Screening And Identification Of A Protopectinase-overproducing Strain And Its Application In Pectin Extraction From Citrus Peel

Citrus peel,a by-product of the citrus processing industry and typically with about 30%(%on dry peel),is one of the main source of pectin in industry.Hunan province is one of province which rich in orange.It was estimated that about 1.5 million ton of orange was harvested each year, and about 20%of which was processed as tin product,and the rest was sold as fresh fruit,while most of the citrus peel has not been used properly or even discarded.It shall be thus obviously meaningful to make such waste into use.This paper mainly includes three parts of research,1)The screening and identification of the strain which used for the fermentation of pectin; 2)The optimization of the fermentation condition;3)The extraction and refining of pectin.Firstly,A protopectinase-overproducing strain CD-01 for pectin production was isolated from a pit soil dumped with perished orange in Changde city,Hunan province.The morphology of strain CD-01 is the same as Aspergillus niger.The 26S rRNA gene sequence(554FR47D015) of strain CD-01 has 100%sequence similarity to that of Aspergillus niger (ATCC 64028).Thus,it was identified and named as Aspergillus niger CD-01.Secondly,the Optimization of the fermentation condition was made based on L₉(3⁴)orthogonal experiments design and the variances analyses, and the optimal condition for producing pectin was as follows:t=36h, T=35℃,pH= 5,and urea as the nitrogen source.Under this condition, the optimum solid-liquid ratio was got,it was 1:15,and the pectin yield could reach up to 24.5%.Thirdly,70%ethanol was proved suitable for precipitating the pectin from the fermentation liquid,after a series of ethanol solution were assayed in terms of recovery of pectin.Referring to the Pectin Standard QB2484-2000,physicochemical properties of the extract were determined, and the extract were assayed and all the indice were accordance with the standard.Moreover,the infrared spectra of the extract was consistant with that of standard pectin.The main composition of the extract was thus to be pectin.