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Cereal Chem. 84(5):423-427An apparatus that allows extraction and enrichment of flavor volatiles of rice during cooking using solid-phase microextraction (SPME) was designed and tested in the Japanese rice cultivar Akitakomachi. Because it is a solvent-free technique, no solvent contaminants were extracted during sampling. This technique enables one to place the fiber of SPME in the effluent of the flavor volatiles of the rice during cooking and it can also be used for simultaneous extraction of those volatiles in the course of the cooking process. Therefore, variations in the composition and amount of volatile compounds of rice during cooking can be determined. The overall flavor volatiles of rice during cooking have been analyzed by using this SPME method. Compounds that have been previously highlighted as flavor volatile markers, such as volatiles from oxidative degradation of lipids, products from thermal decomposition, and fatty acids existing in rice, were extracted directly by SPME in conjunction with this apparatus.

The flavor volatiles in three Japanese rice cultivars, Nihonbare, Koshihikari, and Akitakomachi, during cooking were directly extracted by using a modified headspace solid‐phase microextraction (SPME) method and analyzed by gas chromatography‐mass spectrometry (GC‐MS). A total of 46 components were identified, including aldehydes, ketones, alcohols, and heterocyclic compounds, as well as fatty acids and esters, phenolic compounds, hydrocarbons, etc. The amount of key odorant compounds increased with cooking, while the amount of low‐boiling volatiles decreased. The similarities and differences of the three rice cultivars were determined through a comparison of their volatile components. Nihonbare was characterized by a higher amount of indole but an absence of the chemical class of fatty acid esters. In contrast, both Koshihikari and Akitakomachi had a higher amount of 4‐vinylphenol and an abundance of those esters. Koshihikari and Akitakomachi were quite similar in regard to those flavor volatiles. Furthermore, the observations in the research may suggest that the volatile components at cooking stage (I) were the representatives of the flavor volatiles of uncooked rice, while the volatile constituents at cooking stage (IV) were the representatives of the flavor volatiles of cooked rice.

ABSTRACT:The thermal properties of Bombyx mori silk fibers subjected to heat treatment were examined by thermogravimetry, differential thermal analysis, Fourier transform infrared absorption spectrometry (TG-DTA-FTIR) and scanning electron microscopy (SEM). The color, size, and shape of B. mori cocoon shells were observed as they were heated from 25 to 550°C. Only 1% of the original cocoon shell weight remains as cocoon ash after treatment at 550°C. Inorganic components, such as calcium, potassium, sulfur, magnesium, etc., were detected in the cocoon ash by energy dispersion fluorescent X-ray spectrometry. A sharp decrease in weight was observed in the TG data beginning around 280°C, and an endothermic peak appeared at 308°C, as evidenced by the DTA curves. The IR bands observed at 2380 cm Ϫ1 (OOH stretching), 1760 cm Ϫ1 (CAO stretching), 1503 (NOH stretching), 1085 cm Ϫ1 (CON stretching) and 965 cm Ϫ1 (ONH 2 stretching) become stronger as an exothermic reaction beginning at 280°C takes place. This is probably due to cleavage of the main chain and the accompanying decomposition of the silk fibers. Similarly, a SEM micrograph of silk fibers treated at 300°C shows a microtubule in the middle of the silk fibers of about 25-m diameter. This suggests that the thermal reactions starts in the middle of the silk fiber and forms a microtubule.

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Near infrared (NIR) spectroscopy was investigated as a method for the nondestr uctive measurement of sugar content in intact potato tubers. The NIR spectra (400-1100 nm) of potato samples were acquired by fiber optics in the interactance mode. Calibration models for the prediction of the fructose and glucose contents were developed by a partial least squares statistical analysis method. The calibration model gave standard errors of prediction of 0.26 mg/g for fructose and 0.46 mg/g for glucose. The preliminary results showed that NIR spectroscopy gives a reasonable estimate that can be used for nondestructive sorting of potatoes according to their sugar content.

The effect of multiplicative scatter correction (MSC) on wavelength selection for near infrared (NIR) calibration to determine fat content in raw milk was investigated. Short-wave NIR spectra (700-1100 nm) of raw milk samples were measured. The calibration equations for fat content were performed by multiple linear regression (MLR) using original, second derivative and MSC-treated spectra. It was found that first wavelength selection from the fat absorption band for a calibration equation was generally effective in all cases of original, second derivative and MSC-treated spectra. However, correlation plots did not always work well because of the multiplicative scatter effect presented in the samples. Whereas, correlation plots were still useful in the case of MSC-treated spectra and normalised second derivative spectra, even when the original spectra exhibited a multiplicative scatter effect.

Protein content and protein composition are considered very important factors in influencing the cooking and processing characteristics of rice. In the present study, the possibility of using near infrared refl ectance spectroscopy (NIRS) to measure the protein composition (prolamin, globulin and glutelin) of rice fl our was examined. The NIR spectra (1100-2500 nm) of a total of 119 rice fl our samples with different protein compositions and particle sizes were acquired with a NIR spectrometer. Prediction accuracy of protein content was subsequently examined, revealing a similar accuracy (standard error of prediction (SEP) of 0.22%) to previous studies. NIR calibration models for determining protein composition were also examined using the partial least square (PLS) regression method. The best models were generated using multiplicative scatter correction-pretreated spectra, giving SEP of 0.18%, 0.06% and 0.25% for prolamin, globulin and glutelin, respectively. The fi ndings show that NIR spectroscopy has the potential to serve as a rapid method for predicting the protein composition of rice fl our.