John F. McClelland

Resistant Starch: Promise for Improving Human Health

Ongoing research to develop digestion-resistant starch for human health promotion integrates the disciplines of starch chemistry, agronomy, analytical chemistry, food science, nutrition, pathology, and microbiology. The objectives of this research include identifying components of starch structure that confer digestion resistance, developing novel plants and starches, and modifying foods to incorporate these starches. Furthermore, recent and ongoing studies address the impact of digestion-resistant starches on the prevention and control of chronic human diseases, including diabetes, colon cancer, and obesity. This review provides a transdisciplinary overview of this field, including a description of types of resistant starches; factors in plants that affect digestion resistance; methods for starch analysis; challenges in developing food products with resistant starches; mammalian intestinal and gut bacterial metabolism; potential effects on gut microbiota; and impacts and mechanisms for the prevention and control of colon cancer, diabetes, and obesity. Although this has been an active area of research and considerable progress has been made, many questions regarding how to best use digestion-resistant starches in human diets for disease prevention must be answered before the full potential of resistant starches can be realized.

SINGLE-KERNEL MAIZE ANALYSIS BY NEAR-INFRARED HYPERSPECTRAL IMAGING

The objectives of this research were: (1) to develop a technique for creating calibrations to predict the constituent concentrations of single maize kernels from near-infrared (NIR) hyperspectral image data, and (2) to evaluate the feasibility of an NIR hyperspectral imaging spectrometer as a tool for the quality analysis of single maize kernels. Single kernels of maize were analyzed by hyperspectral transmittance in the range of 750 to 1090 nm. The transmittance data were standardized using an opal glass transmission standard and converted to optical absorbance units. Partial least squares (PLS) regression and principal components regression (PCR) were used to develop predictive calibrations for moisture and oil content using the standardized absorbance spectra. Standard normal variate, detrending, multiplicative scatter correction, wavelength selection by genetic algorithm, and no preprocessing were compared for their effect on model predictive performance. The moisture calibration achieved a best standard error of cross-validation (SECV) of 1.20%, with relative performance determinant (RPD) of 2.74. The best oil calibration achieved an SECV of 1.38%, with an RPD of only 1.45. The performance and subsequent analysis of the oil calibration reveal the need for improved methods of single-seed reference analysis.

Differentiating Writing Inks Using Direct Analysis in Real Time Mass Spectrometry

ABSTRACT: Writing ink analysis is used in establishing document authenticity and the sources and relative ages of written entries. Most analytical methods require removing samples or visibly altering the document. Nondestructive, in situ analysis of writing inks on paper without visible alteration is possible using mass spectrometry with a new ion source called Direct Analysis in Real Time. Forty‐three different black and blue ballpoint, black fluid, and black gel inks were examined. Both dyes and persistent but thermally labile components of the inks contribute to the mass spectra, principally as protonated molecules [M+H]+. Numerous ink components were identified from the spectra. The spectra were placed in a searchable library, which was then challenged with two spectra from each of the 43 inks. The best match for each of the challenge spectra was correct for all but one ink, which matched with a very similar ink by the same manufacturer.

Photoacoustic spectroscopy with condensed samples

A discussion of the photoacoustic spectroscopy of condensed matter is presented with emphasis on the role of the sample and the sample cell in the photoacoustic signal waveform. The spectrometer and sample cell are described, and an experimental evaluation of the system performance is given. Data on various samples are reported, and sample geometry, signal saturation, and scattered light effects are analyzed. The relationship between photoacoustic spectra and absorption and reflection spectra is developed.

Signal saturation effects in photoacoustic spectroscopy with applicability to solid and liquid samples

A simple model of the interaction between the optical and thermal properties of the sample is shown to predict signal saturation in photoacoustic spectroscopy in excellent agreement with measurements on a methylene blue dye solution. The measured onset of signal saturation as a function of the absorption is accurately predicted by the model from the sample’s thermal properties. The effect of light reflection by the sample on the photoacoustic signal is discussed.

Quantitative Depth Profiling of Layered Samples Using Phase-Modulation FT-IR Photoacoustic Spectroscopy

In phase-modulation FT-IR spectroscopy, all wavelengths in a spectrum are modulated at the same frequency and in phase. This factor makes the use of photoacoustic phase data for depth profiling samples much easier in phase modulation than in rapid scan. A method to quantitatively measure layer thickness by using the phase of a substrate spectrum peak is demonstrated with a series of samples consisting of thin polymer Alms on substrates. Additions to the basic method are demonstrated that extend its application to cases where the substrate peak is overlapped by a spectrum peak of the surface film. A linear relationship between phase angle and layer thickness extending to thicknesses greater than twice the thermal diffusion length is demonstrated. Representations of phase modulation data as a family of angle-specific spectra, as magnitude vs. phase curves, and as a power spectrum and phase spectrum pair, each of which is useful for different aspects of depth profiling, are discussed. Calculating these representations from a single pair of orthogonal interferograms is described.

Analysis of Writing Inks on Paper Using Direct Analysis in Real Time Mass Spectrometry

Ink analysis is central to questioned document examination. We applied direct analysis in real time mass spectrometry (DART MS) to ballpoint, gel, and fluid writing ink analysis. DART MS acquires the mass spectrum of an ink while it is still on a document without altering the appearance of the document. Spectra were acquired from ink on a variety of papers, and the spectrum of the blank paper could be subtracted out to produce a cleanly isolated ink spectrum in most cases. Only certain heavy or heavily processed papers interfered. The time since an ink is written on paper has a large effect on its spectrum. DART spectra change radically during the first few months after an ink is written as the more volatile components evaporate, but the spectra stabilize after that. A library-search study involving 166 well-aged inks assessed the ability to identify inks from their DART spectra. The aggregate success rate was 92%.

Photoacoustic signal changes associated with variations in semiconductor crystallinity

A photoacoustic (PA) signal dependence on Si crystal quality has been observed. The signal behavior has been investigated and on the basis of present evidence appears consistent, under conditions described in the letter, with PA theory as recently extended to include two‐layer systems. Results of this study have potential use in laser annealing applications because they may provide a means of rapidly evaluating the degree of recrystallization, using the annealing laser beam set at a lower power level for PA excitation.

Phase References and Cell Effects in Photoacoustic Spectroscopy

In Fourier transform infrared (FT-IR) photoacoustic spectroscopy, advanced scanning and data-handling techniques have placed increasing emphasis on the phase of the photoacoustic signal. Unfortunately, there is no agreement on the best material to use as a phase reference. We have examined the frequency dependence of the signal from several candidate phase references and found that cell effects dominate the absolute phases and magnitudes observed. The absolute phase is exceptionally fast at low frequencies and exceptionally slow at high frequencies because of the cell effects. Accordingly, details such as sample position must be scrupulously controlled to achieve accurate, reproducible results. Because of the cell effects, no candidate material behaves like an ideal phase reference. If relative phases are used, however, glassy carbon comes closest to the ideal, differing from theory by no more than 8° at any frequency examined.

Quantitative Depth Profiling Using Saturation-Equalized Photoacoustic Spectra

Depth profiling using photoacoustic spectra taken at multiple scanning speeds or modulation frequencies is normally impaired by the increase in spectral saturation that occurs with decreasing speed or frequency. Photothermal depth profiling in general is also impeded by the ill conditioned nature of the mathematical problem of determining a depth profile from photothermal data. This paper describes a method for reducing the saturation level in low-speed or low-frequency spectra to the level at high speed or frequency so that all spectra have the same saturation. The conversion method requires only magnitude spectra, so it is applicable to both conventional and phase-modulation photoacoustic spectra. This paper also demonstrates a method for quantitative depth profiling with these converted spectra that makes use of prior knowledge about the type of profile existing in a sample to reduce the instabilities associated with the mathematically ill conditioned task.