Methanol Based Proteins

Methanol can also serve as the source for single-cell protein production. Single-cell proteins (SCP) refers to proteins produced by a variety of microorganisms degrading hydrocarbon substrates while gaining energy [108, 113]. The protein content depends on the type of microorganism; bacteria, yeast, mold, etc. The use of microorganisms in human alimentation has been practiced since ancient times, in the form of yeasts used in brewing and baking, and bacteria in cultured dairy products such as cheese, yogurt, and sour cream. In modern times, the possibility of using proteins produced by microorganisms for animal and human alimentation first emerged in Germany during World War I. The main development of SCP, however, began during the 1950s when the petroleum industry realized that, by the degradation of hydrocarbons, some microorganisms could produce high-quality proteins that were suitable for animal feed or as a nutritional source for human food. Because of the possibility of contamination and build-up of carcinogenic compounds in animals fed with SCP produced from oil products, however, methanol was chosen as a substitute. In contrast with petroleum-derived feeds, methanol is non-carcinogenic, forms a homogeneous solution with the aqueous nutrient salt solutions used in the process, and can be readily separated from the protein products after their formation. A number of companies, including Shell, Mitsubishi, Hoechst, Phillips Petroleum and ICI, have studied the bac terial fermentation process. For some time, ICI operated a commercial plant in Billingham, England, producing 70 000 tonnes of SCP from 100000 tonnes of methanol per year. The bacteria obtained had a very high protein content, with the dried cells containing up to 80% protein (much higher than other types of food such as fish and soybean). As the structure of the bacteria was highly complex, a wide range of amino acids - including in particular aspartic and glutamic acid, alanine, leucine and lysine - was obtained. The overall quality of SCP produced from methanol by the ICI process was very high, and the product sold as an animal feed under the name Pruteen.

Besides serving as a medium for microorganism culture, methanol was also found substantially to increase growth rate in a variety of plants [108]. In plants with C3 metabolism - for which the first product of photosynthesis is a three-carbon sugar - significantly higher photosynthetic productivity has been observed, especially in regions with high light intensity such as the South-Western United States. C3 plants include for example sunflower, watermelon, tomato, strawberry, lettuce, and eggplant. Methanol sprayed onto the plants is rapidly absorbed by the foliage and metabolized to CO2, sugars, amino acids and other structural components. It is thus used as a concentrated source of carbon in place of CO2 (1 mL of liquid methanol contains about as much carbon as 2 000 000 mL of air).

Methanol was also found to be an economic and effective means ofinhibiting the process of photorespiration; this describes the plant uptake of oxygen, which is competing with CO2 uptake for photosynthesis. Oxygen assimilation results in the breakdown of sugars, reversing the photosynthetic process. When exposed to stressful conditions such as high light intensity and high temperatures, the stoma-ta (tiny pores used by the plant to absorb atmospheric CO2) close, reducing the uptake of CO2, and this results in increased photorespiration. This can stop plant growth for several hours during the hottest period of day. The control of photorespiration is, therefore, key to enhancing the photosynthetic yield of plants. Further studies on the effects of methanol on the complex growth mechanism of plants are needed before large-scale applications can be envisioned. Methanol, however, has a good potential to effect significant improvements in crop productivity.

With an increasing world population, agricultural production might encounter difficulties in providing sufficient protein for food and animal feed. The "Methanol Economy" could, therefore, also supplement essential protein needs through SCP.

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