Design of a Functional Food Based on Carbohydrate Polymer Blends

1. Introduction

At the beginning of 2020, derived from the rapid transmission of the SARS-CoV-2 virus (COVID-19) in different countries and its potential danger to health, the World Health Organization (WHO) declared the establishment of a global pandemic as a strategy to mitigate the health emergency [1]. This forced millions of people to shelter in their homes, reducing social interactions and, consequently, physical activity. The society adopted a more sedentary lifestyle, negatively affecting the physical and mental health of the population worldwide. To counteract these harmful effects, the WHO issued a series of recommendations to stay healthy, including physical activity at home, mental health care, reducing alcohol and tobacco consumption, and adopting healthy eating habits. The consumption of healthy foods, although they cannot prevent or cure disease, is essential for the proper functioning of the immune system and considerably reduces the probability of the appearance of other diseases such as obesity, diabetes, heart disease, and some types of cancer. Therefore, it is considered that food plays a preponderant role in the prevention of these conditions that have an impact on public health.

Due to awareness about the prevention of diseases such as diabetes, cancer, and Alzheimer’s, the production of functional foods has become one of the most important biotechnological industries in the last decade, given the growing demand from consumers for seek to lengthen their life expectancy and improve their overall health [2]. In order to promote a good state of health and the reduction of chronic diseases, the regular consumption of functional foods is recommended [3]. Food can be considered functional when, in addition to the nutritional contribution, it provides beneficial effects to a specific function of the organism. Functional food is defined according to the European Society for Clinical Nutrition and Metabolism (ESPEN) guide as a food fortified with ingredients, nutrients, or additional components, with the intention of manifesting specific health benefits [4]. Functional foods contain bioactive compounds in low concentrations, such as antioxidants, glutamine, fatty acids, and even live microorganisms such as probiotics.

Obtaining a functional powdered food by microencapsulation of antioxidants and probiotics, allows the development of a novel food product with technological application. Thus, a powdered functional food was designed and prepared from spray-dried blends of carbohydrate polymers such as maltodextrin and inulin, with quercetin and Bacillus clausii as functional ingredients. This chapter describes the selection of these compounds, the process for obtaining the functional food, some physicochemical characteristics, and a technological application in the form of an equilibrium state diagram.

2. Functional food components

Among the materials for the elaboration of food, carbohydrate polymers are commonly employed, since these can be used as texture modifiers, emulsifiers, carrying agents, fat and sugar substitutes. These materials have properties similar to those of synthetic polymers, including glass transition temperature (Tg) and molecular weight distribution (MWD). In order to prolong the shelf life of a food based on carbohydrate polymers, Tg plays a preponderant role since its value should preferably be higher than the storage temperature. In this sense, maltodextrin and inulin present Tg values slightly below and above 100°C, respectively [5, 6]. Maltodextrins are polymers of D-glucose chains linked by glycosidic α-(1–4) and α-(1–6) bonds, which, depending on the type of ramifications, different dextrose equivalents (DE) may be obtained [7]. The caloric intake is similar to regular sugar of 380 kcal/100 g, and the appearance is a white powder. Due to their chemical composition, they are hygroscopic in nature and present changes in the physical state with the adsorption of moisture [8]. For its part, the chemical structure of inulin is composed of linear chains of fructose molecules joined by β-(2–1) glycosidic bonds terminated by an α-D-(1–2)-glucopyranoside ring group (glucose) [9]. It has a caloric intake of 200 kcal/100 g, and its appearance is a white powder. Unlike maltodextrin, inulin has particles in the form of microscopic fibers. It is also hygroscopic in nature and crystallizes with the adsorption of moisture [10].

Probiotics are defined as live strains of strictly selected microorganisms, which, when administered in adequate amounts, confer a beneficial effect on the health of the host [11]. The effects of probiotics can vary according to the dose used, the strain, and the components with which the final product was formulated. These products may have one or more strains, microorganisms belonging to the genera are usually used: Lactobacillus, Bifidobacterium, Lactococcus, Streptococcus, Enterococcus, gram-positive strains of the genus Bacillus and yeasts of the genus Saccharomyces. An active ingredient present in functional foods is probiotics, which confer benefits through different mechanisms such as the production of bile enzymes, organic acids, satiety hormones, the modulation of the immune system through the increase in the antibody response, the competition for substrates against pathogenic organisms and the interaction with the microbiota [12]. These microorganisms can be added to a large number of products such as fermented milk drinks [13]. Some probiotics can be administered as freeze-dried or in the form of spores, which are activated by having the right environment. In the search to develop products with probiotics that can exert a true effect on health, it is necessary that these contain an adequate number of living cells ranging from 10⁶ to 10⁷ colony-forming units per gram and that these are maintained during the product storage and later during transit through the gastrointestinal tract, after consumption. B. clausii are resistant to heat, gastric pH, and antibiotics and can even tolerate alkaline conditions. They have been reported for the treatment of acute childhood diarrhea of viral origin or associated with antibiotics, showing the reduction of illness time, gastrointestinal symptoms, and frequency of evacuations [14]. B. clausii can also reduce the adverse effects of treatment with Helicobacter pylori, generally treated with antibiotics that cause nausea, inflammation, vomiting, and diarrhea, triggering bacterial resistance [15].

Another type of bioactive compound is antioxidants that have shown the ability to protect, delay cell aging, and strengthen the immune system [16, 17]. Antioxidants are compounds that inhibit unstable free radicals that lead to a chain reaction of cell damage, causing cell aging and chronic degenerative diseases. Among the ingredients present within functional foods are antioxidants; these are added to the products alone or in combination with other compounds that allow a synergism, such as that occurring between vitamin C when regenerating the tocopheryl radical of vitamin E after its oxidation [18]. Antioxidants are added to food with the intention of suppressing lipid, protein, and carbohydrate oxidation, increasing the shelf life of the products, as well as reducing the concentrations of free radicals within the body, to improve the health of the consumer. It is known that the consumption of foods rich in bioactive compounds such as polyphenols is inversely related to the appearance of chronic conditions such as cardiovascular diseases and cancer [19, 20]. Oral intake of quercetin at a dose of 150–730 mg/day for four weeks has shown antihypertensive effects, reducing systolic and diastolic pressure in patients in the first stage of hypertension, while patients with metabolic syndrome who had consumed 150 mg /day of quercetin for five weeks significantly reduced their systolic blood pressure [21]. This antioxidant also has anticancer effects, promoting the loss of cell viability, apoptosis, and autophagy through modulation of the PI3K/Akt/mTOR, Wnt/β-catenin, and MAPK/ERK1/2 pathways [22]. However, the use of these antioxidants by the food industry is limited, since they exhibit a high sensitivity to environmental conditions such as light, oxygen, humidity, and exposure to heat, which causes a decrease or loss of their functional properties.

In order to overcome the aforementioned drawbacks, the food industry has had to implement technologies to minimize or eliminate the loss of functional and nutritional properties of these compounds. Microencapsulation is one of the strategies implemented to preserve or extend the shelf life of foods based on bioactive ingredients [23]. Microencapsulation techniques are used to protect from environmental factors, such as heat, oxygen, and moisture, to the cellular components of probiotic microorganisms or any active ingredient that is sought to be added to a food [24]. Microencapsulation consists of a mechanical and physicochemical process that allows the functional substance or bioactive compound to be trapped within the walls of another material that functions as a protective barrier or carrier agent. The microencapsulated functional ingredients are covered by a food-grade carrier material based on compounds such as carbohydrates, proteins, lipids, or synthetic polymers, as a protective barrier preventing the loss of antioxidants and the survival of microorganisms [25]. Among the encapsulation techniques, spray drying is one of the simplest, cheapest, and fastest methodologies used by both the pharmaceutical and food industries. Products produced by spray drying are economical and obtained with high yields and short residence times [23, 26]. Consequently, heat-sensitive products can be dried at relatively high temperatures without deteriorating their properties such as taste, odor, color, and nutrient content [27, 28]. Products obtained dry typically exhibit high quality, low levels of degradation, and excellent stability properties.

3. Spray drying of systems based on carbohydrate polymers

Spray drying of fruit juices such as orange juice has shown to be an adequate methodology in obtaining nonagglomerated powdered material, with the intrinsic characteristics of the juice such as flavor, color, odor, and nutrient content [10, 29]. In these works, the characterization of the physicochemical properties is based on obtaining a dry material in an amorphous state, using inulin as a carrier agent. The state diagrams obtained at 30°C for the inulin and inulin-orange juice systems showed different phase changes. For the inulin system, a phase change from amorphous to crystalline was observed at a water activity (a_w) of 0.51, while for the complex system, two-phase changes were observed, first from amorphous to a semicrystalline microstructure at a_w of 0.22, and later to the crystalline state at a_w of 0.54 [9]. Subsequently, state diagrams for the inulin system with two different molecular weight distributions were reported [30]. It was found that high molecular weight inulin presented an abrupt phase change, that is, from amorphous to crystalline at a water activity of 0.51. On the other hand, the low molecular weight inulin system presented a moderate phase change, where the intermediate phase was identified as a semicrystalline region between water activities of 0.3–0.5.

Regarding maltodextrins, it was found that their potential application and physicochemical properties directly depend on the molecular weight distribution rather than on the DE, and second, the microstructure remained in the amorphous state throughout the entire range of water activities [8]. Later, the use of two carrying agents (inulin and maltodextrin) in the spray drying of blueberry juice and microencapsulation of antioxidants was compared [31]. Here it was found that both carrier agents work for this purpose; however, maltodextrin with DE 10, presented a greater ability to microencapsulate and preserve antioxidants such as quercetin and resveratrol. Subsequently, the effect of spray-drying conditions on the yield, content, and retention of quercetin and resveratrol was studied, using maltodextrins of different molecular weights as microencapsulating agents [32, 33]. In both studies it was concluded that low molecular weight maltodextrins (MC and M10) performed better as encapsulating materials at a concentration of 23–25% by weight and at drying temperature of 170 and 210°C. A qualitative explanation was given based on the observed results, where it was found that, of the two tested antioxidants, quercetin has greater chemical interactions with maltodextrin, since it presents more functional groups than resveratrol. Likewise, it was concluded that the number of functional groups is more important in molecular interactions than stearic hindrance. Recently, maltodextrin was employed as encapsulating material for the drying of strawberry juice [34]. The properties of the powdered juice showed a dependence on the drying conditions, particularly on the concentration of maltodextrin in the precursor solution. For example, the total phenolic content and antioxidant activity decreased monotonically with increasing maltodextrin concentration. On the other hand, the morphology of particles was observed as agglomerated at the lowest maltodextrin concentration (5% by weight). At intermediate and high maltodextrin concentrations (7.5% and 10%), the particles were observed with a spherical morphology and not agglomerated. The drying temperature did not present a significant effect on the determined properties.

Inulin and lactose were compared as microencapsulating agents for microorganisms (B. clausii) with probiotic properties [35]. Similar values were found for the number of living cells (culturability), suggesting that the microorganisms were protected from thermal degradation by carrier agents during spray drying.

Based on the advances reported in these studies, the possibility of designing a functional powdered food was devised.

4. Experimental procedure

The functional food was prepared from ternary blends containing 25% carrying agent (commercial maltodextrin and low molecular weight inulin) and 75% water enriched with antioxidants (quercetin) and microorganisms (B. clausii). Three systems were prepared by varying the concentration of the carrying agent at different ratios 1:2, 1:1, and 2:1, of maltodextrin to inulin. The drying conditions were set at drying temperatures in the range of 126–234°C, a volumetric flow of 35 m³/h and a pressure of 1.5 bar. Each system was tested for its antioxidant capacity in the sequestration of free radicals of 2,2-diphenyl-1-picrylhydrazil (DPPH*) and the amount of available bacterial cells (culturability) determined in the microencapsulated samples. The system with the best antioxidant characteristics and the largest number of microorganisms was selected to obtain a state diagram at 35°C, which provides information about the stability of the product and helps to predict shelf life. For the complete experimental detail, the reader is referred to references [36, 37].

Physicochemical characterizations included: X-ray diffraction (XRD), scanning electron microscopy (SEM), modulated differential scanning calorimetry (MDSC), moisture adsorption assays, and water activity determination. Diffractograms were obtained in a D8 Advance ECO diffractometer (Bruker, Karlsruhe, Germany) equipped with Cu-K radiation (λ = 1.5406 Å) operated at 45 kV, 40 mA, and a detector in a Bragg-Brentano geometry. Scans were performed in the 2θ range of 5–50°, with step size of 0.016° and 20 s per step. Micrographs were acquired in a field emission SEM (JEOL JSM-7401F, Tokyo, Japan) operated at an accelerating voltage of 2 kV. Powder samples were first dispersed on a double-sided copper conductive tape, then covered with a thin layer of gold utilizing sputtering (Denton Desk II sputter coater, Denton, TX, USA). Tg was determined in an MDSC Q200 (TA Instruments, New Castle, DE, USA) equipped with an RCS90 cooling system. About 10 mg of the sample were encapsulated in Tzero® aluminum pans. Thermograms were acquired in the temperature range of −50 to 250°C with a modulation period of 40 s and amplitude of 1.5°C. The isotherm points were obtained by subjecting the functional food powder to different conditions of relative humidity in the interval a_w of 0.07–0.972. Microenvironments contained 2 g of powder and 100 g of inorganic salt. The systems were equilibrated for 30 days at the storage temperature. After the incubation, water activity (a_w) was determined with an Aqualab Series 3 Water Activity Meter (Decagon Devices, Inc., Pullman, WA, USA).

5. Properties of functional food based on carbohydrate polymers blends

After spray-drying, the appearance of the obtained powders was yellowish in color composed of nonagglomerated fine powder. This was observed for all drying conditions experienced [36].

Morphological characterization is one of the first analyses performed, since it allows observing the shape of the particles obtained after drying and visually predicting whether the microstructure was preserved or collapsed. This is done by means of SEM, preferably at a low accelerating voltage, to avoid damaging the particles with the interaction of the electron beam. Additionally, due to the nonconductive nature of carbohydrate polymers, it is necessary to coat the particles with a thin layer of gold, thereby reducing or eliminating charging effects. Figure 1 shows representative micrographs of spray-dried functional food. The morphology of the particles is not homogeneous, that is, the particles are not completely spherical. In some cases, deflated balloon-shaped particles are observed, and in others, elongated particles. Particle size was in the order of the micrometers, from 5 to 60 μm. The surface of the particles in some cases is observed smooth and, in others, wrinkled. This indicates the effect that temperature has on the preservation of microencapsulating properties. A smooth surface suggests that the active ingredients are trapped within the particle, while a wrinkled surface may allow these ingredients to escape from the particle core or be further exposed to degradation. On the other hand, B. clausii microorganisms were not observed. However, by comparison with the samples without microorganisms, it was found that the particles with elongated morphology corresponded to the microorganisms microencapsulated with the carbohydrate polymer blends.

The microstructural characterization by XRD (Figure 2) showed a broad low-intensity peak corresponding to an amorphous structure, and three low-intensity peaks around 10, 12, and 27°. This indicates that under all drying conditions, the microstructure of the powders is in an amorphous state. This is desirable since in this state, the preservation of the functional ingredients is maintained. On the other hand, the low-intensity peaks suggest the crystallization of some of the components of the functional food.

Part of the thermal characterization involves the determination of the glass transition temperature (Tg) by means of MDSC [38]. With this technique, it is possible to decompose the total heat signal into two signals, the reversible heat flow and the nonreversible heat flow. The Tg event is observed in the reversible heat flux signal, as a slight step change in the slope of the curve. In general, the Tg is affected by the amount of moisture adsorbed, which causes a plasticizing effect, in such a way that the higher the amount of moisture, the lower the Tg value. Figure 3 shows a typical MDSC thermogram for a carbohydrate polymers blend. The upper curve corresponds to the modulated total heat flow. While in the other two heat flow signal curves, different thermal events, their start and termination are indicated. Among these events are distinguished the Tg, the vitrification temperature (Tv), and the decomposition temperature (Td). In the case of the carbohydrate polymer blends, the Tg varied from 15.9 to 60.7°C. This suggests that depending on the selected blend, it should be stored at a temperature preferably lower than the Tg, to avoid the change from the amorphous state to a semicrystalline or fully crystalline state.

The antioxidant activity for the carbohydrate polymers blends and their blanks, determined as the percentage of the reduction of radical (DPPH*) reacted with quercetin after 30 minutes are presented in Figure 4. In this figure are included, the effects of experimental variations such as the type of carrier agent, the drying temperature, and the concentration of solids in the precursor solution. The blue bars correspond to the samples with only maltodextrin, the green bars to the samples containing only inulin, while the red bars correspond to the blends of maltodextrin and inulin. The pattern within each bar indicates the drying temperature: coarse for high temperature (210°C), medium for medium temperature (180°C), and fine for low temperature (150°C). Evidently, inulin (run 4) presented a higher antioxidant activity than maltodextrin and the blends. However, the blends dried at medium (180°C, run 3) and high (234°C, run 5) temperatures presented values close to those of inulin dried at 180°C. This can be explained in terms of the amount of dissolved solids, since the inulin sample (run 4) contains a high solids content (28.8%), while the blends (run 3 and 5) contain a total of 20% of solids, of which 10% corresponds to inulin. In this sense, commercially, the approximate value of inulin is three times greater than that of maltodextrin, for which it is desirable to have a cheaper product but with a relatively high antioxidant activity.

For its part, maltodextrin presented the lowest values of antioxidant activity, suggesting that the chemical interaction between maltodextrin and quercetin is greater than with inulin, which means that the antioxidant agent is not released as easily from this carrier agent. Also, this behavior may indicate that the maltodextrin fails to effectively encapsulate all the antioxidant dissolved in the precursor solution.

The results of the viability tests of the microorganisms were similar; however, some differences were observed that are described below. In general, the culturability values of B. clausii showed a decrease with spray drying. The recorded values ranged from 4.3–8.6 Log₁₀ CFU/g. Conversely, inulin samples presented the lowest culturability values, while maltodextrin samples presented similarly high values than those from the blends. From these samples, the drying temperature influenced the culturability. For example, the inulin sample dried at 150°C showed the highest culturability value of 8.2 Log₁₀ CFU/g, while maltodextrin dried at 150 and 210°C presented also relatively high values of 8.1 and 7.1 Log₁₀ CFU/g, respectively. The blends showed culturability values in the range of 6.9–8.6 Log₁₀ CFU/g, where the low and medium drying temperatures presented the highest values. Clearly, the addition of maltodextrin to the inulin, promoted the microencapsulation and conservation of the B. clausii.

6. The equilibrium state diagram for the functional food blend

A state diagram is a graphical representation of one or several properties of a material and its variation with some experimental variable such as temperature, composition, humidity, and pressure. In general, two types of state diagrams are reported in literature: (i) equilibrium state diagrams, which are those where the samples must remain for the time necessary to reach thermodynamic equilibrium. And (ii) the nonequilibrium diagrams, which are those that are constructed from thermal analysis data at conditions more similar to those used in industrial processes. For the study of the stability of foods during storage, equilibrium state diagrams are preferred, since they involve subjecting powdered samples to different moisture adsorption conditions at a fixed temperature for long times of around 30 days. After this time has elapsed, the physicochemical properties of the samples are studied to build the equilibrium state diagram with these data.

For the blends prepared, it was found that the blend containing 25% maltodextrin and 75% inulin presented a slightly higher value of antioxidant activity [37] in such a way that this blend was selected to be characterized and to build the state diagram. Figure 5 shows the equilibrium state diagram for the functional food based on the carbohydrate polymers. The adsorption isotherm obtained at 35°C is represented by the red solid curve. This isotherm was identified as the Flory-Huggins isotherm (type III), which presented low water adsorption at low a_w, and a relative increase in the adsorption and medium and high a_w. After testing different adjusting models, the Guggenheim-Anderson-de Boer (GAB) model was selected to fit the adsorption data, since this model provides a more accurate description of sorption behavior for most food products in a wide range of a_w [39]. Derived from the GAB model, the calculated monolayer content (M₀) was 2.795 g of water per 100 g of solids, corresponding to a_w of 0.43. This parameter indicates the maximum amount of adsorbed water set as a single layer of water molecules on the surface of the food product. Between the fully dried sample and the monolayer content, the microstructural stability of the food product is maintained. Beyond the M₀ value, and because of the availability of a greater number of water molecules forming secondary layers, the stability of the food product may change as well as biological reactions may be triggered.

The blue dashed curve shows the behavior of the Tg as a function of a_w. As observed, the overall trend is to decrease with the adsorption of water. However, three Tg regions can be envisioned. The first and stable region at Tg slightly above 30°C and a_w values below 0.33. In the second region corresponding to a_w values between 0.33 and 0.75, the Tg rapidly drops to a value of about 19°C. The third region comprises the Tg values below 10°C and a_w above 0.75. According to Roos, Sá, and Sereno, it is recommendable to store the food product at a temperature below the Tg [40, 41].

Other important parameters for the evaluation of the storage conditions of dehydrated food products are the critical water content (CWC) and the critical water activity (CWA). These parameters are obtained from the storage temperature (35°C) and from the intersection with the Tg curve. In the state diagram, this is represented by the dotted green line, which starts at the Tg value of 35°C and passes close to the Tg curve at a value of 31°C and a_w of 0.33. By drawing a vertical line from this point and finding its intersection with the adsorption isotherm, the CWC and CWA values can be located on the Y and X axes, respectively. These parameters were determined as CWC of 1.77 g of water per 100 g of solids and CWA of 0.32. Evidently, the critical parameters were lower than the corresponding values calculated from the monolayer content. This suggests a more rigorous criterion for functional food preservation when selecting critical values.

Another feature included in the state diagram is the one delimited by the dotted vertical lines. These lines divide the diagram into three regions and indicate the changes in the microstructure obtained from the X-ray analysis. The first region corresponds to the amorphous state and extends to a_w of 0.33. This region agrees with the critical values of CWC and CWA and approximates the a_w value of 0.43 derived from the monolayer value. The second region corresponds to a semicrystalline microstructure located at a_w values between 0.33 and 0.75. In this region can be found particles still in the amorphous state as others already partially crystallized. Likewise, this region indicates that the microstructure change of the functional food is gradual, passing from amorphous to semicrystalline and later to fully crystalline. The third region involves the crystalline-rubbery region state at a_w above 0.75. In this region, the microstructure is fully crystallized. Roos also identified three regions and named as (i) the stability zone found in the glassy state, (ii) the critical zone where the glass transition takes place, and (iii) the mobility zone, where the flow occurs [42].

The microstructural changes observed in these three regions of the state diagram can be visually represented by the different morphologies found in the microparticles of the powdered food. In each of these regions, a representative micrograph of the powders subjected to different water activities is included. For the amorphous region, micrometric particles with quasi-spherical morphologies and smooth surfaces are observed. For the intermediate or microstructural transition region, in addition to some amorphous particles, others with irregular morphologies such as a deflated balloon are observed. The irregularity of these particles suggests that they are in a state close to microstructural collapse. In the third region, irregular morphology particles and some agglomerated spherical particles are observed that seem to be fused. Morphological analysis by SEM of functional food powders is important since the surface homogeneity of the microparticles can be related to the encapsulation efficiency [43]. That is, the more surface defects the microparticles present, the more the active ingredients microencapsulated inside the particles can escape or be degraded by external elements such as reactive oxygen species.

Based on the evidence described above from the equilibrium state diagram, the powdered functional food should be stored at a temperature no higher than 31°C and at humidity conditions not exceeding the monolayer content (2.79 g of water per 100 g of solids). At these conditions, the food will retain an amorphous microstructure and microparticles with spherical morphologies and homogeneous surfaces. This will obviously be reflected in the preservation of the functional properties of the powdered feed.

7. Conclusions

In this chapter, the design and obtaining of a spray-dried powdered functional food were described and shown. The food was based on blends of carbohydrate polymers functionalized with an antioxidant and probiotics. The physicochemical properties of the blends showed a synergy between the two polysaccharides (maltodextrin and inulin), since the first presented a beneficial effect on the microencapsulation of B. clausii microorganisms, while the second promoted a greater antioxidant activity of quercetin. Among the carbohydrate polymer blends, the one with the highest inulin content was selected to construct an equilibrium state diagram. This state diagram yielded important information about the optimal and critical storage conditions for the preservation of the microstructure and properties of the functional powdered food. The development of this type of product may contribute to mitigating public health problems such as those derived from a poor diet.

Acknowledgments

The financial support from the Advanced Materials Research Center S.C. (CIMAV) through the support of research projects (grant numbers CCDPI-21/2021 and PI-14-22) is acknowledged. Also, the technical support from Refworks/Proquest, during the editing of the document.

Conflict of interest

The authors declare no conflict of interest.