Unfolding of Poly-L-glutamic Acid by Microbubbling of Supercritical Carbon Dioxide
The conformational changes in α-helical poly-L-glutamic acid caused by microbubbling supercritical CO2 were investigated with circular dichroism spectra. After microbubbling using a micropore filter at 35 and 30 MPa for 30 min, α-helix content decreased to 37%, while without the filter it was 68%. The α-helix structure was significantly decomposed by a high density of CO2. No important changes were observed in heating, autoclaving, or pH-lowering.
Inactivation of Pectinesterase in Valencia Orange Juice by Micro-bubble Supercritical Carbon Dioxide Method.
ミクロバブルSC-CO2法によるバレンシアオレンジ果汁中のペクチンエステラーゼ(PE)の失活化を検討した.PE残存活性に及ぼすフィルターの影響を検討した結果,25MPa, 35℃の条件で30分間処理後の残存活性は,43.1%(未装着)から6.1%(孔径10μmフィルター装着)に低下した.同条件下で孔径2及び7μmのフィルターを装着した場合の残存活性は,それぞれ11.5, 8.5%であったことから,PE不活性化には孔径10μmのフィルター使用が最適であると考えられた.同フィルターを使用して以下の結果を得た.温度35, 45, 55℃の処理条件では,圧力の増加および時間の延長に伴い残存活性が低下した.特に,35℃の条件下でこの低下は著しかった.種々のSC-CO2の密度に対してPE残存活性をプロットした結果,0.79g/cm3以上で急激な活性の低下が認められた.
Physico‐chemical characteristics of orange juice cloud
Orange juice is a suspension of heterogeneous particles in a clear serum. The size of the particles varies between 0·05 μm and a few hundred μm. The particles with a size below 2 μm constitute the stable ‘cloud’. This fraction consists of needle-like crystals of hesperidin, chromoplastids, amorphous (rag) particles and oil globules attached to some of these particles. The adsorption of oil globules on the rag particles enhances their stability in suspension, by decreasing their density. The hesperidin crystals are formed partly by crystallisation immediately after juice extraction. All the cloud particles exhibit a negative charge, which decreases with decreasing pH. However, it seems that hydration rather than electrical charge is responsible for the stabilisation of the cloud. Heat treatment of the juice causes an increase in the number of fine particles at the expense of coarser ones. In this process some extraction of pectin into the serum also takes place but this has little significance on the cloudiness and cloud stability of the juice.