Biovanillin production from lemongrass leaves hydrolysates by Phanerochaete chrysosporium ATCC 24725 in batch culture

Abstract

Biovanillin is one of fungi secondary metabolites, that is widely used as aromatic and flavour compound with high fiscal value. The use of vanillin as flavour for various products is its foremost application in food industries. The global market demand for natural vanillin as flavour stands for less than one percent (1%) of its market demand annually. However, most of the flavour compounds are normally obtained through the process of chemical synthesis, which could cause health problem and environmental hitches. Demand for natural and healthy products coupled with the fact that acid ferulic (FA) extracted from plant materials can be a precursor for biovanilin production makes it relatively inexpensive as a natural product. The research was aimed to extract FA from lemongrass leaves (LGL), which was used as precursor for one-step biovanillin production by Phanerochaete chrysosporium (ATCC 24725) in batch culture. Initially, optimization of the LGL pretreatment practices using liquid hot water with sodium bisulfite (0.5% w/v) towards the release of the FA was investigated with central composite design (CCD). The optimized results produced 0.750 g/L as the highest FA released from the lemongrass leaves hydrolysates (LLH). Considerable alterations of the major LGL contents were observed during the pretreatment process, which increased the cellulose content by 39%. The Fourier transform infrared (FTIR) and field emission scanning electron microscopic (FESEM) analyses confirmed that the lignin which serves as the shielding layer from the LGL components became fragmented, thus decreasing the lignin content by 46%. The total reducing sugar production with enzymatic saccharification using enzymes cocktail (celluclast and viscozyme, 1 % v/v each) improved by up to 8.4-folds as compared to the direct enzymatic saccharification without removing the LGL extracts. Screening of significant factors for biovanillin production using 2-level Factorial Design showed that the biovanillin production processes was affected by the interactive effects of initial FA concentration, incubation temperature, incubation time and initial pH. The highest biovanillin production (0.093 g/L with molar yield 23 %) in shake flasks using the CCD was determined with FA (0.5 g/L), temperature (35 °C), time (72 h), and initial pH (6.0). Application of both pH and dissolved oxygen control strategies in 2 litre stirred tank bioreactor had increased the biovanillin production by 1.41 and 1.53-folds as compared to the optimized experiment using the shake flasks. The evaluation of kinetics from the two-phase pH control strategy demonstrated the performance of P. chrysosporium with the highest specific growth rate (µ) of 0.056 h-1, with an increase in the yield coefficient of biomass formation Yx/s (0.5191 g/g) and maximum cell concentration Xmax (13.0 g/L) by 1.03 and 1.05-folds as compared to one-phase of pH control, respectively. Performance of the kinetics using two-phase dissolved oxygen (DO) control strategy has shown that 80 % saturations of DO during active growth phase with 40 % saturations during production phase were highly essential for enhancement of biovanillin production from LLH by P. chrysosporium using 2 litre stirred tank bioreactor. LGL residue which contained FA can be used as a precursor to produce biovanillin by natural means via one-step bioconversion process with P. chrysosporium in batch culture using 2 litre stirred tank bioreactors.