Orange juice was fermented with S. cerevisiae using natural (NJ) or pasteurized (PJ) juice, at 2 pHs (3.5 or 4.0) and at 2 temperatures of fermentation (10 or 20°C) and 2 of aging (10 or 20°C). Reducing sugars (RS) and total sugars (TS), amino-N and yeast counts were determined during 4 stages: initial, fermentation, bottling and aging (4 months). Sugars and ethanol were determined as well at the end. RS and TS decreased during the fermentation for both musts as well as amino-N, later remaining almost constant. Yeast counts were 2×106/mL (NJ) and 7×106/mL (PJ). Fructose (80-90%) and glucose (<20%) were detected after bottling but not sucrose. Ethanol reached 60-80 g/L (NJ) and 80-85 g/L (PJ). Sugars and amino-N increased slightly during aging, but ethanol decreased in NJ and increased slightly in PJ. Yeast counts decreased. Yeasts metabolized almost all sugars and amino-N during the fermentation for growing; later, during ethanol production there were almost no changes up to bottling, occurring their lysis.

Se fermentaron jugos de naranja (natural, JN, o pasteurizado, JP) con S. cerevisiae a pHs (3,5 ó 4,0), temperaturas de fermentación (10 ó 20°C) y de maduración (10 ó 20°C). Se determinaron azúcares reductores directos (ARD) y totales (ART), N-amínico y recuento microscópico durante 4 etapas: inicial, fermentación, envasado y maduración (4 meses). Al final también se determinaron azúcares y etanol. Los ARD y ART decrecieron durante la fermentación en ambos mostos; el N-amínico también disminuyó, permaneciendo luego casi constante. El recuento de levaduras fue 2×106/mL (JN) y 7×106/mL (JP). En los envasados se detectó fructosa (80-100%) y glucosa (<20%) pero no sacarosa. El etanol alcanzó 60-80 g/L (JN) y 80-85 g/L (JP). Durante la maduración, los azúcares y el N-amínico aumentaron levemente, el etanol disminuyó en JN pero incrementó levemente en J P. El recuento de levaduras disminuyó. Durante la fermentación, las levaduras asimilaron casi la totalidad de azúcares y del N-amínico para crecer; luego durante la producción de etanol no hubo casi cambios hasta el envasado, produciéndose su lisis.

A metodologia de superfície de resposta foi utilizada para a otimização da produção de poligalacturonasa (PG) e pectinesterasa (PE), por A. niger em fermentação submergida. Foi aplicado um Desenho Experimental Composto Central abrangendo 22 experiências, incluindo oito pontos centrais. As variáveis estudadas foram: tempo de fermentação (24 a 120 h), pH (3.5 a 6.5) e concentração inicial de pectina (5 a 20 g/l). A produção máxima de PE foi de 220 U/l, após 74h de cultivo, 20 g/l de pectina e pH 6.5. As condições ótimas para a produção de PG foram pH 4.1, 20 g/l de pectina e 94 h de fermentação, com um valor máximo de 1032 U/l. Sob estas condições, a produção de PE foi baixa (15 U/l). Um extrato líquido com alta atividade PG e baixa atividade PE poderia ser conveniente para ser utilizado no processamento e alimentos, visando reduzir a produção de metanol.

Response surface methodology was used for optimization of polygalacturonase (PG) and pectinesterase (PE) production in submerged fermentation by A.niger. A Central Composite Experimental Design was applied, consisting of 22 experiments, including eight central points. Variables studied were: fermentation time (24 to 120 h), pH (3.5 to 6.5) and initial concentration of pectin (5 to 20 g/l). Maximum PE production was 220 U/l, after 74 h of culture, in a medium containing 20 g/l of pectin (pH 6.5). The optimal conditions for PG production were pH: 4.1, 20 g/l of pectin and 94 h of fermentation with a maximum value of 1032 U/l. Under these conditions, the PE production was low (15 U/l). A liquid extract with high PG activity and low PE activity could be suitable to be used in food processing in order to reduce the production of methanol.

La pectina es un polisacárido de origen vegetal ampliamente usado en las industrias alimenticia y farmacéutica, entre otras, debido a sus particulares propiedades físico-químicas. En este artículo se estudia la actividad solubilizadora de pectina de protopectinasa-SE, enzima producida por el hongo levaduriforme Geotrichum klebahnii, utilizando como sustrato el albedo del limón (parte interna, blanca y esponjosa de la cáscara) y la protopectina (sustancia péctica insoluble en agua, obtenida del mismo tejido). Se evalúa el efecto del tamaño de partícula y de la composición, el pH y la temperatura del medio de reacción, usando el diseño experimental Doehlert. El pH, la temperatura y la concentración de solución amortiguadora de pH (ácido cítrico-citrato de sodio, CitB) ejercen un importante efecto sobre el proceso de solubilización de pectina a partir de protopectina, con un nivel óptimo de solubilización a pH 5,0, 37°C y concentración de CitB = 25 mM. Bajo las condiciones óptimas de reacción se obtuvieron rendimientos de 37 y 28 g de pectina/100 g de tejido (base seca) a partir de protopectina y albedo, respectivamente. La pectina extraída en ambos casos presenta un contenido de grupos urónicos de 60% y un grado de esterificación de 78%.

Pectin is a polysaccharide of vegetal origin widely used in food and pharmaceutical industries, among others, due to its particular physicochemical properties. Pectin solubilizing activity of Protopectinase-SE, an enzyme produced by the yeast-like fungus Geotrichum klebahnii, was studied using lemon albedo (the inner white and spongy part of the peel) and protopectin (the water insoluble pectic substance obtained from the same tissue) as substrates. Effects of substrate particle size and composition, pH and temperature of reaction medium were evaluated using a Doehlert experimental design with response surface. Temperature, pH and buffer (citric acid-sodium citrate, CitB) concentration display an important effect on pectin solubilization process, with optimal solubilization conditions at pH 5.0, 37°C and CitB = 25 mM. Yield of 37 and 28 g of pectin/100 g tissue (dry basis) are achieved under optimal reaction conditions from protopectin and albedo, respectively. In both cases, extracted pectin shows a 60% uronic acid content and 78% esterification grade.