ABSTRACT
The importance of lactic acid (LA) as a food preservative dates back to the beginning of the eighteenth century when scientists tried to understand the preservation and fermentation of sour milk. In 1857, Pasteur discovered that LA was present not as a milk component but as a metabolite produced during fermentation by a living microorganism [1]. Its presence as a natural fermentation metabolite in dairy products promoted preservation of the organoleptic properties for longer periods of time, making it an effective and natural food preservative. This nding initiated wide-ranging application and production of LA, with the rst industrial production by microbial fermentation dating from 1881 [1]. Since then, research has considered new mechanisms of production, alternative microbiological routes, and utilization of various raw materials in order to guarantee efciency, purity, and stability in LA production. The wide application of LA, as a food preservative and other industrial input requires about 130,000-150,000 metric tons per year [2]. According to a Global Industry Analyst announcement in January 2011, this amount is expected to reach approximately 329,000 metric tons by 2015 [3]. Ninety percent of today’s world production of LA is obtained naturally by microbial fermentation of carbohydrates, such as glucose, sucrose, or lactose by homolactic organisms (bacteria or fungi) [1,3]. The rest is obtained synthetically by the hydrolysis of lactonitrile [4] or alternative routes involving catalyzed degradation of sugars, oxidation of propylene glycol
12.1 Introduction 203 12.1.1 History and Consumption of Lactic Acid 203 12.1.2 Preservative Properties of Lactic Acid 204 12.1.3 Determination of Lactic Acid in Food and Beverages 205
12.2 Flow Systems for Lactic Acid Determination 206 12.2.1 Enzymatic Methods 206
12.2.1.1 Applications of Lactate Dehydrogenase 208 12.2.1.2 Applications of Lactate Oxidase 214
12.2.2 Nonenzymatic Methods 217 12.3 Final Remarks 219 References 219
or reaction of acetaldehyde [5]. Microbial fermentation is more advantageous than the chemical process in terms of experimental procedure (method), economic aspects, and environmental aspects because lactonitrile is a subproduct of petrochemical resources [1,6]. Furthermore, chemical synthesis produces only racemic mixtures of LA, which are impracticable as a food preservative [2].
