SUB-TASKS
Extraction of Proteins and Lactic Acid from Grass and Grass Silage Juices
The Green Biorefinery concept for Austria is different from other international projects in so far as it takes into account special needs typical of rural regions in Austria. The main objective is to facilitate a continuous all year round operation of the plant. For that reason, the concept involves not only processing of direct-cut grass, but also of silage, which can be prepared in the growing season and stored in a silo. A wide range of completely different products from grass as a raw material, which can be provided by agriculture on the basis of sustainable methods could be produced in a single plant.
Main characteristics of the Green Biorefinery include:
- Zero-waste and zero-emission extraction of valuable substances from grass (residual material is converted in a biogas plant)
- Non-use of auxiliary materials in the manufacturing process
- Self-sufficient energy supply for the plant
- Serves as an example for the processing and utilization of renewable raw materials (The generation of a variety of products from a single raw material or a mixture of raw materials increases the economic efficiency of manufacturing processes)
Abbildung 1: Functional Diagram of the Austrian Green Biorefinery, © Joanneum Research
Proteins
Proteins are an essential element of the nutrition for humans and animals; they also are an important raw material for technical applications such as adhesives and for the pharmaceutical and cosmetics industries. So far, studies conducted worldwide investigated exclusively the extraction of proteins from the leaves of fresh green plants, which requires a cost intensive campaign operation from May to October. Storing green crop material in the form of silage and the extraction of proteins from silage juice would permit all year round production. This form of protein production has not been studied sufficiently as yet.
One of the studies contributing to the development of a concept for a Green Biorefinery in Austria “Gewinnung von Proteinen aus Grassäften” investigated the aspects below:
- Differences between proteins from direct-cut green material and from silage concerning structure (proteins, peptides, free amino acids), separability, and processing
- Suitability of “GE-free” grass juice proteins for the production of high-performance specialty animal feed (milk substitute)
- Demonstration of potential alternative products for milk substitutes
Abbildung 2: Lucerne Press Juice, © Kornberg Institut
Cooperation with partners from the industry (e.g. the casein manufacturer LACTOPROT AG) and various research institutions (Institut für Ressourcenschonende und Nachhaltige Systeme (RNS) and Institut für Biotechnologie at the TU Graz; BAL Gumpenstein / Institut für Pflanzenbau und Kulturlandschaft, IFA Tulln / Abteilung für Umweltbiotechnologie) is to contribute to the realization of these objectives.
Test series used various species of high-protein grassland biomass (clover/grass mixture, hybrid rye-grass, permanent meadow lucerne, orchard grass), direct-cut and as silage. It has been shown that the technologies used (ultra-filtration and coagulation / centrifuging) can extract only a small part of the crude proteins contained in the juices. Only direct-cut lucerne yielded sufficient amounts of protein. The separation of protein concentrate from direct-cut lucerne would be a technologically feasible method to generate a high-quality product.
The tested silage press juice contained only 5 to 10% of the crude protein available in the silage. This means that none of the tested technologies is suited for an economically reasonable, large-scale separation of proteins from silage juice. However, the silage juices contained a substantial proportion of free amino acids. The separation of these amino acids would require more complex technologies. The analysis of silage amino acids from an economic perspective has nevertheless shown that investing in the further development of new separation technologies will be necessary
Lactic Acid
Lactic acid is much in demand as a raw material for the chemical industry and is used in the production of biodegradable plastics, environmentally friendly solvents, and special chemicals as well as in the foodstuff industries. There is a wide domestic and international market for lactic acid. Currently, Austria’s imports of lactic acid amount to some 770 tons per year. However, the market potential is estimated to be much higher with some 15,000 tons per year.One of the most economical methods of manufacturing lactic acid consists in the fermentation of solids. Ensiling, especially when using green crops, is a process relying on lactic-acid fermentation; this process involves the formation of lactic acid and, at the same time, uses the preservative effect of this substance. Improvements in ensiling technology may increase lactic acid yields to such an extent that a valuable and marketable product will be generated in this process.
Comprehensive studies of the extraction of lactic acid from grass silage have not been conducted as yet. The sub-task “Gewinnung von Milchsäure aus Grassilagesaft” aimed to develop the fundamentals of an integrated separation technology that permits to extract lactic acid and amino acids from grass silage juices thus generating marketable products.
Abbildung 3: Elektrodialysis Installation, BOKU Wien, Institut für Lebensmitteltechnologie
The dry matter contained in silage press juices consists of approx. 30% lactic acid, 8 to 22% sugars, 24 to 34% crude protein, and 23 to 30% of ash. Free amino acids account for 85 to 100% of the crude protein. The extraction of silage press juice requires a highly developed fractioning technology. The first successful trial pressings in 2001, which resulted in an average lactic acid yield of some 50% were followed, in 2002, by dual pressings of silage with a higher moisture content and re-humidification of the first press cake. This method achieved lactic acid yields of approx. 85%. A pilot plant for the fractionation, pre-filtration and press cake conditioning will be realized in the season of 2004 and perform a trial run.
The composition of the grass silage juices (lactic acid and free amino acids) shows a high potential for economic exploitation. However, separation of these products requires the development of new, more complex technologies. An interesting alternative, for example, consists in the re-fermentation of the press juice. This approach was successfully tested and resulted in the conversion of sugar into additional quantities of lactic acid.
In order to promote the development of new separation technologies researchers initiated a cooperation with the Institut für Lebensmitteltechnologie of the Universität für Bodenkultur, Vienna. They tested and assessed various types of process. The proposed methods involve a combination of membrane technologies (ultra and nanofiltration as well as electrodialysis) with chromatography. Electrodialysis was especially successful in separating lactic acid from amino acids and ashes in a two-step process; this method achieved a lactic acid yield of 91%. A combination with chromatography will probably permit to extract various fractions of valuable substances.
Other tests aimed to prepare ethyl lactate, which could be used as a “green” solvent. It has been shown that a sustainable design of the process requires further research and development. An economic calculation performed within the project established the costs to be expected for this process technology.
