Since the Brundtland Report ^[1][17], which proposed sustainable development as a solution for improving the quality of the environment and society in the long term, along with economic development, and also until the Sustainable Development Goals ^[2][18], the ways of production in domains such as agriculture ^[3][4][19,20], construction ^[5][6][21,22], industry ^[7][23] (including the dairy industry ^[8][24]), and, more recently, consumption of different products such as food ^[9][10][1,25] and fashion ^[11][26], or services such as tourism ^[12][27], have been questioned and solutions for making them more sustainable have been proposed.

The case of sustainable dairy is a sensitive one. On one hand, milk and dairy, along with meat and eggs, represent a prime source of superior protein, known for thousands of years, so it is natural to observe increasing trends in the consumption of these products while countries register economic and social development ^[13][14][16,28]; this also being the case of EU Central and Eastern countries, where GDP values increased compared to the EU average ^[15][29]. On the other hand, the intensive dairy farming industry is recognized by the high environmental impact and contribution to global warming, acidification, energy consumption and land occupation ^[16][17][30,31], which makes it unsustainable. Therefore, the alternative may reside in traditional farms with a small production of traditional products ^[18][32] or mountain products ^[16][30], which are increasing on the consumers preference list ^[13][19][16,33].

Regarding the notion of sustainable food, the FAO ^[20][34] envisions it as food that is nutritious and accessible for everyone, while natural resources are managed to support the current and future human needs. Otherwise, there are different accepted characteristics that can make a food product recognized as sustainable, such as plant-based ^[21][35] or insect-based ^[22][36], with a less meat-based composition ^[23][37], seasonal food ^[24][25][38,39], locally grown and produced food ^[25][39], and organic food ^[26][40]. Additionally, there are a series of accepted barriers to consuming sustainable food. For example, cultural barriers as the reluctance to consume cultured meat or insects ^[25][39], financial barriers ^[27][41], or even habituality barriers ^[28][42].

Around the world, milk and dairy have been known as food sources for a long time. Milk is acknowledged as a complete food, composed by all nutrient categories. Moreover, other dairy products such as yogurts are included in the category of functional foods, meaning products that are beneficial for the health and wellbeing of the consumer ^[29][30][2,43].

Several authors mention the importance of milk and dairy consumption especially for pregnant women, children, adolescents, and older people, due to the increased composition of mineral salts and vitamins, responsible for the proper development and maintenance of bones and muscles ^[31][32][33][3,44,45]. Adding on this, Givens ^[31][3] mentions that threats of increased cardiovascular disease due to milk and dairy consumption are disproved by clinical studies, while the correlation between yogurt consumption and type II diabetes needs to be further studied.

Regarding the regular consumption of milk and dairy, studies have determined an average of 2–3 servings per day, depending on the availability of these products and their presence in the culture of a country ^[34][46], being a regular presence in an extended part of the globe ^[35][47].

Since this type of product may contribute to ensuring food security through the nutritional values and its widespread, the level of income should not be a factor of influence in milk consumption. Nevertheless, studies show that lower incomes lead to poorer choices in milk quality ^[36][37][48,49]. Moreover, other research points out that the lower income groups have a higher sensitivity than medium and high-income groups to income and price fluctuations when choosing dairy products ^[38][50]. In addition, the income inequalities significantly influence the quality of life of people in developing countries, including their possibility of spending on high quality food products ^[39][51].

Demographic factors, such as gender, are known to influence the choice of diet. Women pay more attention to low fat diets and healthy diets than men ^[40][52]. Even more, there are studies claiming that men are less willing to pay for higher quality in food products ^[41][53] and read the labels superficially ^[42][54]. Nevertheless, the consumption of milk in men and women should not differ as it has lifelong benefits ^[43][55].

While in general terms, milk refers to the product of the cows, they are not the only type of animal which produces edible milk. Park ^[30][43] observes that the general tendency is to skip the importance and nutritional value of milk coming from other animals, especially since cows have adapted so well in farms all over the world. Hoowever, the milk and dairy coming from other types of animals such as buffalos (mozzarella), sheep and goats (yogurt and chesses) or even donkey (milk) puts renowned specialties on the market. For example, the Italian mozzarella is a certified product made especially from buffalo milk, which offers it a superior taste and texture ^[44][56]. Zicarelli ^[45][57] shows that buffalo milk has a higher nutrient content and a lower cholesterol level than cow’s milk. However, the farming of such animals is more difficult, needing more water and space, and therefore being less suited for large farms ^[44][56]. The case of sheep and goats is also special, as the extensive methods of farming specific to the Mediterranean or Balkan region offer the dairy products particular sensorial qualities and place them among the traditional products sought especially by locals. However, whether they will be able to adapt to the standardized market of the developed countries or they will remain a hard-to-get traditional product is still not known ^[46][47][10,58]. Donkey milk is more known as a treatment for diverse types of affections, such as milk intolerance in infants, having a chemical composition remarkably close to human milk ^[48][49][59,60]. Moreover, using it in the treatment of lung disease, including lung cancer, has raised the interest of scholars ^[50][61]. Depending on the local culture and natural fauna, there are other species of animal that provide sources of milk, which are less known or understood at the general level, such as camels, mares, or reindeers ^[30][51][43,62]. In addition, the innovation vector ^[52][63] has not jumped over the dairy sector. Research and development have presented alternative plant-based results for milk, such as soy milk, rice milk or almond milk ^[53][64].

Nevertheless, due to its high availability and recognizable taste, cow’s milk is expected to be the preferred source for consumers ^[54][65].

Determining the factors that trigger or suppress the purchasing and consumption decision for several types of products has been of interest to researchers and marketers for a long time ^[9][55][1,66]. The universality of these products has attracted attention from researchers in various geographical regions. For example, in Kosovo, a study ^[56][67] revealed that the factors that have a significant influence on the choice of dairy are consumer gender, trust in the products, perceived quality, origin, and price of the purchased product. The Slovak consumers consider that price, taste, and quality of the local dairy are strengths, being perceived as healthy, while the imported products excel in packaging and variety ^[57][68]. Other researchers ^[58][69] show that Chinese consumers are significantly influenced by the country-of-origin of milk and dairy products, trusting them more than the local products, while the preference for a specific country is guided by consumer familiarity and experience with the products, ethnocentrism, and animosity, and even some cultural value differences. For the Italian consumers, the low price and high availability in the supermarkets of cows’ milk are main reasons for consumption, while the health benefits of the donkey milk are seen as superior, but the difficulty of finding it in the supermarkets proves to be a significant barrier ^[59][70].

The sensory properties of milk and dairy products, such as color, smell, taste, fat quantity or density are powerful indicators for consumers in choosing a particular product ^[29][2]. Others focus on factors that may be related to a sustainable choice, such as origin of the products, determining a preference for local and mountain products ^[60][13] or the certification of Good Agricultural Practice, in the case of Japanese consumers ^[61][71]. Other authors observe that basic factors such as availability of products, price and packaging significantly influence the consumers in making a choice for milk and dairy products ^[59][62][70,72].

Some newer factors indicate that not all consumers are open to trying organic products, but there are some for which ethical aspects and green consumerism are motives for purchasing organic products ^[26][40]. Other authors point out that in higher-income countries, green purchases have the role of bringing people closer to the environment. Therefore, sustainable food choice is becoming more pressing especially in these countries ^[63][73]. However, other studies ^[64][74] claim that emerging economies have a higher willingness to pay for environmentally certified food produce. Roman et al. ^[65][75] find that for people who give a higher importance to natural foods, the willingness to eat ecological or organic food increases, while other studies point out that consumers are willing to pay more for sustainable food products or food with sustainable characteristics. For example, Gao et al. ^[19][33] claim that the willingness to pay for sustainable dairy is 40% higher than for regular dairy in the case of Chinese consumers. Other authors ^[66][76] claim that Spanish consumers are willing to pay more for locally grown almonds, as opposed to long traveled almonds. Adding on this, other studies point out that some European consumers are willing to pay more for locally captured fish, due to the trustful standards and effective communication regarding the standards ^[67][77]. Other aspects considered by consumers as worthy of paying more are innovative packaging solutions in the case of milk and dairy ^[68][78], or the provenance from small farms, that actually diminishes the need for organic certification ^[69][79]. Due to these previous studies, we consider that the willingness to pay more for milk and dairy with sustainability related aspects from the Romanian consumers is of further interest. In this case, the hypotheses of the current research were based on the previous studies on the influencing factors of consumption of milk and dairy.

Given previous studies ^{[39][40][41][42][57]}[51,52,53,54,68], we consider that the correlation between gender and the choice criteria for milk and dairy should be further investigated, and we expect that some considerable differences between respondent gender groups would be revealed.