Sous-Vide Processing as a Method for Standardising the Quality of Beef from Holstein-Friesian Bulls: The Effect of Time on Tenderness

Abstract

Beef from dairy breeds such as Holstein–Friesian (HO) often shows high variability in tenderness, particularly in locomotive muscles such as semimembranosus (SM). This study evaluated whether sous-vide (SV) cooking at 60 °C for different times could standardise eating quality across raw material of divergent initial tenderness. SM muscles (2.5–3.0 kg) from HO bulls (n = 22) were vacuum-packed and cooked for 3, 4 or 6 h. Proximate composition, pH, water-holding capacity, colour, Warner–Bratzler shear force (WBSF) and sensory attributes were determined. Raw meat showed uniform chemical composition; however, there were considerable differences in WBSF values (from 30 N to 80 N) in meat cooked using the conventional water-bath cooking method. SV significantly improved tenderness, with cooking losses increasing moderately with time. In line with our hypothesis, sous-vide processing unified the heterogeneous SM muscles in terms of tenderness, with all samples reaching WBSF values below the 42.87 N threshold, and the time of 4 h proved to be the optimal duration. Extending cooking to 6 h provided no additional sensory benefits and increased cooking loss. Colour changes reflected myoglobin oxidation (lower a* and C*, higher h°), whereas juiciness remained stable. These findings indicate that SV for 4 h at 60 °C is the optimal combination, delivering consistent tenderness in SM from HO bulls which can serve as a practical strategy for improving the culinary value of beef from dairy breeds.

1. Introduction

Improving beef tenderness and maintaining consistent quality remain key challenges for food science and the meat industry. Consumer expectations have shifted from price toward consistent sensory, microbiological, and nutritional quality, alongside concerns about sustainability [1,2,3]. In production systems with a high proportion of dairy or dual-purpose breeds such as Holstein–Friesian (HO), carcass traits and eating quality are more variable than in specialised beef breeds, resulting in inconsistent tenderness at retail [4,5,6]. Addressing this variability is therefore a priority for both researchers and industry. Recent studies on sous-vide cooked beef from HO bulls show that post-mortem ageing interacts strongly with sous-vide processing in determining tenderness outcomes [7]. New studies on the semimembranosus (SM) muscle further confirmed that time–temperature combinations are decisive for water-holding capacity and tenderness development [8,9,10].

Muscle type is a critical determinant of beef quality. Locomotive muscles, such as the SM, generally present lower tenderness, a darker colour, and less intramuscular fat compared with back muscles like the longissimus thoracis et lumborum (LTL). The latter is often used as a reference in meat science because of its consistent quality and favourable sensory properties [11,12]. In contrast, SM—being heavily involved in locomotion—shows greater variability and is frequently less acceptable to consumers due to its toughness and darker appearance [13,14]. Consumer studies highlight a paradox: shoppers visually prefer leaner cuts with minimal marbling, believing them healthier, whereas intramuscular fat actually enhances juiciness and flavour [15,16]. This conflict underlines the need for technological solutions that can improve the palatability of lean muscles such as SM while meeting consumer preferences for low visible fat. Recent studies confirm significant differences between SM and LTL under different processing conditions, and show that interventions such as marination or controlled ageing can partially reduce this gap [17,18].

A way of increasing the eating quality of SM muscle might also be sous-vide technology. As a low-temperature, long-time (LTLT) technique, it enables precise control of thermal processing and has gained growing attention in meat science over the past decade. In sous-vide, raw meat is vacuum-packed and cooked at controlled temperatures, typically around 60 °C, for several hours to days, followed by rapid chilling [19,20,21,22]. Compared with conventional methods such as roasting or grilling, sous-vide reduces cooking losses, preserves nutrients, and provides a more uniform texture and flavour [23,24].

A key functional compromise is cooking at around 60 °C, where prolonged heating promotes partial collagen solubilization while avoiding excessive actin-related toughening [25,26]. This balance is particularly relevant for tougher muscles such as SM, where extended sous-vide times can reduce Warner–Bratzler shear force (WBSF) to consumer-acceptable levels [8,27,28,29].

Sous-vide has been applied to beef not only in gastronomy but also in industrial and household contexts. Innovations include coupling sous-vide with pre-treatments such as marination, enzymatic tenderization, or pulsed electric fields, aiming to further enhance tenderness and sensory quality [23,30,31]. Moreover, sous-vide combined with post-mortem ageing improves not only tenderness but also protein digestibility [30]. These developments underline the potential of sous-vide to improve the eating quality of challenging muscles like SM from HO bulls while meeting consumer expectations for leaner, high-quality beef. Recent reviews highlight improvements in packaging, air removal, and time–temperature control as critical to extending shelf life and ensuring microbiological safety [32,33].

To summarise, sous-vide offers a controlled approach that addresses the toughness of SM and supports lean, high-quality beef production. Recent studies confirm its effectiveness in reducing WBSF through extended heating at ~60 °C, and highlight its integration with interventions such as marination or enzymatic tenderization [8,23,30]. Advances in packaging and safety research further strengthen the case for sous-vide in industrial beef processing. Importantly, few studies have focused specifically on SM from HO bulls, a muscle and production system combination with high variability and limited consumer acceptability. Based on these considerations, the objective of this study was to determine the optimal sous-vide time at 60 °C required to achieve acceptable tenderness (WBSF ≤ 42.87 N) in SM muscle of HO bulls, regardless of initial raw material variability. We hypothesised that prolonged sous-vide at this temperature would attenuate differences in raw meat quality and consistently yield beef with WBSF values within the consumer-acceptable range for tenderness. From an applied perspective, this work may provide practical guidance for both meat processors and food service operators seeking to improve the value of beef from dairy breeds.

2. Materials and Methods

2.1. Ethical Approval and Animals

Beef SM muscles were obtained from 22 Polish HO bulls reared at the Agricultural Experiment Station in Bałcyny, Poland. Animals were raised under controlled feeding and management conditions typical for the station. The protocol was approved by the Ethics Committee of the University of Warmia and Mazury in Olsztyn (Decision no. 8/2020). Animals were slaughtered at a commercial slaughterhouse. Carcasses were chilled at 4 °C for 96 h. SM muscles (2.5–3.0 kg each) were excised from the left carcass side and vacuum-packed (25 mbar, chamber pump, double cut-off seal) individually (PA/PE, 70 µm; Inter Arma Ltd., Rudawa, Poland). The total transmission rates of packaging material did not exceed 10 mg/dm² for model liquids, 3% acetic acid, 50% ethyl alcohol (10 days at 40 °C), and isooctane (2 days at 20 °C). The samples were stored at 4 ± 1 °C until day 14 post-mortem.

2.2. Feeding and Management

Calves from the HO herd raised in Bałcyny were reared in a traditional system and fed milk replacer, hay, and a concentrate supplement. After reaching 6 months of age, the bulls were transferred to semi-intensive fattening. They were housed in group pens and fed a total mixed ration (TMR) ad libitum. The TMR consisted of maize silage (MS), 2 kg of concentrate, and a mineral supplement. At the age of approximately 542 ± 8.23 days, when the bulls reached a live weight (LW) of approximately 508.8 ± 6.91 kg, the bulls were transferred to the finishing lane. They were housed in a single pen with 7 m² of floor space per bull. The animals had free access to water and salt licks. For a four-week pre-experimental period, the bulls were adapted to housing conditions and feeding. After this, the feeding experiment began. During the finishing period, which lasted five months, the bulls were fed a complete TMR mixture ad libitum, consisting of the feeds listed in Table S1. The percentage of each feed in the TMR is given in Table S2. The animals remained under veterinary care. None of them experienced any health problems during the experiment. During the fattening period, the animals gained an average of 1170 g per day (Table S3).

2.3. Experimental Overview

After ageing, each SM was divided into two portions corresponding to two stages of the study:

Stage 1—baseline characterisation and initial instrumental tenderness determination. From each muscle, six steaks (2.5 ± 0.2 cm, 120 ± 5 g) were cut: three for raw-meat physicochemical characterisation and three for initial instrumental tenderness after conventional water-bath cooking to 71 °C internal.

Stage 2—sous-vide processing and quality evaluation. From the remaining portion, nine steaks (2.5 ± 0.2 cm, 120 ± 5 g, one steak per pouch) were prepared for sous-vide at 60 °C for 3, 4 or 6 h (three steaks per time; racks to avoid contact). Preliminary validation under the same bath conditions confirmed that the core temperature reached 60 °C within approximately 30–35 min. Thermal validation and microbial safety were considered according to the time–temperature models described by Baldwin [19] and confirmed by subsequent studies [34,35]. After cooking, samples were assessed for cooking loss, sensory attributes and WBSF.

Freezing and Thawing

All prepared, labelled raw samples were frozen at −18 ± 1 °C and stored for 3 months. Before analysis, the samples were thawed at 4 ± 1 °C for 48 h. This procedure was applied uniformly for both Stage 1 and Stage 2 samples. All samples in Stage 1 and Stage 2 underwent an identical three-month freezing period followed by a carefully controlled, standardised thawing procedure, ensuring methodological consistency and minimising potential variation between treatments.

2.4. Stage 1—Raw-Meat Characterisation and Initial Instrumental Tenderness

2.4.1. pH

Raw-meat pH was measured on the day of delivery using a Testo 205 pH meter with a pH/NCT spear electrode (Testo, Titisee-Neustadt, Germany) with automatic temperature compensation. The pH meter was calibrated with pH 4.01 and 7.01 buffers before each session. Measurements were taken by inserting the probe into the geometric centre of the steak (triplicate per sample).

2.4.2. Proximate Composition

From each raw SM, a sample of approx. 120 g was minced twice through 6 mm and 3 mm meshes (ZMM4080, Zelmer S.A., Rzeszów, Poland). Moisture, protein, fat and ash were determined by near-infrared transmission using FOSS FoodScan 2 Lab/Pro (FOSS Analytical A/S, Hillerød, Denmark), approved by AOAC and operated according to PN-A-82109:2010 [36]. Sixteen independent scans per sample were averaged for reporting [37].

2.4.3. Colour

Colour was measured in the CIE L* a* b* system using a Konica Minolta CR-400 chromameter (Konica Minolta Sensing, Inc., Osaka, Japan) with D65 illumination, 10° observer and 2.54 cm aperture, calibrated on the manufacturer’s white tile. Steaks were allowed to bloom for 20 min at 4 ± 1 °C; three readings per steak were averaged. Hue (h°) and Chroma (C*) were calculated per AMSA Meat Color Measurement Guidelines [38].

2.4.4. Free Water and Plasticity

Free water was determined using the Grau–Hamm pressing method with modifications. After colour and pH determinations, 50 g of meat was minced (3 mm mesh). Portions of 0.3 g were placed on Whatman No.1 filter paper on a glass tile, covered with a second tile and loaded with 2 kg for 5 min. The filter paper with the pressed sample and water halo was photographed (Nikon D90, Nikon Corporation, Tokyo, Japan). Images were analysed in NIS-Elements BR 2.20 (Nikon Corporation, Tokyo, Japan); free water (%) was calculated from the stain and sample areas and paper absorptiveness [39,40]. The same imprints were used to determine plasticity (cm²) from the meat-print area [41].

2.4.5. Classification of SM Muscles Based on WBSF Values of Conventionally Cooked Samples

Three steaks per muscle were placed in individual heat-resistant bags and cooked in a stirred water bath at 80 °C (Aquarius M/150Z, Aqua Lab, Warsaw, Poland) until reaching 71 °C internal (continuous core-temperature monitoring with an electronic probe). After overnight chilling (4 ± 1 °C), WBSF was determined (see Section 2.5.5). Based on WBSF, muscles were assigned to tenderness classes per Destefanis et al. [27]: Tender (TD, WBSF < 42.87 N), Intermediate (I, WBSF from 42.87 N to 52.68 N), Tough (T, WBSF > 52.68 N). This strategy was used to determine the tenderness of the research material after standard heating to achieve 71 °C.

2.5. Stage 2—Sous-Vide Processing and Quality Evaluation

2.5.1. Sample Preparation and Packaging

From each SM, nine steaks (2.5 cm) were allocated to 3, 4 or 6 h at 60 °C (three per time). Steaks were vacuum-sealed individually in PA/PE 70 µm sous-vide pouches (Inter Arma, Rudawa, Poland). Tightness of packaging was inspected before cooking.

2.5.2. Sous-Vide Cooking

Cooking was performed in Hendi GN 2/3 sous-vide baths (HENDI, Rhenen, The Netherlands) set to 60.0 °C. Baths were allowed to equilibrate for ≥30 min; set-point and readout were checked against a calibrated digital thermometer. Bags were fully submerged with rack separation to ensure convective flow; the water level was maintained above all packets.

The experiment ran for 8 consecutive days. Each day, samples were distributed to three baths corresponding to 3 h, 4 h, and 6 h; bath identity was randomised across each day for each time. For days 1–5, each bath contained nine samples (three per tenderness class: T, I, TD). On days 6–7, six samples (classes T and I only) were processed per bath, as TD samples were processed earlier. On day 8, nine remaining samples were processed (T n = 3; I n = 6 from two animals). In total, 198 steaks were cooked (22 animals × 9 steaks).

After sous-vide, the samples were swiftly removed and placed in a blast chiller set to a temperature of −1 °C for a duration of 15 min. Vacuum bags were visually inspected after cooking, and no leakage or seal damage was observed. Then the SV bags were opened, and surfaces were blotted with a paper towel.

2.5.3. Cooking Loss and Colour Determination

Cooking loss (%) was calculated according to Equation (1) following the procedure described by Xu et al. [8].

$$\mathrm{C}\mathrm{o}\mathrm{o}\mathrm{k}\mathrm{i}\mathrm{n}\mathrm{g} \mathrm{l}\mathrm{o}\mathrm{s}\mathrm{s}={\displaystyle \frac{\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t} \mathrm{b}\mathrm{e}\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{e} \mathrm{c}\mathrm{o}\mathrm{o}\mathrm{k}\mathrm{i}\mathrm{n}\mathrm{g}-\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t} \mathrm{a}\mathrm{f}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{c}\mathrm{o}\mathrm{o}\mathrm{k}\mathrm{i}\mathrm{n}\mathrm{g}}{\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t} \mathrm{b}\mathrm{e}\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{e} \mathrm{c}\mathrm{o}\mathrm{o}\mathrm{k}\mathrm{i}\mathrm{n}\mathrm{g}}} ·100 (\%)$$

(1)

Additionally, colour (see Section 2.4.3) was measured with the same geometry and at the same points as raw in line with AMSA Meat Color Measurement Guidelines [38] after 20 min of blooming of the freshly cut surface. Samples were then chilled at 4 ± 1 °C overnight prior to instrumental tenderness tests.

2.5.4. Sensory Evaluation

A subset of steaks was evaluated for tenderness and juiciness by a trained six-member panel following PN-ISO 4121 standard [42]. Each of the panellists evaluated nine samples per session (one per time × class combination) in randomised order, masked to time/class, served at 50 ± 2 °C. Samples (25 mm × 60 mm × ~2 mm) were coded with 3-digit numbers, and presented under fluorescent lighting; water and bread were provided for palate cleansing. Scores were assigned on a 1–10 scale (1 = extremely tough/dry; 10 = extremely tender/juicy). Panel training and booth conditions followed procedures described previously for beef assessments in our lab [42].

2.5.5. Warner–Bratzler Shear Force

After overnight chilling (4 ± 1 °C), steaks (the experimental unit for Stage 2) were tempered to room temperature (~1.5 h). Five rectangular cores (10 × 10 × ~40 mm) per steak were cut parallel to fibre orientation and sheared perpendicular using an Instron 5942 universal testing machine (Instron, Norwood, MA, USA) fitted with a V-blade (60° triangular aperture). Crosshead speed: 200 mm/min; load cell: 500 N. The maximum shear force (N) was recorded; data were processed in Bluehill 3 (Instron, Norwood, MA, USA). For each steak, five cores were averaged to one WBSF value per steak.

2.5.6. Statistical Analysis

Data were statistically analysed by the Statistica 13.3 programme (TIBCO Software Inc., Palo Alto, CA, USA). The results were presented as the mean ± standard error of the mean (SEM). For each animal × time, three steak values were averaged to obtain one observation. For Stage 2, a two-way mixed-effects model was used with cooking time (3, 4, 6 h) and initial tenderness class (TD, I, T) as fixed effects, and beef carcass, cooking batch/day, panellist, and number of a sensory session as random effects. This approach avoided inflation of degrees of freedom and ensured that statistical independence was derived from the animal. The normal distribution of the data (Shapiro–Wilk test) and the homogeneity of variance (Levene’s test) were examined. They revealed the normal distribution of data and variance homogeneity; therefore, the significance of differences between the obtained mean values was determined using the Analysis of Variance and Tukey’s Multiple Comparison Test at the significance level of p < 0.05. The non-parametric Kruskal–Wallis test was used to compare the mean values obtained in the sensory assessment.

3. Results

3.1. Initial Classification and Chemical Uniformity of Raw Material

The study aimed to evaluate whether SV cooking at 60 °C for 3, 4, or 6 h allows for achieving the desirable tenderness of beef muscles from HO bulls, regardless of their tenderness class, as determined by WBSF values, according to Destefanis et al. [27].

Table 1. Classification of semimembranosus samples into tenderness groups based on Warner–Bratzler shear force (Destefanis et al. [26] criteria).

Tenderness Classes	Destefanis et al.’s Criteria [26]	WBSF [N]
		Mean Value	SEM
Tough	>52.68 N	56.0	4.0
		55.1	1.7
		79.7	2.9
		54.5	1.3
		54.9	1.8
		58.0	4.0
		52.9	0.3
		53.2	1.2
Intermediate	42.87 N–52.68 N	43.6	2.9
		49.8	2.5
		44.7	2.9
		42.9	1.8
		47.7	1.3
		48.8	1.6
		45.7	2.2
		44.0	4.0
		43.5	1.1
Tender	<42.87 N	30.1	1.3
		42.3	0.5
		33.6	1.3
		36.0	4.0
		40.0	4.0
Summary
Tenderness Classes	Mean WBSF Value in the Group [N]	SEM	Minimum Value [N]	Maximum Value [N]
Tough	59.2	1.8	52.9	79.7
Intermediate	45.9	0.8	42.9	49.8
Tender	35.7	1.4	30.1	42.3

SEM—standard error of the mean, WBSF—Warner–Bratzler shear force.

shows that WBSF values of meat heated to 71 °C in a water bath ranged widely from 30.1 to 79.7 N, indicating substantial variability in baseline tenderness. Three categories were identified: tender (WBSF < 42.87 N; n = 5, mean 35.7 N), intermediate (WBSF from 42.87 N to 52.68 N; n = 9, mean 45.9 N), and tough (WBSF > 52.68 N; n = 8, mean 59.2 N). This variability justifies the search for technological solutions to achieve consistent and acceptable tenderness irrespective of initial raw meat quality.

Table 2. Physicochemical characteristics of raw semimembranosus muscle from Holstein–Friesian bulls according to tenderness classes (mean ± SEM).

Attribute	Tenderness Classes			p Value
	Tough	Intermediate	Tender
pH	5.51 ± 0.01	5.50 ± 0.01	5.50 ± 0.01	0.664
Free water [%]	24.0 ± 0.9	23.7 ± 0.7	25.2 ± 0.7	0.570
Plasticity [cm2]	3.0 ± 0.1	3.14 ± 0.13	3.17 ± 0.10	0.647
Chemical Composition
Moisture [%]	72.2 ± 0.3	72.42 ± 0.25	72.5 ± 0.4	0.734
Protein [%]	23.2 ± 0.3	23.31 ± 0.26	22.44 ± 0.13	0.118
Fat [%]	3.8 ± 0.3	3.26 ± 0.26	3.4 ± 0.5	0.480
Ash [%]	0.86 ± 0.06	0.93 ± 0.08	1.16 ± 0.18	0.154
Colour
L*	34.2 ± 0.6	35.6 ± 0.5	34.9 ± 0.5	0.169
a*	21.1 ± 0.4	20.7 ± 0.5	19.9 ± 0.5	0.265
b*	11.3 ± 0.4	11.3 ± 0.4	10.5 ± 0.4	0.392
C*	24.0 ± 0.5	23.6 ± 0.6	22.5 ± 0.6	0.266
h°	28.0 ± 0.7	28.4 ± 0.6	27.6 ± 0.5	0.712

SEM—standard error of the mean.

demonstrates that the muscles from different tenderness groups were similar in terms of physicochemical properties. No significant differences were observed in pH (~5.5), free water content (23.7–25.2%), or plasticity (3.0–3.2 cm²). Proximate composition (moisture 72.2–72.5%, protein 22.4–23.3%, fat 3.3–3.8%, ash 0.86–1.16%) also did not differ significantly among groups. Meat colour, assessed by L*, a*, b*, C*, and h°, showed similar values regardless of tenderness class. These results indicate that the raw material was chemically homogeneous and that instrumental tenderness remained the primary factor differentiating culinary quality.

3.2. The Effect of Sous-Vide (SV) Time on Cooking Loss, Instrumental Tenderness and Sensory Quality

Generally, SV time affected cooking loss, WBSF values, and tenderness (points), whereas tenderness class affected WBSF and tenderness of cooked beef (

Table 3. Cooking loss (%), Warner–Bratzler shear force (N) and sensory scores of semimembranosus muscle from different tenderness classes after sous-vide cooking at 60 °C for 3, 4, and 6 h (mean ± SEM).

Attribute	SV Time (SVT)	Tenderness Classes (TC)
		Tough	Intermediate	Tender
Cooking loss [%]
3 h		25.8 B ± 0.8	25.4 B ± 1.7	26.6 A ± 0.8
4 h		27.0 AB ± 0.8	27.9 AB ± 0.6	27.4 A ± 0.9
6 h		29.3 A ± 1.3	30.2 A ± 0.5	28.3 A ± 0.8
p value		SVT		0.001
		TC		0.826
		SVT × TC		0.551
WBSF [N]
3 h		38.3 Aa ± 1.3	31.4 Ab ± 1.1	29.8 Ab ± 1.1
4 h		34.1 Ba ± 1.4	30.4 Ab ± 1.2	28.1 Ab ± 1.2
6 h		32.5 Ba ± 2.2	27.6 Ab ± 1.2	21.3 Bc ± 1.2
p value		SVT		0.000
		TC		0.000
		SVT × TC		0.371
Sensory Evaluation
Juiciness [points]
3 h		6.81 Aa ± 0.19	7.35 Aa ± 0.16	7.30 Aa ± 0.20
4 h		6.79 Ab ± 0.19	7.06 Aa ± 0.14	7.4 Aa ± 0.20
6 h		6.77 Ab ± 0.21	6.85 Ab ± 0.20	7.53 Aa ± 0.20
p value		SVT		0.809
		TC		0.000
		SVT × TC		0.095
Tenderness [points]
3 h		6.73 Ba ± 0.19	7.13 Ab ± 0.16	7.20 Bb ± 0.23
4 h		7.06 ABa ± 0.19	7.00 Ab ± 0.14	7.57 Bb ± 0.21
6 h		7.35 Ab ± 0.21	7.59 Ab ± 0.20	8.47 Aa ± 0.18
p value		SVT		0.000
		TC		0.000
		SVT × TC		0.217

SEM—standard error of the mean, ^{A, B}—mean values in columns (SV time) with different superscripts differ significantly at p < 0.05; ^a–c—mean values in rows (tenderness classes) with different superscripts differ significantly at p < 0.05.

). Data were averaged per animal × time combination, and the mixed-effects model included animal as a random effect together with cooking batch/day, judge, and session. The results showed that cooking loss increased gradually with longer SV times (from ~25–26% at 3 h to ~29–30% at 6 h; p < 0.01), independently of tenderness class. WBSF declined significantly with increasing time (p < 0.001). After just 3 h, even samples originally classified as tough reached mean WBSF values below the consumer-acceptable threshold, confirming the tenderising effect of sous-vide treatment. Sensory tenderness scores indicated an improvement in tough and tender classes, with beef SV cooked for 6 h being the most tender (p < 0.001). Juiciness remained relatively stable across times, although slight differences were noted between tenderness classes (p < 0.05).

3.3. The Effect of SV Time on Beef Colour

Generally, the SV cooked beef colour was affected by the treatment time, whereas the tenderness class did not affect the SV cooked beef colour (

Table 4. Colour parameters (L, a, b*, C*, h°) of semimebranosus muscle from different tenderness classes after sous-vide cooking at 60 °C for 3, 4, and 6 h (mean ± SEM).

Attribute	SV Time (SVT)	Tenderness Classes (TC)
		Tough	Intermediate	Tender
L*
3 h		52.2 A ± 0.7	52.0 A ± 0.4	54.4 A ± 0.6
4 h		54.0 A ± 0.8	53.2 A ± 0.6	54.0 A ± 0.4
6 h		55.4 A ± 0.6	52.4 A ± 0.5	55.39 A ± 0.24
p value		SVT		0.588
		TC		0.069
		SVT × TC		0.11
a*
3 h		17.4 A ± 0.4	17.6 A ± 0.3	17.5 A ± 0.5
4 h		16.0 A ± 0.7	15.4 B ± 0.4	16.9 AB ± 0.4
6 h		15.8 A ± 0.4	14.4 B ± 0.6	14.2 B ± 0.5
p value		SVT		0.000
		TC		0.286
		SVT × TC		0.162
b*
3 h		13.14 A ± 0.29	13.55 A ± 0.28	12.3 A ± 0.6
4 h		12.92 A ± 0.21	12.98 A ± 0.26	12.5 A ± 0.3
6 h		13.07 A ± 0.19	13.4 A ± 0.3	13.05 A ± 0.24
p value		SVT		0.344
		TC		0.061
		SVT × TC		0.607
C*
3 h		21.9 A ± 0.5	22.2 A ± 0.4	21.4 A ± 0.7
4 h		20.6 A ± 0.6	20.2 B ± 0.4	21.0 A ± 0.4
6 h		20.53 A ± 0.29	19.7 B ± 0.6	19.3 A ± 0.4
p value		SVT		0.000
		TC		0.636
		SVT × TC		0.422
h°
3 h		37.0 A ± 0.6	37.6 B ± 0.5	35.0 B ± 0.8
4 h		39.6 A ± 1.2	40.2 B ± 0.8	36.7 B ± 0.7
6 h		39.8 A ± 0.8	43.7 A ± 1.0	42.8 A ± 1.1
p value		SVT		0.000
		TC		0.063
		SVT × TC		0.060

SEM—standard error of the mean, ^{A, B}—mean values in columns (SV time) with different superscripts differ significantly at p < 0.05.

). Lightness (L*) and yellowness (b*) were largely unaffected by cooking time or tenderness class (p > 0.05) (Table 4). In contrast, redness (a*) and chroma (C*) decreased significantly with longer times (p < 0.001), particularly after 6 h, indicating pigment denaturation and colour fading. Hue angle (h°) increased significantly (p < 0.001) with time, reflecting a shift toward less red, more brownish hues.

4. Discussion

4.1. Raw Material Quality and Initial Tenderness

The raw SM muscles from HO bulls were chemically uniform across tenderness classes, with no significant differences in proximate composition (moisture, protein, fat, ash), pH, free water content or plasticity. These findings are consistent with reports that HO beef generally exhibits a stable chemical composition, regardless of cattle age or production system [4,5,6,8,31]. However, eating quality variability is more strongly linked to muscle function and connective tissue content than to proximate composition [7]. Noted in our study, the variability in WBSF of beef cooked in a water-bath to 71 °C therefore reflects structural rather than chemical factors, and creates a challenge for the beef industry when processing carcasses from HO bulls.

4.2. Effects of Sous-Vide Processing on Quality Traits

Sous-vide processing at 60 °C induced clear time-dependent effects on quality attributes. Cooking loss increased significantly with longer heating times, consistent with progressive shrinkage of myofibrillar proteins and water expulsion [19,43]. In our study, cooking loss rose from about 26% at 3 h to 27.4% at 4 h and 29.3% at 6 h. Comparable or slightly higher values were reported by Supaphon et al. [24] (28–31% at 60 °C for 6–12 h) and Kathuria et al. [26] (27% at 4 h to 32% at 8 h), while Xu et al. [8] observed somewhat lower losses (~24–25% at 6 h) in hot-boned SM. Yin et al. [18] demonstrated, using enzymatic and proteomic analyses, that sous-vide altered protein structure and improved digestibility, while Zhu et al. [44] linked such structural changes to enhanced tenderness and digestibility. Domínguez-Hernández et al. [25] further confirmed that 60 °C is an optimal temperature for textural improvement in SM.

Tenderness, measured by WBSF, improved markedly with SV cooking time. In our study, values decreased within tenderness classes as follows between 3 h and 6 h: Tough from 38.3 N to 32.5 N, Intermediate from 31.4 N to 27.6 N, and Tender from 29.8 N to 21.3 N. Therefore, it was shown that SV treatment of tough beef enabled achieving the meat products with WBSF below or close to the consumer-desirable tenderness categories: tender (42.87–32.96 N) and very tender (<32.96 N) [27]. Improvements in tenderness are likely related to partial collagen solubilization and weakening of connective tissue cross-links, while actin denaturation remains limited at 60 °C, as reported in previous studies on beef sous-vide systems at similar temperature–time combinations [25,34,35]. Additionally, it should be noted that the freezing and thawing procedures applied in this study might have slightly influenced the muscle microstructure; however, all samples were subjected to identical conditions, which minimises their potential effect on comparative outcomes. Our sensory results supported these mechanisms: panellists consistently scored samples as more tender after longer treatments, aligning with previous observations [45]. The convergence of instrumental and sensory tenderness after prolonged SV is consistent with recent reviews on SV meat quality [26].

Juiciness scores showed only minor differences over time (p = 0.809) and remained relatively stable across treatments. Although the effect of tenderness class was statistically significant (p < 0.001), the numerical differences between classes were small and did not follow a consistent pattern. This agrees with findings that SV cooking preserves water-holding capacity better than conventional methods, since lower temperature reduces rapid moisture loss [20,22]. The slight decline in juiciness in tough-class samples may relate to their higher connective tissue content, which contracts and expels fluid during prolonged heating [10,18,46].

Among colour attributes, mainly redness (a*) and chroma (C*) were affected, both decreasing with time, while hue angle (h°) increased, reflecting myoglobin oxidation and denaturation of heme pigments [21,38]. Lightness (L*) and yellowness (b*) remained largely unaffected. In the SV cooked meat, longer heating times reduce a* and C*; however, the products are often lighter and redder than conventionally cooked beef due to different pigment kinetics at lower temperatures [47]. Comparable patterns were reported in beef and lamb by Macharáčková et al. [48] and Realini et al. [16].

Overall, these results confirm that SV exerts well-defined mechanistic effects on water migration, connective tissue solubilization and pigment stability, leading to improved tenderness and acceptable sensory quality without compromising juiciness or producing excessive cooking loss. A limitation of the present study is that the Hendi GN 2/3 sous-vide bath operates without active water circulation, which may lead to minor temperature gradients despite careful rack spacing and monitoring, and this should be considered when comparing results across different sous-vide systems.

4.3. Determination of Optimal Sous-Vide Time

We hypothesised that SV processed at 60 °C would standardise tenderness across raw material of variable initial quality, bringing all samples to consumer-desirable tenderness levels (<42.87 N) [27]. The results confirmed this hypothesis.

Our results demonstrate that SV at 60 °C effectively unified the tenderness of beef from different tenderness classes. In our study, we applied the 42.87 N threshold proposed by Destefanis et al. [27], who reported that beef with WBSF > 52.68 N and <42.87 N is perceived by most consumers as “tough” and “tender,” respectively, which supports our choice of threshold. According to these authors, consumers are generally unable to distinguish a “very tender” category below 32.96 N, which is why 42.87 N is considered a practical threshold. According to the three-class Destefanis et al. [27] system, even the shortest time (3 h) reduced WBSF values below the consumer-desirable threshold of 42.87 N, indicating that SV treatment ensured tender beef regardless of initial classification. Nevertheless, considering the “very tender” classification (<32.96 N), it should be emphasised that as many as 65% of all tested samples reached this strict threshold. Only the tough group after 3 h and 4 h failed to reach the “very tender” level (Table 3). Despite this, the reduction in WBSF from 38.3 N (3 h) to 34.1 N (4 h) was substantial, and the sensory results showed no significant improvement in tenderness between 4 h and 6 h (7.06 vs. 7.35 points). Thus, extending cooking time from 4 to 6 h yielded only a minor additional decrease in WBSF (~1.6 N) while significantly increasing processing time. This confirms that, from a consumer standpoint, perceived tenderness differences between 4 h and 6 h are minimal, supporting our conclusion that 4 h represents a practical and efficient sous-vide duration.

Considering the marginal gains in tenderness, and the increased cooking time and energy costs, 4 h can be considered the most efficient and practically optimal sous-vide duration, delivering high quality while minimising production input.

From a technological and sustainability perspective, these findings indicate that 4 h at 60 °C represents the optimal compromise: it guarantees desirable tenderness in all samples while avoiding unnecessary extension of processing time, which could increase energy consumption and risk undesirable changes such as oxidation, flavour degradation, nutrient loss, or textural alterations [17,18,47,49,50,51]. Similar conclusions have been reported in other SV studies, where intermediate times provided results equivalent to the longest treatments [24,25]. Sous-vide treatment at 60 °C for 4 h can be considered optimal not only in terms of tenderness and energy efficiency but also as compliant with recognised thermal safety models for beef portions up to 2.5 cm thick [18,34,35]. Thus, 4 h at 60 °C emerges as the most efficient condition for achieving uniform, high-quality beef from HO bulls.

5. Conclusions

The present study demonstrated that semimembranosus muscles from Holstein–Friesian bulls are chemically uniform across tenderness classes, yet display high variability in shear force values due to structural factors. Sous-vide cooking at 60 °C markedly improved tenderness, with only limited effects on juiciness and predictable colour shifts typical of LTLT processing. All tested durations achieved consumer-acceptable tenderness, but 4 h emerged as the most efficient condition, delivering uniform, high-quality beef regardless of tenderness class without the additional time or risk of quality deterioration associated with 6 h.

These findings highlight sous-vide as a robust strategy to standardise eating quality in muscles of lower culinary value from dairy breeds, thereby mitigating raw material variability. From an industrial perspective, adoption of 4 h at 60 °C offers both technological and sustainability advantages, balancing product quality with enhanced energy efficiency.

Future studies should extend beyond instrumental tenderness to evaluate flavour development, protein digestibility, and consumer acceptance across different markets. Integration of sous-vide with novel interventions such as marination, enzymatic treatments, or functional packaging could further expand its applicability and enhance the economic value of beef from dairy systems.