Quantitative analysis of hydrocolloids in food systems by methanolysis coupled to reverse HPLC. Part 1. Gelling carrageenans

A procedure for quantitative determination of gelling carrageenans, namely kappa- and iota-carrageenans, in complex food systems, is presented. It involves three main steps: (i) homogenization and freeze-drying of sample; (ii) mild methanolysis of carrageenans; (iii) reverse HPLC analysis of 3,6-anhydrogalactose dimethylacetal released. The proposed method is specific for gelling carrageenans and allows their determination in the presence of other hydrocolloids such as pectins, alginates, xanthan or galactomannans. Recoveries were generally higher than 80%, with precision of 3.2% and a sensitivity of about 0.03%. Carrageenans may be directly determined in complex food products such as yogurt, gelling milk or pâte without need for prior delipidation, deproteinization or extraction steps.