Профессионально-ориентированное чтение для магистров и аспирантов пищевых специальностей университета (сборник текстов). Михедова Л.Г. - 6 стр.

                                                                        Rapid Enzymatic Procedure – the third approach – is
                                                                     intended to provide a single value for the soluble and insoluble
                  8. Methods of Analysis                             fiber content of the food. Currently under review and likely to
                                                                     be approved by the AOAC this procedure involves enzymatic
   Because the term "dietary fiber" encompasses such a diverse       removal of protein and starch from fat-extracted food. The
group of compounds, the analysis for its content in foods may        residue is corrected for ash and protein content, and the fiber is
be achieved with several approaches. Included among these are        determined gravimetrically. Although rapidly yielding results,
the following three methods:                                         this gravimetric procedure does not comprehensively determine
   Extraction Methods may be used to isolate various fractions       individual fiber components. (2000)
which are then gravimetrically quantified. Formerly the
Association of Official Analytical Chemists (AOAC) method,
                                                                                           9. Puffed Cereals
crude fiber analysis is based on extraction with acid and alkali.
As this procedure does not measure any specific carbohydrate or
                                                                        For the puffing of cereals, i.e., greatly decreasing their bulk
group of carbohydrates, it does not accurately estimate the
                                                                     density, two general methods are used. The first is the sudden
dietary fiber content, nor can it be quantitatively related to the
                                                                     application of heat at atmospheric pressure. In this technique,
fiber content of foods. Neutral and acid detergents are the bases
                                                                     water is vaporized before it has time to diffuse to the surface of
of another, extraction method the Neutral Detergent Fiber
                                                                     the piece. The internal vaporization then expands, or puffs, the
procedure (NDF), for isolating fractions. Originally developed
                                                                     product. The second type is the sudden transfer of a piece
for analysis of animal forages, this method was modified for
                                                                     containing superheated water to a lower pressure, thus allowing
analysis of human foods which are high in fats, protein and
                                                                     the water to suddenly vaporize. Both types depend upon water
starch. It has the advantage of being relatively rapid and is
                                                                     going to a vapor as the driving force. The key to the degree of
useful for estimating the content of insoluble structural
                                                                     puffing is the sudden change in temperature or pressure.
polysaccharides and lignin. A modified NDF is an official
                                                                     Examples of processes using these techniques are given below.
method of the American Association of Cereal Chemists.
                                                                        Oven-puffed rice is an example of the sudden application of
   Analysis of the Individual Components of fiber constitutes
                                                                     heat. Milled rice is cooked at 15 psi until it is uniformly
the second approach for determining the fiber content of food.
                                                                     translucent, dried to 30% moisture, tempered for 24 hr, and
The Southgate procedure, the best known of this type of
                                                                     dried to 20% moisture. The intact kernels are subjected to
analysis, involves removing the individual fractions through a
                                                                     radiant heat to plasticize the outside of the kernel. The kernels
series of extraction steps. After hydrolyzing the fractions, the
                                                                     are bumped (to destroy their internal structure) and again
sugar components are determined by gas-liquid or liquid
                                                                     tempered for 24 hr. Then they are passed through the oven at
chromatography. Although this approach is difficult and time-
                                                                     300°C for about 30 sec. In this technique, the expansion is not
consuming, the detailed analytical data provided by these
                                                                     great, just two to five times.
methods are invaluable in understanding the variability in
                                                                        Pressure-puffed (often referred to as gun-puffed) products
physiological response induced by different sources of fiber.
                                                                     can be made from a dough mixed and steam-cooked to about