AGAR AS A GELLING AGENT - CHEMICAL AND PHYSICAL ANALYSIS

Agars with different performance in bioassays were analysed for physic al and chemical properties. Agars with the highest gel strength had th e best performance, Good performance was also related to a low pH of a suspension of agars and to a low sulphur content. The diffusion rate of ions in gels differed between agars, but could not explain differen ces in agar performance. The time of autoclaving had a marked effect o n the get strength, however, without affecting the performance. Chemic al analysis revealed large differences between agars. The best agars h ad a relatively row salt content, One of the best agars had an extreme ly high content of trace elements. Agar impurities, especially of the trace elements were tightly bound to the agars. Up to 30% of the Muras hige and Skoog (MS) salts were also immobilized in the gel. At pH 4.2, less nitrogen and phosphate were available from the MS medium than at pH 5.7. Chlorine could be washed out completely and appeared To be a good marker for agar quality and purity. With AgNO3, chlorine contamin ation could easily be visualized.