1709
Microwave irradiation induced changes in protein inherent structure, protein chemical profile, protein subfractions and digestive behavior of different types of new hulless barley in the rumen and intestine of dairy cows
The objectives of this study were to evaluate microwave irradiation (MIR) induced changes in nutritive value of three types of hulless barley (Hordeum vulgare) in ruminant nutrition, and to quantify the MIR induced changes in protein molecular structures in relation to protein chemical profiles and digestive behavior in the rumen and intestine of the dairy cow. In this study, three barley varieties with in two consecutive years from 2009 to 2010 were chosen. All samples were cultivated and harvested from the university testing farm. The grains were either kept as raw or irradiated in a microwave, operated at a power of 900 W with irradiation frequency of 2450 MHz, for 3 min (MIR3) or 5 min (MIR5). Mixed procedure of SAS was performed to analyze data with a RCBD model. PROC CRRR was adopted to determine the correlation. Tukey was used to compare treatment means. Significance was declared at P < 0.05. Compared to non-irradiated grains, MIR5 markedly decreased (50.8 to 17.6%) soluble protein and increased NDIP (13.3 to 26.2%) and ADIP (1.0 to 5.3%) in total CP (P<0.05). As consequence, the CNCPS CP rapidly degradable fraction substantially decreased (45.2 to 6.4% CP) with a simultaneous increase in the intermediately degradable (35.8 to 56.2% CP), slowly degradable (12.4 to 20.9% CP) and non-degradable (1.0 to 5.3% CP) fractions (P<0.05). The MIR for 5min decreased soluble CP fraction (6.5 to 0.0%) and degradation rate (8.2 to 3.5% /h) of potentially degradable fraction (P<0.05). As a consequence the RDP markedly decreased (55.7 to 34.1% CP) with a concomitant increase (43.3 to 65.9% CP) in RUP supply to the post-ruminal tract (P<0.05). Except the CNCPS rapidly degradable and in situ soluble fraction, the MIR3 did not alter protein chemical profiles, CNCPS subfraction, rumen degradability and intestinal digestibility of RUP. However, the MIR5 decreased (79.4 to 67.9% RUP) intestinal digestibility of RUP. The molecular structure study revealed that MIR for 3 and 5 min consistently decreased the spectral intensities of amide I and II, α-helix and β-sheet, and increased their ratios. The changes in protein spectral intensities were strongly correlated with the changes in protein chemical profiles, CNCPS subfractions and in situ degradation characteristics. Our results showed that MIR for a short period with a lower energy input can improve the nutritive value and utilization of protein in barely grains.
Keywords: different hulless barley, microwave irradiation, nutrient availability, protein molecular structure