Supercritical extracts of wild thyme (Thymus serpyllum L.) by-product as natural antioxidants in ground pork patties
Introduction
Numerous ground meat products (e.g. patties, meatballs, fresh sausages) and traditional dishes (e.g. sarma, moussaka) are very popular in Serbia and other Balkan countries, chiefly due to their convenience, price and extraordinary flavor (Djordjević et al., 2018). Due to their high flexibility and adaptability, ground meats are popular in the fast-food industry, stores, restaurants and households with great potential in the development of functional meat products (Vasilev et al., 2017).
Besides microbiological growth in processing and during the storage, oxidation of both, lipids and proteins are the key causes of quality deterioration in a fresh or frozen meats and meat products (Xu, Zhu, Liu, & Cheng, 2018). This induces adverse changes in sensory attributes (flavor, color and texture), nutritional value, and forms potential toxic compounds in the products (Cunha et al., 2018; Kumar, Yadav, Ahmad, & Narsaiah, 2015). Several studies have identified that ground meats oxidizes more rapidly than whole cuts (Cullere et al., 2019; Dal Bosco et al., 2019) as grinding disintegrates muscular membranes, and catalases reactions among prooxidant molecules and unsaturated compounds. This particularly targets polyunsaturated fatty acids, while all reactions together promote the formation of free radicals and further propagation of oxidative reactions (Cullere et al., 2019).
The usage of synthetic antioxidants is one of the major approaches for preventing this oxidative reactions, and for extending the shelf life of meat products (Gómez et al., 2018). However, they have various negative healthy connotations, so the modern meat industry is oriented towards various natural alternatives while focusing on plant extracts and essential oils (Pateiro et al., 2018; Šojić et al., 2017, 2019). Plant extracts are interesting since they are marked as GRAS (generally recognized as safe) and have a broad acceptance from consumers (Kumar et al., 2015; Putnik et al., 2018). Additionally, quite often they are less expensive and more effective than their synthetic counterparts (Šojić et al., 2018).
To this end phytochemical screening of wild thyme by-products (Thymus serpyllum L.) extracts confirmed the presence of various bioactives. This includes flavonoids, tannins, terpinoids and other compounds with antimicrobial, antioxidant, antitumor, hypoglycemic and hematological effects (Jovanović et al., 2017; Muhammad Naveed Mushtaq et al., 2013; Nikolić et al., 2014; Wesolowska, Grzeszczuk Jadczak, Nawrotek, & Struk, 2015). Aside from the plants, previous findings revealed that the utilization of the extracts from agro-food industrial by-processing is challenging for further applications in food industry (Panić et al., 2019; Pavlić et al., 2018).
Currently, sustainable extractions that meet the principles of “green” concepts, such as supercritical fluid extraction (SFE), are in the focus of many food science studies that aimed to investigate the application of both, essential oils and the extracts for meat processing (Tomović; Šojić, Jokanović; Škaljac, & Pavlić, 2019). SFE was developed in order to overcome disadvantages of both organic solvent extraction and hydrodistillation and to reduce solvent consumption. Additionally, to preserve energy, shorten processing time, improve selectivity and extraction yield while preventing degradation of target compounds caused by elevated temperature. Furthermore, SFE enables the production of high-quality extracts without the risks of human toxicity caused by traces of organic solvents. At the same time SFE has the ‘green nature’ of the processing that are without negative environmental impacts (Pavlić et al., 2018).
In past years, the application of thyme plants extracts in meat and meat products have been assessed in several studies (Bošković et al., 2017; El Abed et al., 2014; Abdel-Naime et al., 2019, Jayari et al., 2018). El Abed et al. (2014) determined that the addition of Thymus capitata essential oil at concentrations of 0.25 and 1.0% efficiently reduced bacterial growth in minced beef samples. Additionally, Bošković et al. (2017) observed that thyme essential oil at concentration of 0.6% efficiently suppressed the growth of Salmonella spp. in minced pork, that was packaged under vacuum or MAP and stored at 3 °C during 15 days. In the study of Jayari et al. (2018), antibacterial activity was demonstrated against pathogenic bacteria (Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Pseudomonas aeruginosa) when Thymus capitatus and Thymus algeriensis essential oils (3%) were applied in minced beef. Since there is no available literature about the application of wild thyme extracts as antioxidants in meat products with respect to overall quality, the objectives of this investigation were to assess such properties on physicochemical, microbiological, and sensory quality in ground pork patties.
Section snippets
Plant material
By-products of a native wild thyme (Thymus serpyllum L.) from Serbia was donated by the local industry of herbal infusions, Macval Tea D.O.O. (Novi Sad, Serbia). Powdered herbal material were used for production of low-particle size fractions and discarded as by-product after vibro-sifting and fractionation.
Chemicals
2-Thiobarbituric acid, Trichloroacetic acid; Butylhydroxytoluene (BHT), n-Hexane, 1,1,3,3-Tetraethoxypropane, Ellmans reagent (DTNB), and Bovine serum albumin (BSA) all of analytical grade
Chemical profiling and antioxidant activity of T. serpyllum extracts
Wild thyme by-products were valorized as raw material for recovery of antioxidant-rich terpenoids with application as natural additives in meat products. Total extraction yields obtained in samples SFE1 (100 bar and 40 °C) and SFE2 (350 bar and 50 °C) were 0.93% and 2.93%, respectively. Results of SFE1 were in accordance with literature since Žižović, Stamenić, Orlović, and Skala (2006) reported that the wild thyme yield obtained at the same SFE conditions was 0.9%. SFE1 conditions were
Conclusion
By-product of a wild thyme (Thymus serpyllum) from filtered herbal infusion manufacturing was valorized as raw material for recovery of lipid extracts. SFE was applied as environmental method to obtain extracts with high contents of terpenoids, strong in vitro antioxidant activity and potential for utilization as novel “green” food additives. Application of SFE1 and SFE2 decreased discoloration in ground pork patties, successfully reduced lipid and protein oxidation and inhibited microbial
CRediT authorship contribution statement
Branislav Šojić: Conceptualization, Methodology, Writing - original draft. Vladimir Tomović: Conceptualization, Supervision. Sunčica Kocić-Tanackov: Investigation, Writing - original draft. Danijela Bursać Kovačević: Writing - review & editing. Predrag Putnik: Writing - review & editing. Živan Mrkonjić: Investigation, Resources. Saša Đurović: Investigation, Writing - original draft. Marija Jokanović: Software, Formal analysis. Maja Ivić: Resources, Formal analysis. Snežana Škaljac: Resources,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was financially supported by Ministry of Education, Science and Technological Development, Republic of Serbia (451-03-68/2020-14/200134 and 451-03-68/2020-14/200051).
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