Relative Biological Values

Should the nutritional and other considerations permit fortification, a number of zinc sources can be used to fortify grain products. These sources, unlike potential iron sources, appear not to differ appreciably in their relative biological value( ). This was observed in rats fed submarginal (9.5 ppm) zinc diets (Table III). Femur zinc content was used to assess biological values (BVs). Indirectly, this means that product compatibility and cost are likely to be more important than nutritional considerations in choosing the zinc source to be used in cereal fortification. 

Amine and Hegsted (1971) obtained similar carbohydrate effects studying iron absorption. Glucose is the most commonly used source of dietary carbohydrate in semipurified diets. Pennell et al. (1976) reported that beta-lactose in place of sucrose reduced the relative biological value of iron as sodium iron pyrophosphate when fed to rats. However, alpha-lactose or glucose in place of the sucrose did not affect the bioavailability of this iron source. Similarly, the source of fat can affect the bioavailability of dietary iron but, the level of dietary fat has no effect (Mahoney et al., 1980). 

Relative Biological Value calculated by dividing the efficiency of converting iron from the test diets into hemoglobin iron relative to that for diets containing ferrous. sulfate. 

Table II. Iron sources currently used In food enrichment and their relative biological values (RBV) based upon direct feeding.

Figure 2. Chemical and biological changes in iron observed after retort-processing a milk-based beverage (47, 901. As the percent of ionic iron increased, the relative biological value in rats increased geometrically.

Animal studies. In the initial studies (.6), a partially purified monoferric phytate prepared from extracts of wheat bran and two synthetic preparations were bioassayed using rats. The hemoglobin depletion-repletion method was used and the relative biological value (RBV) was computed by slope ratio. Compared to the response to ferrous ammonium sulfate as 100, the RBV for the monoferric phytate prepared from wheat bran was 99, and for the two synthetic preparations 101 and 97. The 95 confidence interval for the preparation from wheat bran was 87-111. The iron of monoferric phytate is highly bioavailable to rats. 

Table IV. Relative Biological Value to Rats of Iron in Wheat Breakfast Cereals...

Relative biological value, percentage based on response to Fe(NHj,)2(S0jj)2-6H20 = 100. 

Figure 2 Relative biological values—NPR and NPU—of soy protein isolate and methionine supplemented soy protein isolates, (a) Soy protein isolate (Met + Cys — 2.6g/16g N) (b) soy protein isolate supplemented with free L-methionine (Met + Cys — 3.5g/l6g N) (c) soy protein isolate supplemented with methioninc-cnriched EPM product (Met + Cys — 3.5g/16g N).

The relative biological values of mineral sources are taken from EMFEMA, 2002, Bioavailability of major and trace minerals, EMFEMA, Bruxelles. (Document available at www.emfema.org)... 

Finally, for mineral sources, the tables present the summary of a literature study performed for the EMFEMA concerning the relative biological value of minerals and trace elements for pigs, poultry and ruminants. 

The tables present the relative biological value of the major sources of minerals (mineral products and organo-metallic complexes) used in Europe for pigs, poultry and ruminants. This review was performed by a group of experts commissioned by the EMFEMA using all the available literature data. 

The following tables present for 12 mineral and trace elements the relative biological values (RBV) of the principal mineral sources (data compiled by EMFEMA). For each mineral, the first source indicated is the one used as a reference, except in the case of phosphorus where the references are different for ruminants and monogastrics. 

---