Effect of alginate concentrations on survival of microencapsulated Lactobacillus casei NCDC-298
Introduction
Probiotics upon ingestion exert health benefits beyond inherent nutrition and should be at the level of 106–107 live microorganisms per gram of product at the time of consumption (Guarner & Schaafsma, 1998; Ouwehand & Salminen, 1998; Shah, 2000). However, the bacteria do not survive during processing in high numbers in dairy products (Dave & Shah, 1996; Hamilton-Miller, Shah, & Winkler, 1999; Kailasapathy & Rybka, 1997) and further research is required to increase the survival.
Since the viability and activity of probiotics are needed at the site of action, these should withstand the host's natural barriers the gastrointestinal tract (GIT) transit. Lactobacillus spp. lack the ability to survive the harsh acidity and bile concentration commonly encountered in the GIT and also the high temperature of dairy processing (Conway, Gorbach, & Goldin, 1987; Gardiner et al., 2000; Hood & Zottola, 1988; Lankaputhra & Shah, 1995; Shah & Jelen, 1990; Silva, Carvahlo, Teixeira, & Gibbs, 2002). However, the stabilization of probiotics using a carrier may improve survival of these microbes in products, both during processing and GIT transition (Goderska, Zybals, & Czarnecki, 2003).
Microencapsulation of probiotics in hydrocolloid beads has been tested for improving their viability in food products and during GIT transit (Kebary, Hussein, & Badawi, 1998; Khalil & Mansour, 1998; Krasaekoopt, Bhandari, & Deeth, 2003). Microencapsulation using gelatin or vegetable gum provides protection to acid-sensitive bifidobacteria (Rao, Shiwnarain, & Mahraj, 1989); however, the most widely used matrix for microencapsulation is alginate (Kailasapathy, 2002). Alginate beads have been found to increase the survival of probiotics by up to 80–95% (Audet, Paquin, & Lacroix, 1988; Jankowski, Zielinska, & Wysakowska, 1997; Krasaekoopt et al., 2003; Sheu & Marshall, 1991; Sheu, Marshall, & Heymann, 1993). Encapsulation of Lactobacillus rhamnosus in alginate improved survival at pH 2.0 up to 48 h, while the free cells were destroyed completely (Goderska et al., 2003). Similarly, the death rate of Bifidobacterium longum, immobilized in alginate decreased proportionately with increasing alginate concentrations (2–4%) and bead size (Lee & Heo, 2000). Microencapsulation of bifidobacteria also exhibited a lower population reduction during exposure to simulated gastric environment and bile solution (Picot & Lacroix, 2004).
Little research has been carried out with an aim to incorporate probiotics into heat-treated foods, due to destruction of live culture during heat treatment. Though encapsulating lactobacilli in calcium-alginate, beads have been found to improve their heat tolerance (Selmer-Olsen, Sorhaug, Birkeland, & Pehrson, 1999), there are no systematic reports on survival of encapsulated probiotics in varying alginate concentrations and release of bacteria from alginate matrix. This paper reports the effect of varying concentrations of alginate on survival of microencapsulated probiotic bacteria after heat treatments (55, 60 or 65 °C for 20 min), low pH and high bile salt concentration.
Section snippets
Microorganisms
A freeze-dried ampoule of Lactobacillus casei NCDC-298 procured from National Collection of Dairy Cultures (NCDC), Karnal, India was activated in chalk litmus milk (37 °C, 24 h) and maintained in a refrigerator (7±1 °C) before being sub-cultured monthly. The culture was reactivated by transferring 2–3 times in MRS broth and the cells were harvested (80 mL) by centrifugation at 2000g for 10 min at 4 °C (Kubota High Speed Centrifuge, Osaka, Japan). The cells were washed twice before resuspending them in
Survival of encapsulated cells in simulated gastric pH and intestinal bile salt solutions
No significant reduction in viable count was observed in free as well encapsulated cells in distilled water (pH 6.5) on incubation for up to 3 h. However, there were significant reductions of free as well 2% alginate encapsulated cells on immediate exposure to pH 1.5. Free cells were drastically reduced to 4.24 and 3.38 log cfu mL−1 at the end of 1 and 3 h at pH 1.5. After 1 h of incubation, viability was significantly higher in 2% alginate beads, than free cells, but was lower as compared
Conclusions
Microencapsulation of L. casei NCDC-298 in alginate beads resulted in better survival than for free cells at low pH, high bile salt concentration and heat treatment. Increasing alginate concentrations also had a positive effect on the survival of L. casei in simulated harsh conditions of GIT and heat processing, without significantly affecting the release of viable cells from microcapsules in simulated colonic pH solution. Further studies on survival of encapsulated lactobacilli in dairy
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