Ruminant pregastric lipases: experimental evidence of their potential as industrial catalysts in food technology

The historical importance of pregastric enzymes in cheese-making is reviewed and the potential for extending their use is discussed in terms of requiring an understanding of their physicochemical parameters. Commericial extracts from the tongues and epiglotti of suckling lambs and calves and adult goats have been processed to yield partially purified samples of the primary pregastric lipase (PGL). The N-terminal sequence and molecular weight of lamb PGL have been determined.

The activity of lamb and goat PGLs against tributyrin has been determined over a range of pH and temperature values. Optimum conditions were pH 6.4, 43°C, and pH 6.0, 52°C, for lamb and goat PGL respectively. The possible influence of the development of a ruminant multi-chambered stomach on the difference in optimal temperature is discussed. A lengthening of the carboxylic acid chain of homoacid triglycerides causes a decrease in hydrolytic activity of lamb PGL but in all cases only a single free fatty acid was released. Against a series of 4-nitrophenylalkanoate esters, maximum activity was observed against the decanoate ester but, in contrast to hydrolysis of the acetate ester which exhibited full Michaelis-Menten kinetics with increasing substrate concentration, activity against the decanoate ester was restricted to the monomeric substrate. Taurocholate inhibits the activity of lamb PGL at concentrations >8 mM. Values of pK₂ equal to 6.69 and 7.92 respectively have been determined for lamb PGL.

Attempts to interesterify coconut oil and cocoa butter, and tributyrin and tricaprylin, catalysed by calf PGL were unsuccessful, although positive results obtained using Candida cylindracea encourage further investigation of alternative methods for immobilizing the PGL. Finally, anhydrous milk fat has been hydrolysed by calf, lamb and goat PGLs and the differences in relative amounts of released free fatty acids have been used to explain the differences in taste which arise when Parmesan cheese is produced using different sources of PGL.     

Characteristics and production of thermostable α-amylase

Thermostable α-amylases have application in a variety of industrial processes and enzymes from a substantial number of thermophilic bacteria and fungi have been screened and characterized to varying degrees. The characteristics of these enzymes are summarized in this review. The genetics of α-amylase production inBacillus subtilis is reviewed and classical and recombinant DNA approaches to increasing α-amylase production are discussed.     

Xylanolytic enzyme production by anAspergillus niger isolate

Production of xylanolytic enzymes by anAspergillus niger CCMI 850 isolate was investigated in batch cultures. The effect of the composition of a fermentation medium that did not include chemical inducers, on β-xylanase, β-xylosidase, α-l-arabinofuranosidase, and total cellulase activity was studied. With 4% xylan as the carbon source, about 65 U/mL of β-xylanase was obtained, whereas the total cellulase activity was undetectable, under the specified conditions. This β-xylanase activity represents the highest reported for a wild-type strain ofA. niger. The effect of pH and temperature on the activity of β-xylanase was studied. Partial characterization of the β-xylanase showed that with insoluble birchwood as substrate theK _m andV _max were 0.3 mM and 19 μmol/min, respectively. Aspects of using the crude β-xylanase preparation for applications in the pulp and paper industry were discussed.     

Purification and partial characterization ofRhizomucor miehei lipase for ester synthesis

A commercialRhizomucor miehei lipase was purified by ammonium sulfate precipitation. Phenyl Sepharose 6 Fast Row hydrophobic interaction chromatography, and DEAE Sepharose Fast Flow anion-exchange chromatography. The recovery of lipase activity was 32% with a 42-fold purification. The molecular size of the purified enzyme was 31,600 Dalton and the pI 3.8. The enzyme was stable for at least 24 h within a pH range of 7.0-10.0, and 96.8% of the enzyme activity remained when kept at 30‡C for 24 h. Further, about 10–30% of the lipase activity was inhibited by K⁺, Li⁺, Ni⁺, Co²⁺, Zn²⁺, Mg²⁺, Sn²⁺, Cu²⁺, Ba²⁺, Ca²⁺, and Fe²⁺ ions and by SDS, but EDTA had no effect. Under the experimental conditions, the optimum temperature for the hydrolysis of olive oil was 50‡C (pH 8.0), and for the synthesis of 1-butyl oleate, 37‡C. It was concluded that hydrolytic activity of lipase alone is not a sufficient criterion for its synthetic potential. The optimal molar ratio of oleic acid and 1-butanol was 2:1 for 1-butyl oleate synthesis. The 1-butyl oleate yield was unaffected by purification of the enzyme after 12 h.     

分解水制氢的KNO3—I2循环之研究：Ⅲ.代替电解反应的一个子循环

本文提出了一个硫酸中间盐子循环用以代替分解水制氢的KNO_3-I_2混合循环中的电解反应,从而使原混合循环变为一个纯热化学循环。     

Enzymatic Synthesis and Polymerization of Cyclic Trimethylene Carbonate Monomer with/without Methyl Substituent

The direct enzymatic synthesis of a cyclic trimethylene carbonate (1,3‐dioxane‐2‐one) monomer with/without a methyl substituent was carried out using dimethyl or diethyl carbonate and 1,3‐diol with the objective of producing aliphatic poly(trimethylene carbonate), a typical biodegradable synthetic plastic. The lipase‐catalyzed condensation of dimethyl or diethyl carbonate with aliphatic 1,3‐diols using immobilized Candida antarctica lipase (lipase CA) in an organic solvent at 70 °C afforded the corresponding methyl‐substituted and unsubstituted cyclic trimethylene carbonates. The cyclic trimethylene carbonates obtained by the reaction of dimethyl or diethyl carbonates with 1,3‐propanediol and 2‐methyl‐1,3‐propanediol were polymerized by lipase to produce the corresponding polycarbonates.

Total TMC yield as a function of the reaction time.     

Express detection of nonylphenol in water samples by fluorescence polarization immunoassay

The development of express method for detection of endocrine-disrupting chemicals (EDC) such as alkylphenols is required for ecological monitoring. Several attempts have been made to produce antibodies against 4-nonylphenol (NP) in recent years. This work describes the production of new antibodies against NP and also summarizes the characterization of antibodies obtained earlier. Three approaches used to produce alkylphenol-specific antibodies are compared; these are based on: 1. omega-(4-hydroxyphenyl)nonanoic or omega-(4-hydroxyphenyl)heptanoic acid NP derivatives designed to mimic the linear NP isomer; 2. 4-aminophenol, which potentially mimics various substituted phenolic compounds with different side-chain structures at position 4 of the benzene ring; and 3. a mixture of branched NP isomers, conjugated to the carrier protein via a benzene ring by the Mannich reaction, and expected to be the closest mimic of NP structure by preserving its natural alkyl moiety.Fluorescence polarization immunoassays based on different combinations of antibody and labeled antigen for screening detection of NP were developed and structural aspects of assay sensitivity and specificity were investigated. The assays based on the antisera raised against omega-(4-hydroxyphenyl)nonanoic acid and NP conjugate via Mannich reaction are capable of express detection of NP with detection limit of 7 microg mL(-1 )and assay dynamic range of 18-300 microg mL(-1).     

Positivity of entropy production in nonequilibrium statistical mechanics

We analyze different mechanisms of entropy production in statistical mechanics, and propose formulas for the entropy production ratee() in a state . When is steady state describing the long term behavior of a system we show thate()0, and sometimes we can provee()>0.     

Optimization of hydrolase efficiency in organic solvents

The application of hydrolases in organic solvents for synthetic purposes is a procedure routinely adopted in organic chemistry, especially for the preparation of chiral building blocks. Numerous studies have shed light on several aspects of the mechanism of hydrolase action in low-water environments. Procedures suitable to improve the catalytic efficiency of enzymes and productivity of the synthetic processes have been reported. These fundamental and applied investigations have made hydrolase-catalyzed reactions in organic solvents of industrial interest. In this article we describe and discuss various approaches adopted to optimize the performance of hydrolases in organic media, with special emphasis on the formulation of the biocatalysts which, under proper conditions, can display an activity equal to that displayed in aqueous buffers.     

Isolation of lipase producer and its performance in enantioselective hydrolysis of glycidyl butyrate

A racemic glycidyl butyrate resolving strain, preliminarily identified as a Rhizopus sp., had been isolated from soil. Its extracellular lipase was found to enantioselectively hydrolyze the (S)-enantiomer of the chiral ester, with optimal activities at pH 5.3 and 42°C. Higher en antioselectivity of theenzyme was observed at lower temperatures, while the best anantioselectivity was obtained at pH 5.5–6.0, with an, E value (enantiomeric ratio) of 57.