Development of Reference Shunt for Short‐Time Alternating High Current Tests and Study of Measuring System

Short‐circuit tests for power circuit breakers and others require alternative short‐time current measurement, from a few kA to over several tens kA. However, the reference measurement system as a national standard or a specified secondary standard instrument to directly perform comparative test as a complete calibration test in high current class has not yet been established globally. The Japan Short‐Circuit Testing Committee (hereinafter referred to as “JSTC”) has therefore developed a shunt resistor that can be used as a standard instrument for high current measurement. Reference system using this shunt resistor is also considered by JSTC. The performance of the newly developed shunt resistor has been checked through several methods, such as resistance measurement, high power current test, high frequency current test, temperature rise test, and interference test. The results of the tests proved satisfactory performance. Resistance of the shunt resistor before and after the tests was invariant and stable. This makes the shunt resistor adequate for a reference in practical use. In addition, evaluation of uncertainty of the whole reference system including this shunt resistor satisfactorily fulfills the requirements of IEC 62475 edition 1.0, 2010.     

Debittering Mechanism in Bitter Peptides of Enzymatic Hydrolysates from Milk Casein by Aminopeptidase T

The bitter peptide fraction present in casein hydrolysates obtained by using three proteases (subtilisin, papain and trypsin) was treated with aminopeptidase T from Thermus aquaticus YT-1. The bitterness of the bitter peptide fraction could be decreased, and it sometimes disappeared completely, with an increase in free amino acids. The percentages of total free amino acids released from each bitter peptide fraction (subtilisin, papain and trypsin) by aminopeptidase digestion for 20 hr were approximately 11%, 8.7%, and 6.5%, respectively. Bitter peptide (α_s1-CN f91-100) was isolated from a tryptic hydrolysate of casein by HPLC, its threshold value of bitterness being 2.9 ppm (w/v). The peptide (α_s1-CN f96-100) obtained from the amino peptidase digestion of this bitter peptide showed no bitterness.     

Milk Curdling by Rennet under High Pressure

The effect of pressure on milk curd formation initiated by rennet was studied under high pressures. The milk used was a 20% solution of skim milk powder in 0.02M CaCl₂. After holding the milk with rennet at 35°C for given periods under high pressure, up to 1300 kglcm², the extent of proteolytic digestion and the curd tension were measured under atmospheric pressure. Rennet and milk protein were not denatured by pressure under the experimental conditions used. The primary phase reaction of milk curdling by rennet (hydrolysis of casein) was not affected by compression. The secondary phase reaction (core formation of casein micelle aggregates) was delayed under high pressure and the tertiary phase reaction (milk curd formation) was accelerated.     

Solid Solutions in the System Taeniolite-Sodium Taeniolite and Their Properties

Solid solutions in the system taeniolite (KMg₂LiSi₄O₁₀F₂)-sodium taeniolite (NaMg₂LiSi₄O₁₀F₂) were synthesized to study the solid solubility and swelling characteristics. Based on their melting behavior, crystals were grown for X-ray structural analysis. A complete solid solution series does not form in this system; there are two types of micas, K-rich taeniolite (0≤ x <0.5, x = Na/Na + K) and Na-rich taeniolite (0.8< x ≤l). The Na-rich taeniolite exhibits swelling properties, which become less pronounced with increasing potassium content. Melting and crystallization behavior were investigated by DTA. Solid solutions with higher sodium content melted at lower temperatures and crystallization occurred over a wide range of temperatures. To obtain larger crystals, the samples containing small crystallites were remelted at slightly above their melting points, then cooled slowly.     

Increase in Curd Tension of Milk Coagulum Prepared with Immobilized Proteases

Curd tension of milk clotted by nine proteases in immobilized or soluble forms was measured by a curd tension meter. In the curd prepared by trypsin, α-chymotrypsin, papain, thermolysin or alkaline-protease in a soluble form, the increasing rate of curd tension was definitely smaller than that of curd formed by rennet. However, curd tension increased linearly when the extent of proteolysis was controlled by employing these proteases in an immobilized form. The amounts of TCA-soluble nitrogenous compounds and sialic acid released at the beginning of clotting were kept constant throughout the incubation time.     

Melting Behavior of Gels Prepared from Isolated Subunits of Collagen

Acid-soluble collagen (ASC) was prepared from fresh pigskin corium, and denatured under mild conditions to obtain a mixture of parent gelatins. The mixture was precipitated with ammonium sulfate and preliminarily fractionated into four fractions by step-wise redissolution in ammonium sulfate solutions of decreasing concentration. From these fractions, substantially pure α1, α2, β₁₁, and β₁₂ peptide chains could be obtained by CM-cellulose ion-exchange chromatography. Differential scanning calorimetry (DSC) of the melting process of these peptide gels demonstrated that the thermal stability of α2-gel was very much lower than that of α1-gel.     

Chemical Characterization of Sardine Meat Powder Produced by Dehydration with High Osmotic Pressure Resin and Defatting with High Pressure Carbon Dioxide

Oils and fishy odor were extracted from the minced sardine meat with liquid carbon dioxide after dehydration with high osmotic pressure resin. This treatment resulted in higher quality minced sardine meat usable as “Surimi.” The lipids of the minced sardine meat defatted with liquid carbon dioxide was half that of undefatted meats; residual lipids were mainly composed of polar lipids such as phospholipids. Although soluble nitrogen and ATPase activity in sardine meat were decreased by dehydration and defatting, the Kamaboko-forming ability was present, and its flavor was improved after defatting. Moreover, sardine meat defatted with liquid carbon dioxide had good stability against protein deterioration and lipid peroxidation.     

Renaturation of α1 Chains from Shark Skin Collagen Type 1

Renaturation of α1 chains from shark skin collagen (1) was measured by the increase in optical rotation and viscosity. The rotation change of the α1(1) chains became constant after 18 hr, while the viscosity increased further with time. Size exclusion chromatographic patterns of renaturation products of α1 (I) chain gave similar results to that of native collagen. The renaturation products remelted with rising temperature in a similar way to the melting of native collagen as judged from the rotation-temperature curve.     

IDENTIFICATION OF ANGIOTENSIN I-CONVERTING ENZYME INHIBITORY PEPTIDES DERIVED FROM THE PEPTIC DIGEST OF SOYBEAN PROTEIN

Peptidic fractions which inhibit angiotensin I‐converting enzyme (ACE) were separated from peptic digests of soybean by ion exchange chromatography and gel filtration. Further separation of the peptidic fractions by ODS HPLC afforded active peptides, the amino add sequences of which were identified by Edman's procedure as: Ile‐Ata (inhibitory against ACE with an IC₅₀of 153 μM), Tyr‐Leu‐Ala‐Gly‐Asn‐Gln (14 μM), Phe‐Phe‐Leu (37 μM), Ile‐Tyr‐Leu‐Leu (42 μM), and Val‐Met‐Asp‐Lys‐Pro‐Gln‐Gly (39 μM). The antihypertensive activity of the soybean peptides was also investigated. Peptide fractions (2.0 g/kg body weight, oral administration) markedly towered the blood pressure of spontaneously hypertensive rats (SHRs).     

Functional Properties of a Peptide of 23 Residues Purified from the Peptic Hydrolyzate of asl-CASEIN: Changes in the Emulsifying Activity During Purification of the Peptide

The pH 4.6-soluble fraction of the peptic hydrolyzate of as 1-casein contained the 23 N-terminal residues, αsl-CN(fl-23), as a major pep-tide. Reversed-phase HPLC indicated that small amounts of other peptides such as αsl-CN(f154-199) were also contained in this fraction. By removing of these peptides, the emulsifying activity (EA) of the αsl-CN(fl-23) fraction was markedly decreased. However, when the removed peptide fraction was added to the purified αsl-CN(fl-23), the EA was increased. Some synergistic effect in the emulsification seemed to exist between αsl-CN(fl-23) and the other peptides. Although the purified αsl-CN(fl-23) had low EA values at neutral pH levels, it showed high emulsifying and surface activities in the acidic pH region.