Kan suksa khwam penpaidai nai kan phalit krot manao chak watsadu luathing lae watthudip rakhathuk bangchanit doi chua Aspergillus niger.

Fermentation using concentrated pineapple peel extract obtained by various treatments revealed that the concentrate treated through the following steps: Reverse osmosis, Ultra filtration and Ion exchange gave best result. However consistent acid yield could not be obtained in fermentation using different lot of concentrate which was produced by the same operation. By using good lot of the substrate, commercial feasible acid yield (64.38 %) was achieved. Chemical analysis of several lots of the concentrate indicated that the one which gave high acid was lower in magnesium content. However experiment was carried out and elucidated that if was not magnesium that play the role. In order to utilize starch raw materials effectively, a study on glucoamylase produced by A. niger An12 was carried out. Maximum enzyme activity of 67,800 - 68,800 units was obtained in solid substrate culture grown in mixture of rice bran and water of 41.2 % moisture content, pH ranging from 4.8 - 5.4 and incubated at 32 deg. celsius for 60 - 78 hours. The enzyme was purified to 12.2 folds using DEAE-Cellulofine and Sephadex G-150 column chromatography. The purified glucoamylase was homogeneous as judged by polyacrylamide disc gel electrophoresis. Molecular weight of the enzyme was estimated to be 59,000 by gel filtration on a Sephadex G-150 column. Optimum conditions for enzyme activity was at 60 deg. celsius and pH 5.0. The enzyme was stable for at least 30 minutes at a pH range of 3.5 - 6.5 and temperature range of 30 - 60 deg. celsius. Solid substrate fermentation on cassava waste using koji as enzyme source as well as inoculum was compared to that using spore inoculum. The results revealed that there was no significant difference between the two procedures concerning either acid yields or fermentation time. On the contrary, koji was better than spores when used as inoculum in submerged fermentation on raw or cooked cassava starch. Approximately 31 - 35 % acid yields was obtained by using raw starch as substrate, whereas 47 - 50 % yields was produced on cooked starch.