Kinetics of fermentation of different Saccharomyces cerevisiae in raspberry must

In modern viniculture selected yeast has been used preferably to ensure a final product with desired quality. These yeasts are selected based on certain desirable characteristics such as resistance to high concentrations of sugars. Yeasts strains used for fruit wine production have to adapt to different sugar composition and concentrations, presence of organic acids, pectin and other components present in the fruit pulp. The objective of this study was to evaluate the performance of different Saccharomyces cerevisiae strains during alcoholic fermentation of raspberry (Rubus idaeus) must. Fermentation parameters such as ethanol yield, productivity and maximum specific rate of cell growth are considered to be essential for good performance in a fermentation process. Raspberry pulp was diluted with a sucrose solution to adjust the sugar concentration to 16° Brix. CaCO3 was added to increase the pH value to 4.0. Batch fermentations were carried out at 22ºC in Erlenmeyer flasks containing 100 ml of raspberry must. The max (h-1) found were 0.08, 0.09 and 0.12 for yeast UFLA CA1162, UFLACA11 and UFLACA15, respectively. The higher yield of ethanol (Yp/s) was 0.48 g/g for yeast UFLA CA15, while the other yeasts showed a an Yp/s of 0.41 g/g. The values found for the biomass yield (Yx/s) were 0.06, 0.07 and 0.08 g/g for yeasts UFLA CA11, UFLA CA1162 and UFLA CA15, respectively. The highest ethanol productivity was found 1.45 g/l.h for yeast UFLA CA15. It was concluded that raspberry must can be fermented by the different S. cerevisiae strains used in this study and based on the kinetic parameters, the yeast UFLA CA15 showed the best fermentation performance in comparison with yeasts UFLA CA11 and UFLA CA1162 in the fermentation of the raspberry pulp

Determination of sulfur compounds in fermented raspberry beverages by GC-PFPD

Volatile sulfur compounds are known to have very powerful and characteristic odours, and can contribute to pleasant or unpleasant aromas of a wine, according to their nature and concentration. Their concentration has a great influence on sensory properties, often being strongly dependent on threshold values, normally low. The determination of sulfur compounds, eluted in a chromatographic column, has been performed using mainly flame photometric detection (FPD), sulfur chemiluminescence detection (SCD), atomic emission detection (AED) and more recently, pulsed flame photometric detection (PFPD). The objective of this study was to determine the sulfur compounds in a fermented raspberry beverage using GC-PFPD. The analyses were made on a Varian CP-3800 gas chromatography equipped with a PFPD detector operating in sulfur mode. Aromatic extracts, obtained by liquid-liquid extraction with dichloromethane, were injected into a 1079 split/splitless injector (splitless for 30 s). The separation was performed with a CP-Wax 52 CB column (50 m x 0.25 mm i.d., 0.2 m film thickness; Chrompack). The oven temperature was programmed from 60 oC (5 min) to 200 oC, at 20 oC/min (final hold for 5 min). The carrier gas was helium with a constant flow rate of 1.2 mL/min. The temperature of the injector and detector was set to 250 oC. The detector voltage was 570 V, the gate delay for sulfur compounds was 6 ms and the gate width was 20 ms. All sulfur compounds were identified by comparing their retention times with those of the pure standards. Raspberry pulp was diluted with water (1:1), sucrose was added to adjust the initial sugar concentration to 160 g/L (sucrose + glucose + fructose) and the pH was corrected to 4 with CaCO3. Batch fermentations (3 L of raspberry must) were carried out at 22 ºC in a bioreactor, after inoculation with 1 g/L of Saccharomyces cerevisiae CAT-1 previously grown in YPD medium. In fermented raspberry beverage were identified and quantified 7 sulfur volatile compounds: furfuryl mercaptan (16.9 g/L), 2-mercaptoethanol (4.7 g/L), 2-(methylthio)ethanol (158.1 g/L), 3-mercapto-3-methylbut-1-ol (4.0 g/L), 3-methylthio-1-propanol (128.9 g/L), 4-mercapto-1-hexanol (1.5 g/L) and benzothialoze (5.7 g/L). The highest concentrations were found for 2-(methylthio)ethanol and methionol (3-methylthio-1-propanol). Methionol, with cauliflower and cabbage descriptors, can be related to the metabolism of yeasts, when methionine is metabolized. It was concluded that liquid-liquid microextraction with dichloromethane followed by GC-PFPD analysis is effective to quantify volatile sulfur compounds produced in fermented raspberry beverages. As expected, the PFPD detector exhibited a quadratic behavior for these compounds

Avaliação do perfil de metabolitos produzidos por diferentes leveduras utilizadas na produção de vinho de frutas

O aroma das bebidas alcoólicas fermentadas resulta da interação de compostos químicos como alcoóis,ésteres, ácidos, aldeídos e cetonas. Estes compostos são produzidos durante a fermentação,principalmente pelas leveduras e bactérias, ou podem estar presentes em pequenas quantidades nas frutas. Os compostos voláteis orgânicos são responsáveis pelo chamado bouquet, aroma e características gerais das bebidas. Durante a fermentação as leveduras podem produzir vários compostos em quantidades diferenciadas, podendo em algumas situações ocorrer a produção de compostos indesejáveis ou a produção de compostos desejáveis em quantidade excessiva. O objetivo deste trabalho foi avaliar a produção de metabolitos (alcoóis, aldeídos, ésteres e ácidos orgânicos) por diferentes leveduras utilizadas na produção de vinhos de frutas. Foi utilizado mosto de framboesa com 16º Brix e pH 4,0. A fermentação foi realizada em frascos contendo 100 mL, nos quais foram inoculados 1 g/L de diferentes leveduras Saccharomyces. Após o término da fermentação os compostos presentes nas bebidas foram analisados por cromatografia gasosa (GC) e cromatografia líquida (HPLC). As leveduras com melhores resultados para produção de compostos voláteis foram a UFLA CA 15, S. bayanus CBS 1505 e CAT-1. Para alcoóis superiores (1-propanol, 2-metil-1- propanol, 2-metil-1-butanol, 3-metil-1-butanol e 2-feniletanol), as concentrações encontradas foram 260, 4 mg/L, 277,6 mg/L e 282,8 mg/L para as leveduras S. bayanus CBS 1505, UFLA CA 15 e CAT-1, respectivamente. Para a levedura VR-1, apesar da alta concentração de alcoóis superiores, foram encontradas elevadas concentrações de ácido acético (2,2 g/L) e metanol (83 mg/L). A presença de elevadas concentrações destes dois compostos é indesejada, pois o ácido acético está diretamente relacionado com a acidez da bebida e o metanol é um composto tóxico. Além do teor desejável de alcoóis superiores, as bebidas produzidas com as leveduras UFLA CA 15, S. bayanus CBS 1505 e CAT-1 apresentaram baixas concentrações de ácido acético e metanol

Efficiency of sugar-to-ethanol conversion by different Saccharomyces cerevisiae strains during raspberry must fermentation

The use of selected yeasts for winemaking gives multiple advantages over the traditional spontaneous fermentation. There is general agreement among experts that these yeasts should show low production of volatile acidity, high tolerance to alcohol, ethanol production according to the amount of sugar present in the must, total fermentation of sugars, high fermentation rate, growth at high temperature, low hydrogen sulfide production, low foaming, killer phenotype, low acetaldehyde production and good glycerol production. The objective of this study was to evaluate the production of ethanol by different Saccharomyces cerevisiae strains from raspberry must. Yeasts were grown in raspberry must with sugar content adjusted to 16º Brix with sucrose syrup and pH 4.0 adjusted with calcium carbonate. Batch fermentations (100 ml) were carried out at 22ºC. Sucrose, glucose, fructose and ethanol were determined by HPLC. The kinetics parameters, ethanol yield factor (Yp/s), fermentation efficiency (Ef), % of substrate conversion to ethanol and ethanol productivity (Qp) were calculated. S. cerevisiae VR-1 gave the highest Yp/s (0.49 g/g), followed by the strains UFLA FW 15 and CAT-1 (0.48 g/g). Among the yeast strains tested, S. cerevisiae UFLA CA 155 had the lowest Ef (77.5%) and S. cerevisiae VR-1 achieved the highest value of Ef (96%) at the end of fermentation. All the yeasts, except S. cerevisiae UFLA FW 1162, showed high values (> 97%) of conversion of substrate to ethanol. S. cerevisiae UFLA FW 15, VR-1 and BG showed the highest Qp of 1.49 g.l-1.h-1. The lowest Qp (1.15 g.l-1.h-1) was found for the strain UFLA FW 1162. It can be concluded that S. cerevisiae VR-1 showed the best performance for ethanol production during raspberry must fermentation