Antimicrobial Characteristics and the Development of Bioactive Protein-Derived Compounds in Fermented Spirulina

Objectives This study aimed to examine the alterations in bioactive compounds—specifically L-glutamic acid (L-Glu), gamma-aminobutyric acid (GABA), and biogenic amines (BAs)—as well as the antimicrobial properties resulting from various fermentation processes using lactobacilli strains on Spirulina biomass. Materials and Methods Lyophilized Spirulina (Arthrospira platensis) powder (Now Foods Company, Illinois, USA) underwent fermentation under two conditions: submerged fermentation (SMF) and solid-state fermentation (SSF), using various lactic acid bacteria (LAB) strains (Lacticaseibacillus paracasei No. 244; Levilactobacillus brevis No. 173; Leuconostoc mesenteroides No. 225; Liquorilactobacillus uvarum No. 245). In the SMF process, Spirulina was combined with sterilized water at a 1:20 w/w ratio, while in the SSF process, the ratio was adjusted to 1:2 w/w. The antimicrobial activity of the Spirulina samples—with the lowest concentrations of BAs and the highest levels of GABA—was assessed against a range of pathogens, including Staphylococcus aureus, Escherichia coli, Acinetobacter baumannii, Staphylococcus haemolyticus, Salmonella enterica, Bacillus cereus, Proteus mirabilis, Klebsiella pneumoniae, Enterococcus faecium, and Pseudomonas aeruginosa. Results The highest levels of L-Glu (3841 mg/kg) and GABA (2396 mg/kg) were detected after 48 hours of SSF with the No. 173 and No. 244 strains, respectively. The choice of LAB strain, fermentation conditions, and the interactions among these factors significantly influenced GABA concentration in Spirulina (p ≤ 0.001, p = 0.019, and p = 0.011, respectively). Notably, SSF resulted in a higher total BA content compared to SMF. Most fermented Spirulina demonstrated remarkable antimicrobial activity against Staphylococcus aureus. When comparing the diameters of inhibition zones (DIZs) between SMF and SSF samples, SSF consistently exhibited greater antimicrobial efficacy. The LAB strain employed in fermentation, along with interactions among LAB × fermentation duration, fermentation duration × SMF-SSF, and LAB × fermentation duration × SMF-SSF, significantly affected the DIZs observed against S. aureus (p ≤ 0.05). Conclusions This study demonstrated that while fermentation leads to the production of beneficial compounds, it may also result in the formation of undesirable substances that need to be monitored in the final products.