Enhanced In Vitro Functionality and Food Application of Lactobacillus acidophilus Encapsulated in a Whey Protein Isolate and (−)-Epigallocatechin-3-Gallate Conjugate

The present study investigated the potential of free radical grafting conjugation of whey protein isolate (WPI) and (−)-epigallocatechin-3-gallate (EGCG), followed by freeze-drying, for the safe delivery of probiotic Lactobacillus acidophilus (LA) upon digestion and in food systems. WPI-EGCG-LA microspheres presented higher encapsulation efficiency (97%) than native WPI-LA (70%) and maltodextrin (MD-LA 75%). The physicochemical characteristics of all microspheres, including moisture content, water activity, and hygroscopicity, were within the acceptable range for the stability of industrial powders. Scanning electron microscopy of WPI-EGCG-LA revealed a glass-like structure, with a smoother and less porous surface area than WPI-LA and MD-LA, as a result of the strong binding affinity between WPIs and EGCG. Particle sizes ranged from 438.4 to 453.3 μm. The structural stability of WPI-EGCG-LA was further confirmed by Fourier transform infrared spectra, which revealed some changes in the protein secondary structure. Thermogravimetric and differential scanning calorimetry analysis showed that WPI-EGCG conjugates had higher thermal stability than native WPIs and MD. Additionally, cells encapsulated in WPI-EGCG conjugates demonstrated higher in vitro survivability and surface hydrophobicity compared to free or WPI- and MD-encapsulated cells. Furthermore, WPI-EGCG-LA microspheres exerted enhanced in vitro antioxidant (78%) and antidiabetic (52%) activities. Finally, the WPI-EGCG conjugates remarkably improved probiotic viability (8.55 ± 0.1 log cfu/g) during 30 days of storage in an apple juice drink of pH (3.2 ± 0.01). Hence, the WPI-EGCG conjugate represents a propitious carrier to enhance probiotic functional properties upon digestion and during storage in low-pH food products.