Parameters afecting the conversion of alginic acid to sodium alginate

The step to convert alginic acid to sodium alginate on the alginate extraction process was studied, using the brown seaweed Macrocystis pyrifera as raw material. The effect of alcohol volume, alcohol-water proportion, pH, and treatment time on the yield and viscosity of the alginate obtained was analyzed. Seven volumes of the mixture alcohol-water in proportion 50:50 were experimented, from 9 to 15 mL g–1 alga. The yield and viscosity were not significantly different in any of the volumes used, however, the stirring with the volume of 9 mL g–1 alga was less efficient, therefore the minimum volume to use in this step was 10 mL g–1 alga. The appropriated proportion of the mixture alcohol-water was determined using five proportions: 50:50, 47:53, 44:56, 40:60, and 37:63. The highest yield and viscosity were obtained using the proportion 50:50. Five pH values from 6 to 10 were experimented to determine the optimum pH for the conversion reaction. The best results were obtained using a pH from 7 to 8 in the alcoholic solution of the conversion step. To determine the minimum time required for the conversion reaction, the fibers of sodium alginate were stirred in an alcoholic solution for 20, 30, 40, 50 and 60 min. The yield and viscosity obtained were not significantly different, therefore, the minimum time to carry out the conversion reaction was 30 minutes to assure a complete reaction. The use of a double planetary mixer is proposed to carry out this step at other level

Batch and continuous flow systems during the acid pre-extraction stage in the alginate extraction process

Acid pre-extraction in the production process of alginates was investigated in two stages using Macrocystis pyrifera as raw material. In the first stage, the possibility of reducing the normality of the hydrochloric acid used in a continuous flow system was tested by varying the concentration of the acid between 0.2 and 0.006N. The percentage of calcium ions exchanged was considered as the variable response. lt was found that with this system it is possible to use 0.05N as the minimum concentration of hydrochloric acid without affecting the alginate yield. In the second stage, the continuous flow system using the conditions established in the first stage was compared to a three batch system at pH 4. It was found that the continuous flow system exchanges 76% of the ions present in the algae, while the batch system exchanges 50%. There is no significant difference in the yield, but the quality of the alginates, measured in terms of viscosity, is 55% greater using the batch system. The use of the batch system reduces hydrochloric acid consumption by 85.9%, water consumption by 25% and therefore reduces production costs

Effect of temperature and extraction time on the process to obtain sodium alginate from Macrocystis pyrifera

The alkaline extraction step of the process to obtain sodium alginate from Macrocystu pyrifera was investigated. We compared cold (28°C) and hot (80°C) treatments to determine the effect of extraction temperature on the yield and viscosity of the final product, using samples collected in Bahia Tortugas, Baja California Sur (Mexico), in the summer of 1994. At 80°C we obtained a yield of 19.10% and a viscosity of 398 cps: at 28ºC the yield was 15.53% and the viscosity was 466 cps. We conclude that hot extraction is more favourable, because the yield is statistically greater and the viscosity is the same. The effect of extraction time was also investigated in the hot process, using samples collected in Bahia Tortugas in the fall of 1990, to determine the minimum extraction time in which we can obtain high yield and quality of the final product. We tested times from 90 to 165 minutes at 80°C. In the temperature range tested, no significant difference was found between the yields or the viscosity. We conclude that the minimum extraction time is 90 minutes; however, to reach the final reaction point, the time must be extended to 120 minutes

Production and properties of agar from the invasive marine alga, Gracilia Vermiculophylla (Gracilariales, Rhodophyta)

The utilization potential, in terms of agar production, of the invasive alga, Gracilaria vermiculophylla, collected at Ria de Aveiro, northwestern Portugal was investigated. The agar yield ranged from 15% to 33%, with pre-extraction treatment with alkali generally increasing the yield. The gel quality (gel strength and apparent Young’s modulus) was best (>600 g cm−2 and >1,000 kPa, respectively) when alkali treatment with 6% NaOH for 3.5 h was performed. At these pretreatment conditions, the effect of extraction time was also investigated and highest yield and best gel quality were obtained with a 2 h extraction time. By employing these extraction conditions, G. vermiculophylla can be a source of industrial food-grade agar. The structure of agar from G. vermiculophylla was determined through chemical techniques and FTIR and NMR spectrometry. It is mainly composed of alternating 3-linked D-galactose and 4-linked 3,6-anhydro-L-galactose, with methyl substitution occurring at 16–19 mol% of C-6 in 3-linked units and 2–3 mol% of C-2 in 4-linked units. A minor sulfation on C-4 of 3-linked units was also detected; while precursor units (6-sulfated 4-linked galactosyl moieties) were found in the native extract.We thank R. Pereira for algal material collection, L. Martins for FTIR analysis, and two anonymous reviewers for valuable comments on the manuscript. RDV was supported by the Portuguese Foundation for Science and Technology, through a post-doctoral grant (SFRH/BPD/34670/2007)

Factors affecting yield and gelling properties of agar

Agar, a gelatinous polysaccharide in the cell wall of many red algal species, is widely used as a gelling, thickening and stabilizing agent. The commercial value of seaweed is judged by their agar content and gel quality. Seaweed materials with higher agar yield and better gelling properties are desired due to the growing demand for agar in the global market. Agar biosynthesis in seaweeds is affected by genetic variations, developmental stages and environmental conditions, while different agar extraction techniques can also affect the yield and quality of agar. In this paper, the effects of different physiological states of seaweed, abiotic and biotic factors, seaweed storage and agar extraction techniques on the agar yield and gelling characteristics, are reviewed. This information is important as a guide for marine aquaculture of potential agarophytes and the possible effects of climate change on the stock of this natural resource