Fresh keeping agent for fresh dendrobium twigs as well as preparation method and use method of fresh keeping agent

The invention discloses a fresh keeping agent for fresh dendrobium twigs as well as a preparation method and a use method of the fresh keeping agent. The fresh keeping agent comprises, in percentage by weight, 1%-4% of food-grade pullulan, 0.1%-2% of food-grade chitosan oligosaccharide, 0.1%-2% of food-grade mannan oligosaccharide, 0.5%-2.5% of food-grade glycerin and the balance of water. The picked fresh dendrobium twigs are subjected to preliminary finishing, immersed in the fresh keeping agent for 30-60 seconds and taken out to be aired; or cuts of the fresh twigs are immersed in the fresh keeping agent for 30-60 seconds, then, the fresh keeping agent is sprayed on the fresh twigs at 360 degrees, the fresh twigs are aired, the fresh twigs treated with the fresh keeping agent are directly put in a shady, cool and dry place for storage or put in the shady, cool and dry place for storage after being subjected to vacuum package or put at the temperature ranging from 4 DEG C to 12 DEG C for cold storage. The raw materials used for the fresh keeping agent are all food-grade, the fresh keeping agent doesn't contain a preservative and is safe, non-toxic, cheap and easy to obtain; the treated fresh twigs can be preserved for one year to one and a half year, and the water loss is smaller than 1%; the germination rate is very low, characteristics and nutritional ingredients of the fresh dendrobium twigs can be kept, and follow-up processing is not affected.