Doctoral Dissertations

Date of Award

8-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science

Major Professor

Qixin Zhong

Committee Members

Jun Lin, Elizabeth Fozo, Tao Wu

Abstract

Due to suppressed metabolisms, powdered probiotics are generally more stable and more convenient for applications than the liquid form, but much work is needed to improve viability of powdered probiotics during processing, storage, and digestions. The goal of this dissertation was to fabricate delivery systems with an enteric biopolymer coating and a core of powdered probiotic ingredients. The principle of preparing powdered probiotics was to directly mix a concentrated cell suspension with hygroscopic food ingredient powders. Amorphous spray-dried lactose (SDL) was first studied to prepared powdered Lactobacillus salivarius NRRL B-30514 in chapter 2. A smaller amount of cell suspension resulted in reduced water activity and lower hypertonic stress and therefore greater viable bacterial counts initially and during subsequent 6-month storage. The suspension: lactose ratio remarkably affected the lactose crystallinity and physiological states of L. salivarius. In chapter 3, milk protein concentrate (MPC) was mixed with SDL at different mass ratios before mixing with the cell suspension. MPC was suggested to preferentially absorb water in cell suspensions, which inhibited the hydration of SDL and thus lowered the hypertonic pressure to the adhered cells. To further improve probiotics viability, amorphous sucrose prepared by co-spray drying with whey protein isolate (WPI) was studied in chapter 4 to utilize the synergistic protection effects of WPI and sucrose. The WPI-Sucrose-probiotics powders (WSPP) with a higher amount of amorphous sucrose showed higher probiotics viability before and after 30-day storage and heating. In order to deliver powdered probiotics, modified rice protein (MRP)-ammonium shellac (NH4SL) enteric composite coatings were studied in Chapter 5 and interactions between MRP and NH4SL were studied. MRP and NH4SL formed complexes to enable suspension of MRP to form smooth films with improved mechanical and enteric properties. A higher content of MRP preserved films better at gastric conditions, and the resultant coating significantly improved the viability of enclosed WSPP pellets after 30-day ambient storage, heating at 80 ºC for 20 min, and during simulated gastrointestinal digestions. The novel, simple and cost-effective approaches studied in the present dissertation to prepare powdered probiotic ingredients are significant to manufacturing solid probiotics-containing products.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS