Effects of replacing beef fat with pre-emulsified pumpkin seed oil on some quality characteristics of model system chicken meat emulsions

In this study, the effects of adding pumpkin seed oil (PSO) in water emulsion to model system chicken meat emulsions (MSME) on product quality and oxidative stability were investigated. MSME were produced by replacing 25% (P25) and 50% (P50) of beef fat with PSO-in-water emulsion (PSO/W) while control treatment was prepared with only beef fat. Addition of PSO/W to the formulation resulted in significant differences in chemical composition and pH values of both raw and cooked MSME treatments. The use of PSO/W produced significant improvements to emulsion stability, oxidative stability and cooking yield of MSME. It was determined that the use of PSO/W formulation results in decreased total expressible fluid values and increased cooking yields of the emulsions. It was observed that the highest cooking yield and the lowest total expressible fluid were found in the sample containing 50% PSO/W. It should be a feasible strategy to produce fat-reduced meat products with healthier lipid profiles by using PSO/W.


Introduction
Fat has an important role in meat products; it helps emulsion stabilization, improves binding properties, water holding capacity and cooking yields as well as provides sensorial characteristics such as juiciness [1,2]. However, diets with high animal fat contents have been related to increased obesity, cardiovascular disease and coronary heart disease due to their high saturated fatty acid and cholesterol contents [3,4,5]. Thus, the meat industry has begun to work on reformulation strategies to produce healthier meat products by decreasing saturated fatty acids, decreasing cholesterol and adding natural antioxidants. One of these strategies is using formulations with vegetable oils, since they are free of cholesterol and have a higher ratio of unsaturated to saturated fatty acids than animal fats [6,7,8]. However, the use of vegetable oils directly in product formulation can cause technological problems and quality loss in meat products [9]. Therefore, pre-emulsions constitute an innovative approach in low-fat product formulations since they can be used in fat reduction processes, beneficially modifying fatty acid profiles, masking off flavors and improving the sensory properties of products [10,11,12].
Pumpkin seed oil (PSO) is rich in bioactive compounds such as polyunsaturated (linoleic and linolenic) fatty acids, β-carotene, lutein, β-tocopherol, chlorophyll and phytosterols, and it is widely used in salads around the world, especially in Hungary, Slovenia and Austria. Due to its color and foaming problem, PSO cannot be used in manufacturing processed foods or processes such as frying [13].
To the best of our knowledge, no research has been performed regarding utilization of PSO in meat model systems or meat products. Therefore, the objective of this study was to investigate the effect of using PSO in oil-in-water emulsion as a fat replacer on the technological characteristics and oxidative stability of model system chicken meat emulsions.

Materials and Methods
The pumpkin seed oil-in-water (PSO/W) emulsion was prepared according to Poyato et al. [14] with modifications. The aqueous phase was prepared with the mixture of egg white powder (5 g/100 g) and water (45 g/100 g). The oil phase (50 g/100 g) was added to the aqueous phase after both phases were heated separately to 55°C. After the emulsification process (6000 rpm, Ultra-Turrax® T25basic), the emulsion was cooled to room temperature and PSO/W was kept under refrigeration (4°C) until use. Three different model system chicken meat emulsions (MSME) were prepared following the procedure described by Cofrades et al. [15] with modifications (table 1). One contained only beef fat (C), two other MSME were prepared by replacing 25% (P25) and 50% (P50) of beef fat with PSO/W. Chicken breast meat and beef fat were passed through a grinder with a 3-mm plate (Arnica, Turkey). The minced meat was homogenized for 1 min in a kitchen-type mixer (Tchibo, Germany) which was placed in cooling bath (2°C). Fat or PSO/W, half of the ice, plus salt and sodium tri-polyphosphate (STPP) were added and mixed for 1 min. The other half of the ice was added and mixed again for 2 mins. Portions of each emulsion (approximately 25 g) were placed in Falcon tubes (50 ml), which were hermetically sealed then centrifuged at 4500 rpm at 4°C for 1 min to eliminate any air bubbles. Samples were heat-treated for 30 min in a water bath at 70 °C, then cooled to room temperature for further analyses. Moisture, protein and ash contents of raw and cooked MSME treatments were determined by AOAC methods [16]. Fat content was evaluated according to Flynn and Bramblet [17], pH values of emulsions were measured by using a pH-meter (WTW pH 3110 set 2, Germany) equipped with a penetration probe. Emulsion stability, recorded as total expressable fluid (TEF), and water holding capacity (WHC) were determined according to Hughes et al. [18]. The weights of meat emulsions before and after cooking were recorded and the cooking yield calculated. Lipid oxidation on days 0, 1 and 4 of storage was evaluated by the TBA method as described by Witte et al. [19]. The data were analyzed by one-way ANOVA using the SPSS software version 20. Differences among the means were compared using Duncan's Multiple Range test. A significance level of p<0.05 was used for evaluations. Chemical compositions and pH values of raw and cooked MSME treatments are shown in table 2. Replacing beef fat with PSO/W showed an increasing effect on moisture and protein contents of raw MSME (p<0.05), since PSO/W contributed water and protein (egg white powder) to the formulation. The fat content of raw MSME decreased with respect to the incremental addition of PSO/W (p<0.05), while no significant differences were observed in ash content (p>0.05). Addition of PSO/W decreased the pH values of raw MSME because of lower pH value of PSO [20].
The highest moisture content was found in P50 after cooking (p<0.05), probably the result of the lower TEF of this treatment. Protein and ash contents of cooked MSME treatments were similar (p>0.05). Addition of PSO/W to the formulation showed significant effects on fat content and pH values of cooked MSME. The highest fat content was found in P25 (p<0.05). The fat content of MSME with added PSO/W (P25 and P50) was more or less constant in raw and cooked MSME treatments; this could be the result of higher emulsion stability of these formulations. The aim of adding pre-emulsified fat or oils is having stable characteristic in meat products. WHC, cooking yield and emulsion stability (TEF%) results of MSME are shown in table 3. WHC of the MSME formulations were similar (p>0.05). PSO/W addition to formulations showed significant effect on emulsion stability of treatments (p<0.05). The highest TEF% values were found in C treatment while replacing beef fat with PSO/W showed a decreasing effect on TEF% values of MSME treatments (p<0.05). Cooking yield depends on the ability of the protein matrix to stabilize both fat and water molecules [5]. The lowest cooking yield was observed in C treatment and higher cooking yields were found when beef fat was replaced with PSO/W (p<0.05). The higher protein content of P25 and P50 treatments could be the reason for their higher cooking yields and more stable emulsions, since more protein could have entrapped water and fat molecules in the system. It is well-known that emulsifiers are amphiphilic in their native state in emulsions because of their hydrophilic and hydrophobic interactions [21]. Another reason for the lower TEF% values and higher cooking yields in P25 and P50 formulations may be due to the amphiphilic properties of egg white powder in PSO/W. Lipid oxidation can have negative effects on the quality of meat and meat products since they can cause sensory attribute (color, texture, odor and flavor) and nutritional quality changes. TBA values of MSME treatments during 4-days storage are shown in table 4. The oxidative status of MSME is strongly influenced by the type of fat/oil used in the formulation. The lower TBA values were found when beef fat was replaced with PSO/W (p<0.05) and this trend was observed during the storage period (p<0.05). The lower TBA values in P25 and P50 could be the result of adding pre-emulsion, which provided a protective effect from lipid oxidation and also added an oil with antioxidant properties to the formulations [22]. There was a slight decrement in TBA values of P50 treatment on day 4, probably due to the result of decomposition of malondialdehydes by bacterial processes [23,24] or further oxidation of malondialdehydes to other products [25,26]. Although the highest TBA values were found in C treatment during storage, these oxidation values were below 1.0 (mg malondialdehyde/kg product), which is the accepted limit for rancidity in meat products [27,28].

Conclusion
The results of this study indicated that replacement of beef fat with pumpkin seed oil-in-water emulsions significantly affected chemical composition and pH values of raw and cooked MSME treatments. PSO/W addition to the formulations resulted lower total expressible fluid values, higher cooking yield and higher oxidative stability during storage. Our study showed that meat products with a healthier lipid profile could be manufactured by using pumpkin seed oil in pre-emulsions.