In vitroavailability of iron and zinc: effects of the type, concentration and fractions of digestion products of the protein

Abstract

An in vitro dialysis method was employed to determine the effect on the Fe and Zn absorption of the type (beef, pork and soyabean) and the amount (10 and 30 g/kg) of protein present. In addition, the effects of low-and high-molecnlar-weight (LMW and HMW respectively) digestion products were investigated.After in vitro digestion and dialysis a lower percentage of N, Fe and Zn was found in the LMW fractions from beef, pork and soyabean proteins when the protein level was increased from 10 to 30 g/kg; the higher level of protein being associated with a lower percentage of hydrolysed protein. The highest percentage levels of intrinsic Fe were always found in the HMW fractions, independent of the type and the level of proteins studied, while in the case of Zn, both HMW and LMW fractions gave similar values.An interaction was found between inorganic Zn and non-haem-Fe. The addition of inorganic Zn (10 pg/ml) caused a significant decrease in the in viiro availability of Fe from soyabean protein, while it did not affect the dialysability of intrinsic Fe from beef and pork proteins. Our results showed that the type and the level of the protein had a positive effect on the dialysability of extrinsic Fe. We postulate that the effect of a protein on the absorption of extrinsic Fe could be accounted for by free amino acids and/or small peptides released during the digestion process and also by the undigested or partiallydigested HMW fractions of hydrolysed proteins which could play a fundamental role in the availability of this essential element.Iron: In viiro availability: Zinc: Protein digestionThe nutritional value of a diet in terms of macrominerals and trace minerals is dependent on much more than their respective contents in the diet. Mineral imbalances can be attributed not only to a deficient intake, but also to the amount of mineral that is bioavailable for physiological processes in the organism. It is well known that many of the interactions between food constituents can result in changes in the bioavailability of nutrients. Several dietary factors have been implicated in changes in the absorption of some trace minerals, for example Fe, Zn, Cu and Mn (Rosenberg & Solomons, 1982;Solomons, 1982;Mills, 1985;Hallberg, 1987;Sandstrom, 1988; Churella & Vivian, 1989;Wapnir & Devas, 1995). One of the factors which appears to play an important role in Fe and Zn absorption is the amount and type of protein in the diet (Cossack & Prasad, 1983;Snedeker & Greger, 1983;Van Dokkum et al. 1986;Greger, 1989;Wapnir, 1989).There have been a number of reports showing that animal tissues in the diet can increase the bioavailability of dietary Fe ; this has been attributed to their protein properties (Layrisse et al. 1984;Berner & Miller, 1985;Politz & Clydesdale, 1988 Gordon & Godber, 1989). The increasing rate of consumption of soyabean-based foods in human diets has caused some observers to express concern about a possible unfavourable effect on Fe and Zn bioavailability. Experiments conducted using different animals have shown a re...

Binding of iron by chicken muscle protein digests: the size of the iron-binding peptides

“…In contrast, Slatkavitz and Clydesdale, 6 using the same protein source, found that peptides larger than 10 kDa bound more iron than smaller peptides. Perez-Llamas et al 11 found that only peptides larger than 6±8 kDa increased the dialysability of iron added to beef peptides, whereas Mulvihill and Morrisey 12 found that peptides smaller than 6± 8 kDa were more effective in this regard than larger peptides. The inconsistencies in these results may well re¯ect differences in methodology, including effectiveness of separation, accuracy of size estimation and, most importantly, whether the iron was present during the digestion or added afterwards to the separated peptides, which must then be recycled through the gastrointestinal pH shift.…”

“…However, there is very little information on the size of peptides which bind iron. Most studies which have addressed this aspect have separated peptides into high-and lowmolecular-weight fractions by dialysis and then determined their iron-binding capacity at neutral pH, 6,11,12 with inconsistent results.…”

Influencia del tipo de proteína y la fuente de hierro en la dieta sobre la absorción de aminoácidos y minerales

“…Animal proteins increase the bioavailability of non-heme iron, while vegetal proteins decrease its availability (18,19). As has been described in the literature, phytates are strong inhibitors and the formation of diferric and tetraferric phytates in the gastrointestinal tract may decrease the availability of iron for absorption.…”

Production of dialysable iron by in vitro digestion of chicken muscle protein fractions: the size of the dialysable iron

“…In contrast, Slatkavitz and Clydesdale, 8 using the same protein, found that peptides larger than 10 kDa bound more iron than smaller peptides. Perez-Llamas et al 20 found that only peptides larger than 6-8 kDa increased the dialysability of iron added to beef peptides, whereas Mulvihill and Morrissey 21 found that peptides smaller than 6-8 kDa were better than larger peptides in producing dialysable iron.…”