What makes protein indigestible from tissue‐related, cellular, and molecular aspects?

Abstract

This paper gives an insight into key factors, which impair enzymatic protein digestion. By nature, some proteins in raw products are already poorly digestible because of structural peculiarities, or due to their occurrence in plant cytoplasmic organelles or in cell membranes. In plant-based protein, molecular and structural changes can be induced by genetic engineering, even if protein is not a target compound class of the genetic modification. Other proteins only become difficult to digest due to changes that occur during the processing of proteinaceous products, such as extruding, boiling, or acidic or alkaline treatment. The utilization of proteinaceous raw materials in industrial fermentations can also have negative impacts on protein digestibility, when reused as fermentation by-products for animal nutrition, such as brewers' grains. After consumption, protein digestion can be impeded in the intestine by the presence of antinutritional factors, which are ingested together with the food or feedstuff. It is concluded that the encircling matrix, but also molecular, chemical, and structural peculiarities or modifications to amino acids and proteins obstruct protein digestion by common proteolytic enzymes in humans and animals.

Insect meals in fish nutrition

“…According to Finke (), the digestibility of proteins/AAs in insects can vary and depends on how much of the AAs are bound to chitin or scleroprotein that is mainly present in adult insect cuticles (Becker & Yu ). However, these proteins or amino acids can be available for fish nutrition because of chitinolytic activity from enzymes such as chitinase in the stomach and chitobiase in the intestine (Lindsay ), which are present in the gastrointestinal tracts of many fish species that have ‘natural diets’ including shrimp, crabs, crayfish and insects (Lindsay & Gooday ; Gutowska et al .…”

In Vitro Methods of Assessing Protein Quality for Poultry

“…Protein feed ingredients may contain free amino acids, peptides of various lengths, secondary structure proteins (α-helix, β-pleated sheets, β-turns and superhelix), tertiary structure proteins and quaternary structure proteins [4]. Secondary structure proteins such as scleroproteins, which include collagen, elastin, and keratin, are poorly digested in simple stomach animals [62]. Protein sources containing high levels of these proteins will have limited bioavailability.…”

“…Protein sources containing high levels of these proteins will have limited bioavailability. Higher protein structural configuration requires more time and higher enzyme concentration to achieve greater hydrolysis [4,62].…”

Effect of heat treatment on forage quality of bio-fortified orange fleshed Ipomea batatas crop residues and roots

“…The increase in insoluble CP was a result of protein precipitation to indigestible Maillard products. Becker and Yu (2013), Meade et al (2005) and Mauron (1990) noted that processing permanently denatures proteins. The preservation of leaves by air-drying may actually improve the value of SP residues as dietary source of protein for livestock.…”