Browsing by Author "Qi, Xiaoxi"

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    Improved Viability of Lactobacillus rhamnosus GG During Storage and Simulated Gastrointestinal Digestion by Encapsulation
    (North Dakota State University, 2021) Qi, Xiaoxi
    Probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. However, the current techniques are still struggling with delivering enough live probiotics into the designated site of action. This project aimed to improve the viability of the probiotic Lactobacillus rhamnosus GG (LGG) under adverse conditions by encapsulation. Properties of the formed microcapsules such as particle size, morphology, mechanical properties, and rheological properties were examined by corresponding methods and equipment, and the viability of LGG under storage and simulated gastrointestinal (GI) digestion was evaluated.First, two modified alginate-based hydrogel bead systems were established on the basis of the reaction between sodium alginate (ALG) and Ca2+ by 1) adding an additional layer of chitosan with three different molecular weights was formed on the surface of alginate particles; 2) partially substituting ALG with low methoxyl pectin (LMP) or κ-carrageenan (KC) to form a double-network since pectin and carrageenan can interact with Ca2+ as well. In the first system, I found that the chitosan oligosaccharide (COS) improved the viability of LGG during storage by reinforcing the mechanical properties. However, no significant improvement on the viability of LGG during GI digestion was observed. In the second hydrogel bead systems, the ALG to LMP ratio of 8:2 in hydrogel provided the stronger inner structure and showed a better protective effect on the viability of LGG during GI digestion. Furthermore, I studied the complex coacervates formed from sugar beet pectin (SBP) and sodium caseinate (SC) or pea protein isolates (PPI) to be as encapsulation wall material for improving the viability of LGG during digestion. The impact of protein type, protein to sugar beet pectin mixing ratio (5:1 or 2:1), as well as the finishing technology (freeze-drying and spray-drying) on the viability of LGG were examined. Spray-dried samples, especially spray-dried PPI‒SBP microcapsules, demonstrated superior performance against cell loss and maintained more than 7.5 Log CFU/g viable cells after simulated GI digestion. Overall, the project demonstrated a great potential for improving the viability of probiotics by encapsulation.