Influence of extraction time on the rheological properties of agar from some Gracilaria species from the Philippines

Abstract

The influence of extraction time on the clean anhydrous yield, rheological properties, dynamic gelling and melting temperatures of 1.5% agar from six species of Gracilaria and one species of Gracilariopsis collected from the Philippines was determined. The lowest agar yield was measured from Gracilaria 'verrucosa' (10.1%) even after 120 minutes extraction while the highest yields were recorded from G. coronopifolia both after 30 (23.5%) and 60-minute extraction times (26.1%) and G. eucheumoides after 120-minute extraction time (27.3%). A 60-minute extraction of G. heteroclada produced gels with the highest breaking strength (1013 g), the maximum cohesiveness (7.4 mm), the greatest breaking energy (7481 g mm), and the greatest stiffness (137.3 g/mm ^-1). Gracilaria blodgettii gave the weakest gel tested. Dynamic gelling temperature was lowest for G. blodgettii at 60 min (28 °C) and highest for G. edulis at 120 minutes of extraction (46.3 °C). Melting temperature was lowest at 30 min extraction for G. salicornia (58.0 °C) and highest at 30 minutes for G. edulis (95.0 °C).

A strong interactive effect of species, extraction time, and rheological properties was observed, but there was no interaction observed among the species, extraction time and temperatures. Each species showed good rheological properties at a specific extraction time.