The theoretical part of the diploma thesis deals with cultivation of the plant Stevia rebaudiana. This plant is 300x sweeter than sucrose. It is often used as a compensation for sugar sweetener, suitable for diabetics and people who suffer from overweight. There is processed the characteristics of the plant, botanical description, conditions of cultivation and chemical composition. There are described the methods of determination of steviol glycosides. The practical part elaborates on a sensorical analysis. This analysis has two parts. The first part is the evaluation of stevia concentrates with the flavour of aronia, sour cherry and beetroot and stevia powder in 10 milk products bought in supermarkets. The second part deals with the evaluation of black tea sweetened with few different easily available sorts of sweetening products. The currently valid legislative in the area of the Czech Republic allows the food industry to use steviol glycosides of high purity under the name E960. The use of the plant stevia or its parts as food isn't enabled.

SyfteSyftet med denna laborativa pilotstudie in vitro var att undersöka hur den mikrobiella sammansättningen och pH i den orala biofilmen påverkades vid upprepad exponering för Stevia (steviosid och rebaudiosid A), sackaros eller en kombination av reb A och sackaros. Ett ytterligare syfte var att studera om isolat av orala bakterier kunde metabolisera reb A i buljongkultur. Material och metodBiofilmer från tre personer blev exponerade för 0,025 % steviosid, 0,025 % reb A eller 10 % Todd Hewitt (TH) under 15 minuter tre gånger dagligen i fyra dagar. Artbestämning gjordes i början och slutet av försöken. Biofilmerna exponerades för 0,025 % reb A och 10 % sackaros eller en kombination av dessa varefter pH-värdet mättes. Vidare studerades 23 bakteriestammar avseende förmåga att metabolisera 0,025% respektive 0,5% reb A. ResultatStreptokocker dominerade i samtliga biofilmer vid försökets slut oavsett om de exponerats för steviosid, reb A eller enbart TH. En pH-sänkning kunde ses hos biofilmerna som enbart blivit exponerade för sackaros eller för en kombination av sackaros och reb A. Däremot kunde endast en marginell pH-sänkning observeras efter exponering för enbart reb A. Ingen av de enskilda bakteriestammar som studerades kunde metabolisera reb A.SlutsatsIngen större skillnad i biofilmens bakteriesammansättning kunde ses efter upprepad exponering för steviosid eller reb A i förhållande till TH.Upprepade exponeringar av reb A i kombination med sackaros gav en liknande pH-sänkning som enbart sackaros, dock sågs ingen pH-sänkning efter exponering för enbart reb A. Enskilda bakteriestammar kunde inte metabolisera reb A. / AimsIn this in vitro laboratory pilot study, the effect on the microbial composition and pH of the oral biofilms after repeated exposure to Stevia (stevioside and rebaudioside A), saccarose or a combination, was investigated. Another aim was to study whether isolate of oral bacteria were able to metabolise reb A in broth bacteria culture.Material and MethodBiofilms from three adult individuals were repeatedly exposed to 0,025% stevioside, 0,025% reb A or 10% Todd Hewitt (TH). Samples were taken at the beginning and at the end of the experiment for cultivation and bacterial identification.Biofilms were exposed to 0,025% reb A and 10% saccharose, either separately or combined, followed by a pH-measurement. Furthermore, 23 bacterial species were studied in regards to ability to metabolize reb A. ResultsAll biofilms were dominated by Streptococcus regardless of whether they were exposed to stevioside, reb A, or TH. A pH-decrease was seen in biofilms exposed to saccharose or a combination of saccharose and reb A. However, only minor changes were noted after exposure to reb A.None of the species studied were able to metabolize reb A.ConclusionNo major differences in the bacterial composition of the biofilms were seen after repeated exposure to stevioside or reb A compared to TH.No pH-decrease after repeated exposure to reb A was noted. Exposure to reb A combined with saccharose resulted in a pH-decrease similar to exposure to saccharose. The bacterial species tested in this study were not able to metabolise reb A.

The aim of the diploma thesis was evaluation of sensoric attributes of blueberry and current jams sweetened by selected Steviol glycosides and their comparing with other sweeteners. For evaluation of sensoric attributes were used rebaudioside A, stevioside, aspartame, erythritol and sugar beet. Stevia rebaudiana var. Bertoni is a persistent plant, which contains sweetening Steviol glycosides, which have a use in food processing. They are available in the area of EU indicated as E960 since 2011. The most used Steviol glycosides are stevioside and rebaudioside A, which are demarcated with a high sweetness, which could be 200-400 times higher than saccharose. The usage of sweeteners is legislatively allowed, which means it is also allowed to do sensoric analyse and detect perception of added substances in food. These analyses evaluate food with the help of sense - perception. Methodical part of the work contains procedure, used methods for gaining evaluation of data from a sensoric analyse after the degustation of jams, which has taken place with the presence of ten judges - an academic students in the working compartment of University of South Bohemia. Respondents entered their evaluation into protocols, which were prepared in advance. The results of diploma thesis are evaluated by the method of Kramer, which is used for this kind of analyse. The critical scale between 20 and 40 with the value of probability P = 95% was defined according to this method. Evaluation is described with the help of graphs and tables, added with a wordily describtion. Conclusion of analyse of diploma thesis is, that the usage of Steviol glycosides is not most suitable way of sweetening jams. Acceptable valuations of jams containing Steviol glycosides were proven in parameters of colour and aroma. The reasons for less successful evaluation of Steviol glycosides could be due to bad pH of food or badly chosen dosing, without combination of other kinds of sweeteners. The best sensory characteristics traditionally showed sugar beet and aspartame followed by rebaudioside A and stevioside, which were placed on the third and forth place from five used sweeteners. The part of the diploma thesis was an evaluation of questionnaire, where the result was, that asked people preferred fruit ingredient of jams (type of fruit, amount) not their way of sweetening while choosing a jam.

The steviolglycosides are the natural, sweet substances from Stevia rebaudiana Bertoni. It affect human health positively and its sweetness is 300x stronger than the sweetness of sucrose. That's why it's used to sweetening the commercial products. Because of its potential properties it's good to have an appropriate method to isolate it. High performance liquid chromatography ( HPLC) is based on the separation of analyte between two immiscible phases with high pressure pump and appropriately chosen stationary phase in the column. Than the analytes come out from the column in different retention times. This master´s thesis follows up selection of the best HPLC system for isolation of the main steviolglycosides and its analysis in commercial products. In the theoretical part of the thesis is described the origin, basic characteristics, botanical description, cultivation and affect to the human health of Stevia rebaudiana Bertoni and its use in food industry. There are also concisely characterized the sweet substances contained in the plant, so called steviolglycosides. Than there are given the theoretical basics of high performance liquid chromatography, HPLC instrumentation and its specific applications at sleviolglycosides with the basic chromatographic parameters. The object of the first experimental part was to research the optimum conditions for time and separation effective chromatographic analysis and select the best chromatographic system for isolation of steviolglycosides. In the second experimental part, I have compared and defined the main steviolglycosides (stevioside, rebaudioside A) in nine selected products, commercially available in Czech republic, with the best chromatographic method. In these products was the contain of the stevioside or rebaudioside A confirmed or refused.