Materials

The quality of three processed meat products, i.e. frankfurters, Polish kabanos sausages, and salami, was compared with the corresponding plant-based analogs. The ingredient lists of meat products and their analogs, declared by manufacturers, are presented in Table 1. The analyzed products were manufactured by the leading Polish suppliers, and they were purchased between October and December 2021 in a hypermarket belonging to a popular international retail chain operating in Europe and Asia. Five items from five different product batches supplied by the same manufacturer were analyzed in each examined product category. The analyzed items were vacuum-packaged in bags to standardize the parameters of the compared products, and their quality was evaluated before the use-by date declared by the manufacturer. The compared products were refrigerated under identical conditions (4°C) until analysis.

Proximate chemical composition analysis

The proximate chemical composition of the products was determined in accordance with the Official Analytical Methods [AOAC, 2005]: moisture content (sample drying at a temperature of 105°C to constant weight), total protein content (Kjeldahl method using Kjeltec™ 2200 auto distillation unit, FOSS Analytical, Hilleroed, Denmark), lipid content (Soxhlet extraction with diethyl ether using Soxtec™ 2050 auto fat extraction system, FOSS Analytical), and ash content (sample incineration at a temperature of 550°C to constant weight).

Fatty acid profile determination

Fatty acid profile in the products was analyzed according to the analytical procedure described by Daszkiewicz & Gugołek [2020]. Fatty acids were separated on the VARIAN CP-3800 gas chromatograph (Varian Inc., Palo Alto, CA, USA) with a flame ionization detector (FID) and a capillary column (length – 50 m, inner diameter – 0.25 mm, film thickness – 0.25 μm). Helium was used as a carrier gas (flow rate – 1.2 mL/min). The results were expressed as proportions (%) of individual fatty acids in total fatty acids.

Color parameter determination

The color parameters – lightness (L^*), redness (a^*) and yellowness (b^*) – were measured in the CIE Lab system [International Commission on Illumination, 1978] using the HunterLab MiniScan XE Plus spectrophotometer (Hunter Associates Laboratory, Reston, VA, USA) with illuminant D65, 10° standard observer angle, and 2.54 cm diameter aperture. The measurements were performed at three different points over the surface area of samples (salami slices and ground frankfurters and kabanos sausages). Chroma (C^*) values were calculated with the formula (1):

Measurement of pH

The pH values of products were measured with the use of a Polilyte Lab electrode (Hamilton Bonaduz AG, Bonaduz, Switzerland) and an inoLab level 2 pH-meter equipped with a TFK 325 temperature sensor (WTW Wissenschaftlich-Technische Werkstatten GmbH, Weilheim, Germany). The samples of products were homogenized in redistilled water (ratio 1:1, w/v) before measurement [Daszkiewicz & Gugołek, 2020].

Statistical analysis

The results were processed statistically using STATISTICA software ver. 13.3 (TIBCO Software Inc., Palo Alto, CA, USA). The effect of the experimental factor (product type – meat products vs. their plant-based analogs) on the evaluated quality attributes of the products was analyzed by Student’s t-test. The significance of differences between groups was determined at p≤0.05.

Proximate chemical composition of meat products and their plant-based analogs

The proximate chemical composition of the compared products is presented in Table 2. Meat products had higher (p≤0.05) dry matter content than meat substitutes, mostly due to their higher (p≤0.05) lipid content. Salami and frankfurters had also higher (p≤0.05) ash content than their plant-based counterparts. Salami contained more (p≤0.05) protein, whereas frankfurters and kabanos sausages contained less (p≤0.05) protein than their respective analogs.

The differences in the proximate chemical composition of meat products and their vegetarian alternatives resulted from the use of different ingredients and production technologies. Plant-based meat analogs contain a considerably lower amount of lipids, a lot of protein, and different amount of water to achieve the desired textural properties and health benefits appreciated by consumers [Kyriakopoulou et al.,2021]. However, the actual protein content of plant-based products may be difficult to determine. It may vary depending on the value of the nitrogen-to-protein conversion factor (NPCF) in the Kjeldahl method. According to Fujihara et al., [2008], the NPCF of 6.25 has been historically applied to all proteins based on the assumptions that all proteins contain 16% nitrogen (100/16 = 6.25) and that all nitrogen is derived from protein. However, research [Krul, 2019] showed that the NPCF of 6.25 overestimates the protein content of many food products due to differences in amino acid profiles and the presence of non-protein nitrogen. This is an important consideration when assessing the actual nutritional and economic value of food products. Koletzko & Shamir [2006] suggested that the use of the NPCF of 6.25 instead of 6.38 for all dairy products would lead to a loss of approximately EUR 80 million in Europe. Therefore, all food market actors (consumers, producers of food raw materials, food processing companies, sales specialists, and nutritionists) are interested in solving the above problem and establishing NPCF values applicable to different proteins in food products that are already on the market and those that will be introduced in the future. This will apply, in particular, to analogs of traditional meat products whose quality, nutritional value and production costs should be assessed equitably. The absence of standardized methods for determining food-specific NPCF values has resulted in continued use of 6.25 [WHO/FAO, 2019]. The NPCF of 6.25 was also used in this study, but it was confronted with the average values of the ingredient-specific NPCF proposed for soybean protein (5.70) [WHO/FAO, 2020] and wheat protein (5.81) [Fujihara et al., 2008] contained in the analyzed plant-based products. As a result, the protein content of vegetarian frankfurters, kabanos sausages and salami, determined by two different methods, differed by 1.84, 3.02 and 1.36 percentage points, respectively (Table 2). The above information may be important for persons who need a balanced diet, including older adults and individuals with special nutritional needs [Reid-McCann et al., 2022], especially that the value of vegetable protein can be decreased due to amino acid composition (insufficient concentration of one or several essential amino acids). According to Hertzler et al. [2020], legumes are often deficient in sulfur-containing amino acids (methionine and cysteine), whereas cereals are poor in lysine. The need for accurate protein quantification in plant-based products was also emphasized by Bakaloudi et al. [2021] who found that vegan diets were lower in protein than all other diet types. This information and the fact that consumers’ knowledge about vegetarian and vegan diets is often insufficient suggest that followers of such diets could have higher risk of developing nutrient deficiencies. Bakaloudi et al. [2021] reported that vegans had low intake of vitamins B₂, niacin (B₃), B₁₂and D, as well as iodine, zinc, calcium, potassium, and selenium. The above authors found that daily vitamin B₁₂intake among vegans was considerably lower (0.24–0.49 μg) than the recommended level (2.4 μg), and calcium intake was also below the norm (750 mg/day) in most vegan diet followers. According to Sanne & Bjørke-Monsen [2022], nutritional education should be improved as vegetarian and vegan diets are becoming increasingly popular. The cited study revealed gaps in nutritional knowledge about vegetarian diets even among Norwegian medical students who declared to be vegetarians.

Bryngelsson et al. [2022] assessed the nutritional quality of plant-based meat analogs available on the Swedish market based on three nutrition labeling systems. In terms of macronutrient content, most categories of meat analogs were healthier options to meat references, primarily due to their higher fiber content and lower content of lipids with saturated fatty acids. In terms of salt content, many plant-based meat analogs were healthy alternatives to processed meat products, but often less healthy options to unprocessed meat products. Similar analyses performed by Cutroneo et al. [2022] for commercial meat analogs available on the Italian market revealed that all analogs had higher fiber content, whereas plant-based burgers and meatballs had lower protein content than their meat counterparts. Sliced meat analogs had also lower salt content. All plant-based products had longer lists of ingredients than the corresponding animal meat products. Due to their long lists of ingredients, most of which are highly refined, meat analogs face criticism for being artificial products [Kyriakopoulou et al., 2021]. Modern consumers expect food products to be healthy, nutritious, and as natural as possible (minimally processed and without additives) [Hüppe & Zander, 2021].

Fatty acid profile of meat products and their plant-based analogs

The fatty acid profile of the compared products, including saturated fatty acids (SFAs), unsaturated fatty acids (UFAs) and fatty acid ratios, are presented in Table 3, Table 4 and Table 5, respectively. Vegetarian frankfurters and salami were characterized by higher (p≤0.05), i.e. more desirable, values of all analyzed indicators of the nutritional value of lipids than their meat counterparts. Vegetarian kabanos sausages had lower (p≤0.05) ratios of unsaturated to saturated fatty acids (UFAs/SFAs), monounsaturated to saturated fatty acids (MUFAs/SFAs) and ratio of hypocholesterolemic fatty acids (UFAs+C18:0) to hypercholesterolemic fatty acids (SFAs–C18:0) (DFAs/OFAs).

The differences in the fatty acid profiles of meat products and their plant-based analogs resulted from the different origin of lipids. Long-chain fatty acids, such as palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), and linoleic acid (C18:2), predominate in lipids of meat and meat products, whereas the contents of polyunsaturated fatty acids (PUFAs) are low [Bohrer, 2019], which was also observed in this study. The proportion of PUFAs is particularly low in meat from ruminants, because they undergo biohydrogenation in the rumen. De Smet et al. [2004] reported that the average PUFAs/SFAs ratio in beef, lamb, and pork (steaks and chops) purchased in supermarkets in the United Kingdom was 0.11, 0.15 and 0.58, respectively. The above ratios are even lower in meat products because processing affects PUFAs [Domínguez et al., 2019].

Vegetable oils/fats and animal fats differ in fatty acid composition and the mutual proportions of fatty acid groups. Different types of edible oils/fats are also characterized by considerable differences in their fatty acid profiles. Orsavova et al. [2015] analyzed the fatty acid composition of 14 edible vegetable oils (safflower, grape, Silybum marianum, hemp, sunflower, wheat germ, pumpkin seed, sesame, rice bran, almond, rapeseed, peanut, olive, and coconut oil) and found that the contents of the major fatty acids varied widely: C16:0 – from 4.6% to 20.0%, C18:1 – from 6.2% to 71.1%, and C18:2 – from 1.6% to 79%. The proportions of fatty acid groups were determined in the following ranges: SFAs – from 6.3% (rapeseed oil) to 92.1% (coconut oil), MUFAs – from 6.2% (coconut oil) to 72.8% (rapeseed oil), and PUFAs – from 54.3% (pumpkin seed oil) to 79.1% (sunflower oil). Technological processes and refinement techniques (pressing, fractionation, isomerization) can also alter the fatty acid composition of vegetable oils/fats [Bohrer, 2019].

The vast majority of vegetable oils/fat used in the production of meat analogs contain mostly UFAs. In the present study, vegetarian frankfurters and salami were produced with the use of rapeseed oil, which contributed to their desirable fatty acid profiles. Increased contents of UFAs, in particular PUFAs, in lipids of plant-based meat analogs, deliver health benefits to consumers. However, they are also susceptible to oxidation, leading to the formation of multiple chemical compounds that negatively affect the sensory properties (flavor, color) of the products, and exert adverse health effects [Domínguez et al., 2019]. Physical technological treatments that can reduce the oxidation of PUFAs in oils include pre-emulsification of oil with non-meat proteins and microencapsulation [Lima et al., 2022b].

Fatty acids have different melting temperatures, therefore oils used in the production of plant-based meat analogs should be carefully selected because they affect the texture of the final product. In order to impart meat-like consistency and mouthfeel, meat alternatives are produced with the use of solid fats extracted from tropical fruit such as coconuts or, less frequently, cocoa beans [Sha & Xiong, 2020]. The dominant fatty acids in coconut oil are lauric acid (12:0), myristic acid (14:0) and palmitic acid (16:0), which account for 46%, 17% and 9% of total fatty acids, respectively [Boemeke et al., 2015]. In the current study, coconut oil was used in the production of vegetarian kabanos sausages, which explains the low values of indicators characterizing the nutritional value of lipids in this product, relative to vegetarian products containing rapeseed oil and meat products. Coconut oil consists mostly of SFAs that account for approximately 90% of its total fatty acids, which has stirred a debate about its potential adverse health effects, by analogy with animal fats. A meta-analysis of clinical trials conducted by Neelakantan et al. [2020] revealed that the consumption of coconut oil contributed to a greater increase in low-density lipoprotein (LDL) cholesterol levels than the consumption of non-tropical vegetable oils. However, coconut oil was not significantly associated with the markers of glycemia, inflammation or obesity. According to Hewlings [2020], the health implications of SFAs should be analyzed in both quantitative (total SFAs content) and qualitative (proportions of individual SFAs) terms. A good example is coconut oil which is classified as saturated fat although most of its fatty acids are medium-chain ones. In contrast, beef contains mostly long-chain SFAs. Medium-chain SFAs are absorbed differently than long-chain SFAs; the former have been associated with several health benefits, including improved metabolic and cognitive functions in humans [Roopashree et al., 2021], which may be linked with reduced oxidative stress [Mett & Müller, 2021]. Nevertheless, the dietary intake of UFAs, in particular PUFAs, should be increased [Snetselaar et al., 2021]. Further research is needed to investigate potential relationships between individual SFAs and the risk of developing certain diseases in order to establish objective guidelines for the dietary inclusion or elimination of selected SFAs.

pH and color of meat products and their plant-based analogs

The pH values and color parameters of the compared products are presented in Table 6. The greatest difference (p≤0.05) in pH was noted between salami and its plant-based analog. The pH of salami was considerably lower because it was manufactured with the use of starter bacterial cultures. According to Bis-Souza et al. [2020], salami is a typical dry fermented sausage, and selected starter cultures are used in the process of its fermentation. Bacteria produce lactic acid that acidifies the product, imparts a distinctive taste, and extends its shelf life [Laranjo et al., 2017]. Considerable differences in average pH values (p≤0.05) were also found between frankfurters and kabanos sausages vs. their plant-based analogs. Vegetarian frankfurters had a higher pH (p≤0.05) than their meat counterparts, and traditional kabanos sausages had a higher pH (p≤0.05) than their vegetarian alternatives. Therefore, there is no clear correlation between product type (meat product vs. meat analog) and its active acidity.

Color measurements revealed (Table 6) that plant-based meat analog of frankfurter was darker in color (lower L^* value, p≤0.05) than its traditional counterpart. All vegetarian products were also characterized by higher (p≤0.05) values of parameters a^* (redness) and b^* (yellowness), and, in consequence, higher (p≤0.05) chroma (C^*) values.

The color of meat alternatives is affected by the type and amount of coloring agents that are added to mimic the color of traditional meat products. According to the information on the labels of the plant-based products analyzed in the present study, they contained the following colorants: pepper extract, fenugreek extract (Trigonella foenum-graecum L.), concentrated beetroot (Beta vulgaris L. subsp. vulgaris) juice, iron oxides and hydroxides. The effect exerted by colorants on the color of meat substitutes depends not only on their type, but also stability. This applies in particular to natural pigments whose stability and brightness are affected by exposure to light, temperature, and pH [Harsito et al., 2021]. Similar observations were made by Ekielski et al. [2013] who analyzed red pepper extract and found that its color was unstable under exposure to intensive light, and that natural pigments were more sensitive to light intensity than to increasing storage temperature. Regardless of the content and transformations of colorants, the color of food products may also be affected by other factors. Herlina et al. [2021] suggested that the darker color (lower brightness) of plant-based meat analogs may be due to a high content of carbohydrates that participate in Maillard reactions. Lipid autooxidation may also significantly affect the color of plant-based products have high contents of UFAs [Barden & Decker, 2016]. According to Kim et al. [2014], moisture can act as a substrate for lipid oxidation. In the current study, plant-based meat analogs contained more carbohydrates (according to the manufacture’s declaration), UFAs (except for kabanos sausages), and water than traditional meat products, which could be responsible for their darker color.