The effects of cell immobilization on the secretion of extracellular proteases and glucoamylase production by Aspergillus niger were investigated under a variety of immobilization techniques and culture conditions. Immobilization was achieved by means of cell attachment on metal surfaces or spore entrapment and subsequent growth on porous Celite beads. Free-suspension cultures were compared with immobilized mycelium under culture conditions that included growth in shake flasks and an airlift bioreactor. Cell attachment on metal surfaces minimized the secretion of proteases while enhancing glucoamylase production by the fungus. Growth on Celite beads in shake-flask cultures reduced the specific activity of the secreted proteases from 128 to 61 U g(-1), while glucoamylase specific activity increased from 205 to 350 U g(-1). The effect was more pronounced in bioreactor cultures. A reduction of six orders of magnitude in protease specific activities was observed when the fungus grew immobilized on a rolled metal screen, which served as the draft tube of an airlift bioreactor.

Sugarcane with a high content of sugar is a potential substrate for making vinegar through alcoholic and acetous fermentation. As an alternative to the longer traditional batch scale vinegar fermentation, a fermentation process involving successive discontinuous cycles of acetification was developed. The cycles standardized for 3 days of shaking (75 rpm) and addition of (NH4) 2SO4 and KH2PO4 were recycled with previous lots of fermentation resulting in vinegar production with a time period of 7.6 days compared with 24 days of batch fermentation. The volatile's characterization of sugarcane vinegar identified 50 compounds with 24 esters, 4 alcohols, 2 phenols (aromatic hydrocarbons), 3 ketones, 6 alkene derivative, 3 carboxylic acids, 1 aldehyde and 8 miscellaneous compounds. Physicochemical characterization of vinegar revealed a maximum total phenol content of 67.09 Ϯ 1.21 mg/100 mL in control while ascorbic acid content of 108.49 Ϯ 1.11 mg/100 mL was best obtained in the treatment of shaking at 75 rpm along with supplements. PRACTICAL APPLICATIONSThe result of this work will have practical applications in providing a less timeconsuming and highly efficient method for vinegar production thus, promoting an impetus to the setting up of natural vinegar production plants in this part of the country.

No abstract

No abstract

No abstract