Gas-chromatographic determination of free sugar in soy protein isolate

Abstract

The results of determination of free sugars (glucose, sucrose, raffinose, stachyose) in soy protein isolates by gas chromatography are presented in the article. The aim of the study was to separately determine glucose, sucrose, raffinose and stachyose in isolates of soy protein (%) by gas chromatography.

Determination of free sugars in soy protein isolates was carried out by gas chromatographic analysis. Glucose, sucrose, raffinose and stachyose, extracted with methanol from samples of soy protein isolates, were concentrated in a fume hood in a stream of nitrogen. Further, the dry residue was silylated with N-methyl-N- (trimethylsilyl) trifluoroacetamide (MSTFA) and chlorotrimethylsilane (TMCS) in pyridine at 60^оC for 1 hour. The resulting solution was diluted 10-fold and part of the solution was placed in a 2-cm³ chromatographic vial. For the analysis, 1μl of the sample was used, which was injected into the evaporator using an autosampler. Separation of free sugars was carried out on the capillary column DB-5HT (phase (5% -phenyl)-methyl polysiloxane). Mobile phase: helium. Detection was carried out using a flame ionization detector of a gas chromatograph. The determination was made using the internal standard - tricaprin. Sugar glucose, sucrose, raffinose and stachyose sugars from SigmaAldrich were used in conjunction with the calculation method to establish the sensitivity coefficients.

During the development of the methodology a number of commercial samples of soy protein isolates were analyzed. The model Sansun 90 DN, Isolate DB 909 and Oil, according to the passport, the carbohydrate content is not more than 0.50%, which is confirmed experimentally. According to the passports, samples SunSoy 690, Pro – Vo 500 and Pro-Vo DR1 carbohydrate content should not exceed 0.10%, however, it was experimentally established that the total content of free sugars in these samples is overstated and is 0.34; 0.25 and 0.30 %, respectively.  Also, overestimation of passport data is observed for the model BS-90 Dalian.

The results of the study are interesting and practically applicable in the field of analytical control of soybean processing products production, in particular, soy protein isolates. As well as this technique is necessary for the incoming quality control of soy protein isolates in the production of baby food.