Fermentative preparation of single cell detritus from seaweed, Undaria pinnatifida, suitable as a replacement hatchery diet for unicellular algae

Abstract

Single cell detritus (SCD) is a product ca. 5.8–11.5 μm in diameter prepared by decomposing seaweed to a cellular level, and is expected to be utilized as a fisheries-diet in place of unicellular algae. The present paper details the culture conditions for the effective preparation of SCD from Undaria pinnatifida based on a fermentative method. The suitable NaCl concentration of the culture water for SCD-preparation was in the range of 2.5–3.5% (w/v) judged from the convenience for culture-treatment and the stability of the SCD-products. The temperature during culture did not make a marked difference on the productivity of the SCD in the range of 5–50 °C. As for the cellulase concentration, the addition of more than 1% was necessary to avoid rotting and to obtain a fermented culture. However, the addition of a microbial mixture composed of a lactic acid bacterium and two species of yeast at the start was effective to obtain a successfully fermented culture at a lower cellulase concentration of 0.25%. Under optimum conditions of culture containing 5% Undaria (on dry basis), 3.5% NaCl, 0.5% cellulase with an addition of the microbial mixture, SCD was produced at 5.8×10 7 cells ml −1 after 6 days of incubation at 20 °C. The presently developed method needs no facilities for temperature conditioning, lightening, and air supplying, but needs only a plastic tank for obtaining the SCD. Here, we suggest a novel fisheries-diet of “marine silage”, which is produced from the combination of two principles, conversion of seaweed to SCD and induction of lactic acid fermentation utilizing activities of a microbial mixture composed of a lactic acid bacterium and yeast.