The Ultrasound-assisted Sulfated Modification Of Dietary Fiber From Apple

Dietary fiber, which is an essential component of the food, has several important physiological functions, such as smoothing intestinal catharsis, avoiding the symptoms of diabetes, decreasing blood-lipid, and so on. Especially the soluble dietary fiber plays an important role in human metabolism. Pomace is rich in dietary fiber, so it can be used to extract the fibers. We extracted soluble dietary fiber from pomace and sulfated modification to improve the physiological functions. All of these will have profound effects on the development and utilization of the resources of apple.In this study, we modified the decolorizing pomace through squeezing and extracted soluble dietary fiber. Sulfamic acid acted as the esterification agent to modify soluble dietary fiber from apple. Firstly, the effects of two reaction medium on the sulfation soluble dietary fiber were investigated. Secondly, we determined the physical and chemical properties of sulfation soluble dietary fiber. Thirdly, the components of sulfation soluble dietary fiber were isolated through the column chromatography and its chemical structure was investigated. Finally, we studied the physiological activities of sulfation soluble dietary fiber, including antioxidant activity and inhibition breast cancer cells. The main results were as follows:(1) Soluble dietary fiber could be sulfated in water medium. The mass ratio of soluble dietary fiber and esterification agent(g:g) 1:3(sulfamic acid:sulfuric acid=2:1), reaction temperature of 60℃, ultrasonic frequency 30 k Hz, and the volume ratio of soluble dietary fiber and water(g:m L) 1:90, reaction time 3h. Under this conditions, the degree of SSDF-1 reached to 0.23.(2) The soluble dietary fiber from apple was sulfated by using ultrasound-assisted sulfamic acid-N,N-dimethylformamide method. The degree of substitution was chosen as the indicator for the single-factor experiment and the orthogonal experiment to optimize the sulfation conditions. The results showed that the optimal technology parameters were as follows: the mass ratio of soluble dietary fiber and sulfamic acid(g:g) 1:3, reaction temperature of 60℃, ultrasonic frequency 35 k Hz, and the volume ratio of soluble dietary fiber and DMF(g:m L) 1:70, reaction time 1.5h. Under the optimal conditions, the degree of SSDF-2 reached to 0.97.(3) Sulfated modification could significantly improve the cation exchange capacity and oil-holding capacity and SSDF-2 was better than SSDF-1. From FTIR, the soluble dietary fiber from apple after sulfated had the typical sulfated functional groups. The results of molecular weight distribution showed that the average molecular weight was reduced after sulfated and molecular weight distribution became narrower. According to scanning electron microscope, the particle size of soluble dietary fiber after sulfated was smaller and the surface became rougher with an internal porous structure.(4) Three components were isolated from the SSDF-1 and SSDF-2 and their main components named SSDF-1b, SSDF-1c, SSDF-2b, SSDF-2c. Six monosaccharides, including mannose, rhamnose, glucuronic acid, glucose, galactose, xylose, were identified in SSDF-1b, SSDF-1c, SSDF-2b and SSDF-2c. Galactose was the main sugar backbone in SSDF-1b and SSDF-2c, while xylose and galactose were the main monosaccharide composition in SSDF-1c and SSDF-2b. The average molecular weight of SSDF-1b was estimated to be 8893 Da. However, SSDF-2b and SSDF-2c were measured to be 45406 Da and 42914 Da, respectively. The results of NMR showed that the SO3-group would be partially sulfated at C-6 of sugar unit in the all components, while the SO3-group would be also sulfated at C-2 of sugar unit in the SSDF-2c.(5) The results revealed that sulfatied modification could significantly improve antioxidant activity of soluble dietary fiber and SSDF-2 showed a stronger antioxidant activity. The oxygen radical absorbance capacity of SSDF-2 was 117.75 which was 1.37 times than that of soluble dietary fiber. In addition, the results showed that sulfatied modification could also improve the capacity of inhibition breast cancer cell MM231. SSDF-1 with low molecular weight showed the slightly stronger inhibition activities than SSDF-2.