substances: Recent trends, current challenges, and future prospects

1Department of Environmental Health Engineering, Food Safety Division, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2Students' Scientific Research Center (SSRC), Tehran University of Medical Sciences, Tehran, Iran 3Student Research Committee, Department of Food Science and Technology, National Nutrition and Food Technology Research Institute, Faculty of Nutrition Science and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran 4Department of Food Science and Technology, Faculty of Nutrition and Food Science, Tabriz University of Medical Sciences, Tabriz, Iran 5Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran 6Student Research Committee, Department of Food Science and Technology, Faculty of Nutrition and Food Sciences, Tabriz University of Medical Sciences, Tabriz, Iran 7Research Center for Pharmaceutical Nanotechnology, Biomedicine Institute, Tabriz University of Medical Sciences, Tabriz, Iran

Chocolates, with the ability to activate pleasure centers in the human brain, could be proposed as a great daily snack (Rajeswari, 2020). In recent years, chocolate consumption worldwide has greatly increased among all age groups (Krittanawong et al., 2021). Cocoa is the primary component of chocolate. At the beginning of the 21st century, the annual production of cocoa worldwide was estimated to be around 2 million tons, increasing to around 3 million tons in 2010 and 5 million tons in 2019 (Araújo et al. 2022).
Therefore, in terms of this high consumption volume of chocolate, it could be considered not only in the economic sphere but also with proper fortification; it can be turned into a functional product with medicinal effects for disease prevention and treatment.
Using low-allergic plant-based substances in formulating chocolates could make them a good transferring vehicle for highvalue-added bioactive ingredients, which may extend their shelf life (Faccinetto-Beltrán et al., 2021). Fortified chocolates with high-value-added plant-based substances could be considered rich sources of antioxidants, vitamins, minerals, and fatty acids. The effect of chocolates enriched with apple and extra virgin olive oil on the parameters of cardiovascular disease (Felice et al., 2019) or the effect of oleuropein-enriched chocolates on diabetes was studied (Del Ben et al., 2020). Hence, consuming the fortified chocolates with high-value-added plant-based substances instead of harmful snacks rich in salt, saturated fatty acids, and sugar can be useful to improve the health of patients with cardiovascular diseases, obesity, overweight, and diabetes (Cicero et al., 2021;Satokari, 2020).
On the other hand, the color and appearance of product are the first parameters which could be affected by fortification (Homayouni Rad et al., 2018). The fortification rate could be varied from 1% to 50%, depending on the food type and consumer acceptance. Consumer acceptance depends not only on the physical or emotional health benefits of fortified food products but also on sensory properties, price, and ease of using products play a crucial role.
Rheological or textural properties of chocolates fortified with plantbased substances could be significantly affected; thus, it provoked industries to use different fortification techniques, such as nanoencapsulation, to overcome induced problems (Chadare et al., 2019).
This review article provides general information on materials that could be used in plain chocolate production, the importance of each production stage, and its role in defects associated with each process. In the following, for the first time, we have paid particular attention to establishing a new connection between the food industry and chocolate's nutritional, health-promoting, and therapeutic effects fortified with plant substances.

| CHOCOL ATE COMP ONENTS
Chocolates mostly contain 25%-5% fat. Cocoa nibs have 55% cocoa butter, which forms nearly 30% of the chocolate. Cocoa butter triglycerides are filled with saturated and monounsaturated fatty acids, including 35% oleic, 34% stearic, and 26% palmitic acid. According to its crystal polymorphic form, the chocolate melting point is between 23 and 37°C (Abdul Halim et al., 2019). Cocoa butter forms at least six different crystal forms. From the perspective of appearance and taste, the best chocolate lipid crystal form is V(β2). Due to its high price and rising consumer demand, cocoa butter may be combined with vegetable oil-based cocoa butter alternatives (CBA). CBA could be classified into three groups, including cocoa butter substitutes (CBS), cocoa butter replacers (CBR), and cocoa butter equivalents (CBE). CBE could be mixed up to 5% with cocoa butter without affecting on physicochemical properties of produced chocolate. CBR should be mixed with cocoa butter so that physicochemical properties are not changed. Hydrogenation should be used on oils, such as soybean oil, rapeseed oil, olive oil, and palm kernel oil, to produce suitable CBR so that they could show possible health problems (Suri & Basu, 2022).
Chocolate contains 50% sugar in the form of sucrose or lactose (in milk chocolate). Fructose or nonsugar bulk sweeteners like sorbitol are used in products for people with diabetes. Due to consumer demand, tooth-friendly or lower calorie chocolates were produced.
Both sugarcane and sugar beets have the same naturally occurring crystalline disaccharide. Sucrose could be converted to inverted sugar using an acidic treatment or the invertase enzyme (Montagna et al., 2019). Sucrose contains more than 40%-50% of solids dispersed in fat and could affect functional properties, such as particle size, sweetness, mouthfeel, and rheological properties of chocolate (Lagast et al., 2018). A 1%-2% change in sugar content affects the price of chocolate and a 5% change affects the flavor (Medina-Mendoza et al., 2021). As part of cow's milk, lactose is used as crystalline lactose to replace part of the sucrose. Two types of lactose are considered, namely A and B. Form A is produced by formal processes and less sweet and soluble than B. Glucose, called dextrose, is difficult to completely dry because it typically contains some water and can absorb water from the surrounding air. Moisture absorption makes molten chocolate very thick and tends to stick together.
Fructose has fewer health problems than sucrose, and because of the lower increase in blood sugar, it could be used to produce chocolate products for people with diabetes (Barišić et al., 2020).
Sugar alcohols are used to produce low-calorie or sugar-free products. Different sugar alcohols have varying amounts of calories.
However, the average is 2.4 kcal/g. Similar to fructose, they are appropriate for diabetics, but they do not promote tooth rot. Polydextrose is an additional form of sugar comprising glucose units cross-linked with trace quantities of alcoholic sugar. Polydextrose is a potential prebiotic, producing 1 kcal/g calorie (less than half of the calorie produced by alcoholic sugars) with minor laxative effects (Sözeri Atik et al., 2020). Other components which are usually used in the chocolate formulation include milk powder, soy lecithin, polyglycerol polyricinoleate (PGPR), and vanillin (Selvasekaran & Chidambaram, 2021).
Moreover, chocolate is one of the products with a broad diversity, and thus materials should be adjusted based on product type.

| CHOCOL ATE PRODUC TION PROCE SS AND REL ATED RE AC TI ON S
Chocolate production is intricate and involves several stages, such as fermentation, drying, roasting, refining, and conching, which affect the quality of the final product (Table 1). During these stages, chemical reactions for the formation of the ideal flavor and aroma of chocolate occur (Barišić et al., 2019). One of the most important reactions which happen in the roasting process and during which aromatic compounds are created is the Maillard reaction. The Maillard reaction occurs between amino groups from proteins or amino acids and carbonyl groups from reducing sugars (Youssef, 2019).
These procedures provide cocoa with its distinctive flavor and aroma. The condensation result of these reactions is converted into 1-deoxy-2-ketosyl via the Amadori rearrangement. Fermentation is less successful at producing amines and aldehydes than roasting. Aldehydes are produced from amino acids in roasted beans by Strecker-type processes (Tunick & Nasser, 2019).
According to the studies, Maillard reaction is intensified at upper roasting temperatures (135 and 150°C) and produces melanoidins, which are high-molecular-weight (HMW) chemicals that give cocoa beans their brown color and distinctive texture. Since cocoa beans have a lower carbohydrate content than coffee beans, it would seem that the formation of HMW melanoidins is more likely to be mediated by lipid oxidation products than by carbohydrates (Tessier, 2021).
During conching, which is the last step of mixing chocolate components and has a great impact on taste, caramelization and Maillard reaction occur. During conching, the amino acid content of chocolate does not change. Its purposes are (1) to remove acetic acid from fermentation and excess moisture and (2) to create favorable changes in viscosity and organoleptic properties (Toker et al., 2019).

| FORTIFIED CHO COL ATE S
In recent years, fortified chocolates have gained a great deal of attention due to their nutritional and functional advantages, as well as their potential to suit the demands of health-conscious individuals who want a better lifestyle. Nutritionists recommended decreasing the consumption of sugary foods to prevent obesity. Fortified chocolates with desirable sensory and taste characteristics could be helpful snacks for obese people (Kaltsa et al., 2021). Furthermore, in terms of unhealthy substances in the chocolate composition and low-protein content, fortification provides a safer and more nutritious product for food market demands. It positively affects body metabolism at all ages (Kruger et al., 2020).
In previous studies, various foods were considered carriers of particular compounds due to their proper use to treat different diseases. The fortification of chocolate with plant-based substances has made it a functional product with effective health properties (Faccinetto-Beltrán et al., 2021). The fortification of chocolate with specific essential components results in a greater nutrient density and sometimes an extended shelf life (Poliński et al., 2021). In recent years, chocolate products were produced from different dried fruits, such as raisins, cranberries, strawberries, apricots, plums, and cherries, rich in easily absorbable compounds, such as minerals, vitamins, and phenolic compounds, which lead to a balanced diet. For instance, it was mentioned that raisins are rich in vitamins, minerals, enough sugar content, and antioxidants like cranberries. Furthermore, strawberries contain not only high amounts of antioxidants such as ellagic acid, quercetin, kaempferol, and flavonoids, which are one of the first disease fighters, but also sufficient amounts of vitamin C, potassium, fiber, and folate. Furthermore, apricots, dried plums, and cherries are good sources of potassium, a wide range of vitamins, and phenolic compounds (Ötleş, 2009 (Martini et al., 2018).
Several studies show that antioxidant capabilities are mostly determined by the basic materials they are derived from. White chocolate's polyphenol content and antioxidant activity are decreased due to the lack of cocoa liquor. This property can be measured by several methods, such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonate (ABTS) assay, and reducing power method (Godočiková et al., 2017).

Processes Efficiency References
Fermentation Proper fermentation is necessary to generate a unique flavor in the final product The bean is dried out in fermentation, so it cannot be spoiled by germination During fermentation, lots of special chemicals responsible for the creation of flavors in cocoa beans are formed Assi-Clair et al. (2019), Beckett (2018), Nurhayati and Apriyanto (2021) Drying After fermentation, the beans must be predried and transported to chocolate factories. Any deficiency during this process will encourage mold to grow on the beans. Mold growth limits the product's usability because of its unpleasant appearance and bad taste. The beans can taste very acidic if they are dried too quickly, so it is preferable to dry them at lower temperatures or by intermittent drying Beckett (2018), Santander Muñoz et al. (2020 Storage and transport If the moisture level of beans comes up to 8%, the mold will grow, so they must be stashed in a way that limits water absorption Barišić et al. (2019), Beckett (2018) Cleaning, breaking, and winnowing These processes make the nibs clean (free from any insects and untidiness), fragile, and appropriately dehulled Barišić et al. (2019), Beckett (2018) Sterilization All microorganisms are killed when the nibs or cocoa beans are exposed to high temperatures for an extended time. The method reduces the total plate count (TPC) to <500 CFU/g while also removing all pathogenic bacteria Mixing Time-temperature combinations in continuous or batch mixers are used for mixing substances during chocolate processing to achieve a consistent formulation Melo et al. (2020) Refining In modern chocolate confectionery, a smooth texture product is so desirable, which was obtained by refining Refiners influence agglomerate degradation and particle size reduction, distribute particles across the contrast level, and cover each with lipid Tempering, lipid crystallization, and continuous phase character A properly tempered chocolate would have an appropriate color, good shape, mold contraction, shininess, improved weight regulation, stability, high heat resistance, and a longer shelf life. When chocolate is not properly tempered, type IV crystals form, which quickly transform into form V. Because mirrored light is disoriented by instability and disorganized crystal growth, this transformation affects color Pirouzian et al. (2020)), Suri and Basu (2022) Casting and molding Any changes in the viscosity of the melted chocolate will stop during filling, affecting the size and weight of the finished product. Detempering occurs when the molds are extremely hot, resulting in the product sticking to the mold impressions, poor shine, and blooming. If they are extremely cold, they will lose their shine and stick to the mold, resulting in more air bubbles and markings on the final product Beckett (2018), Toker et al. (2021) Cooling The molds containing melted chocolate are passed through the freezing section after vibration. This mechanized process involves passing the molds through a cooling chamber, reducing the chocolate temperature to around 12-15°C. The chocolate will solidify into bars Beckett (2018), Sato et al. (2021) Wrapping/packaging The foil creates the strongest protection against water vapor and gas transmission. It helps to maintain the chocolate fragrance at a cool temperature. The chosen paper material should be durable, easy to print on, and at a reasonable price. Then, the chocolate is labeled with the batch number, production date, and expiration date by the machine with oleogels (12%) obtained from β-sitosterol in various ratios (γoryzanol to corn oil at a 2:3 ratio, stearic acid to corn oil at a 1:4 ratio, and lecithin to corn oil at a 4:1 [w/w] ratio). The findings of this study show that among the three oleogels, the one containing β-sitosterol and γ-oryzanol had the hardest texture, the greatest ability to bind oil, and the strongest heat resistance because of the development of intermolecular and fiber tube structures. Chocolate made with γ-oryzanol-based oleogels (cocoa butter and oleogels in a 1:1 ratio) had comparable rheological, crystal structure, texture, and sensory properties to dark chocolate. It appears that the use of oleogels made with bioactive substances that have lower saturated and transfatty acid levels in the chocolate industry could play a significant role in enhancing consumer health.
Spirulina, a microalgae with great protein (nearly 70% of the biomass) and amino acid content, is an innovative and promis-

| NANOE N C A PSU L AT ION OF AC TIVE SUBS TAN CE S
The stability, bioactivity, and bioavailability of active substances are essential to develop fortified foods (Andishmand et al., 2016). Food fortification is challenging because of the incompatibility of the fortifier with the food matrix, storage stability, and the possibility of changes in sensory characteristics (Faccinetto-Beltrán et al., 2021).
Therefore, different delivery techniques rather than the direct addition of active substances were developed to overcome the mentioned problems and make them industrially applicable (Andishmand et al., 2017). Techniques used to nanoencapsulate plant-based substances can be classified as (1) physical methods (such as spray drying, antisolvent precipitation, freeze-drying, extrusion, fluid bed coating, and supercritical fluids); (2) chemical methods (such as polymerization and inclusion complexes); (3) physicochemical methods (such as emulsification, liposomal encapsulation, complex coagulation, and ionic gelation); and (4) electrohydrodynamic methods (such as electrospinning and electrospraying) (Hosseini & Jafari, 2020).
Some of these methods were used for chocolate fortification, which is discussed next (Figure 1).

| Spray drying
Spray drying is the most common method of encapsulating food substances. This method is economical and widely used to flavor compounds. The carrier or wall, such as maltodextrin or another gum, is hydrated in this process, and the ingredients to be encapsulated are added and combined in a certain ratio. The mixture is then injected into the system to create a small droplet (Piñón-Balderrama et al., 2020). When the droplets are exposed to hot air, they quickly F I G U R E 1 Preparation steps of nanoscale delivery systems for encapsulating plant bioactive agents.
lose their moisture, and spray-dried particles are assembled in the product chamber. As a result of the high speed (a few seconds) of the drying process, the product suffers the least loss of biofunctional properties (Assadpour & Jafari, 2019). Working with highly viscous feeds is possible via preheating, particle size, shape, and morphology control, and the design of particles with controlled release properties (Cetinkaya et al., 2021), spray-drying process of several types of juices and concentrates (Sarabandi et al., 2018), herbal extracts (Sarabandi et al., 2019), and vitamins (Terracina et al., 2022)

| Antisolvent precipitation
Another fortification method is antisolvent precipitation in which ultrafine enriching agents are prepared. The basic principle is that the enriching bioactive agents are dissolved in a solvent; the solvent solution is then mixed with an antisolvent. Finally, precipitates are produced, creating conditions that produce spherical particles with smooth surfaces in nano or micro dimensions and a narrow particle size distribution ( To that end, antisolvent precipitation of colloidal nanoparticles in cinnamon extract (LCNP-CE) was used, followed by freeze-drying.
The antisolvent precipitation method produced LCNP-CE, which was used to fortify white and milk chocolates from 0% to 2% w/w.
Results showed fortification with LCNP-CE improved the polyphenol content and antioxidant activities of white and milk chocolate.
Despite minor changes in quality factors (hardness, flow behavior, and color), the final product was within an acceptable range.

| Nanoemulsification
Nanosized emulsions were applied as one of the delivery methods in fortification. The size of this colloidal system varies from 10 to 1000 nm. They have several advantages, including increased physical stability, large surface area, ability to use in various formulations, and improved taste sense. Besides, nanoemulsification has a wide range of applications in food and nutrition, biology, and pharmacology, particularly in high-efficiency encapsulation and directed delivery of substances Islam et al., 2022).

| Liposomal encapsulation
Liposomes Finally, in addition to stability against processing conditions, liposomal encapsulation could extend the oxidative and storage stability of encapsulated substances; thus, it could be a great suggestion for use in plant-fortified chocolate production, which is an excellent source of polyphenolic compounds.

| Fate of nanodelivery systems in the human body
Delivery systems in the nanoscale may have diverse biological fates in the human body, such as levels of absorption, excretion, distribution, and metabolism (Katouzian & Jafari, 2016).  this study showed that the rate of hearing loss (unilateral or bilateral) was significantly lower in those who consumed chocolate (p < .001).

| RECENT TRENDS IN FORTIFIED CHOCOL ATE S
Furthermore, the frequency of chocolate consumption is inversely correlated with the severity of the hearing loss. They hypothesized that chocolate because of having cocoa exerts antioxidant and antiinflammatory properties that improve neurodegenerative diseases.

| CURRENT CHALLENG E S IN FORTIFIED CHOCOL ATE S
Nowadays, the development of functional foods like fortified chocolate, in terms of its matrix as a promising carrier for various wholesome compounds, was considered a new era for novel food products which benefit customers concerned about their health.
Hence, several medicinal plants and biomolecules from microalgae are often used to achieve prospective healthfulness. However, consumers' assessment of fortified products' quality and sensory characteristics play an important role to accept these products (Ekantari et al., 2019).
The fortification of chocolate with natural products could affect the rheological proprieties that the Casson model could best describe. Based on this model, chocolate's yield stress and plastic viscosity as a non-Newtonian fluid could be determined for quality and sensorial controls. The formulation's processing conditions and the type of substances could affect yield stress and plastic viscosity (Cahyani et al., 2019). While in some studies, fortification resulted in higher Casson viscosity, in others there was no variation of this parameter, and the interaction of added substances with other constituents like free fat is fundamental to study this character. For instance, yield value and viscosity are reduced by adding fat content, but moisture values >3% can increase initial tension and viscosity (Godočiková et al., 2017).
Moreover, the distribution of particles in chocolate and their interactions is inversely related to its mechanical properties. The most desirable interval is 15-30 μM as bigger or smaller particles may interfere with its palatability. Regarding the bigger particles of fortification substances, a high polydispersity index can be seen in many cases. Furthermore, appropriate melting behavior as another aspect of rheological and textural properties ranges from 32 to 34°C, which is necessary for proper organoleptic perception (Tolve et al., 2018).
Sensory evaluation is a measurement that can be considered quantitative or qualitative indices that provide the understanding of consumers' satisfaction in terms of appearance, color, melt-in-mouth, texture, unique flavor-taste, and odor in produced chocolates.
Findings from previous research proved that the palatability of these products mainly relies on the degree of their bitterness and mouthfeel. In general, if the correct dose of fortification was chosen, the consumers preferred both plain and fortified samples at close levels (Razavizadeh & Tabrizi, 2021). Moreover, these attributes of fortified chocolate can be affected by various factors, including fermentation and roasting processes and applied flavoring agents. For example, free amino acid and polyphenol compounds may cause significant changes in the formation of chocolate flavor (Kaltsa et al., 2021).
Since color is responsible for consumers' first impression, its evaluation via visualization techniques, colorimetric or spectrophotometric methods, is required. Tannins, made up of epicatechin molecules, are the main class of chemicals found in cocoa that are liable for the development of brown color. Furthermore, further factors, such as the production process of formulated substances and the storage time, could determine the color characteristics. There was no significant difference between plain and fortified chocolates in some cases, while in some studies, the latter group looked brighter based on the substances of the added material (Ekantari et al., 2019). In the following, we summarize the functional properties of different fortified chocolates with plant-based substances (Table 3).

Encapsulated
Three panelists could detect the fishy odor from the fortified sample, and they preferred the flavor of the sample without fortification. Furthermore, no significant difference was seen in the texture of both samples as half of them preferred both samples Hlaing et al. (2020) TA B L E 3 (Continued)

| CON CLUS I ON AND FUTURE PROS PEC TS
As it was observed, in terms of the high volume of chocolate consumption worldwide and the special attention of people of all ages to its consumption, it is possible to achieve a health-oriented and popular product. On the other hand, we should not dismiss any potential negative effects that fortifying active substances may have on the desirable qualities of chocolate. Different fortification methods should be developed and optimized. Considering other quality defects in chocolate that could arise from defective production stages or inappropriate fortification methods, it is possible to produce a health-promoting product with higher functional, nutritional, and healing properties.
Among the plant substances, the substances with rich polyphenol content, such as apple and olive, had a higher effect on treating and reducing the effects of obesity, overweight, hypertension, stress, cardiovascular failure, congestive heart failure, and diabetes. writing -review and editing (equal).

ACK N OWLED G M ENTS
The authors thank Doctor Saeed Mirzaee Ghazani (University of Guelph, Canada) for the critical reading of the manuscript.

CO N FLI C T O F I NTE R E S T S TATE M E NT
There are no conflicts of interest to declare.

DATA AVA I L A B I L I T Y S TAT E M E N T
No datasets were generated or analysed during the current study.

E TH I C S S TATEM ENT
This study does not involve any human or animal testing.