Determination of crude fiber in food analysis
Answers
Dietary fiber can be defined as sum of polysaccharides and lignin that are not digested by human digestive enzymes. The major components of dietary fiber are cellulose, noncellulose such as hemicelluloses and pectin, lignin, and hydrocolloids (gums, mucilages, and algal polysaccharides). Human foodstuffs contain mainly noncellulose polysaccharides, some cellulose and little lignin. The average proportions of noncelluloe polysaccharides. Cellulose and lignin for common foodstuff are about 70%, 20% and 10% respectively(Laura and other 2003).
The crude fiber method was developed in the 1850s to estimate indigestible carbohydrate in animal feeds. Since an easy alternative was not available, fiber in human foods was measured as crude fiber until the early 1970s (except for Southgate in England). Crude fiber method is one of the gravimetric method that measures the organic food residue remaining after sequential digestion with 0.255N sulphuric acid and 0.313N sodium hydroxide solutions, followed by oven-drying at 104ºC overnight and ignition in muffle furnace at 600ºC for 3 hours. The compounds removed are predominantly protein, sugar, starch, lipids and portions of both the structural carbohydrates and lignin. Crude fiber method measures variable amounts of the cellulose and lignin in the sample, but hemicelluloses, pectins, and added gums or hydrocolloids are solubilised and removed. Therefore, crude fibre measurement drastically underestimates dietary fibre in foods since it measures only cellulose and lignin. As a result, crude fiber method is only adequate for determination of fiber in animal feed product, but not suitable for human food analysis as lignin is significant to human health (James N.BeMiller 2003)