New anchovy burgers: a sustainable and nutritious alternative to red meat in fast food

Abstract

This study presents an innovative anchovy burger formulation optimized using response surface methodology and Ideal Profile method. The objective is to create a nutritious, appealing, and environmentally friendly alternative to traditional red meat burgers. The research utilized a two-tiered experimental approach: an initial screening using Plackett-Burman Design to evaluate the impact of various ingredients on cooking yield, texture, and moisture retention, followed by an optimization phase employing a Central Composite Design. Key findings revealed that oat fiber and potato flakes significantly enhance the burger’s cooking yield and sensory characteristics. The optimized formulation, comprising 4% oat fibers and 4% potato flakes, exhibited superior texture and consumer preference. Nutritional analysis demonstrates that the optimized anchovy burger outperforms conventional beef and popular fast food chain burgers in terms of protein content and dietary fibers, while also being a rich source of long-chain polyunsaturated fatty acids. This research contributes to the fast-food industry by offering a product that meets sensory and nutritional requirements while also promoting sustainability. The findings lay a foundation for future studies to further explore the interplay of sensory attributes and consumer preferences, potentially guiding the development of innovative and sustainable fast-food products.

Graphical Abstract

Introduction

The modern food landscape is experiencing a continuous increase in fast food consumption, driven by rapid urbanization and lifestyle shifts (Pachekrepapol et al., 2022). Despite being a staple in contemporary diets, the nutritional drawbacks of red and processed meat products, notably their high fat content and association with various health risks, have garnered substantial concern (Carvalho et al., 2019; Pachekrepapol et al., 2022). Furthermore, the production of red meat is highly resource-intensive, contributing significantly to carbon emissions and environmental degradation. In contrast, forage fish such as anchovies offer a more sustainable alternative due to their lower trophic level, which requires less feed and resources compared to livestock. Specifically, anchovies have a low carbon footprint and are highly efficient in converting feed into edible protein, making them an environmentally friendly choice (Xia et al., 2024). In a 2050 scenario where 10% of global ruminant meat consumption is replaced with forage fish in human diets, Xia et al. (2023) demonstrated significant reductions in ruminant-related total GHG emissions and land use by up to 15% and 10%, respectively. The study also indicated that this dietary change could increase the intake of DHA, EPA, vitamin B12, and calcium, particularly in regions with deficiencies.

The nutritional values of fish, especially forage fish like herring, sardines, and anchovies, are well-documented. These fish are characterized by lower levels of cholesterol and saturated fats, and a rich profile in essential amino acids and omega-3 fatty acids (Ben Atitallah et al., 2019). Recent studies suggest that substituting red meat with forage fish could not only save approximately 750,000 lives annually but also markedly decrease the global burden of diet-related non-communicable diseases (NCDs) (Xia et al., 2024). This substitution could be particularly beneficial in low- and middle-income countries, where forage fish are both affordable and abundant.

Amidst rising health consciousness, there is growing interest in healthier meat products that can satisfy nutritional needs without compromising sensory appeal. Strategies to curtail fat content in meat products, such as utilizing lean meat cuts or substituting fat with dietary fiber and water, have emerged, aiming to balance functional appeal and sensory properties (Carvalho et al., 2019). Furthermore, dietary fiber, known for its beneficial functional properties in mitigating cardiovascular disease, obesity, and other health conditions, has become a focal point in reformulating meat products for improved health outcomes (Carvalho et al., 2019).

In the domain of fish burgers, numerous studies have explored various formulation approaches, ranging from different fish species to the incorporation of vegetables or grains to enhance nutritional profiles and consumer acceptance. The innovative formulation of fish burgers, such as the incorporation of mashed pumpkin or potato, or dietary fiber, exemplifies the ongoing efforts to align fast food products with health and sustainability prerogatives (Ali et al., 2019; Carvalho et al., 2019). The selection of oat fiber and potato flakes in this study is driven by their established benefits in improving texture, moisture retention, and cooking yield in food products (Husein et al., 2019; Ramos-Diaz et al., 2022). Oat fiber is particularly valued for its high beta-glucan content, which is known to lower cholesterol and improve heart health.

The Response Surface Methodology (RSM) has proven to be an effective statistical and mathematical tool in optimizing food formulations to meet these demands, ensuring desirable sensory attributes while enhancing nutritional profiles (Russo et al., 2023). This methodology has been adopted in food science to optimize formulations and processing conditions, ensuring desirable texture and sensory attributes among other quality parameters (Yolmeh & Jafari, 2017). However, very few studies have evaluated the use of RSM for fish burger formulation (Presenza et al., 2022).

In the context of Mediterranean fisheries, the European anchovy (Engraulis encrasicolus) represents the most significant blue fish in terms of volume with a very low market value, making it an ideal ingredient for the development of a product for the large fast-food market (García-del-Hoyo et al., 2023). Besides being a cost-effective source of nutritious and highly digestible protein, it is important to underline the high content of very long-chain polyunsaturated fatty acids (docosahexaenoic and eicosapentaenoic acids), selenium, calcium and B12 vitamin (Gencbay & Turhan, 2016). This nutritional profile gives anchovies a functional food status, contributing to the prevention for cardiovascular, eye, brain and thyroid diseases (Speranza et al., 2012).

This study aims to innovate within the fast-food sector by developing an anchovy burger that not only appeals to the palate but also aligns with broader health and sustainability goals. By leveraging RSM, this research explores various fish burger formulations to maximize consumer acceptance while providing substantial health benefits.

Given the urgent need to address both health and environmental challenges, this research contributes to a growing body of evidence supporting the shift towards more sustainable and nutritious dietary options, paving the way for a healthier future.

Materials and methods

Anchovy burger preparation and ingredients selection

Fresh caught in the Gulf of Naples, ice-preserved and not eviscerated anchovies were purchased from the fish market in Pozzuoli (Italy). The average weight of the anchovies (n = 25) was 22.4 ± 7.5 g while the average length was 10.5 ± 1.1 cm. The anchovies were beheaded, eviscerated and placed for 1 h in a cold water solution at a temperature of + 4 °C containing 5% sodium chloride to properly bleed out the flesh (Lauzon et al., 2009). The anchovies were then filleted by removing the bone and tail. Notably, the skin of the anchovies was not removed since it is perfectly edible. While some fish processing plants remove the skin from small fish to obtain a white fish paste for further processing, we chose to retain the skin. This decision was made because the skin gives only a very light grey appearance to the fresh ground anchovies’ meat. Additionally, since burgers are typically grilled, resulting in browning on the surface, there is no need for a white burger that will become brown during grilling.

The fillets were then placed in a meat grinder with holes with a diameter of 0.5 cm. The ingredients selected for the experiments were: liquid egg white (AIA - Agricola Italiana Alimentare, Torino, Italy), potato flakes (Solanum tuberosum L), sunflower seed oil, and oat fiber (SaporePuro, Torino, Italy).

Screening with Plackett-Burman design

The study utilized a Plackett-Burman design to determine the significant factors influencing cooking yield, texture, and other parameters in anchovy burger formulation. This design considered four ingredients: sunflower seed oil, oat fiber, potato flakes, and egg white, each quantified in percentage (weight/weight). The experimental setup included a single block of 12 base runs, with each run featuring a distinct combination of the ingredients at pre-determined levels. These levels were selected from preliminary trials to span a practical range of values. Following the preparation, the minced anchovies were mixed with varying levels of oil, fiber, potato flakes, and egg whites according to the design table (Table 1).

Table 1 Summary and results of Plackett-Burman experimental design indicating the levels of four factors used in each run for the formulation of anchovy burgers

The minced anchovies were mixed using a mixer with the addition of 0.2% sodium chloride and 0.1% black pepper for all the formulations. The mixed formulations were portioned and then shaped into patties using a burger machine (SIRMAN SA-130, Italy) to ensure uniformity in size, shape and applied pressure. Each burger patty was formulated to have a final weight of 150 g and a diameter of 11 cm.

For the PBD experimental results, the effects of variables were evaluated by the first-order polynomial Eq. (1) as follows:

$$\mathrm Y={\mathrm\beta}_0\;+\;{\textstyle\sum\limits_{\mathrm i=1}^{\mathrm n}}{\mathrm\beta}_{\mathrm i}{\mathrm X}_{\mathrm i}\;+\;\left(i\;=\;1,\;\dots\;,k\right)$$

(1)

Where Y stands for the response, β ₀ stands for the intercept, β _i are the regression coefficients, and X _i stands for the level of the independent factor. These factors which significantly (p ≤ 0.05) affected the Y were identified according to their F-value. The patties were cooked under standardized conditions using a ventilated oven (Smeg-professionals, ALFA420H-2, Guastalla, Italy), at 200 °C, for 10 min, and the cooking yield, texture values, and other relevant parameters were evaluated post-cooking. The results from the experimental runs were analyzed to ascertain the significant factors and their interactions affecting the quality attributes of the anchovy burgers.

Central composite design

The optimization of the anchovy burger formulation was conducted using a Central Composite Design (CCD). Two significant factors, oat fiber, and potato flakes, were considered at five different levels each. The design comprised 13 experimental runs including four factorial points, four axial points, and five center points, carried out in a randomized order to minimize the effects of unexplained variability in the observed responses due to extraneous factors.

The levels of the two factors were chosen based on the results from the preliminary screening using a Plackett-Burman design. The levels for oat fiber and potato flakes were set at 1.171, 2, 4, 6, and 6.82 (% w/w). The coded levels of the factors were -α, -1, 0, + 1, and + α, with α being 1.41421. The anchovy patties were prepared according to the different formulations as suggested by the CCD. The ingredients were mixed thoroughly to ensure a uniform distribution of oat fiber and potato flakes within the anchovy mince. Following this, the mixture was formed into patties each weighing 150 g and with a diameter of 11 cm.

The mathematical relationship of the response (Y) to the significant independent variables X₁ and X₂ is given by the following quadratic polynomial Eq. (2):

$$\mathrm Y\;=\;{\mathrm\beta}_0\;+\;{\textstyle\sum\limits_{\mathrm i=1}^{\mathrm n}}{\mathrm\beta}_{\mathrm i}{\mathrm X}_{\mathrm i}+{\textstyle\sum\limits_{\mathrm i=1}^{\mathrm n}}{\mathrm\beta}_{\mathrm{ii}}\mathrm X_{\mathrm i}^2\;+\;{\textstyle\sum\limits_{\mathrm i=1}^{\mathrm n}}{\mathrm\beta}_{\mathrm{ij}}{\mathrm X}_{\mathrm i}{\mathrm X}_{\mathrm j}$$

(2)

Where Y is the predicted response; X_i and X_j are the coded values; β₀ the independent coefficient; β_{i, j} is the linear coefficient associated with each independent factor (X_{i, j}) and β_ij and β_ii are the coefficients for interaction and quadratic effects, respectively (Russo et al. 2021). The PBD and CCD were made with Minitab (Version 18.1, State College, PA, USA). Analysis of regression and variance (ANOVA) were used to test the effect of each experimental parameter selected from the obtained results. Comparison of means was conducted using ANOVA with Post Hoc Tukey’s test at p < 0.05. The design matrix along with the actual and coded values of the factors is presented in Table 2.

Table 2 Central composite design and results of cooking yield and Texture Profile analysis of anchovy burgers

Evaluation of fish burger characteristics

The 13 formulations of fish burgers were cooked utilizing a forced air oven (Smeg-professionals, ALFA420H-2, Guastalla, Italy), at 200 °C, for 10 min. After the cooking, the fish burgers were analyzed.

Texture profile analysis (TPA)

Texture Profile Analysis (TPA) was conducted using a texture analyzer (TMS-Pro texture analyzer, Food Technology Corporation, Sterling, VA, USA). Cylindrical samples, carved from the fish burgers with a diameter of 3.5 cm and a height of 2.5 cm, were subjected to a two-cycle compression test. The samples were compressed to half of their original height utilizing a cylindrical aluminium probe (P/35 75 mm diameter), at a test velocity of 1 mm s⁻¹ and a post-test velocity of 10 mm s⁻¹. This analysis was conducted on five burgers from each formulation at a temperature of 30 ± 2 °C. The texture attributes extracted from the curves were hardness, gumminess, and chewiness, as delineated by Bourne (1978) (BOURNE et al., 1978).

Each measurement resulted in a force-time curve spanning two cycles, from which various parameters were computed, including gumminess (N), defined as the energy required to disintegrate a food product before swallowing (Szczesniak, 1963), chewiness (N∙mm), defined as the energy required to masticate a food product before swallowing, and hardness (N), defined as the maximum force required for compressing the burgers and corresponding to the peak force of the first compression.

Cooking properties - technological assessment

The weight metrics of the fish burgers were acquired using an analytical balance and digital caliper before and after the cooking process, on three fish burgers from each formulation. The aspects such as cooking yield, reduction in diameter, reduction in thickness and retention of moisture were evaluated as outlined by Presenza et al. (2022), with measurements taken according to the subsequent equations (Presenza et al., 2022):

$$\:\%Cooking\:yield=\:\frac{Cooked\:weight}{Raw\:weight}\:x\:100$$

(3)

$$\%Diameter\;reduction=\:\frac{Raw\:fish\:burger\:diameter-cooked\:fish\:burger\:diameter}{Raw\:fish\:burger\:diameter}\:x\:100$$

(4)

$$\%Thickness\;reduction=\:\frac{Raw\:fish\:burger\:thickness-cooked\:fish\:burger\:thickness}{Raw\:fish\:burger\:thickness}\:x\:100$$

(5)

$$\:\%Moisture\:retention=\:\frac{Cooked\:weight\:x\:\%moisture\:in\:cooked\:fish\:burger}{Raw\:weight\:x\:\%moisture\:in\:raw\:fish\:burger}\:x\:100$$

(6)

Sensory evaluation

Subjects

A total of 56 volunteers were recruited by word of mouth among students, staff of the Department of Agricultural Sciences of the University of Naples Federico II, and people living in Portici (Naples) area. The subjects ages ranged from 20 to 50 years; 39.3% were males and 60.7% were females. Before the sensory evaluation, all participants received written information about the study and signed two copies of the written informed consent according to the principles of the Declaration of Helsinki (1964 and its later amendments) and the ethical standards of the University of Naples Federico II.

Sensory procedure

The Ideal Profile Method (IPM) approach was proposed (Worch & Punter, 2014). First, two preliminary sessions with 7 trained assessors (3 males and 4 females; mean age = 34 ± 6 y.o.) were performed to define the list of descriptive attributes discriminating the different burgers. Assessors were selected for their sensory acuity and their previous experience with other fish products. They were asked to evaluate the burger samples and to elicit the sensory attributes of the product, including only non-technical terms that can be easily understood and evaluated by untrained subjects. Five sensory attributes were selected, which were elicited by at least 70% of trained assessors, and further used to describe the samples (one related to odour, two related to texture and two related to taste) (Supplementary material). After this preliminary phase with trained assessors, the following sensory evaluation was conducted in individual sensory booths by the 56 untrained subjects. The nine samples were first randomized and then split across 2 sessions on the same day to reduce subject fatigue and were monadically presented to the subjects. The average length of each session was about 20 min with a 1-minute break, with freshwater for palate cleansing, between each burger evaluation. The burgers were served at a temperature of 50 ± 5 °C. Before the test, a simple introduction to the evaluation guidelines of the IPM method was provided to the subjects. Then, subjects first evaluated the overall liking of each burger on a 9-point hedonic scale and, secondly, the intensity of the predefined list of sensory attributes was assessed on 10 cm linear scales (0 = too little; 10 = too much). Finally, subjects were asked to rate the intensity of each evaluated attribute for their ideal burger.

Sensory data analysis

A multiple regression analysis was conducted to determine the relationship between the sensory score (termed “overall acceptance”) and a set of independent variables. The analysis was performed using Python’s statsmodels library (Seabold & Perktold, 2010). An Ordinary Least Squares (OLS) regression model was built with “Overall acceptance” as the dependent variable. The sensory data, excluding the overall acceptability, were standardized using the StandardScaler method, ensuring each sensory attribute contributed equally to the analysis (Meshram & Patil, 2023). PCA was then applied to reduce the dimensionality of the data, transforming the original variables into two principal components which captured the maximum variance in the dataset. The ideal profile data were standardized using the same scaler and then projected onto the PCA map. An IdMap was created by plotting both the average coordinates of each formulation (derived from the PCA) and the ideal points on the same plot (Worch & Punter, 2015). A density plot was overlaid to highlight the most preferred sensory profile.

Proximate analysis

The proximate analysis of the anchovy burger was conducted according to established standard methods. Protein content was determined using the Kjeldahl method (AOAC 990.10), which involves acid digestion followed by neutralization and distillation. Total lipid content was quantified by the Soxhlet extraction method (AOAC 960.39), utilizing a solvent extraction process to isolate fats (Leffler et al., 2008). Dietary fiber content was analyzed using the enzymatic-gravimetric method (AOAC 985.29), which involves the enzymatic digestion of non-fiber components using α-amylase and amyloglucosidase (Megazyme Ltd., Ireland) and subsequent gravimetric measurement of the fiber residue (AOAC, 2011). The ash content was determined by incinerating the sample in a muffle furnace at 550 °C until a constant weight was achieved (AOAC 942.05). Fatty acids, particularly polyunsaturated fatty acids like EPA and DHA, were analyzed using gas chromatography (Shimadzu GC-17 A) coupled with a flame ionization detector (GC/FID). This system included a fused silica capillary column (SPTM-2560, 75 m x 0.18 mm, i.d. 0.14 μm film thickness) and employed helium as the carrier gas. Fatty acid methyl esters (FAME) were identified by injecting pure FAME standards from Larodan (Malmoe, Sweden) and comparing their retention times (Russo et al., 2023). The FAME identification was facilitated by the Class-VP chromatography data system software, version 4.6 (Shimadzu Italia, Milan).

Results and discussion

Plackett-Burman screening results

In the initial stage of developing the anchovy burgers formula, a PBD was employed to ascertain the influence of various ingredients on key product characteristics (Table 1). This method facilitated an assessment of each ingredient’s effect on cooking yield, moisture retention, dimensional changes, and textural properties such as hardness, gumminess, and chewiness. Oat fibers were tested due to their known capacity of water and fat retention, which can improve the yield by minimizing water loss during cooking (BIS-SOUZA et al., 2018; Elleuch et al., 2011). Also, their high emulsifying activity and emulsion stability were previously tested in burger formulations (Huber et al., 2016).

Several noteworthy patterns emerged from the analysis of the results. High cooking yields and moisture retention were linked to formulations containing potato flakes and fibers. For example, a formulation with only 4% of both fiber and potato flakes achieved a cooking yield of 82.9% and moisture retention of 75.59%. Potato flakes are known to reduce cooking loss and improve the texture of foods (Lingling et al., 2018), as evidenced by the observed reduction in diameter and thickness in formulations with higher percentages of potato flakes and egg whites, indicating improved shape retention during cooking. Cooking loss, primarily due to water loss from protein denaturation, affects the mass of meat and fish products. (Shahiri Tabarestani & Mazaheri Tehrani, 2014). Our results suggest that the presence of fiber and potato flakes, even in the absence of oil and egg white, significantly contributes to the cooking yield.

Hardness, gumminess, and chewiness varied significantly across runs. For instance, run 12, with 10% oil and no other additives, showed the highest hardness (264.3 N) and chewiness (692.144 mJ). In contrast, run 8 (with 10% oil, 4% fiber, 4% potato flakes, and no egg white) recorded the lowest gumminess (17.24 N) and chewiness (170.001 mJ). However, the textural properties were primarily influenced by the levels of potato flakes and fiber. Runs with a balanced incorporation of these ingredients, like run 8 (which had both at 4%), showcased the lowest levels of hardness and relatively low gumminess and chewiness. This suggests the capacity of potato flakes and fiber to modulate texture, making the burgers neither too hard nor too gummy or chewy. The use of potato flakes is used in the food industry to improve the chewiness of foods such as bread and noodles (Lingling et al., 2018). During fish burgers development, especially those containing anchovy, formulators face challenges, notably in achieving proper “Binding and Textural Integrity”. This critical aspect poses several technological difficulties. The use of a PBD has been instrumental in identifying the diverse impact of these ingredients, leading to more focused formulation strategies aimed at enhancing the burgers’ overall quality. The results of statistical analysis of PBD are summarized and reported in Fig. 1.

Fig. 1

Pareto chart of standardized effect of sunflower oil (A), oat fibers (B), potato flakes (C) and egg white (D) on different responses for anchovy burgers formulation. The responses are: cooking yield, chewiness, thickness reduction, diameter reduction, gumminess and hardness. The effects are displayed in descending order of magnitude

The analysis revealed that the potato flakes played a paramount role, significantly increasing the cooking yield by 16.08% (p < 0.001), indicating their essential contribution to product integrity during cooking. Furthermore, potato flakes significantly reduced the diameter reduction by 6.81 cm (p = 0.0068), hardness by 71.76 N (p = 0.0096), gumminess by 48.77 N (p = 0.0116), and chewiness by 240.55 mJ (p = 0.0017), elucidating their critical influence in enhancing textural properties. Potato flakes are well known to improve the technological properties during burger formulation (Bastos et al., 2014). In fact, in the study of Ali et al. (2011) the cooking yield and water retention capacity improved as the levels of potato flakes increased, resulting in a high overall acceptability for beef patties prepared using potato flakes. The screening process revealed consistent patterns in moisture retention and cooking yield for anchovy burgers. Oat fibers, instead, demonstrated a significant decrease in gumminess by 42.53 N (p-value = 0.0357) and tended to influence thickness reduction and chewiness, suggesting its role in modifying the burger’s mechanical properties. Oat fiber has already garnered recognition in various applications, such as meat alternatives and bread, due to its rich content of water-binding soluble fiber, including β-glucan. In this context, it could be used to enhance the hydration capacity of protein-based polymeric systems, such as fish burgers (Ramos-Diaz et al., 2022).

Egg white was chosen as an ingredient due to its known binding capacity for meat pieces, which can also increase textural stability (Pennisi Forell et al., 2010). However, in this study egg white appeared to marginally influence the cooking yield, showing an impact only on diameter reduction (decrease by 4.58 cm, p-value = 0.002), indicating a non-conclusive role in structural cohesion.

Conversely, sunflower oil did not exhibit a statistically significant impact on any of the assessed parameters, implying its limited role in the textural and cooking performance of the anchovy burger.

These insights from the PBD lay a foundation for the subsequent optimization phase, where the focus will be on fine-tuning the levels of the most influential ingredients, potato flakes and oat fiber, to achieve the desired product quality in the anchovy burgers.

Optimization with central composite design

In the subsequent optimization phase, a CCD was employed to focus specifically on the effects of fiber and potato flakes, following the initial screening with the PBD. This targeted approach was based on the insights gained from the screening phase, which highlighted the significant roles of fiber and potato flakes in influencing the quality attributes of anchovy burgers. Table 2 reports the results along with the experimental design of CCD. Building on the initial observations, the results from the CCD offer deeper insights into the nuanced interplay between oat fibers and potato flakes in anchovy burger formulations.

The statistical analysis of the CCD, applied to the formulation of anchovy burgers with potato flakes and fibers, yielded significant results as summarized in Table 3.

Table 3 Summary (sum of squares) of ANOVA for response of dependent variables

The statistical model revealed that variations in potato flakes and fibers have a highly significant impact (p < 0.001) on the cooking yield, textural properties, and diameter reduction of fish burgers. Potato flakes, in particular, exert a more substantial effect than oat fibers on texture properties such as hardness, gumminess, and chewiness, underscoring their pivotal role in texture determination. The observed variation in cooking yield highlights the moisture-binding capacity of these ingredients, which is essential for preserving product integrity during cooking. The effectiveness of potato flakes in moisture retention is attributed to their starch content, which can gelatinize and absorb water, enhancing both cooking yield and texture. This finding is supported by the study of Spinelli et al. (2016), which demonstrated the benefits of a 10% inclusion rate of potato flakes in sea bass burgers (Spinelli et al. 2016). In our study, a range of 4.0-6.8% potato flakes was sufficient to markedly improve cooking yield and textural qualities.

In terms of textural attributes, the study distinctly highlights the role of oat fibers in modulating the burger’s firmness. Fish meat, including anchovies, has a delicate texture with proteins that can easily denature during processing (Uran & Gokoglu, 2014). The challenge lies in ensuring these proteins adequately bind the burger’s ingredients without becoming too tough or losing their natural texture. Thus, balancing the integrity of the fish protein while achieving a cohesive burger mix is critical (Bainy et al., 2015). Moreover, the water-binding and swelling properties of fibers can lead to the formation of an insoluble three-dimensional network, ultimately enhancing the rheological properties of the continuous phase in hamburger emulsions (Shan et al., 2015). However, excessive oat fibers can result in a burger texture that is too firm or tough, negatively affecting the eating experience due to the need for excessive chewing, as demonstrated in formulation 2. A balanced mix of oat fibers and potato flakes, instead, leads to a softer texture, indicating that potato flakes can mitigate the firming effects of oat fibers. This balance is crucial for optimizing gumminess and chewiness, attributes that, when excessive, are typically viewed unfavourably by consumers. Formulations with lower concentrations of both ingredients exhibited high gumminess and chewiness, suggesting a lack of cohesive elements within the burger’s structure (Oppen et al., 2023). Additionally, the data on diameter reduction supports the textural observations, showing that burgers with higher levels of these ingredients maintained their shape better during cooking, reflecting a more stable structure. This stability is primarily influenced by the release of fat and water and the denaturation of muscle proteins in meat burgers (Shahiri Tabarestani & Mazaheri Tehrani, 2014). Fish muscle instead contains less connective tissue compared with muscle from other mammalians, such as beef and pork. Therefore, the texture alterations resulting from the denaturation of this connective tissue tend to be less significant compared to the changes caused by the denaturation of sarcoplasmic proteins (Ditudompo et al., 2022). As highlighted by Soltanizadeh and Ghiasi-Esfahani (2014), the extent of shrinkage in meat products is significantly influenced by the gelling capacity of burger extenders and their ability to retain moisture and fat. This principle is exemplified in the case of anchovy burgers incorporating oat fibers and potato flakes, where the high moisture retention attributed to oat fibers appears to have effectively mitigated the diameter reduction typically observed during cooking (Carvalho et al., 2019). This aspect is particularly important from a commercial standpoint, as it directly impacts the product’s visual appeal and consumer acceptability.

The surface and contour plots obtained from CCD are reported in Fig. 2, which provide additional insights.

Fig. 2

Surface and contour plots for cooking yield (a), Hardness (b), Gumminess (c), and Chewiness (d) of Anchovy Burgers. Each subplot visualizes the predicted values from the quadratic model, while the contour plot (on the base) offers a 2D perspective of these predictions. Scatter points in red represent the actual experimental data

Figure 2a, representing cooking yield, shows a significant increase at high levels of potato flakes, and a lesser impact for oat fibers, indicating the important role of potato flakes in maximizing the yield. Figure 2b, which depicts hardness, presents a similar landscape, with a pronounced increase in hardness at higher levels of oat fibers, suggesting that excessive fiber content may lead to a firmer burger. Figure 2 collectively suggests that while both oat fibers and potato flakes contribute to the textural profile of the burgers, their effects are distinct and must be carefully balanced. The optimal levels of these ingredients can significantly enhance cooking yield and texture, which is important for consumer acceptance and product success.

These findings not only emphasize the importance of ingredient ratios in fish burger formulations but also highlight the potential of using natural, plant-based ingredients like oat fibers and potato flakes to improve product quality. This is especially relevant in the context of rising consumer demand for healthier, sustainable food options (Aschemann-Witzel et al., 2019; Fiorile et al., 2023).

Sensory results and consumer preference

In Table 4 the correlation coefficients for each variable, previously studied in RSM-CCD, against the overall acceptance mean are reported as well as the statistical parameters of the multiple regression analysis.

Table 4 Multiple regression analysis results for overall acceptance of anchovy burgers

This study employed multiple regression analysis to explore how texture properties influence the sensory appeal (“overall acceptance”) of various anchovy burger formulations. With an R-squared value of 0.938, the model effectively explained 93.8% of the variance in overall acceptance, highlighting the predictive strength of texture parameters. The analysis revealed that while fiber and hardness positively correlate with overall acceptance, the impact of fiber was not statistically significant (p-value = 0.1393), suggesting its influence might be negligible or overshadowed by other factors. This observation aligns with research by Huang et al. (2011) and Souza et al. (2019), indicating that oat fiber’s addition could enhance sensory scores.

Potato flakes also demonstrated a minor negative impact on acceptance, but this was not statistically significant (p-value = 0.1074), hinting at a minimal influence or possible interactions with other ingredients not captured by the model. Potato flakes are mainly starch and are used as binders in fish products, as noted by (Husein et al. 2019).

Conversely, cooking yield and gumminess significantly negatively affected overall acceptance, suggesting that excessive moisture retention or a gummy texture is undesirable. These results underscore the complexity of sensory evaluation, influenced by a combination of texture attributes and possibly other unmeasured factors such as flavor, aroma, and individual preferences, as discussed by Fiorile et al. (2023) and Yousefi et al. (2018) regarding the importance of texture in consumer willingness to consume meat and fish products.

The sensory profile is a crucial point in determining consumer preference and acceptance. Recent researches indicate that texture attributes significantly influence the hedonic appeal of fresh fish and fish-based products (Ben Atitallah et al., 2019; Husein et al., 2019). In this context, understanding consumer perception of sensory attributes is critical. Figure 3 reported the Principal Component Analysis (PCA) biplot which serves as a visual summary of the sensory profiles of anchovy burger formulations that differ by their content of oat fibers (OF) and potato flakes (PF).

Fig. 3

Principal Component Analysis (PCA) biplot of sensory attributes for anchovy burger formulations. Each point represents the sensory profile of a specific burger formulation based on consumer evaluations

The PCA biplot effectively summarizes the sensory attributes of anchovy burger formulations differentiated by varying fiber and potato flake (PF) percentages. The first principal component (PC1), capturing 34.28% of the variance, is predominantly influenced by ‘Hardness’, suggesting that this textural attribute is a principal differentiator among the formulations. The presence of formulations with higher fiber content, such as “6.82% Fibers + 4% PF”, in the vicinity of the ‘Hardness’ vector indicates a perceived firmer texture, potentially attributed to the increased fiber percentage. The second principal component (PC2) explains 23.86% of the variance and is characterized by a contrast between ‘Fish odour’ and ‘Anchovy flavour’ on one side, and ‘Saltiness’ and ‘Pepperiness’ on the other. This separation elucidates distinct flavor profiles; with inherent seafood flavors on one hand and seasoning influences on the other one. The placement of formulations along this axis underscores the impact of taste and flavor-modifying components on the sensory experience of the burgers. Maintaining distinctive fish flavours while achieving the desired blend with other ingredients, especially through cooking and processing, remains a significant challenge in fish burger development (Quadros et al., 2015). It should be noted that that in our sensory analysis no off-flavors were detected during the study phases by the panelists. In fact they were asked to sign some negative aspects that were not listed for scoring.

The positioning of the “6.82% Fibers + 4% PF” formulation suggests a notable association with ‘Hardness’, implying a textural profile that is distinctively firmer than other formulations. This observation is crucial for product development, as it indicates that fiber content significantly influences burgers’ texture, providing a tangible avenue for tailoring product attributes to consumer preferences.

To identify the formulation that most closely approximates the ideal profile, a PCA with Ideal Mapping (IdMap), facilitating the interpretation of the consumer test results, was elaborated (Fig. 4).

Fig. 4

IdMap results of anchovy burger formulations based on sensory attributes. Green shaded area represents the ideal areas shared among consumers. Red ‘X’ markers indicate the ideal product profiles as perceived by consumers

The application of PCA and IdMap techniques provides valuable insights into consumer preferences and the sensory profile of various anchovy burger formulations. The PCA plot reveals a distinct clustering of formulations, indicating variations in sensory perception. Each cluster suggests a unique combination of sensory attributes that define the overall experience of the product. The first principal component (PC1) was influenced by attributes like fish odour and juiciness (variance ratio = 0.342), while the second principal component (PC2) was more affected by hardness and anchovy flavor (variance ratio = 0.248). This suggests that these attributes significantly differentiate the sensory profiles of the formulations. The IdMap technique identified the ideal product profile area, marked by a light green shaded region. Formulations within or near this area are presumed to align closely with the majority of consumer preferences. Notably, formulations such as “1.2% Fibers + 4% PF” and “4% Fibers + 4% PF” were found near the ideal region. This highlights their potential alignment with the ideal sensory profile. The analysis suggests a preference trend towards certain combinations of oat fibers and potato flakes. For instance, the proximity of “1.2% Fibers + 4% PF” to the ideal area indicates a balanced combination that appeals to the subjects. This analysis underscores the multidimensional nature of sensory perception and its impact on consumer preferences in food products. The PCA and IdMap provide a framework for understanding these complex relationships, guiding product development towards formulations that resonate more closely with consumer desires (Worch et al., 2013). For the anchovy burgers, the 4% Fibers + 4% PF corresponds to a combination of ingredients which lead to an average cooking yield of 81.6% which is significantly higher than the other ideal formulation (1.2% Fibers + 4% PF). Also, the 4% Fiber and 4% PF formulation achieved a low gumminess value and a minimal diameter reduction (Table 2), making it an ideal product not only in terms of consumer acceptability but also from a technological point of view. Furthermore, a burger containing 4% fiber qualifies to bear a health claim as a source of fiber. In fact, according to the definitions provided in the annex of EC Regulation 1924/2006, the claim “Source of fiber” or any other synonymous indication can only be used if the product contains at least 3 g of fibres per 100 g of food or at least 1.5 g of fiber per 100 kilocalories (Zicari et al., 2007).

Comparative nutritional analysis

In the fast food industry, the nutritional composition of products is critically important not only for consumer health but also for addressing broader environmental and sustainability concerns. This study focused on the optimization of food formulations to enhance nutritional profiles, particularly through the substitution of traditional meat products with more sustainable seafood options (Keenan et al., 2015). The nutritional analysis presented in Table 5 compares an optimized anchovy burger with typical offerings from major fast food chains and a standard beef burger.

Table 5 Proximate analysis of optimized anchovy burger and comparison with commercial fast-food meat alternatives

The data reveal that the anchovy burger contains higher levels of protein and fibers compared to the hamburgers from Burger King and McDonald’s. Specifically, the anchovy burger contains 18.496 g of protein, significantly surpassing McDonald’s 12.9 g and Burger King’s 14.8 g. It also offers 3.77 g of dietary fibers, considerably higher than the 1 to 1.3 g found in the fast food chain burgers. Importantly, the total lipid content in the anchovy burger is notably lower at 4.404 g, compared to 22.1 g in the common beef burger, highlighting its lower fat profile.

Further emphasizing its health benefits, the anchovy burger provides a rich source of polyunsaturated fatty acids (PUFAs), including 0.53 g of EPA and 0.91 g of DHA. These omega-3 fatty acids are crucial for cardiovascular health, potentially reducing the incidence of heart disease (Russo et al., 2021). The low levels of these essential nutrients in traditional fast food offerings underscore the nutritional superiority of the anchovy burger. Studies like those by Keenan et al. (2015) have explored the beneficial effects of incorporating fish oils into beef burgers, noting enhanced polyunsaturated fatty acid content and potential health benefits in meat products (Keenan et al., 2015).

Compared to established dietary reference values (DRV) set by the FDA and EFSA, the optimal anchovy burger demonstrates significant nutritional benefits. It contains 18.49 g of protein per 100 g, aligning well with the recommended daily intake of protein, which is about 50 g per day according to the FDA and 0.83 g/kg body weight per day by EFSA standards (EFSA, 2012). The burger is particularly advantageous in its fatty acid composition, featuring a lower saturated fat content at 1.14 g/100 g and higher levels of polyunsaturated fatty acids (PUFA) at 1.74 g/100 g, yielding a favorable saturated to unsaturated fat ratio of approximately 0.66. Notably, it is rich in long-chain PUFAs (LC-PUFAs), including EPA (0.48 g/100 g) and DHA (0.82 g/100 g), which far exceed the minimum recommended intake of 250–500 mg per day of EPA and DHA combined (EFSA, 2010). Furthermore, the burger provides 3.77 g/100 g of dietary fiber, substantially surpassing the fiber content in traditional beef and fast food burgers, and aligning well with the FDA and EFSA recommendations of 28 g and 25 g per day, respectively (UDSA, 2020). By offering a product with a superior nutritional profile, the anchovy burger not only meets the growing consumer demand for healthier food choices but also supports a more sustainable food system, given the lower environmental impact of forage fish compared to red meat (Xia et al. 2024).

These results have significant implications for the fast food industry and food policy, suggesting a shift towards the incorporation of more fish-based products that could help mitigate the health and environmental issues associated with traditional fast food diets (Presenza et al. 2022). This shift could be further supported by developing nutrition-sensitive policies that encourage the consumption of sustainable seafood alternatives, like anchovies, which offer both health benefits and environmental advantages.

By integrating such nutritious and eco-friendly options into mainstream fast food menus, the industry can contribute to a healthier public and a more sustainable world, aligning economic success with public health and environmental stewardship.

Conclusion

This study focused on creating a healthier and sensory appealing fast-food option by developing an anchovy burger using RSM. This aligns with the growing consumer demand for nutritious, sustainable, and palatable fast food options. Anchovies, chosen for their high nutritional content and low market value, are the cornerstone of this endeavor, supplemented by key ingredients like oat fibers and potato flakes. Potato flakes, in particular, significantly influenced the cooking yield and textural properties, such as hardness, gumminess, and chewiness. Oat fibers, on the other hand, were instrumental in modifying the burger’s mechanical properties, contributing to a balanced texture that was neither too hard nor too gummy. Moreover oat fibers also give nutritional benefits of fiber inclusion into the final burger. Sensory evaluation played a pivotal role in this study, revealing consumer preferences for texture and taste. The formula with 4% of oat fibers and 4% of potato flakes closely matched the ideal sensory profile. This formulation not only appealed to the consumer palate but also met nutritional goals, highlighting its potential in the fast-food market. Future research could expand on this study by exploring a broader range of sensory attributes and incorporating a larger consumer base. The implementation of the anchovy burger in the fast food industry holds potential due to the low market value and high availability of anchovies, which could support cost-effective production. However, a detailed cost analysis and evaluation of production scalability were beyond the scope of this study. Moreover, Future research should focus on evaluating the shelf-life and storage conditions of the anchovy burgers to ensure their practical applicability and commercialization in the fast-food industry.