Impact of broccoli (Brassica oleracea var. italica) juice and balsamic vinegar on the tenderness, and oxidative stability of the marinated beefsteak during storage

In recent years, the special attention of food industry has been focused on the use of the non-thermal and economical methods to preserve food and increase its shelf life. Among these methods, the utilization of natural antioxidants and antimicrobial compounds has been mentioned. These compounds not only eliminate the side effects caused by the usage of chemical preservatives in long term, but also improve the textural and sensory properties as well as increase the shelf life of meat and their products (Mazaheri Kalahrodi et al., 2021). Quality, tenderness, and taste of the meat are important factors for the customers. Hence, the absence of satisfaction can be the reason for complaints and reduced meat consumption. Marinating by soaking, injection, and vacuum tumbling is one of the most important and convenient procedures to improve meat quality and tenderness. Mixtures containing water, salt, acidic marinades, vinegar, and fruit juices were generally utilized for marinating the meat. In terms of penetration and saving the ageing time, injection is one of the most well-known and widely utilized techniques for meat marinating (Mazaheri Kalahrodi et al., 2020). Meat tenderization through marinating occurs by two primary mechanisms; the first is through decreasing the pH leading to expanding and dissolving the connective tissues and muscle proteins. The second is by providing appropriate conditions to increase the action of intracellular proteases or proteolytic catalysts extricated from the fruits and vegetables. Adding the salts, such as sodium chloride, calcium salt, and phosphate modifies the quality of meat due to the improved ability to maintain the water (Kim et al., 2013). Broccoli (Brassica oleracea var. Italica) is one of the most significant and abundant vegetables which was considered in terms of its taste, anti-cancer, and antioxidant components i.e., sulfurfan, indole-3-carbinol, and selenium. It was presumed that the metalloprotease, cysteine, serine, and aspartic proteases present in the broccoli juice display proteolytic activity on the myofibrillar proteins and connective tissues. Four cysteine proteases and one aspartic protease were recognized in the broccoli juice, which were similar to papain protease (Wang et al., 2004; Rostamani et al., 2021). The most enzymatic activity of the broccoli juice was observed in low pH conditions. The proteolytic activity of the broccoli is equal to 16.9 U/g in acidic pH and the density of Brassica oleracea proteases is about 45-70 kDa (Sun et al., 2016). Furthermore, traditional balsamic vinegar is a conceivably healthy flavoring with a high level of cancer preventive constituents and is rich in phenolic acids and flavonoids (Verzelloni et al., 2007). Nevertheless, there are limited investigations on the meat-softening strategies with balsamic vinegar (Mazaheri Kalahrodi et al., 2021). Therefore, the role of beefsteak marinating with broccoli juice and balsamic vinegar and their effect on the meat quality attributes during 48 hours of tenderization period were investigated.

Firstly, fresh broccoli was homogenized. Then, the blended material was compacted in a triple-layer cheesecloth, and the juice was extracted and centrifuged at 16,000 × g for 5 min at 4 °C. The resulting supernatant (pH 6.56; extraction efficiency: 10.4%) was poured into the topped microcentrifuge tubes and was kept at -18 °C until further testing. Then, the fat-free beefsteaks with a weight of around 1 kg were cut into cubic pieces (10 cm×10 cm×10 cm). Based on the preliminary studies and minimal adverse organoleptic changes, three marinade solutions containing broccoli juice and balsamic vinegar were prepared and injected into the beefsteak cuts as follows: Control: beefsteak without marinade, A: 2.6 g broccoli juice injected into 100 g beefsteak, B: 10 mL balsamic vinegar injected into 100 g beefsteak, C: 2.6 g broccoli juice + 10 mL balsamic vinegar injected into 100 g beefsteak. For better distribution, the treated samples were gently massaged by hand for about 1 min. Then, all samples were transferred to the polyethylene sacks, and were stored at the refrigerated temperature (4 °C) and evaluate the influence of meat marinating on designed tests consisting the pH, Warner-Bratzler shear force, water holding capacity, myofibril fragmentation index, myofibrillar protein solubility, peroxide value, thiobarbituric acid index and the acidic value at 1, 3, 24, and 48 hours intervals. Different samples were used to carry out the time-dependent analysis.

At first glance, the effect of marinade variant, tenderization period as well as their interaction on the evaluated parameters was significant (P<0.05). Accordingly, marinating beefsteak with broccoli juice and balsamic vinegar significantly (P<0.05) reduced the pH and Warner-Bratzler shear force over time. Besides, marination considerably (P<0.05) increased water holding capacity, myofibril fragmentation index, myofibrillar protein solubility, peroxide value, thiobarbituric acid index and the acidic value of all samples compared to control during 48 hours of refrigerated storage. The results of this study showed that the best quality and texture characteristics lead to tenderness preferred by consumers can be achieved by applying 2.6% broccoli juice and 2.6% broccoli juice + 10% balsamic vinegar. Apparently, by increasing the duration of cold storage, the beef tenderness increased. Therefore, the minimum Warner-Bratzler shear force (70.88 N) and maximum solubility of myofibrillar proteins (134.30 mL/g) were observed in the combined treatment at the end of storage (P<0.05). Besides, correlation between myofibril fragmentation index versus myofibrillar protein solubility (R2 = 0.88), peroxide value versus acidic value (R2 = 0.87), and thiobarbituric acid index versus acidic value (R2 = 0.85) of marinated beefsteak with broccoli juice and balsamic vinegar were direct, while indirect relationship was recognized between Warner-Bratzler shear force and myofibrillar protein solubility (R2 = 0.93).

The effect of different treatments on the tenderness and oxidative stability of marinated beefsteaks indicated that the broccoli juice contains efficient proteases that are better activated under acidic conditions. However, acidic conditions make the samples more susceptible to fats oxidation. Thus, it can be concluded that by optimizing the formulation of the broccoli juice and broccoli juice+balsamic vinegar marinades, they could be used as natural meat additives to improve the physicochemical and structural attributes of the beefsteak. Hence, broccoli juice and balsamic vinegar can be used as an effective marinade on a domestic and/or industrial scales as well as their nutritional benefits in preventing background diseases.