An iron binding assay to measure activity of known food sequestering agents: studies with buttermilk solids

Nutrient and plant secondary compound composition and iron-binding capacity in leaves and green stems of commonly used plant browse (Carolina willow; Salix caroliniana) fed to zoo-managed browsing herbivores

Plant secondary compounds are diverse structurally, and associated biological effects can vary depending on multiple factors including chemical structure and reaction conditions. Phenolic compounds such as tannins can chelate dietary iron, and supplementation of animal species sensitive to iron overload with tannins may prevent/treat iron overload disorder. We assessed the nutrient and phenolic composition and iron-binding capacity of Carolina willow (Salix caroliniana), a plant fed to zoo-managed browsing herbivores. Based on studies in other plant species and the chemical structures of phenolic compounds, we hypothesized that the concentration of condensed tannins in willow would be inversely related to the concentration of phenolic glycosides and directly related to iron-binding capacity. Our results indicated that willow nutrient composition varied by year, season, and plant part, which could be taken into consideration when formulating animal diets. We also found that the predominant plant secondary compounds were condensed tannins with minimal phenolic glycosides. Instead of binding to iron, the willow leaf extracts reduced iron from the ferric to ferrous form, which may have prooxidative effects and increase the bioavailability of iron depending on animal species, gastrointestinal conditions, and whole animal processes. We recommend identifying alternative compounds that effectively chelate iron in vitro and conducting chelation therapy trials in vivo to assess potential effects on iron balance and overall animal health.

Plant phenolics and their potential role in mitigating iron overload disorder in wild animals

Phenolic compounds are bioactive chemicals found in all vascular plants but are difficult to characterize and quantify, and comparative analyses on these compounds are challenging due to chemical structure complexity and inconsistent laboratory methodologies employed historically. These chemicals can elicit beneficial or toxic effects in consumers, depending on the compound, dose and the species of the consumer. In particular, plant phenolic compounds such as tannins can reduce the utilization of iron in mammalian and avian consumers. Multiple zoo-managed wild animal species are sensitive to iron overload, and these species tend to be offered diets higher in iron than most of the plant browse consumed by these animals in the wild and in captivity. Furthermore, these animals likely consume diets higher in polyphenols in the wild as compared with in managed settings. Thus, in addition to reducing dietary iron concentrations in captivity, supplementing diets with phenolic compounds capable of safely chelating iron in the intestinal lumen may reduce the incidence of iron overload in these animal species. It is recommended to investigate various sources and types of phenolic compounds for use in diets intended for iron-sensitive species. Candidate compounds should be screened both in vitro and in vivo using model species to reduce the risk of toxicity in target species. In particular, it would be important to assess potential compounds in terms of 1) biological activity including iron-binding capacity, 2) accessibility, 3) palatability, and 4) physiological effects on the consumer, including changes in nutritional and antioxidant statuses.

Phytate: impact on environment and human nutrition. A challenge for molecular breeding

Phytic acid (PA) is the primary storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in PA strongly binds to metallic cations of Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable as nutritional factors. Phytate mainly accumulates in protein storage vacuoles as globoids, predominantly located in the aleurone layer (wheat, barley and rice) or in the embryo (maize). During germination, phytate is hydrolysed by endogenous phytase(s) and other phosphatases to release phosphate, inositol and micronutrients to support the emerging seedling. PA and its derivatives are also implicated in RNA export, DNA repair, signalling, endocytosis and cell vesicular trafficking. Our recent studies on purification of phytate globoids, their mineral composition and dephytinization by wheat phytase will be discussed. Biochemical data for purified and characterized phytases isolated from more than 23 plant species are presented, the dephosphorylation pathways of phytic acid by different classes of phytases are compared, and the application of phytase in food and feed is discussed.

Chemistry of buttermilk solid antioxidant activity

Antioxidant activity of buttermilk solids was assessed by analyzing for relative reducing activity, sulfhydryl content, and ferrous and ferric iron binding affinity. These experiments were followed by monitoring the affinity of buttermilk solids to scavenge both hydroxyl and peroxyl radicals in vitro. Notable relative reducing activity of buttermilk solids to L-ascorbic acid (43.80 to 85.85% over a range of 5.0 to 10.0 mg) was attributed in part to the sulfhydryl content (28.8 microM). Buttermilk solids sequestering activity was greater for ferrous than ferric ion. These chemical properties of buttermilk solids corresponded to a significant affinity to scavenge Fenton-induced hydroxyl radical over a range of 5 to 10 mg. A significant affinity of buttermilk solids to protect against lipid peroxidation, tested using an in vitro model lipid system, was also observed at both 0.1 and 0.2% (wt/vol). These findings demonstrated that buttermilk solids possess significant antioxidant activity, thereby suggesting potential use as a value-added ingredient for stabilizing food matrixes against lipid peroxidation reactions.