No abstract

The present paper describes the application of pyrolysis-mass spectrometry (PYMS) to the analyses of lignocellulosic materials. Dehydrogenation lignin polymers (DHPs) with various syringyl/guaiacyl (S/G) ratios, and a standard, milled wood lignin from Aesculus turbinata Blume, were pyrolyzed at 500°C for 4 s and the volatile products were ionized by low-voltage (20 eV) electron impact. The PYMS spectra of the lignins are shown with identification of most mass peaks. Of the observed mass peaks, the intensities of the monomeric peaks corresponding to monomethoxyphenols (m/z 124, 137, 138 and 180) and dimethoxyphenols (m/z 154, 167, 182 and 210) were sensitive to the S/G ratio shifts of the DHPs. Changes in the monomeric mass peak intensities reflected those in the yields of the corresponding products determined by pyrolysis-gas chromatography (PYGC). The S/G pyrolytic ratios, calculated from the summed mass peak intensities of syringyl and guaiacyl monomeric products, showed a linear correlation with syringaldehyde/vanillin (S/V) ratios determined by nitrobenzene oxidation. This finding suggested that the S/V ratios of lignocellulosic materials are predicted from the S/G pyrolytic ratios obtained by PYMS. Similar linear correlations were observed also between the S/G pyrolytic ratios determined by PYGC and the S/V ratios, for the DHPs and for Japanese hardwoods. Unlike the PYGC method, however, the PYMS method does not need time-consuming determinations of the response factor of each product to a flame ionization detector. This advantage may outweigh the inherent problems of PYMS, such as the ambiguous structural assignment of the mass peaks in the quantitative PYMS analyses of lignocellulosic materials. The dimeric mass peaks, which were hardly detected in an analytical system with a gas chromatograph, also contributed to the mass spectra.

No abstract

The taste stimulus glucose comprises approximately half of the commercial sugar sweeteners used today, whether in the form of the di-saccharide sucrose (glucose-fructose) or half of high-fructose corn syrup (HFCS). Therefore, oral glucose has been presumed to contribute to the sweet taste of foods when combined with fructose. In light of recent rodent data on the role of oral metabolic glucose signaling, we examined psychopharmacologically whether oral glucose detection may also involve an additional pathway in humans to the traditional sweet taste transduction via the class 1 taste receptors T1R2/T1R3. In a series of experiments, we first compared oral glucose detection thresholds to sucralose thresholds without and with addition of the T1R receptor inhibitor Na-lactisole. Next, we compared oral detection thresholds of glucose to sucralose and to the non-metabolizable glucose analog, α-methyl-D-glucopyranoside (MDG) without and with the addition of the glucose co-transport component sodium (NaCl). Finally, we compared oral detection thresholds for glucose, MDG, fructose, and sucralose without and with the sodium-glucose co-transporter (SGLT) inhibitor phlorizin. In each experiment, psychopharmacological data were consistent with glucose engaging an additional signaling pathway to the sweet taste receptor T1R2/T1R3 pathway. Na-lactisole addition impaired detection of the non-caloric sweetener sucralose much more than it did glucose, consistent with glucose using an additional signaling pathway. The addition of NaCl had a beneficial impact on the detection of glucose and its analog MDG and impaired sucralose detection, consistent with glucose utilizing a sodium-glucose co-transporter. The addition of the SGLT inhibitor phlorizin impaired detection of glucose and MDG more than it did sucralose, and had no effect on fructose, further evidence consistent with glucose utilizing a sodium-glucose co-transporter. Together, these results support the idea that oral detection of glucose engages two signaling pathways: one that is comprised of the T1R2/T1R3 sweet taste receptor and the other that utilizes an SGLT glucose transporter.