Study of improvement on stability of anthocyanin modified by malic acid acylation from Lycium ruthenicum

Due to the poor stability of natural anthocyanins from lycium ruthenicum, its application in the food and medical industry is limited.In order to improve its stability, the anthocyanins of lycium ruthenicum were modified by malic acid.In the p H3.5 system, improving retention rate of acylated anthocyanin under 90℃water bath was as the effect of indicators.The single factor experiment designs were used in order to investigate the effect of mass ratio of malic acid to anthocyanins, the stirring time and reaction temperature on acylation.The orthogonal experiment was used to optimize the acylation reaction conditions, and the results of acylation were proved by FT-IR spectrum and ultraviolet absorption spectroscopy.The photochemical and thermal stability of acylated anthocyanins were studied.Finally, the kinetic model of thermal degradation about the anthocyanin was constructed and verified.The optimization reaction conditions were gotten as follows.It is showed that the ratio of malic acid to anthocyanins was 1∶3.5, and stirring time was 5 h under 50℃.The retention rate of lycium ruthenicum anthocyanin was increased by 26.39%.The light stability of acylated anthocyanins was increased by 17%comparing to anthocyanins.Prediction model of thermal degradation is t= (lnρ₀-lnρ₁) / (0.3765exp (-742.7/T) ) for anthocyanins.Prediction model of thermal degradation of acylated anthocyanin is t= (lnρ₀-lnρ₁) / (0.2640exp (-685.8/T) ) .The half-lives of anthocyanin and acylated anthocyanin were 15.09 and 18.32 h, respectively, predicted by thermal degradation kinetics model at 80℃.The retention rates of anthocyanins were 53.2%and 48.7%, respectively, close to the half of prediction value predicted thermal degradation kinetics model.Experiments show that acylation by malic acid is practicable for improving stability of anthocyanin from lycium ruthenicum.