Agars of Gelidiella acerosa of west and southeast coasts of India Kamalesh Prasad, A.K. Siddhanta * , M. Ganesan, B.K. Ramavat, B. Jha, Pushpito K. Ghosh Marine Algae and Marine Environment Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar, 364 002 Gujarat, India Received 8 June 2004; received in revised form 12 July 2006; accepted 12 July 2006 Available online 1 September 2006 Abstract Seventeen agar samples were extracted from Gelidiella acerosa (Forsskal) Feldmann and Hamel (Rhodophyta, Gelidiales) specimens collected from nine different sites on the Indian coast—five from southeast coast and four from the west coast. The agar samples were analysed. The stability characteristics of the gels of selected agar samples were studied by rheometry under applied stress conditions, i.e. variation of the storage (G 0 ) and loss moduli (G 00 ) were studied under varying frequency and duration (time) of the stress applied. Yield, apparent and dynamic viscosities, gelling and melting temperatures, 3,6-anhydrogalactose (3,6-AG), sulphate contents and TGA (Ther- mogravimetric Analysis) measurements of the products were done. It was observed that the best quality agar was produced by G. acerosa occurring in the Gulf of Mannar region in the southeast coast. The gel strengths and the viscosities of agars extracted from Gelidiella acerosa occurring in the Gulf of Mannar ranged from 500 to 700 g cm 2 and 33 to 45 cP for 2001 collections and for 2002 collections the corresponding values were 450 to 845 g cm 2 and 55 to 67 cP respectively. On the other hand, for the agar samples extracted from the west coast of India, the gel strength and viscosities values ranged from 225 to 400 g cm 2 and from 15 to 30 cP, respectively. The agars obtained from G. acerosa collected from southeast coast have been found to be suitable for bacterial culture and molecular biology. This is the first report of superior quality of agar from the Indian agarophytes. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Gelidiella acerosa; Agar; Viscoelasticity; TGA; ANOVA 1. Introduction Gelidiella acerosa (Forsskal) Feldmann et Hamel is a warm water tropical alga. It occurs in Indian, Pacific and Atlantic Oceans (Srinivasa Rao, 1972) and is one of the main sources of raw material for the manufacture of agar in the Philippines. Moreover, there is limited information available in the primary literature on the characteristics of agar from G. acerosa (Gazon-Fortes, 1985). The world’s first source of agar was Gelidium from Japan in the begin- ning of the seventeenth century, but at the turn of the twentieth century the increasing demand for phycocolloid exceeded the supply of this alga. Since then Gracilaria has played an important role in the production of agar (Armisen, 1995). Various species of Gracilaria have been exploited in India to produce food grade agar. The agar obtained from these seaweeds, especially members of Gel- idiaceae, is of superior quality and widely used in a number of preparations in biomedical, food, cosmetics and phar- maceutical industries (Armisen, 1995). However, due to the poor quality of agar obtained from Gracilaria in India, researchers concentrated on the extraction of agar from other varieties of seaweeds of family Rhodophyceae. G. acerosa is one of the red seaweeds, which has been reported to be a source of good quality agar (Armisen, 1995). Agars are industrially important for their excellent thickening or gelling abilities (Selby and Whistler, 1993; Therkelsen, 1993). The physical properties and texture of agar gel are significant factors in determining its application, especially in the food industry. Hutardo-Ponce and Umezaki (1988) have reported the rheological properties of agars from Gracilaria spp. occurring in the Philippines, they were also successful in producing gels with the best rheological properties among the species tested (Hutardo-Ponce and 0960-8524/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2006.07.028 * Corresponding author. Tel.: +91 278 2561 354; fax: +91 278 2567562/ 2566970. E-mail address: aks@csmcri.org (A.K. Siddhanta). Bioresource Technology 98 (2007) 1907–1915