RESUMEN
Glycosidases are widely used in food and pharmaceutical industries due to its ability to hydrolyze the glycosidic bonds of various sugar-containing compounds including glycosides, oligosaccharides and polysaccharides to generate derivatives with important physiological and pharmacological activity. While glycosidases often need to be used under high temperature to improve reaction efficiency and reduce contamination, most glycosidases are mesophilic enzymes with low activity under industrial production conditions. It is therefore critical to improve the thermo-stability of glycosidases. This review summarizes the recent advances achieved in engineering the thermo-stability of glycosidases using strategies such as directed evolution, rational design and semi-rational design. We also compared the pros and cons of various techniques and discussed the future prospects in this area.
Asunto(s)
Glicósido Hidrolasas/genética , Oligosacáridos , Polisacáridos , Ingeniería de ProteínasRESUMEN
The storage and transportation of raw milk at low temperatures promote the growth of psychrotrophic bacteria and the production of thermo-stable enzymes, which pose great threats to the quality and shelf-life of dairy products. Though many studies have been carried out on the spoilage potential of psychrotrophic bacteria and the thermo-stabilities of the enzymes they produce, further detailed studies are needed to devise an effective strategy to avoid dairy spoilage. The purpose of this study was to explore the spoilage potential of psychrotrophic bacteria from Chinese raw milk samples at both room temperature (28 °C) and refrigerated temperature (7 °C). Species of Yersinia, Pseudomonas, Serratia, and Chryseobacterium showed high proteolytic activity. The highest proteolytic activity was shown by Yersinia intermedia followed by Pseudomonas fluorescens (d). Lipolytic activity was high in isolates of Acinetobacter, and the highest in Acinetobacter guillouiae. Certain isolates showed positive β-galactosidase and phospholipase activity. Strains belonging to the same species sometimes showed markedly different phenotypic characteristics. Proteases and lipases produced by psychrotrophic bacteria retained activity after heat treatment at 70, 80, or 90 °C, and proteases appeared to be more heat-stable than lipases. For these reasons, thermo-stable spoilage enzymes produced by a high number of psychrotrophic bacterial isolates from raw milk are of major concern to the dairy industry. The results of this study provide valuable data about the spoilage potential of bacterial strains in raw milk and the thermal resistance of the enzymes they produce.
Asunto(s)
Animales , Bacterias/genética , Proteínas Bacterianas/química , Biopelículas , Frío , Productos Lácteos , Endopeptidasas/química , Estabilidad de Enzimas , Microbiología de Alimentos , Calor , Lipasa/química , Leche/microbiología , Péptido Hidrolasas/química , Fosfolipasas/química , ARN Ribosómico 16S/genética , Alimentos Crudos/microbiología , beta-Galactosidasa/químicaRESUMEN
In this study,thermo-adapted(Ta)PPR vaccines were assessed for their stability at 25,37,40,42 and 45℃ in lyophilized form using two extrinsic stabilizers(lactalbumin hydrolysate-sucrose(LS)and stabilizer E)and in reconstituted form with the diluents(1 mol/L MgS04 or 0.85% NaCl). The lyophilized vaccines showed an expiry period of 24-26 days at 25℃,7-8 days at 37℃ and 3-4 days at 40℃. LS stabilizer was superior at 42℃ with a shelf-life of 44 h,whereas in stabilizer E,a 40 h shelf-life with a comparable half-life was observed. At 45℃,the half-life in stabilizer E was better than LS and lasted for 1 day. Furthermore,the reconstituted vaccine maintained the titre for 48 h both at 4℃ and 25℃ and for 24-30 h at 37℃. As both the stabilizers performed equally well with regard to shelf-life and half-life,the present study suggests LS as stabilizer as a choice for lyophilization with 0.85% NaCI diluent,because it has better performance at higher temperature. These Ta vaccines can be used as alternatives to existing vaccines for the control of the disease in tropical countries as they are effective in avoiding vaccination failure due to the breakdown in cold-chain maintenance,as this vaccine is considerably more stable at ambient temperatures.