Selective detection of starch in banana fruit with Raman spectroscopy.

To develop an analytical method for rapid quantification of starch in agricultural produce, we measured the Raman spectra of ripening banana fruit and compared the obtained data to those of standard starch, sugar, and fiber chemical samples. Standard starches exhibited distinctive Raman bands, which were similar to the spectral features in green banana before ripening. Moreover, these banana-derived Raman bands gradually weakened during 10 d of storage. Standard sugars (glucose, sucrose, and fructose) exhibited Raman bands in both solid and liquid states, whereas standard fibers exhibited broad spectra and no such bands. Although the sugar content increased, no sugar bands were observed in the banana fruit even after ripening. A correlation was found between the Raman bands and starch content obtained by chemical analysis. These results demonstrate that Raman spectroscopy can selectively provide information regarding starch in banana fruit and be applied as an analytical method for rapid starch quantification.

Mechanism for enhancing the growth of mung bean seedlings under simulated microgravity.

To elucidate a mechanism for enhancing mung bean seedlings' growth under microgravity conditions, we measured growth, gene expression, and enzyme activity under clinorotation (20 rpm), and compared data obtained to those grown under normal gravity conditions (control). An increase in fresh weight, water content, and lengths were observed in the clinostat seedlings, compared to those of the control seedlings. Real-time PCR showed that aquaporin expression and the amylase gene were upregulated under clinorotation. Additionally, seedlings under clinorotation exhibited a significantly higher amylase activity. Near-infrared image showed that there was no restriction of water evaporation from the seedlings under clinorotation. Therefore, these results indicate that simulated microgravity could induce water uptake, resulting in enhanced amylase activity and seedling growth. Upregulated aquaporin expression could be the first trigger for enhanced growth under clinorotation. We speculated that the seedlings under clinorotation do not use energy against gravitational force and consumed surplus energy for enhanced growth.

Determination of starch crystallinity with the Fourier-transform terahertz spectrometer.

We measured the terahertz (THz) spectra of native, amorphous, and dried starches derived from corn and potato using the Fourier-transform (FT) system and compared these spectra to the X-ray diffraction (XRD) patterns. Both native corn and potato starches had seven absorption peaks in the terahertz regions, but five peaks were observed in the amorphous states. While spectral changes slightly occurred in corn starch even after drying, increase and decrease in the terahertz peak intensities were obtained in potato starch during drying. Similar changes in both starches during amorphization and drying were obtained in the X-ray diffraction patterns, and the correlations were found between terahertz peaks and the X-ray signals. Since the intensity of the peak at 9.0 THz was correlated with crystallinity obtained using an X-ray diffraction (r2 = 0.98), our data indicate that the Fourier-transform terahertz spectrometer can be a new analytical device to measure the starch crystallinity.

Useful tissues in cabbage head for freshness evaluation with visible and near infrared spectroscopy.

To determine which cabbage head tissues are useful for evaluating freshness using spectroscopic technology, we stored wrapped and unwrapped cabbage heads for up to 30 d, and measured visible and near infrared spectra (420-2500 nm) of the 1st-10th leaf layers and cores. We found that spectral changes in leaves were affected both by leaf layer and storage conditions, while continuous spectral changes were observed in the cores regardless of storage condition. These spectral changes in the leaves and cores were consistent with color images and water content. While we developed good models for estimating the storage days from the 1st and 2nd leaf layers and the cores of unwrapped cabbages, only core spectra provided a high correlation with storage days in wrapped cabbages. These data demonstrated that the cabbage core is sensitive to storage duration and its spectra are useful for evaluating freshness decline regardless of storage condition.

Quantification of starch content in germinating mung bean seedlings by terahertz spectroscopy.

To investigate the potential of terahertz spectroscopy to monitor and quantify starch in plants, terahertz spectra (3.0-13.5 THz) of mung bean plants 1-7 days after germination were examined and compared to those of starch and its constituent saccharides (standard reagents). Day 1 seedlings showed similar spectral features with standard starch, and absorption peaks gradually disappeared in the subsequent 6 day growth period. To interpret this result and identify useful peaks for starch quantification, standard starch and day 1 seedlings were hydrolyzed by α-amylase in vitro. Since both standard starch and seedlings showed that absorption peak at 9.0 THz disappeared after amylase hydrolysis, this peak is sensitive to changes in starch. Additionally, intensity of this peak was correlated with starch content as quantified by chemical analysis (r = 0.98). Our results indicate terahertz spectra of seedlings can provide an identifiable peak that is attributed to starch and not affected by the constituent saccharides.