Optimization Of Agar Extraction From Local Seaweed Species (Gracilaria Salicornia) In Tanzania For Tissue Culture Of Pleurotus Hk-37

ABSTRACT

This study aimed at developing agar extraction protocol from local Gracilaria salicornia species and investigates its physico-chemical characteristics, production cost and application in tissue culture of Pleurotus HK-37. Purposive sampling was used in collection of Gracilaria salicornia during dry (northeast monsoon) period in 2016 at Chwaka bay, Zanzibar, Tanzania. A 33 factorial experimental design was used in the extraction of treated agar whereby three independent variables of NaOH concentration (10, 20 and 30% w/v), alkali pretreatment duration (0.5, 1 and 2 hours) and extraction temperature (115, 120 and 125°C) were used to determine the optimal conditions for production of high quality agar. Agar yield, gel strength, sulfate content, gelling and melting temperatures were evaluated as dependent variables for a combination of independent variables. The optimal conditions were observed at 30% NaOH concentration, 2 hours alkali pretreatment duration and 120°C extraction temperature. The gel strength of the agar obtained under these conditions was 510.26 ± 16.2 g/cm2 at a cost of 160.83 USD per 500 g as compared to 178.7 USD per 500 g of the imported commercial agar with similar properties (613.8 ± 10.4 g/cm2 ). Mycelial growth rate (mm/day) of Pleurotus HK-37 was measured on five different PDA media prepared from extracted agars. Oxoid Agar powder, Bacteriological PDA media was used for comparison. The average mycelial growth rate on the extracted PDA media ranged between 9.87 ± 1.44 and 14.9 ± 0.85 mm/day. It is concluded that local agar is capable of replacing relatively expensive imported agar for most of general purposes. This offers a new possibility of using locally available low cost agar in place of commercial agar as an alternate option for tissue culture of mushroom species such as Pleurotus HK-37.