Optimization of the optimal extraction process and α – glucosidase inhibitory activity of quinoa bran and saponins using response surface methodology
Chenopodium quinoa Willd. is native to the Andes mountain region of South America and is the main traditional food of the Inca indigenous people. It has a history of consumption and cultivation of over 5000 to 7000 years. Quinoa has rich nutritional value, rich in total phenols and flavonols, and has antioxidant, immune regulatory, and anticancer activities. In the early 1960s, China began to introduce quinoa resources. In recent years, the planting area of quinoa in China has rapidly expanded. In 2019, the estimated planting area of quinoa in China exceeded 20000 square meters, with a total output of 20000 to 30000 tons. Quinoa bran (i.e. the outer seed coat of quinoa) contains a large amount of triterpenoid saponins, but the saponins have a bitter taste. Before consuming quinoa, it is often removed by washing or grinding, so a large amount of quinoa bran is produced during the actual production and processing of quinoa. However, the current utilization of quinoa bran is only simple processing for use as feed. If quinoa bran can be utilized, the comprehensive utilization value of quinoa can be improved. Triterpene saponins have anti-inflammatory, anti-tumor, anti atherosclerosis and anti diabetes activities. In addition, it has been reported that albumin in quinoa bran has antioxidant and ACE inhibitory activities. Its 50% ethanol extract has protective effects on carbon tetrachloride induced liver injury and fibrosis in mice by activating the antioxidant enzyme system and blocking the TGF – β 1 pathway. At the same time, studies have found that polyphenols and saponin extracts from unprocessed quinoa have high inhibitory activity on α – glucosidase.

At present, there are no relevant literature reports on the ultrasonic extraction process of total saponins from quinoa bran. This experiment used quinoa bran as the experimental material to optimize the ultrasonic extraction process of total saponins. On the basis of single factor experiments, the liquid to material ratio, ethanol concentration, ultrasound time, and ultrasound temperature were selected as independent variables, and the extraction yield of total saponins from quinoa bran was used as the response value. The response surface methodology was used to optimize the ultrasound extraction process of total saponins from quinoa bran. This experiment also examined the inhibitory activity of the extract on alpha glucosidase under the optimal extraction process conditions. At the same time, an enzyme reaction kinetics equation was established to analyze its inhibition kinetics, and the inhibition mechanism of quinoa bran extract on alpha glucosidase was explored, in order to explore the development potential of quinoa bran as an alpha glucosidase inhibitor and provide theoretical basis and data support for the further development and utilization of quinoa bran.

The optimal process for ultrasonic extraction of saponins from quinoa bran was optimized using response surface methodology, with a liquid to material ratio of 15mL/g, 75% ethanol ultrasonic extraction, ultrasonic time of 1.5 hours, and ultrasonic temperature of 45 ℃. The total saponin extraction yield was 2.370% ± 0.022%. This process has simple conditions, easy operation and control, good stability, and overcomes the disadvantages of conventional methods such as long extraction time and cumbersome heating treatment steps.

The experiment on the inhibitory activity of α – glucosidase showed that the total saponin extract of quinoa bran had significantly stronger inhibitory activity than the commercially available α – glucosidase inhibitor acarbose (P<0.05), and it is expected to isolate safe and effective α – glucosidase inhibitors from it. Inhibition mechanism and enzyme kinetics studies have shown that the total saponin extract of quinoa bran is a reversible mixed inhibition type, which provides a reference for clarifying the mechanism of quinoa bran extract in reducing postprandial blood glucose and provides data basis and technical support for its high-value utilization. In addition, the active substance basis and in vivo activity of quinoa bran in inhibiting alpha glucosidase can be further studied through isolation and preparation, as well as the establishment of related animal models.