5660

5282

كارشناسي ارشد

علوم و صنايع غذايي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده كشاورزي

1389

سيزده،82ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

محمود شيخ زين الدين، صبيحه سليمانيان زاد

مهدي كديور

3/12/89

جواد كرامت، آذرشاه پيري

مهندسي كشاورزي

ID5282

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Optimization of Exopolysacchraide Production by Lactobacillus rhamnosus Using RSM Design Abstract Most of the biothickeners in current use by food industry are polysaccharides from plants e g starch pectin locust bean gum guar gum or seaweeds carrageenan alginate Because most of the plant carbohydrates used need some form of chemicall modification therefore microbial exopolysaccharides EPS as an alternative class of biothickeners has atracted interest of many researchers in recent years Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products where they serve as viscosifying stabilizing emulsifying or jell agents Since most lactic acid bacteria LAB are food grade microorganisms with GRAS status Generally Recognized As Safe the use of the secreted EPS as natural alternatives to produce all natural food products without additives from LAB has received increased attention The aim of this study was to determine the optimum conditions for EPS production by L rhamnosus to achieve maximum EPS production Potential of four strains of L rhamnosus Lr M2 Lr 519 Lr GG Lr 7469 were determined for their ability for EPS production in Sucrose Man Rogosa and Sharpe Su MRS medium The highest amount EPS was obtained for strain Lr 519 To enhance EPS production by Lr 519 the ability of Lr 519 for EPS production in skimmed milk and MRS medium were studied The EPS production by Lr 519 in skimmed milk was higher than that in the MRS medium In second stay of study to investigat the influence of carbon source on EPS production sucrose glucose and lactose were added at concentration 20 g L to skimmed milk culture The EPS production by Lr 519 in skimmed milk enriched with sucrose was higher than that in presence of skimmed milk contaning other sugars To investigat the influence of nitrogen source on EPS production yeast extract yeast nitrogen base YNB peptone and tryptophan were added at concentration 20 g L to skimmed milk cultures The EPS production by Lr 519 in skimmed milk enriched by yeast extract and YNB was higher than that in skimmed milk enriched of other nitrogen sources In this study a polysaccharide free nitrogen source YNB was chosen to avoid interference of compounds found in yeast extract that interfere with EPS purification and quantification To determine the optimum conditions for EPS production by Lr 519 in skimmed milk medium the influence of combined effects of sucrose and YNB concentrations incubation time and pH on EPS production during batch cultures was tested with a central composite design CCD using a response surface methodology RSM A significant relationship was observed between all factors linear and squared and EPS production except YNB concentration which did not have a linear effect on EPS production The highest EPS concentration 248 mg L was obtained at incubation time of 60 h pH 5 5 sucrose concentration of 3 and at YNB concentration of 0 5 The optimum incubation time pH sucrose and YNB concentration for EPS production were 49 h 5 8 24 6 and 10 g L respectively with a predicted yield of 235 mg L of exopolysaccharide liter The actual EPS production under these conditions was 239 mg L indicate efficiency of the chosen model This study showed the potential of L rhamnosus 519 as a suitable strain for producing EPS in skimmed milk medium and improving EPS production Key words Exopolysaccharide EPS Lactic acid bacteria L rhamnosus 519 Response Surface Methodology RSM

محمود شيخ زين الدين، صبيحه سليمانيان زاد

مهدي كديور

جواد كرامت، آذرشاه پيري