Study On The Detection Technique Of Fructooligosaccharides In Four Kinds Of Foods

Fructooligosaccharides(FOS) are a group of functional compounds, which is formed by β-(2�'1) linked fructofuranosyl unit, with degrees of polymerization(DP) ranging from 2 to 9. Being a new nutrition enhancer, FOS is widely added in foods. According to the enzymatic production, FOS are subclassified in two series: short-chain fructooligosaccharides(sc-FOS) and inulooligosaccharides(IOS). The first series is composed by a terminal glucose unit and fructose unit chains called GFn, whose major components are 1-kestose(GF2), nystose(GF3) and fructofuranosylnystose(GF4); while the second series only has fructose unit chains called Fm, whose major components are inulotrioses(F3), inulotetraoses(F4) and inulopentaoses(F5). However, due to the absence of commercial standards, the quantitative analysis of IOS in foods is performed by enzymatic hydrolysis to break down all fructans into fructose. This way leds to poor accuracy and repeatability. Therefore, developing a rapid and accurate detection method of FOS in foods is still a challenge.At present, the reported methods for preparation and purification of IOS standards have the disadvantages on poor separation effective and time-consuming operation. In this study, the pure F3, F4 and F5 were separated from the IOS mixture by two gel-filtration columns, and then detected by refractive index detection. The purity of the obtained fractions were checked by HPAEC-PAD. It is showed that F3 and F4 fractions are pure(the purity is above 95%). Although F5 fraction is still mixed with GF4, the amount of F5 can be calculated through subtracting the amount of GF4.The reported methods for the determination of FOS in foods have the disadvantages on complex pretreatment, bad separation effective and repeatability. In this study, a high performance anion-exchange chromatography coupled with pulsed amperometric detection(HPAEC-PAD)method has been developed, based on optimization of the sample pretreatment and chromatographic separation conditions. The samples were extracted with deionized water and defatted by On Guard II RP pretreatment column. The separation was accomplished on a Carbo Pac PA 200 column by gradient elution. The mobile phases consisting of deionized water, 0.2 mol/L Na OH and 0.4 mol/L Na Ac were used. The flow rate was 0.4 m L/min and the column temperature was 30 °C. The injection volume was 25 μL.Based on the developed methods, four kinds of foods using FOS as an additive were detected, including milk powder, infant formula rice powder, flour strings and solid drink. The results showed a good linear response in the concentration range of 0.05-10 mg/L(r>0.9980). The limits of quantification were 0.07, 0.02, 0.04, 0.02, 0.03 and 0.10 mg/L for GF2, GF3, GF4, F3, F4 and F5, respectively. The recoveries at three spiked levels varied from 81.8% to 118.2% in milk, rice flour and flour samples, with the relative standard deviations below 4.9%. The developed HPAEC-PAD method is successfully separated short-chain FOS from IOS. The method is simple, accurate and sensitive, and is suitable for the simultaneous determination of six individual FOS and IOS components in four kinds of foods.