An Overview on Nutritional Aspects of Plant-Based Beverages Used as Substitutes for Cow’s Milk

The presence of milk in meals and products consumed daily is common and at the same time the adoption of a milk-free diet increases due to milk allergy, lactose intolerance, vegan diets, and others. Therefore, there is an increasing demand for plant-based beverages, which present variable and, sometimes, unknown nutritional characteristics. This study sought to compare the nutritional aspects of plant-based beverages used as substitutes for cow’s milk described in scientific studies. Therefore, we used a review of the scientific literature on PubMed, Google Scholar, Scopus, Web of Science, Google Patents, Embase, and ScienceDirect databases. The inclusion criteria were scientific studies referring to plant-based beverage used as an alternative to cow’s milk; published in the English language; present data on the serving size, ingredients, and nutritional composition, containing at least data on energy and macronutrients of plant-based beverages. Ingredients and data on energy, macronutrients, and, if available, dietary fiber and some micronutrients of plant-based beverages were collected. Data were obtained from 122 beverages of 22 different matrices, with soy being the most used (27.87%, n = 34). The variation in the amount of nutrients found was 6–183 Kcal/100 mL for energy value; 0.00–22.29 g/100 mL for carbohydrate; 0.06–12.43 g/100 mL for protein; 0.00–19.00 g/100 mL for lipid; 0.00–4.40 g/100 mL for dietary fiber; 0.00–1252.94 mg/100 mL for calcium; 0.04–1.40 mg/100 mL for iron; 0.84–10,178.60 mg/100 mL for magnesium; 0.00–343.43 mg/100 mL for sodium. Salt was the most commonly found added ingredient in plant-based beverages. Some beverages have reached certain amounts of cow’s milk nutrients. However, studies have pointed out differences in their qualities/types. Thus, attention is needed when replacing milk with these alternatives.


Introduction
Milk is the "lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows" [1]. Worldwide, cow's milk and its derivatives are consumed by more than 6 billion people [2], on average of 116.50 kg/inhabitant/year [3], standing out mainly due to its content of high biological value proteins and calcium [4][5][6].
Considering other beverages, 32.79% (n = 40) were commercial plant-based beverages used as alternatives for cow's milk from different brands whose nutritional values were obtained from the labels [52][53][54]57]; 12.30% (n = 15) had their nutritional composition evaluated using USDA (United States Department of Agriculture) Food Composition Database [23]. Table 1 shows the nutritional composition, ingredients and specifications on the origin of the beverages. The identification information (authors, year of publication and country of origin) collected from the studies is presented in Appendix B.
Considering Table 1, the energy value ranged from 6 to 183 Kcal/100 mL, the carbohydrate content ranged from 0.00 to 22.29 g/100 mL, the protein content ranged from 0.06 to 12.43 g/100 mL, and the lipid content ranged from 0.00 to 19.00 g/100 mL. The most caloric beverage collected and with the highest lipid content is the coconut-based beverage from the Real Thai brand [54]. Four rice-based beverages of different types (parboiled, brown, polished and red) presented the lowest lipid value [30].
The least caloric and with the lowest protein content is the tucumã almond-based beverage extracted at a temperature of 55 • C [35]. The beverage collected with the highest protein content is the concentrated fluid from stage 5 of the crioconcentration process that the sapucaia nut-based beverage was submitted to [47].
Regarding carbohydrates, the sesame-based beverage that contains maltodextrin as an ingredient has the highest carbohydrate content [34], while the sunflower seed-based has the lowest carbohydrate content [45]. Among the beverages collected that dietary fiber values were provided for (18.03%, n = 22), this nutrient content ranged from 0.00 to 4.40 g/100 mL. An oat-based beverage has the highest dietary fiber content [50], while three rice-based beverages of parboiled, polished and red rice types [30], and a coconut-based beverage [52] have the lowest dietary fiber value.
With regard to the collected micronutrients, the amount of beverages that provided these data were 44.26% (n = 54) for calcium, 6.56% (n = 8) for iron, 13.11% (n = 16) for magnesium, and 22.95% (n = 28) for sodium. The calcium content ranged from 0.00 to 1252.94 mg/100 mL, iron content ranged from 0.04 to 1.40 mg/100 mL, magnesium content ranged from 0.84 to 10,178.60 mg/100 mL, and sodium content ranged from 0.00 to 343.43 mg/100 mL.
The concentrated fluid from stage 5 of the crioconcentration process that the sapucaia nut-based beverage was submitted has a higher content of calcium, magnesium, and sodium [47]. An almond-based beverage has the highest content of iron [58].
Three rice-based beverages (with brown, parboiled and red rice types) [30], one soybased beverage and two coconut-based beverages [23] have the lowest calcium content. A rice-based beverage made with broken polished rice has the lowest content of iron and magnesium [46]. Considering sodium, three rice-based beverages (with brown, polished and red rice types) presented the lowest sodium content [30].
Nutritional values obtained from the label.
Beverage prepared (subjected to 8.00 kGy of gamma radiation) and analyzed for the study.   Excluding water and the matrix from the beverages, the most commonly found ingredients in plant-based beverages were salt (50 times), sugar (21 times), vitamin E (tocopherol) (20 times), tricalcium phosphate (18 times) and gellan gum (17 times) (Figure 1).

Nutritional Content Variations
This review confirmed that plant-based beverages' nutritional content depends on different aspects, such as the type of raw material used to produce it, the process, and the added ingredients [11,21].

Processing Performed
The sapucaia nut-based beverage (the sapucaia nut (Lecythis pisonis) is a Brazilian species found in the Amazon and Atlantic Forest) was subjected to crioconcentration in block (method of total freezing followed by partial thawing of the solution, under gravitational separation), capable of concentrating solid matter by removing water in ice form [47]. This process concentrates nutritional compounds, such as protein, carbohydrate, calcium, and magnesium, influencing the beverage's nutritional content [47]. This concentrated water-soluble extract can be used as an ingredient for other food products to improve their nutritional content as selenium, in which the concentrated extract could reach 10,037 μg/g [47].
The hot grinding method-capable of inactivating the lipoxygenase enzyme of the water-soluble soy extract that causes its typical "beany" flavor- [63] and the cold grinding method (traditional oriental method) were performed to obtain water-soluble soy extract [44]. The cold-extracted beverages

Nutritional Content Variations
This review confirmed that plant-based beverages' nutritional content depends on different aspects, such as the type of raw material used to produce it, the process, and the added ingredients [11,21].

Processing Performed
The sapucaia nut-based beverage (the sapucaia nut (Lecythis pisonis) is a Brazilian species found in the Amazon and Atlantic Forest) was subjected to crioconcentration in block (method of total freezing followed by partial thawing of the solution, under gravitational separation), capable of concentrating solid matter by removing water in ice form [47]. This process concentrates nutritional compounds, such as protein, carbohydrate, calcium, and magnesium, influencing the beverage's nutritional content [47]. This concentrated water-soluble extract can be used as an ingredient for other food products to improve their nutritional content as selenium, in which the concentrated extract could reach 10,037 µg/g [47].
The hot grinding method-capable of inactivating the lipoxygenase enzyme of the water-soluble soy extract that causes its typical "beany" flavor- [63] and the cold grinding method (traditional oriental method) were performed to obtain water-soluble soy extract [44]. The cold-extracted beverages had a higher moisture content and, consequently, lower concentrations of proteins and total solids than the hot-extracted beverages [44].
A study analyzed the effect of physical and antioxidant treatments on the lipoxygenase enzyme activity in a soy-based beverage [43]. The author observed that the protein and lipid content of BRS-213 cultivar's beverages subjected to physical treatments (irradiation-5.00 kGy; thermal-80 • C) with tocopherol supplementation were higher than the control sample. The study showed that adequate heat treatment increases lipids and proteins content, as well as their solubility and digestibility [43].
The physical treatments (irradiation-5.00 kGy; thermal-80 • C) with tocopherol supplementation in BRS-213 cultivar's beverages also increased the macronutrient concentration compared to the control sample due to lower moisture content [43]. Furthermore, the beverages produced with the EMB-48 soy cultivar subjected to heat treatment had a significant increase in lipid and protein content [43]. The hydrothermal processing of the soy-based beverage caused a rupture in the soy cell wall, allowing the passage of lipids and proteins, which was responsible for increasing the content of these nutrients [43].
As for irradiation (conservation technique) to which soy-based beverages were subjected, a study [42] verified a significant reduction in the protein content when increasing the dose of gamma radiation. Deamination (release of the amine group from the rupture of the peptide bonds of the amino acid, forming ammonia) was mentioned as a possible cause [42]. However, this process may have improved the protein quality since deamination makes it more hydrophilic, increasing its solubility and digestibility [42].
Another aspect in producing plant-based beverages capable of influencing its nutritional content is the raw material:water ratio. A study [48] found higher macronutrient and energy concentration in the soy-based beverage with a 1:8 ratio (soy:water) than in those with a 1:10 and 1:12 ratio. These results were expected since water dilution implies nutrients dilution in the final product.

Added Ingredients
In the production of plant-based beverages, the addition of other ingredients may improve the nutritional profile, the functional or sensory properties of the beverage [22,64]. Salt, sugar, syrups, flavorings, vanilla essence, cocoa, apple juice concentrated, and others are incorporated to improve sensory aspects, mainly the flavor [42,64]. In addition to enhancing flavor, salt and sugar are usually added in beverages and foods to improve texture or shelf-life [65].
Cow's milk presents a mild and typical flavor, neither sweet nor salty, characterized mainly by the balance between lactose and salt [4]. Therefore, it is common to find salt in plant-based beverages, as well as ingredients for a sweet flavor (sugar, maltodextrin, apple juice, agave syrup, vanilla extract). It is important to highlight that the use of ingredients like sucrose, maltodextrin, and fructose might negatively impact the glycemic index and salt also might impair the nutritional quality. The consumption of foods with low (<55) and medium (56-69) glycemic index is recommended, especially to control blood glucose levels [20,23]. A low glycemic load diet is related to a lower risk of diabetes, cardiovascular disease, and obesity [66].
Sugar is often used to improve sensory quality but influences the nutritional quality negatively. In the studies by Barros and Venturini Filho [44] and Karimidastjerd and Kilic-Akyilmaz [60], the plant-based beverages with added sugar are more caloric and with higher amounts of carbohydrate than those without added sugar. In the sesamebased beverages studied by Reis [34], the carbohydrate amount of the sample added with maltodextrin is almost twice the amount of the pure sesame-based beverage. Consequently, the sample with maltodextrin is more caloric [34].
Other ingredients commonly found in plant-based beverages are vegetable oils, such as sunflower oil. Martínez-Padilla et al. [53] pointed out that the addition of these oils can provide a smooth mouthfeel similar to that of cow's milk, and Aydar et al. [64] mentioned its use in order to improve the silky aspect.
A study [22] showed that it is possible to add starch in plant-based beverages as a plant-derived thickening agent and pectin or locust bean gum to improve the texture. Reis [34] used maltodextrin to improve the stability of the beverage and Sethi et al. [19] referred to the use of sodium bicarbonate as an alkalizing agent, which might prevent destabilization by sedimentation of solid particles in the beverage.
A study [39] used enzymes in the quinoa-based beverage preparation, with the addition of the Termamyl enzyme for the dextrinization process and the amyloglucosidase enzyme for saccharification. In food industry, inulin can be used as a texture modifier, sugar or fat substitute, and it also has a prebiotic effect on the human organism [67].
Due to the nutritional composition of most plant-based beverages (not similar to that of cow's milk-high in protein and calcium) and nutritional losses during the processing of the raw material, in plant-based beverages the addition of vitamins (e.g., A, D, E, B2, folic acid, B12), minerals (e.g., calcium, zinc) and proteins (usually isolated or extracted from sources, for example, peas or soy) is frequent, trying to achieve a similar composition to cow's milk [68]. However, other vitamins and minerals are added with different functions. Barros [43] added tocopherol (vitamin E) with the function of antioxidant treatment of beverages.
Zinc gluconate, zinc oxide, calcium carbonate, tricalcium phosphate and monocalcium phosphate are some of the micronutrient compounds used as food fortifiers [69]. Algae Lithothamnium calcareum is mentioned by Scholz-Ahrens et al. [54] as another source of calcium added to plant-based beverages. Although these beverages are often fortified, the added nutrients are not always bioavailable as those naturally present in milk [68].
Tricalcium phosphate can be used for several functions as an acidity regulator, buffer, anticaking agent, clouding agent, emulsifying, firming agent, flour treatment agent, humectant, moisture-retention agent, raising agent, stabilizer and texturizing agent; calcium carbonate can be used as an acidity regulator, anticaking agent, surface colorant, firming agent, dough conditioner, and stabilizer [70]. Some of these functions are important in plant-based beverages, but they were not discussed in the studies that use them.
The function of gums as food additives can also be used in plant-based beverages. In this sense, gellan gum is used as a gelling agent, stabilizer, and thickener; locust (or carob) bean gum and guar gum are used as an emulsifier, stabilizer, and thickener; xanthan gum as an emulsifier, foaming agent, stabilizer and thickener; gum arabic (acacia gum) is used as a bulking agent, carrier, emulsifier, glazing agent, stabilizer and thickener [70].

Comparison of Nutritional Composition: Plant-Based Beverages and Cow's Milk
As a reference for comparing the nutritional composition of the types of plant-based beverages, the nutritional composition (per 100 g) of a whole cow's milk obtained from USDA are energy (64 Kcal), carbohydrate (4.65 g), protein (3.28 g), lipid (3.66 g), calcium (119.00 mg), iron (0.05 mg), magnesium (13.00 mg) and sodium (49.00 mg) [71]. Due to the FAO [71] document not showing the dietary fiber value of this whole cow's milk, this nutrient's reference was established as 0.00 g/100 mL according to other milk present in the USDA FoodData Central [72].

Carbohydrate
Almost 27.87% (n = 34) of the studied beverages were higher in carbohydrate content than the cow's milk (4.78 g/100 mL). Regarding differences in composition, the carbohydrate in cow's milk is mostly lactose-contributes to the use of vitamin D and the absorption of calcium, phosphorus and magnesium in the intestine-while plant-based beverages are lactose-free [4,21,71] and flavor lactose substitutes most used are sugar, maltodextrin, apple juice, and agave syrup.
The GI value is usually influenced by the type of sugar, with each type having a GI value [66]. Jeske et al. [66] presented the GI of maltose (105), sucrose (61), fructose (19), and lactose (46). Some of the plant-based beverage samples mentioned above had added sugar or sweeteners, such as agave syrup (present in cashew, macadamia and quinoa samples), apple concentrate (present in the soy sample from Provamel), sucrose (present in hazelnut, almond and soy original from Alpro) and maple syrup (present in the carob/almond sample) [66]. Agave syrup and apple concentrate are high in fructose, while sucrose and maple syrup contributed to high sucrose values [66]. Additionally, products that have ingredients rich in starch are high in glucose and/or maltose. Rice-based samples presented high maltose and glucose content and sample based on oat, which contains β-glucan capable of reducing GI, was high in maltose [66].

Protein
Of the plant-based beverages studied, 16.39% (n = 20) have a higher amount of protein than the cow's milk (3.37 g/100 mL). Regarding protein quality, the Digestible Indispensable Amino Acid Score (DIAAS) is the recommended measure for analyzing it [73]. From the DIAAS cut-off values, the food can be characterized as "excellent/high" (value equal to or greater than 100) and "good/source" (between 75 and 99) [73].
The DIAAS method is indicated to replace the Protein Digestibility Corrected Amino Acid Score (PDCAAS) based on some considerations, such as using a single value of fecal crude protein digestibility in the PDCAAS method for correction for digestibility, while the DIAAS use "true ileal amino acid digestibility for the dietary indispensable amino acids" [73]. It is also pointed out an overvaluation of the protein quality of foods that contain antinutritional factors and an inadequate estimate of the protein quality of high-quality proteins due to a non-attribution of extra nutritional value by the PDCAAS method [73].
Proteins provide amino acids that perform essential functions in the body, such as structural, defense, transport, and regulatory [23,74]. The deficiency of essential amino acids, which must be ingested in the diet, can reduce protein synthesis and physiological and biochemical changes [74]. Thus, attention is needed when replacing milk with a plant-based beverage regarding protein, and a diet needs to be planned to guarantee an adequate aminogram.

Lipid
The percentage of plant-based beverages studied in which lipid content is higher than cow's milk (3.76 g/100 mL) is 13.11% (n = 16). The lipid in cow's milk is mainly composed of saturated fatty acids, while plant-based beverages tend to have a higher content of unsaturated fatty acids and are cholesterol-free [4,6,20,23,53]. However, there may be exceptions, as mentioned by Chalupa-Krebzdak et al. [23], Craig and Fresán [20] and Vanga and Raghavan [6] the case of coconut-based beverage that has a high content of saturated fatty acids.
The high consumption of foods rich in saturated fatty acids and cholesterol is associated with an increased risk of developing cardiovascular diseases, while the consumption of polyunsaturated fatty acids corresponds to a risk reduction factor for these diseases [74]. Despite that, studies have shown that the consumption of dairy products does not negatively affect human cardiovascular health [23,53,75]. Chalupa-Krebzdak et al. [23] mentioned as possible cause that "many nutrients in dairy products that may offset the effects of potentially harmful levels of dietary saturated fatty acids".
The isocaloric replacement of saturated fatty acids for polyunsaturated has collaborated to reduce LDL and total cholesterol in humans [23,74]. In this sense, the lipid composition of the plant-based beverages does not have to be the same as that of cow's milk regarding the nutritional aspect [23] but is necessary to evaluate its need considering sensory and technological aspects. Chalupa-Krebzdak et al. [23] pointed out that replacing milk with plant-based beverages, except for some coconut-based beverages, can decrease the intake of saturated fatty acids in the diet.
Although coconut-based beverage has a high content of saturated fatty acids [6,20,23], it contains medium-chain fatty acids (MCFAs) that can be converted into ketone compounds, which are favorable in brain functioning [14]. In addition, Vanga and Raghavan [6] report that lauric acid, which mainly contributes to raise high-density lipoprotein (HDL) cholesterol levels and, consequently, reduce levels in the bloodstream of low-density lipoprotein (LDL) cholesterol, is present in coconut fats.

Dietary Fiber
The consumption of dietary fiber might contribute to intestinal regulation, the reduction of blood cholesterol and glucose, and it is also associated with a lower incidence of diabetes, cardiovascular disease, gastrointestinal disorders and colon cancer [74,76]. Among the plant-based beverages that present dietary fiber data, most (81.82%, n = 18) have a higher dietary fiber content than cow's milk reference (0.00 g/100 mL). In this sense, plant-based beverages have an advantage. Unfortunately, due to the studies' lack of data, it was not possible to link the fiber content and GI in the samples analyzed.

Micronutrients
Calcium is a nutrient that stands out in milk and is essential for bone and dental structure, muscle function, and nerve conduction [54,74]. The calcium values of plant-based beverages ranged from 0.00 to 1252.94 mg/100 mL and 44.44% (n = 24) of the plant-based beverages were greater than the cow's milk (122.21 mg/100 mL). These beverages with a higher calcium content (except for the beverages based on sapucaia nut, which went through crioconcentration as previously mentioned), were all fortified with calcium.
As mentioned earlier about fortification, many commercial plant-based beverages are fortified with calcium to achieve cow's milk's amount [21]. Despite this, there are plant-based beverages that are not fortified. The substitution of milk for these non-fortified beverages when the diet is not balanced, calcium and other nutrients may be deficient [21].
Moreover, the bioavailability of the fortifier, and not only the amount of the nutrient, should also be taken into account [54]. As an example of calcium, Craig and Fresán [20] mention that calcium absorption from tricalcium phosphate is considerably less than milk, while calcium carbonate is equivalent to milk.
Magnesium is another essential micronutrient contained in milk [4]. Considering the studied beverages in which the magnesium data were provided (ranging from 0.84 to 10,178.60 mg/100 mL), most of them (87.50%, n = 14) have higher magnesium content than cow's milk (13.35 mg/100 mL). The sapucaia nut-based beverages have a very high magnesium content per 100 mL, exceeding the Tolerable Upper Intake Level (UL) for this nutrient [77]. Therefore, as previously mentioned, these beverages can be used as ingredients in other food products for nutritional purposes [47].
Iron is not naturally contained in appreciable amounts in cow's milk [71]. Considering iron content of the beverages that present these data (ranging from 0.04 to 1.40 mg/100 mL), only a rice-based beverage (12.50%, n = 1) [46] presented lower amount, however close, than the whole cow's milk (0.05 mg/100 mL). With that, plant-based beverages have a certain advantage in terms of quantity, mainly considering a vegetarian diet that, in general, lacks iron [78].
Sodium is a component of salt and it is also found in milk [28]. Craig and Fresán [20] pointed out that consumers are generally concerned about the content of this mineral in plant-based beverages for health reasons. The high consumption of this nutrient is associated with noncommunicable diseases [28]. Among the plant-based beverages that present sodium data that ranged from 0.00 to 343.43 mg/100 mL, 53.57% (n = 15) of the beverages have higher sodium values than cow's milk (50.32 mg/100 mL). These beverages with a higher sodium content (except for the beverages based on sapucaia nut, which went through the process of crioconcentration as previously mentioned [47]), are commercial beverages that have salt as an ingredient [52]. Despite this, other beverages contain salt as an ingredient that has a lower sodium content than this cow's milk [52,55].
Unfortunately, the function of salt in these beverages that present sodium information and have salt as an ingredient has not been reported. However, Karimidastjerd and Kilic-Akyilmaz [60] reported adding salt to the beverage to balance the flavor, and Pinelli et al. [79] used salt to produce a quinoa-based beverage to increase the protein content.

Limitations
Lastly, the main limitation of this study is that not all studies provided the information in a more homogeneous way, which did not allow the realization of more elaborate statistics and the grouping of data. Additionally, as limitation, the lack of some data on the micronutrients studied and more information on the quality/type of nutrients for all types of beverages studied for a complete analysis.

Conclusions
The demand for plant-based beverages used as substitutes for cow's milk is increasing worldwide. In that sense, there is a wide variety of these beverages and new ones are constantly emerging. Despite some similarities to cow's milk, such as appearance, this review showed that the nutritional aspects of these beverages vary widely (energy value varied from 6 to 183 Kcal/100 mL; carbohydrate from 0.00 to 22.29 g/100 mL; protein from 0.06 to 12.43 g/100 mL; lipid from 0.00 to 19.00 g/100 mL; dietary fiber from 0.00 to 4.40 g/100 mL; calcium from 0.00 to 1252.94 mg/100 mL; iron from 0.04 to 1.40 mg/100 mL; magnesium from 0.84 to 10,178.60 mg/100 mL; sodium from 0.00 to 343.43 mg/100 mL).
Our initial hypothesis, that plant-based beverages are lower in protein and calcium than cow's milk, was partially confirmed given that some samples presented similar or higher protein and calcium content than cow's milk. A commercial soy-beverage (with apple concentrate, algae Lithothamnium calcareum, and salt) and sapucaia nut-based beverage (under crioconcentration process) exceeded the amount of protein and calcium compared to cow's milk, proving to be good alternatives regarding these parameters.
Different types of raw material used, the added ingredients, the extraction process, and the treatments were used to improve the nutritional content of plant-based beverages aiming to be healthier and similar to cow's milk. Soy is the most common matrix used in the plant-based beverages studied. Based on the ingredient list of the studied products, salt was the added ingredient that most frequently appeared, followed by sugar. However, considering all the sources of ingredients used to sweeten plant-based beverages, all of them presented a type (or combination) of sweetener ingredient, probably in higher amounts than salt aiming to improve sensory characteristics and acceptance. However, it was not possible to analyze it in this study due to the lack of information in some studies about the quantity of the ingredients. Further studies are necessary to evaluate the amount of each ingredient in plant-based beverages and its impacts on individuals' health.
It is necessary to pay attention to the substitution of cow's milk by these alternatives considering the nutritional quality. Due to the diversity of nutrients' type and amount of nutrients found in the studies analyzed, it is noteworthy that most plant-based beverages cannot completely fulfill the replacement of cow's milk regarding nutritional quality. Some of them present ingredients (legumes, almonds, nuts, seeds, etc.) that can also be allergenic for some individuals and their use should be evaluated with caution for allergic individuals. Therefore, having nutritional monitoring is important for an adequate replacement of cow's milk in the diet. The choice of plant-based beverage will depend on the objective (nutritional or sensory) that the person is looking for to use this product and their preferences/restrictions. Thereby, this study can be useful in choosing the best alternative to compose their diet.