Efecto espaciotemporal en las propiedades fisicoquímicas del agar nativo de Gracilaria parvispora (Rhodophyta) en el Pacífico Mexicano Tropical (Oaxaca-Chiapas)

Background: Gracilaria parvispora is an invasive red seaweed located in coastal lagoons along the Tropical Mexican Pacific. Gracilaria species are the main source of agar around the world. Goals: Spatial and seasonal trends of the properties of native agar from the invasive seaweed G. parvispora were determined in three localities in the states of Oaxaca and Chiapas belonging to coastal lagoons along the Tropical Mexican Pacific: Ballenato, Paredón, and San Vicente. Methods: Native agar was obtained from dry samples of seaweed and the agar yield, gel strength, melting and gelling temperatures, hysteresis, and sulfate and 3,6-anhydrogalactose content were determined for each sample. Moreover, the polysaccharide structures and the location of sulfate groups in agar samples were identified. Results: The phycocolloid is a polysaccharide agar type. The agar yield was significantly different between seasons and localities, with the highest values during the dry season (19.9 ± 0.004 %) at Paredón (20.6 ± 0.01 %). Gel strength, melting temperature and gel hysteresis showed significant spatial differences; the highest values were obtained in Ballenato (367.3 ± 14.2 g cm−2, 80.2 ± 1.4 °C, 44.3 ± 2.2 °C, respectively); gelling temperature did not show significant differences between localities or seasons. Chemical properties were significantly different between seasons: 3,6-anhydrogalactose content was higher during the dry season (36.2 ± 0.2 %), and sulfate content was higher during the rainy season (12.69 ± 0.21 %). Salinity was significantly different between seasons, and the highest was obtained during the dry season (38.7 ± 0.1). Surface water temperature varied between localities, and the highest mean value was recorded at Paredón (32.5 ± 0.2 °C). Conclusions: The chemical properties of the G. parvispora native agar were lower than the standards for food and industrial use.Antecedentes: Gracilaria parvispora es un alga roja invasora que se encuentra en lagunas costeras del Pacífico Mexicano Tropical. A nivel mundial, las especies de Gracilaria son la fuente principal de agar. Objetivos: Se determinaron las tendencias espaciales y temporales de las propiedades del agar nativo de G. parvispora en tres localidades de los estados de Oaxaca y Chiapas, pertenecientes a lagunas costeras del Pacífico Mexicano Tropical: Ballenato, Paredón y San Vicente. Métodos: Se determinó el rendimiento del agar, la fuerza de gel, la temperatura de fusión y gelificación, la histéresis, y el contenido de sulfatos y 3,6-anhidrogalactosa del agar nativo obtenido de muestras secas de macroalga. Además, se identificaron las estructuras de los polisacáridos y la posición de los grupos sulfato en las muestras. Resultados: El ficocoloide es un polisacárido tipo agar. El rendimiento mostró diferencias significativas entre localidades y temporadas, con valores mayores durante la temporada de secas (19.9 ± 0.004 %) y en Paredón (20.6 ± 0.01 %). La fuerza de gel, la temperatura de fusión y la histéresis mostraron diferencias espaciales significativas; con valores más altos para las muestras de Ballenato (367.3 ± 14.2 g cm-2, 80.2 ± 1.4 °C, 44.3 ± 2.2 °C, respectivamente); la temperatura de gelificación no mostró diferencias significativas entre localidades o temporadas. Las propiedades químicas mostraron diferencias significativas entre temporadas: el contenido de 3,6-anhidrogalactosa fue mayor durante la temporada de secas (36.2 ± 0.2 %), y el contenido de sulfato fue mayor durante la temporada de lluvias (12.69 ± 0.21 %). La salinidad fue significativamente diferente entre temporadas, con mayor valor para la temporada de secas (38.7 ± 0.1). La temperatura superficial del agua varió entre localidades, la más alta se registró en Paredón (32.5 ± 0.2 °C). Conclusiones: Las propiedades químicas de G. parvispora fueron menores a los estándares para su uso industrial y alimenticio

Optimización del proceso de extracción de alginato de sodio, a partir del alga café Macrocystis pyrifera.

IMPRESO Y PD

Seasonal variation on size and chemical constituents of Sargassum sinicola Setchell et Gardner from Bahia de La Paz, Baja Califoria Sur, Mexico

Investigation on seasonal variation in size and chemical constituents of Sargassum sinicola Setchell et Gardner from Bahía de La Paz, Baja California Sur, Mexico, was carried out from a control bed and compared with an experimental bed with artificial nutrients added. No significant differences were found between the control and experimental thalli for size or chemical composition, except for iodine and raw fiber. For control thalli the results were: size 7.5–56.0 cm, alginate yield 7.2–13.7%, viscosity 58.7–191.7 millipascal seconds (mPa s), mannitol 2.9–8.1%, raw fiber 5.5–7.5% and iodine 0.020–0.141%; while in the experimental thalli the size ranged from 7.5 to 80.3 cm and the alginate yield was 7.8–10.4%, viscosity 41.4–163.4 mPa s, mannitol 2.9–8.3%, raw fiber 5.9–10.7% and iodine 0.021–0.098%. These variations were related to its natural growth cycle, and showed reductions during the senescence period. Results suggest that S. sinicola is not affected by relatively low nutrient concentrations, and could be considered as raw material for alginate productio

Pilot plant scale extraction of alginates from Macrocystis pyrifera. 3. Precipitation, bleaching and conversion of calcium alginate to alginic acid

Three steps of the alginate production process were studied at pilot plantlevel. The effect of the amount of calcium chloride used during theprecipitation was measured in terms of filtration time of the precipitatedcalcium alginate. Three different proportions of calcium chloride per gramof alginate were tested. The best proportion used was 2.2 parts ofcalcium chloride per one part of alginate, yielding a filtration rate of 97.9L min-1 on a screen area of 1.32 m2. The method ofadding the solutions and the degree of mixing are discussed as other factorsaffecting the precipitation step. The effect of bleaching the calciumalginate with sodium hypochlorite (5%) was studied. Seven proportions,ranging from 0 to 0.77 mL of sodium hypochlorite per gram of sodiumalginate were tested. The effect of hypochlorite was compared foralginates with three different viscosities. Using alginates with mediumviscosity (300–500 mPa s), the best proportion was 0.4 mL hypochloriteper gram of alginate, yielding an alginate of light cream color with 20%less viscosity than the control. Alginates with lower viscosity showed asmaller loss of viscosity. The effect of pH during conversion of calciumalginate to alginic acid was determined using four combinations of pH,ranging from 2.2 to 1.6, in three acid washings. The extent of conversionwas determined by measuring the percent reduction of the alginate viscosity(RV) in 1% solution before and after adding a sequestrant of calcium. When a pH 1.8 or 1.6 was used for each washing, only two washings werenecessary to produce a RV lower than 40% (maximum recommended). The use of pH 2 required three acid washings to produce the same effect. The pH 2.2 did not remove enough calcium, even with three washings,the RV of the resulting sodium alginate being greater that 40%. Theresults of these experiments provide the information that producers needwhen deciding the best parameters to obtain a product with the desiredcharacteristics

Pilot plant scale extraction of alginates from Macrocystis pyrifera. 4. Conversion of alginic acid to sodium alginate, drying and milling

The last three steps of the alginate production process were studied:conversion of alginic acid to sodium alginate, drying, and milling. Threemethods were used to follow the conversion reaction: measuring the pH (a) intheethanol-water liquid of the reaction mixture, (b) after dissolving a sample ofthe fiber taken from the reaction mixture, (c) after dissolving the driedsodiumalginate obtained from the reaction. To obtain a neutral dried sodium alginate,in the first method the pH should be adjusted to 9, and in the second the pHshould be adjusted to 8. The best method to control the reaction was todissolvea sample of the fiber and adjust the pH to 8. The best proportion to reach thecritical point, where pH just begins to rise, was 0.25 parts of sodiumcarbonateto 1 part of alginate in the initial dry algae. A pH above 7 may produce abreakdown of the molecule, reducing significantly the viscosity of the finalalginate. Four different temperatures were used to dry the alginate: 50, 60,70,and 80 °C. Drying time to reach 12% moisture ranged from 1.5h at 80 °C to 3 h at 50°C. The best drying temperature was 60 °C for2.5 h. The effect of drying temperature on alginate viscosity wasdependent on the alginate type. Low and medium viscosity alginates were notsignificantly affected, but alginate with high viscosity was reduced by 40 to54% using the temperature range of 60 to 80 °C. A fixed hammermill was used to reduce the particle size of the dried sodium alginate.Particlesize measurements showed that after a first milling the product contained 76%large particles (20–60 mesh) and 24% fine particles (80–120 mesh).After a third milling the product still contained 42.9% large particles. Nosignificant effect was found on alginate viscosity because of the millingsteps