Gelati̇n hydrogels synthesis, swelling/degradation behaviours investigation and formation of suitable i̇mmobi̇li̇zed li̇pase-gelatin hydrogels systems

In this study, it was aimed to produce a serial of gelatin hydrogel for utilizing in lipase immobilization. In order to do that gelatin hydrogels containing glutaraldehyde crosslinking in different values were prepared and the gelation percentages were calculated. It was found that with increase of the amount of crosslinking, gelation percentages increased as well. The swelling behaviour of hydrogels were investigated as a function of time. The percentage swelling of all the hydrogels were increased with time and after 48 hours constant percentage swelling were observed. It was determined that with increase of the amount of crosslinking, the swelling percentages increased as well. G-1 hydrogel was determined as the most swollen hydrogel at pH=7.4 and 37ºC. The swelling behaviours of hydrogels were also investigated by changing the temperature. The swelling values increased with temperature and maximum swelling percentage were observed at 40ºC for all the hydrogels. The swelling behaviours of hydrogels were also investigated by changing pH. It was observed that all the hydrogels were swollen more at low pH values but the percentage swelling values decreased with the increasing pH values and after at pH=5.0 it reincreased. The degradation behaviours of hydrogels were observed in terms of time at pH=7.4 and 37ºC. It was observed that G-1 hydrogel containing the least crosslinking degradated completely in 14 days, other hydrogels degradated completely in almost 30 days.By benefiting from the results of the gelation and swelling/degradation tests, G-2 hydrogel was chosen as in accordance with lipase immobilization. In order to determine the most efficiency lipase immobilization conditions, lipase was immobilized to the chosen G-2 hydrogel in different concentrations with the method of covalent bond by using carbodiimide (CDI). The FTIR analyzes were made for confirming the realization of the immobilization. The activities of immobilized and free lipases were examined and it was seen that free lipase was more active than immobilized lipases. After the kinetic parameters of the free and immobilized lipases, Km and Vmax, were assayed. Km and Vmax were calculated for free lipase as Km value is 0.290 mM, Vmax value is 0.089 mM.dak-1 and for immobilized lipase Km value is 0.422 mM, Vmax value is 0.080 mM.dak-1. After 48 days of storage at 4ºC, free and immobilized lipases retained %32 and %92 their orginal activities, respectively. Gelatin hydrogel immobilized lipase used repeatedly 10 times in a day and it was retained %68 their orginal activitiy.