Introduction

Aspartame, a-L-aspartyl-L-phenylalanine methyl ester (APM) (Fig. 1), is an artificial sweetener whose sweetness is about 200 times stronger than sucrose by weight. Its sweetness was found accidentally by a researcher of Searle Research Laboratories, where APM was produced as an intermediate of a C-terminal tetrapeptide of gastrin (1). Its strong sweetness allows reduction of the amount of calorie sweetener added to foods to achieve a sweetness equivalent to that from sucrose. Although other intense sweeteners often exhibit a slightly bitter aftertaste, APM has none (2). Its sweet taste is close to that of sucrose, a traditional sweetener and the standard of sweetness. Therefore, the demand for APM has grown rapidly since its approval by the Food and Drug Administration (FDA) in 1981. Worldwide APM consumption is currently over 10,000 tons per year, and it is the most common intense sweetener for beverages, tabletop sweetener, ice cream, chewing gum, and so forth. APM is produced by two methods: a chemical method, used by Nutrasweet in the United States and Ajinomoto in Japan, and an enzymatic method, used by Holland Sweetener Company, a joint venture of TOSOH (formerly Toyo Soda Manufacturing) in Japan and DSM in the Netherlands. In the enzymatic method, an APM precursor, N-benzyloxycarbonyl-APM (Z-APM) is produced by a protease-catalyzed condensation reaction of N-benzyloxycarbonyl-L-aspartic acid (Z-L-Asp) and L-phenylalanine methyl ester (L-PheOMe). The advantages of the enzymatic method are that a racemic substrate can be used and there is no production of /-aspartame (/-APM) (Fig. 1). The reduction of enzyme consumption was, however, desirable for further cost reduction. In the present article, the APM production process with the protease reaction and various efforts to reduce the enzyme consumption therein are described.

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