Microbial Lactic Acid Production from Renewable Resources - Sustainable Biotechnology: Sources of Renewable Energy - page 223

and Bacillus coagulans DSM 2314 [21]. Moldes et al [86] investigated the lactic
acid production by Lb. delbruechii NRRL-B445 from NaOH-pretreated wood with
SSF and a 67% conversion of cellulose into lactic acid and productivity of 0.94 g/l · h

were achieved in fed-batch operation supplying with fresh nutrient and enzymes.
Most research on lactic acid production focus on the conversion of the cellulose
fraction of lignocellusic biomass. Lb. pentosus, Lb. brevis and Lc. lactis can fer-
ment pentoses to lactic acid. Especially, Lb. pentosus can ferment hexose (glucose)
through the EMP pathway under anaerobic conditions producing lactic acid as the
sole product. This strain can also convert pentoses (xylose and arabinose) to equal
moles of lactic acid and acetic acid through PK pathway [17]. Lb. pentoses ATCC-
8041 has been used for converting glucose, xylose and arabinose in the hydrolytes
of trimming vine shoots, barley bran husks, and corn cobs to lactic acid in SHF
process. After 40-h fermentation, glucose, xylose and arabinose were almost com-
pletely utilized. The highest lactic acid yield of 0.76 g/g pentose was achieved by
using hydrolysate from trimming vine shoots [16]. L. pentoses ATCC-8041 was also
used for lactic acid production from aqueous-ammonia-treated corn stover by Zhu
et al [17]. Lactic acid yield of 0.65 g/g and productivity of 0.7 g/l h were achieved

with fed-batch SSF process. Lb. bifermentans DSM 20003 has been used to convert
glucose, arabinose and xylose from wheat bran hemicellulosic hydrolysate to lactic
acid [77]. The maximum lactic acid yield, productivity and sugar utilization were
0.83 g/g consumed carbohydrate, 1.17 g/l

·

h, and 76%, respectively.
The filamentous fungus R. oryzae can also metabolize xylose as the sole
carbon source to produce lactic acid. Ruengruglikit and Hang [88] obtained lac-
tic acid yield of 0.3 g/g and productivity of 0.31 g/l

·

h from corncobs using
R. oryzae after 48 h of fermentation. Lactic acid yield of 0.80 g/g and productiv-
ity of 0.99 g/l

·

h was obtained with R. oryzae HZS6 from corncob liquors obtained
from acid hydrolysis [87].
Other raw materials, including sludges, have been used to produce lactic acid via
SSF without any pretreatment due to the large amounts of short fiber cellulose and
polysaccharide degradation products in the sludge. Lactic acid yield of 0.97 g/g
carbohydrates and productivity of 2.9 g/l

·

·

h were obtained from biosludge with
Lb. rhamnosus ATCC 7469 [82]. Lb. rhamnosus ATCC 9595 was another strain
used to produce lactic acid from the Kraft pulp mill biosludge and lactic acid yield
of 0.38 g/g biosludge and productivity of 0.87 g/l · h were obtained with SSF [81].

5 Expert Commentary and 5 Year View

In the United States, Archer Daniels Midland (ADM) and Natureworks LLC (Joint
venture of Cargill and Teijin) are currently producing lactic acid from corn and other
starchy biomass using microbial fermentation technology. The produced lactic acid
at ADM is targeted for PLA and ethyl lactate (a solvent which dissolves many plas-
tics and can soften the plastic for removal from a surface). Natureworks LLC is the
first company to offer a family of commercially available biopolymers derived from