Abstract
Cellulases can be applied as macerating and peeling enzymes in the orange juice processing industry. In this work, indigenous cellulose-degrading microorganisms were isolated from orange juice processing waste through successive enrichment procedures using carboxymethyl cellulose (CMC) as the sole carbon source. A total of 24 microbial isolates were screened for their ability to grow in CMC liquid medium, resulting in the selection of seven isolates. The latter were further assessed by determining their endo-1,4-β-d-glucanase, exo-1,4-β-d-glucanase, and β-1,4-d-glucosidase activities, of which their respective activities were as high as 3.89, 10.67, and 10.69 U/mg protein. All cellulose-degraders selected belonged to the genus Paenibacillus, although to distinct operational taxonomic units related to P. xylanexedens, P. tundrae, and P. pabuli (operational taxonomic unit—OTU#1) and to P. wynnii, P. odorifer, and P. donghaensis (OTU#2) spectrum. Regarding the cellulase activities of the orange juice processing waste, endo-1,4-β-d-glucanase activity (4.00 ± 0.11 U/g) was exerted only extracellularly, whereas exo-1,4-β-d-glucanase (2.60 ± 0.19 U/g) and β-1,4-d-glucosidase (5.69 ± 0.23 U/g) activities were exhibited both extracellularly and intracellularly. In conclusion, orange juice processing waste can be considered as a valuable source for the isolation of cellulose-degrading microbiota with potential uses in beverage industry, solid state fermentation and energy production.
Highlights
Oranges are one of the most cultivated and processed citrus fruits, with 23.89 million tons of orange juice being annually consumed worldwide [1]
All cellulose-degraders selected belonged to the genus Paenibacillus, to distinct operational taxonomic units related to P. xylanexedens, P. tundrae, and P. pabuli and to P. wynnii, P. odorifer, and P. donghaensis (OTU#2) spectrum
Fruit juices mainly consist of long polymeric saccharides like cellulose, hemicellulose, pectin, and starch, which are considered the major constituents of orange dietary fibers [4]
Summary
Oranges are one of the most cultivated and processed citrus fruits, with 23.89 million tons of orange juice being annually consumed worldwide [1]. Due to the high moisture content, which exceeds 80% of the fresh fruit biomass, oranges are considered to be spoiled crops. By valorizing orange fruits through conversion into various crop-processing products, mainly juice and sweet commodities, food lifetime duration is expanded, creating new business challenges [2]. The fruit juice industry has become one of the largest agro-industrial sectors worldwide. An increased global interest has been sighted on juice production and commercialization [2,3]. Fruit juices mainly consist of long polymeric saccharides like cellulose, hemicellulose, pectin, and starch, which are considered the major constituents of orange dietary fibers [4]. A β-1,4-linked glucose-based biopolymeric carbohydrate, is the major plant structural polysaccharide and the most abundant biomolecule in the biosphere [5]
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