Semi-continuous production process of corn vinegar in stirred tank reactor using fixation of Acetobacter aceti WK on surface of luffa sponge

Abstract

Previous study by the authors showed that an alternative process to an airlift fermenter in the green vinegar production process could use a loofa sponge (a natural agricultural fibrous material) as the supporting material for Acetobacter aceti WK. Subsequently, aim of this study was production of green vinegar in a stirred tank reactor (STR). The filtered corn wine was supplied to the STR using fixation of A. aceti WK cells on the surface of a loofa sponge cut to a thickness of 2.5 cm. The loofa sponge was left in the STR until 60% of fermenting volume had been used. The charging rate of fresh, filtered corn wine for a semi-continuous production process was investigated. The highest acidification rate (ETA) was achieved at a charging rate of 30%. After 14 d of the adaptation period, the average acidity of 4.1±0.1% was produced during six cycles of fermentation at 30°C and 1vvm aeration supply within 40 d, while the ETA was in the range 0.0028%/h to 0.0067%/h. Scanning electron microscopy (SEM) showed that the surface of the loofa sponge acted as a good fibrous structure for cell fixation of A. aceti WK in the STR.