Isolation of Debaryomyces hansenii and selection of an optimal strain to improve the quality of low-grade beef rump (middle gluteal) during dry aging.

OBJECTIVE: The objective of this study was to evaluate the effect of Debaryomyces hansenii isolated from dry-aged beef on the tenderness and flavor attributes of low-grade beef during dry aging. METHODS: Five D. hansenii strains were isolated from dry-aged beef samples. The rump of low-grade beef was inoculated with individual D. hansenii isolates and subjected to dry aging for 4 weeks at 5°C and 75% relative humidity. Microbial contamination levels, meat quality attributes, and flavor attributes in the dry-aged beef were measured. RESULTS: Of the five isolates, the shear force of dry-aged beef inoculated with SMFM201812-3 and SMFM201905-5 was lower than that of control samples. Meanwhile, all five isolates increased the total free amino acid, glutamic acid, serine, glycine, alanine, and leucine contents in dry-aged beef. In particular, the total fatty acid, palmitic acid, and oleic acid contents in samples inoculated with D. hansenii SMFM201905-5 were higher than those in control samples. CONCLUSION: These results indicate that D. hansenii SMFM201905-5 might be used to improve the quality of beef during dry aging.

Identification of Optimal Fermentation Temperature for Dry-Fermented Sausage Using Strains Isolated from Korean Fermented Foods.

This study aims at identifying the optimal fermentation temperature for dry-fermented sausage using strains isolated from Kimchi (GK1, Pediococcus pentosaceus-GK1; NK3, P. pentosaceus-NK3), Doenjang (D1, Debaryomyces hansenii-D1), and commercial fermented sausage (S6, spontaneously generated Penicillium nalgiovense-S6). The microbial population, pH, moisture content, color, thiobarbituric acid reactive substance (TBARS), volatile basic nitrogen (VBN), and electronic nose (E-nose) were analyzed to identify the optimal fermentation temperature. The dry-fermented sausages were inoculated with three types of starter cultures [CS (commercial starter culture), GD (GK1 + D1 + S6), and ND (NK3 + D1 + S6)]. The fermentation was performed for 3 days at 20 °C and 25 °C, and dried for 28 days. The Lactobacillus spp. plate count and TBARS showed significantly higher values in the 25 °C group than in the 20 °C group (p < 0.05). The Staphylococcus spp. plate count of GD and ND were significantly higher than CS group at all temperatures. On day 31, the moisture content and VBN values of all groups were less than 35 % and 20 mg%, respectively. According to E-nose, the highest amount of acetoin was detected at the GD group fermented at 25 °C. Thus, the optimal fermentation temperature is expected at 25 °C after using GD in the manufacturing of dry-fermented sausages.

Identification of Microorganisms Associated with the Quality Improvement of Dry-Aged Beef Through Microbiome Analysis and DNA Sequencing, and Evaluation of Their Effects on Beef Quality.

The objective of this study was to isolate and identify the microorganisms, especially yeasts and molds, related to the improvement of beef quality during dry-aging of beef through microbiome analysis, and to examine the possibility of using them as starter culture strains to improve the efficiency of dry-aging beef production. Beef sirloins were dry-aged for 28 days using different wind speeds (0, 2.5, and 5 m/s) at 1 to 3 °C and 75% relative humidity, and microbial compositions were confirmed by microbiome analysis. Mold and yeast samples were plated on potato dextrose agar supplemented with 10% tartaric acid, and the isolated colonies were identified by DNA sequencing. The isolates were subjected to microbial characterization (morphological characterization, growth condition, and enzyme activity). Microbiome analysis showed that the dominant microorganisms were molds and yeasts identified as Pilaira anomala SMFM201611 and Debaryomyces hansenii SMFM201707. Pilaira anomala SMFM201611 and D. hansenii SMFM201707 were inoculated into 24 sirloins of the lowest grade. All samples were dry-aged for 0, 14, 21, and 28 days and analyzed for microbial growth, pH, shear force, ultrastructure, and flavor compounds (free amino acids and free fatty acids). Inoculation with P. anomala SMFM201611 and D. hansenii SMFM201707 improved tenderness and cause the breakdown of myofibrils by proteolysis. Both microorganisms also produced free amino acids and fatty acids through proteolytic and lipolytic activities. These results indicate that P. anomala SMFM201611 and D. hansenii SMFM201707 isolated and identified from dry-aged beef can improve the quality of low-grade beef during dry-aging. PRACTICAL APPLICATION: During dry-aging, mold and yeast improve the quality of dry-aged beef. Pilaira anomala SMFM201611 and Debaryomyces hansenii SMFM201707 isolated from dry-aged beef can improve tenderness by breaking down myofibrils. Both microorganisms improve flavor by producing free fatty acids and amino acids, and the taste and aroma characteristics of low-grade beef may be improved during the dry-aging process.

Changes in microbial composition on the crust by different air flow velocities and their effect on sensory properties of dry-aged beef.

Beef rumps (middle gluteal) were dry aged for 28 days using different air flow velocities of 0, 2.5, and 5 m/s (DA0, DA2.5, and DA5, respectively). The microbial composition, physicochemical traits (moisture, pH, and shear force), flavor compounds (inosine 5'-monophosphate, reducing sugar, free amino acid, and free fatty acid), and electronic tongue profile were analyzed at day 0, 14, and 28. No molds or yeasts were detected until day 14. On day 28, Pilaira anomala was found to be the most abundant in DA0, whereas DA2.5 and DA5 showed increased composition of Debaryomyces hansenii. With that, the significant changes in physicochemical traits and flavor compounds occurred. In addition, the pattern of flavor compounds and taste attributes from DA0, which had different mold and yeast compositions, were discriminable from DA2.5 and DA5. Therefore, our results suggest that air flow can affect microbial composition on the crust, possibly resulting in different sensory properties of dry-aged beef.