Hydrolysis of isolated coffee mannan and coffee extract by mannanases of Sclerotium rolfsii.

Different mannanase preparations obtained from the filamentous fungus Sclerotium rolfsii were used for the hydrolysis of coffee mannan, thus reducing significantly the viscosity of coffee extracts. Mannan is the main polysaccharide component of these extracts and is responsible for their high viscosity, which negatively affects the technological processing of instant coffee. Coffee mannan was isolated from green defatted Arabica beans by delignification, acid wash and subsequent alkali extraction with a yield of 12.8%. Additionally, coffee extract polysaccharides were separated by alcohol precipitation and were found to form nearly half of the coffee extract dry weight. These isolated mannans as well as the mannan in the coffee extract were efficiently hydrolysed by the S. rolfsii mannanase, which resulted in significant viscosity reductions. Concurrently, the reducing sugar content increased continuously due to the release of various mannooligosaccharides including mannotetraose, mannotriose, and mannobiose. Both a partially purified, immobilised and a soluble, crude mannanase preparation were successfully employed for the degradation of coffee mannan.

Biogas production from Jatropha curcas press-cake.

Seeds of the tropical plant Jatropha curcas (purge nut, physic nut) are used for the production of oil. Several methods for oil extraction have been developed. In all processes, about 50% of the weight of the seeds remain as a press cake containing mainly protein and carbohydrates. Investigations have shown that this residue contains toxic compounds and cannot be used as animal feed without further processing. Preliminary experiments have shown that the residue is a good substrate for biogas production. Biogas formation was studied using a semicontinous upflow anaerobic sludge blanket (UASB) reactor; a contact-process and an anaerobic filter each reactor having a total volume of 110 L. A maximum production rate of 3.5 m3 m"3 d"1 was obtained in the anaerobic filter with a loading rate of 13 kg COD m~3 d"1. However, the UASB reactor and the contact-process were not suitable for using this substrate. When using an anaerobic filter with Jatropha curcas seed cake as a substrate, 76% of the COD was degraded and 1 kg degraded COD yielded 355 L of biogas containing 70% methane.