Administration of probiotic cultures would increase the functional attributes of plant-based matrices and consequently the competitiveness of production. Hence, the current study investigated the antioxidant properties of sauerkraut utilising natural fermentation or the commercial probiotic strains, Lactiplantibacillus plantarum 01 (LP01) and Lacticaseibacillus rhamnosus 04 (LR04) (Probiotical SpA, Novara, Italy), as single starter cultures.
White cabbages were shredded, mixed with sea salt (2.0% w/v), and packed into glass jars. The experimental samples were inoculated with spray-dried LP01 or LR04 (1 × 106 cfu/g of sauerkraut) and compared to a non-inoculated control group. Sauerkraut was fermented under anaerobic conditions at 20°C. The Folin–Ciocalteu method was used for the determination of total phenolic content (TPC) at 0, 21, and 28 days. The in vitro antioxidant capacity was assessed using ferric reducing antioxidant power (FRAP assay) and free radical scavenging activity (ABTS and DPPH assays).
The highest TPC (202.38 mg GAE/100 g DW), FRAP (205.3 mg GAE/100 g DW), and DPPH (57.5 mg GAE/100 g DW) values were observed in LP01 samples at day 21, but the amount declined for LP01 and LR04 groups at the final fermentation stage (p ≤ 0.05). In this sense, excessive fermentation time may result in nutrient depletion, which can negatively affect the vitality of fermenting microorganisms and consequently the antioxidant activity. Regarding the ABTS assay, control values at day 21 were similar to those obtained with LP01 and LR04 treatments (p ≥ 0.05). However, at day 28, ABTS scavenging activity was higher for naturally fermented cabbages (542.4 mg GAE/100 g DW) (p ≤ 0.05).
In light of the growing consumer interest in vegetable-based functional foods, cabbage fermentation with LP01 for 21 days presents an opportunity to create a probiotic-rich sauerkraut that increases TPC and antioxidant activity estimated by FRAP and DPPH methods.
