Master Degree / Yüksek Lisans Tezleri
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Master Thesis Lactic Acid Production by Lactobacillus Casei Nrrl B-441 Immobilized in Chitosan Stabilized Ca-Alginate Beads(Izmir Institute of Technology, 2005) Gündüz, Meltem; Harsa, Hayriye Şebnem; Harsa, Hayriye Şebnem; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyHaving two optically active forms, D(-) and L(+) lactic acid has long been used in the food, chemical, textile, pharmaceutical and other industries. 90 % of the worldwide production of lactic acid is by bacterial fermentation. Recently, there is an increasing interest in the production of L(+) lactic acid, since it is a potential substrate for polylactic acid that is biocompatible and can be used for medical purposes. Whey, which is a by-product of dairy industry, contains approximately 5 % (w/v) lactose. Since whey has a high BOD content, it possesses serious environmental problems. Whey lactose is a good substrate for lactic acid bacteria and can be used for L(+) lactic acid fermentations. This study focuses on the production of lactic acid from whey by Lactobacillus casei NRRL B-441 immobilized in chitosan stabilized Ca-alginate beads. Higher lactic acid production and lower cell leakage were observed with alginate-chitosan beads compared with Ca-alginate beads. The highest lactic acid (131.2 g/l) was obtained with cells entrapped in 1.3-1.7 mm alginate-chitosan beads prepared from 2 % Na-alginate. acid production and lower cell leakage were observed with alginate-chitosan beads compared with Ca-alginate beads. The highest lactic acid (131.2 g/l) was obtained with cells entrapped in 1.3-1.7 mm alginate-chitosan beads prepared from 2 % Na-alginate. The gel beads produced lactic acid for 10 consecutive batch fermentations without marked activity loss and deformation. Response surface methodology was used to investigate the effects of three fermentation parameters (initial sugar, yeast extract and calcium carbonate concentrations) on the concentration of lactic acid. No previous work has used statistical analysis in determining the interactions among these variables in lactic acid production by immobilized cells. Results of the statistical analysis showed that the fit of the model was good in all cases. Initial sugar, yeast extract and calcium carbonate concentrations had strong linear effects on lactic acid production. Maximum lactic acid concentration of 136.3 g/l was obtained at the optimum levels of process variables (initial sugar concentration.147.35 g/l, yeast extract concentration. 28.81 g/l, CaCO3 concentration.97.55 g/l). These values were obtained by fitting of the experimental data to the model equation. The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in lactic acid production using alginate-chitosan immobilized cells.Master Thesis Kinetic Modelling of Lactic Acid Production From Whey(Izmir Institute of Technology, 2004) Altıok, Duygu; Tokatlı, Figen; Tokatlı, Figen; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyLactic acid is a natural organic acid, which is used in pharmaceuticals, chemical, textile and food industries. Since only L(+) lactic acid is found in normal human metabolism, the microbial production of L(+) lactic acid has great interest in recent years. Use of whey lactose to produce lactic acid by fermentation process is favourable due to the low cost of whey and its high organic matter content. Whey is suitable medium for some fermentations. However, its high lactose content makes it a potential environmental pollutant. The disposal problem of this pollutant could be overcome by utilization of whey lactose in the lactic acid production.The aim of this study was to develop a kinetic model for lactic acid productionfrom whey by Lactobacillus casei, which is a homofermentative lactic acid bacteria andcapable of producing L(+) lactic acid. Within this context, several batch fermentationexperiments in fermenter were performed at 37 C and pH 5.5. Seed culture that was produced in shake flask fermentations was used as the inoculum for the fermenter.Before the fermentation experiments, some of the proteins in whey were denatured by heat treatment and separated by centrifugation. This treatment decreased the protein amount from 11.15 % to 5.2 % in whey powder. The lactic acid production was associated with the biomass growth up to a certain time, but then a non-growth associated lactic acid production was observed in most of the fermentations except for the 9.0 g l-1 initial substrate fermentation run, where all the substrate was utilized when the stationary phase was attained. The maximum theoretical productivity was obtained as 2.4 g lactic acid l-1 h-1 in the fermentation with S0 equals to 35.5 g l-1. The kinetic parameters were obtained from different fermentation runs. mmax and KS were found as 0.265 h-1 and 0.72 g l-1, respectively. The average product yield coefficient, YPS, was determined as 0.682 g lactic acid (g lactose)-1.The modified form of logistic equation with product inhibition term for biomassThe modified form of logistic equation with product inhibition term for biomass growth, Luedeking and Piret equation for product formation and substrate utilization considering the consumption of substrate for product formation and maintenance, described most of the fermentation experiments in this study with high accuracy (SSE range was 0.0804-0.1531). The toxic powers in these inhibition terms, h and f, made the model applicable for the fermentation experiments with low and high initial substrate concentrations. In case of high initial substrate concentration fermentation (S0. 95.7 g l-1), the same model explains only the exponential phase of biomass and its product formation eventhough the substrate consumption is predicted very well.product formation eventhough the substrate consumption is predicted very well.