Isolation and Identification of a Bioflocculant-Producing Strain and Application in Rice Vinegar Clarification

A bioflocculant-producing bacterium S-3# was isolated from fresh sand bones 40-50 cm underground in the desert region of China’s Ningxia Province. It was identified as Paenibacillus sp. based on 16S rDNA sequence along with its biochemical and morphological characteristics. Chemical analysis found that the bioflocculant from S-3# is mainly composed of extracellular polysaccharide. Researchers observed no noticeable change (above 91%) in its flocculating activities in pH range 2.0-9.0 in kaolin suspensions and hypothesized that it could be useful in clarification of rice vinegar (pH 2.9-3.5). Using one-factor-at-a-time experiments, dosage of bioflocculant, temperature of flocculation system and metal cations were investigated for their efficacy on rice vinegar clarification. The Box-Behnken design, an experimental design for Response Surface Methodology (RSM), was also used to create a series of 17 runs to optimize the operating conditions. Quadratic regression models with estimated coefficients were developed to describe the suspended particle removals of rice vinegar. Results showed that the optimal flocculation conditions were 3.94 mg/L bioflocculant, 0.32 mM CaCl₂ and flocculation system temperature of 41.5°C, respectively. These findings were in reasonable agreement with the modeled values. Under these conditions, the increase rate of transmittance (λ = 900 nm) of rice vinegar ranged over 240.63% under these conditions.