98
2.3 Production of IA from Different Sustainable Feedstocks
Glucose is the preferred feedstock for industrial production of IA that contributes to
more than 25% of the total IA manufacturing cost. However, the high cost of glucose ($0.35–$0.60 kg
−1
) has driven R&D initiatives towards utilization of alternative inexpensive raw materials to make IA production economically competitive to
petrochemical-based products [66]. Starch-rich sources (corn, potato, and cassava)
have emerged as compelling alternatives because of their high purity, low cost, and
abundance [67]. Corn starch undergoes gelatinization when subjected to heating.
Thus, hydrolysis of corn starch is performed by using mineral acid or enzymes that
prevent gelatinization of corn starch. When hydrolysis of corn starch was performed
over enzymes, hydrochloric or sulfuric acid before fermentation, A. terreus cells
essentially needed a supplementary nitrogen source to begin the fermentation [68].
Although corn starch contains low concentrations of nitrogen, it is insufficient
for cell growth. In contrast, when hydrolysis is performed with nitric acid, fermentation proceeded well without additional ingredients. This indicates that nitric acid
works as an acid as well as nitrogen source for A. terreus. Acid-hydrolyzed sample
of corn starch was subjected to fermentation at pH 2 before autoclaving at 121 °C
for 20 min. Higher than 60 g L
−1
IA was yielded in flask fermentation from 140 g L
−1
of corn starch by A. terreus TN-484 [69]. Petruccioli et al. found that the productivity of IA was significantly affected by the degree of hydrolysis [67]. They achieved
18.40 g L
−1
IA titers from corn starch saccharified at 85 dextrose equivalents by
A. terreus NRRL 1960. The yield of IA was further increased to 63% by ultraviolet,
chemical, and mixed mutagenic treatment of wild-type A. terreus SKR10 strains [70].
The synthesis of IA from corn starch is a time-consuming and multiple-step process. To reduce the overall production time, Li et al. proposed an integrated process
in which saccharification and fermentation steps were combined by overexpressing
the glucoamylase gene in A. terreus strain. The IA titer reached 77.60 g L
−1
by
genetically engineered A. terreus from liquefied corn starch [26]. Researchers have
also screened other starch-rich wastes for the production of IA. Potato starch wastes
yielded high amounts of IA, which could be due to the higher glucose content [71].
A. terreus from mangrove soil has been recently isolated and utilized for the production of IA in a large volume (3 L) bioreactor [72]. The deionization of potato waste
removed the inhibitory ions like phosphate and improved the yield of IA. Under
optimized fermentation conditions, 29.69 g L
−1
IA was produced by A. terreus
strain C1.
In search of new alternative microorganisms, E. coli and A. niger species have
been successfully tested for the production of IA from starch-rich feedstocks.
Okamoto et al. proposed a direct IA production process by employing α-amylase
expressing E. coli [73]. In this process, two α-amylases from Bacillus amyloliquefaciens NBRC 15535
T
(BBA) and Streptococcus bovis NRIC 1535 (SBA) were
selected for hydrolysis of starch. With 1% starch released from SBA hydrolysate,
E. coli produced 0.15 g L
−1
IA after 69 h cultivation by pH-stat method, while BBA
displayed no noticeable activity. Gnanasekaran et al. investigated the feasibility of
K. Avasthi et al.
2.3 Production of IA from Different Sustainable Feedstocks
Glucose is the preferred feedstock for industrial production of IA that contributes to
more than 25% of the total IA manufacturing cost. However, the high cost of glucose ($0.35–$0.60 kg
−1
) has driven R&D initiatives towards utilization of alternative inexpensive raw materials to make IA production economically competitive to
petrochemical-based products [66]. Starch-rich sources (corn, potato, and cassava)
have emerged as compelling alternatives because of their high purity, low cost, and
abundance [67]. Corn starch undergoes gelatinization when subjected to heating.
Thus, hydrolysis of corn starch is performed by using mineral acid or enzymes that
prevent gelatinization of corn starch. When hydrolysis of corn starch was performed
over enzymes, hydrochloric or sulfuric acid before fermentation, A. terreus cells
essentially needed a supplementary nitrogen source to begin the fermentation [68].
Although corn starch contains low concentrations of nitrogen, it is insufficient
for cell growth. In contrast, when hydrolysis is performed with nitric acid, fermentation proceeded well without additional ingredients. This indicates that nitric acid
works as an acid as well as nitrogen source for A. terreus. Acid-hydrolyzed sample
of corn starch was subjected to fermentation at pH 2 before autoclaving at 121 °C
for 20 min. Higher than 60 g L
−1
IA was yielded in flask fermentation from 140 g L
−1
of corn starch by A. terreus TN-484 [69]. Petruccioli et al. found that the productivity of IA was significantly affected by the degree of hydrolysis [67]. They achieved
18.40 g L
−1
IA titers from corn starch saccharified at 85 dextrose equivalents by
A. terreus NRRL 1960. The yield of IA was further increased to 63% by ultraviolet,
chemical, and mixed mutagenic treatment of wild-type A. terreus SKR10 strains [70].
The synthesis of IA from corn starch is a time-consuming and multiple-step process. To reduce the overall production time, Li et al. proposed an integrated process
in which saccharification and fermentation steps were combined by overexpressing
the glucoamylase gene in A. terreus strain. The IA titer reached 77.60 g L
−1
by
genetically engineered A. terreus from liquefied corn starch [26]. Researchers have
also screened other starch-rich wastes for the production of IA. Potato starch wastes
yielded high amounts of IA, which could be due to the higher glucose content [71].
A. terreus from mangrove soil has been recently isolated and utilized for the production of IA in a large volume (3 L) bioreactor [72]. The deionization of potato waste
removed the inhibitory ions like phosphate and improved the yield of IA. Under
optimized fermentation conditions, 29.69 g L
−1
IA was produced by A. terreus
strain C1.
In search of new alternative microorganisms, E. coli and A. niger species have
been successfully tested for the production of IA from starch-rich feedstocks.
Okamoto et al. proposed a direct IA production process by employing α-amylase
expressing E. coli [73]. In this process, two α-amylases from Bacillus amyloliquefaciens NBRC 15535
T
(BBA) and Streptococcus bovis NRIC 1535 (SBA) were
selected for hydrolysis of starch. With 1% starch released from SBA hydrolysate,
E. coli produced 0.15 g L
−1
IA after 69 h cultivation by pH-stat method, while BBA
displayed no noticeable activity. Gnanasekaran et al. investigated the feasibility of
K. Avasthi et al.