Fortification of cow and soymilk kefir with pomegranate peel extracts: Impact on physicochemical, microbial viability, and sensory properties

Abstract

Kefir is a fermented beverage valued for its probiotic-associated properties, although its antioxidant capacity remains relatively moderate. Pomegranate peel, a phenolic-rich agro-industrial by-product, offers potential as a sustainable fortifying ingredient for functional beverage development. This study investigated the effects of pomegranate peel extract (PPE) addition (0–20%, w/v) on the physicochemical, microbiological, antioxidant, and sensory characteristics of cow milk and soymilk kefir. Kefir samples were prepared using a commercial starter culture and evaluated for total phenolic content (TPC), antioxidant activity, pH, viscosity, viable lactic acid bacteria (LAB) counts, and sensory acceptance. PPE fortification significantly increased (p < 0.05) TPC and antioxidant activity in both kefir matrices. TPC increased from 55.31 to 182.87 mg GAE/g in cow milk kefir and from 60.91 to 199.29 mg GAE/g in soymilk kefir. LAB counts also increased substantially, with more than a two-fold increase in cow milk kefir and an approximately five-fold increase in soymilk kefir. PPE significantly reduced viscosity in cow milk kefir, while soymilk kefir remained rheologically stable, indicating a matrix-dependent response. Sensory evaluation revealed no statistically significant differences (p > 0.05) in taste, aroma, or color, although higher PPE levels tended to show lower numerical sensory scores, particularly in soymilk kefir. These findings indicate that PPE can enhance the phenolic content, antioxidant potential, and LAB viability of both dairy- and plant-based kefir. Moderate inclusion levels (5–15%) appeared to provide the most balanced functional and sensory profile, supporting the potential use of PPE as a natural fortifying ingredient in fermented beverage formulations.