Because many questions arise regarding the use of immobilization technology to consistently produce a high quality beer, this work focuses on the effects of using an immobilization matrix in the fermentation process. The aim of this study was to explore the feasibility and potential uses of immobilization on sensorial characteristics such as color, flavor, and headspace compounds of stout beer, when using batch fermentation. Batch production of beer was conducted as a standard ale process for stout beer production. For the immobilized yeasts fermentation, cells were microencapsulated in alginate, by using the Thiele modulus procedure for microcapsule design. Glucose concentration, cell multiplication, cell viability, specific gravity, pH, Brix, and ethanol were monitored throughout the fermentation process. Both, sensorial analysis (statistic triangle tests) and instrumental methods (gas chromatography to measure headspace compounds and visible spectrophotometer to quantify the color) were used to evaluate characteristics of the beer that was produced from immobilized and free yeast fermentations. Free and immobilized yeasts fermentation showed no significant difference (p> 0.05) for all variables of interest. The profile of headspace compounds was different, perhaps because of changes in yeast's behavior and the presence of secondary metabolites. However, immobilization did not have a significant impact on the beer flavor, as detected by the sensorial triangle test.

RESUMENPredicción molecular de los triglicéridos de la grasa láctea de oveja por cromatografía líquida de alta eficacia en fase inversa.El análisis por cromatografía líquida de alta eficacia de los triglicéridos de la leche de oveja obtuvo 115 picos individuales. Los triglicéridos componentes de los picos cromatográficos fueron estimados mediante ecuaciones matemáticas que relacionaban el log k' de los picos cromatográficos con las variables moleculares, número equivalente de carbonos (NEC) de los posibles triglicéridos, y longitud de cadena (LC) y número de dobles enlaces (DE) de cada uno de los ácidos grasos del triglicérido. Para la estimación de la composición triglicérica de la grasa láctea se consideraron solamente los 12 ácidos grasos mayoritarios obtenidos en el análisis por cromatografía de gases de la fracción triglicérica total.Los triglicéridos que presentaron altos porcentajes según el cálculo de la composición al azar fueron considerados los principales componentes moleculares cuando en un pico cromatográfico se predecía más de un triglicérido. Los triglicéridos estimados más abundantes en la grasa láctea de oveja fueron C4:o-Ci6:o-Ci6:o, C6:0-Ci4:0-Ci6:0, C4:0"Ci4:0-Ci6:0, C4:0-Ci6:0-Ci8:1 y C6:0"Ci4:0-Ci8:1. PALABRAS-CLAVE: Cromatografía líquida de alta eficaciaLeche de oveja -Predicción molecular -Triglicérido. SUMMARY Molecular prediction of the triglycerides of sheep milk fat by reverse-phase high-performance liquid chromatography.115 individual peaks were obtained by high-performance liquid chromatography of the sheep milk fat. Triglyceride components of the chromatographic peaks were predicted by means of mathematical equations relationing the log k' of the chromatographic peaks to the molecular variables, equivalent carbon number (ECN) of the possible triglycerides, and chain length (CL) and number of double bounds (DB) of each of the fatty acids of the triglyceride. The 12 main fatty acids obtained by gas chromatography of the total triglyceride fraction were used to estimate the triglyceride composition of the sheep milk fat.The triglycerides presenting high random percentages were considered the principal molecular species when more than one triglyceride were predicted in a chromatographic peak. The main estimated triglycerides of the sheep milk fat were C4:o-Ci6:o-Ci6:o, C6:0"Ci4:0"Ci6:0, C4:0"Ci4:0"Ci6:0i C4:0-Ci6:0"0i8:1 and C6:0-Ci4:0"Ci8:1.

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