Shridhar K. Sathe

Phytates in legumes and cereals

Publisher Summary This chapter discusses that the knowledge of phytic acid had its beginning in the discovery by Hartig, who isolated small particles or grains (which were not starch grains) from the seeds of various plants. Phytic acid has been generally regarded as the primary storage form of both phosphate and inositol in almost all seeds. The amount of phytic acid varies from 0.50% to 1.89% in cereals (except polished rice), from 0.40% to 2.06% in legumes, from 2.00% to 5.20% in oil seeds except soybeans and peanuts (grouped under legumes), and from 0.40% to 7.50% in protein products. Many foods and seeds contain myo-inositol hexaphosphate as an important source of phosphorus, and accurate methods for its determination are needed. Phytase (meso-inositol hexaphosphate phosphohydrolase, EC 3.1.3.8) is widely distributed in plants, animals, and fungi. In mature cereal grains, legumes, and oil seeds, the major portion of the total phosphorus is present in the form of phytic acid (phytate). Experiments with animals have suggested that phytic acid in plant foods complexes with dietary essential minerals such as calcium, zinc, iron, and magnesium and makes them biologically unavailable for absorption. The correlation of phytate with the cooking quality of peas was first suggested by Mattson. Phytic acid, myo-inositol 1,2,3,4,5,6-hexakis dihydrogen phosphate serves as the main phosphorus store in mature seeds and grains. In cereals and legumes, phytic acid content ranges from 0.14% to 2.05%, which accounts for 18 to 88% of the total phosphorus.

Dry bean tannins: A review of nutritional implications

Tannins are one of several antinutritional factors present in dry beans and are located mainly in the seed coat or testa. The tannin content of dry beans ranges from 0.0 to 2.0% depending on the bean species and color of the seed coat. Many high tannin bean varieties are of lower nutritional quality than low tannin varieties of beans. Naturally occurring food legume tannins are reported to interact with proteins (both enzyme and nonenzyme proteins) to form tannin-protein complexes resulting in inactivation of digestive enzymes and protein insolubility. Both in vitro and in vivo studies indicate that bean tannins decrease protein digestibility, either by inactivating digestive enzymes or by reducing the susceptibility of the substrate proteins after forming complexes with tannins and absorbed ionizable iron. Other deleterious effects of tannins include a lowered feed efficiency and growth depression in experimental animals. The antinutritional activity of bean tannins can be reduced by processing (1 or a combination of 2 or more methods), for example dehulling, soaking, cooking and germination. Genetic selection also may help in breeding varieties low in tannins. Potential chemical treatments such as use of tannin complexing agents are discussed.

Tree Nut Allergens

Allergic reactions to tree nuts can be serious and life threatening. Considerable research has been conducted in recent years in an attempt to characterize those allergens that are most responsible for allergy sensitization and triggering. Both native and recombinant nut allergens have been identified and characterized and, for some, the IgE-reactive epitopes described. Some allergens, such as lipid transfer proteins, profilins, and members of the Bet v 1-related family, represent minor constituents in tree nuts. These allergens are frequently cross-reactive with other food and pollen homologues, and are considered panallergens. Others, such as legumins, vicilins, and 2S albumins, represent major seed storage protein constituents of the nuts. The allergenic tree nuts discussed in this review include those most commonly responsible for allergic reactions such as hazelnut, walnut, cashew, and almond as well as those less frequently associated with allergies including pecan, chestnut, Brazil nut, pine nut, macadamia nut, pistachio, coconut, Nangai nut, and acorn.

Chemical, nutritional and physiological aspects of dry bean carbohydrates—A review

Abstract The current knowledge of dry bean carbohydrates related to their composition, nutritional value and physiological attributes in humans is reviewed. Dry bean carbohydrates represent up to 60% of the total seed weight and starch is the major constituent. Molecular and physicochemical properties of legume starches are also discussed. Data to indicate the possible involvement of the raffinose family of oligosaccharides in flatulence production are given.

Walnuts (Juglans regia L): proximate composition, protein solubility, protein amino acid composition and protein in vitro digestibility†

Walnuts contained 16.66% protein and 66.90% lipids on a dry weight basis. Non-protein nitrogen values ranged from 6.24 to 8.45% of the total nitrogen when the trichloroacetic acid concentration was varied within the range 0.25–1.0 M. Albumin, globulin, prolamin and glutelin respectively accounted for 6.81, 17.57, 5.33 and 70.11% of the total walnut proteins. Walnut proteins were minimally soluble at pH 4.0. The majority of total walnut protein polypeptides had estimated molecular weights in the range 12 000–67 000. The Stokes radius of the major protein in walnuts (glutelin fraction) was 66.44 ± 1.39 A. Lysine was the first limiting essential amino acid in total walnut proteins as well as in the globulin and glutelin fractions. Leucine and methionine plus cysteine were the second limiting essential amino acids respectively for the prolamin and albumin fractions. Hydrophobic and acidic amino acids dominated the amino acid composition in all protein fractions. Native and heat-denatured walnut glutelins were easily hydrolysed by trypsin, chymotrypsin and pepsin in vitro. © 2000 Society of Chemical Industry

Dry bean protein functionality.

ABSTRACT:  Dry beans are an important source of proteins, carbohydrates, dietary fiber, and certain minerals and vitamins in the human food supply. Among dry beans, Phaseolus beans are cultivated and consumed in the greatest quantity on a worldwide basis. Typically, most dry beans contain 15 to 25% protein on a dry weight basis (dwb). Water-soluble albumins and salt-soluble globulins, respectively, account for up to 10 to 30% and 45 to 70% of the total proteins (dwb). Dry bean albumins are typically composed of several different proteins, including lectins and enzyme inhibitors. A single 7S globulin dominates dry bean salt soluble fraction (globulins) and may account for up to 50 to 55% of the total proteins in the dry beans (dwb). Most dry bean proteins are deficient in sulfur amino acids, methionine, and cysteine, and therefore are of lower nutritional quality when compared with the animal proteins. Despite this limitation, dry beans make a significant contribution to the human dietary protein intake. In bean-based foods, dry bean proteins also serve additional functions that may include surface activity, hydration, and hydration-related properties, structure, and certain organoleptic properties. This article is intended to provide an overview of dry bean protein functionality with emphases on nutritional quality and hydration-related properties.

Comparison of the autolyzed and unautolyzed forms of μ- and m-calpain from bovine skeletal muscle

Bovine skeletal muscle mu- and m-calpain autolyze when incubated with Ca2+. During the first 30 to 300 s, autolysis: (1) has little effect on the specific proteolytic activity of either mu- or m-calpain when assayed at 5 mM Ca2+; and (2) produces two new proteolytically active forms of calpain in addition to the original mu- and m-calpain. The four proteolytically active forms of calpain are: (1) autolyzed mu-calpain, having polypeptide subunits of 76 and 18 kDa and requiring 0.60 microM Ca2+ for half-maximal activity; (2) mu-calpain with 80- and 28-kDa subunits and requiring 7.1 microM Ca2+ for half-maximal activity; (3) autolyzed m-calpain with 78- and 18-kDa subunits and requiring 180 microM Ca2+ for half-maximal activity; and (4) m-calpain with 80- and 28-kDa subunits and requiring 1000 microM Ca2+ for half-maximal activity. All four forms of the calpains have similar pH optima (7.4 to 7.6) and almost identical circular dichroism spectra in the far ultraviolet (all four have little secondary structure with 26-30% alpha-helix and less than 10% beta-sheet structure). Autolyzed mu- and unautolyzed mu-calpain are fully activated proteolytically by Mn2+ with activity starting at 125 microM Mn2+. Autolyzed m-calpain is also activated by Mn2+ up to 80% of the maximum proteolytic activity obtained with Ca2+; Mn2+ activation begins at 320 microM Mn2+. Unautolyzed m-calpain has only 6 to 8% as much activity in the presence of Mn2+ as it does in the presence of Ca2+. Autolysis increases the axial ratios of the calpains from 3.5 to 4.6 for mu-calpain and from 3.7 to 5.0 for m-calpain (assuming 20% hydration). The estimated length of the calpain molecules increases by 13% upon autolysis from 73 to 84 A for mu-calpain and from 76 to 90 A for m-calpain (assuming 20% hydration). The autolyzed calpains elute after their unautolyzed counterparts off a DEAE-ion exchange column. Because autolyzed forms of the calpains are not found in DEAE elution profiles of cell extracts, bovine skeletal muscle cells must contain very little (less than 5% of total calpain) or none of the autolyzed form of the calpains.

Ana o 2, a Major Cashew (Anacardium occidentale L.) Nut Allergen of the Legumin Family

Background: We recently cloned and described a vicilin and showed it to be a major cashew allergen. Additional IgE-reactive cashew peptides of the legumin group and 2S albumin families have also been reported. Here, we attempt to clone, express and characterize a second major cashew allergen. Methods: A cashew cDNA library was screened with human IgE and rabbit IgG anti-cashew extract antisera, and a reactive nonvicilin clone was sequenced and expressed as a fusion protein in Escherichia coli. Immunoblotting was used to screen for reactivity with patients’ sera, and inhibition of immunoblotting was used to identify the corresponding native peptides in cashew nut extract. The identified allergen was subjected to linear epitope mapping using SPOTs solid-phase synthetic peptide technology. Results: Sequence analysis showed the selected clone, designated Ana o 2, to encode for a member of the legumin family (an 11S globulin) of seed storage proteins. By IgE immunoblotting, 13 of 21 sera (62%) from cashew-allergic patients were reactive. Immunoblot inhibition data showed that the native Ana o 2 constitutes a major band at approximately 33 kD and a minor band at approximately 53 kD. Probing of overlapping synthetic peptides with pooled human cashew-allergic sera identified 22 reactive peptides, 7 of which gave strong signals. Several Ana o 2 epitopes were shown to overlap those of the peanut legumin group allergen, Ara h 3, in position but with little sequence similarity. Greater positional overlap and identity was observed between Ana o 2 and soybean glycinin epitopes. Conclusions: We conclude that this legumin-like protein is a major allergen in cashew nut.

Epitope mapping of a 95 kDa antigen in complex with antibody by solution-phase amide backbone hydrogen/deuterium exchange monitored by Fourier transform ion cyclotron resonance mass spectrometry.

The epitopes of a homohexameric food allergen protein, cashew Ana o 2, identified by two monoclonal antibodies, 2B5 and 1F5, were mapped by solution-phase amide backbone H/D exchange (HDX) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and the results were compared to previous mapping by immunological and mutational analyses. Antibody 2B5 defines a conformational epitope, and 1F5 defines a linear epitope. Intact murine IgG antibodies were incubated with recombinant Ana o 2 (rAna o 2) to form antigen-monoclonal antibody (Ag-mAb) complexes. mAb-complexed and uncomplexed (free) rAna o 2 were then subjected to HDX. HDX instrumentation and automation were optimized to achieve high sequence coverage by protease XIII digestion. The regions protected from H/D exchange upon antibody binding overlap and thus confirm the previously identified epitope-bearing segments: the first extension of HDX monitored by mass spectrometry to a full-length antigen-antibody complex in solution.

Effects of food processing on food allergens.

Food allergies are on the rise in Western countries. With the food allergen labeling requirements in the US and EU, there is an interest in learning how food processing affects food allergens. Numerous foods are processed in different ways at home, in institutional settings, and in industry. Depending on the processing method and the food, partial or complete removal of the offending allergen may be possible as illustrated by reduction of peanut allergen in vitro IgE immunoreactivity upon soaking and blanching treatments. When the allergen is discretely located in a food, one may physically separate and remove it from the food. For example, lye peeling has been reported to produce hypoallergenic peach nectar. Protein denaturation and/or hydrolysis during food processing can be used to produce hypoallergenic products. This paper provides a short overview of basic principles of food processing followed by examples of their effects on food allergen stability. Reviewed literature suggests assessment of processing effects on clinically relevant reactivity of food allergens is warranted.