Conditions Governing Food Protein Amyloid Fibril Formation—Part I: Egg and Cereal Proteins

Abstract

Conditions including heating mode, time, temperature, pH, moisture and protein concentration, shear, and the presence of alcohols, chaotropic/reducing agents, enzymes, and/or salt influence amyloid fibril (AF) formation as they can affect the accessibility of amino acid sequences prone to aggregate. As some conditions applied on model protein resemble conditions in food processing unit operations, we here hypothesize that food processing can lead to formation of protein AFs with a compact cross β‐sheet structure. This paper reviews conditions and food constituents that affect amyloid fibrillation of egg and cereal proteins. While egg and cereal proteins often coexist in food products, their impact on each other's fibrillation remains unknown. Hen egg ovalbumin and lysozyme form AFs when subjected to moderate heating at acidic pH separately. AFs can also be formed at higher pH, especially in the presence of alcohols or chaotropic/reducing agents. Tryptic wheat gluten digests can form fibrillar structures at neutral pH and maize and rice proteins do so in aqueous ethanol or at acidic pH, respectively.

Conditions Governing Food Protein Amyloid Fibril Formation. Part II: Milk and Legume Proteins

“…Hence, as summarized by Jansens et al. (), different factors such as heating mode, time, temperature, pH, moisture content, protein concentration, shear or the presence of alcohols, chaotropic/reducing agents, enzymes, salt, and/or other food constituents govern fibrillation of food proteins in model systems. Especially amyloid(‐like) fibrillation of egg and milk proteins has been extensively studied by heating these proteins at high temperatures (for example, 80 °C to 95 °C) and acidic pH (≤2.5) for several hours to days.…”

“…Conditions that favor aggregation thus usually require the destabilization of the folded native state, but if any general rule can be extracted harsher conditions tend to favor less ordered systems than milder denaturing conditions, which tend to favor the highly ordered AFs, whose technofunctional properties are thought to be attractive for food applications. Hence, as summarized by Jansens et al (2019), different factors such as heating mode, time, temperature, pH, moisture content, protein concentration, shear or the presence of alcohols, chaotropic/reducing agents, enzymes, salt, and/or other food constituents govern fibrillation of food proteins in model systems. Especially amyloid(-like) fibrillation of egg and milk proteins has been extensively studied by heating these proteins at high temperatures (for example, 80°C to 95°C) and acidic pH (≤2.5) for several hours to days.…”

“…In some cases, the growth of protofibrils ends when loops are formed (Kalapothakis et al., ). The amino acid sequences that are frequently involved in fibrillation and actually promote the formation of β‐sheet structures are called core or amylogenic regions (Jansens, Rombouts, et al., ). Such core regions are usually short sequences (5 to 15 amino acids) with a high hydrophobicity and low net charge (De Baets, Schymkowitz, & Rousseau, ).…”

“…Such core regions are usually short sequences (5 to 15 amino acids) with a high hydrophobicity and low net charge (De Baets, Schymkowitz, & Rousseau, 2014). Identified and predicted core regions in food proteins and their importance in aggregation have been reviewed by Jansens et al (2019). Both intrinsic (amino acid composition, hydrophobicity, and so on) and extrinsic (temperature, time, pH, ionic strength, shear flow, and so on) factors impact the level and morphology of specific food protein aggregates as well as the exact aggregation mechanism (Jansens, Lambrecht, et al, 2019).…”

“…Identified and predicted core regions in food proteins and their importance in aggregation have been reviewed by Jansens et al (2019). Both intrinsic (amino acid composition, hydrophobicity, and so on) and extrinsic (temperature, time, pH, ionic strength, shear flow, and so on) factors impact the level and morphology of specific food protein aggregates as well as the exact aggregation mechanism (Jansens, Lambrecht, et al, 2019). Knowledge on core regions of food proteins and the impact of processing thereupon is of key importance to create new functionalities for proteins in food (Jansens, Rombouts, et al, 2019).…”