Co-extrusion Encapsulation of Probiotic Lactobacillus acidophilus Alone or Together with Apple Skin Polyphenols: An Aqueous and Value-Added Delivery System Using Alginate

Abstract

This study presents one novel aqueous delivery system that was produced by co-extrusion technology using 1 % and 0.5 % alginate solutions as the shell wall and the core medium, respectively, to encapsulate probiotic bacteria (PB) Lactobacillus acidophilus alone or in combination with a value-added apple skin polyphenol extract (ASPE). The survival of PB was evaluated in a model milk drink at 4 °C for 50 days and under acidic conditions (in acidic water at pH 2 and 37 °C for 120 min). Two types of ASPE were prepared using an ethanolic or aqueous method and subjected to analyses of total extracted polyphenol content (TEPC), total antioxidant activity (TAA), vitamin C content, uronic acid (UA) content and polyphenol (PP) composition. The microencapsulation efficiency for all the obtained alginate beads was >96 %, with the beads in roughly spherical shape and with smooth and intact surfaces. The PB co-encapsulated with an ASPE had significantly (P < 0.05) greater viability in milk than the unencapsulated PB in milk. After 50 days of storage at 4 °C in milk, the cell loss was only 0.13 and 0.16 log CFU (colony forming units)/mL milk for the PB co-encapsulated with the aqueous or ethanolic ASPE, respectively, compared with 1.1 log CFU/mL milk for the unencapsulated PB and 0.34 log CFU/mL milk for the PB encapsulated without ASPE. The co-encapsulation of PB with an aqueous or ethanolic ASPE also greatly protected PB against the current strong acidic condition with cell loss 2.61 and 2.78 log CFU/g fresh bead, respectively. A much lower cell loss was detected for the PB encapsulated alone (3.08 log CFU/g fresh bead) than for the unencapsulated PB (5.41 log CFU/g fresh bead). The differences between the aqueous and ethanolic ASPE in TAA and bioactive contents apparently caused the difference in PB viability in milk or the current acidic system, which potentially leads to a slightly varied nutritional value of the final encapsulated products. It is feasible and beneficial to use apple skin (a fruit waste) as a bioactive ingredient (containing polyphenols, pectin and vitamin C) to preserve the viability of PB via encapsulation technology. The selection of an aqueous or ethanolic ASPE ultimately depends on the required bioactive composition and PB viability of the final encapsulated product.