Extraction of agar from locally grown Gracilaria verrucosa and development of gelatin free set-yoghurt product using agar

Abstract

Seaweed agar is an important healthy food item, though it is not extracted at commercial level in Sri Lanka. This study investigated an agar extraction method that render high agar yield and development of agar incorporated gelatin free yoghurt targeting the needs of vegetarian communities. The technologies developed, in this study, to extract food grade agar from locally available Gracilaria verrucosa and to produce agar incorporated yoghurt which has potential to commercialize as an industry. Agar was extracted using G. verrucosa under optimum conditions: Dried G. verrucosa was soaked in an acetic acid solution at pH 5 for 30 min; soaked G. verrucosa was pressure-cooked with 45 times volume of water for 20 min; the agar extract was allowed to set in trays for 6 h at 25±2 ºC; the resulted gel layers were frozen for 8 h and thawed for 4 h at 25±2 ºC. The melted water was drained out and gel layers were cut into strips. Gel strips were dried at 45 ºC for 36 h and dried agar were ground to obtain a fine agar powder. A gelatin free set-yoghurt product was developed using extracted agar as a texture stabilizer. The developed yoghurt (0.25% agar) which scored high for sensory quality attributes, showed similar sensory properties as in gelatin (0.61%) containing yoghurt (p>0.5). The pH and titratable acidity of the seaweed yoghurt were 4.5 and 0.85% (w/w) respectively on 15th day of storage at 4±2 ºC. Agar extracted from G. verrucosa contained 80.1% (w/w) of dietary fiber. It was found that seaweed yoghurt contains 0.18% (w/w) of dietary fiber content. Agar contained set yoghurt consists of 77.34, 3.40, 3.10, 0.75 and 22.66% (w/w) of moisture, protein, fat, total ash and total solid content, respectively.