Studies On Bioactivities Of Fresh Yam

Yams, the tubers of Dioscorea spp., have been used as health food and herbal ingredients intraditional Chinese medicine. Recently, several beneficial properties of yams were reported in theliterature. The processing parameters, rheological properties of the yam mucilage, improvedphenol-sulfuric acid method to determine the polysaccharide of yam, the extraction ofpolysaccharide and the bioactivities of yam were studied in this paper.(1) In order to make full use of the fresh yam, for its high content of water, the process ofdehydration followed by drying was carried out. The fresh yam was steeped in alkaline medium(NaOH). At the conditions of concentration 7%, temperature 85℃ and time 8 min, the fresh yamwas steeped completely and the edible yield reached 81.7%. The optimal decolorant was confirmedas 03%Vc+0.3%Na2SO3 in the decoloration test. On the basis of above test, the yam slurry wasdehydrated by different method. The dehydration rate of material was 69.58% at the centrifugationrate of 7900r/min.(2) Chemical composition of the crude and purified YTM (Yam Tuber Mucilage) was determinedand viscosity was evaluated. The polysaccharide and protein content of crude and purified YTMwas 20.70%,37.67% and 48.93%,16.32%, respectively. Results indicated that the yam syrupexhibited pseudoplastic behavior. Viscosity of yam syrup decreased as the concentration ofmucilage decreased in the syrup . Viscosity also decreased with increasing of heating temperature.The value of pH had great effect on the viscosity. It exhibited a maximum value at the pH4.16.There is a great stability of yam syrup at temp.<60℃ and heating time had different effects on thestability of yam syrup.(3) The phenol-sulfuric acid method was improved for the determination of yam polysaccharide.Results suggested that this method was a simple, accurate and rapid method. According to thismethod, the maximum wavelength was 490nm, the factor of polysaccharide-to-glucose was 1.67and the average value of recoverable rate was 98.54%. The IR spectrum of purified polysaccharideshowed a typical functional group of normal polysaccharide. And GC results indicated that thepurified polysaccharide fraction of yam consisted of rhamnose, arobinose, mannose, glucose andgalactose.(4) The effect of temperature, time, yam-to-water ratio and concentration of alcohol on theextraction yield of polysaccharide were investigated. With single factor and orthogonal design, anoptimum extracting conditions of fresh yam was obtained. The optimum conditions wereyam-to-water (1:9), 50℃, 2.5hr and 75% alcohol, respectively. In this condition, the extractionyield of polysaccharide was 0.2449%/fresh yam. The deproteination of two different methods werealso compared.(5) The crude and purified YTM, crude and purified polysaccharide, different extraction of freshyam and its residue exhibited antioxidant activities in a series of in vitro test, including reducingpower test, anti-lipid peroxidation of linoleic acid and lecithin liposome assays,1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, hydroxyl radical and superoxide radical scavengingassays, using butylated hydroxytoluenue (BHT) and ascorbic acid for comparisons. These resultssuggest that the eight different extraction of fresh yam tuber might play roles as antiradical andantioxidants except the crude and purified polysaccharide on superoxide radical scavenging assay.