Lactic acid fermentation has great advantage over other bioconversions. The stoichiometry for homofermentation from hexose can be expressed,

СДА———— * 2C3HA

whilst lactate and acetate are formed from pentose without the release of carbon dioxide.

C5H10O5——— ► C3HA + C2H402

As indicated in the above stoichiometry, neither reaction loses any atoms of car­bohydrate during bioconversion. Thus, bioconversion using lactic acid fermenta­tion does not produce carbon dioxide and does not lose any material. Thus, this is an excellent counter-measure against the global problem of carbon dioxide accu­mulation. Processes by which glucose and xylose are first formed from lignocellu — losic agricultural waste and next converted into lactic acid (from hexose) /or lac­tic acid and acetic acid (from pentose) are an anaerobic bioconversion; and resulting organic acid is transformed into commodity chemicals such as polylac­tate, biodegradable plastics, by synthetic methods. Recent technology involved in polylactate production can blend the various forms of polyester such as PHA to improve the characteristics of the plastics. Our laboratory has developed the fer­mentation technology to produce PHB from lactic acid and acetic acid (9,10) and this PHB could be used for preparing mixtures of polylactate and PHA whose characteristics is better than that of lactate homopolymer.

Lactococcus lactis 10-1 isolated in our laboratory (11) is capable of effi­ciently fermenting xylose up to 50 g/1 initial concentration into acid (12,13). However, the rate of fermentation in xylose medium is slower than in glucose medium but a high dilution rate culture with cell recycling could be applied to stimulate xylose consumption rate overcoming lactate inhibition (14). We have observed an interesting phenomenon that NRSP, the product from natural rubber

waste, changed the molar ratio of the two products (lactic acid/ acetic acid) of lactic acid fermentation using xylose to increase lactic acid production (unpub­lished).

Bioconversion through lactic acid fermentation can therefore contribute to the reduction of the carbon dioxide concentration in atmosphere. We propose a new concept of biochemical industry named "Lactate Industry" (15,16) in which biomass is converted into lactic acid without carbon dioxide release and no ele­mental loss. The resulting lactic acid could be used to produce commodity chemi­cals such as biodegradable plastics. Used plastics would be digested into carbon dioxide by composting and recycled back to biomass by photosynthesis (Fig. 5).

2. Conclusion

Elevated levels of carbon dioxide in the atmosphere is a serious problem that will interfere with life of all organisms on the planet. To solve this crisis and to allow our continued survival, a favorable ecosystem in which all elements are recycled in the biosphere from the organic state to the inorganic state has to be maintained. Excess carbon dioxide is released into atmosphere by the consump­tion of fossil fuel to support our comfortable way of life. Carbon dioxide emission from non biological action can not yet be balanced by the recycling of elemental carbon in the biosphere. However, new technology introduced as a counter­
measure to this environmental problem will inevitably results in other changes to our ecosystem. Such change is sometimes serious problem that all living organisms in the earth never have.

To tackle the global task of reduction of carbon dioxide accumulation through the application of biotechnology, we must assess the other risks that the introduction of the new technology could cause. We have to avoid these dangers we would be suffered by the new technology.

[1] CFPP = Cold-filter plugging point, b) tbs = to be standardized.

The iodine value (IV; see Table III) has been included in the European standards and is based on rapeseed oil as biodiesel feedstock. It is set at IV = 115, which would exclude soybean oil (neat vegetable oils and their methyl esters have nearly identical I Vs) as biodiesel feedstock. The discussion in the previous section, however, shows that

[3] Corresponding author

© 1997 American Chemical Society