Acetic acid pretreatment in agar extraction of Philippine <i>Gelidiella acerosa</i> (Forsskaal) Feldmann et Hamel (Rhodophyta, Gelidiales)

Abstract

Application of different pre-extraction treatments and extraction methods were used to isolate agar from Gelidiella acerosa. Acetic acid pretreatment entailed soaking the sample in 0.5% acetic acid for 1 hour at 16-20 °C. Alkali pretreatment entailed treatment with l N NaOH at 90°C for 1 hour and eutralization in weak acid for another hour at 16-20 °C. Native agar was extracted directly from air dried samples. One hour extraction using steam pressure at 15-2PSI and boiling at 100 °C in a water bath were applied respectively. Comparative analysis showed that the acetic acid pretreated and autoclaved sample gave the highest agar yield (29.8 ± 2.41%) and gel strength (676 ± 4 g cm"2) among the extraction methods applied. Other physico-chemical properties of acid-modified agar were measured. Relative viscosity of a 1.0% solution at 65 °C ranged from 5-70 cps. A melting temperature of 90-98 °C is comparable to that of the agars from most Gelidiales, while a gelling temperature of 42-47 °C is relatively high which is suspected to be associated with a number of chemical variables masking or altering the basic structural unit of agar. Temperature hysteresis (difference between gelling and melting temperatures) at 48—50 °C was comparable to that of Difco Bacto agar tested at 50 °C.