An increasing use of vegetable protein is required to support the production of protein-rich foods which can replace animal proteins in the human diet. Amaranth, chia and quinoa seeds contain proteins which have biological and functional properties that provide nutritional benefits due to their reasonably well-balanced aminoacid content. This review analyses these vegetable proteins and focuses on recent research on protein classification and isolation as well as structural characterization by means of fluorescence spectroscopy, surface hydrophobicity and differential scanning calorimetry. Isolation procedures have a profound influence on the structural properties of the proteins and, therefore, on their in vitro digestibility. The present article provides a comprehensive overview of the properties and characterization of these proteins.

Chia protein isolates (CPI) were obtained through isoelectric precipitation under two different conditions in order to compare their structural properties. Extraction was carried out at pH 10 or 12, whereas precipitation pH was fixed at 4.5. Samples were named as CPI10 or CPI12, according to their extraction pH (10 or 12, respectively). The recovery of chia proteins was higher when the extraction was carried out at pH 12 (17% for CPI12 and 13% for CPI10); however, CPI12 protein content (775g/kg) was slightly lower than CPI10 protein content (782g/kg). Both samples showed similar SDS-PAGE pattern. Protein dispersions of both isolates led to highly stabilized particles due to their negative ζ potential (around-54 mV). CPI10 has a higher proportion of small particles in suspension, revealed by a lower d3,2 value. Spectroscopic techniques showed that CPI10 presented higher content of β-helix than CPI12, resulting in higher thermal stability. This observation was supported by FT-IR spectroscopy since CPI10 presented less unordered structure than CPI12. The energy of endotherms obtained in CPI12 was considerably lower than in CPI10. Extraction at higher alkaline conditions led to a more denatured protein conformation with a higher content of random structure (18.1% for CPI10 and 22.9% for CPI12).

Please cite this article as: López, Dé.N., Ingrassia, R., Busti, P., Wagner, J., Boeris, V., Spelzini, Darí., Effects of extraction pH of chia protein isolates on functional properties, Abstract 24The aim of this work was to study the effect of the extraction pH on the functional 25 properties of chia protein isolates (CPI). Samples were named as CPI10 or CPI12, 26 according to their extraction pH, 10 or 12, respectively. Functional properties were 27 significantly modified by the extraction pH. Color properties revealed that CPI12 presented 28 a lower L* (47.8±0.9 for CPI10 and 30±1 for CPI12) due to enhanced protein-polyphenol 29 interactions. Besides, a higher b* value was obtained for CPI12 (7.0±0.3 for CPI12 and 30 5.6±0.7 for CPI10), as a result of a higher ash content. CPI12 showed a higher WAC 31 probably due to a higher exposure of polar amino acids (4.4±0.1 g/g and 6.0±0.2 g/g), 32 whereas CPI10 showed a higher ability to bind oil (7.1±0.2 g/g and 6.1±0.2 g/g for CPI10 33 and CPI12, respectively). CPI10 proved more appropriate as an emulsion stabilizer than 34 CPI12, which could be due to its higher surface hydrophobicity, protein solubility and 35 negative net charge. The d 4,3 (µm) was 29.5±0.4 and 20.4±0.3 in emulsions stabilized with 36 CPI12 and CPI10, respectively. Although both isolates underwent heat gelation, they 37 exhibited a weak gel behavior. Overall, CPI10 may be more suitable for the food industry 38 as a meat replacer or extender.39

Highlights  Chia proteins were isolated from defatted milled seeds at pH 10 (CPI10) or 12 (CPI12)  The interfacial behavior of these isolates was related to their extraction conditions  Foams from CPI10 were more stable due to the formation of a thicker interfacial film  CPI10 showed a greater ability to retard liquid drainage  CPI12 showed better emulsifying properties whereas poorer foaming properties

Functional properties of amaranth, quinoa and chia proteins and the biological activities of their hydrolyzates

BACKGROUND: Rice bran (RB), a by-product of the rice milling industry, constitutes around 10% of the total weight of rough rice. The interest in the use of RB is centered on its nutritional quality, its low cost, and its extensive worldwide production. As RB is commonly used for oil extraction, the defatted rice bran (DRB) is obtained as a second by-product. The aim of this work was to obtain a defatted rice bran concentrate (DRBC), enriched in protein and fiber, from defatted rice bran flour (DRBF) and to determine its physicochemical and emulsifying properties. RESULTS: To obtain the DRBC, the starch was efficiently hydrolyzed (> 98%) with -amylase and amyloglucosidase, with a concomitant increase in the proportions of crude protein (from 154.7 to 274.3 g kg −1 ) and total dietary fiber (from 276.1 to 492.3 g kg −1 ). Defatted rice bran concentrate exhibited a loss of protein solubility and increased surface hydrophobicity compared with DRBF. Defatted rice-bran concentrate dispersions with and without previous ultrasound treatment were prepared. The sonication led to an increase in the apparent viscosity. Emulsions were prepared with dispersions with and without previous ultrasound treatment and showed high stability in quiescent conditions over 28 days. However, the emulsions prepared with dispersions treated with ultrasound resulted in lower D 4,3 values and higher elastic and viscous moduli. CONCLUSION: The rice bran concentrate can be used to obtain stable oil-in-water (O/W) emulsions, including both soluble andinsoluble fractions, in acidic and neutral conditions. These innovative findings thus contribute to increasing the added value of this important by-product of the rice-milling industry. Surface hydrophobicity (H 0 )Aromatic surface hydrophobicity was determined on a soluble protein fraction of samples prepared as detailed above, following the approach described by Fernández-Fernández et al., 31 based on J Sci Food Agric 2020; 100: 1336-1343

Orange peels, soybean hulls, Ilex paraguariensis and Platanus x hispanica were evaluated as solid substrates in order to produce peptidases from Aspergillus niger NRRL3 (PAN) under solid-state fermentation. The mixture of soybean hulls and orange peels enabled fungal development and showed the highest peptidase production. The optimal conditions for PAN production were found to be as follows: soybean hulls/orange peels mass ratio, 0.25; initial pH, 7.05; K 2 HPO 4 43.5 g/L and 4.03 g/L NaNO ; inoculation with 5000 conidia per 3g of solid substrate; incubation conditions, 30°C for 5 days. Under these conditions, the peptidase activity was 1000 ± 100 AU/mL. PAN concentration was performed by adsorption on a DEAE-cellulose matrix. The subsequent purification was carried out by gel filtration on Sephadex G-100, with a global purification factor of about 9. PAN proved to belong to the serinetype of peptidases, its highest peptidase activity being at 65 °C. However, proteolysis at 60 °C proved more suitable due to the differences in the inactivation rate. Besides, PAN showed high stability over a pH range of 4 to 11. Taking all this into account, we herein describe the production and purification of a serine peptidase from Aspergillus niger NRRL3 for the first time.

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