Determination of Starch, Reducing Sugar and Sucrose in Flavored Squid by DNS Photometric Method

For determination of starch, reducing sugar and sucrose in flavoured squid, 2 portions of sample (3-5 g each) were taken. In one portion of the sample, after dissolution with water and hydrolysis of hydrochloric acid solution, the sample solution was subdivided into 2 aliquots, one for determination of reducing sugar contained originally, and another for determination of total reducing sugar including those derived from sucrose by hydrolysis. For another portion of the sample, after removal of fat by extraction with ether and separation of sucrose by dissolution with water, the insoluble was refluxed in hydrochloric acid solution to have the starch hydrolyzed to give monosaccharide, and after filtration, the filtrate was used for determination of starch. Aliquots of 2.0 mL was taken separately from each of the 3 sample solutions described above and contents of reducing sugar (or mono saccharide) in these aliquots were determined by the DNS photometry by conversion calculation. Standard glucose solution was used to prepare calibration curve. An imporatant revision on the procedure of separation of sucrose in the preparation of sample solution for determination of starch was made by replicating the water-dissolution process by 3-5 times according to the sucrose content in the sample, thus leading to a great decrease of residual amount of soluble sucrose in the insoluble. For instance, in 2 samples of flavoured squid with low and high contents of sucrose, amounts of sucrose remained in the insoluble found by the orignal procedure were 27.0 mg·g^-1 and 62.2 mg·g^-1, while the amounts found by the revised procedure were decreased to 0.32 mg·g^-1 and 0.63 mg·g^-1, with rate of lowering of 98.8% and 99.0%. Hence, accuracy of analytical results of starch contents was ensured by the modified procedure.