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Relationship of protein molecular structure to metabolisable proteins in different types of dried distillers grains with solubles: a novel approach
- Peiqiang Yu, Waldo G. Nuez-Ortín
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- Journal:
- British Journal of Nutrition / Volume 104 / Issue 10 / 28 November 2010
- Published online by Cambridge University Press:
- 02 July 2010, pp. 1429-1437
- Print publication:
- 28 November 2010
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To date, there has been no study of protein molecular structures affected by bioethanol processing in relation to protein nutritive values of the new co-products of bioethanol production. The objective of the present study was to investigate the relationship between protein molecular structures (in terms of protein α-helix and β-sheet spectral intensity and their ratio and amide I to amide II spectral intensity and their ratio) and protein rumen degradation kinetics (rate and extent), estimated protein intestinal digestibility and total truly absorbed protein in small intestine (metabolisable protein) in different types of dried distillers grains with solubles (DDGS), such as wheat DDGS, maize DDGS and blend DDGS (wheat:maize = 70:30). The protein molecular structures of the different types of DDGS affected by processing were identified using diffuse reflectance IR Fourier transform spectroscopy. The results showed that the protein structure α-helix to β-sheet ratio in the DDGS had a strongly negative correlation with estimated intestinal digestibility of ruminally undegraded protein (%dRUP, R − 0·95, P = 0·04), tended to have a significant correlation with the protein PC subfraction (which was undegradable and contained proteins associated with lignin and tannins and heat-damaged proteins) (R 0·91, P = 0·09) and had no correlation (P>0·10) with rumen degradation kinetics (rate and extent), total intestinally absorbed protein supply and degraded protein balance. However, the protein amide I to amide II ratio in the DDGS had a strongly positive correlation with soluble crude protein (CP) (R 0·99, P < 0·01), protein PA subfraction (which was instantaneously solubilised at time zero) (R 0·99, P < 0·01), protein PB2 subfraction (which was intermediately degradable) (R − 0·95, P = 0·04) and total digestible CP (R 0·95, P = 0·04). The amide I to amide II ratio also had strongly negative correlations with ruminally undegraded protein (%RUP: R − 0·96, P = 0·03) and the degraded protein balance (OEB: R − 0·97, P = 0·02), but had no correlation (P>0·10) with the total intestinally absorbed protein supply. Multiple regression results show that the protein structure α-helix to β-sheet ratio was a better predictor of %dRUP with R2 0·92. The amide I to II ratio was a better predictor of the degraded protein balance with R2 0·93 in the DDGS. In conclusion, the changes in the protein molecular structure α-helix to β-sheet ratio and the amide I to amide II ratio during bioethanol processing (either due to fermentation processing or due to heat drying) were highly associated with estimated protein intestinal digestibility and degraded protein balance, but were not associated with total intestinally absorbed protein supply from the DDGS to dairy cattle. The present study indicates that a potential novel method could be developed based on the protein molecular structure parameters to improve the estimation of protein value after a validation in a large-scale in vivo study is done.
Protein secondary structures (α-helix and β-sheet) at a cellular level and protein fractions in relation to rumen degradation behaviours of protein: a new approach
- Peiqiang Yu
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- Journal:
- British Journal of Nutrition / Volume 94 / Issue 5 / November 2005
- Published online by Cambridge University Press:
- 08 March 2007, pp. 655-665
- Print publication:
- November 2005
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Studying the secondary structure of proteins leads to an understanding of the components that make up a whole protein, and such an understanding of the structure of the whole protein is often vital to understanding its digestive behaviour and nutritive value in animals. The main protein secondary structures are the α-helix and β-sheet. The percentage of these two structures in protein secondary structures influences protein nutritive value, quality and digestive behaviour. A high percentage of β-sheet structure may partly cause a low access to gastrointestinal digestive enzymes, which results in a low protein value. The objectives of the present study were to use advanced synchrotron-based Fourier transform IR (S-FTIR) microspectroscopy as a new approach to reveal the molecular chemistry of the protein secondary structures of feed tissues affected by heat-processing within intact tissue at a cellular level, and to quantify protein secondary structures using multicomponent peak modelling Gaussian and Lorentzian methods, in relation to protein digestive behaviours and nutritive value in the rumen, which was determined using the Cornell Net Carbohydrate Protein System. The synchrotron-based molecular chemistry research experiment was performed at the National Synchrotron Light Source at Brookhaven National Laboratory, US Department of Energy. The results showed that, with S-FTIR microspectroscopy, the molecular chemistry, ultrastructural chemical make-up and nutritive characteristics could be revealed at a high ultraspatial resolution (∼10 μm). S-FTIR microspectroscopy revealed that the secondary structure of protein differed between raw and roasted golden flaxseeds in terms of the percentages and ratio of α-helixes and β-sheets in the mid-IR range at the cellular level. By using multicomponent peak modelling, the results show that the roasting reduced (P<0·05) the percentage of α-helixes (from 47·1 % to 36·1 %: S-FTIR absorption intensity), increased the percentage of β-sheets (from 37·2 % to 49·8 %: S-FTIR absorption intensity) and reduced the α-helix to β-sheet ratio (from 0·3 to 0·7) in the golden flaxseeds, which indicated a negative effect of the roasting on protein values, utilisation and bioavailability. These results were proved by the Cornell Net Carbohydrate Protein System in situ animal trial, which also revealed that roasting increased the amount of protein bound to lignin, and well as of the Maillard reaction protein (both of which are poorly used by ruminants), and increased the level of indigestible and undegradable protein in ruminants. The present results demonstrate the potential of highly spatially resolved synchrotron-based infrared microspectroscopy to locate ‘pure’ protein in feed tissues, and reveal protein secondary structures and digestive behaviour, making a significant step forward in and an important contribution to protein nutritional research. Further study is needed to determine the sensitivities of protein secondary structures to various heat-processing conditions, and to quantify the relationship between protein secondary structures and the nutrient availability and digestive behaviour of various protein sources. Information from the present study arising from the synchrotron-based IR probing of the protein secondary structures of protein sources at the cellular level will be valuable as a guide to maintaining protein quality and predicting digestive behaviours.