The safety and quality of agri-food products is a critical public concern over the years. In order to guarantee human heath, it is essential to develop a rapid and non-destructive tool for assuring ...high-quality agri-food products in the market. Terahertz (THz) spectroscopic imaging is an emerging non-destructive technique. THz wave with the frequency range between the infrared and the microwave can penetrate many commonly used nonpolar dielectric materials and indicate vibrational modes of many biomolecules, which make it an extremely attractive tool for agri-food products inspection.
This current paper presents the THz sources and fundamentals of THz spectroscopic imaging technique and discusses chemometric methods applied in THz spectra for qualitative and quantitative analysis. In addition, recent advances in its applications for the safety and quality control of agri-food products over the years 2012–2017 are reviewed. Finally, some perspectives on the current situation and future trends of using THz technique are addressed.
It is expected that THz technique combined with chemometric methods has great potential for agri-food products evaluation, and continuous wave THz imaging performs better for identifying low-density foreign bodies embedded in foodstuffs as compared to X-ray imaging. Additionally, THz technique shows the ability to detect packaged agri-food products. The future development of cost-effective and portable THz spectrometer with high sensitivity will make this technique in practical applications.
•Nondestructive evaluation of safety and quality of agri-food products is needed.•Principle of terahertz spectroscopy and imaging technique is introduced.•Chemometrics applied in terahertz spectroscopy are discussed.•Recent applications of terahertz spectroscopy and imaging technique are reviewed.
•UiO-66(NH2)@Au SERS platform with adsorbability and SERS-activity was synthesized.•New coccine and orange II were measured by SERS platform with satisfactory R2.•LOD was 0.4015 mg/L for new coccine ...and 0.0546 mg/L for orange II.•New coccine and orange II in food matrices were analyzed with acceptable recovery.
Synthetic dyes have been widely applied to food processing, but abuse of colourants in food may pose risks to human health. To analyze new coccine (NC) and orange II (OII) in food, a versatile surface-enhanced Raman scattering (SERS) platform was proposed. A metal-organic framework (MOF, UiO-66(NH2)) with octahedral crystal structure was synthesized and gold nanoparticles were grown on the MOF surface to fabricate UiO-66(NH2)@Au versatile SERS platform. The UiO-66(NH2)@Au displayed much better SERS performance than gold nanoparticles with high R2 of 0.9684 for NC and 0.9912 for OII and low LOD of 0.4015 mg/L for NC and 0.0546 mg/L for OII. The recoveries of NC and OII in Mirinda soft drink and paprika ranged from 82.92 to 109.63%. This study provided a sensitive and rapid method for determination of NC and OII through UiO-66(NH2)@Au, and the proposed SERS platform revealed great potential for analyzing synthetic colourants in food samples.
A cysteamine functionalized core shelled nanoparticles (Au@Ag-CysNPs) was presented for simultaneous and rapid detection of sodium thiocyanate (STC) and benzoic acid (BA) preservatives in liquid milk ...using surface-enhanced Raman spectroscopy (SERS) technique. A spectrum covering 350–2350 cm−1 region was selected to detect STC with concentrations ranging from 0.5 to 10 mg/L and BA with concentrations ranging from 15 to 240 mg/L in milk samples. Characterization of nanoparticles using high-resolution TEM confirmed that the successful synthesis of Au@AgNPs with core (gold) size of 28 nm and shell (silver) thickness of about 5 nm was grafted with 120 μL of 0.1 nM cysteamine hydrochloride. Results showed that Au@Ag-CysNPs could be used to detect STC up to 0.03 mg/L with a limit of quantification (LOQ) of 0.039 mg/L and a coefficient of determination (R2) of 0.9833 in the milk sample. For detecting BA, it could be screened up to 9.8 mg/L with LOQ of 10.2 mg/L and R2 of 0.9903. The proposed substrate was also highly sensitive and the employed method involved only minor sample pretreatment steps. It is thus hoped that the new substrate could be used in the screening of prohibited chemicals in complex food matrices in future studies.
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•SERS could simultaneously and rapidly screen adulterants in milk.•Cysteamine functionalized core shelled nanoparticles were proposed as substrates.•Benzoic acid was evaluated for the first time in liquid milk using SERS method.•Sodium thiocynate and benzoic acid of up to 0.03 and 9.8 ppm were detected•The proposed method was ecofriendly and easy to follow.
Nowadays, near-infrared spectroscopy (NIR) has become one of the most efficient and advanced techniques for analysis of food products. Many relevant researches have been conducted in this regard. ...However, no reviews about the applications of NIR for liquid food analysis are reported. Therefore, this review summarizes the recent research developments of NIR technology in the field of liquid foods, focusing on the detection of quality attributes of various liquid foods, including alcoholic beverages (red wines, rice wines, and beer), nonalcoholic beverages (juice, fruit vinegars, coffee beverages, and cola beverages), dairy products (milk and yogurt), and oils (vegetable, camellia, peanut, and virgin olive oils and frying oil). In addition, the classification and authentication detection of adulteration are also covered. It is hoped that the current paper can serve as a reference source for the future liquid food analysis by NIR techniques.
Fresh fruit are important for a healthy diet, however, their shelf-life can be shortened because of ethylene, a key phytohormone associated with the ripening process. Therefore, detecting ethylene ...concentration on trace level and regulating its activity by safe and effective approaches are of paramount importance in extending postharvest shelf-life and controlling maturity of fruit.
In this review, ethylene detection technologies as well as ethylene regulating strategies are discussed, aiming to develop more innovative and effective approaches. Effects of ethylene on quality and shelf-life of fruit are presented. Ethylene detection and monitoring technologies available such as gas chromatography, electrochemical, optical, chemical methods, especially novel methods such as those based on colorimetric, luminescence, metal-organic frameworks, organic field effect transistors and surface enhanced Raman spectroscopy are described. In addition, shelf-life extending technologies for ethylene control, removal or inhibition such as suppressing ethylene synthesis, scavenging or oxidizing or adsorbing ethylene, and blocking ethylene receptor are summarized. Finally, future perspectives on developing strategies that can simultaneously satisfy the requirements of sensitivity, rapidness and on-line for wide utilization in ethylene monitoring of fresh products are also given.
It is expected that miniature and sensitive ethylene detection techniques combined with feasible ethylene control methods should be an effective solution for fruit quality maintenance and shelf-life extension. However, each type of sensors and ethylene control strategies currently available has their own advantages and limitations. Therefore, attempts should be made to exploit more effective ethylene detection and controlling technologies.
•Ethylene concentration affects postharvest shelf-life and maturity of fruit.•Detecting and regulating C2H4 is important in fruit postharvest management.•Commercially available C2H4 detection methods have specific application fields.•Nanotechnology should be employed to achieve in-situ and rapid C2H4 detection.•Dynamic controlled atmospheres can be refined to avoid CO2 and low O2 injury.
•Spectral absorption index was used to extract spectral morphological features.•Spectra pretreated by multiplicative scatter correction were better than the raw.•The absorption values proved to be ...better than the reflectance for building models.•Moisture content was effectively predicted by the spectral morphological features.
Spectral absorption index was proposed to extract the morphological features of the spectral curves in pork meat samples (longissimus dorsi) under the conditions including fresh, frozen–thawed, heated–dehydrated and brined–dehydrated. Savitzky–Golay (SG) smoothing and multiplicative scatter correction (MSC) were used for calibrating both the spectral reflectance and absorbance values. The absorption values were better than the reflectance values and the calibrated spectra by MSC were better than the raw and SG smoothing corrected spectra in building moisture content predictive models. The optimized partial least square regression (PLSR) model attained good results with the MSC calibrated spectral absorption values based on the spectral absorption index features (R2P=0.952, RMSEP=1.396) and the optimal wavelengths selected by regression coefficients (R2P=0.966, RMSEP=0.855), respectively. The models proved spectral absorption index was promising in spectral analysis to predict moisture content in pork samples using HSI techniques for the first time.
This study aimed to simultaneously predict different textural features in grass carps fillets (Ctenopharyngodon idella) during vacuum freeze drying using hyperspectral imaging models developed based ...on integrated group wavelengths in the range of 400 nm–1000 nm. Warner-Bratzler shear force (WBSF) is commonly used as an objective indicator for tenderness evaluation in fish products. First, partial least squares regression (PLSR) was employed to develop a quantitative function between the textural variations and the spectra extracted from the acquired hyperspectral images in the full spectral range at mean and median. Then the important wavelengths most related to WBSF, hardness, gumminess and chewiness were separately selected by regression coefficients (RC) from PLSR. Moreover, the integrated wavelengths for all the textural characteristics were determined by RC by considering all the individual group wavelengths. Finally, PLSR was conducted using different simplified group wavelengths and the performance of all the simplified models at mean or median were compared. The results showed that the integrated group wavelengths at median spectra proved to be the best for simultaneous prediction of WBSF (RP2 = 0.8774), hardness (RP2 = 0.8523), gumminess (RP2 = 0.7982) and chewiness (RP2 = 0.8453). The current study should widen the applications of hyperspectral imaging in the food industry.
•HSI was used to predict textural features in vacuum freeze dried fish slices.•Mean and median spectra were compared in performance of the predictive models.•Integrated group wavelengths were selected for predicting different textures.•Visualization was realized for displaying WBSF, hardness, gumminess and chewiness.
The freezing medium temperature and the freezing rate are two important parameters that affect the quality of frozen product. The traditional measurement of freezing parameters will destroy the ...integrity of the sample and can only be implemented during the freezing process. This study aimed to develop nondestructive hyperspectral imaging (HSI) methods to rapidly detect freezing parameters. The spectral features of the porcine meat samples in frozen state were studied, in which 90 pieces of porcine samples were frozen by different methods with different freezing medium (air and liquid) at different temperatures (from −20 to −120 °C) and freezing rates (from 0.307 to 5.1 cm/h). The result showed that the freezing process would strongly influence spectra of the frozen sample. The reflectance increased with the decrease in freezing medium temperatures, and the negative correlation reached a highly significant level. The freezing parameters did not change the position of the spectral peaks but altered the spectral intensity. Most changes were near 1070, 1172, 1420, 1586, and 1890 nm. The partial least-squares regression spectral models exhibited good performance for predicting freezing medium temperatures
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. The study confirmed that could be used for measuring freezing parameters of frozen product. This novel method will not damage the sample integrity, and measurement can be implemented anytime rather than only during the freezing process by traditional methods.
Lycopene is a biologically active phytochemical reported in fruit. Conventional techniques such as high performance liquid chromatography (HPLC) and thin layer chromatography (TLC) have been in ...existence for measuring lycopene in fruit, but these methods are destructive with relative accuracy and speed. Other novel spectroscopic and imaging approaches, which are more reliable and fast, have recently been developed to investigate complex components such as lycopene, total soluble solids, etc. in fruit. The current review attempts to highlight the potential of both conventional and novel techniques in evaluating lycopene contents of fruit. The novel techniques include both spectroscopic methods such as near infrared spectroscopy and Raman spectroscopy and spectral imaging approaches such as multispectral imaging, hyperspectral imaging and Raman imaging. The principles of these techniques are summarized, their detailed applications are discussed, and future trends are also presented. Both traditional and novel techniques highlighted in the current review can be used for assessing the distribution and concentration of lycopene in various fruit. Although novel spectroscopic and spectral imaging approaches may in the near future replace conventional methods, because conventional methods are typically often offline, destructive and time-consuming, which also require the use of chemicals.
For survival and quality of human life, the search for better ways to ensure food safety is constant. However, food contaminants still threaten human health throughout the food chain. In particular, ...food systems are often polluted with multiple contaminants simultaneously, which can cause synergistic effects and greatly increase food toxicity. Therefore, the establishment of multiple food contaminant detection methods is significant in food safety control. The surface-enhanced Raman scattering (SERS) technique has emerged as a potent candidate for the detection of multicomponents simultaneously. The current review focuses on the SERS-based strategies in multicomponent detection, including the combination of chromatography methods, chemometrics, and microfluidic engineering with the SERS technique. Furthermore, recent applications of SERS in the detection of multiple foodborne bacteria, pesticides, veterinary drugs, food adulterants, mycotoxins and polycyclic aromatic hydrocarbons are summarized. Finally, challenges and future prospects for the SERS-based detection of multiple food contaminants are discussed to provide research orientation for further.
