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

Effects of protein morphological structures on the cereal processing, sensorial property and starch digestion: a review

In cereals, the protein body and protein matrix are usually two morphological protein structures. However, processing treatments can affect protein structures, change protein bodies into the matrix, or induce a change in the matrix structure; therefore, the processing-induced matrix was listed as the third morphological structure of the protein. Previous research on the effect of proteins was mainly based on protein content and composition, but these studies arrived at different conclusions. Studying the effect of protein morphological structures on sensorial property and starch digestion can provide a theoretical basis for selecting cultivars with high sensorial property and help produce low-glycemic index foods for people with diabetes, controlling their postprandial blood sugar. This study aimed to review the distribution and structure of protein bodies, protein matrices, and processing-induced matrices, as well as their influence on cereal sensorial property and starch digestion. Therefore, we determined the protein morphological structures in different cereal cultivars and summarized its impact. Protein bodies mainly have steric stabilization effects on starch gelatinization, whereas the protein matrix serves as a physical barrier surrounding the starch to inhibit water absorption and α-amylase. Processing can change protein morphological structures, enabling protein bodies to act as a physical matrix barrier.

Structural Properties of Quinoa Protein Isolate: Impact of Neutral to High Alkaline Extraction pH

In this work, we extracted proteins from white quinoa cultivated in the northeast of Qinghai-Tibet plateau using the method of alkaline solubilization and acid precipitation, aiming to decipher how extraction pH (7-11) influenced extractability, purity and recovery rate, composition, multi-length scale structure, and gelling properties of quinoa protein isolate (QPI). The results showed that protein extractability increased from 39 to 58% with the increment of pH from 7 to 11 whereas protein purity decreased from 89 to 82%. At pH 7-11, extraction suspensions and QPI showed the similar major bands in SDS-PAGE with more minor ones (e.g., protein fractions at > 55 or 25-37 kDa) in suspensions. Extraction pH had limited effect on the secondary structure of QPI. In contrast, the higher-order structures of QPI were significantly affected, e.g., (1) emission maximum wavelength of intrinsic fluorescence increased with extraction pH; (2) surface hydrophobicity and the absolute value of zeta-potential increased with increasing extraction pH from 7 to 9, and then markedly decreased; (3) the particle size decreased to the lowest value at pH 9 and then increased to the highest value at pH 11; and (4) denaturation temperature of QPI had a large decrease with increasing extraction pH from 7/8 to 9/10. Besides, heat-set QPI gels were formed by loosely-connected protein aggregates, which were strengthened with increasing extraction pH. This study would provide fundamental data for industrial production of quinoa protein with desired quality.

Processing Enhances Coix Seed Prolamins Structure and Releases Functional Peptides after Digestion: In Silico and In Vitro Studies

Dipeptidyl peptidase-IV (DPP-IV) is a key target for the treatment of type 2 diabetes mellitus. It is possible that peptides that precisely regulate DPP-IV could be released from coix seed prolamins (CSP), but whether this happens has not yet been investigated. We performed the in silico digestion of CSP and predicted the bioactivity, absorption, transport, toxicity, and allergenicity of the resulting peptides. The simulation predicted that 47 non-toxic bioactive peptides would be released. After screening these, we found that 64.58% of them could possess DPP-IV inhibitory activity. The effect of thermal processing on the amino acid composition and structural properties of CSP was determined, and the DPP-IV inhibitory activity of its digestion-derived peptides was also assessed. The results showed that processing could change the flavour of coix seed and the supply of amino acids. After processing, the spatial conformation of CSP changed from ordered to disordered, and the peptide content and the DPP-IV inhibitory activity of its digestion products significantly increased by 19.89-30.91% and 36.84-42.02%, respectively. These results support the hypothesis that processing can change the protein structure and increase the probability that bioactive peptides will be released. They also have important implications for the development of bioactive peptides and the intensive processing of coix seeds.

Mechanisms of heat-mediated aggregation behavior of water-soluble cod protein

Cod proteins (CPs) are considered potential functional ingredients for developing gel-based foods, but present studies on the aggregation behavior of CPs upon heating remain limited. With this respect, the heat-induced aggregation kinetics of CPs at a subunit level was investigated. Based on different centrifugal forces, CPs aggregates were divided into three fractions: large-sized, intermediary-sized, and small-sized aggregates. SDS-PAGE and diagonal SDS-PAGE indicated that myosin heavy chains exhibited a higher affinity with actin to form intermediary-sized and large-sized aggregates; tropomyosin and myosin light chains were hardly engaged in the thermal aggregation and formed small-sized aggregates. The highly-polymerized aggregates adopted considerable transitions of helix-to-sheet in protein structures, whereas the structure of small-sized aggregates featured substantial helix-coil transitions. Furthermore, molecular interactions at different heating stages were revealed. These novel insights might advance our knowledge on the heat-induced aggregation behavior of CPs and provide fundamental information for the application of CPs in gel-based foods.