Characterization of the microchemical structure of seed endosperm within a cellular dimension among six barley varieties with distinct degradation kinetics, using ultraspatially resolved synchrotron-based infrared microspectroscopy

Abstract

Barley varieties have similar chemical composition but exhibit different rumen degradation kinetics and nutrient availability. These biological differences may be related to molecular, structural, and chemical makeup among the seed endosperm tissue. No detailed study was carried out. The objectives of this study were: (1) to use a molecular spectroscopy technique, synchrotron-based Fourier transform infrared microspectroscopy (SFTIRM), to determine the microchemical-structural features in seed endosperm tissue of six developed barley varieties; (2) to study the relationship among molecular-structural characteristics, degradation kinetics, and nutrient availability in six genotypes of barley. The results showed that inherent microchemical-structural differences in the endosperm among the six barley varieties were detected by the synchrotron-based analytical technique, SFTIRM, with the univariate molecular spectral analysis. The SFTIRM spectral profiles differed (P < 0.05) among the barley samples in terms of the peak ratio and peak area and height intensities of amides I (ca. 1650 cm(-1)) and II (ca. 1550 cm(-1)), cellulosic compounds (ca. 1240 cm(-1)), CHO component peaks (the first peak at the region ca. 1184-1132 cm(-1), the second peak at ca. 1132-1066 cm(-1), and the third peak at ca. 1066-950 cm(-1)). With the SFTIRM technique, the structural characteristics of the cereal seeds were illuminated among different cultivars at an ultraspatial resolution. The structural differences of barley seeds may be one reason for the various digestive behaviors and nutritive values in ruminants. The results show weak correlations between the functional groups' spectral data (peak area, height intensities, and ratios) and rumen biodegradation kinetics (rate and extent of nutrient degradation). Weak correlations may indicate that limited variations of these six barley varieties might not be sufficient to interpret the relationship between spectroscopic information and the nutrient value of barley grain, although significant differences in biodegradation kinetics were observed. In conclusion, the studies demonstrated the potential of ultraspatially resolved synchrotron based technology (SFTIRM) to reveal the structural and chemical makeup within cellular and subcellular dimensions without destruction of the inherent structure of cereal grain tissue.

Figure 1

Typical synchrotron-based FTIR spectrum of endosperm tissue within a cellular dimension. (a) Whole mid-IR region: ca. 4000–800 cm⁻¹. (b) Fingerprint region: ca. 1800–800 cm⁻¹. (c,d) Amide I peak area and height: ca. 1650 cm⁻¹. (e,f) Amide II peak area and height: ca. 1550 cm⁻¹. (g,h) Cellulosic compounds peak area and height: ca. 1240 cm⁻¹.

Figure 2

Typical synchrotron-based FTIR spectrum of endosperm tissue within a cellular dimension. (a) Total carbohydrate peak area region: ca. 1184– 950 cm⁻¹. (b,c) Carbohydrate first component peak area and height: ca. 1150 cm⁻¹. (d,e) Carbohydrate second component peak area and height: ca. 1080 cm⁻¹. (f,g) Carbohydrate third component peak area and height: ca. 1025 cm⁻¹.