Service Quality in Hospitality and the Sustainability Effect: Systematic Literature Review and Future Research Agenda

This article presents a systematic review of the literature on quality of service and sustainable practices in the hospitality sector with the objective of analyzing the state of the art, identifying gaps for future lines of research, and defining a future research agenda. The number of articles on these topics, although not particularly high, does demonstrate a growing trend. Despite this growth, however, several untreated lines of research were detected in three specific areas. In the first area, emphasis is placed on the critical factors that affect the quality of service. In the second area are the specific practices and tools of sustainability and quality of service that affect development and business success. Finally, the third section analyses the impact of strategies and the management of sustainable practices and quality of service with respect to business development. Research questions have been defined for each area.


Introduction
In global terms, with respect to rapid growth and social, economic, and environmental impact, the tourism industry is one of the most important industries in the world [1][2][3]. In recent years, the hospitality sector has faced the challenges that come with being part of the trends of globalization, localization, personalization, and concern for the environment [4,5]. Many studies have focused on improving the performance of tourism and hotels [6,7]. In addition, there is a positive relationship between quality of service and customer satisfaction in the hotel industry [8][9][10], as well as between quality of service and the consumer's perception of quality [11]. Consequently, to survive and achieve successful results, quality improvement is key in a sector as competitive as the hospitality industry [12][13][14]. Therefore, hospitality companies' good management of these quality of service practices will allow their development and success [15].
Additionally, sustainability is considered an important element in terms of reputation. In the hospitality sector, certifications of sustainable practices form a competitive advantage [16], and they give businesses a better reputation among customers [17,18]. Previous studies show a positive association between environmental practices and business success in the hospitality sector [19,20]. Sustainable development has been a growing topic in the years since the origination of this concept in 1987 from the World Commission on Environment and Development (WCED) [21].
The importance of this sector is reflected in the global economy, as it accounts for 10.4% of all global economic activity; moreover, it represents one in ten jobs worldwide [3]. The importance of sustainable tourism is reflected by its inclusion in the Sustainable Development Goals (SDGs) set by the United Nations (UN) for the year 2030 [22,23]. Specifically, SDG 8 deals with sustainable economic growth, and full occupation is one of its indicators, including policies that help promote sustainable tourism and create local employment [24].
The inclusion of sustainability in quality management should have a positive impact on the results of the company, but in no case should it lead to a reduction in the quality of other services.
Given the aspects described above, the present systematic review of the literature aims to identify the main factors and sustainable practices of quality of service to determine how they impact the development and success of companies in the hospitality sector (hotels and restaurants). In addition, the findings in this study will allow us to detect future lines of research to explore and provide a research agenda for future researchers.
This paper is divided into five sections. The introduction describes the theorical framework of the topic. The second section explains the methodology used: a qualitative research was done through a systematic literature review. The content analysis of the selected literature review is described in the third section which is divided in three areas. Then, a discussion is provided through the topic and several research questions are identified for creating a future research agenda. Lastly, conclusions are presented with implication for academics and practitioners.

Methodology
In this study, we propose a systematic review that addresses the management of service quality and the effect of sustainable practices in the hospitality sector. This review offers a general description of the different scientific contributions made to date that adopt reproducible methods [25]. Defining this systematic methodology in ten steps, beginning with the identification of keywords and even validating the documents with the citation method [26]. Petticrew and Roberts suggest a conceptualization of the systematic review focused on striving to identify, evaluate, and synthesize all relevant studies on the defined topic; they propose a structured review in twelve steps [27]. Easterby-Smith et al. define two main processes for the systematic review [28]. The first attempts to define the review protocol and the relevance of the research studies in its specific field of research. The second process identifies the main findings to define gaps in research in this field of knowledge. Aiming to see the complete panorama, excluding these methodologies, the diagram of systemic revisions and metanalysis PRISMA were taken in consideration in order to select the articles [29]. The PRISMA method allows us to identify and select the paper with a higher quality and interest, through 4 phases: identification, screening, eligibility and inclusion [30].
After the previous contributions and in accordance with Centobelli et al. [31] and Cerchione and Esposito [32], and with the contributions of the previous authors, the literature review was organized in two stages. In the first stage, by PRISMA, a flow chart was built in order to identify and select the articles included in the analysis. In the second stage, the analysis of the included papers was carried out.
The first stage, searching for and selecting articles, had two key steps: (a) Searching for scientific articles: This section defines the keywords and selects the databases in which the search will be performed. (b) Selection of scientific articles: Criteria are defined to include or exclude articles found in the databases, and the selection of these articles is performed according to the criteria. This step is shown in Figure 1 through the PRISMA Flow diagram. In the second stage, content description and analysis, there were also two key steps: (a) Description: Articles are classified according to different perspectives to obtain a summary image. (b) Analysis of content: The articles are selected and classified based on the defined criteria are reviewed and exhaustively studied. The analysis should highlight the strengths and weaknesses of the literature and identify and define future lines of research.

Search Stage
The articles were selected from the Scopus and Web of Science databases between 1990 and February 2019, although the oldest article found was from 2004. The keywords set to perform the search were "service quality", "quality service", "service quality management", "service quality practices" or "service quality polices", combined with "hospitality", "restaurants" or "hotels", and combined with "sustainability", "sustainable" or " sustain*". In the latter, the use of the asterisk allows us to also find those variations of "sustain" with other endings that may be related to the topic of study. We added one final criterion to refine the search: we selected only scientific articles that were available in English or Spanish.
A total of 144 articles were found with our criteria in the two databases (Table 1).

Selection Stage
Two selection criteria were defined to identify the articles that allowed us to focus and approach the subject under investigation in a clear way. These criteria are found in Table 2. With the first criterion in Table 2, we delimit the selection of articles to only those whose titles and abstracts focus on the management of service quality with reference to sustainable practices in the hospitality sector. The 144 articles were classified into the following four lists in table 3:


List A includes articles that discuss the two main concepts, service quality management and sustainable practices, in the hospitality sector.  List B includes articles that focus only on service quality without considering sustainable practices and the sector.  List C includes articles that focus only on sustainable practices without considering the quality of service and the sector.  List D includes articles that focus on the hospitality sector without determining key aspects regarding service quality and/or sustainable practices. The articles included in list B (40 articles), list C (23 articles), and list D (41 articles) are excluded because they are not focused on the scope of the research. The articles included comply completely with criterion 2, which allows us to view and analyze the content of each article to determine whether they fall within this article's scope of research. Through this process, a total of 40 articles was selected for the next stage of analysis.

Descriptive Analysis of the Results
The main objective of the descriptive analysis stage was to offer an overview of the articles analyzed that focus on service quality in the field of hospitality and that address sustainability. To carry out this analysis, four perspectives were defined as follows:

Articles by Time
In Figure 2, we see that the year with the largest number of articles published is the year 2017. Furthermore, only six articles were published before 2010. Most of the articles were produced between 2010 and 2020, and thus, we observe a growing trend of contributions on this topic in recent years.

Articles by Journals
Through the SCImago Journal Rank (SJR) platform, eight thematic areas can be identified, which are identified by journal in Table 4. These areas are as follows: Business, Management, and Accounting; Decision Sciences; Economics, Econometrics, and Finance; Environmental Science; Social Sciences; Computer Science; Psychology; Agricultural and Biological Sciences.   Table 4 shows that the vast majority of articles share the category of Business, Management, and Accounting, but we also see that this research topic has an important cross-sectional aspect and involves journals focused on different topics, such as Psychology, Computer Science, and Environmental Science, among other categories. Table 5 shows the distribution of the articles by methodology used. As shown, the quantitative methodology is the most commonly used in most articles, well ahead of qualitative and mixed methodologies. Of the 40 articles, 29 were based on a quantitative methodology. The 29 quantitative articles were into ten surveys, seventeen models and two mathematical models. The two qualitative articles contain a theoretical section and a case study. The nine articles based on mixed methodology combine quantitative and qualitative methodologies.

Articles by Areas
To obtain a complete overview of the body of the literature studied, the documents were divided into three thematic areas. These three areas are analyzed in the content analysis section.
1. "Factors influencing service quality in hospitality", where the main critical success factors linked to sustainability in the management of service quality in the hospitality sector are identified. Nine articles were selected. 2. "Service quality and sustainability practices for hospitality", where sustainable practices for service quality in hospitality are analyzed. Ten articles were selected. 3. "Impact of service quality and sustainability on hospitality performance", which shows the relationship and impact of quality of service on different types of successes and improvements. Twenty-one articles were selected.

Content Analysis Stage
The content analysis stage provides us with a detailed overview of the content of the 40 articles. This overview illustrates the various problems covered by the literature on service quality and sustainability in the hospitality sector. The articles are classified into three content areas: Area 1factors influencing service quality in hospitality; Area 2-service quality and sustainability practices for hospitality; Area 3-impact of service quality and sustainability on hospitality performance. The three sections are shown in detail in the following paragraphs.

Factors Influencing Service Quality in Hospitality
The first area contains nine articles that discuss factors influencing the quality of service in hospitality, defining an area of study by quantitative and qualitative methods. In this first section, a main trend of the literature is analyzing the critical factors of sustainable success that affect the quality of service in the hospitality sector. The factors found can be classified as follows: The first group of factors identified are (1) Environmental factors, which explain their impact through the ecological components of the surroundings [33,34], the equipment used for the service [35] as well as the product itself that is served must be environmentally friendly [33,36], such as other sustainable practices that the company carry out [37]. The second group of factors can be classified as (2) Business factors, that explain the relationship with the success of the service quality based on the management of the Human Resources, the settlement and formation adapted in order to improve their environmental behavior, and that have a positive effect on the costumer perception of the service quality [38,39]. Another group of factors is composed by the (3) Human Factors, these demarcate, according to their gender and intellectual capital, better practices accompanied with an improvement in their environmental behavior and have an impact on the enhancement of their competitiveness and the satisfaction of the customer, as a result of a higher quality perception [40,41].
Aside from these factors gathered in these three categories, in the literature is also mentioned the impacts that are determined according to the type of customer. It is possible to identify in the client different factors, such as the economic and motivational ones that cannot be classified as sustainable but have influence on the success of the company. The economical factor can divide into segments the customers, according to their economic capacity, social class, occupation [35]. The motivational factors explain the purpose of the trip [41], the aim and the motivation for a service with a sustainable approach and a higher quality.
Due to all the previous factors explained, relational factors appear. These relational factors study the effects of the satisfaction and the loyalty of the customer with a typology of practices and the quality of the service [34,37]. These relational factors have a positive impact on the development of the company [40].
However, the literature does focus on several specific key factors but does not go into great detail with others, such as environmental factors and sustainable practices. Other, more sociopolitical factors that do not appear in the literature could also be analyzed. In this area, many more concrete factors could be differentiated and analyzed. In addition, it is not determined whether or not these factors are pure; that is, if their presence has a positive impact but their absence is not negative for the quality of the service, or if their presence has a positive impact, but their absence exerts negative impact.
This section indicates that it is necessary to delve into key factors and determine their impact to implement a clearer classification.

Service Quality and Sustainability Practices for Hospitality
In the second area, 10 articles were analyzed-the articles focus on the practices that are carried out to create the quality of sustainable service in the hospitality sector.
For some years, there have been studies, all of which conclude that the behavior of the consumer and the green practices of the hospitality sector have a positive relationship, because they influence the purchase decision of the customer and their satisfaction [42,43]. Prud'homme and Raymond (2013) are the first to detail the influential green practices on the satisfaction and decision of the customer. The practices of the 3Rs, recycle-reuse-reduce, have a positive influence on the quality and the satisfaction [44]. These practices also have an impact on the cost and the internal processes of the company. It is for this reason that it is determined that internal process practices, the learning of the organization, the quality increase and the cost reduction, and sustainable and effective practices, have a positive influence on the reputation and the results of the company [45].
Another studied practice is more linked to the product that is offered in the service itself, in which the product has a very positive influence on consumer decision, considering the sustainable proximity products that have respected the environment for its production are appreciated [46]. Nevertheless, for obtaining these products it should be considered the supply chain, and in this stage also appear the sustainable practices, such as the reuse of products, social practices, the information, communication and technology, as well as the environmental monitoring [47].
Many of the practices mentioned above have influence for obtaining environmental protection certificates. Therefore, the fact is that these types of practices and obtaining the certificates have a positive influence on the business performance [48].
Lastly, there are the practices linked to human resources matters, in which the employers training focused on these sustainable practices, is linked to an increase in quality service and consequently on the company's sustainability [49,50]. The employers' motivation and consciousnessraising are important to promote sustainable practices on the product or service offered. Good sustainable consumption practices, for example on food, have a positive impact on the sustainability [51], and therefore on the perceived quality by the customer and on the business success.
One weakness found in the literature is the lack of differentiation in the size of hospitality businesses and whether such differences exert different influences in the implementation of the practices and their impact. Likewise, it does not examine the star classification of hotels in depth or in a quantification of its real impact on company results.

Impact of Service Quality and Sustainability on Hospitality Performance
In the third area, the literature shows us which aspects of environmental practice strategies and the management of service quality have an impact. After analyzing the 21 articles that make up this section, it was determined separately that environmental and the service quality practices have a direct effect on different elements.
Regarding environmental practices, the elements which are impacted can be classified as follows: economic and financial performance, environmental and relational performance. Concerning the impact on economic and financial performance, it is proven that a higher environmental strategy implementation has a positive impact on occupation and incomes [52]. This association is due to one of the most influential factors on purchasing decision is the customer perception of the green quality, green value and information of cost savings [53]. Furthermore, sustainable factors make customers willing to pay a higher price [54]. As we can determinate the relationship with the customer is an important aspect that should be considered-it is for this reason that the impact on relational performance is the key to the success of the company. Considering that environmental practices have a positive effect on the consumer's satisfaction and on customer's loyalty [55], the customer is willing to pay more if the service offered is done with these kinds of practices [56]. Therefore, if the company wants to increase the result indicators and the customer's loyalty, it should make more practices related to sustainability [57,58]. All these practices, besides the implications on business factors, as we have seen, have a very positive effect on environmental performance [52].
On the other hand, we find service quality practices that impact the following performances: economic and financial performance, relational performance and innovation performance. In regard to the impact on economic and financial performance it is noted that the service quality is the most important reason why a hotel is chosen [59,60]. The previous statement is understandable considering that a better service quality increases the perceived quality by the customer [61,62]. Therefore, an improvement in service quality will have a positive impact on the company performance [63,64]. Furthermore, within the five dimensions, safety, empathy, trust, sensitivity and tangibility of quality service [65], those with a higher impact are trust, tangibility an empathy. This fact concurs with the importance of the impact on the relational performance, inasmuch service quality practice affects directly and positively the corporate image and, through these, impact indirectly on customer loyalty [66][67][68]. These practices not only have an effect on consumer loyalty, but also impact satisfaction [69,70] and reputation [71]. Both the quality of the tangible elements and the service of the staff increase the perceived satisfaction of the clients. The quality of the tangible elements has more impact on local companies while the quality of the service of the staff affects global companies more [72]. In the studies of Kandampully et al. (2011) and Cham and Easvaralingam (2012) it is determined that constant improvement and innovation on the factors that influence on the quality of service must occur. This show us that it should also be considered the innovation and improvement performance, since is essential that the different service quality practices are improved and innovated in order to an improve quality [68]. This growth will positively affect company competitiveness [73]. Aside from the constant improvement and innovation, the relationship between market orientation and organizational success should be considered, since the quality of the service has a direct and positive connection with this relationship.
Although there are several positive impacts of each of the practices, we find only that the combination of environmental practices and service quality have a positive impact on (1) purchase decision making and (2) customer satisfaction. Due to the importance of both practices in the development of the company and its improvement in the result, this limitation is very significant. This limitation reflects the need to investigate the combined effect of the two practices on different elements of the business. This fact is key to decision making of the companies' managers.

Discussion
Once the content of the literature had been analyzed, we could identify the strengths and weaknesses that each area presents, and they will be discussed in the following section.
Regarding the first area, in which critical success factors that positively impact the quality of service in the hospitality sector stand out, the literature highlights five factors: (1) environmental factors, (2) business factors, (3) human factors, (4) motivational and customer factors, and (5) relational factors. The latter factor is influenced by the above factors because they have a positive effect on the relationship between the company and the customer and are relevant to the managers and the decision makers, considering that the relational factors have repercussions in the development and results of the company. However, the correlation among these five factors jointly it is not identified in the literature and it can be an important gap to solve that will allow practitioners to make decisions about the company. RQ1: Which correlation has critical success factors jointly in the quality of service? Moreover, the literature does not clearly determine if these factors are pure factors; such factors exert positive impacts when present, but their absence does not negatively impact the quality of service. In contrast, other factors exert positive impact, but their absence exerts negative impact. Furthermore, the literature does not delve into determining the possible relationships and consequent influence among the factors themselves and their combinations. Investigating this fact is of utmost importance, since knowing if several factors are correlated could help determine which business decision to make in order to implement a typology of practices or both of them. Therefore, to find out if the implementation of environmental practices combined with the implementation of service quality practices cause an improvement on both, the correlation between them should also be studied.
Such omissions indicate that it is necessary to delve into key factors and determine their impact to create a clearer classification. This study allows us to formulate these questions for future research.
RQ2: Could it be determined if factors are pure and exert a positive impact on the quality of service in hospitality?
Nevertheless, in the literature, we do not find that socio-political factors (partners' power, socialization, behavior, orientation) are analyzed in depth. The literature, in consequence, focuses on the above factors. However, environmental factors and sustainable practices are not covered in detail by the literature, which treats them more broadly. The next step will be to shed light in the relation within the socio-political factors because of their importance in the hospitality that is not shown in the literature. Therefore, a more detailed study of these factors would bring light both academic and professional level in order to study its effects and put into practice.
RQ3: How do sociopolitical factors influence sustainability and quality of service in the hospitality sector?
Concerning the second area, which contains articles focused on the practices and tools used in the hospitality sector, the literature analyses the specific practices of sustainability and quality of service that influence business success within the hospitality sector. The practices that are found and analyzed are as follows: (1) the 3Rs (reduce, recycle, and reuse); (2) ecological concern; (3) sustainability in internal operations; (4) increased quality and reduction in costs; (5) sustainable organizational learning; (6) sustainability and effective cost management; (7) sustainable food; (8) environmental certifications; environmental monitoring; (9) social practices; (10) sustainability in human resources. All these practices discussed in the literature exert positive influence, albeit to differing degrees, on customer's perception of quality and on business success.
The main weakness in the literature is that practices are only examined individually, and it does not take into account their impact jointly, as we could also see in the first area. These practices must be studied in depth to differentiate and detect the different degree of influence among them and to conclude which practices are more effective for business.
RQ4: What is the impact of the application of sustainability and quality service practice on business and financial performance of the company?
However, despite all these practices found in the literature, there is no comprehensive system of practices regarding the environment and quality of service to achieve a positive perception of quality from the customer and good business results, nor is there a comprehensive system that is differentiated by the various characteristics of companies. Therefore, based on our content analysis, we view as a weakness this lack of differentiation by characteristics such as company size, the hotel's number of stars, and other segmentation characteristics in the performance of sustainable practices and quality of service that help companies achieve success. There is also a lack of studies examining how these practices impact financial performance. In addition, there is no model to quantify the real impact of such practices on companies' results, this would be important for the companies because it would allow an optimal decision making. These gaps in the literature allow us to identify the following lines for future research.
RQ5: According to the segmentation by characteristics such as size of the company, stars, location, are there differences in the impact of practices of quality service and sustainability?
Regarding the third area, the knowledge on the relationship between strategies of environmental practices and the management of service quality practices regarding the development of the company shows different factors and effects in each topic.
On the one side, the literature highlights that environmental practices have a positive influence on six development factors such as: (1) purchase decision making, (2) customer loyalty, (3) customer satisfaction, (4) willingness to pay a higher price, (5) occupation and (6) results indicators.
The content analysis of this area reveals the necessity to investigate and discover other factors which together have a positive overall impact. We find that only (1) decision-making in the purchase and (2) customer satisfaction positively influenced development factors. What is more, decisionmaking and customer satisfaction have only been studied individually and also it is important to know which the effects are to apply them jointly and to know if this positive impact is bigger together than individually. This fact will allow companies to apply (or not) strategies together. However, other factors should have a positive impact in the development of the company. Knowing the importance for practitioners in this topic, academics must extend the actual literature for solving that important and practical gaps.
This analysis also opens the field to more empirical research of what type and what degree of impact such practices have on company development. From these gaps, the following questions can be formulated for future research.
RQ6: What impact do environmental and quality of service practices have when they are applied together in the development of the company?
Finally, after analyzing the three areas detected in the literature, it is shown how there are several gaps where more thorough investigation should be done. First of all, it must be analyzed what kind of correlation exists between the two types of practices, in order to determine if the implementation of both will have effects on the same direction. Once done, the effects that they have jointly must be deeply analyzed, as well as the different concrete practices both of service quality and sustainability.

Conclusions
This article conducted a systematic review of the literature on service quality management and sustainability in the field of hospitality. This review has allowed us to present a unified contextual framework in which certain gaps in the literature can be identified and with which we can define new lines of research to expand the literature.
Regarding the research question, this review's main objective is to identify the sustainable factors that positively influence the quality of hospitality service, sustainable practices, and service quality and the impact of service quality and sustainability in service on the success of hospitality.
A descriptive analysis was carried out that provides an overview of the articles selected in the literature review. This analysis offers a summary of the documents that address the subject of the study. In reference to the methodology used, most articles are based on quantitative methodologies, and a few have a more qualitative or mixed point of view. This content analysis of the articles included has provided a description of the main problems covered by the research on quality of service and sustainability in the hospitality sector. The research agenda proposed based on our analysis allows us to provide guidance for future lines of research and to draw conclusions for academics and professionals.
A content analysis has also been performed, that allows us to detect and delimit literature in three areas. The first one refers to critical factors of sustainable success that affect the quality of service in the hospitality sector; five have been identified: (1) environmental factors, (2) business factors, (3) human factors, (4) motivational and customer factors, and (5) relational factors. The second area refers to ten main practices that companies do to improve their quality of sustainable services in the hospitality sectors. Finally, in the third area critical factors of environmental practices and quality of service are analyzed. We can determine that the only factors that can be found in both categories are (1) decision-making in the purchase and (2) customer satisfaction.
For academics, the highlighted and identified research gaps and the consequent questions proposed represent possible lines of research to improve and contribute knowledge to the content of these research areas. Studies in these research areas should not only investigate the impact of sustainable practices and quality of service in a company in a generic way but should also consider differentiation according to the companies' differing characteristics.
Therefore, the proposed research agenda with 6 research questions should offer future researchers the opportunity to develop a comprehensive framework of sustainable practices and quality of service, in addition to the ability to study the impact and influence such practices have on companies' development.
Regarding professionals, the review of the literature has shown that there are joint environmental practices and quality of service that positively influence (1) purchase decision making and (2) customer satisfaction. However, there remains much to demonstrate from other practices and key factors of the company that can positively influence development factors. This study has shown how such practices influence company development factors, but not in conjunction with sustainable practices and service quality. This avenue can mark the future lines of action that companies in the hospitality sector must pursue to obtain greater success from these practices, which are increasingly important in the sector. However, the professional will also be interested in the results of studies of practices and impacts segmented by size of the company, quality, and other characteristics, to implement those that best suit the company and sector.
All these conclusions invite us to pursue these new lines of research to obtain results and thus expand knowledge in the area and sector of the hotel trade, specifically in restaurants and hotels.