Sustainable Management of Fruit By-Products Through Design Thinking: Development of an Innovative Food Product

Abstract

Sustainable development and the circular economy have become key challenges in the modern food sector, calling for innovative solutions that reduce waste and promote the efficient use of resources. The aim of this study was to develop a functional food product by utilizing by-products from chokeberry processing, thereby contributing to circularity in food systems. The integration of design thinking with fermentation of chokeberry pomace is presented in this study as an approach to developing value-added food ingredients. Qualitative consumer research (focus group interviews, n = 36) identified preferences and expectations regarding functional foods containing by-products. Conducted by an interdisciplinary team, the project followed five stages, involving both qualitative and quantitative research. Liquid surface fermentation was performed using Aspergillus niger, selected for its proven ability to enhance the antioxidant capacity and polyphenol content of plant matrices. The optimal process was 2-day fermentation under controlled pH conditions with glucose supplementation, which significantly enhanced the quality and nutritional value of the final product. Antioxidant activity (ABTS, FRAP, CUPRAC assays), total polyphenols, anthocyanins, and proanthocyanidins were determined, showing significant increases compared to non-fermented controls. The outcome was the development of a dried, fermented chokeberry pomace product that meets consumer expectations and fulfils sustainability goals through waste reduction and innovative reuse of fruit processing by-products.

1. Introduction

The design of new food products, particularly health-promoting foods, is increasingly the subject of scientific research, and the practical activities undertaken in this area are being carried out on a growing scale [1,2,3,4,5]. This process is being framed within the broader context of sustainable development, which calls for the creation of innovative solutions that minimise the environmental impact of food production. The development of a new food product is a complex process involving inter-stage feedback. The specificities of the food industry are even more critical because the food product development process is influenced by many different areas, such as technology, marketing, and consumer research [6]. Given its multifaceted nature, designing and developing food products is a costly and time-consuming endeavour with a high risk of failure. However, food companies can minimise the cost, time, and risk of failure by implementing activities related to the effective and efficient management of new food product development process [7].

According to a structured design thinking approach, project management emphasises observation, collaboration involving multidisciplinary teams, rapid learning, visualisation of ideas, rapid prototyping, and simultaneous business analysis, allowing it to be used in many areas, including problem redefinition [8,9]. Design thinking is usually visualised as an iterative series of five main stages: empathy with the user, diagnosis (defining the problem), ideation (generating ideas for solutions), prototyping, and testing [10]. Design thinking is a systemic, critical, and creative approach to solving multifaceted problems and finding solutions based on an understanding of human values, needs, emotions, and desires [11]. It is part of a broader paradigm of human-centred design. According to this way of thinking, everyone is an expert on their own life and therefore knows best how they feel when using a service or product and whether their expectations are met [12]. Within this paradigm, the following attitudes are desirable when designing: creative courage, thinking through creation, iteration, acceptance of ambiguity, and learning from inevitable failures. In the context of food product innovation, design thinking facilitates the integration of consumer expectations related to taste, texture, nutritional value, sustainability, and convenience into product development. This approach enables developers to systematically translate consumer insights into technological processes and formulations that align with market needs. The design thinking method makes it possible to quickly create technologically and economically feasible solutions to meet user needs [13]. The concept of design thinking significantly contributes to food innovation in designing sustainable food products and services that meet consumer needs [14].

Today’s fermented food market is dominated by dairy products, often containing probiotic microorganisms. However, non-dairy fermented products, especially those based on vegetables or fruits, are increasingly popular among consumers [15,16]. Several studies have confirmed that fermentation can increase plant extract antioxidant activity [17,18,19]. The results suggest that metabolic hydrolysis affects the growth of phenolic compounds. Moreover, during fermentation, plant cell walls decompose, releasing biologically active compounds, including antioxidants [18]. Fermentation can also affect the production of enzymes such as proteases and α-amylases, which chelate metal ions [20].

Chokeberry pomace, a valuable by-product generated during food processing, has been identified as a rich source of polyphenols and other antioxidants [21]. Kapci et al. [22] confirmed its high content of biologically active compounds with antioxidant potential, although fresh chokeberries exhibited higher antioxidant capacity compared to pomace. These characteristics make chokeberry pomace a promising secondary raw material for developing functional food ingredients that contribute to sustainable production and health promotion [16,23]. The higher content of polyphenols and proanthocyanidins in chokeberry pomace than in juice and fruit was also confirmed by other authors [24,25]. The growth of the non-dairy fermented food market is driven by growing consumer awareness of the importance of healthy eating habits that can help prevent lifestyle diseases. Consumers are increasingly seeking products with health-promoting benefits that go beyond basic nutrition, such as foods fortified with vitamins, fibre, or probiotic microorganisms [15,16]. Few studies have reported increased bioactive compound content in fermented chokeberry processing by-products [26]. However, fermented pomace is not used in food products.

The aim of this study is to develop a new food product using a structured design thinking approach. The novelty of this study is related to the use of fermented chokeberry processing by-products as an alternative source of valuable ingredients, encouraging a circular bioeconomy through the design of new food products. To our knowledge, no prior research has comprehensively applied design thinking to guide the development and optimisation of fermented chokeberry pomace as a functional ingredient. We hypothesise that this approach will yield a prototype with improved antioxidant properties and attributes aligned with consumer expectations.

2. Materials and Methods

The design thinking method was used to conduct the study, resulting in an innovative food product that also provided a thorough understanding of the context of food design and the target consumer [27]. The research process was extensive and consisted of both qualitative and quantitative methods. The entire research work of the interdisciplinary team was divided into five stages, following the design thinking approach: (1) deep knowledge and proper understanding of the final consumer of the product (consumer empathisation), (2) interpretation of the results and defining the appropriate problem, (3) ideation (creating innovative product solutions), (4) product prototyping, and (5) testing (evaluating and improving solutions) (Figure 1).

A description of the five phases of the design thinking approach is included here to present the overall study framework, while the subsequent sections detail the specific qualitative and experimental methods applied in each phase.

2.1. Empathising with the Consumer and Defining the Problem

In the implementation of the study, i.e., consumer empathisation and problem definition, a qualitative approach was used, the essence of which was to understand the ways in which the surveyed entities think, assess, and react. To determine how consumers perceive functional food produced in a sustainable process, a qualitative research method, namely focus group interviews, was used. Focused interviews were conducted with three groups of 12 consumers selected on the basis of target criteria specific to each study. Participants were recruited from adult consumers of functional food products residing in large cities with a population of 500,000 or more. Both men and women participated in the study. Inclusion criteria included age over 18 years and regular or occasional consumption of functional food products. The interviews were performed according to a moderation scenario common to all groups participating in the study, which included two aspects: (1) the characteristics of the attributes of functional products with sustainable features in the food category and (2) the role of functional products with sustainable features in the food system. The interview scenario was structured in thematic areas to explore consumer perceptions and expectations regarding functional foods and the use of by-products. The discussion guide included an introductory part (experience with functional foods), detailed questions on purchasing criteria, barriers, and preferences, and questions about the willingness to accept products containing by-products of aronia processing. Specific questions covered, for example, the most frequently consumed functional products, motivations for purchase, perceived obstacles, preferred product features, and expectations regarding product communication and pricing. During the sessions, the participants also evaluated examples of aronia pomace applications from the literature and ranked their preferences. The interview concluded with a summary of key insights identified by each participant. The study using focused interviews was conducted in October 2022. A detailed transcript was prepared based on the recorded discussion. This material was subjected to expert analysis, which involved preparing a written report on the main results, referred to as key insights. Then, following the principles of qualitative data analysis, the results were organised, the material was categorised according to the main research problems, and the obtained data was sorted [28]. The collected information was then analysed, and the problems were defined. Based on the identification of the experiences, behaviours, and needs of the surveyed respondents, the team developed a list of problems for the target group in the form of generative questions.

2.2. Generation of Ideas

After determining the key features, the project team generated solutions through brainstorming, ensuring that the product met the requirements. The team generated ideas that required not only substantive knowledge on a given topic but also team members’ ingenuity, courage, and creativity. At this stage, it is also essential to evaluate creative ideas selected from as large a pool as possible and then carefully assess whether the proposed food product meets all the key features. The team decomposed the ideas into obligatory, feasible, and far-reaching and within the scope of the activities of the interdisciplinary project team. At the end of this phase, the number of ideas was narrowed down to the few most promising ones. The impact effort matrix was used to analyse and prioritise the importance of ideas in terms of expected effects and necessary expenditure [8].

2.3. Development of Prototypes

The Nero variety chokeberries were collected from the Marwice Horticultural Farm. In the first stage, the fruits were cleaned and sorted (including removing rotten and damaged fruits), followed by washing. Chokeberry pomace was obtained after cold pressing under laboratory conditions. The obtained pomace was weighed and frozen at −18 °C and then subjected to the freeze-drying process. The drying process was performed for 16 h in a TG-15 freeze dryer. After freeze-drying, the plant material was ground using a KN 295 Knifetec™ grinder (FOSS, Hilleroed, Denmark). Until fermentation, powders from freeze-dried pomace were stored in doy pack-barrier packaging with limited access to light and air and at room temperature.

The fungal strain Aspergillus niger was used for inoculation of the samples by growing the moulds in PDA medium at 29 °C ± 1 °C for 10 days before application in the microbial measurements. Aspergillus niger was selected based on literature reports demonstrating its capacity to enhance the antioxidant potential and modify the polyphenol profile of plant-based materials during fermentation [17,26]. The inoculum containing the spores and hyphae of the fungus was prepared by washing the fungal growth from the agar surface with sterile NaCl (0.85%) saline solution and shaking it for 20 min at 200 rpm/min with glass balls. The number of spores in suspension was counted in a Bürker chamber.

Chokeberry pomace was used as a substrate for liquid surface fermentation (LSF). Glass Erlenmeyer flasks were used as reactors. Chokeberry pomace was weighed (10 g) and placed in a flask. Then, sterile NaCl (0.85%) saline solution or nutrient solution containing glucose (30 g/L) was added to obtain the final volume of the suspensions (100 mL). For the samples without glucose supplementation, the measured pH before incubation was in the range of 2.86–2.97 or adjusted to 5.30–5.45 using potassium carbonate. For the glucose-supplemented samples, the pH was in the range of 2.88–2.97 (measured) or adjusted to 5.27–5.60. The standard pH metre and combination electrode were used for pH measurements. The variation in initial pH values and the inclusion or exclusion of glucose were intended to investigate how environmental parameters modulate fungal fermentation, particularly the growth of A. niger and the extraction and stability of phenolic compounds with antioxidant properties. The spores of A. niger were inoculated into the flask with the chokeberry pomace samples to reach a final concentration of 1–2 × 10⁷ spores/g of chokeberry pomace [29]. The control samples without an inoculum were always run in parallel. The LSF systems were incubated at a constant temperature of 29 °C ± 1 °C for 2, 5, and 8 days in a laboratory incubator New Brunswick Innova 42 (Eppendorf, Hamburg, Germany). An overview of the experimental setup, including all fermentation variants, is presented in Figure 2.

After this part of the experiments, the solid fractions of chokeberry pomace were lyophilised after treatment with liquid nitrogen at 13 Pa and −40 °C for 24 h. The liquid residues of the reaction mixtures were collected in 20 mL vials and stored at −20 °C, but were not analysed in this study, as the research focused exclusively on the fermented pomace intended for use as a food ingredient.

This fermentation procedure, although based on standard microbiological techniques, was integrated within the design thinking process as the prototyping and testing phase aimed at verifying the product concept developed in response to consumer expectations.

2.4. Methods of Prototype Testing

The fermented and freeze-dried black chokeberry pomace (1 g) was extracted three times (3 × 20 min) with 10 mL of a 60% ethanol solution according to the methodology developed by Sady et al. [30]. The samples collected on day 0, prior to fermentation, were also prepared and extracted in the same manner and served as non-fermented controls. The extraction was performed in a UP200HT ultrasonic homogeniser bath (Hielscher Ultrasonics, Teltow, Germany). The extracts obtained were centrifuged for 15 min, filtered through a Büchner funnel and combined. The prepared extracts were stored at −20 °C until analysis.

2.4.1. Total Polyphenol Content (TPC)

The total polyphenol content (TPC) was determined using the Folin−Ciocalteu method previously described by Roman et al. [31]. A 10% (v/v) aqueous solution of Folin–Ciocalteu reagent was prepared and incubated in the dark at room temperature for 1 h. Then, 2700 μL of 5 mM Na₂CO₃ (sodium carbonate), 150 μL of the test sample, and 150 μL of diluted Folin−Ciocalteu reagent were mixed. The absorbance of the samples was measured at 750 nm after 15 min at room temperature. Three independent test samples were prepared from each extract. The results are presented as the arithmetic mean ± SD in milligrams of gallic acid per litre. The tests were performed using U-5100 cuvette spectrophotometer (Hitachi, Tokyo, Japan).

2.4.2. Total Anthocyanin Content (TAC)

Total anthocyanin content (TAC) was measured using the pH-differential method according to Giusti and Wrolstad [32]. The sample extract was then diluted with two buffer solutions (pH 1 and 4.5). Briefly, 0.05 mL of the sample and 2.7 mL of KCl/HCl buffer at pH 1 or 2.7 mL of sodium acetate (NaOAc)/HCl buffer at pH 4.5 were mixed and left for 10 min at ambient temperature in a dark place. The absorbance versus prepared reagent blank containing the appropriate buffer instead of the sample was recorded at λ = 510 nm and λ = 700 nm.

The TAC concentration was calculated using the following equation:

$$TMA={\displaystyle \frac{A·MW·DF·1000}{\epsilon }},$$

where A = (A₅₁₀ − A₇₀₀)_{pH 1.0} − (A₅₁₀ − A₇₀₀)_{pH 4.5}; MW is the molecular weight (449.2 g/mol) of cyanidin-3-glucoside (Cy-3-Glu); DF denotes the dilution factor; $\epsilon$ = 26 900 L × mol⁻¹ × cm⁻¹ is the molar extinction coefficient for Cy-3-Glu; and 10³ is the factor for conversion from grams to milligrams.

The results are expressed in milligrams of Cy-3-Glu per litre and are presented as the arithmetic mean ± SD of the measurements of three independent test samples prepared for each extract. Cuvettes (optical path of 1 cm) and a UV-VIS-NIR spectrophotometer V-770 (Jasco, Tokyo, Japan) were used for the tests.

2.4.3. Total Proanthocyanidins (TPAC)

The total proanthocyanidin (TPAC) content was measured using the method described by Prior et al. [33]. Briefly, 0.1 mL of the respective sample was mixed with 0.5 mL of 4-(dimethylamino)cinnamaldehyde (DMAC) reagent (0.05 g DMAC in 50 mL of ethanol/water/HCl (75/12.5/12.5 v/v/v)). The mixture was then left in the dark for 30 min at ambient temperature. The absorbance versus prepared reagent blank containing the ethanol/water/HCl solution (75/12.5/12.5 v/v/v) instead of the sample was recorded at λ = 640 nm, and (+)-catechin dissolved in ethanol/water/HCl (75/12.5/12.5 v/v/v) was used as a reference. The results are expressed in milligrams of catechin per litre and are presented as the arithmetic mean ± SD of the measurements of three independent test samples prepared for each extract. Cuvettes (optical path of 1 cm) and a UV-VIS-NIR spectrophotometer V-770 (Jasco, Tokyo, Japan) were used for the tests.

2.4.4. ABTS Assay

Antioxidant activity was assessed using the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) method and according to the protocol described by Nowak et al. [34]. Briefly, a 7 mM solution of ABTS in a 2.45 mM aqueous solution of K₂S₂O₈ (potassium persulfate) was incubated for 24 h in the dark at room temperature. The incubated solution was then diluted with 50% (v/v) methanol to obtain an absorbance of 1.00 ± 0.02 at 734 nm. To 2500 μL of stock solution, 25 μL of the test sample was added, and after 6 min of incubation at room temperature, absorbance at 734 nm was measured. The results are expressed in millimolar of Trolox per litre.

2.4.5. FRAP Assay

The ferric ion-reducing potential was measured using the ferric-reducing antioxidant power (FRAP) method, as previously described by Roman et al. [31]. The working solution was prepared by mixing 1 volume of 10 mM TPTZ (2,4,6-tripyridyl-s-triazine) (dissolved in 40 mM HCl), 1 volume of 20 mM FeCl₃ (iron(III) chloride), and 10 volumes of acetate buffer (pH 3.6). Subsequently, 2320 µL of the working solution was mixed with 80 µL of the test sample. Absorbance was measured at 593 nm after 15 min at room temperature. The results are expressed in millimolar FeSO₄ per litre.

2.4.6. CUPRAC Assay

The reducing ability of cupric ions was evaluated using the cupric ion-reducing antioxidant capacity (CUPRAC) method, based on the methodology described by Roman et al. [31], with slight modifications. Briefly, 500 μL of 0.01 M aqueous CuCl₂ (copper(II) chloride) solution, 500 μL of 7.5 mM neocuproine solution in 96% ethanol, 500 μL of 1 M acetate buffer (pH 7), 300 μL of distilled water, and 250 μL of the extract were thoroughly mixed. Absorbance was measured at 450 nm after 30 min at room temperature. The results are expressed in millimolar of Trolox per litre.

The results are presented as the arithmetic mean ± SD of the measurements of the three independent test samples prepared for each extract. Cuvettes (optical path of 1 cm) and a UV-VIS spectrophotometer U-5100 (Hitachi, Tokyo, Japan) were used for the tests.

2.4.7. HPLC Analysis

The concentration of phenolic acids in the fermented extracts from chokeberry pomace was determined by high-performance liquid chromatography (HPLC-UV) using an HPLC system from Knauer Smartline series (Knauer, Berlin, Germany) and a slightly modified method described by Nowak et al. [35]. The analysed extracts were selected for each fermentation condition based on the time point showing the highest antioxidant activity and total polyphenol content. The tested components were separated on a 125 mm × 4 mm column (C18) containing Eurospher 100 with a particle size of 5 μm. The HPLC analysis was carried out in isocratic mode with a mobile phase composed of 1% (v/v) acetic acid and MeOH (93:7 by volume), and the flow rate was 1 mL/min. The column temperature was set to 25 °C. The wavelength of the detector was set to 280 nm. Then, 20 µL of the sample was injected into the column. Individual phenolic acids were identified using reference substances by comparing retention times. Standard curves were generated by preparing individual phenolic acid solutions with concentrations of 0.00078%, 0.00156%, 0.00312%, 0.00625%, 0.0125%, and 0.025%. The standard curve was then plotted for each compound: protocatechuic acid (y = 67832x + 1.3704; R² = 0.999), gentistic acid (y = 37925 = 0.3976; R² = 0.999), m-salicylic acid (y = 9567.1x + 0.8702; R² = 0.999), vanilic acid (y = 20766x + 1.6397; R² = 0.999), caffeic acid (y = 21941x − 3.8051; R² = 0.999), and chlorogenic acid (y = 11324x − 1.6823; R² = 0.999). Before HPLC analysis, the samples were diluted three times. All samples were analysed thrice, and the results are presented as the arithmetic mean ± SD.

2.5. Statistical Analysis

The results are presented as the arithmetic means of at least four parallel determinations. Basic descriptive statistics were calculated for the parameters. The mean values were compared using an analysis of variance. One-way ANOVA was used to assess differences in means among the experimental groups. Significant differences between individual groups (fermentation time or measured vs. determined pH) were evaluated using Tukey’s test (α < 0.05) and Statistica 13.3 (StatSoft, Krakow, Poland). In statistical estimation, Pearson correlation coefficients (r) between the results of antioxidant activity obtained using the ABTS, FRAP, and CUPRAC methods, as well as the total polyphenol, anthocyanin, and proanthocyanidin contents, were calculated using Statistica 13.3. A value of p < 0.05 was considered statistically significant.

3. Results and Discussion

3.1. Empathising with the Consumer

The first stage of the research was to determine how food consumers perceive functional foods produced in the process of sustainable development. For this purpose, the study was conducted using a qualitative research method, namely, focus group interviews.

In the study, the participants in the focus group interviews were asked to declare the characteristics of food that they considered functional and sustainable. Functional food produced in the process of sustainable development was described oppositely to food perceived as conventional: “it may have health-promoting effects, for example, with the addition of vitamins”, “it has health benefits, therefore it meets individual specific needs of consumers”, and “these are products with reduced sugar content and reduced fat and cholesterol”. From these responses, it can be concluded that functional food is only partially associated with sustainable features. Regarding consumption habits, the participants most often mentioned products enriched with vitamins, minerals, and proteins, such as fermented juices with vitamin C, freeze-dried bars with berries, and fruit teas. They did not indicate other bioactive substances and noted that in some categories of functional food, the available products were too obvious and repetitive, suggesting a need for greater diversity. The distinguishing features of functional foods with sustainable characteristics include the origin of raw materials and products, their methods of preparation or processing, and the inclusion of fermented products with certain health-promoting properties. The participants emphasised that product ingredients and the degree of processing are essential determinants of functional character. When asked to provide examples of such products, they consistently described them as natural, minimally processed, and fully utilising raw materials. Illustrative comments included: “a functional and sustainable product is a natural, unprocessed product”; “healthy, natural product”; “unprocessed, the most simple, without any frills or chemicals”; “it should maintain a low degree of product processing”; “a product in which the raw material is used in 100%”; and “a product that fits into the trend of reducing food waste, complete use of the raw material”.

The summary of the qualitative research results, based on the participants’ focused interviews, revealed that the functional food market is constantly evolving in terms of product offerings. However, slightly less development is observed for functional foods with sustainable characteristics. In the respondents’ opinion, there are visible trends in the well-being and upcycling of domestic by-products of chokeberry processing, and the role of chokeberry pomace was particularly emphasised. According to the surveyed consumers, the functional character of sustainable food may be influenced by changing trends and consumption patterns. Moreover, health prevention encourages consumers and food producers to look for alternative dietary ingredients with health-promoting properties.

3.2. Problem Definition

The next stage involved analysing the collected information and defining the problems. By identifying the experiences, behaviours, and needs of the surveyed respondents, the team developed a list of problems for the target group in the form of generative questions (

Table 1. Identification of consumer experience, behaviour, and needs and generative questions.

Consumer Experience	Consumer Behaviour	Consumer Needs	Generative Questions
Functional food consumers rarely associate food products with sustainable features. They understand functional food as a supplement to vitamins, minerals, and proteins (they do not see other bioactive substances).	Functional food consumers are aware, care about their health, and seek opportunities to increase their body immunity.	Functional food consumers feel the need to enrich products with bioactive substances that benefit their well-being.	How can consumers of functional foods benefit from the addition of chokeberry pomace, which positively impacts their well-being by increasing their knowledge about the health-promoting ingredients present in this product?
Functional food consumers consume foods with functional properties (beneficial health effects); however, in some categories, product propositions are too boring and require variety.	Functional food consumers buy foods that benefit the health and are looking for intriguing foods.	Functional food consumers need to consume intriguing foods.	How can functional food consumers provide products containing the addition of chokeberry pomace with new taste sensations to lower their dietary monotony?
Functional food consumers eat natural and minimally processed food products because they are aware that they are of higher quality and positively impact human health.	Functional food consumers look for products that do not contain artificial ingredients.	Functional food consumers feel a need to balance the organoleptic characteristics and the low degree of processing associated with the addition of chokeberry pomace.	How can functional food consumers provide high-palatability products with the addition of chokeberry pomace while maintaining the advantages of colour and low degree of product processing?

).

Knowledge of the target group, derived from the focus group interviews conducted in the first stage, and the identification of problems and their sources in the second stage allowed us to define the requirements for the designed product:

• The product should consist of natural ingredients and limited food additives whenever possible while remaining attractive to consumers in line with the ‘clean label’ trend;
• The product should be characterised by a sustainable approach to using chokeberry processing by-products, encouraging the use of a circular bioeconomy;
• The product should have a higher antioxidant potential than a conventional product;
• The product should maintain a low processing degree.

3.3. Ideation

The impact effort matrix technique allowed for the structure of the ideas generated during brainstorming and led to the selection of the best possible solution. The team decided to develop fermented, dried chokeberry pomace as a sustainable product consisting of natural additives with high antioxidant properties and low processing degree.

During the planning of the fermentation process, it should be remembered that the mechanisms that positively influence antioxidant activity are different, so it is necessary to optimise the parameters of the experimental fermentation design [19]. Therefore, fermented chokeberry pomace was obtained using variable process parameters, namely fermentation time, pH, and glucose supplementation. Aspergillus niger was used to perform the fermentation process in chokeberry pomace because it was found to affect the antioxidant capacity of plant raw materials and alter their chemical composition depending on fermentation time [17,26].

3.4. Prototyping

At the prototyping stage, physical artefacts were created to illustrate an inexpensive way to solve the problem using the minimum viable product concept. This involved creating a product with sufficient functionality to meet the needs of potential users and to collect and analyse their opinions. The team developed 16 prototypes of fermented, dried chokeberry pomace (Figure 2).

3.5. Testing

The final step was to submit the developed prototypes for verification. Fermented chokeberry pomace was analysed for the content of compounds with antioxidant potential, including polyphenols, anthocyanins, and proanthocyanidins.

The evaluation of antioxidant activity using the ABTS, FRAP, and CUPRAC methods showed that among the fermented extracts without glucose supplementation, the samples incubated for 5 days at a measured pH (2.86–2.97) exhibited the highest antioxidant activity (

Table 2. Comparison of the TPC, TAC, TPAC, and antioxidant activity by ABTS, FRAP, and CUPRAC assays in fermented chokeberry pomace without glucose supplementation.

pH	Measured pH (2.86–2.97)				Determined pH (5.30–5.45)
Fermentation Time (Days)	0	2	5	8	0	2	5	8
TPC (mg GA/L)	1405.45 ± 70.37 a;A	2765.99 ± 45.33 b;B	3406.05 ± 70.37 c;B	2739.18 ± 105.60 b;B	1666.83 ± 46.07 a;B	2739.18 ± 95.55 b;B	2538.12 ± 98.67 b;A	1898.06 ± 217.72 a;A
TAC (mg Cy-3-Glu/L)	321.58 ± 3.89 b;B	506.18 ± 4.37 d;B	339.06 ± 2.40 c;A	279.24 ± 3.10 a;B	257.32 ± 3.47 b;A	471.68 ± 3.13 d;A	290.81 ± 4.34 c;A	145.91 ± 11.32 a;A
TPAC (mg Cat/L)	170.41 ± 6.87 a;B	564.25 ± 1.95 b;B	912.37 ± 27.98 d;B	761.49 ± 9.70 c;B	142.42 ± 1.70 a;A	496.97 ± 12.25 c;A	722.45 ± 10.03 d;A	422.53 ± 4.88 b;A
ABTS (mmol Trolox/L)	7.32 ± 0.80 a;A	14.52 ± 0.72 c;A	16.96 ± 0.34 d;B	12.79 ± 0.54 b;B	7.75 ± 0.24 a;A	12.99 ± 0.74 c;A	11.31 ± 0.68 b;A	7.43 ± 0.30 a;A
FRAP (mmol FeSO4/L)	17.31 ± 0.22 a;B	27.47 ± 0.44 b;B	35.81 ± 0.76 c;B	25.32 ± 0.73 d;B	14.82 ± 0.22 a;A	25.90 ± 0.56 b;A	25.09 ± 0.68 b;A	14.91 ± 0.38 a;A
CUPRAC (mmol Trolox/L)	13.84 ± 0.65 a;A	35.87 ± 0.06 c;B	37.57 ± 0.90 c;B	33.78 ± 0.77 b;B	14.87 ± 0.81 a;A	33.45 ± 0.75 b;A	32.10 ± 0.84 b;A	16.15 ± 0.68 a;A

Data are expressed as mean ± standard deviation. Within each pH condition, means that do not share the same lowercase letter (a, b, c, d) are significantly different at p < 0.05 between fermentation times. Uppercase letters (A, B) indicate significant differences (p < 0.05) between measured and adjusted pH at the same fermentation time.

). The antioxidant activities were 16.96 ± 0.34 mM Trolox/L, 35.81 ± 0.76 mM FeSO₄/L and 37.57 ± 0.90 mM Trolox/L for the ABTS, FRAP, and CUPRAC methods, respectively. A similar dependence was observed in the TPC and TPAC and proanthocyanidin, where the highest concentrations (3406.05 ± 70.37 mg GA/L and 912.37 ± 27.98 mg Cat/L, respectively) were also found in the extract incubated for 5 days at the measured pH. However, in the group of extracts without glucose supplementation, at a determined pH (5.30–5.45), the highest antioxidant activity and TPC were found in the extracts after 2 days of fermentation. In contrast, an inverse dependence was observed for fermented extracts supplemented with glucose (

Table 3. Comparison of the TPC, TAC, TPAC, and antioxidant activity by ABTS, FRAP, and CUPRAC assays in fermented chokeberry pomace with glucose supplementation.

pH	Measured pH (2.88–2.97)				Determined pH (5.27–5.60)
Fermentation Time (Days)	0	2	5	8	0	2	5	8
TPC (mg GA/L)	1944.98 ± 72.73 a;A	3677.49 ± 53.20 c;B	2786.10 ± 68.92 b;B	1747.26 ± 46.07 a;A	1465.77 ± 34.83 a;B	2380.62 ± 46.07 c;A	2461.04 ± 92.14 c;A	1800.88 ± 35.75 b;A
TAC (mg Cy-3-Glu/L)	300.33 ± 31.73 b;B	804.92 ± 10.52 c;B	319.25 ± 5.65 b;B	151.08 ± 2.23 a;A	246.17 ± 7.25 b;A	424.81 ± 20.87 d;A	279.63 ± 3.38 c;A	193.91 ± 7.47 a;A
TPAC (mg Cat/L)	199.07 ± 1.84 a;A	733.96 ± 21.71 d;B	521.44 ± 9.00 c;A	297.36 ± 6.01 b;A	144.94 ± 8.34 a;A	334.24 ± 12.22 b;A	578.05 ± 11.41 d;B	396.51 ± 9.27 c;B
ABTS (mmol Trolox/L)	7.89 ± 0.41 a;B	19.15 ± 0.67 d;B	11.05 ± 0.34 c;A	9.47 ± 0.50 b;A	6.07 ± 0.34 a;A	10.01 ± 0.17 b;A	13.35 ± 0.41 c;B	9.03 ± 0.58 b;A
FRAP (mmol FeSO4/L)	16.78 ± 0.67 a;B	44.68 ± 0.78 c;B	25.16 ± 0.88 b;A	16.57 ± 0.77 a;A	12.57 ± 0.70 a;A	21.61 ± 0.04 c;A	23.29 ± 0.95 c;A	16.96 ± 0.78 b;A
CUPRAC (mmol Trolox/L)	43.38 ± 1.05 c;B	59.90 ± 1.09 d;B	33.49 ± 1.00 b;A	21.12 ± 0.57 a;A	14.12 ± 0.74 a;A	24.74 ± 0.69 b;A	31.74 ± 0.81 c;A	23.43 ± 0.97 b;B

Data are expressed as mean ± standard deviation. Within each pH condition, means that do not share the same lowercase letter (a, b, c, d) are significantly different at p < 0.05 between fermentation times. Uppercase letters (A, B) indicate significant differences (p < 0.05) between measured and adjusted pH at the same fermentation time.

). The optimal incubation time of the extracts for the measured pH was 2 days, whereas for the pH determined, it was 5 days. As observed in extracts without glucose supplementation, the highest antioxidant potential and TPC were observed in extracts incubated at the measured pH. In this group of extracts, the highest antioxidant activities were as follows: 19.15 ± 0.67 mM Trolox/L for the ABTS method, 44.68 ± 0.78 mMFeSO₄/L for the FRAP method, and 59.90 ± 1.09 mM Trolox/L for the CUPRAC method. The total polyphenol, proanthocyanidin, and anthocyanin contents were 3677.49 ± 53.02 mg GA/L, 733.96 ± 21.71 mg Cat/L, and 804.92 ± 10.52 mg Cy-3-Glu/L, respectively. By analysing the effect of incubation time, pH, and glucose supplementation, we can conclude that the optimal conditions for obtaining fermented extracts from chokeberry pomace with high antioxidant potential, high polyphenol content, and high anthocyanin content using A. niger involve a 2-day incubation process at a measured pH with glucose supplementation. The shorter optimal fermentation time observed in the glucose-supplemented samples (2 days) compared to the non-supplemented samples (5 days) may be attributed to differences in fungal metabolism and substrate utilisation. The presence of glucose as an additional carbon source likely accelerates microbial growth and enzyme production, leading to the faster release of phenolic compounds and increased antioxidant activity. In contrast, under glucose-free conditions, the fungus relies mainly on carbohydrates naturally present in chokeberry pomace, resulting in slower fermentation dynamics and delayed achievement of maximum bioactivity.

Dulf et al. [26] assessed the impact of solid-state fermentation (SSF) using A. niger and Rhizopus oligosporus on the antioxidant activity, polyphenol content, and lipid composition of chokeberry pomace extracts. During both fermentation processes, a >1.7-fold increase in phenolic compound content was observed in the fermented extracts. They also observed a significant increase in antioxidant activity, as evaluated by the DPPH and TEAC assays. The effects of fermentation time (0, 2, 6, 9, and 12 days) were then examined. The optimal time for A. niger fermentation, in terms of total polyphenol and flavonoid content, was 9 days (1703.5 mg GAE/100g DW and 264.0 mg QE/g DW, respectively), whereas the anthocyanin content was highest in extracts fermented for 2 days. Extending the fermentation time with A. niger for 12 days decreased the total polyphenol and flavonoid content in the tested extracts. In the bioinoculation of A. niger, antioxidant activity significantly decreased on the ninth day of fermentation, but it stabilised on the 12th day. A slight increase and stabilisation of the antioxidant activity, as determined using the DPPH method, in extracts fermented with A. niger can be partly attributed to the presence of organic compounds not belonging to phenols, such as aromatic amines, peptides, and amino acids, which are released during fungal autolysis and may react with the DPPH radical [36]. Dulf et al. [26] and Martinez-Avila et al. [36] used SSF, whereas the present study used LSF to prepare chokeberry pomace. Increased antioxidant activity of fermented tartary buckwheat extracts prepared with A. niger was observed up to the 6th day of the fermentation process, followed by a decrease and stabilisation between the 20th and 24th days, as observed by Zhang et al. [17].

A decrease in antioxidant activity assessed using the ABTS, CUPRAC, and FRAP methods, as well as TPC, was observed on the eighth day of fermentation, regardless of the pH of the process and glucose supplementation. The statistical analysis of the obtained results showed that in the group of chokeberry pomace fermented at the measured pH, the differences in the results obtained using the ABTS, FRAP, CUPRAC, and Folin–Ciocalteu methods between the samples incubated for 2 and 5 days were generally statistically significant, with the exception of the antioxidant activity assessed using the CUPRAC method for samples without glucose supplementation. In the fermented extract group at the determined pH, these differences were generally statistically insignificant, with the exception of the antioxidant activity assessed using the ABTS method for samples without glucose supplementation and the CUPRAC and ABTS methods in the group of extracts with glucose supplementation. Statistically significant correlations were observed between the antioxidant activities obtained using the ABTS, FRAP, and CUPRAC methods, as well as TPC, TAC, and TPAC. The exceptions were the TAC and TPC results, which did not correlate with each other to a statistically significant degree (

Table 4. Correlation coefficients between antioxidant activity, TPC, TMA, and TPAC of fermented chokeberry pomace (p < 0.05).

	FRAP (mM FeSO4/L)	CUPRAC (mM Trolox/L)	ABTS (mM Trolox/L)	TAC (mg Cy-3-Glu/L)	TPAC (mg Cat/L)
TPC (mg GA/L)	0.953	0.838	0.948	0.704	0.877
FRAP (mM FeSO4/L)		0.841	0.963	0.804	0.814
CUPRAC (mM Trolox/L)			0.810	0.741	0.640
ABTS (mM Trolox/L)				0.724	0.851
TAC (mg Cy-3-Glu /L)					s.i.

s.i.—statistically insignificant.

).

Analysis of the effect of the measured (~2.9) and determined (~5.4) pH on antioxidant activity and polyphenol content showed that samples incubated at a lower pH generally exhibited higher potential. The exceptions in which antioxidant activity was significantly higher in the fermented extract group at the determined pH were samples incubated for 8 days (CUPRAC method) or 5 days (ABTS method) with glucose supplementation. Hur et al. [20] identified pH as one of the most important parameters influencing fermentation. pH significantly affects microorganism growth and enzyme degradation in the cell wall. These factors affect the distribution and stability of phytochemicals, directly affecting the position and pKa of hydroxyl moieties. This resulted in polyphenol deprotonation, which affected the antioxidant activity of the fermented samples. Compounds susceptible to pH changes include anthocyanins [37] and catechins [38]. Nielsen et al. [37], in a study on the stability of selected anthocyanins in blackcurrant juices in the pH range of 0.6–5.2, observed that approximately 90% of the tested anthocyanins remained stable up to pH 3.3. At pH 3.8, they noted minimal signs of instability, whereas at pH > 4.5, they noted a significant decrease in the stability of the tested compounds.

Another factor that may affect the differences in antioxidant activity and total polyphenol, anthocyanin, and proanthocyanidin contents of the fermented chokeberry pomace tested is glucose supplementation. The highest properties were observed in samples supplemented with glucose, except for the proanthocyanidin content. However, when comparing individual results obtained for fermented chokeberry pomace prepared under analogous conditions (incubation time and pH), where glucose supplementation was used as a variable, it was observed that the samples prepared without glucose supplementation often exhibited higher activity. This trend was particularly apparent in the samples incubated for 5 and 8 days at the measured pH and in the control samples and those subjected to 2-day incubation at the determined pH. Leitao et al. [39] noted the beneficial effects of glucose supplementation on the antioxidant activity and total polyphenol content of fermented papaya extracts. Based on the results of the samples obtained via spontaneous fermentation, bioinoculation of Gluconobacter oxydans, and bioinoculation combined with glucose supplementation, they concluded that bioinoculation combined with glucose supplementation led to the biotransformation of papaya polyphenols into phenol metabolites with enhanced antioxidant potential. It should also be noted that the microorganisms involved in the fermentation process obtain energy mainly from carbohydrates. Leitao et al. [39] noted that adding glucose to a medium may increase the production of pyruvate, which is an intermediate product in the fermentation process.

In the next research stage, the extracts from the fermented chokeberry pomace with the highest antioxidant activity, TPC, and TPAC were analysed for the content of phenolic acids using HPLC. Phenolic acids in fruits are mainly found in peels, where they are bound and form their structure. Hydrolysis or extraction is required to release large amounts of these compounds [40]. An increasingly used alternative to extraction and hydrolysis is enzymatic hydrolysis by various microorganisms during fermentation. The participation of some microorganisms increases the content of valuable ingredients in plant extracts [41]. Some species of fungi, such as Aspergillus sp., are known for their ability to produce enzymes that degrade the cell wall, resulting in the isolation of biologically active components from plant material [42]. Phenolic acids, which, according to the available literature, dominate in chokeberry pomace, were selected for identification. In previous studies, chlorogenic and protocatechuic acids were identified in chokeberry pomace [24,43], as well as caffeic acid [44], which is important for the subsequent use of fermented chokeberry pomace. In our studies, we consistently observed a significant increase in the content of individual phenolic acids in fermented pomace in both samples with and without glucose supplementation (

Table 5. Phenolic acids in fermented chokeberry pomace without glucose supplementation (mg/100 mL).

pH	Measured pH (2.86–2.97)		Determined pH (5.30–5.45)
Fermentation Time (Days)	0	5	0	2
Protocatechuic acid	0.57 ± 0.32 a;A	7.52 ± 0.05 b;B	0.74 ± 0.05 a;A	3.84 ± 0.11 b;A
Gentisic acid	2.74 ± 0.47 a;A	7.72 ± 0.35 b;B	3.51 ± 0.37 a;A	5.90 ± 0.34 b;A
m-Salicylic acid	0.12 ± 0.08 a;A	0.06 ± 0.04 a;A	0.94 ± 0.26 a;B	0.11 ± 0.06 b;A
Vanillic acid	2.62 ± 0.11 a;B	28.55 ± 0.35 b;A	0.95 ± 0.12 a;A	14.35 ± 0.56 b;A
Caffeic acid	n.d.	1.89 ± 0.03 a;B	0.72 ± 0.03 a;A	1.48 ± 0.07 b;A
Chlorogenic acid	1.51 ± 0.13 a;A	2.95 ± 0.10 b;B	n.d.	2.41 ± 0.19 b;A

n.d.—not detected. Data are expressed as mean ± standard deviation. Within each pH condition, means that do not share the same lowercase letter (a, b) are significantly different at p < 0.05 between fermentation times. Uppercase letters (A, B) indicate significant differences (p < 0.05) between measured and adjusted pH at the same fermentation time.

and

Table 6. Phenolic acids in fermented chokeberry pomace with glucose supplementation (mg/100 mL).

pH	Measured pH (2.88–2.97)		Determined pH (5.27–5.60)
Fermentation Time (Days)	0	5	0	2
Protocatechuic acid	2.58 ± 0.10 a;B	5.38 ± 0.08 b;B	0.68 ± 0.04 a;A	4.87 ± 0.06 b;A
Gentisic acid	9.01 ± 0.65 a;B	11.30 ± 0.89 b;B	2.60 ± 0.51 a;A	2.24 ± 0.60 a;A
m-Salicylic acid	2.19 ± 0.11 b;A	0.12 ± 0.08 b;A	n.d.	0.06 ± 0.04 a;A
Vanillic acid	4.75 ± 0.06 a;B	20.56 ± 0.36 b;B	0.82 ± 0.12 a;A	15.91 ± 0.11 b;A
Caffeic acid	1.32 ± 0.13 a;B	1.09 ± 0.10 a;A	0.77 ± 0.01 a;A	1.09 ± 0.11 b;A
Chlorogenic acid	3.31 ± 0.11 a;B	4.62 ± 0.40 b;B	1.04 ± 0.06 a;A	1.35 ± 0.11 b;A

n.d.—not detected. Data are expressed as mean ± standard deviation. Within each pH condition, means that do not share the same lowercase letter (a, b) are significantly different at p < 0.05 between fermentation times. Uppercase letters (A, B) indicate significant differences (p < 0.05) between measured and adjusted pH at the same fermentation time.

). Figure 3 shows an example chromatogram of fermented chokeberry pomace without glucose supplementation on the fifth day of fermentation at a measured pH. In the analysed extracts, protocatechuic, gentisic, m-salicylic, vanillic, caffeic, and chlorogenic acids were identified. In most of the fermented chokeberry pomace, a significant increase in the content of these compounds was observed on both the second and fifth days of fermentation. The content of these compounds in the group of extracts without glucose supplementation ranged from 0.06 ± 0.04 mg/100 mL for m-salicylic acid to 28.55 ± 0.35 mg/100 mL for vanillic acid. A significantly higher content of phenolic acids was found in the extract obtained in a 5-day fermentation process at the measured pH compared with the extracts obtained in a 2-day fermentation process at the determined pH. The highest amount of vanillic acid was present in the extracts fermented at the measured pH, which increased significantly compared with the control sample, from 2.62 ± 0.11 to 28.55 ± 0.35 mg/100 mL. Similarly, a significant increase in protocatechuic and gentisic acids was observed, the amounts of which in the extract fermented for 5 days were 7.52 ± 0.05 and 7.72 ± 0.35 mg/100 mL, respectively. The content of vanillic acid in the extracts obtained at a fixed pH increased from 0.95 ± 0.12 mg/100 mL in the control sample to 14.35 ± 0.56 mg/100 mL in the extract obtained after 2 days of fermentation. Similar trends in phenolic acid content were found in the group of extracts with glucose supplementation, in which the amounts of these compounds ranged from 0.064 ± 0.043 mg/100 mL for m-salicylic acid to 20.56 ± 0.36 mg/100 mL for vanillic acid. In this group, most of the phenolic acids were present at significantly higher levels in the extracts at pH 2.88–2.97 than in the extracts at pH 5.27–5.60. An increase was observed for vanillic and gentisic acids in the extract on the second day of fermentation (20.56 ± 0.36 and 11.30 ± 0.89 mg/100 mL, respectively), which was significant compared with the amounts found in the control samples (4.75 ± 0.06 and 9.01 ± 0.65 mg/100 mL, respectively). However, for extracts at the determined pH, the vanillic acid content increased from 0.82 ± 0.12 mg/100 mL (control extracts) to 15.91 ± 0.11 mg/100 mL (5th day of fermentation).

Other authors have also confirmed an increase in the content of these compounds in plant pomaces subjected to fermentation. For example, a significant increase in the content of chlorogenic acid in chokeberry pomace was observed on the 2nd, 6th, 9th, and 12th days of fermentation with A. niger [26]. The increase in phenolic compounds in fermented plant extracts is attributed to the action of cellulolytic, lignolytic, and pectinolytic enzymes, which are mainly produced during fungal growth [45]. These enzymes effectively break down cell wall components and hydrolyse the ester bonds that connect individual phenolic compounds to the cell wall.

Consequently, this process increases the levels of valuable secondary metabolites in the extract [26]. In our study, we observed a significant increase in vanillic acid content in the fermented extracts compared with the control. During fermentation, some strains of fungi, such as A. niger, can form vanillic acid by the degradation of ferulic acid. Ferulic acid metabolism occurs essentially through the degradation of the propane chain, leading to vanillic acid production [46]. Vanillic acid is formed via the biotransformation of lignocellulosic by-products by fungi. This occurs because fungi possess a specific enzyme system. For example, during the metabolism of ferulic acid by P. fluorescens, vanillic acid is secreted as an end product by vanillin dehydrogenase during the biotransformation of vanillin [47]. An interesting observation in our research was the decrease in the content of m-salicylic acid in the fermented extracts compared with the control samples. The probable cause of the degradation of some phenolic acids is the action of various enzymes secreted by A. niger, especially esterases [40]. Other authors observed a fivefold decrease in 4-hydroxybenzoic acid content in extracts fermented with A. niger [40]. 4-Hydroxybenzoic acids and 3-hydroxybenzoic acids (m-salicylic acid) belong to the monohydroxybenzoic acid group, which are easily broken down by microorganisms [48].

The fermentation method of dried chokeberry pomace significantly affected selected quality parameters, and different optimisation conditions cause changes in the content of the analysed bioactive compounds. The optimal treatment was fermentation with bioinoculation using A. niger, which lasted 2 days at a measured pH with glucose supplementation. Increasing the pH of the extracts without supplementation shortened the optimal fermentation time to 2 days, whereas in the group supplemented with glucose, the optimal fermentation time was extended from 2 to 5 days. Extending the fermentation time to 8 days had a negative impact on the tested potential of the extracts, regardless of the pH and supplementation. Results suggest that fermentation at a lower (measured) pH resulted in fermented, dried chokeberry pomace with higher antioxidant activity, TPC, TAC, and TPAC, compared with the process conducted at a higher (established) pH.

Building on the findings that the fermentation method of dried chokeberry pomace significantly influences quality parameters and bioactive content, it is crucial to situate this within a broader sustainability framework in food production.

Effective management of food by-products has become a cornerstone of sustainable development strategies and efforts to minimise environmental degradation. Materials previously regarded as waste are now increasingly repurposed as chemical substitutes, enhancing the viability of environmentally friendly technologies, despite ongoing challenges related to cost and operational efficiency [49]. In the food sector, these by-products often possess high levels of bioactive compounds, offering potential nutritional and health benefits when reintroduced into food systems—thereby supporting circularity and reducing reliance on primary resources [50]. The strategic reintegration of such materials across industries not only contributes to ecological goals but also opens economic opportunities and fosters more efficient resource utilisation, consistent with the principles of a circular economy [51,52].

Research practices themselves should also reflect resource-conscious thinking. In this study, the application of design thinking (DT) aligns with this perspective. Its iterative structure enables researchers to simulate, prototype, and refine solutions in virtual settings before committing to physical development, thereby conserving materials, time, and financial input. In doing so, DT facilitates the transformation of waste streams into valuable assets. For example, whey, a common by-product of cheese-making, has been successfully converted into high-value nutritional components—an approach that illustrates how rethinking waste can lead to innovative resource recovery [53]. Likewise, biotechnology methods such as enzymatic-assisted and fermentation-assisted extraction allow for the recovery of functional compounds from food by-products, reducing dependence on virgin materials and strengthening the sustainability of food processing systems [54,55].

As Leal Filho et al. [56] emphasise, design thinking provides a robust framework that combines analytical rigour with creative exploration, offering tools and processes that are especially suited to tackling sustainability-related challenges. Buhl et al. [9] further demonstrated how this methodology fosters innovation aimed at long-term sustainability. A critical aspect of this approach is its focus on user experience. By prioritizing consumer needs and behaviours, DT ensures that sustainable products do not compromise usability or desirability [57,58].

By integrating waste reduction and the upcycling of by-products into early stages of product development, design thinking supports the emergence of circular strategies that reduce environmental burdens while enhancing resource efficiency [59,60]. In this way, design thinking not only enables more sustainable innovation but also offers a practical and flexible pathway toward the systemic transformation of food production. Future research should focus on evaluating the safety and regulatory compliance of the proposed ingredients in accordance with European Union food legislation. Particular attention will be given to the requirements of Regulation (EC) No 178/2002 [61] on general food law and Regulation (EU) 2015/2283 [62] on novel foods. Where applicable, a full risk assessment dossier will be prepared and submitted to the European Food Safety Authority (EFSA) as part of the pre-market authorisation process for novel foods. This step is essential to ensure the safety, transparency, and legal viability of incorporating the ingredients into food formulations intended for the EU market.

4. Conclusions

The design thinking method was successfully used to design and develop a new food product: dried fermented chokeberry pomace using Aspergillus niger. The quality of the powder depends mainly on the fermentation process used and the selected parameters. Based on the results for the antioxidant potential, TPC, TAC, and TPAC of the designed prototypes, we conclude that variable parameters, namely incubation time, pH, and glucose supplementation, influence the properties of fermented dried chokeberry pomace. Based on this study, dried fruit samples fermented for 2 days at a measured pH with glucose supplementation were selected for further improvement. This solution aligns with the consumer-identified needs of the target consumer group; however, additional analyses are necessary, including an analysis of changes in its quality during product storage. The feedback obtained allows us to improve the solution or return to previous stages if, for example, it is necessary to redefine a previously described problem, because design thinking is essentially a non-linear approach. By dividing the design process into five iterative stages, the design thinking method is easy to follow and implement in the food production sector. The results provide a solution that allows for a thorough understanding of the product design context and the target consumer. Importantly, this approach also supports sustainable food innovation by promoting the valorisation of food industry by-products, reducing waste, and encouraging the responsible use of natural resources throughout the product development cycle.