Meat spoilage (MS) is a complex microbial ecological process involving multiple specific microbial interactions. MS is detrimental to people's health and leads to the waste of meat products which caused huge losses during production, storage, transportation, and marketing. A thorough understanding of microorganisms related to MS and their controlling approaches is a necessary prerequisite for delaying the occurrence of MS and developing new methods and strategies for meat product preservation. This mini-review summarizes the diversity of spoilage microorganisms in livestock, poultry, and fish meat, and the approaches to inhibit MS. This would facilitate the targeted development of technologies against MS, to extend meat's shelf life, and effectively diminish food waste and economic losses.

Baylisascaris schroederi, an intestinal nematode of the giant panda, is the cause of the often fatal disease, baylisascariasis. Glutathione S-transferases (GSTs) are versatile enzymes that can affect parasite survival and parasite-host interactions and, are therefore, potential targets for the development of diagnostic tests and vaccines. In this study, we identified a full-length cDNA that encoded a novel, secretory sigma-like GST (Bsc-GSTσ) from a B. schroederi-omic dataset. Following cloning and sequencing, sequence and structural analyses and comparative modeling were performed using online-bioinformatics and proteomics tools. The recombinant Bsc-GSTσ (rBsc-GSTσ) protein was prokaryotically expressed and then used to detect antigenicity and reactivity using immunoblotting assays. In addition, the native protein in female adult B. schroederi was located via immunofluorescence techniques, while the preliminary ELISA-based serodiagnostic potential of rBsc-GSTσ was assessed in native and infected mouse sera. Bsc-GSTσ contained a 621-bp open reading frame that encoded a polypeptide of 206 amino acids with two typical sigma GST domain profiles, including a GST_N_Sigma_like at the N-terminus and a GST_C_Sigma_like at the C-terminus. The presence of an N-terminal signal sequence indicated that Bsc-GSTσ was a secretory protein. Sequence alignment and phylogenetic analyses showed that Bsc-GSTσ was a nematode-specific member of the Sigma class GSTs and shared the closest genetic distance with its homologue in Ascaris suum. Further comparative structure analyses indicated that Bsc-GSTσ possessed the essential structural motifs (e.g., βαβαββα) and the consensus secondary or tertiary structure that is typical for other characterized GSTσs. Immunolocalization revealed strong distributions of native Bsc-GSTσ in the body hypodermis, lateral chords, gut epithelium, gut microvilli, oviduct epithelium, and ovaries of adult female worms, similar to its homologue in A. suum. Building on good immunogenic properties, rBsc-GSTσ-based ELISA exhibited a sensitivity of 79.1% and a specificity of 82.0% to detect anti-B. schroederi IgG antibodies in the sera of experimentally infected mice. This study presents a comprehensive demonstration of sequence and structural-based analysis of a new, secretory sigma-like GST from a nematode, and its good serodiagnostic performance suggests that rBsc-GSTσ has the potential to detect B. schroederi and, therefore, could be used to develop an ELISA-based serological test to diagnose baylisascariasis in giant pandas.

Fermentation of meat products refers to a series of physical, biological or chemical changes in raw meat that occurs under the actions of enzymes or via microbial fermentation and results in the formation of meat products with special flavours, colours and textures that have a long history in China. These products have a unique fermented flavour, bright colour and longer shelf life than ordinary meat products, and some have proteins that are more easily absorbed by the body due to the fermentation of beneficial bacteria. Flavour development in meat products is a dynamic process. During the processing and storage of fermented meat products, the breakdown of proteins and fats is accelerated due to the addition of different fermenting agents. Moreover, the physicochemical reactions that occur within the meat products and the actions of microorganisms during the fermentation process result in the production of flavour compounds, which will determine the final flavour characteristics of the fermented meat product. This paper reviews the flavour characteristics of Chinese dry-cured hams, sausages, bacon, cured fish and sour meat and analyses the flavour substance composition of various products. Due to the differences in the raw materials, processes, auxiliary materials and fermentation processes of various types of fermented meat products in China (ham, sausage, bacon, etc.), the flavour substances contained in the various types of fermented meat products in China are different from each other. However, most fermented meat products in China are cured and fermented, and therefore, they share similarities in terms of their flavour substance composition. The flavour substances in fermented meat products mainly include alcohols, ketones, aldehydes, acids, phenols and aromatic hydrocarbons. The study of such flavour characteristics is of great significance in fermented meat product quality, and provides certain theoretical references for the study of domestic fermented meat products.

Deep spoilage is a cyclical and costly problem for the meat industry. Mianning ham is a famous dry-cured meat product in Sichuan, China. The aim of this work was to investigate the physicochemical characteristics, sources of odor, and associated microorganisms that cause spoilage of Mianning ham. High-throughput sequencing and solid-phase microextraction–gas-chromatography (SPME-GC-MS) techniques were used to characterize the physicochemical properties, microbial community structure, and volatile compounds of spoiled Mianning ham and to compare it with normal Mianning ham. The results showed that spoiled ham typically had higher moisture content, water activity (a_w), and pH, and lower salt content. The dominant bacterial phylum detected in deeply spoiled ham was Firmicutes (95.4%). The dominant bacterial genus was Clostridium_sensu_stricto_2 (92.01%), the dominant fungal phylum was Ascomycota (98.48%), and the dominant fungal genus was Aspergillus (84.27%). A total of 57 volatile flavor substances were detected in deeply spoiled ham, including 11 aldehydes, 2 ketones, 6 alcohols, 10 esters, 20 hydrocarbons, 6 acids, and 2 other compounds. Hexanal (279.607 ± 127.265 μg/kg) was the most abundant in deeply spoiled ham, followed by Butanoic acid (266.885 ± 55.439 μg/kg) and Nonanal (165.079 ± 63.923 μg/kg). Clostridium_sensu_stricto_2 promoted the formation of five main flavor compounds, Heptanal, (E)-2-Octenal, 2-Nonanone, Hexanal, and Nonanal, in deeply spoiled ham by correlation analysis of microbial and volatile flavor substances.

Mianning ham is a traditional meat product in China. In this experiment, solid-phase microextraction–gas chromatography (SPME-GC-MS) and high-throughput sequencing were used to study the effects of adding Penicillium lanosum and adding the mixture of Penicillium lanosum and Staphylococcus equorum on the flavor and microbiology of Mianning ham. The results showed that the addition of the ferments resulted in an increase in the abundance of both the dominant bacterial phylum (Thick-walled Bacteria) and the dominant fungal phylum (Ascomycota). The variety of volatile flavor substances and key flavor substances increased after adding fermentation agents. A free amino acid analysis showed that hams from the Penicillium lanosum and Staphylococcus equorum group had significantly higher umami flavor amino acids than the control group and Penicillium lanosum group. Therefore, inoculation with Penicillium lanosum and Staphylococcus equorum favored the dominant bacteria and flavor of Mianning ham.