Chang-Hua Xu

Rapid determination and chemical change tracking of benzoyl peroxide in wheat flour by multi-step IR macro-fingerprinting.

BPO is often added to wheat flour as flour improver, but its excessive use and edibility are receiving increasing concern. A multi-step IR macro-fingerprinting was employed to identify BPO in wheat flour and unveil its changes during storage. BPO contained in wheat flour (<3.0 mg/kg) was difficult to be identified by infrared spectra with correlation coefficients between wheat flour and wheat flour samples contained BPO all close to 0.98. By applying second derivative spectroscopy, obvious differences among wheat flour and wheat flour contained BPO before and after storage in the range of 1500-1400 cm(-1) were disclosed. The peak of 1450 cm(-1) which belonged to BPO was blue shifted to 1453 cm(-1) (1455) which belonged to benzoic acid after one week of storage, indicating that BPO changed into benzoic acid after storage. Moreover, when using two-dimensional correlation infrared spectroscopy (2DCOS-IR) to track changes of BPO in wheat flour (0.05 mg/g) within one week, intensities of auto-peaks at 1781 cm(-1) and 669 cm(-1) which belonged to BPO and benzoic acid, respectively, were changing inversely, indicating that BPO was decomposed into benzoic acid. Moreover, another autopeak at 1767 cm(-1) which does not belong to benzoic acid was also rising simultaneously. By heating perturbation treatment of BPO in wheat flour based on 2DCOS-IR and spectral subtraction analysis, it was found that BPO in wheat flour not only decomposed into benzoic acid and benzoate, but also produced other deleterious substances, e.g., benzene. This study offers a promising method with minimum pretreatment and time-saving to identify BPO in wheat flour and its chemical products during storage in a holistic manner.

Rapid discrimination of three marine fish surimi by Tri-step infrared spectroscopy combined with Principle Component Regression

A Tri-step infrared spectroscopy (Fourier transform infrared spectroscopy (FT-IR) integrated with second derivative infrared (SD-IR) spectroscopy and two-dimensional correlation infrared spectroscopy (2DCOS-IR)) combined with Principal Component Regression (PCR) were employed to characterize and discriminate three marine fish surimi (white croaker surimi (WCS), hairtail surimi (HS) and red coat surimi (RCS)). The three surimi had similar IR macro-fingerprints (similarity>0.7) especially for the absorption bands of amide groups. Compared to the other two surimi, however, RCS had a middle strong characteristic peak of lipids at 1745 cm(-1), indicating that RCS had the highest content of lipids. SD-IR spectra of the three surimi enhanced the spectral resolution and amplified the small differences, especially at about 1682 cm(-1), 1679 cm(-1), 1656 cm(-1) and 1631 cm(-1), suggesting that the three had different profiles of proteins. Moreover, evident differences were observed in 2DCOS-IR spectra of 1500-1800 cm(-1). WCS had one strong (1620 cm(-1)) and three weak auto-peaks (1520 cm(-1), 1552 cm(-1), 1706 cm(-1)). HS had three strong (1621 cm(-1), 1648 cm(-1), 1708 cm(-1)) and two weak auto-peaks (1523 cm(-1), 1553 cm(-1)), whereas RCS had one strong (1623 cm(-1)) and three weak auto-peaks (1525 cm(-1), 1709 cm(-1), 1738 cm(-1)). Furthermore, sixty batches of surimi (twenty for each surimi) were objectively classified by PCR. It was demonstrated that the Tri-step infrared spectroscopy combined with PCR could be applicable for discrimination of precious marine fish surimi in a direct, rapid and holistic manner.

A rapid analytical and quantitative evaluation of formaldehyde in squid based on Tri-step IR and partial least squares (PLS)

Formaldehyde abuse for retaining squid freshness is detrimental to public health. The aim is to establish a rapid and quantitative detection method of formaldehyde in squid for screening massive samples. A linear relationship between formaldehyde concentration in squid and formaldehyde concentration in squid soaked water was observed using HPLC. Chemical profile variances of squids were rapidly analyzed by Tri-step infrared spectroscopy. Specifically, with increasing formaldehyde concentration, peak intensities of 2927cm-1 (vas(CH2)), 1081cm-1 (glycogen), 1631cm-1 (β-sheet proteins) decreased while 1655cm-1 (α-helix proteins) increased. Spectral curve-fitting results further disclosed that β-sheet proteins were transformed to α-helix and β-turn conformations. Furthermore, a quantitative prediction model based on IR spectra was established by PLS (R2, 0.9787; RMSEC, 5.51). The developed method was applicable for rapid (c.a. 5min) and quantitative analysis of formaldehyde in squids with LOD of 15mg/kg.

Enhanced chemical and spatial recognition of fish bones in surimi by Tri-step infrared spectroscopy and infrared microspectroscopic imaging

Surimi is an intermediate product with an increasing popularity worldwide. Discrimination of impurities like fish bones in surimi has become an urgent issue owing to the food safety and the improved requirements for assessment methods in identification of surimi quality and grades. A Tri-step infrared spectroscopy, including Fourier transform infrared spectroscopy (FT-IR), second derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2DCOS-IR) has been applied to integrally discriminate different contents (1%-8%) of fish bones in surimi at macro-scale. Meanwhile, attenuated total reflection infrared spectroscopy (ATR-IR) microspectroscopic imaging has been employed to recognize and identify the location of fish bones (less than 1.0 mm in size) in micro-scale. Fishbone characteristic infrared absorption peak at 1011 cm-1 contributes to surimi peaks at 1045 cm-1 and 988 cm-1 confirmed by calculation of their peak heights and ratios of peak areas in original spectra. SD-IR spectra enhance the difference in range of 1440-500 cm-1, and specifically peak intensity at 599 cm-1 is significantly increased in surimi with 3%-8% fish bones. Moreover, 2DCOS-IR spectra reveal that surimi containing fish bones have increased intensity of auto-peaks at 525 cm-1, 519 cm-1, 512 cm-1 and 505 cm-1 mainly contributed by hydroxyapatite and collagen. In ATR-IR microspectroscopic images, a clear fishbone shape (800 × 200 μm) corresponding to its visible image is clearly observed in principal component (PC) score image, which is confirmed as a fish bone by corresponding pixel spectra. Furthermore, the single-wavenumber image shows the spatial chemical distribution of various components for both the fish bone and surimi. Consequently, fish bones can be integrally recognized by physical and chemical imaging manners. It has been demonstrated that the developed Tri-step infrared spectroscopy and ATR-IR microspectroscopic imaging could be applicable for rapidly recognizing impurities and adulterants in surimi.

Rapid identification of pearl powder from Hyriopsis cumingii by Tri-step infrared spectroscopy combined with computer vision technology

Pearl powder, an important raw material in cosmetics and Chinese patent medicines, is commonly uneven in quality and frequently adulterated with low-cost shell powder in the market. The aim of this study is to establish an adequate approach based on Tri-step infrared spectroscopy with enhancing resolution combined with chemometrics for qualitative identification of pearl powder originated from three different quality grades of pearls and quantitative prediction of the proportions of shell powder adulterated in pearl powder. Additionally, computer vision technology (E-eyes) can investigate the color difference among different pearl powders and make it traceable to the pearl quality trait-visual color categories. Though the different grades of pearl powder or adulterated pearl powder have almost identical IR spectra, SD-IR peak intensity at about 861cm-1 (v2 band) exhibited regular enhancement with the increasing quality grade of pearls, while the 1082cm-1 (v1 band), 712cm-1 and 699cm-1 (v4 band) were just the reverse. Contrastly, only the peak intensity at 862cm-1 was enhanced regularly with the increasing concentration of shell powder. Thus, the bands in the ranges of (1550-1350cm-1, 730-680cm-1) and (830-880cm-1, 690-725cm-1) could be exclusive ranges to discriminate three distinct pearl powders and identify adulteration, respectively. For massive sample analysis, a qualitative classification model and a quantitative prediction model based on IR spectra was established successfully by principal component analysis (PCA) and partial least squares (PLS), respectively. The developed method demonstrated great potential for pearl powder quality control and authenticity identification in a direct, holistic manner.

Analysis of protein structure changes and quality regulation of surimi during gelation based on infrared spectroscopy and microscopic imaging

A developed Fourier transform infrared spectroscopy (FT-IR) was employed to investigate changes of protein conformation, which played significant roles in maintaining stable protein networks of white croaker surimi gel, exploring the relationship between protein conformation and surimi gel networks. Spectra of surimi and gels with different grades (A, AA, FA and SA) were analyzed by tri-step FT-IR method and peak-fitting of deconvolved and baseline corrected amide I bands (1600~1700 cm−1). The result showed that α-helix was the main conformation of surimi proteins. During surimi gelation, α-helix of myosin partially transformed into β-sheet, β-turn and random coil structures. β-sheet and random coil structures were the main protein conformations maintaining the structure of surimi gel, of which β-sheet made the main contribution to gel strength. Scanning electron microscopy (SEM) result revealed that surimi gels had a fibrous and homogeneous network structure. Moreover, ordered interconnections between three-dimensional proteins networks of gels were inclined to emerge in higher grade surimi, in agreement with the gel strength results. It was demonstrated that the tri-step FT-IR spectroscopy combined with peak-fitting could be applicable for exploration of surimi protein conformation changes during gelation to deepen understanding of its effect on gel quality.

Rapid recognition of marine fish surimi by one-step discriminant analysis based on near-infrared diffuse reflectance spectroscopy

ABSTRACT A rapid and nondestructive near-infrared diffuse reflectance spectroscopy method combined with multivariate analysis was developed to discriminate different species and grades of marine fish surimi. Principal component analysis and discriminant analysis were applied to classify the species and quality grades of surimi. The results showed that excellent classification was obtained after optimizing spectral pretreatment. For the discrimination of three species of surimi, the correct classification rate of the calibration as well as the validation datasets were 98.5% and 100%, respectively, using the discriminant analysis method after multiplicative scatter correction pretreatment. For four grades of surimi, discriminant analysis provided 98.9% and 100% correct classification rate for calibration and validation datasets, respectively, after multiplicative scatter correction pretreatment. It was demonstrated that near-infrared diffuse reflectance spectroscopy integrated with discriminant analysis had significant potential as a rapid and accurate approach for rapid discrimination of surimi species and grades.