Supplementation of nitrogen sources and growth factors in pineapple waste extract medium for optimum yeast (Candida utilis) biomass production
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Date
2009
Authors
Cheong, Mun Wai
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Abstract
Various nitrogen sources and growth factors were respectively incorporated
into the growth medium from juice extracted from pineapple waste (PWE) and their
effects on C. utilis biomass production, yield and productivity were studied.
Experiments were conducted in conical flasks containing PWE medium at 3 oBrix,
initial pH of 4.5 and inoculum of 7.8% v/v (106 cells/mL), incubated at 30 °C with
shaking of 100 rpm. Significant increase (p<0.05) in biomass was observed when a
single nitrogen source (0.09% total nitrogen, w/v) was added with the following
order; yeast extract C1 = NH4H2PO4 > peptone ≥ KNO3 ≥ yeast extract C2 =
(NH4)2SO4. Addition of combined C1 and NH4H2PO4 with the absence of additional
growth factor, did not increase (p>0.05) the biomass production but the productivity
of 1.84 gL-1h-1 was recorded when PWE medium was added with 1:1 (N-based) C1
and NH4H2PO4. Nitrogen-supplemented PWE medium added with 300 μg/L
thiamine or 100 μg/L pyridoxine enhanced the yeast growth (p<0.01). Response
surface methodology (RSM) was conducted in order to study the interactions
between nitrogen sources and growth factors by using central composite design
(CCD). Optimum concentrations of these factors on maximum biomass were
determined as well. Findings indicated that biomass was significantly influenced by
the composition of growth medium where the NH4H2PO4 and thiamine are the most
influential factors (p<0.05). Optimum concentration of C1 and NH4H2PO4 was
0.05% and 0.10% respectively and this is equivalent to 4.4 g/L and 8.2 g/L. The
optimum concentration of thiamine and pyridoxine was 325 μg/L and 250 μg/L
respectively. The optimum fermentation condition produced biomass of 7.57 g/L
with biomass yield of 0.48 g biomass per g reducing sugar utilised.
Batch growth kinetics of C. utilis in a 2-L fermenter containing PWE,
optimum PWE and YEPG medium were studied. Optimum PWE was significantly
enhanced the biomass (11.73 g/L) compared to PWE (8.57 g/L) as the consequence
of improved growth rate (0.96 h-1). Saturation constant (Ks) and doubling time (tD)
were reduced while productivity (P) and yield over substrates (Yx/s) were improved
simultaneously. However, the oxygen demand (SOUR) of C. utilis in optimum PWE
increased dramatically and oxygen became the limiting growth factor. Ability of C.
utilis to utilise sucrose in PWE medium after a certain period of fermentation time
was depicted by the electron micrographs showing deposition of endoplasmic
reticulum along the periphery of cell membrane indicating enzyme synthesis which
was not observed in YEPG medium.
Description
Master
Keywords
Chemical science , Nitrogen sources , Pineapple waste extract , Biomass production