Extraction and stability of naphthoquinones pigments from walnut green husks

The enzymatic- assisted ultrasound- extraction of naphthoquinones pigments from walnut green husks was optimized using response surface methodology. The effects of several operating parameters,namely enzyme dosage,ultrasonic time,ultrasonic temperature,liquid / solid ratio,on the yield of naphthoquinones pigments from walnut green husks were studied.The effects of illuminations,temperature,oxidants,reducing agent,metal ions on the pigments stabilities were also studied.Results indicated that the highest yield of naphthoquinones pigments of8.22% was achieved when the extraction was carried out with enzyme added amount of 1.0%,ultrasonic time for90 min,ultrasonic temperature of 70 ℃,ratio of liquid- solid 72 ∶ 1( m L / g),which was 0.13% of relative error compared with the predicted value. Stabilities tests showed that naphthoquinones pigments from walnut green husks had better lightfastness,anti- oxidation- reduction,storage tolerance in the range of 0 ~ 7 days and thermotolerance in the range of 80 ℃.Metal ions Al~(3+)、Zn~(2+)、Fe~(3+) had a certain hyperchromic effect for pigments,and hyperchromic effect of Fe3 +was the most significant. There was no effect of Mg~(2+)、Ca~(2+)、Na~+、K~+ on the pigments.The ultrasonic bonding enzymatic extraction technology was simple,viable,and the extracted pigments had better stability.