Digestibility of conventional, alternative and novel protein sources to be used as sustainable components of animal feed
Year: 2025
Type: dissertation
Abstract: The increasing global demand for more sustainable and efficient animal feed calls for the investigation of alternative protein sources to reduce the reliance on traditional ones. As poultry is the primary source of meat, there is an urgent need to prioritise protein quality in poultry feed. Currently, multiple in vitro techniques are used to assess protein quality and digestibility, but a consensus has yet to be established for chicken feed. This study aimed to employ the INFOGEST static in vitro digestion model, a globally standardised protocol designed to mimic gastrointestinal digestion for assessing nutrient bioaccessibility, to evaluate the protein quality and digestibility of traditional, alternative and novel protein sources, and to compare the digestibility values derived from laboratory experiments with those obtained from an in vivo chicken trial. Protein digestibility was assessed in a range of novel feed ingredients. These protein sources included commercial soybean and rapeseed products, yeast samples, microbial proteins, and casein as a reference. Results showed a strong positive correlation between the values obtained and those from the company supplier regarding crude protein content and amino acid content (p < 0.001). Clostridium sp. showed superior digestibility compared to sunflower meal (p < 0.05) and a higher DIAAS (0.70 and 0.49, respectively). Interestingly, Clostridium sp had a high lysine digestible indispensable amino acid ratio (DIAAR) of 1.87. The digestible indispensable amino acid scores (DIAAS) for yeast protein isolates were exceptionally high, varying from 0.77 for dried pot ale yeast to 1.75 for brewer’s yeast 2, with lysine and sulphur-containing amino acids being the limiting amino acids, respectively. The non-absorbable fraction weights of rapeseed meal, rapeseed protein concentrate, and sunflower protein concentrate after digestion were significantly higher (p < 0.05) than that of casein. Casein and sunflower meal lysine digestibility were significantly higher (p < 0.05) than that of other protein isolates, except for AlphaSoy Gold. Lysine digestibility of rapeseed meal was significantly lower than for AlphaSoy Gold, sunflower protein concentrate, sunflower meal and casein. Lysine was the limiting amino acid for sunflower-based and rapeseed-based protein isolates, with DIAAS varying from 0.81 to 1.14. Pea protein concentrate and soya-based protein sources had a DIAAS between 0.52 and 0.90, with sulphur-containing amino as limiting amino acids. Total amino acid digestibility of soybean meal (SBM), AlphaSoy and sunflower expeller at inclusion levels of 30%, 45% and 60% ranged from 60.80% to 100.00%. For most amino acids, SBM digestibility was significantly lower than AlphaSoy and sunflower expeller (p < 0.05), irrespective of the inclusion level. DIAAS values ranged from 0.32 – 0.58 for SBM, 0.59 – 0.80 for AlphaSoy and 0.67 – 0.76 for sunflower expeller. Sulphur-containing amino acids were the limiting factor for all, except for sunflower expeller, where lysine was limiting. Protein digestibility was assessed in a range of bacteria using the same in vitro method. Bacteria showed variability in amino acid content, digestibility, and DIAAS values using the in vitro digestion method. Thermus thermophilus and Psychrobacter frigidicola showed relatively high total amino acid digestibility (84.0% and 88.4%, respectively), significantly higher than Cupriavidus necator with polyhydroxybutyrate (PHB) (54.3%, p < 0.05). Sulphur-containing and aromatic amino acids were the most common limiting factors across bacteria, with DIAAS values ranging from 0.34 for Thermus thermophilus to 0.72 for Methylococcus capsulatus. The correlation between PHB content and total amino acid digestibility in Cupriavidus necator showed a strong negative correlation (r = -0.8211) but the correlation was not statistically significant (p = 0.1790). A chicken trial (Ross 308) was conducted using formulated feeds composed of SBM, AlphaSoy or sunflower expeller, with inclusion levels of 30%, 45%, or 60% for each protein source. In vivo digestibility was determined as apparent ileal digestibility (AID) using ileal digesta collected from the chicken trial, while in vitro digestibility was assessed using the INFOGEST static in vitro digestion model. In vitro digestibility values slightly exceeded in vivo values, with minimal differences. However, in vitro methods consistently overestimated the digestibility of lysine, leucine, valine, isoleucine, and phenylalanine, while underestimating methionine, threonine, and histidine. In conclusion, this study illustrates the effectiveness of the INFOGEST model in distinguishing protein quality among various protein sources and emphasises the importance of adopting standardised evaluation methods to advance the creation of sustainable feed solutions.
Author: Cochetel, Noriane
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W7217648916