Characterization of Quality Properties in Spoiled Mianning Ham

Abstract

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.

Keywords: Mianning ham; deep spoilage; high-throughput sequencing; physicochemical properties; volatile compounds.

Figure 1

Venn diagram of bacterial diversity of Mianning hams. The figures in different compartments mean the numbers of bacterial specific for or common to Mianning hams of different qualities.

Figure 2

Relative abundance of bacterial community proportions at the phylum (a) and genus (b) levels in Mianning ham. Different colors represent different bacterial communities, and the size of the color area represents the relative abundance (percentage) of bacterial community at the phylum (a) and genus (b).

Figure 3

Venn diagram of fungal diversity of Mianning hams. The figures in different compartments mean the numbers of fungal specific for or common to Mianning ham of different qualities.

Figure 4

Relative abundance of fungal community proportions at the phylum (a) and genus (b) levels in Mianning ham. Different colors represent different fungal community and the size of the color area represents the relative abundance (percentage) of fungal community at the phylum (a) and genus (b).

Figure 5

Heat map of hierarchical clustering analysis of main flavor substances in Mianning ham. Each row represents a flavor substance and each column represents a ham sample. The redder the color, the higher the content of volatile compounds; the bluer the color, the lower the content of volatile compounds.

Figure 6

Correlation network of dominant microbial genera and key flavor substances of Mianning ham. The dominant bacterial genus and the dominant fungal genus are on the left and right, respectively. Additionally, the main flavor substance of Mianning ham is in the middle. The red line indicates a positive correlation between the two components and the blue line indicates a negative correlation between the two components.