Wenjia Zhu

Norovirus is a major cause of acute viral gastroenteritis in humans. Molecular biology-based detection methods play a pivotal role in ensuring accurate and specific diagnosis. The inclusion of Qβ phage particles as armored positive controls in these assays can further enhance their reliability and specificity. Herein, we discuss rational design strategies to improve the stability of Qβ bacteriophage capsid proteins armored with RNA using Discovery Studio 2019 protein design software. Amino acid mutation sites were deter-mined based on changes in folding free energy differences (ΔΔGmut). These single-site mutations were subsequently evaluated using molecular dynamics simulations. Wild-type and mutant recombinant expression plasmids were constructed and transformed into Escherichia coli BL21 (DE3) for cloning and expression. The stability of Qβ virus-like particles (VLPs) was assessed using real-time fluorescence RT-qPCR. The results showed that structurally intact and uniformly distributed wild-type and single-site mutant VLPs were successfully obtained. Stability analyses indicated that at 4 °C, 25 °C, 37 °C, 45 °C, and 60 °C, the single-site mutant exhibited a significantly lower rate of degradation than the wild-type. In conclusion, rational design enables the generation of single-site mutant VLPs with enhanced stability, providing a safer and more stable standard reference material for the molecular detection of foodborne viruses.

Listeria monocytogenes is a high-risk pathogenic bacterium associated with ready-to-eat foods and poses a potential threat to consumer health. This study aimed to investigate the prevalence, characterization and genetic diversity of L. monocytogenes in ready-to-eat raw salmon and trout products obtained from physical stores and online stores in China. Out of 150 samples analyzed, 23 (15.3%) were positive for L. monocytogenes. Among these positive samples, three (12%) were from Japanese restaurants, four (16%) from farmers markets, one (2.9%) from large supermarkets and fifteen (30%) from e-commerce platforms, and only one sample showed a contamination level exceeding 100 most probable number (MPN)/g. The isolates from positive samples demonstrated a concrete public health risk through several findings: twenty-three L. monocytogenes exhibited varying degrees of cytotoxicity, ranging from 7.6% to 71.8%. Compared with the reference strain ATCC 19115, five of these isolates were highly cytotoxic, a result that was validated by mouse survival rate experiment, which also confirmed their high virulence at tested dose. All isolates were resistant to cefuroxime sodium, ceftriaxone, cefepime and nalidixic acid, and 13% showed resistance to sulphamethoxazole-trimethoprim. Three serogroups were identified, with serogroup Ⅰ.1 (1/2a, 3a) being the most prevalent (65.2%). These isolates were grouped into eight sequence types, with ST8 (34.8%) and ST87 (30.4%) dominating. All isolates carried virulence genes associated with LIPI-1 andmultiple internalin genes (inlA, inlB, inlJ and inlK), confirming their potential pathogenicity. Additionally, the isolates harbored antimicrobial resistance genes lin and FosX. The five highly virulent isolates exhibited the highest genetic similarity to J2-031 (GCA_000438645.1) and C1-387 (GCA_000438605.1). The results provided valuable information for Chinese regulatory authorities to strengthen the risk monitoring of L. monocytogenes in ready-to-eat raw salmon and trout products.

Tuna are economically important as food resources in food markets. However, because tuna is often processed into steaks or fillets, the meat can be difficult to identify through morphological features. For effective fishery management and to protect the rights of consumers, it is necessary to develop a molecular method to accurately identify the species used in tuna products. Herein, we discovered five single-nucleotide polymorphism (SNP) sites via 2b-RAD sequencing and developed five SNP-based real-time polymerase chain reaction assays for the rapid identification of five highly priced tuna species. Three species-specific TaqMan systems were designed to identify albacore tuna (Thunnus alalunga), bigeye tuna (T. obesus), and southern bluefin tuna (T. maccoyii) and two cycling systems were designed to identify yellowfin tuna (T. albacares) and Atlantic bluefin tuna (T. thynnus). The systems showed good specificity and sensitivity (sensitivity of 0.0002 ng μL⁻¹ for albacore tuna, bigeye tuna, and southern bluefin tuna and 0.002 ng μL⁻¹ for yellowfin tuna and Atlantic bluefin tuna). Both systems were able to distinguish the target species from other species in a specific, sensitive, and accurate manner. Thus, these methods can be employed for the identification of species used in tuna products, protecting consumers and producers from economic fraud.

Kelp is a traditional healthy food due to its high nutritional content; however, its relatively high contents of iodine and arsenic have raised concerns about its edible safety. This study explored the effects of different cooking treatments on the contents of iodine and arsenic in kelp, evaluated the bioaccessibility and bioavailability of iodine and arsenic in kelp using in vitro digestion, and compared the differences in the transport characteristics of iodine in kelp and KIO₃ using a Caco-2 monolayer cell transport model. The results show that the content of target elements that reached systemic circulation could be reduced by cooking and gastrointestinal digestion. The highest reductions in iodine and arsenic were 94.4% and 74.7%, respectively, which were achieved by boiling for 10 min. The bioaccessibility and bioavailability of iodine and arsenic were significantly improved by a cooking treatment. However, the contents of iodine and arsenic decreased significantly, with the bioaccessibility of iodine reducing from 3188.2 μg/L to 317.0 μg/L and that of arsenic reducing from 32.5 μg/L to 18.1 μg/L in the gastric phase after boiling. The findings also show that the efficiency of iodine transport in kelp and KIO₃ was positively correlated with the transport time and negatively correlated with the concentration of iodine. With the increase in the iodine concentration, the rate of iodine transport in kelp decreased from 63.93% to 3.14%, but that of KIO₃ was stable at around 35%, which indicates that the absorption efficiency of iodine from kelp was limited, even when too much kelp was ingested. In conclusion, the edible safety of kelp is significantly improved after cooking. The risk of excessive iodine and arsenic intake caused by consuming kelp is extremely low, and as an effective iodine supplement source, kelp has higher edible safety compared with KIO₃. This study clarifies the safety of algae based on iodine and arsenic contents and also provides a basis for the formulation of food safety standards.