Extraction and Characterization of Proteins from Pachyrhizus ahipa Roots: an Unexploited Protein-Rich Crop

Abstract

Pachyrhizus ahipa is an unexploited crop known to be rich in proteins compared to other edible roots and tubers. These proteins are not prolamins, thus ahipa represents an interesting new source of ingredients for gluten-free foods. In this work, ahipa proteins (AP) were extracted and partially characterized in pursuit of their use as food ingredients. The effect of ultrasound treatment on protein extraction efficiency was evaluated. AP were characterized by their size, amino acid composition, surface hydrophobicity, intrinsic fluorescence, FTIR spectra, solubility, and thermal and emulsifying properties. AP were efficiently removed from the vegetal tissue using PBS or water, regardless of the use of ultrasound, but not easily recovered by precipitation. This protein fraction was composed of small proteins, with sizes ranging from 9 to 30 kDa, and highly polar. AP resulted particularly rich in aspartic acid (59% of the total amino acid content), for which they can be classified as Asp-rich proteins. Their elevated content of acidic groups was evidenced in the ATR-FTIR spectrum. The amide I band deconvolution as well as the low surface hydrophobicity and denaturation enthalpy indicated that these proteins are mainly unordered structures. The emulsifying properties of AP were enhanced when the concentration was increased from 0.1 to 1% (w/v) but resulted lower than those of soy protein. The high polarity, small size, and low isoelectric point make AP particularly suitable for acidic food matrices. Keywords Acidic proteins . Aspartic acid . Gluten-free ingredients . Ahipa roots . Tuberous roots . Food proteins

Variation in Nutritional Components in Roots From Ahipa (<em>Pachyrhizus ahipa</em> (Wedd.) Parodi) Accessions and an Interspecific Hybrid (<em>P. Ahipa</em> × <em>P. Tuberosus</em> (Lam.) Spreng.)

“…Hence, the necessary essential amino acids may be acquired from other plant or animal sources [38]. In both ahipa and the X207 hybrid, the primary amino acid found in proteins was aspartate (Table 4), as it was also reported in proteins isolated from market-purchased ahipa roots [17]. The relatively high concentration of free amino acids provided by fresh roots (Table 6), where the amide asparagine was predominant, followed by the amino acids glutamate and arginine (Table 7), should not be despised for their nutritional, functional values.…”

“…In a previous study, Forsyth and Shewry [10] did not find storage proteins in ahipa roots but proteins related to tuber metabolism and growth. Recently, root proteins have been characterized, and their possible food applications have been suggested [17].…”

The use of ultrasound in the South Cone region. Advances in organic and inorganic synthesis and in analytical methods

“… Improved the mass transfer due to penetration of the solvent into the sample matrix. [204] Total isothiocyanates Brassicaceae vegetables UAE ES: water 10 g sample, 1: 5 w/v mg mL −1 (sample/solvent ratio), sonicated (USB) 40 kHz, 600 W for 5 min Enhanced the extraction due to disruption of cell walls Reduced particle-size Improved the mass transfer of the cell contents [205] Inulin Jerusalem artichoke tubers UAE ES: distilled hot water – Efficient extraction [206] Proteins Pachyrhizus ahipa Roots UAE ES: water 200 g of sample with 200 mL of distilled water, sonicated (UP) five pulses of 1 min at 600 W ------ [207] Water-soluble carbohydrates Sotol plant (Dasylirion leiophyllum) PEST ES: distilled water Sonothermal treatment (ST): 2 kg of sotol strips, in 20 L water, sonicated 25 kHz, 1135 W/m 2 (ultrasound intensity) Pre-enzymatic sonothermal treatment (PEST): 2 kg of sotol plant, 20 L of a 50 mM buffer solution of sodium acetate (pH4.5), 10 mL of Pectinex® Ultra, sonicated 25 kHz, 1135 W/m 2 (ultrasound intensity), 40 °C for 6 h Increased in temperature decreased the cavitation effect [208] …”

“…According to the results, UAE using aqueous solvents was the most appropriate strategy for the extraction of bioactive compounds from both P. cruentum and P. purpureum . Water was also the optimal solvent selected by Argentinian researchers for the extraction of total isothiocyanates [205] , inulin [206] , proteins [207] and water-soluble carbohydrates [208] . This last work was carried out by the Universidad Nacional del Sur (Argentina) in collaboration with three Mexican universities: The Autonomous University of Chihuahua, the National Autonomous University of Mexico and the Autonomous University of Coahuila.…”

Variation in Nutritional Components in Roots from Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) Accessions and an Interspecific Hybrid (P. ahipa × P. tuberosus (Lam.) Spreng.)

“…In a previous study, Forsyth and Shewry [10] did not find storage proteins in ahipa roots but proteins related to tuber metabolism and growth. Recently, root proteins have been characterized, and their possible food applications have been suggested because their chemical properties as highly digestible components for gluten-free foods or even as emulsifiers for dressings [17].…”