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  • Irpex lacteus was well known as an edible


    Irpex lacteus was well known as an edible and medicinal mushroom. It had been reported that I. lacteus could produce a thermostable α-galactosidase [17]. The reported α-galactosidase from I. lacteus, however, seemed to be unsuitable for the practical application due to its poor hydrolysis ability toward RFOs and low yield. Moreover, its sequence data was not known. In this study, a new α-galactosidase gene from I. lacteus (ILgalA) was cloned and successfully expressed in P. pastoris. The purified rILgalA was characterized comparing with many other α-galactosidases. In addition, the removal effect of RFOs from soymilk by rILgalA was also investigated.
    Materials and methods
    Results and discussion
    Conclusion In the present study, the first α-galactosidase gene from Irpex lacteus was cloned and successfully expressed in P. pastoris. rILgalA possessed excellent thermal and pH stability as well as strong resistance to digestive proteases. Compared to other counterparts studied by far, rILgalA demonstrated much higher specific activities and the highest catalytic efficiencies toward RFOs. In addition, the enzyme rapidly and thoroughly degraded the anti-nutritive RFOs in soymilk. These excellent characters suggest that rILgalA has a great application potential in the food and feed industries for the elimination of RFOs. The following is the supplementary data related to this article.
    Conflict of interests
    Acknowledgements This work was supported by the Project of (grant number 2018SKLAB6-14).
    Introduction The enzyme β-galactosidase (EC has great importance in the food industry, as it hydrolyzes the lactose present in milk, reducing the effects of lactose maldigestion (Gekas & López-Leiva, 1985). The study of the molecular interaction between β-galactosidase with other compounds is relevant, due to the presence of several other components, such as proteins, carbohydrates, salts, and Minocycline HCl in dairy products. The literature indicates that several components can modify the β-galactosidase structure, enhancing or prejudicing its catalytic activity (Illanes, Altamirano, & Cartagena, 1994). A few of the substances known to inhibit the enzyme are silver ions, copper ions (Wutor, Togo, & Pletschke, 2007), tetracycline hydrochloride (Gao, Bi, Zuo, Jia, & Tang, 2017), and copper oxide nanoparticles (Rabbani, Khan, Ahmad, Maskat, & Khan, 2014). Conversely, there are also substances that increase β-galactosidase activity, such as milk proteins (Greenberg & Mahoney, 1984), and calcium and ferrous ions, at low concentrations (Wutor et al., 2007). Tannins are among the components known to interact with β-galactosidase (Carmona et al., 1996, Chauhan et al., 2007). They belong to the class of polyphenols, one of the most widespread groups in plants, and are found in a great variety of food and beverages, such as strawberries, walnuts, pecans, cumin, vanilla, cinnamon, green tea and grape juices (Carmona et al., 1996, Chauhan et al., 2007). They belong to the class of polyphenols, one of the most widespread groups of compounds in plants, and are found in a wide variety of foods and beverages (Haslam, 1979). Traditionally tannins are often considered to be nutritionally undesirable because they can form complexes with various proteins, thereby reducing their digestibility (Bate-Smith and Swain, 1962, Hagerman, 1989). In addition, other reported antinutritional and toxic effects of the compound include a depression in food/feed intake, formation of the less digestible tannin-dietary protein complexes, inhibition of digestive enzymes, malfunctions in digestive tract, and toxicity of absorbed tannin or its metabolites (Price et al., 1980, Singleton, 1981, Salunke and Chavan, 1990). The β-galactosidase–tannin interaction is pertinent since they can prejudice human and animal nutrition. Some studies demonstrate that tannins cause adverse effects on β-galactosidase activity. Carmona et al. (1996) presented that condensed black bean tannins induced inhibition of digestive enzymes, such as β-galactosidase, α-amylase, maltase, and sucrose in vitro assays. Additionally it was found that due to the tannin, the in vitro glucose uptake by rat-everted intestinal sleeves also decreased. Similar results were obtained for virtually every digestive enzyme including pectinase, amylase, lipases, proteolytic enzymes, β-galactosidase, cellulase, and microbial enzymes involved in fermenting cereal grains (Chung et al., 1998, Chung et al., 1998). Additionally, He, Lv, and Yao (2006) concluded that the decreases on the catalytic activity of digestive enzymes with the addition of tannins are caused by the great numbers of tannins hydroxyl groups that change the enzymes configurations. The tannins negative effects were also observed in vivo studies. Ngwa, Nsahlai, and Iji (2003) evaluated the effect of different diets consisted of pasture straw (negative control), straw supplemented with alfalfa (Alfalfa diet) and pods (rich in tannins) to South African Merino rams. It was observed that the pod diets rich in tannins, limited the growth and the activity of β-glucosidase and β-galactosidase enzymes. Studies in rat intestines also demonstrated that the tannic acid caused an inhibition in β-galactosidase for adults and suckling rats, this effect being more pronounced in the suckling animals. In the study it was concluded that tannic acid is a potent intestinal inhibitor of β-galactosidase, which could modulate intestinal functions (Chauhan et al., 2007). Finally, more recently, studies presented that the inclusion of tannin fava bean seeds in turkeys dietary decreased significantly the activity of bacterial α- and β-galactosidases (Zdunczyk et al., 2018).