Amaranth (Amaranthus hypochondriacus) vicilin subunit structure

Modulation of physico-chemical and technofunctional properties of quinoa protein isolate: Effect of precipitation acid

The typically low solubility and gelation capacity of plant proteins can impose challenges in the design of high-quality plant-based foods. The acid used during the precipitation step of plant protein isolate extraction can influence protein functionality. Here, acetic acid and citric acid were used to extract quinoa protein isolate (QPI) from quinoa flour, as these acids are more kosmotropic than the commonly used HCl, promoting the stabilisation of the native protein structure. While proximate analysis showed that total protein was similar for the three isolates, precipitation with kosmotropic acids increased soluble protein, which correlated positively with gel strength. Microstructure analysis revealed that these gels contained a less porous protein network with lipid droplet inclusions. This study shows that the choice of precipitation acid offers an opportunity to tailor the properties of quinoa protein isolate for application, a strategy that is likely applicable to other plant protein isolates.

Dynamic digestion of a high protein beverage based on amaranth: Structural changes and antihypertensive activity

An amaranth beverage (AB) was subjected to a simulated process of dynamic gastrointestinal digestion DIDGI®, a simple two-compartment in vitro dynamic gastrointestinal digestion system. The structural changes caused to the proteins during digestion and the digesta inhibitory capacity of the angiotensin converting enzyme (ACE) were investigated. In gastric compartment the degree of hydrolysis (DH) was 14.7 ± 1.5 % and in the intestinal compartment, proteins were digests in a greater extent (DH = 60.6 ± 8.4 %). Protein aggregation was detected during the gastric phase. The final digesta obtained both at the gastric and intestinal level, showed ACE inhibitory capacity (IC50 80 ± 10 and 140 ± 20 μg/mL, respectively). Purified fractions from these digesta showed even greater inhibitory capacity, being eluted 2 (E2) the most active fraction (IC50 60 ± 10 μg/mL). Twenty-six peptide sequences were identified. Six of them, with potential antihypertensive capacity, belong to A. hypochondriacus, 3 agglutinins and 3 encrypted sequences in the 11S globulin. Results obtained provide new and useful information on peptides released from the digestion of an amaranth based beverage and its ACE bioactivity.

Modifying quinoa protein for enhanced functional properties and digestibility: A review

Quinoa (Chenopodium quinoa Willd.) is a pseudocereal plant that originally came from South America. The trend of consuming quinoa is propelled by its well‒balanced amino acid profile compared to that of other plants. In addition, its gluten‒free nature makes quinoa a promising diet option for celiac disease patients. Protein accounts for approximately 17% of the quinoa seed composition and quinoa protein possesses excellent quality. Quinoa protein is mainly composed of 11S globulins (37%) and 2S albumins (35%), both of which are stabilized by disulfide bonds. To date, the alkaline extraction method is the most commonly used method to extract quinoa protein. The functional properties and digestibility of quinoa protein can be improved with the help of various modification methods, and as a result, the application of quinoa protein will be extended. In this review, the extraction method, modification of functional properties and digestibility of quinoa protein are thoroughly discussed, providing insights into the application of quinoa protein in plant‒based foods.

Heat-induced denaturation and aggregation of protein in quinoa (Chenopodium quinoa Willd.) seeds and whole meal

Physical barriers hinder about 20-25% of the protein from being extracted from whole meal. Heat-induced denaturation and aggregation of protein in quinoa seeds and in whole meal was investigated. Maximally 37% of the protein in seeds covalently aggregate when boiling for 15 min. Although embryonic cell walls surrounding protein bodies remain intact during boiling of seeds, protein aggregation is not hindered. 11S Globulin monomers first dissociate into their acidic and basic subunits which further assemble into large (> 500 kDa) mainly disulfide-linked aggregates. 2S Albumins are not involved in covalent aggregation but partially leach during seed boiling. The presence of disrupted food matrix constituents in whole meal delays denaturation and causes less aggregation of protein in whole meal than in seeds. Globulins still dissociate into their subunits but less and mainly small covalent aggregates (ca. 100-500 kDa) are formed. These novel insights allow developing new quinoa-based food products.

Amaranth as a Source of Antihypertensive Peptides

Amaranth is an ancestral crop used by pre-Columbian cultures for 6000 to 8000 years. Its grains have a relevant chemical composition not only from a nutritional point of view but also due to the contribution of components with good techno-functional properties and important potential as bioactive compounds. Numerous studies have shown that amaranth storage proteins possess encrypted sequences that, once released, exhibit different physiological activities. One of the most studied is antihypertensive activity. This review summarizes the progress made over the last years (2008-2020) related to this topic. Studies related to inhibition of different enzymes of the Renin-Angiotensin-Aldosterone system, in particular Angiotensin Converting Enzyme (ACE) and Renin, as well as those referring to potential modulation mechanisms of tissue or local Renin-Angiotensin-Aldosterone system, are analyzed, including in silico, in vitro, in vivo, and ex vivo assays. Furthermore, the potential use of these bioactive peptides or products containing them, in the elaboration of functional food matrices is discussed. Finally, the most relevant conclusions and future requirements in research and development of food products are presented.

Amaranth Lemon Sorbet, Elaboration of a Potential Functional Food

In the present work, amaranth proteins were used as a functional ingredient of formulated food. An amaranth lemon sorbet, a healthy alternative dessert for celiac, vegan and any consumer that chooses to follow a conscious diet, was elaborated and characterized. The sorbet base mixture behaved like a pseudoplastic and thixotropic fluid, with a Kokini viscosity of 0.42 ± 0.07 Pa.s, a suitable value for elaborating products with good thickness characteristics. Aeration rate of the sorbet was 36.15 ± 3.48, an overrun value within the expected range of 30-50%, indicating that amaranth proteins presented adequate foaming properties in low pH elaboration conditions. Moreover, the stability study showed that the sorbet did not suffer significant changes in its structure over time during the first two months of storage at -20 °C. Sensory evaluation evidenced panelists accepted the product (8 ± 1, acceptability assay) and related it with airy, creamy and healthy attributes (CATA assay). Finally, simulated gastrointestinal digestion was able to release peptides capable of inhibiting fibrin clot formation (IC₅₀ = 3.4 ± 0.1 mg protein/mL), demonstrating that amaranth proteins could be used as a good foaming ingredient in the elaboration of potential functional foods with antithrombotic activity.

Antiproliferative Effect of Amaranth Proteins and Peptides on HT-29 Human Colon Tumor Cell Line

Antiproliferative effect of Amaranthus mantegazzianus proteins and peptides released after simulated gastrointestinal digestion (DH% 37.8 ± 3.8) was investigated on human colon cancer cell line HT-29. Inhibition of proliferation of HT-29 cells was exhibited after a 24 h treatment with different concentrations of amaranth protein isolate (API) and the peptides released after digestion (DGS), presenting IC₅₀ values of 1.35 ± 0.12 and 0.30 ± 0.07 mg soluble protein/mL, respectively. Lactate dehydrogenase assay indicated that both samples caused the loss of membrane integrity and cell lysis over HT-29 cells, and DAPI fluorescence microscopies evidenced typical apoptotic features. Moreover, Annexin V-FITC flow cytometry showed a significant increase of early apoptotic and late apoptotic/necrotic HT-29 cells compared to untreated ones, and caspase-3 assay confirmed the apoptosis induction with a 43.0 ± 10.3 and 65.8 ± 12.7% increase of caspase-3 activity produced by a 2 mg/mL treatment of API and DGS, respectively. In conclusion, amaranth peptides successfully released after simulated gastrointestinal digestion would exert a potential antiproliferative activity over HT-29 tumor cells. This effect was linked to the induction of cell necrosis and apoptosis, supporting the idea of using amaranth proteins as a potential food alternative ingredient for functional foods.

Proteases catalyzing vicilin cleavage in developing pea (Pisum sativum L.) seeds

Legume species differ in whether or not the 7S globulins stored in seeds undergo proteolytic processing during seed development, while preserving the bicupin structure and trimeric assembly necessary for accumulation and packing into protein storage vacuoles. Two such cleavage sites have been documented for the vicilins in pea cotyledons: one in the linker region between the two cupin domains, and another in an exposed loop in the C-terminal cupin. In this report, we explain the occurrence of vicilin cleavage in developing pea by showing that the storage vacuoles are already acidified before germination, in contrast to soybean and peanut where acidification occurs only after germination. We also show that the two cleavage reactions are catalyzed by two different proteases. The vicilin cleavage at the linker region was inhibited by AEBSF (4-(2-aminoethyl)benzenesulfonyl fluoride), indicative of a serine protease. The cleavage in the C-terminal cupin domain was sensitive to the sulfhydryl-reactive reagents p-chloromercuriphenylsulfonate and iodoacetate, but not to E-64 (N-[N-(L-3-transcarboxyirane-2-carbonyl)-l-leucyl]-agmatine), characteristic of the legumain class of cysteine proteases. During seed development, we found the predominant vicilin cleavage in this pea cultivar (Knight) to be at the site in the second cupin domain; but after germination, both sites were cleaved at about the same rate.

Proteins of Amaranth (Amaranthus spp.), Buckwheat (Fagopyrum spp.), and Quinoa (Chenopodium spp.): A Food Science and Technology Perspective

There is currently much interest in the use of pseudocereals for developing nutritious food products. Amaranth, buckwheat, and quinoa are the 3 major pseudocereals in terms of world production. They contain high levels of starch, proteins, dietary fiber, minerals, vitamins, and other bioactives. Their proteins have well-balanced amino acid compositions, are more sustainable than those from animal sources, and can be consumed by patients suffering from celiac disease. While pseudocereal proteins mainly consist of albumins and globulins, the predominant cereal proteins are prolamins and glutelins. We here discuss the structural properties, denaturation and aggregation behaviors, and solubility, as well as the foaming, emulsifying, and gelling properties of amaranth, buckwheat, and quinoa proteins. In addition, the technological impact of incorporating amaranth, buckwheat, and quinoa in bread, pasta, noodles, and cookies and strategies to affect the functionality of pseudocereal flour proteins are discussed. Literature concerning pseudocereal proteins is often inconsistent and contradictory, particularly in the methods used to obtain globulins and glutelins. Also, most studies on protein denaturation and techno-functional properties have focused on isolates obtained by alkaline extraction and subsequent isoelectric precipitation at acidic pH, even if the outcome of such studies is not necessarily relevant for understanding the role of the native proteins in food processing. Finally, even though establishing in-depth structure-function relationships seems challenging, it would undoubtedly be of major help in the design of tailor-made pseudocereal foods.

Antithrombotic and Antioxidant Activity of Amaranth Hydrolysate Obtained by Activation of an Endogenous Protease

Ingestion of diets with antithrombotic and antioxidant components offer a convenient and effective way to prevent and reduce the incidence of cardiovascular diseases. The aim of the present work was to obtain an amaranth hydrolysate by the activation of an endogenous aspartic protease, to establish adequate experimental conditions, and to evaluate its antithrombotic and antioxidant activity in order to assess its potential application as an ingredient in functional foods. The results obtained not only confirmed the presence of an endogenous protease in the amaranth isolate, but also allowed us to select an adequate incubation conditions (pH 2, 40 °C, 16 h). The hydrolysate obtained (degree of hydrolysis 5.3 ± 0.4 %) showed potential antithrombotic activity (IC50 = 5.9 ± 0.1 mg soluble protein/mL) and had more antioxidant activity than the isolate, indicating that the activation of the protease released bioactive peptides from amaranth proteins. Decreasing the pH is a simple and cheap process and is another way to obtain potential functional ingredients with bioactive compounds.

Physicochemical, functional and angiotensin converting enzyme inhibitory properties of amaranth (Amaranthus hypochondriacus) 7S globulin

BACKGROUND

Amaranth 7S globulin is a minor globulin component and its impact on the properties of an amaranth protein ingredient depends on its proportion in the variety of amaranth being considered. Some physicochemical, functional and angiotesin I-converting enzyme (ACE) inhibitory properties of amaranth vicilin were studied in this work and compared with the 11S globulin.

RESULTS

Fluorescence spectroscopy results indicated that 7S globulin tryptophans were more exposed to the solvent and, by calorimetry, the 7S globulin denaturation temperature (T(d) ) was found lower than the 11S globulin T(d) , suggesting a more flexible structure. The 7S globulin surface hydrophobicity was higher than that of the 11S globulin, which is in agreement with the better emulsifying properties of the 7S globulin. The solubility in neutral buffer of the 7S globulin (851 ± 25 g kg(-1) ) was also higher than that of the 11S globulin (195 ± 6 g kg(-1) ). Bioinformatic analyses showed the presence of ACE inhibitory peptides encrypted in 7S tryptic sequences and peptides released after in vitro gastrointestinal digestion showed a high ACE-inhibitory capacity (IC(50) = 0.17 g L(-1) ), similar to that of 11S globulin peptides.

CONCLUSION

Compared with the 11S globulin, the 7S globulin presents similar ACE inhibitory activity and some functional advantages, better solubility and emulsifying activity, which suits some food requirements. The functional behavior has been related with the structural properties.