Lactic acid production from corn fiber by fermentation and purification with ion-exchange resins

Lactic acid is an important product that is used in a wide range of industrial area in recent years due to its different usage properties. Its use in industries such as food, pharmacy, cosmetics, and medicine has enabled its market to grow rapidly. Especially in today's world where the green industry is gaining importance the interest in lactic acid has increased. The use of lactic acid in the production of polylactic acid (PLA), which is the main raw material of bioplastic as a biodegradable material, has further increased this importance. In the production of lactic acid, it is important to benefit from carbohydrate-containing wastes of different industries as a source of carbohydrates in terms of both recycling and cheap raw material source. Starch and sugar industries are among the most important of this resource like agricultural industry. Corn fiber obtained as a by-product in industries producing starch from corn is utilized in the feed industry. Utilizing corn fiber only in the feed industry can be considered wasteful in terms of its starch content. The use of sugar obtained by both hydrolysis of the starch and part of cellulose in corn fiber in the lactic acid production and also the use of remaining non-hydrolyzed cellulose in feed industry, increases the economic value of fiber since it is used as a source of carbohydrate. In this study, the sugar obtained by the hydrolysis of both the starch and the cellulose in the corn fiber produced as a by-product of corn after the wet-milling process of the starch production industry is aimed to be used as a substrate in the production of lactic acid by fermentation. It is aimed to determine the hydrolysis conditions that will keep the fermentation yield high and also obtain the maximum sugar concentration with hydrolysis. The lactic acid produced was tried to be purified from the fermentation medium by using an ion-exchange resin process. As a result of hydrolysis maximum 9% total sugar concentration was obtained. In fermentation, lactic acid concentration of 6,12% was achieved with a yield of 71%. As a result of the ion-exchange resin processes, an average of 98% lactic acid was provided. In order to determine the effect of sugar concentration on lactic acid production efficiency, 9% total sugar which is obtained as a result of hydrolysis processes was diluted to 6% and 3% and fermentation studies were also carried out. Lactic acid production yields were found as 73% and 72%, respectively. It was observed that the recovery rates, from the fermentation medium, of the lactic acid obtained as a result of fermentation using diluted sugar concentrations are reduced. Keywords: Corn fiber, fermentation, lactic acid, ion-exchange resin