Abstract:The "glucose-linked wavelength" in the short-wavelength nearinfrared (NIR) region, in which the light intensity reflected from the hand palm exhibits a good correlation to the blood glucose value, was investigated. We performed 391 2-h carbohydrate tolerance tests (CTTs) using 34 participants and a glucose-linked wavelength was successfully observed in almost every CTT; however, this wavelength varied between CTTs even for the same person. The large resulting data set revealed the distribution of the informative wavelength. The blood glucose values were efficiently estimated by a simple linear regression with clinically acceptable accuracies. The result suggested the potential for constructing a personalized low-invasive blood glucose sensor using short-wavelength NIR spectroscopy. Biomed. Mater. Eng. 26(S1), S447-S453 (2015).
Evaluating the maturity of peach fruit is desirable during both the preharvest and postharvest periods, and flesh firmness (FF) is a representative maturity index. Although a non-destructive FF measurement technique using visible (VIS) and near-infrared (NIR) spectroscopy has been developed, the principle has been unclear. This study was conducted to examine the structure of the FF prediction model by comparing with that of the model for measuring water-soluble pectin (WSP) content. Those two prediction models have the same information regions related to the colors of pericarp and mesocarp (chlorophyll) and to a water band in the NIR region. Moreover, a statistical heterospectroscopy analysis between NIR and 1H nuclear magnetic resonance (NMR) spectra suggests the possibility that absorptions of methanol and succinate as well as galacturonic acid embedded in a water band play important roles in predicting FF. This approach would enhance the reliability of nondestructive VIS-NIR prediction models in many practical situations.
Non-invasive techniques for the analysis of blood glucose are desirable not only for clinical use but also for the determination of the glycaemic index (GI) of foods. Factors that affect the accuracy of non-invasive blood glucose measurements by near infrared (NIR) spectroscopy were identified and examined to establish the optimal conditions for the analysis. Calibration models were obtained by means of partial least squares regression. Several experiments revealed that a good calibration model could be obtained using spectra (700-1100 nm) acquired from the palm of the hand with a large interactance probe fixed to a table provided that spectral acquisition and blood glucose analysis are performed simultaneously. The accuracy of the calibration model developed is clinically acceptable; the coefficient of multiple determination was 0.85 and the standard error of cross-validation was 9.7 mg dL −1. An analysis of a model solution confirmed that NIR spectroscopy in the short-wavelength region 700-1100 nm is capable of measuring glucose concentrations of the order of 0.01% (10 mg dL −1) in blood. The determination of the GI of foods by using the present method will be examined in the near future.
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