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Foods, consumer products and cosmetics belong to a wide range of colloidal and non-colloidal materials. Often, they are composite materials comprising several classes of fluid and solid constituents, including biopolymer gels, particulate suspensions, emulsions and foams. Length scales relevant for such materials may be anywhere between those associated with the molecular conformation of the ingredients up to long-scale dimensions of processing flows. The corresponding time scales may be in the sub-millisecond regime during aggregation of the ingredients or up to years during the shelf life of the final product. Rheological research of food material focuses on both the interaction between its ingredients, which might exhibit a complex rheological response function themselves and the influence of processing on the food structure and its properties. This brief overview summarizes suitable food rheology approaches and is grouped by the degree of abstraction of length scales and interactions.

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The effects of added ascorbic acid and particle size on iron absorption from ferric pyrophosphate were evaluated in adult women (9-10 women/study) based on erythrocyte incorporation of iron stable isotopes (57Fe or 58Fe) 14 days after administration. Three separate studies were made with test meals of iron-fortified infant cereal (5 mg iron/meal) and the results are presented as geometric means and relative bioavailability values (RBV, FeSO4 = 100%). The results of study 1 showed that iron absorption was significantly lower from ferric pyrophosphate (mean particle size 8.5 microm) than from FeSO4 in meals without ascorbic acid (0.9 vs. 2.6%, p < 0.0001, RBV 36%) and in the same meals with ascorbic acid added at a 4:1 molar ratio relative to fortification iron (2.3 vs. 9.7%, p < 0.0001, RBV 23%). Ascorbic acid increased iron absorption from ferric pyrophosphate slightly less (2.6-fold) than from FeSO4 (3.7-fold) (p < 0.05). In studies 2 and 3, RBV of ferric pyrophosphate with an average particle size of 6.7 microm and 12.5 pm was not significantly different at 52 and 42% (p > 0.05), respectively. In conclusion, the addition of ascorbic acid increased fractional iron absorption from ferric pyrophosphate significantly, but to a lesser extent than from FeSO4. Decreasing the mean particle size to 6.7 microm did not significantly increase iron absorption from ferric pyrophosphate.

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