion of extracellular polysaccharides, the viscosity and the transmittance of the casein solution, the viscosity of the solution of whey protein, and transparent luminosity and the electrical conductivity of the milk fat solution. LBZ-1 at low concentration, can reduce the surface tension of the whey protein solution, the LBZ-2 can reduce the surface tension of the solution and the particle diameter of the milk fat. Under different pH conditions, extracellular polysaccharides can increase the viscosity of the three solutions, and high molecular weight extracellular polysaccharide thickening ability. As the pH increased, the decline in the conductivity and transmittance of the casein solution, the light transmittance and increase in the surface tension of the whey protein solution, the conductivity decreased to decrease the conductivity of the solution and the surface tension of the milk fat. Casein is mainly affected by the impact of the macromolecules of the extracellular polysaccharide, milk fat, the main, to be influenced by small molecules exopolysaccharide, whey protein by the combined effect of the two.

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CLC: > Industrial Technology > Light industry,handicrafts > Food Industry > The dairy processing industry > Basic science
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