Dialdehyde starch-enclosed silver nanoparticles substrate with controlled-release "hotspots" for ultrasensitive SERS detection of thiabendazole

Pesticide residues have long been a major concern for food safety. In this study, a dialdehyde starch-encapsulated silver nanoparticles composite with controlled-release "hotspots" was developed as a surface-enhanced Raman scattering (SERS) substrate. At room temperature, most of the Ag NPs were encapsulated in dialdehyde starch, which is beneficial for improving stability, and when heated to the gelatinization point, Ag NPs are completely released and abundant hot spots are formed. We demonstrated sensitive detection of thiabendazole (TBZ) in or on the surface of an apple by means of two ways, i.e., detecting the analyte in solution after pretreatment and in-situ detecting the analyte by using a flexible paper-based substrate. The results showed that the detection limits of TBZ by the two ways were 0.052 ppm and 0.051 ppm respectively, and the recoveries of TBZ range from 96.80 % to 105.46 %. Overall, this SERS substrate shows great potential for pesticide residue detection in food.

Effect of acrolein, a lipid oxidation product, on the formation of the heterocyclic aromatic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in model systems and roasted tilapia fish patties

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Acrolein was able to contribute to PhIP formation.

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Acrolein facilitated Strecker degradation of phenylalanine.

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Acrolein increased the formation of some key intermediates of PhIP.

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Acrolein reacted with phenylalanine, creatinine, and PhIP to form adducts.

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The oxidation of tilapia fish increased the PhIP formation in the roasted fish patties.

The effect of acrolein on the formation of the 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was investigated in a chemical model. Acrolein was found to increase PhIP formation at each tested addition level. 0–0.2 mmol of acrolein increased PhIP formation dose-dependently, while high levels of acrolein (>0.2 mmol) did not further increase PhIP formation. Mechanistic study showed that acrolein addition decreased the residue of phenylalanine and creatinine, but increased the content of some key intermediates. Further analysis indicated that acrolein can react with phenylalanine, creatinine, and PhIP to form adducts. These results suggested that acrolein was able to contribute to PhIP formation as a consequence of its comprehensive ability to facilitate Strecker degradation of phenylalanine and react with phenylalanine, creatinine, and PhIP. In addition, oxidation of the tilapia fish increased the PhIP formation in the roasted fish patties, further supporting the potential contribution role of lipid oxidation products to the formation of PhIP.

Effects of the Deacetylation Degree of Chitosan on 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) Formation in Chemical Models and Beef Patties

The effects of the deacetylation degree (DD) of chitosan on heterocyclic aromatic amine formation were investigated in chemical models and beef patties. The results in model systems showed that at lower addition levels (10 mg), chitosan with 85% DD showed the strongest inhibitory effect against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation, while chitosan with a higher DD (95%) or a lower DD (72 and 50%) did not show any significantly inhibitory effect. Further mechanism study showed that chitosan addition reduced the content of Maillard reaction intermediates including phenylacetaldehyde and the aldol condensation product but increased the PhIP precursor creatinine residue in the chemical model, indicating that chitosan at least partially competed with creatinine to react with phenylacetaldehyde to inhibit PhIP formation. In roast beef patties, 0.15% (w/w) chitosan (85% DD) significantly reduced the formation of PhIP, MeIQx, 4,8-DiMeIQx, Harman, and Norharman by 56.21, 33.32, 31.35, 25.14, and 28.12%, respectively. Moreover, chitosan significantly inhibited the formation of aldehydes in roast beef patties, further confirming the above-mentioned inhibition mechanism. However, the addition of chitosan might promote fatty acid oxidation. In addition, chitosan addition below 0.15% (w/w) had no significant effect on the textural properties of the roast samples.

Inhibitory effect of selected hydrocolloids on 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) formation in chemical models and beef patties

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mutagen and a rodent carcinogen mainly formed in thermally processed muscle foods. Hydrocolloids are widely used as thickeners, gelling agents and stabilizers to improve food quality in the food industry. In this study, the inhibitory effects of eight hydrocolloids on the formation of PhIP were investigated in both chemical models and beef patties. 1% (w/w) of carboxymethylcellulose V, κ-carrageenan, alginic acid, and pectin significantly reduced PhIP formation by 53 %, 54 %, 48 %, and 47 %, respectively in chemical models. In fried beef patties, κ-carrageenan appeared to be most capable of inhibiting PhIP formation among the eight tested hydrocolloids. 1% (w/w) of κ-carrageenan caused a decreased formation of PhIP by 90 %. 1% (w/w) of κ-carrageenan also significantly reduced the formation of other heterocyclic aromatic amines including MeIQx and 4,8-DiMeIQx by 64 % and 48 %, respectively in fried beef patties. Further mechanism study showed that κ-carrageenan addition decreased the PhIP precursor creatinine residue and reduced the content of Maillard reaction intermediates including phenylacetaldehyde and aldol condensation product in the chemical model. κ-Carrageenan may inhibit PhIP formation via trapping both creatinine and phenylacetaldehyde. The structures of adducts formed between κ-carrageenan and creatinine and κ-carrageenan and phenylacetaldehyde merits further study.

Role of α-Dicarbonyl Compounds in the Inhibition Effect of Reducing Sugars on the Formation of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

The effect of reducing sugars on formation of PhIP in fried pork was investigated, and the underlying mechanisms were revealed by studying the reaction pathways between α-dicarbonyl compounds (α-DCs) and PhIP. The addition of reducing sugars (such as glucose) greatly reduced the amount of PhIP in fried pork from 15.5 ng/g to less than 1.0 ng/g. The amount of PhIP decreased significantly with an increasing level of added α-DCs in model systems. Similarly, the addition of methylglyoxal (MGO) decreased significantly the levels of phenylalanine (Phe) and creatinine (Crn) but increased significantly the level of phenylacetaldehyde (PEA). 2-Amino-1-methyl-5-(2-oxopropylidene)-imidazol-4-one and N-(1-methyl-4-oxoimidazolidin-2-ylidene) amino propionic acids were identified in MGO/Crn and MGO/Crn/Phe model systems and fried pork with glucose. These results revealed that the degradation products of reducing sugars-α-DCs-play an important role in inhibiting formation of PhIP by reacting with key precursors of PhIP and itself.