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125 Chapter V Discussion transitional segment of the GIT, such as the duodenum, where the conditions are microaerophilic, rather than anaerobic. Whether, Bsh activity is correlated with high tolerance to bile salts is still under debate. While some researchers argue that deconjugation of bile salts might be a detoxification mechanism of vital importance to the Lactobacillus cell, and thus play an important role during colonization in the gastrointestinal tract (Tannock et al., 1989; De Smet et al., 1995; Usman and Hosono, 1999; De Boever et al., 2000), others infer that the higher toxicity of the deconjugated salts might more strongly affect the viability of the bacterium (Grill et al., 2000). Bsh activity is a controversial probiotic property, particularly because the primary bile salts can be hydroxylated by 7α-hydroxylating bacteria in the gut (e.g. clostridia) and thus converted to secondary bile salts which are pro-carcinogenic (Marteau et al., 1995). Tanaka et al. (1999) observed a correlation between the habitat of lactic acid bacteria species and the presence of Bsh activity. For instance, lactic acid bacteria isolated from human intestine or faeces were Bsh positive, whereas those of food-origin were mostly Bsh negative (Tanaka et al., 1999). In contrast, all selected strains of this study exhibited Bsh regardless of their origin (traditionally fermented food or human meconium). Bsh activity is considered a functional property, which has also been suggested to be important in lowering serum cholesterol levels (du Toit et al., 1998; Pereira et al., 2003). Accordingly, deconjugation of bile acids to primary bile salts by Bsh positive bacteria leads to an increased demand of cholesterol from which bile salts are synthesised de novo in the liver, and thus may lead to decreased serum cholesterol. All the six isolated strains possessed Bsh activity, and therefore their potential in lowering cholesterol levels should be further investigated. This is a valuable trait for probiotic bacteria, which may be connected with either survival or colonization in the gastrointestinal tract. However, the significance of their Bsh activity is not yet clear and this
126 Chapter V Discussion trait may play a positive role in reduction of serum cholesterol levels, would need to be further investigated in vivo. Lactose mal-digestion may be improved with therapy, utilizing bacteria from fermented milk products which contain the lactose cleaving enzyme β-galactosidase (Hove et al., 1999; Szilagyi, 2002). Probiotic bacteria characterized in this study might also be used for compensation of lactase insufficiency. Some authors sustain that yogurt bacteria are more efficient for treatment of lactose intolerance, because they do not survive gastrointestinal conditions as well as probiotic bacteria. Thus, the yoghurt bacteria release the lactase enzyme after disruption of the cell wall as a result of bile sensitivity in the small intestine (Gilliland and Kim, 1984; Schrezenmeir and de Vrese, 2001). On the other hand, Zarate et al. (2000) reported that β-galactosidase activity was severely affected at pH 2. Therefore, if the enzyme is not released during the passage through the stomach, the activity of the enzyme is preserved until it reaches its site of action i.e. small intestine. This is also supported by a study in humans on the improvement of lactose intolerance with fermented milks (Mustapha et al., 1997), where it was shown that a L. acidophilus strain, which exhibited the lowest β- galactosidase activity and lactose transport but the greatest bile and acid tolerance among the strains tested, was the most effective in improving lactose digestion and tolerance. Thus, Mustapha et al. (1997) proposed that bile and acid tolerance may be other important factors to consider when Lactobacillus strains are selected for improving lactose digestion and tolerance. Another aspect is that lactose can also be used as carbon source for growth by β- galactosidase-positive bacteria, and it has therefore been proposed as a potential prebiotic sugar (Szilagyi, 2002). However, the use of this sugar as a prebiotic in persons with lactose intolerance would obviously not be recommended. In this study, strains such as L. casei LAM-1 or LAM-2 possessed good tolerance to gastrointestinal conditions and high β-
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Characterization of Lactobacilli is
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their encouragement, insightful com
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5. Mukesh Kumar and Abhijit Ganguli
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2.3.2.9 Cholesterol lowering 2.3.2.
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3.12.4 Measurement of intracellular
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List of Abbreviations ABTS 2,2-azin
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LIST OF TABLES Tables Page No. Tabl
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Chapter 1 INTRODUCTION
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2 Chapter I: Introduction Recent re
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4 Chapter I: Introduction Gram-posi
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6 Chapter I: Introduction food-born
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Chapter I1 REVIEW OF LITERATURE
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Chapter II1 MATERIALS & METHODS
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50 Chapter III Material and methods
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4.1 Isolation of Lactobacilli IV. R
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Appendix II Fig. 3.1. Standard curv
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