Isolation And Structural Identification Of The Main Composition In Bamboo

Bamboo as one of the most important biomass resources has the characteristics of wide distribution, fast growth and many applications. It can be used to make materials and energy based on biomass for higher utilization value. The chemical composition of bamboo consists mainly of celluloses, hemicelluloses, lignin and lipophilic. So it is significant to study on the chemical composition for replacement of fossil resources, energy-saving and emission reduction, developing a low-carbon economy, and increaseing the peasants'income. In this paper, (1) The five classes of free fatty, sterols, waxes, steryl esters, and glycerates in lipophilic extractives from the four species of bamboo culms (Sinocalmus affinis (Rendle) Mcclure, B.rihida Keng et Keng f., Phyllostachys bambusoides Sieb. et Zucc. f. shouzhu Yi, and Phyllostachys incarnata Wen) were separated to fifty four individual compounds by GC with a medium-length and high-temperature capillary column. Meanwhile, the structure of lipophilic were further characterized and the content of phenols in lipophilic were determined. (2) The bamboo lignins were obtained by sequential extractions with distilled water, 0.5% and 1% NaOH, 60% ethanol containing 1% NaOH, and 3%, 5% and 8% NaOH with a solid to liquid ratio of 1:20 g/ml at 60 oC for 3 h. Moreover, the chemical composition and structure of lignins were investigated. (3) At the same time, the chemical composition and structure of hemicelluloses from bamboo in process (II) were carried out. All results are reported as follows.1. Lipophilic: free fatty acids (6.49-29.15%), monoglycerides (0.83-10.50%), waxes (0.25-4.72%), and sterols (1.03-3.92%) were the dominant compositions identified in the four species of bamboo culms. In addition, non-lipids determined from the extractives were composed of small amounts of phenolic compounds (0.86-4.77%), azelaic acid (0.90-5.95%), maleic acid (0.67-3.12%), and some quantities of co-extracted polysaccharides. The yield of extractives from B.rihida Keng et Keng f. was the highest and the yield of extractives from Sinocalmus affinis (Rendle) Mcclure was the lowest, while Phyllostachys bambusoides Sieb. et Zucc. f. shouzhu Yi contributed the highest lipophilic content (54.79%).2. Lignin: the successive extractions together resulted in dissolution of 62.26% original lignins. Seven lignin fractions contained rather low amounts of neutral sugars (0.01-1.11%), and small amounts of ester-linked p-coumaric (0.08-2.37%) and ferulic acids (0-1.69%) and of ether-linked p-coumaric (0.02-0.65%) and ferulic acids (0.01-0.27%). The weight-average molecular weights ranged between 970 and 3430 g/mol. Furthermore, the bamboo lignins comprised high amounts of syringyl and noticeable guaiacyl together with small amounts of p-hydroxyphenyl units. Moreover, theβ-O-4 linkage is a major linkage type and small amounts ofβ-βandβ-5 linkages are also present in the lignin molecules.3. Hemicelluloses: the yields of seven fractions together accounted for 80.1% of total available hemicelluloses. The molecular weights of these polymers varied between 3760 and 36000 g/mol. Sugar composition studies showed that the water-soluble hemicelluloses consisted mainly of glucose, while xylose, arabinose and glucuronic acid were the major sugars in alkali-soluble hemicelluloses. Moreover, the structure of the polysaccharides in the two fractions obtained from 3% and 8% NaOH were determined by ¹H, ¹³C NMR spectroscopy and 2D 1H-13C heteronuclear single correlation techniques (HSQC). It was found that the bamboo hemicelluloses are O-acetyl-(4-O-methylglucurono)-arabinoxylans, and their structural element could be first identified as below:→4)[4-O-Me-α-D-GlcpA-(1→2)][2-O-Ac][2,3-di-O-Ac][α-L-Araf-(1→2)][α-L-Araf-(1→3)]-β-D-Xylp-(1→.