Characterization of the microbiota and chemical properties of pork loins during dry aging

Abstract

Dry aging (DA) allows for the storage of meat without packaging at 0 to 3°C for several weeks. It enhances the production of pleasant flavors, tenderness, and juiciness in meat. Due to the long storage period and roles of indigenous microbiota in the maturation of several meat products, the microbiota of DA meat is of interest in terms of microbial contributions and food hygiene but has not yet been characterized in detail. This study identified the microbiota of pork loins during DA using culturing and culture-independent meta-16S rRNA gene sequencing and elucidated its characteristics. The amounts of free amino acids and profiles of aroma-active compounds were also monitored by high-performance liquid chromatography and gas chromatography, respectively. The meta-16S rRNA gene sequencing revealed that Pseudomonas spp. generally dominated the microbiota throughout DA; however, the culturing analysis showed marked changes in the species composition during DA. Acinetobacter spp. were the second most dominant bacteria before DA in the culture-independent analysis but became a minor population during DA. The cell numbers of yeasts showed an increased tendency during DA, and Debaryomyces hansenii was the only microorganism isolated from all meat samples throughout DA. Well-known foodborne pathogens were not observed in two microbiota analyses. The amounts of free amino acids were increased by DA, and the number of aroma-active compounds and their flavor dilution values markedly changed during DA. Most microbial isolates showed positive reactions with proteolytic and lipolytic activities, suggesting their contribution to tenderness and aroma production in DA meats.

Keywords: Debaryomyces; Pseudomonas; aroma; dry-aging pork; microbiota; proteolysis.

FIGURE 1

Changes in free amino acid contents during DA of pork loins. Different lowercase letters supplemented with bars are significantly different (p < 0.05). *detected as cystine in the system used (HPLC Amino Acid Analysis System, Shimadzu)

FIGURE 2

Viable cell numbers in DA pork loins on nutrient agar (black line), PDA agar (gray line), and MRS agar (dashed line). No significant differences (p > 0.05) were observed among the different time points

FIGURE 3

PCoA of 16S rRNA gene sequencing data at the genus level. Red, blue, and green symbols indicate data obtained from meat samples aged for 0, 20, and 40 days, respectively

FIGURE 4

The relative abundance of each genus in pork loins with/without DA