In order to reduce energy input in direct ethanol production from raw starch by co-immobilized Aspergillus awamori(A) and Zymomonas mobilis(Z), A-Z 36 culture system which was changed to anaerobic after 36 h of aerobic fermentation without sterilization was investigated. This immobilized cell system can not be carried out under unsterile conditions because of growth of microbial contaminants from original medium. Among some food additives such as sorbic acid, benzoic acid, dehydroacetic acid, p-hydroxybenzoic acid, Vantocil IB and Neupectin-L, Vantocil IB and Neupectin-L were a potent antibacterial agent in A-Z 36 culture cell system and were not affected in hydrolysis of substrate as compared with the case of control. Ethanol yield(6.9 g/ℓ) in system of addition of 0.1% Neupectin-L was slightly higher than that in control(6.4 g/ℓ). When 2% starch was fed five times in fed-batch culture with 0.1% Neupectin-L, ethanol yield and productivity were 34 g/ℓ and 2.0 g/ℓ/day, respectively.