Effect Of Ultrafine Grinding On Processing And Functional Properties Of Insoluble Dietary Fiber From Coffee Peel

In recent years,with the improvement of people's living standard,more and more people begin to pay attention to the balance of diet.Dietary fiber,one of the nutrients,is favored by people.Many studies have shown that dietary fiber has high physiological activity due to its existence of many active functional groups,including the ability to prevent constipation,obesity,gallstones,colon cancer,diabetes,coronary heart disease and other diseases,as well as the ability to resist oxidation and adsorb toxic and harmful substances.Coffee peel is a by-product of coffee processing,most of it is discarded,resulting in waste of resources and environmental pollution.However,its dietary fiber content is high,and it is mainly insoluble dietary fiber(IDF).Therefore,appropriate modification methods can be used to convert part of IDF into soluble dietary fiber(SDF)for better processing and functional characteristics.In this paper,the ultra-fine grinding technology is used to physically modify the coffee peel in order to improve its processing and functional characteristics,and the ultra-fine grinding coffee peel powder is added to biscuits for application,which provides a new idea for the deep processing and comprehensive utilization of coffee peel and has important guiding significance.(1)Coffee peel is used as raw material,and coffee peel powder with different particle sizes is obtained through traditional crushing and superfine crushing.By measuring the physical properties,adsorption properties and structural characteristics of powders with different particle sizes,it is shown that the water holding capacity,swelling capacity,oil holding capacity,solubility and cation exchange capacity of the powder are improved to different degrees with the reduction of particle sizes.The swelling and solubility increased significantly from 3.86 mL/g to 6.14 mL/g and 13.23%to 44.50%,respectively.The adsorption capacity of the powder to glucose,nitrite and cholesterol also increases with the decrease of particle size,and the difference between ultrafine powder and traditional powder is significant.The structural characterization of powders with different particle sizes shows that ultrafine grinding does not significantly change the structural composition.(2)IDF from coffee peel extracted by microwave-assisted alkali method was used as raw material,and IDF powder with different particle sizes was obtained by traditional and ultra-fine pulverization.By measuring the dietary fiber composition,physical properties and adsorption properties of IDF powder,it is found that ultrafine grinding redistributes the composition of IDF,reduces the content of IDF,increases the content of SDF,and at the same time improves the physical properties of IDF powder to a certain extent.Its swelling property and solubility both increase with the decrease of particle size,but its water and oil holding properties increase first and then decrease with the decrease of particle size,also its adsorption properties show a similar trend with water and oil holding properties.When the particle size is about 35.25 ?m,the adsorption values for glucose,nitrite,cholesterol and sodium cholate reach the highest point.SEM images show that excessive pulverization will destroy the network structure of fibers.FTIR results showed that ultrafine grinding did not significantly change its chemical composition.Thermogravimetric analysis shows that ultra-fine pulverization has no obvious effect on the thermal stability of IDF and can be applied to food processing industry within 300?.X-ray diffraction shows that IDF in coffee peel is a typical cellulose type I crystal structure,and the crystallinity decreases from 42.34° to 35.54° with the decrease of particle size.(3)Using IDF from coffee peel with different particle sizes as raw materials,the contents of polyphenol compounds in bound and free forms and their antioxidant capacity were determined respectively.It was found that the contents of total phenols,total flavonoids and total phenolic acids of various monomers increased with the decrease of particle size.In addition,the antioxidant activity of DPPH,ABTS and FRAP increased with the decrease of particle size,which was consistent with the change trend of polyphenol content.Finally,using ultra-fine crushed coffee peel as raw material,the crisp biscuit was made by replacing part of flour with 5%,10%,15%,20%,30%.It was found that the biscuit with 5%replacement ratio obtained a higher sensory score,and at the same time it also showed the unique color and aroma of coffee peel.However,if the addition ratio was too high,it would have adverse effects.