Moreover to evaluate the properties

Moreover, to evaluate the properties of immobilized β-glucosidase further, the anti-protease test was also carried out. The result showed that the residual activity of the β-glucosidase@ZIF-8 was higher than that of the nano-SiO2@β-glucosidase and free β-glucosidase. Because free β-glucosidase and the nano-SiO2@β-glucosidase were directly exposed to trypsin in the anti-protease experiment, the residual activity was lower than that of the β-glucosidase@ZIF-8. As a type of extracellular enzyme, β-glucosidase had a certain degree of resistance to protease, so the residual activity of nano-SiO2@β-glucosidase was similar to that of free β-glucosidase. In industrial production, the reaction conditions were often not as mild as that in laboratory. There were many factors that would affect the activity of enzyme, including the presence of protease. Therefore, the high ability to resist protease would extremely help the application of immobilized enzyme in industry. We also measured the reusability of immobilized β-glucosidase. As we all know, one of the most promising advantages of immobilized enzyme was the reusability, which would reduce the costs greatly in industry. So it is important to study the number of Tunicamycin of immobilized β-glucosidase. The recyclability proved that immobilized β-glucosidase has stable characteristic under reaction conditions and can be reused for many times without substantial loss in activity in comparison with free β-glucosidase. The nano-SiO2@β-glucosidase and the β-glucosidase@ZIF-8 both retained high activity after catalyzing the substrate reaction five times, which provided huge potential for the application of immobilized β-glucosidase. Besides, the process of the two kinds of immobilized β-glucosidase were also compared. The nano-SiO2@β-glucosidase using covalent method with glutaraldehyde as a crosslinker and the β-glucosidase@ZIF-8 using co-precipitation method. The immobilization of β-glucosidase by ZIF-8 was easier than nano-SiO2 because the former had the advantages of high efficiency and easy operation. Therefore, the immobilization of β-glucosidase by ZIF-8 will successfully promote the practical use of β-glucosidase in industry. However, because the environment was alkaline during the immobilization process using ZIF-8 as the support, many applications of β-glucosidase@ZIF-8 in industry may be unusable by the limited pH range of use. Though the disadvantages, the resistance to protease of β-glucosidase@ZIF-8 was quite interesting. For future work, many other enzymes will be immobilized by ZIF-8 to validate the good performances. Besides, some measures will also be taken to improve immobilization yield and transfer efficiency of the β-glucosidase@ZIF-8.
Conclusions Using SiO2 nanoparticles and ZIF-8 as the carrier, the β-glucosidase was immobilized via crosslinking and encapsulation method, respectively. The optimal pH and temperature had no obvious difference among free β-glucosidase, nano-SiO2@β-glucosidase and β-glucosidase@ZIF-8. After immobilization, the stability of β-glucosidase was improved greatly, and the recyclability test proved that immobilized β-glucosidase can be reused for many times. Moreover, the resistance to protease of β-glucosidase@ZIF-8 was better than that of nano-SiO2@β-glucosidase and free β-glucosidase, which provided huge potential for the application of β-glucosidase@ZIF-8 in industry.
Introduction Apple consumption is known to reduce the risk of chronic diseases, such as cancer, cardiovascular diseases and type 2 diabetes (Boyer & Liu, 2004; Guo, Yang, Tang, Jiang, & Li, 2017). The protective effect has mainly been attributed to polyphenols, and in particular to the chemical families of flavones (e.g. luteolin, apigenin), flavonols (e.g. quercetin, kaempferol), flavanols (e.g. catechin, epicatechin), hydroxycinnamic acids (e.g. chlorogenic acid) and anthocyanidins (Boyer & Liu, 2004; Hanhineva et al., 2010; Shoji et al., 2017). Apple phytochemicals affect carbohydrate metabolism and glucose homeostasis at different sites (Hanhineva et al., 2010). Individual phenolic compounds (e.g. catechol, catechin, chlorogenic, ferulic and caffeic acid) extracted from apple reduced intestinal glucose uptake through SGLT1 transporter inhibition (Schulze et al., 2014). Some phenolic compounds also inhibited the enzyme α-glucosidase, which plays a key role during carbohydrates digestion (Agustinah, Sarkar, Woods, & Shetty, 2016; Tadera, 2006). Bortolotto and Piangiolino (2013) reported that an apple extract inhibited the activity of α-amylase and α-glucosidase by 70% and 90%, respectively. Despite these studies showed the potential of apples in facing the risk of type 2 diabetes, the relationship between the whole fruit intake and the reduced diabetes risk has not been fully elucidated yet. Most effects have actually been demonstrated on simplified systems obtained upon extraction of bioactive compounds from the original matrix (Williamson, 2013).