Probiotic Lactic Acid Bacteria Fermentation Modulates the Bioactive Properties of Sprouted and Unsprouted Amaranth Seed

This study aims to investigate the functional and biochemical characteristics of sprouted and unsprouted red and black amaranth flours by fermentation with four probiotic strains (<i>Lactiplantibacillus plantarum</i> MIUG BL21, <i>Lactiplantibacillus pentosus</i> MIUG BL24, <i>Lacticaseibacillus rhamnosus</i> MIUG BL38, and <i>Lactiplantibacillus paraplantarum</i> MIUG BL74). Aqueous extracts from freeze-dried fermented products derived from sprouted and raw seed of two <i>Amaranthus</i> species (<i>Amaranthus cruentus</i>-red amaranth and <i>Amaranthus hypochondriacus</i>-black amaranth) were characterised for their acidification and phytochemical profiles by titrimetric, spectrophotometric and chromatographic methods, and their antioxidant activities by ABTS and DPPH assays. Water-soluble proteins were evaluated by SDS-PAGE analysis. Nine phenolic acids (gallic acid, protocathechic acid, syringic acid, ellagic acid, ferulic acid, cinnamic acid, caffeic acid, <i>p</i>-coumaric acid, and chlorogenic acid) and twelve flavonoids (epicatechin gallate, hesperitin, quercetin, apigenin, luteolin, naringenin, quercetin 3-glucoside, isorhamnetin, peonidin 3-O rutinoside, epicatechin, keracyanin, and rutin trihydrate) were identified in the extracts of amaranth samples. The titratable acidity ranged from 0.59 to 5.50 mL of 0.1 N NaOH. Total flavonoid content (TFC) varied from 1.09 to 4.67 mg CE/g DW; whereas, total phenolic content (TPC) fluctuated from 1.99 to 5.76 mg GAE/g DW. The spectrum of ABTS and DPPH values was from 17.49 to 56.82% and 0.60 to 35.50%, respectively. More biologically active compounds were found in red amaranth-based samples, both sprouted and unsprouted, compared to black amaranth-based samples. There was a moderate correlation between the TPC and the antioxidant activity. The fermentation of red amaranth with <i>L. rhamnosus</i> MIUG BL38 led to a global increase in the protein background intensity, consistent with protein hydrolysis. Overall, sprouting and probiotics fermentation improved the fermentative performance of the amaranth seeds, enabling their effective use as a nutritive food with potential health-promoting properties.