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Iron is a micronutrient critical to fundamental biological processes including respiration and photosynthesis, and it can therefore impact primary and heterotrophic productivity. Yet in oxic environments, iron is highly insoluble, rendering it, in principle, unavailable as a nutrient for biological growth. Life has "solved" this problem via the invention of iron chelates, known as siderophores, that keep iron available for microbial productivity. In this work, we examined the impact of siderophore synthesis on the speciation, mobility, and bioavailability of iron from rock-forming silicate minerals-shedding new light on the mechanisms by which microbes use mineral substrates to support primary productivity, as well as the consequent effects on silicate dissolution. Growth experiments were performed with Shewanella oneidensis MR-1 in an oxic, iron-depleted minimal medium, amended with olivine minerals as the sole source of iron. Experiments included the wild-type strain MR-1, and a siderophore synthesis gene deletion mutant strain (ΔMR-1). Relative to MR-1, ΔMR-1 exhibited a very pronounced growth penalty and an extended lag phase. However, substantial growth of ΔMR-1, comparable to MR-1 growth, was observed when the mutant strain was provided with siderophores in the form of either filtrate from a well-grown MR-1 culture, or commercially available deferoxamine. These observations suggest that siderophores are critical for S. oneidensis to acquire iron from olivine. Growth-limiting concentrations of deferoxamine amendments were observed to be ≤5-10 µM, concentrations significantly lower than previously recorded as necessary to impact mineral dissolution rates. X-ray photoelectric spectroscopy analyses of the incubated olivine surfaces suggest that siderophores deplete mineral surface layers of ferric iron. Combined, these results demonstrate that low micromolar concentrations of siderophores can effectively mobilize iron bound within silicate minerals, supporting very significant biological growth in limiting environments. The specific mechanism would involve siderophores removing a protective layer of nanometer-thick iron oxides, enhancing silicate dissolution and nutrient bioavailability.

Millets are a traditional staple food of the dryland regions of the world and are rich in essential nutrients like protein, fatty acids, minerals, vitamins, and dietary fiber. Also, millets commonly synthesize a range of secondary metabolites to protect themselves against adverse conditions. These factors are collectively termed anti-nutritional factors and the existence of these factors in millets might reduce the accessibility of the nutrients in humans. Some of these factors include protease inhibitors, tannins, non-starch polysaccharides-glucans, phytates, and oxalates each of which might directly or indirectly affect the digestibility of nutrients. Methods like soaking, germination, autoclaving, debranning, and the addition of exogenous enzymes have been used to reduce the anti-nutritional factors and elevate the bioavailability of the nutrients. This review summarizes various methods that have been used to improve nutrient bioavailability, specifically emphasizing the use of enzymes to improve nutrient bioavailability from millets. © 2021 Society of Chemical Industry.

The impact of traditional African preservation methods on the contribution of vegetables to household micronutrient needs (Recommended Dietary Allowance: RDA) has largely remained unquantified. Using Acholi subregion of Uganda as a case area, this study examined using the predominant vegetables consumed in fresh and preserved forms (cowpeas—Vigna unguicullata, okra/lady fingers—Abelmoschus esculentus, Malakwang—Hibscus cannabinus, and eggplants—Solanum melongena), the effect of major traditional vegetable preservation methods (sun drying, boiling and sun drying, and salting and sun drying) on the contents of micronutrients (vitamin A, iron, zinc, calcium, magnesium, and phosphorus), the levels of antinutritional factors (total polyphenols, oxalate, tannins, and phytate), bioavailability of iron and zinc, and the contribution of vegetables to the cumulative annual household RDA for micronutrients. Laboratory analysis showed that all the preservation methods, except the sun drying method reduced the contents of micronutrients by 20%–82% (p ≤ .05). The contents of antinutritional factors reduced by 1%–80% while in vitro bioavailability of iron and zinc increased by 21%–296% (p ≤ .05). Nutritional computation revealed that except for calcium, the preservation methods combined, reduced the contribution of the vegetables to cumulative annual RDA for other micronutrients by 28%–60%. These results demonstrate that improvements in bioavailability of essential nutrients (iron and zinc) by traditional preservation methods investigated are associated with significant loss of micronutrients which culminates in significant reduction in the contribution of cultivated vegetables to household RDA for micronutrients. Traditional African preservation methods should be optimized for nutrient retention., This study examined the effect of traditional African vegetable preservation methods on the contribution of vegetables to household needs for micronutrients. The results showed that the traditional methods improve mineral bioavailability but negatively affects the contribution of vegetables to household mironutrient needs due to excessive loss of nutrients.

There are dilemmas in the minds of consumers with respect to sugar consumption - they would like to consume sugars for sweetness, but in a healthy (and perhaps guilt free!) way. In a sense, consumers believe that if sugar does not appear as an ingredient on the product label, but is intrinsic in the food (and will appear as a nutrient), it is 'good'. As an ingredient, however, it is viewed as a 'bad chemical' associated with tooth decay and obesity. The reality is that unless processing induced modifications have occurred, the sugar molecule within a plant tissue is the same molecule structure as present in purified sugar. The same calorific value. However, there is an argument that humans eat too refined food and that if sugars were eaten in their natural context (e.g. within a fruit), their presence and concentration would be in harmony (where different nutrients complement and balance the sugar concentration) with the human body. This reflects the process of eating, satiety, presence of other nutrients (including water) and the associated impact of the indigestible components of plant foods on the transit/nutrient bioavailability control and thus benefits through the gut. The authors explore these issues in this article and seek to provide a scientific basis to different sides of the argument - sugar is good or bad depending on how (in which format and how much/how concentrated) it is consumed. More importantly perhaps, how should sugar consumption - an important nutrient - be managed to optimize the benefits but reduce the disadvantages? © 2020 Society of Chemical Industry.

Numerous studies have addressed the positive effects of organic amendments on soil and plant productivity under short-term field studies. However, to date, few studies have been conducted on the effects of organic amendment on the orchards where high nutrient bioavailability is required. This study deals with the effects of biochar and compost on soil quality, growth and yield of a replanted apple orchard in the northeast of Iran.; Results: Biochar+compost application resulted in 37% and 300% higher soil total organic carbon and available phosphorus content, respectively, during the first 3 years of experimentation compared to control. Similarly, trunk diameter and shoot number of apple trees increased 23-26% by the end of the first year. Nevertheless, there were no significant changes in fruitfulness, fruit weight or starch pattern index as productivity indices.; Conclusion: Biochar and compost were beneficial in improving soil quality, mainly by increasing soil nutrient content and decreasing soil bulk density, and in increasing plant growth at early growth stages of apple orchards. However, they failed to enhance overall yield and fruit quality, most likely due to their limited ability to suppress apple replant disease. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

The occurrence of anti‐nutritional constituents in plants is an important factor that negatively affects bioavailability of nutrients and effectiveness of plant‐based foods in complementary feeding in rural areas in developing countries. However, proven methods that improve bioavailability of nutrients and tailored for application in processing complementary foods among rural communities are largely lacking. This study examined the efficacy of a traditional malting technology practiced by the Acholi ethnic community of northern Uganda to improve protein digestibility and bioavailability of iron and zinc from millet–sesame–soy composite containing 200, 300, and 550 kcal meant for complementary feeding of children aged 6–8, 9–12, and 13–23 years old, respectively. The technology involves washing and soaking of ingredients for 12 hr; malting ingredients individually for 48 hr with water changed after every 6 hr; and sun‐drying malted ingredients for 72 hr. Results showed that the level of anti‐nutritional factors significantly reduced (p ≤ 0.05) in all the composite formulae except the content of total phenolics in 200, tannins in 300 and 550 kcal, composite formula, respectively. In vitro protein digestibility significantly improved (p ≤ 0.05) in all the composite formulae except in the 200 kcal formula. Iron bioavailability significantly increased (p ≤ 0.05) in all the composite formulae except in the 550 kcal energy category. Improvement in zinc bioavailability was only observed in the 300 kcal formula. However, there were significant reductions (p ≤ 0.05) in the level of caregiver preferences for sensory properties and overall acceptability of the composites. These results demonstrate that the traditional malting technology has potential to improve nutrient bioavailability in plant‐based foods but requires improvement in order to increase its efficacy and mitigate negative effects on sensory appeal.

The true bioavailability of a nutrient being intrinsically coupled to the specific food matrix in which it occurs remains poorly considered in nutrition science. During digestion, the food matrix and, in particular, the structure of food modulate the extent and kinetics to which nutrients and bioactive compounds make themselves available for absorption. In this perspective, we describe an integrated look at the effect of structure on nutrient bioavailability in plant foods. Based on this integrated look, cell wall integrity and the particle size of the plant material during its transit in the small intestine determine the bioavailability of plant nutrients; in turn, cell wall integrity and particle size are determined by the level of oral processing and, accordingly, what subsequently escapes digestion in the upper intestine and is utilized by colon microbiota. Ultimately, the effect on nutrient digestion is linked to food structure through each step of digestion. A consideration of the structure rather than just the composition of foods opens up possibilities for the design of healthier foods. © 2018 Society of Chemical Industry.

Author(s): Lee, Lianna Y; Mitchell, Alyson E | Abstract: BACKGROUND:Activated almonds are raw almonds that have been soaked in water for 12-24 h at room temperature, sometimes followed by a 24 h drying period at low temperature (50 ± 5 °C). This treatment is thought to enhance the nutrient bioavailability of almonds by degrading nutrient inhibitors, such as phytic acid or d-myo-inositol hexaphosphate (InsP6 ), through the release of phytase or passive diffusion of InsP6 into the soaking water. Over a wide pH range, InsP6 is a negatively charged compound that limits the absorption of essential nutrients by forming insoluble complexes with minerals such as iron and zinc. It is hypothesized that hydrating the seed during soaking triggers InsP6 degradation into lower myo-inositol phosphates with less binding capacity. RESULTS:Anion-exchange chromatography coupled with tandem mass spectrometry was used to quantify myo-inositol mono-, di-, tris-, tetra-, penta-, and hexaphosphates (InsP1-6 ) in raw pasteurized activated almonds. At least 24 h of soaking at ambient temperature was required to reduce InsP6 content from 14.71 to 14.01 µmol g-1 . CONCLUSIONS:The reduction in InsP6 is statistically significant (P l 0.05) after 24 h of activation, but only represents a 4.75% decrease from the unsoaked almonds. © 2018 Society of Chemical Industry.

Fermentation and sprouting have been shown to increase nutrient bioavailability and modify the functional properties of foods. Application of these methods in the preparation of infant foods and complementing cereals with legumes will address nutrient density and viscosity problems associated with infant foods. Infant foods were formulated from blends of treated bambara nut and pearl millet. Functional properties, pasting properties, and sensory acceptability of the blends were studied. Millet and bambara nut were soaked separately in water and allowed to ferment for 48 hr at room temperature. While for sprouting, millet and bambara nut were soaked for 12 and 24 hr, respectively, at room temperature, and soaked seeds were separately sprouted for 48 hr. After fermentation and sprouting, the seeds were oven‐dried and then milled into a flour of 0.6 mm size. The flours were formulated to six (A, B, C, D, E, and F) complementary diets. The results show that sample E had the suitable water absorption capacity, while, for oil absorption capacity, various blends showed suitability except samples A and B. In terms of swelling capacity, sample F (6.52 ± 0.01%) was the suitable at 60°C. Treatment and blending significantly influenced trough, final viscosity, and pasting time. In sensory acceptability, sample B was adjudged the best. This study revealed that sample C was the best in respect to functional and pasting properties for infant food; however, sample B received the best general acceptability.

Background: The interest in stable natural colorants for food applications continues to grow. A red pigment extracted from the leaf sheaths of a sorghum variety (Sorghum bicolor) with a high content of apigeninidin is widely used as a biocolorant in processed foods in West Africa. This study compared the colour and anthocyanin composition from traditional extraction methods to determine options for improvement and use of the red biocolorant from dye sorghum in the food sector.; Results: Sorghum biocolorant was commonly applied in fermented and heated foods. Traditional extraction methods predominantly differed in two aspects, namely the use of an alkaline rock salt (locally known as kanwu) and the temperature of the extraction water. Cool extraction using the alkaline ingredient was more efficient than hot alkaline and hot aqueous extractions in extracting anthocyanins. The apigeninidin content was three times higher in the cool and hot alkaline extracts than in the aqueous extract.; Conclusion: Cool and hot alkaline extractions at pH 8-9 were the most efficient methods for extracting apigeninidin from dye sorghum leaf sheaths. Broader use of the sorghum biocolorant in foods requires further research on its effects on nutrient bioavailability and antioxidant activity. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Nutrient bioavailability is crucial for vegetation establishment and organic matter cycling after major ecosystem disturbance such as open pit mining. In this study, the stockpiling and organic matter admixing effects on nutrient bioavailability were examined in soils used for reclaiming oil sands disturbed sites in northern Alberta, Canada. Stockpiled and directly salvaged peat mineral soil mix (PMM) and forest floor mineral soil mix (FFMM), the two main oil sands reclamation soils, and a nutrient poor mineral sub-soil (SS) were used in this experiment. Reclamation soils were inter-mixed at different ratios (PMM to FFMM or SS at 60:40, 80:20 and 90:10) to examine the organic matter admixing effects. Significant stockpiling effects on nutrient bioavailability and microbial functions were mostly observed in FFMM. Microbial biomass C was greater, and mineralization of lignin substrate was lower in both stockpiled PMM and FFMM soils compared to the directly salvaged soils. Significant fertility benefit was found in the FFMM-admixed SS and PMM soils through an increase in N and K availability. FFMM admixing also increased microbial functional diversity and assimilation rate compared to the non-admixed soils. Mineralization of polymeric substrates was the main driver of nutrient availability in stockpiled PMM, whereas carboxylic acids and carbohydrates were the major drivers in directly salvaged PMM, as indicated by the Random Forest models. The findings suggest that stockpiling effects are much stronger in FFMM than in PMM, and FFMM admixing to reclamation soils may provide nutritional and microbial functional benefits, especially in nutrient-poor soils.

Maize is a staple human food eaten by more than a billion people around the world in a variety of whole and processed products. Different processing methods result in changes to the nutritional profile of maize products, which can greatly affect the micronutrient intake of populations dependent on this crop for a large proportion of their caloric needs. This review summarizes the effects of different processing methods on the resulting micronutrient and phytochemical contents of maize. The majority of B vitamins are lost during storage and milling; further loss occurs with soaking and cooking, but fermentation and nixtamalization (soaking in alkaline solution) can increase bioavailability of riboflavin and niacin. Carotenoids, found mainly in the kernel endosperm, increase in concentration after degermination, while other vitamins and minerals, found mainly in the germ, are reduced. Mineral bioavailability can be improved by processing methods that reduce phytic acid, such as soaking, fermenting, cooking, and nixtamalization. Losses of micronutrients during processing can be mitigated by changes in methods of processing, in addition to encouraging consumption of whole-grain maize products over degermed, refined products. In some cases, such as niacin, processing is actually necessary for nutrient bioavailability. Due to the high variability in the baseline nutrient contents among maize varieties, combined with additional variability in processing effects, the most accurate data on nutrient content will be obtained through analysis of specific maize products and consideration of in vivo bioavailability.

Food structure research has historically focused on building and stabilizing specific structural elements. Precise execution of unit operations in food processing is required to ensure consistent structure formation, but does not explain why a particular structure is desirable. The pattern by which food structure breaks down during oral processing, generating texture, flavor and taste, determines the acceptability of a food. However, breakdown patterns and textural perception associated with desirable food qualities are not well understood. Food materials are classified based on their physical state (liquids, semisolids or solids) and interactions with surfaces (adhesive or nonadhesive). Physical and chemical processes during oral processing are used to further characterize each food category. Typical processes include particle reduction, dissolution, hydration, removal of food from oral surface and bolus formation. This review presents a framework for classifying food materials and material transformations during oral processing in order to identify their contributions to texture perception. Practical Applications There is a constant desire to reformulate or modify foods based on economic, sustainability, health and dietary considerations. One goal of a reformulated food is to change the composition but cause no significant changes in flavor, taste and textural properties associated with desirability. An alternative goal is to modulate a specific textural element to make the food more acceptable to a target population (e.g., those with compromised chewing ability). Both goals require an understanding of the fundamental elements that cause specific textural properties. This manuscript presents an overview of how the breakdown of food structure during oral processing generates the cognition of textural properties. Once textural properties are understood based on specific elements of structural transitions, this will allow for development of textures for specific market segments (e.g., vegan, gluten free or swallowing disorders) as well as the ability to control nutrient bioavailability and flavor release.

Leaching is a mechanism for the release of nutrients from litter or senesced leaves that can drive interactions among plants, microbes, and soil. Although leaching is well established in conceptual models of litter decomposition, potential nutrient solubility of mineral elements from recently senesced litter has seldom been quantified. Using a standardized extraction (1:50 litter-to-water ratio and four-hour extraction) and recently senesced leaf litter of 41 tropical tree and liana species, we investigated how solubility varies among elements, and whether the solubility of elements could be predicted by litter traits (e.g., lignin, total element concentrations). In addition, we investigated nutrient forms (i.e., inorganic and organic) and ratios in leachate. Water-soluble elements per unit litter mass were strongly predicted by total initial litter element concentrations for potassium (K; r2 = 0.79), sodium (Na; r2 = 0.51) and phosphorus (P; r2 = 0.66), while a significant but weaker positive relationship was found for nitrogen (N; r2 = 0.36). There was no significant relationship for carbon (C) or calcium (Ca). Element-specific solubility varied markedly. On average 100% of total K, 35% of total P, 28% of total Na, 5% of total N, 4% of total Ca, and 3% of total C were soluble. For soluble P, 90% was inorganic orthophosphate. The high solubility of K, Na, and P as inorganic orthophosphate suggests that these nutrients can become rapidly available to litter microbes with no metabolic cost. Few common predictors of decomposition rates were correlated with element solubility, although soluble C (milligrams per gram of litter) was negatively related to lignin content (r2 = 0.19; P < 0.004). Solubility of elements was linked within a species: when a species ranked high in the soluble fraction of one element, it also ranked high in the solubility of other elements. Overall nutrient-specific patterns of solubility from recently senesced litter emphasize that litter elements cannot be treated equally in our conceptual and empirical models of decomposition. The relatively high potential solubility of P as orthophosphate from fresh litter advances our understanding of ecological stoichiometric ratios and nutrient bioavailability in tropical forests.

Fruit bodies of about 200 mushroom species are consumed throughout the world, preferably as a delicacy. Knowledge of their chemical composition, nutritional value and health-promoting effects has expanded dynamically during the last few years. Dry matter (DM) is low: commonly about 100 g kg⁻¹ . The usual contents of protein, lipids and ash are 200-250, 20-30 and 80-120 g kg⁻¹ DM, respectively. Various carbohydrates form the remaining DM. Nevertheless, great variations occur both among and within species. Energy is low, usually 350-400 kcal kg⁻¹ of fresh fruit bodies. The nutritional contribution of mushroom protein derived from earlier data seems to be overestimated. Fat content is low with markedly prevailing in linoleic acid and oleic acid, while the proportion of n-3 fatty acids is nutritionally marginal. The main carbohydrates are chitin, glycogen, trehalose and mannitol. Information on fibre content and composition is limited. Health-promoting β-glucans are an auspicious group of polysaccharides. High potassium content is characteristic of mushrooms. Several species can accumulate very high levels of both detrimental trace elements, particularly cadmium and mercury, and radiocaesium isotopes if growing on heavily polluted substrates. Mushrooms seem to be a considerable source of ergosterol, provitamin D₂, and phenolids with antioxidative properties. Hundreds of flavour constituents have been identified, particularly with eight-carbon aliphatic chains. Data on changes of mushroom components under various preservation conditions and culinary treatments have been fragmentary. Even more limited is knowledge of nutrient bioavailability.

Summary The bioaccessibility, or amount of a nutrient available for gastrointestinal absorption, can be determined using an in vitro digestion model, the addition of the resultant digestate to a caco-2 transwell model system yields an approximation of nutrient bioavailability. The objective of the present study was to compare the bioaccessibility and bioavailability of α-tocopherol and retinol from a range of digested foodstuffs. Minced pork, beef and turkey and apple sauce, bread and mayonnaise were supplemented with α-tocopherol-acetate and retinol-acetate prior to being subjected to an in vitro digestion procedure. The aqueous fraction of each of the digested foodstuffs was then added to a caco-2 transwell model and the transepithelial transport was determined. The findings of the present study indicate that α-tocopherol and retinol are more bioaccessible from supplemented meat products than from supplemented apple sauce, bread and mayonnaise. It was found that turkey meat facilitated the highest bioaccessibility and subsequent cellular uptake and transport of retinol. The cellular uptake and secretion of α-tocopherol was similar for all samples.

The changes in the physical, chemical, and nutritional properties of ingredients during and post processing in a domestic mixer grinder are studied. Spices are powdered to release flavor but higher temperature during grinding and storage has deteriorative effects on its quality. Pastes and purees are prepared due to recipe requirements but grinding also releases characteristic flavors and some nutrient bioavailability. Storage leads to development of rancidity, off-color, and off-flavors. Batter from lentil and rice is ground and mixed before fermentation but storage leads to changes in acidity, nutrient content, taste, and texture of the final product. Flour is prepared from rice and chickpea lentil due to their versatility to be used in different food preparation applications. High speed grinding with increase in temperature leads to necessary starch damage but also has some drawbacks. Storage leads to color changes and reduces the suitability to some applications. Practical applications In this research paper, the authors analyze the current grinding practices of food ingredients like spices, puree, paste, batter, and flours by consumers in Indian kitchens. The findings of this paper will help the consumer understand the changes that occur in the physical, chemical, and nutritional properties of the ingredients. Based on such understanding, authors recommend grinding practices for the sensory and nutritional benefits. To further the understanding, future research projects can delve deeper to understand the changes that occur during high speed grinding and address the characteristics that affect the properties and cause detrimental reactions. Further research can also help understand the nutritional benefits of fresh grinding.

Summary 1. It is an uncontested paradigm that an adequate supply of the macronutrients nitrogen (N) and phosphorus (P) is critical for maintaining phytoplankton primary production in aquatic ecosystems; it has also been suggested that there is an optimal total N : total P ratio for this globally significant process. 2. This ratio, normally assessed by chemical determination of the major dissolved N and P species, poses a dilemma: do chemical measurements actually reflect the bioavailable fraction of these nutrient pools? Accurate determination of the various N and P species and their fluxes into phytoplankton cells is notoriously difficult. 3. To provide a possible solution to this difficulty, we engineered strains of the cyanobacterium Synechococcus sp. strain PCC 7942 that ‘report’ on N and P bioavailability via a bioluminescent signal. These strains were used to quantify, for the first time, bioavailable concentrations of these essential macronutrients in a freshwater lake. 4. Only a small fraction (0.01–1%) of the chemically determined P may actually be bioavailable to this unicellular cyanobacterium and, by inference, to the phytoplankton community in general. In contrast, bioavailable N comprises most of the dissolved N pool. Consequently, bioavailable N : P ratios based on these assays are higher then those based on chemical determinations, indicating that P limitation in Lake Kinneret is more extensive then previously thought.

BACKGROUND: Previous studies have demonstrated the capacity of a new type of mineral fertiliser, known as rhizosphere-controlled fertiliser (RCF), to supply adequate nutrition to plants while minimising nutrient losses. This fertiliser family is based on the presence a phosphoric matrix composed of metal–humic–phosphates, soluble not in water but in the rhizospheric acids released by plant roots as an expression of nutritional needs, principally citric acid. The aim of this study is to investigate the capacity of the RCF matrix and other phosphorus-containing products to induce the recovery of phosphorus-deficient maize plants. RESULTS: The results showed that RCF-based P fertilisers were able to facilitate plant recovery, measured by the dry root and shoot weights, to the same extent as a water-soluble P fertiliser (monopotassium phosphate). This fact was well correlated to both the variation pattern of citric and trans-aconitic acids in the shoot and roots during the treatment, and P shoot and root contents. Likewise the analysis of the variation of P concentration in the nutrient solution during the treatment indicates that plant recovery is associated with the capacity of the plant to mobilise P from the different fertiliser matrices studied. CONCLUSION: These results confirm the findings obtained in previous in vitro studies and indicate the suitability of RCF strategy for the preparation of mineral fertilisers with a nutrient release pattern more sensitive to plant nutritional needs. Copyright © 2009 Society of Chemical Industry

Understanding the controls on interactions between soluble organic compounds and the solid soil matrix is important in understanding soil organic matter dynamics in general, including specific impacts on pedogenic processes, nutrient bioavailability, and C sequestration. This study investigated the pH-dependent relationship between low-molecular-weight organic acids (LMWOAs) and variable-charge soils as a control on the retention of an otherwise highly mobile and bioavailable class of organic compounds. Sorption isotherms of three LMWOAs (one amino acid [glycine], one monocarboxylic acid [propionic acid], and one dicarboxylic acid [malonic acid]) were generated for three forest soils using batch equilibration techniques. Before equilibration, soils were saturated with KCl to control for competing ions, and both soils and solutions were adjusted to one of three pH levels (4.0, 6.0, or 8.0 ± 0.1). Bioavailability was assessed by generating desorption isotherms for each LMWOA-pH combination as well as through laboratory incubations for mineralization rates. Results indicate that sorption of the three LMWOAs followed the general trend: malonic acid » glycine > propionic acid. Sorption tended to increase with acidity and short-range-ordered aluminosilicate content, and was correlated (r = 0.69, P < 0.001) with the magnitude of the difference between the positive charge on the mineral surface and the negative charge of the LMWOA. This trend remained true for the amino acid, which demonstrated sorptive maximums that were more strongly correlated with anion exchange (r = 0.62, P = 0.1) than cation exchange (r = 0.05, P = 0.9). These observations, coupled with decreased desorption and lower mineralization rates at lower pH levels, suggest the potential for an electrostatic mechanism to contribute to the abiotic retention of organic matter in variable-charge soils under acidic conditions.

Critics charge that agricultural managers routinely overdose their fields with chemical N and P to levels that exceed the soil's capacity to adsorb these materials, creating a situation that promotes hypoxia in Iowa lakes. Soil colloidal particles, capable of forming complexes with inorganic and organic N and P, control the equilibrium concentration of dissolved nutrients in lake waters. However, it should be realized that adsorbed nutrients also exhibit strong influences on the potential of sediments to undergo dispersion, a condition that may directly impact nutrient bioavailability. Thus, direct links may exist between adsorbed nutrient compositions and flocculation/dispersion properties of lake colloidal material. This paper presents work involving four Iowa lakes undertaken to determine relationships between ion composition and the dispersion potential of sediments. Surface waters and lake-bottom grab samples were collected at three separate collection times from August to October. Samples were characterized for dissolved and adsorbed cations. Dispersion potential of each water sample was characterized by relating the total suspended solids concentration to the absorbance at 560 nm. It was found that sediment dispersion was easily predictable by a simple yet significant linear correlation with the concentration ratio of Na (CR Na = [Na]/[Ca] - 1/2 ) in solution. This correlation was further improved by including Na concentration, CR K , electrical conductivity, temperature, and solution P concentrations into the model. Nonlinear inter-dependences were found between TSS and cation exchange capacity (CEC), and adsorbed Na, K, P, and heavy metals. Our analysis suggests that solution/solid phase constituents influenced the dispersion behavior of sediments through subtle manipulations of the excess surface charge.

We discuss the concept of colimitation of primary productivity in aquatic environments, with an emphasis on reconciling this concept with recent advances in marine bioinorganic chemistry. Colimitations are divided into three categories on the basis of their mathematical formulations and visualizations: type I, independent nutrient colimitation (e.g., N and P); type II, biochemical substitution colimitation (e.g., Co and Zn); and type III, biochemically dependent colimitation (e.g., Zn and C), where the ability to acquire one nutrient is dependent upon sufficient supply of another. The potential for colimitation occurring in the marine environment and the critical importance of understanding nutrient bioavailability are discussed.

The 2005 Dietary Guidelines for Americans recommend that consumers choose a variety of nutrient-dense foods. Nutrient density is usually defined as the quantity of nutrients per calorie. Food and nutrition professionals should be aware of the concept of nutrient density, how it might be quantified, and its potential application in food labeling and dietary guidance. This article presents the concept of a nutrient density score and compares nutrient density scores for various 100% fruit juices. One hundred percent fruit juices are popular beverages in the United States, and although they can provide concentrated sources of a variety of nutrients, they can differ considerably in their nutrient profiles. Six methodologies were used to quantify nutrient density and 7 100% fruit juices were included in the analysis: apple, grape, pink grapefruit, white grapefruit, orange, pineapple, and prune. Food composition data were obtained from the USDA National Nutrient Database for Standard Reference, Release 18. Application of the methods resulted in nutrient density scores with a range of values and magnitudes. The relative scores indicated that citrus juices, particularly pink grapefruit and orange juice, were more nutrient dense compared to the other nonfortified 100% juices included in the analysis. Although the methods differed, the relative ranking of the juices based on nutrient density score was similar for each method. Issues to be addressed regarding the development and application of a nutrient density score include those related to food fortification, nutrient bioavailability, and consumer education and behavior.

Spatio-temporal variations in nitrogen and phosphorus concentrations in groundwater were analysed and related to the variations in hydrological conditions, vegetation type and substrate in an alluvial ecosystem. This study was conducted in the Illwald forest in the Rhine Plain (eastern France) to assess the removal of nutrients from groundwater in a regularly flooded area. We compared both forest and meadow ecosystems on clayey-silty soils with an anoxic horizon (pseudogley) at 1•5–2 m depth (eutric gley soil) and a forest ecosystem on a clayey-silty fluviosoil rich in organic matter with a gley at 0•5 m depth (calcaric gley soil). Piezometers were used to measure the nutrient concentrations in the groundwater at 2 m depth in the root layer and at 4•5 m depth, below the root layer. Lower concentrations of nitrate and phosphate in groundwater were observed under forest than under meadow, which could be explained by more efficient plant uptake by woody species than herbaceous plants. Thus NO3-N inputs by river floods were reduced by 73% in the shallow groundwater of the forested ecosystem, and only by 37% in the meadow. Compared with the superficial groundwater layer, the lowest level of nitrate nitrogen (NO3-N) and the highest level of ammonium nitrogen (NH4-N) were measured in the deep layer (under the gley horizon at 2•5 m depth), which suggests that the reducing potential of the anoxic horizon in the gley soils contributes to the reduction of nitrate. Nitrate concentrations were higher in the groundwater of the parcel rich in organic matter than in the one poorer in organic matter. Phosphate (PO4-P) concentrations in both shallow and deep groundwater are less than 62 to 76% of those found in surface water which can be related to the retention capacity of the clay colloids of these soils. Moreover, the temporal variations in nutrient concentrations in groundwater are directly related to variations in groundwater level during an annual hydrological cycle. Our results suggest that variations in groundwater level regulate spatio-temporal variations in nutrient concentrations in groundwater as a result of the oxidation–reduction status of soil, which creates favourable or unfavourable conditions for nutrient bioavailability. The hydrological variations are much more important than those concerning substrate and type of vegetation.

Microbial activity in the soil surrounding plant roots contributes to nutrient bioavailability, crop growth, and soil biodiversity and fertility. Colonization of the rhizosphere and the rhizoplane in particular requires early establishment on root surfaces where sources of nutrients are abundant. In this study, we investigated the physical interactions taking place between bacteria and the root surface when a root tip enters unexplored regions of soil. We developed a theoretical framework that generalizes the prevailing approaches for describing root growth kinematics and bacterial growth and adhesion on root surfaces. We found that the root elongation rate, bacterial attachment rate, and root cap carrying capacity are key traits for successful establishment. Models also indicate that chemotaxis is more important for radial transport and adhesion than for longitudinal movement of bacteria. Controls on bacterial attachment are required for both efficient root colonization and subsequent dispersal of bacteria in soil. The findings of this study help to understand the establishment of the structure and composition of microbial communities in soil.

Accurate measures of nutrient bioavailability are important in understanding nutrient cycles. Bioavailability is related to both the diffusion rate of the nutrient through the soil and nutrient solution concentration at any given time. The purpose of this work was to investigate the use of ion exchange resin impregnated membranes as a potential bioavailability measure. We propose that the ion sink membranes (IS) will integrate soil nutrient concentration and effective nutrient diffusion rates, resulting in a more complete measure of nutrient bioavailability. The IS are applied directly to the soil and recovered after fixed time intervals. The rate at which ions are adsorbed by the IS is directly related to c²Dₑ, where c is the labile P concentration and Dₑ is the effective diffusion coefficient. We refer to this value as the IS bioavailability index of a given nutrient. This index provides an integrated measure of ion diffusion, sorption-desorption rates, and solution concentration. The resulting bioavailability index can then be correlated with plant nutrient uptake. The IS bioavailability index for P and Fe correlated well with P extracted by ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA) in saturated soils across a range of soil Fe and P concentrations. In addition, plant P uptake under saturated conditions correlated with the IS bioavailability index across a range of soil P concentrations.

Nutrient bioavailability is a highly recognized concept to which great importance is attached, yet which lacks clear definition. Ambiguities in terms and methodologies used to determine bioavailability have contributed greatly to the lack of clear definition. An attempt has been made in this article to clarify some of the terminology associated with the concept of bioavailability. Factors that affect bioavailability have been discussed in terms of environmental, organic and physiological occurrences. The effect of these factors is related to nutrient metabolism. Also, the relationship of the multitude of methodologies used to study nutrient bioavailability with the hierarchy of terms used to describe it is established. Finally, the care that is needed in the interpretation of bioavailability research, which is critical to the understanding of implications derived from this concept, is emphasized through specific examples.