Abstract
This review examines the production of the biopolymer curdlan, synthesized by Agrobacterium species (sp.), on processing coproducts and plant lignocellulosic hydrolysates. Curdlan is a β-(1→3)-D-glucan that has various food, non-food and biomedical applications. A number of carbon sources support bacterial curdlan production upon depletion of nitrogen in the culture medium. The influence of culture medium pH is critical to the synthesis of curdlan. The biosynthesis of the β-(1→3)-D-glucan is likely controlled by a regulatory protein that controls the genes involved in the bacterial production of curdlan. Curdlan overproducer mutant strains have been isolated from Agrobacterium sp. ATCC 31749 and ATCC 31750 by chemical mutagenesis and different selection procedures. Several processing coproducts of crops have been utilized to support the production of curdlan. Of the processing coproducts investigated, cassava starch waste hydrolysate as a carbon source or wheat bran as a nitrogen source supported the highest curdlan production by ATCC 31749 grown at 30 °C. To a lesser extent, plant biomass hydrolysates have been explored as possible substrates for curdlan production by ATCC 31749. Prairie cordgrass hydrolysates have been shown to support curdlan production by ATCC 31749 although a curdlan overproducer mutant strain, derived from ATCC 31749, was shown to support nearly double the level of ATCC 31749 curdlan production under the same growth conditions.
Highlights
Curdlan is an extracellular polysaccharide synthesized by Agrobacterium species that has a complex tertiary structure [1,2,3].The unbranched, high-molecular-weight polysaccharide is composed of approximately 135 glucosyl residues linked by β-D-(1→3)bonds [2,4]
With nitrogen depletion being critical in the synthesis of curdlan, curdlan production in a ntrC mutant strain of ATCC 31749 was investigated after growth in a glucose-containing medium [42]
The findings indicated that 3% high maltose corn syrup supported less curdlan production by ATCC 31749 or the mutant strain than if 3% glucose or maltose served as the carbon source in the medium after 120 h of growth at 30 ◦ C [23]
Summary
Curdlan is an extracellular polysaccharide synthesized by Agrobacterium species (previously classified taxonomically as Alcaligenes faecalis var. myxogenes) that has a complex tertiary structure [1,2,3]. It has been reported that curdlan shows no toxicity, carcinogenicity or any effect on animal reproduction [9]. Curdlan has applications in the food and pharmaceutical industries [5,6,9,10,11]. Curdlan can serve as a thickening agent in the food industry such as in jellies, noodles and ice cream [4,5]. Curdlan has been used to encapsulate several drugs [11] This biopolymer can be hydrolyzed using acid hydrolysis as well as by enzyme degradation [4]. Other non-food uses of curdlan are as an additive to cement to improve its fluidity due to its ability to absorb water or as an enzyme immobilization support [15]
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