Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1996
Publication Date: N/A
Interpretive Summary: A relatively rapid total dietary fiber (TDF) method was adopted by AOAC International in 1985, a modification was approved in 1991. Since then other comparable but cost-effective methods have been published, one of these was developed in our laboratory. In an earlier study, we compared our method with the modified official method by analyzing a variety of nuts and seeds. TDF values were very similar between the two methods, however we found the fat removing step for most nuts needed further investigation. In this study, we incorporated 2 different extraction methods prior to the analysis of TDF and non-starch polysaccharide fractions for the same nut samples. Results indicated that supercritical fluid extraction (SFE) was more efficient in the initial removal of non-carbohydrate components. Our findings showed that conventional fat extraction using petroleum ether or hexane will lead to overestimation of the dietary fiber value for nuts. This knowledge is very important to users of database which contain TDF values from earlier analyses using conventional extraction procedures. This work also introduces a novel application of SFE in the area of fiber analysis, and it will encourage its use by other analysts.
Technical Abstract: Total dietary fiber (TDF) and non-starch polysaccharide (NSP) contents of eight edible nuts and seeds were compared after pretreatment with three lipid extraction methods. Portions of ground materials were extracted by: 1) n-hexane, followed by 80% methanol. 2) n-hexane:acetic acid (95:5 v:v). 3) supercritical fluid - carbon dioxide. TDF was determined according to a simplified enzymatic-gravimetric method developed in our laboratory. Defatted samples were gelatinized in water and incubated with amyloglucosidase; 95% ethanol was added to the hydrolyzates, and the residues were collected on tared glass crucibles. NSP was determined as described by Englyst and coworkers. Dietary fiber values for all nuts and seeds using any of the extraction methods ranged from 3.47 g/ 100 g for cashew to 28.56 g/ 100 g for sunflower seed. Non-starch polysaccharide values ranged from 2.43 g/ 100 g for pecan to 5.56 g/ 100 g for peanuts. With the exception of sunflower seed, supercritical fluid extracted samples had lower TDF content but similar amounts of NSP compared to the samples extracted by the other two methods.