Structural And Functional Properties Of Dietary Fiber From Chestnut Rose Residue Modified By Steam Explosion

Chestnut rose is a kind of hard and prickly fruit that is widely distributed in Guizhou province with a high annual yield.Because of its sour and rough taste,chestnut rose is difficult to eat directly and therefore was mostly used as a raw material to make juice or be further processed into other products.The residue after the juice-making caused a large amount of resource waste.The content of dietary fiber in chestnut rose residue is rich but the insoluble dietary fiber(IDF)accounts for more than 80%,which limited its direct application in food processing.Steam explosion is an efficient and pollution-free method that can alter the structure of materials by the chemical acidolysis of steam water and the physical shear forces by the explosion.This method was mainly used in cellulose modification of wood and straw.In this study,the dietary fiber in chestnut rose residue was modified by steam explosion treatment(SE),and it was found that the SE could significantly promote the transformation of IDF to the soluble dietary fiber(SDF)in chestnut rose residue.Meanwhile,the structural and functional properties of SDF and IDF in chestnut rose residue were all changed.The content of SDF and IDF of chestnut rose residue was extracted and determined by the enzymegravimetric method.The single factor and response surface methodology were used to determine the conditions of SE for optimum the SDF extraction yield in chestnut rose residue.The optimal conditions were as follows: chestnut rose residue powder size: 60,pressure: 0.87 MPa,and pressure time: 97 s.Under such a setting,the extraction rate of SDF from chestnut rose residue was 15.82�0.31%,which was 69.95�2.51% higher than that before the modification.The structural properties of IDF and SDF from chestnut rose residue were both changed after SE.The IDF after SE had a fluffy and rough surface with many folds,and its specific surface area was 2.52 times higher than that before SE.Furthermore,part of the lignin,cellulose,and hemicellulose in IDF were degraded to small molecules and the crystallinity of IDF was slightly increased from 31.93% to 32.45% after SE.However,the thermal stability of the IDF after SE had no significant change.In terms of structural changes of SDF,its surface showed a more porous foam structure after SE,and the specific surface area was increased 14 times than that before modification.After SE,part of the crystalline zone of SDF was transformed into the amorphous zone,and the content of short chain SDF and hydroxyl groups were both increased.In addition,the hydrogen bonding of SDF was stronger and therefore the thermal stability of SDF was improved after SE.The experimental results further showed that SE can enhance the functional properties of SDF and IDF.After modification,the water holding capability of IDF was increased from 6.77�0.33g/g to7.92�0.27g/g,and the swelling capability was increased from1.01�0.11 m L/g to 2.00�0.09 m L/g.The oil holding capacities of IDF and SDF were increased 0.3 times and 2.9 times than those before SE,respectively.In addition,the capacity of hypoglycemic,cation exchange,nitrite adsorption and cholesterol absorption of IDF and SDF were all improved after SE.However,in terms of antioxidant capacity,the modified SDF and IDF in chestnut rose residue were only showed better scavenging ability on hydroxyl radicals,but the scavenging ability on DPPH and ABTS radicals was slightly decreased.