A molecular dynamics simulation study concerning thermal stabilization of proteins by amorphous sugars was reviewed. First, a survey of several molecular simulations, especially molecular dynamics (MD) simulation, was described. Then the outlines of our experimental and MD simulation studies were reported as an example of studies on thermal stabilization of proteins by sugars. In the experimental study, thermal stability of enzymes in samples obtained by freeze drying of sugar-enzyme solutions was discussed. It was found that the thermal stabilizing effect of sugars was prominent when sugars were glassy state (amorphous) in samples. Focusing on a specific sugar, the thermal stabilizing effect was different depending on its crystallinity. As for MD simulation study related to the above experiment, it was found that thermal vibration of proteins was depressed more in case that sugars were amorphous than crystalline. The depression of vibration depended not only on the number of hydrogen bonds between sugars and the surface of protein, but also on the mean lifetime of those hydrogen bonds. It seems promising that molecular simulations, including MD simulation, will become more and more important tools which give us complemental information to experiments.
Cleaning-in-place (CIP) of food processing equipment usually requires a huge amount of water. For reduction of water required in its final rinsing step, performance of air-water two-phase flow as a rinsing medium was studied. Horizontal and vertical straight pipes of 23 mm inner diameter were artificially soiled with millet jelly and rinsed with air-water two-phase flow at flow rates of 400, 600, and 800 L/min for air and 2, 3, and 4 L/min for water. At the lowest flow rate of air, the two-phase flow was not completely annular and rinsing efficiency was quite low. At higher air flow rates, however, the two-phase flow was shown to save about 90% of rinsing water with no or slight extension of rinsing time, compared with water flow rinsing at 40 L/min. For non-straight piping parts (tees, elbows, and a diaphragm valve), the air-water two-phase flow was shown to save about 80% of rinsing water but to take twice as much rinsing time as 40 L/min water flow.
Two types of bigeye tuna meats, fatty muscle (chu-toro) and lean muscle (akami), were stored at -5, -10, and -15℃ and the effects of temperature and fat content on metmyoglobin (metMb) and nonheme iron (Fe3+) formation were determined using Electron Paramagnetic Resonance (EPR). For the sample meats, two high spin iron peaks on the EPR spectra were detected. The first peak appeared in the range of 90-130 mT and was identified as a signal of high-spin metMb, while the second peak, which appeared in the range of 140-170 mT, was determined to be a signal of high-spin nonheme iron. Peak intensity and half-width were used to determine metMb and nonheme iron content. The rates of metMb and nonheme iron formation in chu-toro and akami were slower as the storage temperature was lower. Chu-toro exhibited a quick initial increase in metMb, however, the metMb content turned decreasing after reaching a maximum, while nonheme iron increased monotonically. Meanwhile, for akami, the metMb exhibited a slower initial increase before reaching a maximum value, and remained constant during the storage period investigated, while the nonheme iron exhibited a small increase. These results suggest that once metMb is formed during frozen storage, iron ion (Fe3+), i.e., nonheme iron, is subsequently released from the porphyrin rings of a proportion of the metMb. That is, a type of compensatory reaction is occurring. Therefore, metMb content during frozen storage would exhibit time course curves with peak values. Notably, in case of high fat tuna meat, this phenomenon might be of significance.
Because it does not involve heating, “freeze-concentration” is one of the most suitable methods for concentrating thermally unstable materials, for instance, aroma components. We, therefore, tried to prepare a concentrate of the aroma components of peach fruits by progressive freeze-concentration. Condensated water containing the aroma components of peach fruits was obtained by vacuum distillation of fresh juice using a rotary evaporator, and was further concentrated by progressive freeze-concentration. When the distillation-condensate was concentrated 11.6 times (volume to volume) by the progressive freeze-concentration, the major aroma components of peach fruits (γ-decanolactone, (E)-2-hexen-1-ol, 1-hexanol, (Z)-3-hexenyl acetate and so on) were concentrated almost to the theoretical limit, about 8-12 times. The aroma components that were incorporated in the ice phase were less than 0.5％, even in the worst cases ((E)-2-hexen-1-ol). In summary, the aroma components of peach fruits were very effectively concentrated to a high degree with good yields by progressive freeze-concentration.