Research On The Storage And Processing Properties Of Dendrobium Officinale

Dendrobium officinale is a precious traditional Chinese medicinal herb with very high nutritional value and be entitled the reputation of "a mircle material that can save our lives" in China. Dendrobium officinale has been record as a new food resource that "can be used in health food development" in "Chinese pharmacopoeia". So it has a very good development prospect in food industry. This study took one year age fresh Dendrobium officinale as the main research object to explore the change rules of quality during cold storage under different temperatures and then chose three different kinds of drying methods to compare and analyse the influence of drying methods on the dehydration properties and the quality.In the end, the influence on rheological properties of Dendrobium officinale juice by different treatments during products development process were studied in order to provide guidance for the development and application of Dendrobium officinale in food industry. The main research achievements are as follows:(1) The content of water, cellulose and polysaccharide of Dendrobium officinale is 82.84g/100 g,10.22g/100 g and 4.65g/100g(wet base) respectively. But the protein and fat content is very low, the sum is less than 1g/100 g.(2) The results of quality changes during storage showed that the temperature had a significant effect on the sensory quality and physical-chemical indexes. It appeared signs of mould and germination and the sensory quality was unacceptable after 35 d during storage under 25℃. But the changes are slow under low temperatures and the sensory quality was still acceptable after 91 d storage. The weight loss, shrinkage and cellulose content increased with the extension of storage time. The three indexes changed faster under 25℃ storage than low temperatures. And there were no significant change(P>0.05) between 0 and 5℃. The content of water, chlorophyll and polysaccharide decreased with the extension of storage time. Also these three indexes changed faster under 25℃ storage than low temperatures. The most suitable storage temperature range is 0~5℃.(3) The study showed that the dehydration mostly occurred throughout under falling rate of internal mass transfer during drying. The drying temperatures had significant effect on moisture content and drying rate, and the drying rate sped up with temperature increasing during hot-air and vacuum drying. The hot-air drying rate is slower than that of vacuum drying but faster than freeze drying. The result of sensory quality analysis showed that freeze drying had outstanding advantage in maintaining sensory quality than the other drying methods. Drying methods and temperatures had great effect on color values and chlorophyll contents. The results showed that freeze drying had a higher color(L*,-a*, b*) index and chlorophyll retention rate than another two drying methods while hot-air drying had a greatest effect on the two indexes. The study also indicated that drying methods had great effect on water activity(aw) and the order of different drying methods was: freeze drying > vacuum drying > hot-air drying and aw decreased with temperature increasing. Freeze drying can reduced the loss of polysaccharide compared with another two drying methods and lower temperature meant long drying time which may bring more loss to polysaccharide.(4) The apparent viscosity of Dendrobium officinale juice(0.58oBrix) decreased with shear rate increasing. The results of power function equation matching showed that n=0.6854,n <1 and the model of Dendrobium officinale juice was Pseudoplastic fluid without thixotropy.(5) The apparent viscosity of Dendrobium officinale juice increased fast with soluble solid content(SSC) increasing. The results of power function equation matching aslo indicated that n decreased with SSC increasing, which meant Dendrobium officinale juice was more like Pseudoplastic fluid. The equation model of ?=1195.5C2.7327(R2=0.9636) can reflect the relationship between apparent viscosity and SSC. Besides the temperature also had big effect on apparent viscosity, which can be predicted by Arrhenius mathematic model(y=4608.4x-16.592, R2=0.9928) in practice.(6) The study investigated different processing conditions on of rheological properties of Dendrobium officinale juice and the results showed p H and sucrose additive amount all had a significant effect on the apparent viscosity. The apparent viscosity decreased with p H falling while the apparent viscosity showed irregular change rule with sucrose additive amount increasing. The heat treatment can break the stablility of Dendrobium officinale juice system that was consisted of polysaccharide molecules, which made the apparent viscosity decrease. The result indicated that the Dendrobium officinale juice system consisted of polysaccharide molecules had good stablility and there were no significant changes after been treated by ultra-high pressure(UHP).