Despite value chains approach have been developed since the years 1990, labor in agri-food value chains is a relative new topic discussed by the international scientific community, as the 343 articles identified have been published since 2000 (Figure 2). However, we observed an increasing number of publication overtime. Until 2011, the new topic is launched with few articles published and cited by year. Between 2012 and 2016, the interest of researchers continues to rise, as the number of articles and citations were twice as high as the previous period. Since 2017, the consolidation of the topic is ongoing, considering that the number of articles and citations strongly increased. According to this trend, labor in agri-food value chains is a topic under construction by the international scientific community, with a promising expansion and consolidation in the next years.

The identified articles included research from 82 countries. The countries that published at least 10 papers between 2000 and 2020 are displayed in Figure 3. England, United States and Germany are the high publishers, since they are responsible for 55% of articles. Kenya, India, South Africa, Ethiopia, and Mexico are among the high publishers, despite developed countries are prevalent.

Almost 200 journals and more than 1,000 authors published about labor in agri-food value chains over the past 21 years, which indicates that this is a theme with a large audience. Regarding the journals, the multidisciplinary or interdisciplinary perspective are prevalent among the high publisher ones, whether they are focused in the upstream (e.g., agricultural production) or downstream (e.g., food) part of the chain. However, 80% of journals published at most two articles between 2000 and 2020 (Figure 4).

Regarding the authors, the high publisher ones are responsible for 18% of overall publications. However, 98% of authors published at most two articles over the past 21 years, which shows a strong punctual and fragmented contributions regarding analysis of labor in agri-food value chains (Figure 5).

The reference articles are displayed in Table 1, which were mainly published in multidisciplinary journals related to development studies (i.e., World Development, Journal of Development Studies…) or journals related to economics (i.e., Ecological Economics, Annual Review of Resource Economics). Based on keywords, we observed that international community was strongly interested by labor standards and other types of standards (e.g., private standards, private social standards, sustainability, codes of conduct, corporate codes, certification), global value chain governance, and contract labor (Table 1). Four of the reference authors (Barrientos S., Riisgaard L., Tallontire A., Mutersbaugh, T.) had articles among the high cited ones. Moreover, Gereffi G., author of seminal articles for the value chains approach, is co-author in two high cited articles.

The network analysis of keywords allowed us to identify four research domains on labor in agri-food value chains: (1) labor governance in global agri-food value chains through standards, (2) employment in agri-food value chains and impacts on socioeconomic conditions of rural areas, (3) gender issues and agri-food value chains, (4) labor and upgrading in global agri-food value chains (Figure 6).

Labor governance in global agri-food value chains through standards is the first research domain, which is focused on the analysis of how agri-food value chain agents coordinate labor issues within the chain. Standards are the main mechanism of governance used by the agents, principally private standards—including certification (e.g., fair trade)—to regulate several issues, whether they are directly or indirectly linked to labor, such as sustainability, food quality and safety. The highlighted empirical studies are related to diverse of agri-food value chains (e.g., livestock, flower, coffee, banana, aquaculture) in African countries (e.g., Kenya, Tanzania, Ethiopia, Egypt), and rice value chain in Asian countries (e.g., Asia, Vietnam). The paper by Raynolds et al. (2007) provide us an example of studies developed in this research domain. The authors compared five third-party certifications and showed their differences on governance structure, including environmental and social standards, and the alignment of social standards to ILO conventions for decent work (e.g., rights to association and collective bargaining, freedom from discrimination and unequal pay, no forced or child labor, minimum social and labor conditions, rights to safe and healthy working conditions) (Raynolds et al., 2007).

The second research domain, “employment in agri-food value chains and impacts on socioeconomic conditions of rural areas,” is related to the socioeconomic impacts of agri-food value chain development in rural areas. It is focused on to two connected factors. The first factor is employment creation and income generation (e.g., employment, wages, income) due to the inclusion of smallholder farmers in global markets, including contracting farming. The second factor is the impacts of employment creation and income generation on broader socioeconomic conditions of rural areas, which cover poverty reduction, livelihood food security, and rural development. For example, Rich and Wanyoike (2010) assessed the multi-dimensional socioeconomic impacts of the 2007 Rift Valley Fever Outbreak in livestock value chains in Kenya, which included employment and income reduction, food insecurity among producers, and economic losses throughout the value chain (Rich and Wanyoike, 2010).

Gender issues and agri-food value chains is the third research domain. A gendered analysis throughout the value is focused on the women labor—but not limited to-, the benefits to be included in agri-food value chains (e.g., empowerment), and constraint to keep competitive in chains. Regarding the fish value chains, Murphy et al. (2020) identified the gender-based market constraints and their impact on retailers enterprise economic performances (Murphy et al., 2020).

The fourth research domain is labor and upgrading in global agri-food value chains. Upgrading is understood as the path to higher value-added activities aiming to improve profits, technology, knowledge and skills. The economic upgrading regards improvements in processes, product, and technology, which impact value chain efficiency. The social upgrading regards improvement in the rights, employment conditions and benefits for workers. Based on examples from agri-food sector and non-agricultural sectors (garment, information technology), Barrientos et al. (2011a) showed how the relationship between economic and social upgrading address decent work issues while increasing the value added Barrientos et al. (2011b).

An increasing literature body is using the value chain approach to investigate how interactions between upstream and downstream chain agents are impacting and being impacted by labor issues in the agri-food sector, such as power relations for the compliance with fundamental labor rights in banana plantations and workers collective bargain (Riisgaard, 2005), or the adoption of fair trade certification to demonstrate the adoption of social standards along the chain (Raynolds et al., 2007; Valkila and Nygren, 2010). We showed that labor in agri-food value chains has international audience, and the consolidation of this new scientific community is in progress. However, knowledge production in this field must become consistent overtime. This condition implies in a radical change of the current pattern, which is characterized by mainly advances of a restraint leading scientific network and irregular contributions of several authors around the world.

The lead scientific network is composed mainly by developed countries publishing about labor in agri-food value chains, principally England, USA, Germany. However, we identified that developing countries are included among the main producers of scientific knowledge in this field, especially Kenya, India, and South Africa. The highlighted contributions from developed and developing countries are a specificity of the value chains scientific community, and previous reviews regarding labor studies in agriculture showed that Africa, Asia and Latin America are data-providing regions (Oliveira et al., 2017; Malanski et al., 2019, 2021b). This could be linked to the increasing participation of developing countries in the global agri-food trade (Poonyth, 2021), which provides a diversified empirical conditions for research, since countries have different socioeconomic and institutional conditions for the expansion of the agri-food activities and trade.

This scenario was the basis to the development of four main research domains on labor in agri-food value chains: (1) labor governance in global value chains through standards, (2) employment in value chains and impacts on socioeconomic conditions of rural areas, (3) gender issues and value chains, (4) labor and upgrading in global value chains (Figure 6). Among them, labor governance is the biggest. Governance is a major topic in the value chain approach, since the coordination of chain agents is essential to ensure that activities within the value chain works (Humphrey and Schmitz, 2001; Gereffi et al., 2005). Governance in an agri-food value chain is headed by a key agent that coordinates other chain agents. Considering that agri-food chain is a buyer-driven value chain (Kaplinsky and Morris, 2000), retailers are identified as key agents in global agri-food trade (Freidberg, 2003; Dolan, 2004; Kritzinger et al., 2004; Lee et al., 2012).

However, the literature also highlights the important role of international bodies in value chain governance, which is the case of ILO and FAO, with advanced decent work guidelines in global trade (Barrientos et al., 2011b; FAO, 2014; Posthuma and Rossi, 2017). Decent work guidelines were largely assimilated in standards regulating labor issues in agri-food value chains (Barrientos et al., 2003; Raynolds et al., 2007; Grammont and Flores, 2010; Valkila and Nygren, 2010; Riisgaard and Hammer, 2011; Ahsan et al., 2018). In addition, non-governmental organizations and civil society are pressuring chain agents against employment pre-carity and poor working conditions (Riisgaard, 2005; Brown and Getz, 2008; Piao et al., 2019). Consumers awareness about these labor issues is rising and they are more attentive to standards (e.g., certifications, labels) when purchasing an agricultural product (Janssen and Hamm, 2012; Grunert et al., 2014; Liu et al., 2019).

Nevertheless, the effectiveness of the standards as mechanisms to improve employment and working conditions is not a consensus in the international literature (Barrientos et al., 2003; Barrientos, 2008; Riisgaard, 2009; Grammont and Flores, 2010; Valkila and Nygren, 2010; Riisgaard and Hammer, 2011; Lee et al., 2012; Pegler, 2015; Ahsan et al., 2018). This situation sheds some light in the contradictions about the upgrading capacity of agri-food value chains. Both economic and social upgrading of agents within a value chain are main arguments to support the development of value chains, especially considering the benefits for upstream agents in developing countries (Barrientos et al., 2011a; Trienekens, 2011). On the one hand, the literature from the perspective of downstream agents highlights that the development of value-adding activities improves technology, profits and knowledge for upstream agents, the creation of employment is associated to the demand for higher skilled workers as a consequence (Carr et al., 2000; Barrientos et al., 2011a,b). That literature more focused in economics considered labor as a resource, thus labor costs where the main issue when discussing the relation between labor and economic upgrading in global trend (Barrientos et al., 2011b). On the other hand, the literature from the perspective of upstream agents highlights that inclusion in value chains do not necessarily improves employment and working conditions (Barrientos et al., 2011a,b). The literature more focused in socioeconomics considered labor under several aspects when discussing labor and social upgrading, as worker's rights, decent work, labor regulation, employment and working conditions (Dolan, 2004; Riisgaard, 2005; Pegler, 2015; Staelens et al., 2018; Matheis and Herzig, 2019). Such contradictions between economic and social upgrading of agri-food value chains regarding labor issues are related to the development of flexible and precarious employment and work (Barrientos et al., 2011b), principally for the most socioeconomic vulnerable people (e.g., women and migrants) in the upstream part of the value chain (Barrientos et al., 2003, 2019; Dolan, 2004; Tallontire et al., 2005; Grammont and Flores, 2010; Milbourne and Coulson, 2021).

The development of agri-food value chains in rural territories impacts socioeconomic conditions of people. However, the nature of impacts is controversial. As we indicated above, lack of decent work is a central concern, which negatively affects the sustainable development of agri-food value chains (FAO, 2014). While some authors argue that agri-food value chains plays a key role in promoting regional development through integration of farms in markets and stimulating value-adding activities in food transformation and marketing (Lie et al., 2012; Maertens et al., 2012; Hardesty et al., 2014; Christiaensen et al., 2020). Increasing income and decreasing food insecurity in poor households, as well as poverty reduction in rural areas through employment creation and farmers market inclusion are the main benefits indicated by authors (Lie et al., 2012; Maertens et al., 2012). These arguments are even more highlighted when considering that 75% of poorest people in the world live in rural areas (FAO, 2018).

Women are among the most vulnerable socioeconomic workers in agri-food sector (Tallontire et al., 2005; Barrientos et al., 2019). Some authors indicated that women inclusion in agri-food value chains contribute to decrease the gender gap and increase women empowerment through several actions (e.g., equal payment for men and women, maternity rights, female specific training, family-friendly policies), which can rely on the adoption and the compliance with gendered labor standards (Barrientos et al., 2019; Raynolds, 2021). Despite the advances, gender inequalities remain as a major concern for sustainable agri-food value chain, such as institutional barriers to active voice of women in cooperatives (Wijers, 2019), strong concentration of male workers in packaging, transportation and marketing (Masamha et al., 2018; Murphy et al., 2020), unequal decision-making power in households (Oduol et al., 2017; Bullock et al., 2018; Masamha et al., 2018), difficulties to access production assets (Deere and Leon, 2003; Doss, 2018; Kang et al., 2020).

The main labor issues are addressed by value chains agents though standards, principally labor standards (Riisgaard and Hammer, 2011), or those associate with social standards (Raynolds et al., 2007; Riisgaard, 2009), and certifications regulating broad sustainable parameters, which includes the social ones (e.g., fair trade) (Raynolds et al., 2007; Valkila and Nygren, 2010). Those standards are strongly linked to decent work guidelines defined by international bodies, such as ILO and FAO (Raynolds et al., 2007; Riisgaard and Hammer, 2011; FAO, 2014), and several field work showed their impacts on employment conditions, income generation and wages, working conditions, safety work, and gendered issues (Barrientos et al., 2003; Dolan, 2004; Grammont and Flores, 2010; Valkila and Nygren, 2010; Ahsan et al., 2018; Masamha et al., 2018; Murphy et al., 2020). Despite the advances in the value chain literature body covering the broad socioeconomical impacts of regulation of labor issues trough social standards, we identified some critical blind spots regarding the governance of labor in agri-food value chains.

We understand that standards for agricultural production and processing, food quality and food safety also impact labor, and these impacts are not necessarily addressed by labor or social standards. For example, UK retailers requirement regarding food quality and flexible supply (i.e., according to demand) resulted in long working days varying between 8 and 16 h per day in 6 days a week in large horticultural farms in Kenya (Dolan, 2004). USA retailers or processing plants requirements regarding food quality and food safety resulted in changes in agronomic practices and buildings to produce tomato all year-round and changed work pattern from seasonal to “permanent year-round” in large and very large farms in Mexico (Grammont and Flores, 2010). Multinational export enterprise's requirements for high-quality mango are better achieved by smallholder farmers in Costa Rica when labor is performed by family workers than employees (Zúñiga-Arias et al., 2008). Therefore, these mechanisms of labor governance in agri-food value chains have implications on issues like new tasks to perform due to changes in agronomic practices, rhythms to perform tasks—whether within a working day or over the year, and work organization though delegation of “critical” tasks to employees.

Another blind spot is how the compliance with standards are impacting the insertion of upstream agents in market, and its consequences for value chain. For example, the application of European Union standards for milk quality in Bulgarian dairy sector resulted in: (1) an outflow of 55% dairy farms supplying dairy industry for EU market due to aging of the household, health problems and an increase in off-farm employment, and (2) the structuration of dairy companies processing milk for domestic market or for export outside EU, as they not complied with EU standards (Van Herck and Swinnen, 2015).

Considering that labor in agri-food value chains is a new scientific community, we intended to identify some blind spots, rather to cover all of them. Moreover, other research topics can emerge overtime according to interactions between upstream and downstream agents, local and global labor dynamics, public and private governance of labor, food production and processing, and consumers' demands. A suggestion for future research is to build a typology based on a detailed analysis of topic diversity, including disciplines, approaches, methods in each one.