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Mesoporous silica particles were prepared by the sol-gel method from different alkoxysilane precursors and used as a host matrix for encapsulation of glucoamylase, an enzyme widely used in fermentative industry. The aim was to investigate the physico-chemical properties of the different silica powders and their effect on the enzyme kinetics. The encapsulated enzymes followed Michaelis-Menten kinetics. The Michaelis constant (KM) and the maximum rate of starch hydrolysis reaction (Vmax) were calculated according to the Michaelis-Menten and Lineweaver-Burke plots. The values of the Michaelis constant (KM) of the encapsulated enzymes were higher than those of the free enzyme. The temperature and pH influence on the activity of free and immobilized glucoamylase were also compared. The results of this study show that the enzymes immobilized in organic/inorganic hybrid silica matrixes (obtained by the sol-gel method), allowing the entrapped glucoamylase to retain its biological activity, are suitable for many different applications, (medicinal, clinical, analytical).

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Wheat (Triticum aestivum L.) is the basic cereal in human and animal nutrition. Every month, wheat is harvested somewhere in the world. In Romania, a country with a temperate-continental climate, the wheat is harvested between June and July, while the sowing is carried out between September and October. Climatic and meteorological factors during these periods can influence the nutritional quality of wheat. The aim of this study was to analyse the influence of annual average temperature and the amount of precipitate on the chemical composition and on the value of metabolizable energy of the wheat, respectively. The climatic and meteorological data used in this study come from NMA database. Were analysed the periods September 2017 - July 2018 (period 1, noted with 2018 - the year of harvesting) and September 2018 - July 2019 (period 2, noted with 2019 - the year of harvesting), respectively. For the chemical analysis, the NIR (Near InfraRed spectroscopy) method was used. The calculation of metabolizable energy was performed based on the ATWATER system, a system applicable to both human and animal nutrition. The statistical analysis of the climatic and meteorological data showed that the annual average temperature for period 1 was lower compared to the temperatures of period 2. Also, the precipitations were more abundant in period 1 compared to period 2. There were no significant statistical differences for any of the climatic and meteorological factors assayed during the analyzed periods. Following the statistical correlations between the nutrients studied by chemical analysis, for those 2 periods, significant differences were observed (p <0.001). The humidity of wheat grains harvested in 2018 was higher (average = 13.03%) compared to that of grains harvested in 2019 (average = 10.72%). The protein content was lower in 2018 (average = 10.02%) than in 2019 (average = 11.04%); and similar results were obtained for the fibre content (average 2018 = 2.17%; average 2019 = 2.96%). Also, the value of metabolizable energy was lower for wheat harvested in 2018 (average = 3517.90 kcal/kg) compared to 2019 (average = 3611.04 kcal/kg). In conclusion, the results of this study highlight the influence of temperature and precipitation on the chemical composition of wheat, thus having a direct impact on the nutritional quality of this grain for human and animal nutrition.

Amyloglucosidase (AMG) from Aspergillus niger was encapsulated in various matrices derived from tetraethoxysilane, methyltriethoxysilane, phenyltriethoxysilane and vinyltriacetoxysilane by different methods of immobilization. The immobilized enzyme was prepared by entrapment in two steps, in one-step and entrapment/deposition, respectively. The activities of the immobilized AMG were assayed and compared with that of the native enzyme. The effects of the organosilaneprecursors and their molar ratios, the immobilization method, the inorganic support (white ceramic, red ceramic, purolite, alumina, TiO2, celite, zeolite) and enzyme loading upon the immobilized enzyme activity were tested. The efficiency of the sol-gel biocomposites can be improved through combination of the fundamental immobilization techniques and selection of the precursors