الفهرس 
Lactic acidOnly 14 pages are availabe for public view
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Abstract
The present investigation dealed with utilization of xylose as a carbon source for the production of lactic acid and nisin Z by the strain of Lactococcus lnc/is 10-1. By-PI-oducts of some food industry, residuals of crops, wood, etc. contain large amounts of hemicellulose which yields xylose upon hydrolysis. So, the experi~nents were designed to use xylose as a carbon source in the cultivation media for lactic acid and nisin Z production. Furthermore, because the microorganism is a homolactic fermenter such fermentation would not produce carbon &oxide from the degradation of plant biomass and would thus result in, although sniall reduction in the atmospheric concentration of this gas. I<csullso f i~lvc~tigcuil~l I~>(: i~~u~m~al nrizcdi n the following pointy: I- Lactic acid production: 1- The results with pH-state batch culture using various concentrations of xylosu (i.c. 30, 50 and 130 &L) and 10% (vlv) inoculum size of preculture time for four hours showed that the most suitable xylose concentration for lactic acid production by Lactococcus lactis 10-1 was 50 gmL. This concentration gave the hghest level of xylose conversion rate with the highest level of all tested products (L-lactate, DL-lactate and acetate) except D-lactate which attained its hghest level with 30 gm/L of oxylose concentration. Also, using inoculum size 10% (vlv) and pre-culture time of four hours reduced the fermentation time to a great extent. 2- EIcclrodialysis l’cr~ncnlationm ethod with microlillcr (ED-M1:) was used in ordcr to stimulate thc fermentation process by releasing the effect of end products. This method enhanced the fermentation process and increased lactatc product1 VI ty by reducing the fermentation time to about 83% and 58% compared to fermentation time used in conventional batch culture (pH-state) with xylose concentrations of 50 and 80 gm/L, respectively. 3- Continuous culture with pH-dependent feed and turbidity control system was used to increase the cell density of microorganism owing to the advantages of continuous culture. For this purpose, different concentrations of xylose and several dilution rates were tested and the results showed that: a) The concentration of all tested products decreased with increasing the dilution rate with the same concentration of xylose. b) Productivity of the end products (gm/L/h) was increased with increasing the dilution rate. C) ’l’he residual xylose in spent medium followed the same trend of lactate productivity. For controlling of residual xylose in spent mecisurn, there are two ways: using low concentration of xyPose in the fresh medium, or using low dilution rate. d) Xylose concentration of 20 gm/L with dilution rate of 0.22 h-1 gave relatively the best results for lactate and acetate productivities with low concentration of residual xylose in spent medium compared with other xylose concentrations and ddution rates.