Urease activity and urea hydrolysis rate under coupling effects of moisture content,temperature,and nitrogen application rate

The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects of the three factors on urease activity(V_(0)),hydrolysis rate constant(K_(u)),and activation energy(Ea)and establishing the quantitative model for K_(u) under the coupling condition.Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃,and 35℃),moisture contents(θ)(60%,80%,and 100%of field capacities),and nitrogen application rates(F)(247 mg/kg,309 mg/kg,371 mg/kg,and 433 mg/kg).The urea content was measured daily.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on V_(0) and K_(u) were in the descending order:T,F,T^(*)F,θ,T^(*)θ,F^(*)θ,T^(*)θ^(*)F.The effect of single factor and two-factor coupling on V_(0) was extremely significant(p<0.01),whereas the effect of the three-factor coupling on V_(0) was negligible.The effects of three factors and their interaction on K_(u) were extremely significant(p<0.01).The effects of moisture content,nitrogen application rate,and their interaction on Ea were in the descending order:F,θ,F^(*)θ.The effects of two factors and their interaction on Ea were not significant.The mean absolute percentage error(MAPE)values of the established K_(u-1)(θ,T,F)and K_(u-2)(θ,T,F)models were 3.14%and 4.60%,respectively.The MAPE of the traditional Arrhenius model K_(u-3)(T)was 6.75%.The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model.The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of K_(u).

玉米蛋白水解条件的优化研究

本试验是以玉米黄粉为底物,采用碱性蛋白酶为水解酶进行水解。采用二次旋转回归设计,以温度、酶与底物浓度比和pH三因素进行水解,得出玉米黄粉的最佳水解条件是[S]=8%、[E]/[S]=3.3%、pH =9.85、T=45℃、水解时间(t)=4.5h。在这种水解条件下蛋白回收率>73%。

Synthesis and Characterizations of 1,4-butanediol( BDO )-Regulated Poly( ε-caprolactone)(PCL) Waterborne Polyurethane with Controlled Biodegradability for Medical Applications

Waterborne polyurethane(WBPU)with controlled biodegradability and biocompatibility was synthesized by using poly(ε-caprolactone)(PCL)as the polyglycol,isophorone diisocyanate(IPDI)as the isocyanate,2,2-bishydroxymethylbutyric acid(DMPA)as the chain extender and 1,4-butanediol(BDO)as the hard-segment regulating agent.We found that BDO content significantlyinfluencedmechanicalproperties,degradable performances and cyto-biocompatibility of PCL-WBPUs.Increasing the BDO content in PCL-WBPU enhanced its tensile strength and decreases strain.Enzymolysis and hydrolysis properties were also regulated by BDO content,but with different mechanisms.Cytobiocompatibility was evaluated with ATDC5 cells.The results show that the biodegradability of PCL-WBPU is significantly determined by BDO content,which exerts a serious influence on its polymer structure,leading to resultant degradable properties.

Physical and chemical changes of rapeseed meal proteins during toasting and their effects on in vitro digestibility

Background： Toasting during the production of rapeseed meal（RSM） decreases ileal crude protein（CP） and amino acid（AA） digestibility. The mechanisms that determine the decrease in digestibility have not been fully elucidated. A high protein quality, low-denatured, RSM was produced and toasted up to 120 min, with samples taken every 20 min. The aim of this study was to characterize secondary structure and chemical changes of proteins and glucosinolates occurring during toasting of RSM and the effects on its in vitro CP digestibility.Results： The decrease in protein solubility and the increase of intermolecular β-sheets with increasing toasting time were indications of protein aggregation. The contents of NDF and ADIN increased with increasing toasting time.Contents of arginine, lysine and O-methylisourea reactive lysine（OMIU-RL） linearly decreased with increasing toasting time, with a larger decrease of OMIU-RL than lysine. First-order reactions calculated from the measured parameters show that glucosinolates were degraded faster than lysine, OMIU-RL and arginine and that physical changes to proteins seem to occur before chemical changes during toasting. Despite the drastic physical and chemical changes noticed on the proteins, the coefficient of in vitro CP digestibility ranged from 0.776 to 0.750 and there were no effects on the extent of protein hydrolysis after 120 min. In contrast, the rate of protein hydrolysis linearly decreased with increasing toasting time, which was largely correlated to the decrease in protein solubility, lysine and OMIU-RL observed. Rate of protein hydrolysis was more than 2-fold higher for the untoasted RSM compared to the 120 min toasted material.Conclusions： Increasing the toasting time for the production of RSM causes physical and chemical changes to the proteins that decrease the rate of protein hydrolysis. The observed decrease in the rate of protein hydrolysis could impact protein digestion and utilization.