Impact of a phenol-enriched extract from olive vegetation water on the oxidative stability of low-nitrite würstels

The reduction of nitrites in cooked meat products is becoming a topic of primary importance, both for manufacturers and for consumers. However, their complete or partial replacement with a single natural compound is a challenge, due to the multifunctional characteristics of nitrites. One possible approach is the use of natural antioxidants from Mediterranean vegetal sources, such as olives and their processing by-products, which are rich in phenolic compounds. In particular, olive mill wastewaters (OMWW) generated during virgin olive oil production contain the majority of hydrophilic phenols (mainly secoiridoids and its derivates, which are found exclusively in the Oleaceae family), which are known to have high antioxidant and antimicrobial activities. Thus, if phenols are extracted from OMWW and purified by suitable membrane technology, they can be used for the formulation of healthier cooked meat products, with a reduced content of nitrate salts. The aim of this study was to evaluate the effect of an extract rich in phenols (PE), obtained from OMWW, on the oxidative stability and sensory characteristics of steam-cooked and grilled würstels during storage. The steam cooked würstels were prepared with beef (50%), lean pork (20%) and lard (30%), ice (20%), salt (1.25%), ascorbic acid (0.02%), aromas (0.33%) and liquid smoke (0.05%). The ingredients were homogenized until complete emulsion and, the dough was then divided into four batches: Control (NO2 150 mg/kg) and 3 PE-enriched samples (W1, W2 and W3, with PE 200 mg/kg + NO2 35/150/0 mg/kg). The emulsion was bagged into a collagen bowel and cooked in a steam oven until 72°C. After cooling in the blast chiller, würstels were peeled, vacuum-packed, pasteurized at 75°C for 20 min and stored under alternating exposure to fluorescent light at 4±2°C for 30 days. Steam cooked würstels were sampled at fixed time periods (0, 15 and 30 days of storage) and frozen at -80°C. At the same sampling times, the same number of steam cooked würstels from each batch were grilled at 200°C for 3.30 min per side until 70°C was reached at core. After processing and grilling, about 60% of total phenols were retained in PE samples. Regarding primary lipid oxidation, peroxide value (PV) in the control sample tripled in 30 days, while in W1 and W3 samples the final PV were 74% and 71% lower, respectively. Furthermore, no significant effect of storage on the PV of PE samples was observed. The steam-cooked control sample showed an increase in both conjugated dienes and trienes during storage, while these parameters remained almost constant in ungrilled PE samples. After grilling, all samples showed the classical bell-shape behavior of primary oxidation products. Regarding secondary lipid oxidation, VOCS largely confirmed the role of PE in limiting the increase of C5 and C6 saturated aldehydes that derive from lipid oxidation, being up to 36% lower in PE samples than in the control after 30-day storage, and up to 25% lower after grilling. In addition, grilled samples had TBARs values that were about 2 times higher than those of steam-cooked würstels, confirming the pro-oxidant effect of grilling. However, TBARs in both steam-cooked and grilled control würstels were lower than those of the PE samples during storage. Regarding COPs and COR%, no significative differences were found between PE and control steam-cooked würstel samples. No taste anomalies were detected for all products, confirming their stability during chilled displaying. Samples were only discriminated by a grayer color, which is due to the addition of a lower quantity of NO2 in the formulation of PE samples. This study confirms that it is possible to produce healthier low-nitrate würstels with improved oxidative stability by using PE from OMWW, thus representing a good strategy to valorize by-products of the olive oil food chain and to promote industrial symbiosis.