(471f) Lactic Acid Fermentation with the Supplementation of Fish Wastes

In recent years, much attention has been paid to the great potential of L-lactic acid in the manufacture of biodegradable plastics and approximately 90% of L-lactic acid is produced by lactic acid bacteria fermentation every year. Lactic acid bacteria exist generally in nutritious habitats so that they have developed a typical metabolism that is devoid of most biosynthetic activities. Therefore, they need specific minerals, vitamins, specific peptides and some unknown nutrients to ensure their optimum growth. Commonly, yeast extract (YE) is used in laboratory scale fermentations as a nutrient source. As YE is not economically attractive, it is desired to find some new nutrients suitable for an industrial process and to replace YE. In this study, fish wastes were chosen as a nutrient source for lactic acid production due to the background that fishing industry creates large amount of wastes every year in Japan and elsewhere so there is increasing demand for effective and ecological techniques to treat the wastes. Some researches have been conducted in the production of fish protein hydrolysate, the production of single cell protein from shrimp-shell wastes, the lactic acid fermentation for ensilation of shrimp wastes and the production of peptones from autohydrolyzed fish viscera. However, most of them were treated by enzymatic hydrolysis and there were few studies on using fish wastes as a nutrient source for lactic acid production. Since enzymatic hydrolysis has the disadvantages in slow reaction rate and high cost due to the requirements of feedstock pretreatment, enzyme production and enzyme recovery, fish wastes were hydrolyzed with a new acid-hydrolysis in this study and the acid-hydrolysis was examined through evaluating the performance of fish waste hydrolyzate (FWH) in lactic acid production. The unhydrolyzed fish wastes were very poor in lactic acid production while the fish wastes hydrolyzed by the proposed acid-hydrolysis were very good and, especially, 6.8% FWH had greater productivity than 20 g/L YE. Compared with the low-cost nutrients reported, the FWH had the highest performance in lactic acid production. Considering its low cost, FWH could be a potential nutrient and a substitute for YE, with an environmental solution in addition.