Growth and kinetics of Lactobacillus plantarum in the fermentation of edible Irish brown seaweeds

The aim of the present study was to see the applicability of using brown edible seaweeds as a sole source of nutrition for the growth of lactic acid bacteria. Growth kinetics of lactic acid bacteria (LAB; Lactobacillus plantarum) was studied using three species of edible Irish brown seaweeds Himanthalia elongata, Laminaria digitata and Laminaria saccharina. As part of the screening process, growth of the LAB was carried out on raw and heat treated forms of seaweeds. The seaweed species in their raw state could not support the growth of L. plantarum. Heat treatment resulted in almost 4 times increase in the total sugar content in L. digitata and L. saccharina broth which allowed the growth of L. plantarum for 24h after which the cell number started decreasing. The Laminaria spp. contains a high content of laminaran polysaccharide which can be fermented by LAB. In case of H. elongata, neither raw nor heat treated forms could be fermented; even though the total sugar content increased 4.6 times upon the application of heat. Kinetics of cell growth, lactic acid and acetic acid production was evaluated at different agitation rates in heat treated seaweeds. A maximum logCFU/ml of 10 was achieved at the end of 16–24h of fermentation for L. saccharina and L. digitata, respectively. The cell growth increased and lactic acid accumulation decreased as the agitation speed was increased from 0 to 100rpm. Maximum lactic acid accumulation of 2.5g/l was achieved under static (0rpm) conditions. The production of acetic acid was very minimal during the entire course of fermentation. Experimental data was mathematically modelled to optimize the cell growth and lactic acid production with respect to the different rotation conditions. The results of this study present an indication of the potential of fermentation of seaweeds using LAB with a possibility towards the development of a range of functional foods.