A total of 21 kinds of recycled high-density polyethylene (rHDPE) in contact with food were selected from three companies. Migration experiments were performed by contacting these samples with two representative food simulants (95% ethanol and 4% acetic acid) at 60 ℃ for 10 days. The migration of substances to food simulants was detected by gas chromatography quadrupole time-of-flight-mass spectrometry (GC-QTOF-MS). Altogether 161 substances were selected and classified into four grades in decreasing order of toxicity (Ⅰ–Ⅳ), among which 59 substances belonged to grades Ⅲ and Ⅳ, and their predicted octanol/water partition coefficient (XLogP) was greater than that of the substances belonging to grades Ⅰ and Ⅱ. Benzene and substituted derivatives accounted for the highest proportion of all selected substances. Special attention should be paid to phenylester plasticizers, degradation products of antioxidants and polycyclic aromatic hydrocarbon (PAHs). Changes in the migration of substances from the samples were analyzed using orthogonal partial least squares-discriminant analysis (OPLS-DA), and it was found that the migration of substances from the final products was elevated compared with that from the masterbatch samples. This study can provide a theoretical basis for the analysis and safety risk assessment of migrating substances in rHDPE in contact with food.

In this study the antibacterial effect of oxidized starch (OST) was analyzed by the inhibition zone method and the effect of OST on preserving the quality of strawberries was investigated by measuring mass loss percentage, decay incidence and total viable count. The results indicated that OST exhibited potent antimicrobial effects against common pathogenic bacteria such as Staphylococcus aureus and Escherichia coli, as well as penicillium, a common spoilage organism of strawberries. The higher the proportion of carboxyl groups in OST, the stronger the antimicrobial effect. Specifically, the diameters of the zones of inhibition of OST containing 57% carboxyl (OST-57) against Staphylococcus aureus, Escherichia coli, and penicillium were (29.00 ± 0.87), (28.00 ± 1.73) and (15.75 ± 0.65) mm, respectively. OST-57 coating effectively inhibited the growth of total viable count, significantly reduced the mass loss percentage and decay incidence of strawberries (P < 0.05), delayed the change of hardness and chewiness during the ripening process of strawberries, and preserved the contents of soluble solids, anthocyanins, and other nutrients (P < 0.05). To sum up, OST-57 can effectively delay the ripening and senescence of strawberries, and thus has application value for the post-harvest preservation of vegetables and fruits as a new coating material.

Commercially available straw samples were collected for compositional analysis by Fourier transform infrared (FT-IR) spectroscopy, and the non-targeted analysis of volatile compounds in the straw samples was performed by gas chromatography-mass spectrometry (GC-MS). The compounds were identified using retention index, the National Institute of Standards and Technology (NIST) mass spectral library and mass spectrometry-data-independent acquisition (MS-DIAL) deconvolution, and relevant databases were used for traceability analysis and to identify compounds of safety concern. The results showed that the samples were all found to comprise PLA alone or mixed with poly(butyleneadipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) in different proportions. Totally 41 volatile substances were detected by GC-MS, and 173 volatile substances by headspace GC-MS (HS-GC-MS), mainly plastic additives and pesticides and detergents that may originate from raw materials, and the safety of some substances should be of concern. The results of GC-MS and HS-GC-MS were complementary to each other, which is beneficial for more accurate analysis of volatile substances. This study provides a basis for the analysis and safety risk assessment of volatile substances in commercially available PLA straws.

Liquid chromatography-mass spectrometry (LC-MS) was used to determine the migration of the isomers of diaminotoluene (TDA) and diaminodiphenylmethane (MDA). The migration levels of TDA and MDA from 10 samples of laminated food packaging bags to 4% acetic acid were investigated. In addition, salting-out and sugaring-out assisted liquid-liquid extraction combined with LC-MS was used to explore the effect of sodium chloride and sucrose on the migration of 2,4’-MDA and 2,2’-MDA from laminated food packaging bags to 10% ethanol and water. The results showed that 4,4’-MDA, 2,4’-MDA and 2,2’-MDA were detected in four samples, and the total migration of MDA in one of the samples exceeded 10 μg/kg. The presence of salt and sugar had a significant effect (P < 0.05) on the migration of 2,4’-MDA and 2,2’-MDA to 10% ethanol and water. The migration levels decreased significantly (P < 0.05) with increasing salt and sugar contents in food simulants (2, 5, 10, 15, 20 g/100 mL). Adjustment of food simulants may be needed for packaging material migration tests on foods with high salt or sugar content.

In this study, physical characterization and monitoring of volatile organic compounds (VOCs) were investigated on recycled polyethylene terephthalate (rPET) from a mechanical recycling process and rPET bottles made with different rPET contents, with the aim of tracing the source of rPET and assessing its safety when use as a food contact material. It was found that rPET had a similar thermal stability to that of virgin PET (vPET). rPET bottles did not show any significant changes in groups or structure and exhibit similar crystallization and melting behaviors to vPET. However, there were minor mechanical scratches in the surface micromorphology of rPET bottles, and the color of rPET bottles became darker, greener and yellower as the content of recycled material increased. The solid-state polycondensation process was found to play an important role in the removal of VOCs, as detected by headspace gas chromatography-mass spectrometry (HS-GC-MS), resulting in a very small amount of residual VOCs in rPET. Four VOCs (acetaldehyde, glycol and nonanal at levels less than 1.00 mg/kg; 2-methyl-1,3 dioxolane at levels of 1.72-5.76 mg/kg) were detected in the rPET bottles. This study shows that rPET bottles are qualified for reuse in food contact in terms of thermal properties, structure, morphology and VOC residues, although there is variability in color.

A method based on gas chromatography-mass spectrometry (GC-MS) was developed for the determination of the residues of 2,4-di-tert-butylphenol (2,4-DTBP), butylated hydroxytoluene (BHT) and its derivatives 2,6-di-tert-butyl-p-benzoquinone (BHT-Q) and 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) and their migration to isooctane from wheat straw-based plastic lunchboxes. The effects of food handling practices such as microwaving, steaming, and refrigeration on the migration of these four substances were explored. The experimental results showed that the migration behaviors of 2,4-DTBP, BHT, BHT-Q and BHT-CHO from plant fiber-based plastic products to food simulants were mainly related to the types of food simulants, residue amounts and actual application scenarios. Repeated microwaving, cooking and freezing of straw-based plastic lunch boxes might affect (or even slightly increase) the release of some compounds, but their concentrations remained relatively low and tended to decrease with increasing number of repeated cycles, and even the migration of the compounds became negligible after several consecutive applications. BHT-Q, BHT, 2,4-DTBP, and BHT-CHO migrating from wheat straw-based plastic lunch boxes were found to be relatively safe for consumers.