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In this study, extracts of shallot skin, flesh and whole bulbs were evaluated their inhibitory effect on xanthine oxidase activity in vitro. The results showed that the effect of shallot skin extract was superior to the extracts from flesh and whole bulb. The extraction of flavonoid from shallot skin was comprehensively investigate using one-factor-at-a-time and response surface methodology based on multivariable linear regression and artificial neural network. Four established models accurately illustrated the quantitative relationship between temperature, time of extraction, solvent and total flavonoids content, yield of extraction. The optimal conditions were determined as: temperature of 85 °C, time of 120 min and ethanol concentration of 50%. The IC50 values on xanthine oxidase of the extracts in optimal and sub-optimal conditions were 3.23 and 21.09 µg/mL while the total flavonoids contents were 20.26% and 13.89%, respectively. The docking results suggested that isorhamnetin-3-glucoside and other flavonoids in shallot skin might play a key role in xanthine oxidase activity of shallot extract.

Celery seed is a potential medicinal material for the development of anti-gout agents because of its uric acid-lowering, xanthine oxidase inhibitory, anti-inflammatory and analgesic effects. In this study, the process of extraction of flavonoid from celery seed was optimized using response surface methodology. Various algorithms were used in order to model the relationship between output response (yield of extraction, total flavonoid content) and input parameters (ethanol concentration, temperature and solvent/solid ratio). The best model was established using multiple linear regression (MLR) algorithm. The optimal conditions were determined as follows: ethanol concentration: 90%; temperature: 90°C and the solvent/solid ratio: 4 ml/g. At these conditions, the yield of extraction was 11.57 ± 1.46% and the total flavonoid content was 4.922 ± 0.312 mg/g. The xanthine oxidase inhibitory effect of apigenin - the main flavonoid of celery seed, was evaluated with the IC50 value of 0.247 µg/ml (95% CI 0.129–0.617 µg/ml). It was suggested that flavonoid might play a key role in the xanthine oxidase inhibitory activity of celery seed extract.

Xanthine oxidase inhibitory activity of celery seed extract was predicted from UV–Vis spectrum using five different algorithms: multiple linear regression, artificial neural network, support vector regression, random forest and partial linear regression. The optimal parameters of each model established by these methods were examined carefully and the best model was selected. The results showed that the model obtained by partial linear regression had the best quality with coefficient of determination R2 = 0.9618, correlation coefficient of leave-one-out cross validation Q2 = 0.8746, average absolute deviation MAD = 0.0671, root mean square error RMSE = 0.0761 and the accuracy of the model with train and test were 99.29% and 96.69%, respectively. Our findings suggest that this model could be an effective method for rapidly determining xanthine oxidase inhibitory activity of herbal medicine, particularly celery seed extract from UV–Vis spectra. However, more investigations are required in order to improve the performance of the partial linear regression model.