Belén Max

Biotechnological production of citric acid.

This work provides a review about the biotechnological production of citric acid starting from the physicochemical properties and industrial applications, mainly in the food and pharmaceutical sectors. Several factors affecting citric acid fermentation are discussed, including carbon source, nitrogen and phosphate limitations, pH of culture medium, aeration, trace elements and morphology of the fungus. Special attention is paid to the fundamentals of biochemistry and accumulation of citric acid. Technologies employed at industrial scale such as surface or submerged cultures, mainly employing Aspergillus niger, and processes carried out with Yarrowia lipolytica, as well as the technology for recovering the product are also described. Finally, this review summarizes the use of orange peels and other by-products as feedstocks for the bioproduction of citric acid.

Citric acid production from orange peel wastes by solid-state fermentation

Valencia orange (Citrus sinensis) peel was employed in this work as raw material for the production of citric acid (CA) by solid-state fermentation (SSF) of Aspergillus niger CECT-2090 (ATCC 9142, NRRL 599) in Erlenmeyer flasks. To investigate the effects of the main operating variables, the inoculum concentration was varied in the range 0.5·103 to 0.7·108 spores/g dry orange peel, the bed loading from 1.0 to 4.8 g of dry orange peel (corresponding to 35-80 % of the total volume), and the moisture content between 50 and 100 % of the maximum water retention capacity (MWRC) of the material. Moreover, additional experiments were done adding methanol or water in different proportions and ways. The optimal conditions for CA production revealed to be an inoculum of 0.5·106 spores/g dry orange peel, a bed loading of 1.0 g of dry orange peel, and a humidification pattern of 70 % MWRC at the beginning of the incubation with posterior addition of 0.12 mL H2O/g dry orange peel (corresponding to 3.3 % of the MWRC) every 12 h starting from 62 h. The addition of methanol was detrimental for the CA production. Under these conditions, the SSF ensured an effective specific production of CA (193 mg CA/g dry orange peel), corresponding to yields of product on total initial and consumed sugars (glucose, fructose and sucrose) of 376 and 383 mg CA/g, respectively. These results, which demonstrate the viability of the CA production by SSF from orange peel without addition of other nutrients, could be of interest to possible, future industrial applications.

Extraction of Phenolic Acids by Alkaline Hydrolysis from the Solid Residue Obtained after Prehydrolysis of Trimming Vine Shoots

Contents of hydroxycinnamic and hydroxybenzoic acids were determined in trimming vine shoots after sequential treatments of prehydrolysis and alkaline hydrolysis. These treatments allow the complete use of the main fractions involved: cellulose, hemicelluloses and lignin. The alkaline hydrolysis was studied using a factorial design where reaction time (in the range 30-120 min), temperature (50-130 degrees C), and NaOH concentration (4-12 wt % of solution) were the independent variables. The interrelationship between dependent and operational variables was well fitted (R(2) > 0.90) to models including linear, interaction and quadratic terms. Ferulic acid was the most abundant hydroxycinnamate with concentrations ranging from 25.7 to 141.0 mg/L followed by p-coumaric acid (15.5-31.5 mg/L). Gallic acid was the hydroxybenzoic acid released in higher concentration (in the range 2.5-164.6 mg/L). Because of their properties and low toxicity, these compounds are widely used in the food, pharmaceutical and cosmetic industries. Additionally, ferulic acid is used as feedstock for the biotechnological production of flavorings and aroma compounds, including vanillin and vinylguaiacol, or as a constituent in the preparation of foods and skin protection agents, or as a cross-linking agent for the elaboration of food gels. Consequently, ferulic acid solutions can be obtained from renewable plant cell wall materials as a prospective pathway.

Characterization of vinasses from five certified brands of origin (CBO) and use as economic nutrient for the xylitol production by Debaryomyces hansenii

Vinasses coming from the five CBOs of Galicia, north-western Spain, were characterized, and successfully employed as economic nutritional supplements for xylitol production by Debaryomyces hansenii. All fermentations can be modelled showing kinetic patterns fairly described by the mathematical models. No negative effect of the phenolic compounds in the liquid phase on the initial volumetric rate of product formation (r(P)(0)) was observed. Multiple linear regression analysis was used to describe the effect of metals and initial xylose acting on P(max) and Y(P/S). Zn was the most influential variable. Besides, partial least-squares regression models show a clear separation, based on the first two principal components, between the whole vinasses and the liquid fractions, which provided the higher P(max), with the exception of CBO 4, where P(max)=40.4 g/L, was achieved using the solid and liquid fraction.

Evaluation of wine vinasses as alternative nutrients in biotechnological processes Evaluación de vinazas vínicas como nutriente alternativo en procesos biotecnológicos

Vinasses are acidic effluents with high organic content, including acids, carbohydrates, phenols and unsaturated compounds with high chemical and biological oxygen demand. Their discharge into public watercourses promotes a high and toxic contamination of the medium, resulting in significant environmental problems. However, the search for alternative, financially competitive nutrient sources to carry out biotechnological procedures is particularly interesting, considering that nutrients such as yeast extract or peptone can represent up to 30–40% of the final cost of the process. Vinasses were assayed to transform sequentially concentrated synthetic media containing glucose and xylose into lactic acid and xylitol by Lactobacillus rhamnosus and Debaryomyces hansenii, respectively. Using 30 g/L of vinasses without tartaric acid extraction, 24.2 g of lactic acid/L and 17.1 g of xylitol/L were produced, showing that these nutrients can represent an interesting alternative to minimise the final cost of the products achieved. Las vinazas son efluentes ácidos con alto contenido orgánico, incluyendo ácidos, carbohidratos, fenoles y compuestos no saturados con elevados contenidos en demandas biológica y química de oxígeno. Su vertido en cursos de agua pública promueve una elevada y tóxica contaminación del medio, dando lugar a importantes problemas ambientales. Por otro lado, la búsqueda de nutrientes alternativos, que representen una fuente económicamente competitiva para llevar a cabo los procesos biotecnológicos es particularmente interesante, teniendo en cuenta que algunos nutrientes como extracto de levadura o peptona pueden representar hasta el 30–40% del coste final del proceso. En este trabajo se ensayaron vinazas para llevar a cabo la transformación secuencial de medios sintéticos concentrados, que contienen glucosa y xilosa, en ácido láctico y xilitol empleando cepas de Lactobacillus rhamnosus y Debaryomyces hansenii, respectivamente. Utilizando 30 g/L de vinazas sin extracción de ácido tartárico, se alcanzaron 24,2 g/L de ácido láctico y 17,1 g/de xilitol, mostrando que estos nutrientes pueden representar una alternativa interesante para minimizar el coste final de los productos obtenidos.