Immobilization and characterization of C‐S lyase from onion(Allium cepa) bulbs

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Abstract
Cysteine sulfoxide lyase (C‐S lyase; EC 4.4.1.4), the enzyme responsible for flavor potentiation in minced Allium tissues, was immobilized by entrapment within an alginate gel. Both the free and immobilized C‐S lyase had an optimum pH of 7.5 for activity. Also, similar Km values were observed for both forms of the enzyme using (±)‐S‐methyl‐L‐cysteine sulfoxide (± MCSO; 14.2–19.2 mM) and an alk(en)yl‐L‐cysteine sulfoxide extract (0.9–1.8 mM) prepared from onion bulbs. Both forms of the enzyme were stable for 6–8 weeks at 4°C. At 25°C, the immobilized enzyme was fully stable for 5 weeks whereas the free enzyme lost 50% of its activity within 2 weeks. As the alginate content in the gel was increased from 0.25 to 3%, the % yield of activity of the immobilized enzyme system decreased from 65 to 44%. However, as % alginate content was increased, the yield of active enzyme immobilized in the gel increased from 62 to 97%. Reaction of both the free and alginate‐entrapped C‐S lyase with (±) MCSO resulted in the production of a distinctive cabbage‐like aroma. Onion aroma was liberated when either form of the enzyme was recombined with an odorless alk(en)yl‐L‐cysteine sulfoxide extract from onion.