The effects of alkali treatment time and extraction time of native agar and alkali treated agar obtained from Gracilaria vermiculophylla were studied. The response characteristics were mainly agar yield and gel strength.Alkali treatment was carried out at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h. Agar yield and gel strength decreased with the increase in the time of the alkali treatment. The highest yield (15.3%) and highest gel strength (1,064 g cm −2 ) were obtained at 0.5 h, and therefore this time was used for the next experiment. The extraction of both native and alkali treated agars was carried out at 1.5, 2.0, 2.5, and 3.0 h. The best extraction time for alkali treated agar was 1.5 h, and for native agar 2.5 h. The alkali treated agar obtained with the different alkali treatment and extraction times showed higher melting (92.4-99.7°C) and gelling (35.7-39.6°C) temperatures. Native agar was lower in melting (60.2-64.1°C) and gelling (20.4-23.4°C) temperatures. The 3,6-anhydrogalactose content decreased with increasing alkali treatment time, with the opposite effect during the extraction of native and alkali treated agars.

The brown alga Eisenia arborea is the second most abundant brown alga along the western coast of the Baja California Peninsula of Mexico. Samples of E. arborea were collected in Bahía Asunción, BCS, over 10 months. Chemical composition was analyzed from dried alga (%, dw): moisture (10.34%), protein (9.44%), ash (24.77%), lipids (0.60%), fiber (5.22%), and carbohydrates (49%). Gross energy was 9.8 kJ g −1 . Seven minerals were analyzed and the four most abundant were K, Na, Mg, and Ca, ranging from 907 to 7,946 mg.100 g −1 . The concentrations of six vitamin levels were also determined: A, C, E, D 3, B 2 , and B 1 . Seventeen amino acids were analyzed and the most abundant were glutamic acid, aspartic acid, and leucine. Total fatty acids ranged from 21 to 65 mg.100 g −1 (dw). Individual concentrations were also determined for arachidonic acid, alpha linolenic acid, linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid. Saponins, cyanogenic glycosides, and alkaloids were not detected. Our results suggest that E. arborea is a good candidate to be tested as supplement food for animals, including humans. It contains essential amino acids, is low in lipids and fiber, and could be a source of vitamins and minerals.

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Gracilaria vermiculophylla, from Baja California Sur, Mexico, was studied in order to determine the seasonal variation of yield and quality of native and alkaline agar during 2007-2008. The highest alkaline agar yield was obtained in summer (17%) and the highest gel strength in spring (1,132 gcm −2 ). The highest melting temperature was 98°C (winter). The highest gelling temperature was 68°C (summer). The values obtained are within the range of the most important Gracilaria species harvested worldwide. During the agar extraction step, the best results were obtained after 30 min of alkali treatment with sodium hydroxide (7%), after which the quality decreased significantly. We produced Colagar from G. vermiculophylla which consists of the seaweeds treated with sodium hydroxide and dried. The yield and quality of the agar obtained from the Colagar shows stability in both yield and quality during 1 year of storage, suggesting that alkali treatment is a good method of avoiding agar hydrolysis during storage.