Study on the onset mechanism of bio-blister degradation of polyolefin by diatom attachment in seawater.

It is essential to develop a mechanism for lowering the molecular weight of polyolefins to achieve biodegradation in seawater. In this study, a polypropylene/polylactic acid blend sample was first subjected to photodegradation pretreatment, and it was confirmed that in pure water, the acid generated promotes the polypropylene degradation (autoxidation), while in alkaline seawater, the promotion was inhibited by a neutralization reaction. In the autoxidation of polyolefins in alkaline seawater, aqueous Cl- was also the inhibitor. However, we found that autoxidation could be initiated even in seawater by lowering the pH and using dissociation of ClOH (called blister degradation). The blister degradation mechanism enabled autoxidation, even in seawater, by taking advantage of the ability of diatoms to secrete transparent exopolymer particles (TEP) to prevent direct contact between the surface layer of polyolefins and alkaline seawater. We named blister degradation in seawater with diatoms as bio-blister degradation and confirmed its manifestation using linear low-density polyethylene (LLDPE)/starch samples by SEM, IR, DSC and GPC analysis.

Itaconic acid production using sago starch hydrolysate by Aspergillus terreus TN484-M1.

Sago starch was hydrolyzed using either chemical agents, or enzymes at various pH and concentrations. Hydrolysis using 5000 AUN/ml (0.5%, w/v) glucoamylase exhibited the highest itaconic acid yield up to 0.36 g/g sago starch, whereas hydrolysis using nitric acid at pH 2.0 yielded 0.35 g/g sago starch. The medium was optimized and the composition was (g/l) 140 sago starch, 1.8 corn steep liquor, 1.2 MgSO(4).7H(2)O and 2.9 NH(4)NO(3). When the optimal conditions of hydrolysis and medium composition were applied to itaconic acid production in a 3-l jar fermentor, the itaconic acid production was 48.2 g/l with a yield of 0.34 g/g sago starch. This was filtered from the cultured broth and 37.1g of itaconic acid was recovered with a purity of 97.2%. This result showed that sago starch could be converted to a value-added product with only a simple pretreatment.

Scale-up of L-lactic acid production by mutant strain Rhizopus sp. MK-96-1196 from 0.003 m3 to 5 m3 in airlift bioreactors.

In order to study the feasibility of commercial-scale L-lactic acid production by Rhizopus sp. MK-96-1196 using large scale airlift bioreactors (ALBs), a scale-up study from 0.003 m3 to 5 m3 ALB was carried out using oxygen transfer rate (OTR) as the scale-up criterion. Enhanced L-lactic acid production was achieved at OTRs higher than 0.28 (g-O2/l/h) irrespective of the scale of the bioreactor in question: in the range of 0.003 m3 to 5 m3, more than 90 g/lL-lactic acid was produced with a yield of approximately 80%, based on the initial glucose concentration. In future research, we plan to design an ALB greater than 3000 m3 (working volume: 2000 m3) for further studies on the production of L-lactic acid in large quantities.

Stereoblock poly(lactic acid): synthesis via solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) and poly(D-lactic acid).

Stereoblock poly(lactic acid) consisting of D- and L-lactate stereosequences can be successfully synthesized by solid-state polycondensation of a 1:1 mixture of poly(L-lactic acid) and poly(D-lactic acid). In the first step, melt-polycondensation of L- and D-lactic acids is conducted to synthesize poly(L-lactic acid) and poly(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these poly(L-lactic acid) and poly(D-lactic acid) are melt-blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt-blend is subjected to solid-state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high-molecular-weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher-molecular-weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in M(w) of stereoblock poly(lactic acid) (sb-PLA) as a function of the reaction time.

Production of D-lactic acid by bacterial fermentation of rice starch.

D-Lactic acid was synthesized by the fermentation of rice starch using microorganisms. Two species: Lactobacillus delbrueckii and Sporolactobacillus inulinus were found to be active in producing D-lactic acid of high optical purity after an intensive screening test for D-lactic acid bacteria using glucose as substrate. Rice powder used as the starch source was hydrolyzed with a combination of enzymes: alpha-amylase, beta-amylase, and pullulanase to obtain rice saccharificate consisting of maltose as the main component. Its average gross yield was 82.5%. Of the discovered D-lactic acid bacteria, only Lactobacillus delbrueckii could ferment both maltose and the rice saccharificate. After optimizing the fermentation of the rice saccharificate using this bacterium, pilot scale fermentation was conducted to convert the rice saccharificate into D-lactic acid with a D-content higher than 97.5% in a yield of 70%. With this yield, the total yield of D-lactic acid from brown rice was estimated to be 47%, which is almost equal to the L-lactic acid yield from corn. The efficient synthesis of D-lactic acid can open a way to the large scale application of high-melting poly(lactic acid) that is a stereocomplex of poly(L-lactide) and poly(D-lactide). Schematic representation of the production of D-lactic acid starting from brown rice as described here.

Enhanced production of L-lactic acid by ammonia-tolerant mutant strain Rhizopus sp. MK-96-1196.

By a monospore isolation technique, Rhizopus sp. MK-96-1 was selected from colonies of Rhizopus sp. MK-96, which was isolated from the soil sample collected in Fujieda, Japan, and used as a parent strain. By the ammonia-concentration-gradient agar plate technique after mutation using N-methyl-N'-nitro-N-nitrosoguanidine (NTG) method, a mutant strain designated Rhizopus sp. MK-96-1196 producing more than 90 g/l L-lactic acid under pH control using liquid ammonia in an airlift bioreactor was successfully isolated. Compared with the parent strain, this mutant strain produced about twofold the amount of L-lactic acid in half fermentation time under the same culture conditions. Ammonium L-lactate was recovered and purified as free L-lactic acid via n-butyl L-lactate. The ammonia used for pH control in the fermentation broth was recovered as liquid ammonia during the recovery and purification process and subsequently reused for the next fermentation. Thus, we have developed a new highly purified L-lactic acid production process without producing recalcitrant wastes, e.g., CaSO4 (gypsum).

Production of L-lactic acid from corncob.

The optimum temperature, initial pH, amount of added enzyme and substrate (corncob) for the hydrolysis of corncob by Acremonium cellulase were 35 degrees C, 4.5, 10 u/g-corncob and 100 g/l, respectively. Under the optimum conditions, more than 55 g/l of reducing sugars were hydrolyzed from 100 g/l of corncob to 34 g/l of glucose and 12 g/l of xylose based on dried corncob. More than 25 g/l of L-lactic acid was produced from this enzymatic hydrolyzate and less than 5 g/l of xylose remained in the 3-l airlift bioreactor. The production of L-lactic acid by simultaneous saccharification and fermentation (SSF) was also carried out in the 3-l airlift bioreactor using Acremonium thermophilus (cellulose-producer) and Rhizopus sp. MK-96-1196 (lactic acid-producer). More than 24 g/l of L-lactic acid was produced from 100 g/l of untreated raw corncob.

Optimization and scale-up of L-lactic acid fermentation by mutant strain Rhizopus sp. MK-96-1196 in airlift bioreactors.

We determined the optimum culture conditions such as inoculum size, initial starch concentration, pH during the fermentation and aeration rate for L-lactic acid production by Rhizopus sp. MK-96-1196 in a 3-l airlift bioreactor. More than 90 g/l of L-lactic acid was produced from only partially enzymatically hydrolyzed corn starch with a production rate of 2.6 g/l/h and a product yield of 87% based on the starch consumed under the optimum conditions in the 3-l airlift bioreactor. Scale-up from the 3-l to a 100-l airlift bioreactor for L-lactic acid fermentation was carried out using V(s)(cm/s) as a scale-up criterion. The production rates and yields of L-lactic acid in both bioreactors appeared to be fairly well correlated with k(L)a (1/h).