Tadashi Nagai

Adsorption characteristics of tryptic fragments of bovine β- lactoglobulin on a stainless steel surface

As a strategy for the analysis of the mode of protein adsorption onto stainless steel surfaces, peptides obtained by tryptic digestion of bovine beta-lactoglobulin were subjected to adsorption experiments after identification of their primary structures. In the presence of 1 mM KOH, the peptides were scarcely adsorbed onto the surfaces of stainless steel particles from the peptide mixture. The adsorption experiments on isolated peptides showed that the affinities of the peptides for stainless steel surfaces in the presence of 1 mM HNO3 were significantly different from each other. Peptides without any acidic amino acid residues were scarcely adsorbed onto the surface, whereas some peptides with acidic amino acid residues were found to be irreversibly adsorbed onto the surfaces in the acidic pH region. As for the latter peptides, the amount adsorbed on the surface increased with increasing ionic strength. These results indicated that the carboxyl groups on the side chains of the peptides play an important role in the adsorption. Furthermore, the adsorption behavior of beta-lactoglobulin itself was found to be very similar to that of one of the latter peptides.

Performance of protease as a cleaning agent for stainless steel surfaces fouled with protein

Abstract Cleaning experiments were performed by feeding protease solutions as cleaning agents into a packed column of stainless steel particles fouled with β-lactoglobulin or gelatin. By evaluating the initial desorption rate constants (first-order rate constants) and residual amounts of protein, the cleaning efficiencies of the proteases were compared. The initial desorption rate constant depended on the kind of protease used and also on the type of protein to be removed. It increased with protease concentration and reached a constant value at a limit concentration. Kinetic analysis of the proteolytic reactions catalyzed by the proteases revealed that protease with a large V max EK m value for the proteolytic reaction resulted in a large value of the initial desorption rate constant in the enzymatic cleaning at a low protease concentration. The Km value affected the limit concentration of protease yielding a saturation of initial desorption rate constant.

Fractal surface of starchy materials transformed with hydrophilic alcohols

Abstract A fractal analysis and a transformation of the surface structures of native potato starch, wheat flour, and rice flour were attempted. Log-log plots of the specific surface area versus the mean particle diameter showed that the surfaces of these materials were fractal. Transformation with ethanol and freeze-drying not only increased the specific surface area up to about 25 m 2 /g for the potato starch gel powder, but also increased the fractal dimension from about 2·3 to about 3·0 for each material. Scanning electron micrographs of the native and transformed potato starch powders are shown.

Effects of pH on the in Vitro Sorption of Mutagens to Dietary Fibers

Dietary fibers, alginate and defatted corn fiber, sorbed food mutagens, Trp-P-1 and Glu-P-1, which are heterocyclic amines formed in the cooking process. The sorption behavior of the heterocyclic amines to defatted corn fiber and alginates was analyzed under pH-controlled conditions. Glu-P-1 and alginic acid had pKa values of 4.2 and 3.6, respectively, whereas Trp-P-1, which showed alkaline in solution, possessed two pKa values of 4.8 and 7.7. Defatted corn fiber, which was mainly composed of cellulose and hemicellulose, did not show a significant pKa value. The amount of sorbed Trp-P-1 to the alginates increased as the pH value of the buffer was elevated, and was much more than that sorbed to defatted corn fiber at each pH condition. These results suggest that the alginates held the amino group of Trp-P-1 or Glu-P-1 on their carboxyl group as a cation exchanger.

Adsorption of Protein onto Stainless Steel Particle Surface and its Desorption Behavior

The adsorption and desorption of β-lactoglobulin were studied using stainless steel particles. The amount of β-lactoglobulin adsorbed was influenced by various factors such as temperature, pH, incubation time, and the protein concentration. The desorption behavior was analyzed by feeding NaOH or proteolytic enzyme solution into a glass column packed with the stainless steel particles on which the protein had been adsorbed and subsequently measuring its elution profile at the outlet. The amount of the protein remaiming on the stainless particles decreased accoring to a first-order kinetics at the initial stage of desorption, and then gradually reached a constant value. The desorption rate constant and the remaining amount were studied under various conditions.

Fractal Analysis of Porous Structure and Improvement of Physical Properties of Food Materials by Increase of Specific Surface Area

食品 の示す多種多様 な機能や物性は,化 学的成分組成 とその空間的構造 としての不均一構造の反映 と考え られ る.食 品の不均一構造 は分子拡散や熱伝導 などの移動現 象,生 化学 変化 の平衡 ・非平衡過程,破 壊 や粘弾性 とい った力学的物性 になどに影響を及ぼ し,そ の結果 さまざ まな機 能に深 く関与 して いると考え られる.従 って,食 品の微細構造 を変換 ・制御す ることが可能 であれば食 品 に新 たな機能 が付与で きる可能性 がある.し か し,従 来 より食 品の諸性質 と成分組成の対応 関係 につ いて はよ く 研究 されてきたが,食 品の ような複雑 な不規則構造を定 量化 する手法が未発達であ ったため,食 品の構造 と諸性 質 の対応 を検討 した例 は少なか った. 本研究で は,食 品の物性 に影響 を与え る微細構造 の定 量的把握を 目的 と して,澱 粉 やアルギ ン酸の粉体試料 に 対 して,触 媒 や機能性 ガ ラス等 の分野 で行なわれてい る1)~4)微細構造の変換を行 い,多 孔質試料の調製 を試み た.ま た,そ れ ら試料 の表面 キ ャラクタ リーゼー ション を,従 来よ り行 なわれている電子顕微鏡による観察,比 表面 積 の測定,細 孔分 布の測定 に加 え, 1975年MANDELBROTに よ り創成 された5),自 然界の様 々な現象や複 雑な構造 の定量化 が可能 とされて いるフラクタル解析 に よ って も行な った.更 に,多 孔質 に微細構造が変換 され た試料を用いて,様 々な物性 を測定 し,微 細構造 と食品 機能の相関を把握 し,構 造変換 による機能改善について も検討 した.