Terahertz Spectroscopic Identification of Roast Degree and Variety of Coffee Beans.

In this study, terahertz time-domain spectroscopy (THz-TDS) was proposed to identify coffee of three different varieties and three different roasting degrees of one variety. Principal component analysis (PCA) was applied to extract features from frequency-domain spectral data, and the extracted features were used for classification prediction through linear discrimination (LD), support vector machine (SVM), naive Bayes (NB), and k-nearest neighbors (KNN). The classification effect and misclassification of the model were analyzed via confusion matrix. The coffee varieties, namely Catimor, Typica 1, and Typica 2, under the condition of shallow drying were used for comparative tests. The LD classification model combined with PCA had the best effect of dimension reduction classification, while the speed and accuracy reached 20 ms and 100%, respectively. The LD model was found with the highest speed (25 ms) and accuracy (100%) by comparing the classification results of Typica 1 for three different roasting degrees. The coffee bean quality detection method based on THz-TDS combined with a modeling analysis method had a higher accuracy, faster speed, and simpler operation, and it is expected to become an effective detection method in coffee identification.

Studies on qualitative and quantitative detection of trehalose purity by terahertz spectroscopy.

Terahertz spectroscopy was used to qualitatively and quantitatively analyze four samples (three brands) of trehalose produced in China and other countries. The results show that the main characteristic peak was greatly affected by concentration, and the optimal detection concentration of trehalose was determined to be 25%-55% by transmission scanning. There were six significant characteristic absorption peaks in the trehalose spectrum, meaning that terahertz spectroscopy can be used for qualitative analysis, analogous to infrared spectroscopy. Moreover, the terahertz spectrum can effectively distinguish the three isomers of trehalose, whereas infrared spectroscopy cannot. Thus, it was found that the current commercially available trehalose is the α,α-isomer. Quantitative analysis of the three brands of trehalose using terahertz spectroscopy matched the purity trends found by high-performance liquid chromatography analysis, with the order of purity from highest to lowest being TREHA, Pioneer, and Huiyang. The actual quantitative values did differ between the two detection methods, but the variation in the values from the same sample obtained by the two detection methods was less than 5%, confirming that terahertz spectroscopy is very suitable for the rapid and relative quantitative detection of trehalose.

Full-time response of starch subjected to microwave heating.

The effect of non-ionizing microwave radiation on starch is due to a gelatinization temperature range that changes starch structure and properties. However, the changes in starch upon microwave heating are observable throughout the heating process. We compared the effects on starch heating by microwaves to the effects by rapid and regular conventional heating. Our results show that microwave heating promotes the rapid rearrangement of starch molecules at low temperatures; starch showed a stable dielectric response and a high dielectric constant. Microwave heating changed the Cole-Cole curve and the polarization of starch suspension at low temperatures. A marked transition at 2.45 GHz resulted in a double-polarization phenomenon. At temperatures below gelatinization, microwave-induced dielectric rearrangement and changes in the polarization characteristics of starch suspensions reduced the absorption properties; at temperatures above gelatinization, these characteristics became consistent with conventional heating. Throughout the heating process, microwaves change the electrical response and polarization characteristics of the starch at low temperatures, but on the macro level, there is no enhancement of the material's microwave absorption properties. In contrast, with the warming process, the starch exhibited a "blocking effect", and the absorption properties of the starch quickly returned to the level observed in conductive heating after gelatinization.

The influence of metal ions on the dielectric enhancement and radical generation of rice starch during microwave processing.

In this study, the effect of the enrichment of rice starch with metal ions on its capability to generate free radicals during microwave processing was investigated. The underlying mechanism was explored from two aspects: dielectric and thermal properties. Rice starch was modified with ions of iron, copper, manganese and calcium. The modified starches were analyzed in terms of dielectric properties, activation energy (Ea) and thermodynamic characteristics of gelatinization. The quantity and character of the free radicals were analyzed using electron paramagnetic resonance (EPR). The results showed that the metal ions could change the dielectric property and inter structure of rice starch, thus influencing the ability of rice starch to generate radicals under microwave irradiation.

Effects of the components in rice flour on thermal radical generation under microwave irradiation.

The relationships between radical generation under microwave irradiation and the components of various types of rice flour were investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to characterize the radicals found in rice flour samples. The EPR spectra revealed that several types of radical (carbon-centered, tyrosyl and semiquinone) were localized in the starch and protein fractions of the rice flour. The signal intensity of the free radicals was observed to increase exponentially with increasing microwave power and residence time. The rice bran samples exhibited the greatest free radical signal intensity, followed by the brown rice samples and the white rice samples. This finding was consistent for both the native and the microwaved samples. The ratio of rice starch to rice protein also played an important role in the generation of radicals.

Influence of microwave parameters and water activity on radical generation in rice starch.

Radical generation in rice starch under microwave treatment as well as the related chemical bond changes were investigated by electron paramagnetic resonance (EPR) and Raman spectroscopy. Samples with water activity of 0.4 and 0.7 have been treated and analyzed. It was found that microwave power level and water content could influence the amount of radicals along with the radical components and their contribution. Raman spectra showed corresponding changes in vibrational features of chemical bonds. During storage the signal intensity started to drop after a short period of increase. Rice starch radicals were relatively stable and could exist a long time in room temperature. Through signal simulation, 3 main components were separated from the original spectra and the evolving process was investigated. The main component was the radical located on C1 position in the glucose ring.

Study of the optimisation of puffing characteristics of potato cubes by spouted bed drying enhanced with microwave.

BACKGROUND: In commercial deep-fat frying of potato chips, the oil content of the final products ranges from 35 to 45 g 100 g(-1) (wet basis). High-temperature frying may cause the formation of acrylamide, making the products unhealthy to the consumer. The aim of this research was to explore a new method, spouted bed microwave drying, to produce healthier puffed snack potato cubes as possible alternatives to oil-fried potato chips. The influence of drying conditions of the spouted bed microwave drying on puffing characteristics of potato cubes were studied and compared with the direct microwave and hot air drying method. RESULTS: Tandem combination drying of microwave-enhanced spouted bed drying (MWSB) could achieve a good expansion ratio, breaking force and rehydration ratio. The puffing characteristics of potato cubes were significantly affected (P < 0.05) by moisture content before starting microwave power in spouted bed microwave drying, by microwave (MW) power, and by the original size of potato cubes. CONCLUSION: The optimum processing parameters were the moisture content at the start of microwave power (60%), the size of potato cubes (10-12 mm), and microwave power (2-2.5 W g(-1))