Fish gelatin may have unpleasant odor that adversely affects its applications. Powdered activated carbon (PAC, 0.5–2.0% w/v), diatomaceous earth (DE, 0.1–0.5% w/v) and β-cyclodextrin (CD, 1.0–3.0% w/v) were used to purify tilapia (Oreochromis niloticus) skin gelatin at various absorption temperature and time (30–50 °C; 10–60 min). The use of all three materials at optimized conditions could lead to a significant improvement in the clarity of 6.67% (w/w) gelatin solutions: the transmittance was increased from 85 to 92–93% at 640 nm, and the color was changed from light yellow to colorless. There were 18 volatile compounds (11 aldehydes, 4 alcohols, and 3 other compounds) identified from the tilapia gelatin solution, and the number was reduced to 12 after the DE treatment (0.5%, 50 °C, 30 min) and to 9 after the PAC treatment (1.5%, 40 °C, 30 min). The amounts of all detectable compounds were greatly decreased after the PAC (decreased 12–89%) and β-CD treatments (decreased 35–96%), but less satisfied results were obtained with the DE treatments.

Deterioration of deep frying oils used by street vendors is one of the major food safety concerns. Fourier transform infrared (FTIR) spectroscopy coupled with partial least squares (PLS) regression was applied for rapid evaluation of the quality of deep frying oils collected from different street vendors (n = 109) using various frying processes in Shanghai. The levels of free fatty acids (FFA), total polar compounds (TPC), and viscosity of oils were determined with conventional methods and used as reference values for developing PLS models. The FFA (0.07–1.78 mg (KOH)/g) of all tested frying oils were below the maximum allowed value, while 5.5 % of oils had TPC (3.19–54.47 %) above the maximum allowed value (27 %) based upon the related chinese standards. FTIR coupled with PLS regression resulted in less satisfying results for FFA determination (predictability for soybean oils: R2 = 0.709, SEP = 0.14, RPD = 1.83), but showed great promise for rapid determination of viscosity (model predictability: R2 = 0.921–0.945, SEP = 0.68–0.71, RPD = 3.54–3.98) and TPC (predictability for soybean oils: R2 = 0.790–0.931, SEP = 1.89–2.94, RPD = 2.16–3.55) of frying oils from different commercial settings. Developing separated PLS models for shortening and non-shortening oils improved predictability, particularly for the analysis of TPC.

Crystal violet (CV) is forbidden but still used in some aquaculture operations due to its low cost and high effectiveness against some fish diseases. Surface-enhanced Raman spectroscopy (SERS) coupled with partial least squares (PLS) regression is applied to analyze trace amounts of CV and its metabolite leucocrystal violet (LCV) in fish fillets. Two different laser sources (633 and 780 nm) and three different gold nanosubstrates (included gold nanospheres and two commercial gold substrates) were used as SERS substrates to achieve optimal analytical results. Gold nanoparticles (diameter 55.4 ± 4.5 nm) as synthesized via a reduction method resulted in better sensitivity and accuracy results than the two commercial substrates. The minimum detectable concentration for CV standard solutions was 0.5 ng/mL with the use of gold nanospheres as substrate, compared to 10 and 50 ng/mL with the two commercial substrates. The R2 of actual CV concentrations versus the values predicted (cross-validation) with PLS models ranged from 0.963 to 0.989. For CV contaminated fish muscles, the minimum detectable concentration of CV was 1 ng/g, and the PLS model (n = 64, 20 for prediction) for total CV and LCV in fish muscles was less satisfied (cross-validation R2 = 0.889; prediction R2 = 0.857) compared to those for standard solutions due to the interferences of nontargeted components in fish extract, but the results still indicated the possibility of applying SERS with chemometrics to determine trace amounts of CV and LCV in complex sample systems, such as fish muscles.

Illegal fish drugs used in aquaculture have raised serious concerns due to their negative effects on public health and environment. In this study, surface-enhanced Raman spectroscopy (SERS) was applied to analyze prohibited aquaculture drugs including enrofloxacin, furazolidone and malachite green (MG). Principal component analysis (PCA) and partial least squares (PLS) regression were used for spectral data analyses. For standard solutions, although no satisfied results were obtained for enrofloxacin, furazolidone and MG could be detected at 800 ng mL−1 and 100 ng mL−1, respectively. The R2 of actual values vs. values predicted with PLS models for furazolidone and MG was 0.970 and 0.915, respectively. A clear segregation between furazolidone and MG was observed using PCA. Furazolidone and MG in tilapia fillets could be detected at 1 μg g−1 and 200 ng g−1, respectively, and their PLS models yielded R2 of 0.922 and 0.843, respectively, showing potential for analyses of fish drugs with SERS.Highlights► SERS, a novel technology, was applied as an alternative method to analyze prohibited drug residues. ► Standard solutions of fish drugs and contaminated fish fillets were tested. ► Chemometric methods were applied to overcome inconsistency of SERS spectral features. ► SERS showed great promise for detection and determination of trace amounts of residual fish drugs.

Ractopamine is approved for use in swine to improve carcass leanness in the United States, but banned in the European Union and China because ractopamine residue may pose health risks. This study investigated the possibility of applying surface-enhanced Raman spectroscopy (SERS) for analysis of ractopamine in swine urine. Ractopamine (0.1–10 μg mL–1) was added to urine samples collected from 20 swine to prepare a total of 240 samples. A simple centrifugation, a liquid–liquid extraction (LLE) method, and a more complicated method involving liquid–liquid extraction and solid-phase extraction (LLE-SPE) were used to extract ractopamine from urine samples. Principal component analysis (PCA) and partial least-squares (PLS) regression were used for spectral data analyses. Although no satisfactory result was obtained with the centrifugation method, ractopamine could be detected at levels of 0.8 and 0.4 μg mL–1 with the LLE and LLE-SPE extraction methods, respectively. The R2 of the PLS model of actual ractopamine values versus predicted values was 0.74 for the LLE method and 0.73 for the LLE-SPE method. The SERS method with simple sample preparation has great potential for rapid analysis of ractopamine in swine urine.