Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
lucerne (alfalfa) exhibit protein contents from 12 to 18% (alfalfa only) DM, specifically
coming from ribulose 1,5 biphosphate-carboxylase/oxygenase (rubisco, E.C.
4.1.1.399), which is easily recovered by pressing fresh grasses to yield a press cake
and the so-called green juice suspending about 20% of diverse matter, turning to
brown juice after heating to 80°C and extraction of proteins. These serve at present
as forage but might be also a human nutrient when former pastures for cattle are
restructured as sources of raw materials for green biorefineries. The reduction of
cattle will also reduce the emission of CH 4 (which as a greenhouse gas is ca. 30
times more effective than CO 2) to 200 × 10 6 t/a. About 800 × 10 6 t CH 4 stems from
rice fields and marshes or lakes, besides anthropogenic contributions.
Green/brown juices contain 20 to 40% water-soluble carbohydrates (WSCs)
fermentable by lactobacilli to lactic acid. One or two percent suffices for perfect
silage of grass bales to maintain green refineries as CH 4 producers in the course of
one year. Exhaustive fermentation yields 70 to 120 kg/t dry grass upgradable to
aminium dilactide. 14 The finally resulting biodegradable polymer can replace films
or foils made so far from polyethylene, polypropylene, or related plastics, and help
combat many environmental problems.
21.6 GREEN BIOREFINERIES FOR ETHANOL
PRODUCTION
Besides glucose, other sugars of WSCs are also fermetable 15 ; for example, galactose,
xylose, mannose, fructose, rhamnose, maltose, or sucrose, present either as WSC or
as oligomers or polymers in the press cake (PC) as hemicelluloses or cellulose
(fibers/lignocelluloses). PC-hemicelluloses are suspendable in dilute NaOH and
subsequently depolymerized by weak acids. Such hydrolyzates yield ethanol by
fermentation. PC celluloses require a more severe treatment:
1. Hydrolysis in weak acids (0.3% sulfuric acid) at 175°C for 10 h, neutralization
by lime, and fermentation. The BIOL-version at 250°C needs only
seconds in 0.5% H 2SO 4 in a horizontal double-wall reactor equipped with
transporting screws. 1 The remaining lignin is apt to regreen deserts or
furnishes an aromatic fraction on pyrolysis, replacing benzene in the
“postoil” age. The lignin content of grasses ranges from 6 to 21%, impeding
the hydrolysis of fibres. Consequently, sugarcane (bagasse) and bamboo
(20–22% lignin) require severe digesting, almost comparable with
that of wood (20–30% lignin).
2. Application of thermophile enzymes adapted for the industry to operate
between 70 and 80°C to attack specific substrates, for example, pentosanes
making up 7–10% of softwood and 17–25% of hardwood. 1 The resulting
ethanol distills at 78°C, that is, under enzyme-active conditions
(AGROPOL process).
Ethanol has been produced from starchy sources by civilized people for millennia.
The world shortage of oil in 1973 provoked its use as a fuel with unexpected success.