Response surface design for accumulation of selenium by different lactic acid bacteria

Area of Science:

• Microbiology
• Biotechnology
• Food Science

Background:

• Lactic acid bacteria (LAB) like Lactobacillus delbrueckii ssp. bulgaricus (Lb) and Streptococcus thermophilus (St) are crucial in food fermentation.
• Selenium (Se) is an essential trace element with significant antioxidant properties.
• Enhancing LAB with selenium can improve their functional properties and potential health benefits.

Purpose of the Study:

• To optimize selenium accumulation in Lb and St under various cultivation conditions.
• To evaluate the antioxidant activities of selenium-enriched LAB.
• To characterize the selenium-enriched LAB using spectroscopic and microscopic techniques.

Main Methods:

• Response surface methodology (RSM) using Design-Expert software for optimization.
• Single-factor experiments to determine optimal initial pH, inoculum dose, and temperature.
• Fourier Transform Infrared (FT-IR) spectroscopy for qualitative analysis.
• Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDS) for morphology and elemental composition.

Main Results:

• Optimal conditions determined: Lb (pH 5.96, 6.73% inoculum, 33.24°C) and St (pH 6.37, 6% inoculum, 40°C).
• High Se enrichment efficiency achieved: 94.34% for Lb and 97.05% for St.
• Se-enriched LAB exhibited enhanced DPPH and ABTS free radical scavenging activities and increased reducing power.
• FT-IR confirmed similar functional groups (carbonyl, carboxyl, hydroxyl) in Se-enriched strains.
• SEM-EDS verified elemental selenium nanoparticles on cell surfaces, indicating detoxification.

Conclusions:

• Cultivation conditions significantly impact selenium accumulation in Lb and St.
• Optimized Se enrichment substantially boosts the antioxidant capacity of these LAB strains.
• Se-enriched LAB possess potential as functional ingredients with enhanced health-promoting properties and detoxification capabilities.