Supercritical extracts of wild thyme (Thymus serpyllum L.) by-product as natural antioxidants in ground pork patties

Highlights

• Wild thyme lipid extracts were obtained by supercritical fluid extraction (SFE).

• Extracts were protective against color degradation.

• Extracts were utilized as natural additives in ground pork patties.

• Extracts prevented lipid and protein oxidation in pork patties.

• Extracts prolonged shelf-life in applied meat products.

Abstract

The effects of wild thyme by-products (Thymus serpyllum L.) from supercritical fluid extraction SFE1 (100 bar and 40 °C) and SFE2 (350 bar and 50 °C) on the quality of ground pork patties evaluated by pH, CIE-color, lipid (TBARS test) and protein oxidation (thiol group content) and microbiological profile. SFE extracts were added to ground pork patties as: 0.075 μL/g of SFE1 (T1), 0.150 μL/g of SFE1 (T2), 0.075 μL/g of SFE2 (T3), 0.150 μL/g of SFE2 (T4), while SFEs (T5) was control without any extracts. SFE1 and SFE2 were protective against color degradation. Moreover, the addition of SFE1 and SFE2 significantly reduced lipid and protein oxidation in the patties (p ≤ 0.05). Furthermore, lower concentration of SFE2 reduced total plate count to <6 log cfu/g after 3 days of storage. Obtained results indicated that SFEs of wild thyme by-product are useful as natural antioxidants and antimicrobial agents in meat processing.

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.