## 1 Introduction  
The idea of conducting corporate social responsibility (CSR) has undergone phenomenal growth in recent decades and has been rolled out in diverse sectors globally, such as the European banking industry [1], Vietnamese coffee sector [2], Jordanian pharmaceutical industry [3], the U.S. restaurant industries [4], Chinese food industry [5], and so on. Indeed, this positive signal has attracted increasing interest from corporations due to the advantages of adopting CSR into their business strategy [6; 7; 8]. Some recent studies have stated the critical role of CSR activities; for example, the positive effects of CSR on the firm's financial performance [9; 10], the value perception by consumers is generated [11], corporate reputation, consumer's satisfaction, or competitive advantage of the company [12; 13; 14]. Thus, two major characteristics contribute to CSR simply understanding as follows: firstly, the relationship between corporate responsibility and the firm's stakeholders, including internal and external. Secondly, toward sustainable development, which obligation has divided into three major issues: enhancing the economy, protecting the environment, and contributing to local society. Hence, CSR initiatives have been conducted and considered an excellent tool to attain sustainability [15; 16; 17]. In terms of supply chain management (SCM), the structure starts from the first stage known as upstream suppliers to the last step known as downstream customers; thus, there are many relationships among stakeholders in the supply chain that must be solved and predicted [18; 19; 20]. Additionally, the positive signal from CSR initiatives can enhance SCMperformance and may obtain a sustainable supply chain; thus, the number of studies integrating CSR initiatives into SCM has also been gradually becoming popular and diverse in many different industries worldwide [14; 21; 22]. Hence, adopting CSR initiatives into SCM may have been affected by various factors or barriers [18; 19]. The customer is at the last stage of the supply chain but also plays a decisive role in the sales of products and impacts the economic responsibility of the firms. However, there are only a few studies concerning the relationship between customers and manufacturers, which have an influence on CSR ideas, especially the food supply chain [16; 17]. The food supply chain has several particular characteristics compared to other sectors; thereby, research integration of CSR initiatives into the food SCM is attaining much attention due to its contribution to sustainability, particularly in transitional economies [23]. From some of the existing CSR-SCM studies about stakeholder theory, they have demonstrated that businesses' efforts to adopt CSR activities into corporate governance policies to satisfy the interests of shareholders and stakeholders because SCM plays a role as the critical interface with suppliers or agency services, for instance, logistics services, transport providers, service of yards and warehouses [24; 25]. Unfortunately, only a few studies consider the optimal model related to SCM stakeholders; meanwhile, the excellent role of CSR programs in SCM sustainability has not been considered properly, particularly in transitional economies [21; 22]. Thus, this research aims to propose an optimal model for the food supply chain, which can adopt CSR initiatives into the food SCM. In this way, supporting the food company has a social contribution as well as obtaining superior financial performance. This study has some research questions as follows:  
_RQ1. What is the optimal social charity amount for per unit product selling?_  
_RQ2. What is the optimal production run time of the manufacturer?_  
_RQ3. What is the optimal return rate of used products from the customer?_  
This study makes several contributions to the published literature regarding CSR and SCM.