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Lignocellulose Bioavailability with Near-Infrared (NIR) Direct Reflectance Spectroscopy Probe. By D. A. Flores
The Problem and the Potential. |
Recent studies have been undertaken for the utility of direct-probe devices by near-infrared (NIR) and medium-infrared (MIR) reflectance using an optic fiber device connected to a laser with a desktop processing unit and software against a white ceramic blank to pick up wavelengths characteristic within the infra-red range. |
The mention in this chapter of the book it is in is to shed light on the topic of NIR and MIR reflectance spectroscopy calculation techniques to extract or interpret the raw data from chemical samples called the chemometric approach including the use of statistical treatments. And the resulting information can relate to calculated lignin content, and structural qualities like bond distribution, molecular weights and functional group distribution including the calculation of the so-called syringyl:guaiacyl ratios being correlatable inversely to more subunit coverage along the NDF major component in plant cell wall structures due to having less cross-linkages and thus more coverage and recalcitrance to breakdown as a barrier layer with crude fiber. |
The Quantity and Quality of Ligneous Moieties for Digestible Neutral Detergent Fibre (DNDF) and Its Measurement. |
Studies have indicated that chemical linkages or bond types, e. g. cross-linking of seminal phenolic units within the cell wall directly influences digestibility a candidate being ferulic acid cross-linking such as with ester- and ether-linked para-coumaric acid (pCA). |
To calculate the quantity of lignin the use of multiple bands or signals are proportional to the amount of lignin at the molecular level. Reference or standards need purification beforehand before a "standard curve" can be obtained and used from spectra that is measured. It has also been established that the number of samples must be sufficient for proper model validation. The sample numbers can range from one dozen to several to be used for practice and a fraction set aside as an independent testing set of samples for validation.
Because the sample takes a few seconds and up to a few minutes to take with the probe's reading and does not result in destruction of the sample, it is ideal for high throughput analyses like high volume quality control of feed sampling with the feed manufacturer and in other cases for food analyses as has been done in the past, a so-called robust quality, also for fat, protein. |
Also, in another sense for feeds, the concern now in research is to find a more accurate parameter for correlating with fiber, and beyond, its energy digestibility as an expression of availability resulting from animal metabolism in feeds. There are three approaches for measuring such a basic parameter, namely, in vitro fermentation with rumen fluid or liquor, in saco by loading a pouch suspended in the rumen through a fistulaed opening and recovering the "difference" after with the sacs and finally in vivo studies with animal trials over time and collecting, feed samples, the orts or remains, and faecal output to get a whole body reading. Basically, a whole set-up comprises the direct reflectance fiber-optic based probe, the ceramic blank for comparison of 100% reflectance in material, and software (cf. WInISI 1.05 software) used with a Pentium III Hewlett-Packard (HP) stand alone desk computer unit in one study from Foss (R) (Denmark) using similarly NIR technology for cereal grain feed samples (see: I. Gonzalez-Martin et al., 2005).
The Dimension of Physically Effective Fiber (PEF) to In Vivo Digesibility for Assessing Availability. |
There should be comment made on another separate parameter called physically effective fibre (PEF) taking into account the toughness of feed substrate towards communition or particle size reduction as it is chewed upon by the animal, another dimension of digestion in addition to the enzyme-based and physical peristaltic mixing and reduction to fiber's chemical subunits. It is believed that when the PEF parameter is combined with more accurate and consistent NIR spectral measurements for lignin that a more comprehensive model is used to describe fiber's digestion and a much more reliable prediction equation generated for use. There are other factors that need delineation before correlates are better made such as the species of crop, stage of cropping or their maturation and other agronomic conditions, viz. weather including predicting drought and floods with climate change on the rise these days world-wide, controlling irrigation, the type and rate of fertilizer application, soil conditioning including type, with native and organic soil types, its tillage and the resident microbiome, practices of crop rotation. The effort to complete the model or picture of factors accounting for fibre digestibility or availability in feed from harvest will be daunting although precision agriculture in the future controls conditions for plant growth and development, soil conditions, and meteorological conditions with engineered applicators, drones, smart technology and GPS coordination or control via satellite above may narrow down variance in measured parameters and make more accurate predictions for farm advisories to make and use them to optimize yield from crops and feeding for animal livestock.
Concluding Remarks.
The recent finds of L. E. Chase and colleagues (2017) have stipulated that rather than just the fractionation of a plant's constituency as correlating with digestibility data as has been reported in the past as the detergent fraction of NDF and basically the phenolic composition of the lignin fraction are not real significant indicators of digestion (viz. rate and extent), but rather cross-linkages between ferulic acid and para-coumaric acid (p-CA) esters and ethers among lignin and carbohydrate complexes which are, to add a further complication, distributed among different plant fractions but not in the same way across different families. |
(Assay of chemical bonds as chemically deduced through reactivity in standards to quantify their distribution as to type and no. will have to be performed together with in vivo, in saco, rumen studies to make selection rules as to which bands in their near-IR spectra correlates are the most sensitive indicators as to their readiness or recalcitrance to bond breaking by mixing, mastication, physically speaking and via enzyme action by major cellulolytic microbial spp. (e. g. bacteria and fungi).
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1. I. Gonzalez-Martin, N. Alvarez-Garcia and J. L. Harnandez-Andaluz. 2005. Instantaneous Determination of Crude Proteins, Fat and Fibre in Animal Feeds Using Near Infrared Reflectance Spectroscopy Technology and a Remote Reflectance Fibre-Optic Probe. Ani. Feed Sci. Tech. 128: 165-171. 2. E. Raffrenato, R. Fievisohn, K. W. Cotanch, R. J. Grant, L. E. Chase and M. E. Van Amburgh. 2017. Effect of Lignin Linkages with Other Plant Cell Wall Components on In Vitro and In Vivo Neutral Detergent Fiber Digestibility and Rate of Digestion of Grass Forages. J. Dairy Sci. 100: 8119-8131. |
(c) 2026-2027. Skye Blue Press Corporation. Port Coquitlam. BC Canada V3B 1G3.
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Last update of this entry: March 19, 2026
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