## 2 Materials and Methods
### Research Protocols
#### 2.2.7 Shear Force Determination  
The shear force was determined using the ZWICKI 1120 apparatus (Zwick-Roell GmbH & Co. KG, Ulm, Germany). From the grilled meat samples, a cross-section of 1 \(\times\) 1 cm was taken, oriented with the longitudinal arrangement of muscle fibers (five individual measurements). The maximum cutting force of the sample was measured using a Warner-Bratzler attachment fitted with a flat knife, along with the knife's penetration depth, until the sample was fully cut. The measurements were performed on samples at ambient temperature. The test was conducted at a speed of 50 mm/min with an initial force of 0.5 N, using a measuring head with a range of 2-1000 N [21]. 2.2.8. Sensory Evaluation of the Quality of Dry-Aged Beef  
Sample preparation. Before heat treatment, the meat pieces, 2.0 cm thick steaks (cut using an automatic cutter, Ma-Ga, 250 W; 50 Hz, Bydgoszcz, Poland), were allowed to sit until they reached room temperature. They were then grilled on a hot contact grill (PK2745E, 3000 W, 60 Hz, Potiis GmbH, Goettingen, Germany) at 250 \({}^{\circ}\)C for 3 min to achieve a medium-rare level of doneness. After grilling, the steaks were left to rest, and 4.0 cm \(\times\) 2.5 cm sections were cut perpendicular to the muscle fibers for sensory evaluation. The meat samples were placed in odorless, disposable plastic containers with lids, each marked with a unique three-digit code. 2.2.9. Sensory Consumer Study  
The examination took place within a controlled laboratory environment. A total of 40 consumers, organized into 4 groups, were invited to take part in this study at the Institute of Human Nutrition, Warsaw University of Life Sciences. This study involved participants who identified themselves as regular beef consumers. The consumer study comprised two stages. Initially, participants evaluated the aroma of raw steaks. They were presented with three sets of two steaks samples each: a control and one treated with _M. flavus_. Consumers assessed their preference for the aroma of these steaks before they were subjected to the thermal process. Then, the next step of this study involved evaluating the samples after grilling. The evaluated attributes were aroma, tenderness, juiciness, flavor, and overall liking. Consumers rated each meat sample using a 9-point hedonic scale, with endpoints ranging from 1 (extremely dislike) to 9 (extremely like) [22]. These coded samples were evaluated after following grilling, with the samples averaging 60 \({}^{\circ}\)C. The evaluation and condition mode were established based on the procedures described by [PERSON] et al. [23] and by [PERSON] and [PERSON] [22]. The sensory and consumer study was conducted as described by the Helsinki Declaration [24] and with the regulation and approval of the Ethical Commission No 15/2021. 2.2.10. Determination of Volatile Compounds  
About 5 g of meat sample (cut into pieces about 2 cm) was placed in 20 mL vials and sealed. The absorption time in SPME sampling, using a DVB/CAR/PDMS fiber (Merck KGAA, Darmstadt, Germany) (1 cm long), was 50 min at 70 \({}^{\circ}\)C. After injecting the fiber into the GC/MS apparatus (GCMS-QP2010, Shimadzu Corporation, Kyoto, Japan), the process of desorption lasted 120 s (splitless mode). A polyethylene glycol column (30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m, Restek GmbH, Bad Homburg, Germany) was used to separate the volatile compounds. The column flow of helium was 0.64 mL/min. The temperature program of separation was as follows: 40 \({}^{\circ}\)C (10 min. ); next, 5 \({}^{\circ}\)C/min to 200 \({}^{\circ}\)C (2 min. ); and 220-250 \({}^{\circ}\)C at a rate of 20 \({}^{\circ}\)C/min, holding time at 250 \({}^{\circ}\)C (10 min.). The interface, ion source, and injector were working at 250 \({}^{\circ}\)C [25]. The mass spectra of the tested compounds were registered in the range of 40-450 m/z, with an ionization energy of 70 eV. The identification of volatile compounds was performed based on the analysis of mass spectral databases, e.g., NIST or Wiley.