Impact of ethanol bioprocessing on association of protein structures at a molecular level to protein nutrient utilization and availability of different co-products from cereal grains as energy feedstocks
Introduction
As to protein value, most of published studies in the literature often focus on protein composition, not protein molecular structure. Protein quality relies not only on total protein content but also on inherent structures, such as protein secondary structures matrix, protein and carbohydrate combined matrix on the molecular basis [1], [2], [3]. Protein secondary structures mainly composed of alpha-helix and beta-sheet as well as a small amount of beta-turn and random coil [4], [5]. The secondary structures impacted on protein quality, protein utilization and availability [6], [7].
The great deal of co-products such as dried distiller grains with solubles (DDGS) has been produced with the high use of cereal grains (corn, wheat and barley) as energy stocks for ethanol and beer producing. Due to starch removal, the remaining chemical components in the distillers grains products become concentrated approximately threefold compare to the parent grain [8], [9]. Since its high protein content, DDGS has become a protein sourced feedstuff and is widely used in animal feed and livestock production industry. A systematical study on dry matter, mineral and other nutrient profiles of these co-products has been conducted using conventional ‘wet’ chemical analysis. On the other hand, several studies have been reported the information with protein structures. Especially the unique studies on correlation between protein molecular structure spectra and protein chemical and nutrient profiles, protein utilization and availability have been conducted by our research team in recent years. However, the research report how the molecular structure changes were associated with nutrient availability in the rumen and intestinal and total nutrient supply is still limited. Therefore, study on the protein molecular structures of these co-products can help us to have a better understanding to protein nutritional value.
The objectives of this study were: (1) to determine the protein chemical profiles, protein degradation and intestinal digestion of the co-products from cereal grains; (2) to reveal the protein molecular structures (in terms of amide I and amide II intensity and their ratio; ɑ-helix and β-sheet intensity and their ratio); (3) to investigate the relationship between protein molecular structures and chemical profiles, protein subfractions partitioned by Cornell Net Carbohydrate and Protein System (CNCPS), protein degradation and digestion; (4) to determine the most important structural features for the co-products from cereal grains. In this study, the hypothesis is that the protein molecular structure was associated with protein utilization and availability. Different ethanol and beer-making co-products have different protein molecular structures and different protein degradation and digestion behaviors.
Section snippets
Different types and sources of co-products from cereal grain
In this study, five corn DDGS and two barley DDGS samples were collected from seven different manufactures in the north of China from 2012 to 2013. They were numbered as “1, 2, 3, 4, 5, 6, and 7” samples according to the order of sampling.
This work was performed on substrates of unknown provenance, for which the chain of custody is not known. The species and the cultivars cannot be specified and while the authors BELIEVE that this work exemplifies the difference between DDGS processing - there
Protein profiles and protein subfractions
The detailed protein profiles and subfractions of the co-products are presented in Table 1. The results showed that the parameters of associated with protein, such as CP, NDICP, ADICP and SCP, were significant difference (p < 0.05) among the DDGS samples from different plants and derived from different grains. The changes in protein profiles among DDGS samples may be occur during processing, such as amount of added solubles, partial protein degradation during fermentation and Maillard product
Conclusion
In summary, different types and sources of the co-products from ethanol processing based cereal grain as energy feedstock in this study showed difference in protein nutrient and utilization profiles and protein internal structural makeup. Although the CLA and PCA analyses revealed similarity in protein molecular spectra, some protein molecular spectral feature of the co-products have relationship with protein nutrient utilization and availability to some extent. The difference in protein
Acknowledgments
Our research programs are supported by the Thousand-Talent-People Award Project in Tianjin, the Ministry of Agriculture Strategic Feed Research Chair Program, and the Natural Sciences and Engineering Research Council of Canada (NSERC-Individual Discovery Grant, Canadian federal government). The authors also thank Z. Niu (Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada) for his support with laboratory analysis and H. Xin for her help in ATR-FT/IR spectral
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