Fractionation and characterization of poly(β-L-malic acid) produced by Aureobasidium melanogenum ipe-1

Poly (beta-L-malic acid) (PMLA) is attracting industrial interest for its potential application in medicine and other industries, whose functions primarily depend upon its molecular size and chemical structure. Up to now, the fractionation and characterization of PMLA produced by Aureobasidium spp. were still unclear. In this study, the product from A. melanogenum ipe-1 was effectively fractionated using 300 and 50 kDa membranes. During the filtration, the mechanisms of membrane fouling were illegible since the PMLA can both reject and permeate the membrane, while the main fouling mechanism varied between standard blocking and complete blocking during the diafiltration. After fractionation, 14.0, 8.4 and 77.6 % of the PMLAs with M(w)s of 75,134, 21,344 and 10,056 Da were distributed in the 300 kDa retentate after diafiltrating, 50 kDa retentate after diafiltrating, and the 50 kDa permeate, respectively. The M-w/M(n)s of the PMLAs were 4.12, 1.92, and 1.12 in the three fractions. Based on characteristic spectra of NMR, HPLC and FTIR, the product was not usual L-malic acid monomers, but glucoseterminated PMLA. The glucose was located at the terminal hydroxyl of PMLA. These results would serve as a valuable guide for process design and practical operation in subsequent industrial application.

Automated summary

Poly(beta-L-malic acid) (PMLA) produced by Aureobasidium spp. was effectively fractionated using 300 and 50 kDa membranes. The results showed that 14.0%, 8.4% and 77.6% of the PMLAs were distributed in the 300 kDa retentate, 50 kDa retentate, and the 50 kDa permeate, respectively. The product was identified as glucoseterminated PMLA based on characteristic spectra of NMR, HPLC and FTIR.