**3. Methodology**

We conducted a single case study to achieve the research objective and answer the research questions. Case studies are suitable for exploratory, descriptive, and explanatory research. Case studies are differentiated into multiple and single case studies according to the number of research objects. If a research object is analyzed in detail, single case studies are methodologically suitable [40]. In order to be able to develop a holistic governance approach for sustainability enhancements in food supply chains while considering the interactions and dynamics between all participants, we decided to conduct a single case study.

Following Yin [40], the methodological approach for case study research is divided into four phases: planning and design (1), data collection (2), data analysis (3), and reporting (4).

First, we developed the research goal, determined the research questions, designed the study, and selected the case. The analyzed food supply chain was selected because the final products (confectioneries) are advertised as particularly environmentally and socially sustainable. The trading company aims to enhance sustainability in the food industry and wants to trade exclusively organic and fair-trade products. The trading company claims that all individual stages of the supply chain act sustainably, allowing comprehensive insights into the sustainability governance of the whole supply chain. It is striking that all actors in the supply chain do not implement their sustainability efforts due to political pressure. Instead, actors behave sustainably out of their own intention: "[ . . . ] it has to be [ . . . ] good for the environment, good for the business and good for the people [ . . . ]" (IP2). Most companies in the supply chain are therefore motivated and committed to ensuring that their business activities are as sustainable as possible.

Additionally, the sustainability standards required by the trading company exceed all legal minimum sustainability standards in the affected countries. Thus, few companies also increase the sustainability of their activities due to pressure from supply chain partners. The actors may only be part of the supply chain if they implement the sustainability standards set by the trading company, as these are, for example, required for marketing the end product. Actors who normally only comply with legal sustainability requirements (e.g., company D) therefore implement higher sustainability standards in order to earn money as a manufacturer in the supply chain.

We conducted semi-guided expert interviews at each stage of the supply chain. The interview guide consisted of four different interview sections. First, the partners were welcomed, the interview topic was introduced, and a mutual understanding of the most important terms was created (1). Afterward, the governance and coordination of the supply chain (2), sustainability in the organization and the supply chain (3), and, in the last section of the interviews, sustainability governance in the examined supply chain (4) were discussed. We selected at least one interviewee from each stage of the supply chain, from the raw material production to the food retailer (Table 1). The experts were selected based on their role in the companies. In order to make statements about supply chain processes and their sustainability, plant managers, purchasing managers, supply chain managers, and sustainability managers were mainly interviewed. The interviewees have an average professional experience in their current job position of over five years. Overall, the interviews at each company lasted an average of 1 h and 5 min. It was not possible to interview a representative of the raw material production cooperative in South America in person because they do not have a sufficient internet or phone connection. Instead, a comprehensive questionnaire based on the interview guide was completed by the farm.


**Table 1.** Interview participants.

The audio recordings of the interviews were transcribed and served as the primary data source. The structured and qualitative content analysis of the transcripts was performed according to Mayring [41] and was supported by the analysis software *MAXQDA 2020*. *MAXQDA* allowed us a software-based coding of the interview transcripts to structure the data analysis. The coding categories were first deductively derived from the preliminary theoretical consideration and the interview guide. Three categories were formed at the first coding level. The first category "General Information" includes all statements about the interview partners, the company or introductory formalities. The second category "Governance Mechanisms" includes all parts of the interviews in which mechanisms are named or described that manage and coordinate supply chains and contribute to increasing sustainability. In the third category "Sustainability", all passages of the interviews that refer to the three dimensions of sustainability are coded. In order to better assess and distinguish the statements in the interviews, several subcodes were assigned to each coding category. The category of "Governance Mechanisms", for example, was divided into formal and informal mechanisms, and within these categories, further subcategories regarding the individual mechanisms (e.g., contracts, audits and monitoring) were listed.

During the analysis of the interview transcripts, additional sub-categories were inductively developed and implemented into the coding system. For example, "obstacles to sustainable supply chains" were coded, which describe blockages that stand in the way of a more sustainable coordination of supply chains and reveal more about the actual application intentions of the individual mechanisms.

*MAXQDA* can help by creating overviews of code overlaps, e.g., of all text passages in the transcripts that deal with informal governance mechanisms and social sustainability aspects simultaneously. This allows a more precise and reliable analysis of the interviews since the researcher has a quicker overview of all text passages relevant to a certain topic and can easily detect agreements and contradictions between the interviewees.

The interviewees' answers and comments mainly refer to the examined supply chain. In some cases, they also reflect general experiences regarding sustainability governance from other food supply chains. These comments are also considered as supplementary information in the results and discussion section to present the sustainability efforts at each stage of the supply chain more comprehensively.

While the interviews serve as the primary data source, we also collected secondary data to verify the interviewees' statements. For this purpose, we analyzed documents and websites of the examined companies (e.g., sustainability reports) for aspects related to sustainability governance. This data triangulation makes it possible to identify contradictions in the primary data and, if necessary, to clarify them together with the interviewees. The results of the data analysis are presented in the next section, and the conclusions, which can be drawn from the analyzed data, are highlighted in the discussion section.
