Alkaline sensitivity of lipase activity in oat flour: Factors contributing to inhibition

• Published in: Journal of cereal science Vol. 21; no. 1; pp. 79 - 85
• Main Authors: Liukkonen, K., Johnsson, T., Laakso, S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 1995; Elsevier
• Subjects: alkalinity; Biological and medical sciences; Cereal and baking product industries; flour; Food industries; Fundamental and applied biological sciences. Psychology; inhibition; lipase; oat; oatmeal; pH adjustment; triacylglycerol lipase; FFA; pH adjustment; oat; TG; lipase; TLC; FA; GLC; Oat meal; Enzyme; Triacylglycerol lipase; Esterases; Lipolysis; Optimization; Carboxylic ester hydrolases; Wet process; Manufacturing process; Cereal product; pH; Hydrolases; Basic medium; Model test
• ISSN: 0733-5210; 1095-9963
• DOI: 10.1016/S0733-5210(95)80011-5

The lipase catalysed hydrolysis of triglycerides was studied in order to elucidate the factors that are responsible for the alkaline sensitivity of lipolysis in oat flour slurries above pH 8. An aqueous model system was used, in which oat flour extract or lipase of Candida cylindracea was incubated for 1 h with commercial 9 mM triolein (99%) or with 0·8% (w/v) of the triglyceride fraction of oat at pH range 7–9. At values higher than pH 8, hydrolysis was reduced to 0–20% of that observed at optimum pH of around 7, independent of the enzyme or substrate used. Therefore, the efficiency of inhibition markedly exceeded the values obtained in previous studies within the same pH range. At least four phenomena contribute to the inactivation: (1) instant reduction of catalytic activity upon elevation of pH; (2) time-dependent reduction of activity during approximately 30 min of incubation at alkaline pH; (3) increased sensitivity of the hydrolysis reaction to pH at low substrate concentrations; and (4) increased pH sensitivity of hydrolysis in the presence of detergents or dispersing agents. Consequently, even slight pH adjustment into the alkaline range offers protection against lipolysis. Furthermore, the efficiency of this pH adjustment is dependent on how many of the above four contributing factors are included in an application.