No description available.

Kombucha is a fermented tea beverage consumed for its probiotics and functional properties and has a unique sensory profile driven by the properties of tea polyphenols and fermentation products, including organic acids. Fermentation temperature and sucrose content affect the fermentation process and the production of organic acids, yet less is known about the impact on the sensory profile and consumer acceptance. Thus, we aim to examine the impact of sucrose concentration and fermentation temperature on sensory attributes and liking. For this study, kombucha tea was fermented at three different concentrations of sucrose and fermented at two temperatures for 11 days. Fermentation was monitored by pH, brix, and titratable acidity, and consumers (n=104) evaluated the kombucha for sensory attributes and overall liking. Fermentation temperature resulted in significant differences in titratable acidity, with higher temperatures producing more organic acids, resulting in higher astringency, and suppressed sweetness. The lower fermentation was reported as significantly more liked, with no difference in liking between the 7.5% and 10% sucrose kombucha samples. Overall, sucrose concentration had less of an impact on overall liking, and the sensory profile and fermentation temperature, which drives the fermentation rate and production of organic acids, strongly influenced the sensory profile.

Electrical Impedance Spectroscopy (EIS) is a relatively new method applied to food quality assessment. EIS allows relatively inexpensive assessment, is fast, easy to operate and non-invasive. It has been adopted for investigation of fundamental electrical properties of plant tissues. Although the applications of EIS for food quality determination have been reported previously, the analytical relationships between electrical impedance properties and quality criteria have not yet been fully developed. Further exploration is thus important in acquiring more data on electrical impedance characteristics of fruits and vegetables and researching new approaches for determination of their quality. This dissertation aims to investigate the electrical impedance properties of fruits and vegetables, and explore the relationship between impedance and quality criteria. In particular, the present dissertation outlines experimental research conducted on relationships between impedance properties and fruit tastes as well as the impedance changes observed during ripening process. Impedance measurement to monitor moisture content changes in the progress of drying is also included in this research. In summary, the impedance properties have merits in fruits and vegetables quality assessment. The current used subjective visual inspection and assessment could be replaced by the EIS based approach as it is a more precise measurement of food quality. Further study is required to give this method practical value.

A novel non-destructive method of grape berry analysis is presented that uses reflected light to predict berry composition. The reflectance spectrum was collected using a diode array spectrometer (350 to 850 nm) over the 2009 and 2010 growing seasons. Partial least squares regression (PLS) and support vector machine regression (SVMR) generated calibrations between reflected light and composition for five berry components, total soluble solids (°Brix), titratable acidity (TA), pH, total phenols, and anthocyanins. Standard methods of analysis for the components were employed and characterized for error. Decomposition of the reflectance data was performed by principal component analysis (PCA) and independent component analysis (ICA). Regression models were constructed using 10x10 fold cross validated PLS and SVM models subject to smoothing, differentiation, and normalization pretreatments. All generated models were validated on the alternate season using two model selection strategies: minimum root mean squared error of prediction (RMSEP), and the "oneSE" heuristic. PCA/ICA decomposition demonstrated consistent features in the long VIS wavelengths and NIR region. The features are consistent across seasons. 2009 was generally more variable, possibly due to cold weather affects. RMSEP and R2 statistics of models indicate that PLS °Brix, pH, and TA models are well predicted for 2009 and 2010. SVM was marginally better. The R2 values of the PLS °Brix, pH, and TA models for 2009 and 2010 respectively were: 0.84, 0.58, 0.56 and: 0.89, 0.81, 0.58. 2010 °Brix models were suitable for rough screening. Optimal pretreatments were SG smoothing and relative normalization. Anthocyanins were well predicted in 2009, R2 0.65, but not in 2010, R2 0.15. Phenols were not well predicted in either year, R2 0.15-0.25. Validation demonstrated that °Brix, pH, and TA models from 2009 transferred to 2010 with fair results, R2 0.70, 0.72, 0.31. Models generated using 2010 reflectance data did not generate models that could predict 2009 data. It is hypothesized that weather events present in 2009 and not in 2010 allowed for a forward calibration transfer, and prevented the reverse calibration transfer. Heuristic selection was superior to minimum RMSEP for transfer, indicating some overfitting in the minimum RMSEP models. The results are demonstrative of a reflectance-composition relationship in the VIS-NIR region for °Brix, pH, and TA requiring additional study and development of further calibrations.

The evaluation of changes during fermentation of heat-modified milk in connection with different fermentation temperatures was main goal of this thesis. Titrable acidity, active acidity and growth dynamics of bacteria strains - Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus were observed during fermentation process.

Diploma thesis is focused on chemical characteristics of nine selected sweet cherry varieties in nine parameters. Total and soluble solids were analyzed with these results 13.07–16.58 % for total and 14.67–19.50 °Brix for soluble solids, ash content 0,31–0,39 %, titratable acidity 5.44–9.91 g of malic acid per 1 kg of fresh cherries and formol number 14.45–23.73 ml of 0.1 M NaOH per 100 g of cherries. Then there were analyzed crude proteins content calculated from total nitrogen content determined by Kjeldahl method with results 0.41–0.68 % of crude proteins. Molecular absorption UV/VIS spectrophotometry was used for determination of total phenolic substances 0.30–0.89 g of gallic acid per 1 kg of cherries and total content of anthocyanins 128–848 mg of cyanidine-3-glucoside in 1 kg of cherries. Saccharides were determined by high performance liquid chromatography (HPLC) with ELSD detector. Content of glucose was 45.45–59.49 g/kg and fructose 46.88–60.01 g/kg. All results are compiled using tables and graphs and discussed. Experimental part of the thesis also describes principles and procedures of every analysis, so it can be reproduced. In theoretical part there is described botanical characteristic of cherry tree (Prunus avium L.), active substances contained in its fruits and their use in food industry. At the end of the theoretical part there is described instrumentation of high-performance liquid chromatography.

Diploma thesis is focused on the chemical analysis of the juices of black, red and white currant and jostaberry (Ribes a Ribes x culverwellii). The theoretical part is focused to the definition of fruit, fruit importance in human nutrition, description of Ribes and Ribes x culverwellii genuses, active substances in the currants and the jostaberry, description of selected chemical parameters and the determination of some of them. The procedures of determining for the following chemical parameters are described in the experimental section: determination of reducing sugars, determination of total and soluble solids, formol number, pH, titratable acidity, determination of total phenols and anthocyanins and determination of vitamin C in two samples jostaberry, six varieties of black currants, one variety of white currant and two varieties of red currants. Based on the evaluation of the obtained results, the comparison was made with different varieties and the thesis that "overall comparison of the different varieties in the content of phenolic compounds, vitamin C and anthocyanins appears to be the most promising variety of blackcurrant demon. It should however be noted that the highest content of phenolics and anthocyanins were determined in jostaberry„ has been suggested.