Abstract
The solubility of plant protein isolates is a key determinant of their potential application. Two protein isolates (PI) from ethanol-treated industrial rapeseed meal, PI10.5–2.5 and PI2.5–8.5, were prepared by sequential isoelectric precipitation of alkali-extracted proteins (pH 12) starting from pH 10.5 to 2.5 or from pH 2.5 to 8.5, respectively. Biochemical analyses revealed that PI2.5–8.5 contained a higher amount of crude protein (72.84%) than PI10.5–2.5 (68.67%). In the same protein isolate, the level of total phenols (0.71%) was almost two-fold higher than that in PI10.5–2.5 (0.42%). No glucosinolates were established in both protein isolates. SDS-PAGE analysis demonstrated that PI10.5–2.5 contained 10 to 15 kDa protein fractions in a relatively higher amount, while PI2.5–8.5 was enriched in 18 to 29 kDa protein fractions. PI10.5–2.5 exhibited high solubility, varying from 41.74% at pH 4.5 to 65.13% at pH 6.5, while PI2.5–8.5 was almost two-fold less soluble under the same conditions. Up to pH 5.5, the addition of NaCl at 0.03 and 0.25 M diminished the solubility of PI2.5–8.5, while the solubility of PI10.5–2.5 was increased. The supplementation of PI10.5–2.5 with 0.25 M NaCl enhanced the protein solubility to 56.11% at pH 4.5 and 94.26% at pH 6.5. The addition of 0.03 M NaCl also increased the solubility of this protein isolate but to a lower extent. Overall, the approach for sequential precipitation of proteins influenced the biochemical characteristics, protein fractional profile and solubility of prepared protein isolates.
Highlights
Providing sufficient and high quality protein is important when the world’s population is expected to grow to almost 10 billion by 2050 [1]
This study aimed to evaluate the influence of sequential isoelectric precipitation methodology on biochemical characteristics and solubility of rapeseed meal protein isolates
The biochemical analyses revealed that PI2.5–8.5 contained a higher amount of crude protein (72.84%) than PI10.5–2.5 (68.67%) (Table 1)
Summary
Providing sufficient and high quality protein is important when the world’s population is expected to grow to almost 10 billion by 2050 [1]. Sociodemographic change, as well as the global increase of middle classes, drives the food industry to the production of new proteins by efficient utilization of natural resources and gentle care of the environment [2]. Among them, rapeseed meal proteins are considered prospective nutritive and functional ingredients for the food industry [4,5]. The most common approach to prepare protein-rich ingredients, namely protein isolates (PI), is by isoelectric precipitation after extraction with NaOH [6,7,8,9]. The precipitation occurs at a single pH where the solubility of the proteins is the lowest which, diminishes their potential practical application.
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