Pigment removal from canola oil using chlorophyllase

Abstract

AbstractFrost‐damaged or prematurely harvested canola seed (rapeseed) may yield oil with a high chlorophyll content (50–60 µg/ml). Enzymatic hydrolysis of chlorophyll, added to buffer/surfactant, buffer/acetone or buffer/acetone/canola oil, to produce water‐soluble chlorophyllide (green pigment) was studied using a crude chlorophyllase preparation (acetone‐dried chloroplasts) from 15 to 20‐day‐old sugar beet seedlings. In buffer/surfactant, the optimum pH for enzyme activity was temperature dependent. At 30 C and 0.24% Triton X‐100 (or 30% acetone), chlorophyllase showed maximum activity toward a crude chlorophyll preparation over the range of pH 8–10. At 60 C, the activity was more than twofold higher, with a sharp maximum at ∼pH 8. Mg2+ enhanced the activity with an optimal concentration of 50 mM. At pH 7.5, 50 C and in the presence of only 6% acetone, the enzyme showed high affinity for chlorophyll (Km=15µM or 13.5 µg/ml), suggesting that the natural chlorophyll concentrations found in green canola oils might facilitate high enzymatic efficiencies. The crude enzyme was stable in buffer/acetone at pH 7.5 and 50 C for at least two hr.With acetone concentrations as low as 6%, maximum enzyme activities in buffer and buffer/canola oil required intensive mixing (homogenization) of the various substrate, enzyme and liquid phases. In general, the rate and extent of chlorophyll hydrolysis were greater in buffer than in buffer/oil. In both reaction systems, chlorophyll hydrolysis slowed down with time due to accumulation of phytol, which proved to be a competitive inhibitor (Ki=11 µM or 3.3 µg/ml). The other hydrolysis product, chlorophyllide, did not affect enzymatic activity.Crude canola oil used in the reconstitution of green oil did not support enzymatic chlorophyll hydrolysis without prior degumming and desoaping. The optimum buffer/oil ratio of the reaction mixtures was above 2/1 (v/v).