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  • 1
    Publication Date: 2021-05-19
    Description: Gracilaria gracilis farming was conducted in the Bizerte lagoon (North of Tunisia) at two depths (0.5 and 2.5 m) using various initial fragment weights (5, 20, and 40 g) in order to investigate the alga growth, agar yield, and quality. IR spectra of agar were performed in comparison to the commercial one. Moreover, the proximate biochemical composition of seaweeds was investigated. The results showed that the highest daily growth rate and agar yield were recorded at 0.5 m, using 5 g as initial fragment weight (5.98 ± 1.98% day−1, 14.87 ± 1.91% dw, respectively). Maximum gel strength was 356.67 ± 15.25 g cm−2 at 2.5 m using an initial weight of 20 g. Gelling and melting temperatures varied from 34.33 ± 0.57 to 35.50 ± 0.57 °C and from 77.00 ± 1.00 to 85.00 ± 0.50 °C, respectively. IR analysis revealed that some spectra were similar, while others were different. The highest dry matter (22.68 ± 1.77%) and ash content (35.25 ± 0.02% of dw) were recorded at 2.5 m, using initial weights of 20 and 5 g, respectively. The maximum carbohydrate and the crude protein contentswere obtained at 0.5m, using 5 g as initialweight (9.52 ± 0.36 and 5.83 ± 0.7% dw, respectively). The highest R-phycoerythrin content was recorded at 0.5m(0.050 ± 0.007 mg g−1 dw), while the maximum of total lipid content was recorded at 2.5 m with initial weight of 5 g (3.58 ± 0.63% dw). Our findings indicated that growth and biochemical composition of G. gracilis depend on the depth and initial fragment weights.
    Description: In Press
    Keywords: Gracilaria gracilis ; Red seaweed ; Culture ; Agar ; IR spectroscopy ; Biochemical composition
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp. 2499–2512
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  • 2
    Publication Date: 2021-05-19
    Description: The present study aims to investigate the effects of irradiance and salinity on the growth and agar yield in early stages of development of carposporelings and young tetrasporophytes of Gracilaria gracilis in the laboratory conditions. Three levels of irradiance, photoperiod and salinity were tested. The results showed that the highest growth in basal disc of carposporelings was recorded at 8:16h light/dark, 60 μmol photons m-²s-1, and a salinity of 40 psu after four weeks of culture. The optimal percentage of erect fronds occurred at 16:8 h light/dark, 32 μmol photons.m-² s-1 and a salinity of 30 psu .The highest weight (about 6000mg) of juvenile tetrasporophytes was recorded at 40psu after 228 culture days. The maximum of length was also obtained at 40 psu at the end of the study. The best agar yield was recorded at 8:16 h light/ dark and a salinity of 20 psu. This study proved that Gracilaria may be cultivated using spores in order to obtain mature plants and then extract useful compounds such as agar.
    Description: Cette étude a été réalisée sur les carpospores et les petites plantules (tétrasporophytes juvéniles) qui en sont issues de la rhodophycée Gracilaria gracilis de la lagune de Bizerte. Elle a pour objectif de tester l’effet de trois intensités lumineuses, photopériodes et salinités sur la croissance et le rendement en agar-agar. Les résultats montrent que la croissance la plus importante des carpospores a été enregistrée sous une intensité lumineuse de 60 μ mol photons m-2s-1, une photopériode de 8 :16 h et une salinité de 40 psu (260 ± 64.48 μm) après quatre semaines de culture. Le pourcentage le plus élevé (100 %) des frondes érigées a été obtenu en fin de culture sous 32 μ mol photons m-2s- 1, une photopériode 16 : 8 h et une salinité de 30 psu. Le poids le plus élevé (environ 6000 mg) des petites plantules issues des carpospores a été enregistré après 228 jours de culture à 40 psu. La longueur maximale (16.25 ± 0.36 cm) a également été obtenue à une salinité de 40 psu. Le rendement en agar-agar a atteint 30.75 ±7.15 % du poids sec de l’algue avec les valeurs les plus faibles d’intensité lumineuse, de photopériode et de salinité. Cette étude a mis en évidence la possibilité de culture de Gracilaria à partir des spores afin d’obtenir des plantes adultes et d’en extraire par la suite des substances d’intérêt tel que l’agar-agar.
    Description: Published
    Keywords: Gracilaria gracilis ; Growth ; Carposporelings ; Tetrasporophytes ; Irradiance ; Salinity ; Agar
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.141-150
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  • 3
    Publication Date: 2021-05-19
    Description: Ce travail a porté sur la culture au laboratoire de carpospores et de tétraspores issues de deux algues rouges : Gracilaria gracilis et G. bursa-pastoris de la lagune de Bizerte. Différentes conditions d’intensité lumineuse et de photopériodes ont été testées. Les résultats ont montré que la meilleure croissance des carpospores a été enregistrée sous la photopériode de 8/16 et une intensité lumineuse de 2000 lux et ceci pour les deux espèces. Pour les tétraspores, l’optimum de croissance a eu lieu à la même photopériode mais à 3600Lux pour Gracilaria gracilis et 2000 Lux pour G. bursa-pastoris. Ces résultats montrent certaines convergences vis-à-vis de leurs exigences en lumière mais aussi certaines divergences dont on devrait en tenir compte dans le futur pour cultiver les deux espèces à une plus grande échelle.
    Description: This study has been carried out on the carpospores and tetraspores of the two seaweeds Gracilaria gracilis and G. bursa-pastoris collected in theBizerte lagoon . Both types of spores were cultivated in laboratory conditions. Different irradiation levels and light / dark cycles were tested. The results showed that the highest growth of carpospores was recorded at 8:16 light/ dark cycle and 2000 Lux. While the best growth of tetraspores was obtained at 3600 Lux in G. gracilis and 2000 Lux in G. bursa-pastoris, the two at 8:16 photoperiod. These results showed some slight similarity of the two species but in the same time some differences in irradiance requirements. These differences are very important to take into account for the future cultures in a large scale.
    Description: Published
    Keywords: Gracilaria gracilis ; Carpospores ; Culture ; Tétraspores ; G. bursa-pastoris
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.89-99
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