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Article

Microwave–Assisted OSA–Faba Bean Starch Production for Probiotic Microencapsulation

by
Mayra Esthela González-Mendoza
1,
Fernando Martínez-Bustos
2,
Eduardo Castaño-Tostado
1,
María del Carmen Cortez-Trejo
1 and
Silvia Lorena Amaya-Llano
1,*
1
Facultad de Química, Universidad Autónoma de Querétaro, Cerro de las Campanas S/N, Querétaro 76010, Queretaro, Mexico
2
Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Unidad Querétaro, Libramiento Norponiente 2000, Real de Juriquilla, Querétaro 76230, Queretaro, Mexico
*
Author to whom correspondence should be addressed.
Polysaccharides 2025, 6(3), 81; https://doi.org/10.3390/polysaccharides6030081 (registering DOI)
Submission received: 29 May 2025 / Revised: 4 July 2025 / Accepted: 6 September 2025 / Published: 7 September 2025
Browse Figures
Versions Notes

Abstract

Probiotics offer significant health benefits; however, their efficacy is often compromised by low survival rates in stressful conditions. Microencapsulation using modified starches presents a promising strategy to enhance probiotic viability. This study aimed to evaluate microwave-assisted octenyl succinic anhydride (OSA) modification of faba bean starch to provide a protective matrix for the microencapsulation of Lactobacillus rhamnosus GG (LGG) through spray drying. Starch was extracted from faba beans and hydrolyzed, and a factorial design was employed for OSA esterification (3% w/w) using a conventional microwave (30 or 60 s at power levels of 2 or 10). The starches were characterized, and the most effective treatment was selected for the microencapsulation of LGG, varying the inlet temperature (120 and 140 °C) and flow rate (7 and 12 mL/min) at 30% solids content. Microwaves significantly reduced the processing time for starch esterification. Microwave-assisted OSA modification produced starches with low viscosity (<0.015 Pa·s), high amylose and resistant starch content, and good solubility, making them suitable for probiotic encapsulation. The microencapsulation of LGG resulted in a powder yield of 41–55%, with particle sizes ranging from 5 to 20 µm and survival rates of 81–90%. This study presents an effective method of producing OSA-modified starch from faba beans using microwave energy, demonstrating strong potential for probiotic delivery applications.

1. Introduction

Starch, a naturally abundant carbohydrate, is widely employed as an encapsulating material for various compounds, including vitamins, lipids, essential oils, flavors, pharmaceuticals, pigments, polyphenols, herbicides, proteins, and microorganisms such as probiotics [1]. Both native and modified starches, derived from different botanical sources, as well as products from starch hydrolysis (e.g., maltodextrins), have been employed for these purposes [2]. The use of starch is primarily due to its accessibility, cost-effectiveness, and versatile functional properties, including water retention and viscosity modulation [1,2].
Effective microencapsulation systems must protect probiotics from the harsh conditions of the upper gastrointestinal tract and ensure their release in the colon [3]. Among the various types of starch, resistant starch (RS) has garnered significant interest since, unlike rapidly digestible starch or common maltodextrins, RS reaches the colon largely intact and may serve as a substrate for beneficial microbiota. These attributes make RS particularly effective in enhancing the viability and delivery of several probiotics during storage and gastrointestinal transit [4,5,6,7,8].
RS is classified into five types, with type 4 RS being chemically modified through reactions such as etherification or esterification [9,10]. For microencapsulation purposes, the most commonly modified starches are OSA starches [2]. These materials are produced through alkaline reactions between starch granules and octenyl succinic anhydride in aqueous suspensions [11,12,13]. In addition to their protective functions, OSA starches are valued for their emulsifying capacities and thermal stability [14]. Furthermore, the U.S. Food and Drug Administration (FDA) permits their use in food applications, with a maximum of 3% OSA. Currently, various botanical sources, including corn, rice, potato, quinoa, lentils, and beans, have been utilized to produce OSA starches [15,16].
Leguminous crops such as chickpeas, peas, and faba beans represent unconventional but promising sources of starch, with content ranging from 25 to 50%. Among these, faba bean starch is notable for its high RS content and fine granule size, making it a strong candidate for use in probiotic microencapsulation [17,18]. Despite these favorable characteristics, native starch tends to produce highly viscous solutions, complicating encapsulation processes, particularly when techniques such as spray drying are employed. In this context, chemical modification serves as a viable alternative.
Microwave energy (ME) has emerged as a compelling substitute to conventional heating methods for starch modification. Operating within frequencies of 300 MHz to 300 GHz, ME facilitates rapid and uniform heating through dipolar polarization and dielectric heating, significantly altering the structural and rheological properties of starch [19,20,21]. Previous studies have successfully demonstrated the use of ME for the hydrolysis and esterification of various starch sources, including corn, rice, potato, pea, cassava, and lentils [22,23,24,25,26,27,28,29].
In our previous work [30], several faba bean starches with varying degrees of hydrolysis were produced through a dry route using ME. These starches exhibited low viscosity values, high amylose content, and high solubility, indicating the potential to produce thermo-protectant matrices for probiotics in spray-drying microencapsulation. However, acid hydrolysis resulted in a reduction in RS compared to the native starch. Following esterification, an increase in RS content was anticipated. Moreover, the existing literature on the use of faba bean starch for the development of delivery systems is still limited, with no published studies reporting its chemical modification via conventional methods or ME. This study aimed to evaluate the OSA modification of two faba bean starches with differing degrees of hydrolysis, using microwave energy for probiotic microencapsulation by spray drying. The central objectives were to chemically modify faba bean starch via ME-assisted OSA esterification, characterize the physicochemical properties of the modified starches, and encapsulate LGG by spray drying using these materials. The significance of this work lies in the introduction of an efficient method based on ME for the production of high-functionality encapsulating materials from underutilized legume starches. Furthermore, this research contributes to advancing sustainable food processing technologies while enhancing the delivery and viability of probiotic formulations.

2. Materials and Methods

2.1. Materials

Faba bean seeds (Vicia faba var. Major) were purchased from a local market in Queretaro (Queretaro, Mexico). OSA was acquired from Sigma Aldrich Co. [St. Louis, (MO), USA], while N-LOK starch was sourced from Ingredion México S.A. Starch K-RSTAR and K-AMYL kits were obtained from Megazyme Int. (Wicklow, Ireland). Lactobacillus rhamnosus GG ATCC 53103 was provided by CHR HANSEN [Milwaukee, (WI), USA]. All other reagents were of analytical grade, unless otherwise specified.

2.2. Faba Bean Hydrolysis and OSA Modification

Faba bean starch was extracted and hydrolyzed as previously reported [30]. Two hydrolyzed faba bean starches (HFBSs) were prepared by moisturizing the starch to 40% humidity using an HCl solution, followed by microwave treatment at power level 6 (Panasonic NN-SB646S, Beijing, China). For HFBS2, 2 mL/100 mL of HCL was used, followed by microwave treatment for 30 s. For HFBS8, 4 mL/100 mL of HCL was used, followed by microwave treatment for 60 s. Subsequently, these materials underwent chemical modification through microwave energy using a fractional factorial design (23) for esterification. The factors and levels used were the type of starch, HFBS2 and HFBS8; the time (t), 30 and 60 s; and the power level (P), 2 and 10. Time and power levels were determined based on preliminary experiments. The hydrolyzed starch was solubilized, and 3% w/w of n-octenyl succinic anhydride reagent (OSA, d.b.) was added. The pH was then adjusted to 8.5 using a 1% NaOH solution. The samples were subjected to microwave treatments as detailed in Table 1 and then allowed to cool, and the pH was adjusted to 7.0 with 2% NaOH. Finally, the modified starches were dried at 40 °C for 24 h, processed in a mill (Krups GX4100, Mexico City, Mexico), and sieved through a 60-mesh sieve to obtain modified faba bean starches (MFBSs).
For comparative purposes, a succinylated faba bean starch was produced following a conventional method described elsewhere [31]. Briefly, a slurry of starch (40 g/100 mL water) was hydrolyzed with HCl at a final concentration of 3.4 g of pure HCl/100 g of starch at 50 °C with constant stirring for 6 h. The pH was then adjusted to 5.0 using NaOH (5% p/v), and the hydrolyzed starch was obtained by centrifugation (10 min, 6000 rpm), washing with distilled water, and drying in an oven at 45 °C for 48 h, followed by milling and sieving. For the production of conventionally modified faba bean starch (CFBS), a slurry of hydrolyzed starch was prepared (45 g/100 mL water) and vigorously stirred while the OSA reagent (3% w/w) was added dropwise over 2 h. The mixture was allowed to react for a total of 6 h while maintaining the pH between 8.5 and 9.0 using NaOH (5% p/v). The pH was then adjusted to 5.0 using HCl (5% v/v) before centrifugation (10 min, 6000 rpm), drying at 45 °C, milling, and sieving.

2.3. Characterization of OSA Starches

2.3.1. Degree of Substitution (DS)

The degree of substitution was determined according to the method described by Kweon et al. [32]. A starch–OSA sample (5 g, dry weight) was combined with 25 mL of a 2.5 M HCl solution in isopropyl alcohol. The mixture was thoroughly stirred for 30 min, after which 100 mL of a 90% (v/v) aqueous isopropyl alcohol solution was added, and the suspension was stirred for an additional 10 min. The suspension was then filtered through a glass filter, and the residue was washed with a 90% isopropyl alcohol solution until Cl− could no longer be detected using a 0.1 M AgNO3 solution. The starch was redispersed in 300 mL of distilled water, and the dispersion was boiled for 20 min. The starch solution was titrated with a standard 0.1 M NaOH solution, using phenolphthalein as an indicator. A native starch blank was titrated simultaneously. The degree of substitution (DS) was calculated according to Equation (1):
DS = (0.162 × V × M/W)/[1 − 0.210 × V × M/W]
where V is the volume of aqueous sodium hydroxide solution used during titration, M is the molarity of the aqueous sodium hydroxide solution, and W is the weight of the sample.

2.3.2. FTIR Analysis

Fourier transform infrared spectroscopy (FTIR) spectra were obtained using a Spectrum GX spectrometer [Perkin Elmer, Boston, (MA), USA] equipped with a diffuse reflectance accessory [Pike Technology model, Boston, (MA), USA]. The powdered samples were mixed with KBr (ratio 1:100 w/w) and scanned over a wavenumber range of 400 to 4000 cm−1.

2.3.3. Resistant Starch (RS), Amylose, Amylopectin, and Reducing Sugars

RS, amylose, and amylopectin content was determined using commercial enzymatic kits, namely Megazyme K-RSTAR for RS and Megazyme K-AMYL for amylose and amylopectin, respectively, following the supplier’s specifications. For reducing sugar determination, the 3,5-dinitrosalicylic acid (DNS) method was followed [33].

2.3.4. Viscosity Profiles

The viscosity profile was evaluated as previously reported [30]. Briefly, 2 g of the sample was mixed with 28 mL of distilled water, and measurements were performed using a Rapid Visco Analyzer Model Super 4 [Newport Scientific PTY Ltd., Sydney, (NSW), Australia] according to the specifications of AACC Method 61-02 [34]. The initial temperature (50 °C) was held for 1 min and then increased to 92 °C at a heating rate of 5.5 °C/min. Once the specified temperature was reached, this temperature remained constant for 5 min, after which cooling was performed at the same heating rate until a final temperature of 50 °C was achieved, which was held for 2 min. The total run duration was 23 min. The results obtained from the equipment were expressed in viscosity units (Pa·s).

2.3.5. Water Absorption Index (WAI) and Water Solubility Index (WSI)

The WAI and WSI were determined according to the methodology reported by Anderson et al. [35].

2.4. LGG Encapsulation by Spray Drying

The LGG strain was resuspended in 100 mL of MRS broth and incubated [Felisa®, Guadalajara, (JAL), Mexico] at 37 °C until an optical density of approximately 1 at λ = 600 nm was reached, corresponding to 10 logarithms of colony-forming units (CFU) per milliliter (log CFU/mL) of concentration. Microencapsulation was performed using a spray dryer [BÜCHI Mini Spray Dryer B-290®, Flawil, (St. Gallen), Switzerland]. Each bacterial suspension was centrifuged at 10,000× g for 10 min, followed by two peptone washes (0.5%). Finally, the sediment was resuspended in 100 mL of a solution containing OSA–starch and homogenized at 7000 rpm for 1 min [IKA® T18 digital ULTRA TURRAX®, Wilmington, (DE), USA] [31,36,37]. A factorial design (22) was employed, with the inlet temperature (120 and 140 °C) and flow rate (7 and 12 mL/min) as factors. The nozzle diameter was 0.7 mm, and the solids suspension was maintained at 30% w/v. The response variables were the yield and survival. The yield percentage was calculated based on the solids in the suspension and those obtained after spray drying.

2.5. Characterization of Microencapsulated LGG

2.5.1. Bacterial Count and Encapsulation Efficiency

To determine cell viability, LGG cells were fully released from the microcapsules by rehydrating 1 g of the spray-dried powder in 9 mL of MRS broth and vortexing. Appropriate dilutions were created for plate counts on MRS agar (incubated at 37 °C for 24 h under anaerobic conditions). The colony-forming units per milliliter [36,38] were reported. The number of viable cells before (N0) and after drying (N) was evaluated and expressed as the encapsulation efficiency according to Equation (2) [39]:
% EE = (N/N0) × 100

2.5.2. Water Activity

The water activity of the microencapsulated LGG was determined using a water activity instrument [AquaLab, Pawkit, Decagon®, San Francisco, (CA), USA].

2.5.3. Morphology of Microencapsulated LGG

Electronic micrographs of powdered microencapsulated LGG were obtained using a field emission scanning electron microscope [FE-SEM, S-4700, Hitachi, (Ibaraki), Japan]. The dried samples were placed directly onto double-sided carbon tape and sputter-coated with gold before observation at various magnifications.

2.5.4. DSC

The thermal properties of microencapsulated LGG were determined using a differential scanning calorimeter [DSC Mettler Toledo, model 821, Schwerzenbach, (Zh), Switzerland]. A sample weighing 3 mg and 7 mg of distilled water were placed in a 40 µL aluminum crucible and sealed tightly. The crucible was heated from 30 to 200 °C at a rate of 10 °C/min. The melting temperature of the microcapsules (Tm) was determined directly from the thermogram.

2.6. Statistical Analysis

All experiments were conducted with three replications. Mean values and standard deviations (SD) were computed. The experimental data were analyzed using analysis of variance (ANOVA). All analyses were performed using the R software [version 4.4.0, Newark, (NJ), USA].

3. Results and Discussion

3.1. Characterization of Modified Starches

Table 2 summarizes the degree of substitution (DS) and the resistant starch, amylose, and reducing sugar content of the succinylated faba bean starches. Although the microwave power and time did not significantly affect the variables studied (p > 0.05), two distinct behaviors emerged, depending primarily on the hydrolyzed starch used for chemical modification.
The DS, which represents the average number of hydroxyl groups substituted per glucose unit, ranged from 0.003 to 0.023. According to the U.S. Food and Drug Administration (FDA), a maximum of 3% OSA starch is allowed for food applications, corresponding to a theoretical DS limit of 0.023 [40], which aligns with the values obtained here. Modified starches derived from HFBS8 (Table 1; MFBS2, -4, -6, and -8) exhibited higher degrees of substitution. Previous studies confirmed that HFBS8 underwent a greater degree of hydrolysis than HFBS2 [30]. Variations in chemical substitution among starches are typically attributed to differences in amylose packing within amorphous regions, as well as the organization of amylose and amylopectin in the granule structure [41]. A reduction in amorphous regions and an increase in relative crystallinity are known to limit the accessibility or penetration ability of succinic anhydride [42]. In contrast, enhanced hydrolysis in HFBS8 (vs. HFBS2) likely increased the amorphous content, creating more reactive sites for succinylation.
Interestingly, starches with higher resistant starch (RS) content exhibited lower degrees of substitution. This inverse relationship likely stems from the presence of retrograded amylose, which may impede succinylation. Han et al. [43] reported similar findings in ultrasonically treated corn starch.
Concerning RS content, the acid hydrolysis of faba bean starch reduced RS compared to the native form, likely due to the extensive cleavage of glycosidic linkages [30]. However, esterification led to an increase in RS content. Treatments using HFBS2 starch (Table 1; MFBS1, -3, -5, and -7) displayed higher RS levels, ranging from 11.6 to 13.3%, which can be attributed to its initially higher RS content (8.6%) compared to that of HFBS8 (4.7%) [31].
Based on the RS levels in hydrolyzed starches, succinylation yielded a 39% average increase for treatments using HFBS2 and a 104% increase for those using HFBS8. This considerable improvement likely reflects the higher amylose content in HFBS2, which promotes retrogradation and resistant starch formation. The post-esterification amylose content varied significantly depending on the type of hydrolyzed starch. HFBS2 previously exhibited amylose content of 31.1%, whereas HFBS8 showed a markedly higher value of 82% [30]. In the current study, microwave treatment further increased the amylose levels to 31.6–38.4% for HFBS2-based samples and 84.3–89.4% for those derived from HFBS8, due to additional cleavage.
Microwave treatment during succinylation also elevated the reducing sugar content, as expected. Microwave energy promotes the disintegration of starch granules, particularly amylose [21]. Initially, the hydrolyzed faba bean starches contained 0.58 g/L (HFBS2) and 4.63 g/L (HFBS8). After microwave-assisted chemical modification, the reducing sugar levels increased to 0.89–1.43 g/L and 14.26–15.43 g/L for HFBS2 and HFBS8, respectively. The greatest rise was observed in HFBS8-derived samples (MFBS2, -4, -6, and -8), likely due to extensive depolymerization during hydrolysis [30].
The FTIR spectra of hydrolyzed starches, conventionally esterified samples, and microwave-esterified starches are shown in Figure 1. All samples displayed similar profiles (Figure 1A). Compared with unesterified starch (HFBS), the spectra of the modified starches (CFBS and MFBS) exhibited new peaks at approximately 1726 cm−1 and 1567 cm−1 (Figure 1B). These findings are consistent with earlier studies by Simsek et al. [44], Zhang et al. [45], and Dewi et al. [46], which reported esterification-related peaks around 1750 cm−1 and 1570 cm−1, 1724 cm−1 and 1572 cm−1, and 1729 and 1568 cm−1, respectively. The peak at 1726 cm−1 corresponds to the characteristic C=O stretching vibration, suggesting the formation of carbonyl ester groups, while the peak at 1567 cm−1 reflects the asymmetric stretching vibration of the RCOO− carboxylate group. These results confirm the effective substitution of hydroxyl groups in the starch, forming ester-type bonds.
Notably, modified starches derived from the hydrolyzed starch HFBS8 showed greater intensity in the band located in the range 3000–3600 cm−1 associated with OH− groups (Figure 1A). As mentioned, HFBS8 presented a higher degree of hydrolysis than HFBS2 [30], which explains the greater exposure of OH− groups related to hydrogen bonding, enhancing solubility and absorption, as discussed later.
The viscosity profiles of the modified starches are shown in Figure 2. Viscosity is a critical property for wall materials in spray-drying microencapsulation processes, where low viscosities are preferred for optimal atomization [47]. Compared to conventional esterification (CFBS), microwave-assisted modification resulted in a greater viscosity reduction, approaching or even falling below that of the commercial N-LOK starch, a specialized low-viscosity carrier used for the encapsulation of flavors, fats, oils, and vitamins.
As previously reported, native faba bean starch exhibited the maximum viscosity of 0.976 Pa·s [30]. Following hydrolysis and microwave-assisted esterification, viscosities below 0.015 Pa·s were obtained. This outcome is particularly noteworthy, as conventional industrial starch modification typically involves partial acid hydrolysis coupled with intensive hydrothermal or enzymatic treatments. In contrast, the present study demonstrates that environmentally friendly approaches, such as the application of microwave energy, can produce starches with desirable viscosity characteristics. The lowest viscosity values were recorded for starches derived from HFBS8 (MFBS2, MFBS4, MFBS6, and MFBS8), which can be attributed to their higher degrees of hydrolysis, as previously indicated by their elevated reducing sugar content.
In addition, the water solubility index (WSI) and water absorption index (WAI) are critical parameters in evaluating starch suitability in food applications. In the context of spray-drying microencapsulation, water solubility is especially important for wall material performance [48]. Microwave energy significantly enhanced starch solubility. Initially, hydrolyzed starches exhibited WSI values of 8.3% and 49.5% for HFBS2 and HFBS8, respectively [30]. After OSA modification via microwave energy, the WSI values increased to 16.3–22.2% for HFBS2-based starches and 62.5–71.2% for those derived from HFBS8 (Figure 3A). The higher WSI values observed in HFBS8-derived starches are likely due to their greater degrees of hydrolysis and increased exposure to hydroxyl (OH−) groups, as supported by the FTIR analysis. Notably, MFBS6 exhibited the highest WSI value among all modified samples.
Regarding the WAI, although no significant differences were observed among treatments (Figure 3B), succinylation generally led to an increase. Before chemical modification, the hydrolyzed starches exhibited WAI values between 2 and 3% [30]. Following the chemical modification, the WAI values increased to a range of 3 to 6%. This rise can be attributed to the combined effects of microwave energy and succinylation. Succinylation introduces bulky substituent groups that disrupt intramolecular hydrogen bonding, enhancing the interaction between water molecules and the OH groups on starch chains [49]. Additionally, further hydrolysis during microwave-assisted succinylation may contribute to elevated WSI and WAI values [30]. As shown in Figure 3, all MFBS1–8 starches demonstrated higher WSI and WAI values than conventionally succinylated faba bean starch.
Microwave-assisted OSA esterification yielded modified starches with enhanced viscosity and WSI properties, making them suitable for spray-drying encapsulation. Among the treatments, MFBS2, MFBS4, MFBS6, and MFBS8 demonstrated particularly favorable viscosity and WSI characteristics, identifying them as strong candidates for use as wall materials. Selecting an appropriate modification method, degree of hydrolysis, physical treatment, and processing sequence allows for the customization of starch molecular structures tailored for specific encapsulation purposes [50]. In this regard, the innovative microwave-assisted succinylation method applied to non-conventional faba bean starch demonstrates promising potential for food industry applications, particularly encapsulation, while also offering significant energy and time savings compared to conventional esterification processes (seconds vs. hours).

3.2. LGG Microencapsulation by Spray Drying and Microcapsule Properties

MFBS6 was selected for LGG based on its optimal characteristics for spray drying, including the lowest viscosity and highest WSI values. In addition, MFBS6 is rich in amylose and contains resistant starch. These components have been associated with improved capsule viability, likely due to their prebiotic effects and structural reinforcement of the microcapsules [51].
Table 3 presents the outcomes of the four treatments used for LGG microencapsulation with MFBS6 as the wall material. As anticipated, higher inlet temperatures corresponded to increased outlet temperatures. Yields ranged from 45 to 51%, with no statistically significant differences observed between treatments. The reported yields for probiotic microencapsulation vary widely, from 5 to 80% [52,53]. Using wall materials similar to MFBS6, such as the commercial starch N-LOK, yields up to 50% have been reported [54].
More importantly, Table 3 presents data on microorganism survival following spray-drying. No statistically significant differences were observed among treatments, except between MCLGG2 and MCLGG3. In all cases, the encapsulation efficiency exceeded 80%, with a viability reduction of approximately 1 log unit. The highest encapsulation efficiency was observed for MCLGG3 (90 ± 2.6%), underscoring the strong potential of MFBS6 as a wall material for probiotic strains such as LGG. For comparison, the encapsulation efficiencies of probiotics using OSA-modified starches have varied: Chen et al. [55] reported 94% efficiency for Pediococcus acidilactici encapsulated with OSA–wheat starch; Cruz-Benítez et al. [56] reported 64–65% for Lactobacillus pentosus microencapsulated with OSA–cassava starch; and Arslan et al. [54] obtained similar results to those presented here for Saccharomyces cerevisiae microencapsulation (89.53%) employing N-LOK starch.
The spray-dryer operating conditions, including the airflow, feed rate, and temperature, are key determinants of final product quality. The optimization of these parameters, along with appropriate wall material selection, can enhance probiotic survival and overall viability [57,58,59]. The favorable outcomes observed in this study suggest that both the functional characteristics of microwave-succinylated faba bean starch (e.g., viscosity and WSI) and the spray-drying parameters employed were suitable to maintain high LGG viability. Nevertheless, if further improvement in viability is desired, a detailed optimization process may be warranted.
Regarding the properties of the LGG microcapsules, no significant differences were found in water activity (aw), which remained consistently around 0.2 across all treatments (Table 3). In general, powders with aw values of 0.6 or lower are considered microbiologically and biochemically stable, with ideal values below 0.25 [60], as observed in the present work.
Scanning electron microscopy was employed to assess the morphological quality of the microcapsules. As shown in Figure 4, the particles exhibited shriveled, spherical shapes without pores or surface cracks. The shrinkage and surface depressions were likely caused by particle contraction during drying and cooling. Emulsion properties (such as viscosity and solids concentration) and process parameters (e.g., temperature, nozzle size, pressure) are known to influence the final particle size. In this study, the particle sizes across all treatments ranged from approximately 5 to 20 µm. These results are consistent with the findings of Cortés et al. [61], who observed a similar morphology and dimensions in Bifidobacterium breve microcapsules prepared using modified amaranth starch. Similar findings have also been documented by Arslan et al. [54], Rodríguez-Restrepo et al. [52], Muhammad et al. [7], Nunes et al. [62], and Tao et al. [53].
To assess the thermoprotective effect of microencapsulation on probiotic cells, thermograms of the LGG microcapsules and the non-encapsulated microorganisms were obtained. As illustrated in Figure 5, free LGG cells exhibited a thermal transition peak at 124.9 °C (melting peak), corresponding to ribosome denaturation—a known indicator of cellular inactivation. Lee and Kaletunc [63], in a calorimetric study of E. coli and Lactobacillus plantarum, identified this event as a primary indicator of whole-cell inactivation, attributed specifically to ribosomal denaturation. These authors observed high peak temperatures above 100 °C and related them to thermostable cell wall proteins or lipopolysaccharides. In the present study, encapsulation increased the melting temperatures of LGG to a range of 130–157 °C, suggesting enhanced interfacial structural integrity and improved thermal stability among the microcapsules. This thermal shift likely reflects improved ribosomal protection conferred by the succinylated faba bean starch. However, to fully confirm this protective effect, further evaluation of microbial viability under high-temperature conditions is recommended.

4. Conclusions

This study presents an efficient method for the modification of faba bean starch using microwave-assisted esterification with octenyl succinic anhydride (OSA). The process was completed in a significantly shorter time (seconds) compared to the conventional method (6 h), while achieving substantial improvements in resistant starch content (an increase of 39–104%). The modified starches exhibited desirable properties for spray-drying encapsulation, including low viscosity and high solubility. Using OSA-modified faba bean starch as a wall material, the microencapsulation of Lactobacillus rhamnosus GG yielded encapsulation efficiencies ranging from 45% to 51%, with the probiotic survival rates reaching up to 90%. The resulting microcapsules demonstrated favorable physicochemical and morphological attributes, effectively maintaining probiotic viability. Overall, these findings highlight the potential of microwave-assisted OSA esterification as a green, time-efficient approach to producing functional starch-based encapsulants. Further investigation is warranted to assess the performance and stability of these microcapsules in real food systems and their impacts on product quality and probiotic efficacy.

Author Contributions

Conceptualization, M.E.G.-M. and S.L.A.-L.; methodology, M.E.G.-M. and F.M.-B.; validation, E.C.-T. and M.d.C.C.-T.; formal analysis, M.E.G.-M., M.d.C.C.-T. and E.C.-T.; investigation, M.E.G.-M.; resources, S.L.A.-L. and F.M.-B.; data curation, M.d.C.C.-T.; writing—original draft preparation, M.E.G.-M. and M.d.C.C.-T.; writing—review and editing, F.M.-B., E.C.-T. and S.L.A.-L.; visualization, M.E.G.-M. and M.d.C.C.-T.; supervision, S.L.A.-L.; project administration, S.L.A.-L.; funding acquisition, S.L.A.-L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by a scholarship (Number 731138) of the National Council of Science and Technology (CONACyT, now SECIHTI, Mexico) and Facultad de Química, Universidad Autónoma de Querétaro (México, FCQ202128).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Data are available on reasonable request to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
OSAOctenyl succinic anhydride
LGGLactobacillus rhamnosus GG
RSResistant starch
MEMicrowave energy
HFBSHydrolyzed faba bean starch
MFBSModified faba bean starch
CFBSConventionally esterified faba bean starch
DSDegree of substitution
FTIRFourier transform infrared transmission spectroscopy
WSIWater solubility index
WAIWater absorption index
MCLGG Spray-dried Lactobacillus rhamnosus GG microcapsules

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Polysaccharides 06 00081 g001
Figure 1. (A) FTIR spectra of succinylated faba bean starches; (B) Approach to areas of interest in the FTIR spectra of succinylated faba bean starches. HFBS: Hydrolyzed faba bean starch. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch.
Figure 1. (A) FTIR spectra of succinylated faba bean starches; (B) Approach to areas of interest in the FTIR spectra of succinylated faba bean starches. HFBS: Hydrolyzed faba bean starch. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch.
Polysaccharides 06 00081 g001
Polysaccharides 06 00081 g002
Figure 2. Viscosity profiles of succinylated faba bean starches. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch. N-LOK: Commercial succinylated starch.
Figure 2. Viscosity profiles of succinylated faba bean starches. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch. N-LOK: Commercial succinylated starch.
Polysaccharides 06 00081 g002
Polysaccharides 06 00081 g003
Figure 3. (A) WSI and (B) WAI of succinylated faba bean starches. WSI: Water solubility index. WAI: Water absorption index. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch. Different superscript letters in the same figure indicate statistically significant differences (α = 0.05).
Figure 3. (A) WSI and (B) WAI of succinylated faba bean starches. WSI: Water solubility index. WAI: Water absorption index. CFBS: Conventionally modified faba bean starch. MFBS: Microwave-modified faba bean starch. Different superscript letters in the same figure indicate statistically significant differences (α = 0.05).
Polysaccharides 06 00081 g003
Polysaccharides 06 00081 g004
Figure 4. SEM micrographs of microencapsulated LGG. (A) MCLGG1. (B) MCLGG2. (C) MCLGG3. (D) MCLGG4. LGG: Lactobacillus rhamnosus GG. MCLGG: Lactobacillus rhamnosus GG microcapsules using succinylated faba bean starch.
Figure 4. SEM micrographs of microencapsulated LGG. (A) MCLGG1. (B) MCLGG2. (C) MCLGG3. (D) MCLGG4. LGG: Lactobacillus rhamnosus GG. MCLGG: Lactobacillus rhamnosus GG microcapsules using succinylated faba bean starch.
Polysaccharides 06 00081 g004
Polysaccharides 06 00081 g005
Figure 5. LGG thermograms before and after encapsulation. LGG: Lactobacillus rhamnosus GG. MCLGG: Lactobacillus rhamnosus GG microcapsules using succinylated faba bean starch.
Figure 5. LGG thermograms before and after encapsulation. LGG: Lactobacillus rhamnosus GG. MCLGG: Lactobacillus rhamnosus GG microcapsules using succinylated faba bean starch.
Polysaccharides 06 00081 g005
Table 1. Fractional factorial design 23 for the chemical modification of starch by microwave energy.
Table 1. Fractional factorial design 23 for the chemical modification of starch by microwave energy.
SampleStarchPower LevelTime (s)
MFBS1HFBS2230
MFBS2HFBS8230
MFBS3HFBS2260
MFBS4HFBS8260
MFBS5HFBS21030
MFBS6HFBS81030
MFBS7HFBS21060
MFBS8HFBS81060
MFBS: Modified faba bean starch.
Table 2. Degree of substitution, resistant starch, amylose, and reducing sugars.
Table 2. Degree of substitution, resistant starch, amylose, and reducing sugars.
SampleDegree of SubstitutionResistant Starch (%)Amylose (%)Reducing Sugars (%)
CFBS0.020 ± 0.0040 ab11.8 ± 1.42 ab23.3 ± 1.26 c0.05 ± 0.00 b
MFBS10.015 ± 0.0075 abc11.8 ± 0.96 ab38.4 ± 2.89 b0.89 ± 0.23 b
MFBS20.023 ± 0.0005 a9.6 ± 1.13 ab89.1 ± 4.40 a15.43 ± 0.91 a
MFBS30.013 ± 0.0050 abc11.6 ± 1.11 ab37.8 ± 1.92 b1.43 ± 0.39 b
MFBS40.022 ± 0.0017 ab9.6 ± 1.50 b84.3 ± 4.47 a15.11 ± 0.61 a
MFBS50.005 ± 0.0059 c13.3 ± 1.01 a36.9 ± 2.25 b1.07 ± 0.48 b
MFBS60.015 ± 0.0071 abc9.5 ± 1.89 b84.3 ± 4.21 a15.06 ± 0.77 a
MFBS70.003 ± 0.0029 c12.2 ± 1.46 ab31.6 ± 1.87 bc1.25 ± 0.03 b
MFBS80.009 ± 0.0055 bc9.5 ± 0.95 b84.6 ± 4.84 a14.26 ± 0.99 a
CFBS: Conventionally modified faba bean starch. MFBS: Microwave-esterified faba bean starch. Different superscript letters in the same column indicate statistically significant differences (α = 0.05).
Table 3. Yield, efficiency, and aw of spray-dried LGG microcapsules.
Table 3. Yield, efficiency, and aw of spray-dried LGG microcapsules.
Inlet (°C)Outlet (°C)Flow Rate (mL/min)Yield (%)Initial Viable Cells
(log UFC)		Final Viable Cells 1
(log UFC)		EE (%)aw
MCLGG112086 ± 4.0 ab745 ± 2.9 a10.5 ± 0.0 a9.0 ± 0.3 a86 ± 3.7 ab0.19 ± 0.03 a
MCLGG214097 ± 6.9 a751 ± 1.7 a10.5 ± 0.0 a8.5 ± 0.2 a81 ± 1.7 b0.15 ± 0.02 a
MCLGG312084 ± 3.5 b1246 ± 3.7 a10.4 ± 0.1 a9.3 ± 0.2 a90 ± 2.6 a0.20 ± 0.02 a
MCLGG414092 ± 2.5 ab1248 ± 1.2 a10.5 ± 0.0 a8.8 ± 0.1 a84 ± 1.2 ab0.21 ± 0.05 a
MCLGG: Spray-dried LGG microcapsules. EE: Efficiency. Different superscript letters in the same column indicate statistically significant differences (α = 0.05). 1 Total viable cells after spray drying.
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González-Mendoza, M.E.; Martínez-Bustos, F.; Castaño-Tostado, E.; Cortez-Trejo, M.d.C.; Amaya-Llano, S.L. Microwave–Assisted OSA–Faba Bean Starch Production for Probiotic Microencapsulation. Polysaccharides 2025, 6, 81. https://doi.org/10.3390/polysaccharides6030081

AMA Style

González-Mendoza ME, Martínez-Bustos F, Castaño-Tostado E, Cortez-Trejo MdC, Amaya-Llano SL. Microwave–Assisted OSA–Faba Bean Starch Production for Probiotic Microencapsulation. Polysaccharides. 2025; 6(3):81. https://doi.org/10.3390/polysaccharides6030081

Chicago/Turabian Style

González-Mendoza, Mayra Esthela, Fernando Martínez-Bustos, Eduardo Castaño-Tostado, María del Carmen Cortez-Trejo, and Silvia Lorena Amaya-Llano. 2025. "Microwave–Assisted OSA–Faba Bean Starch Production for Probiotic Microencapsulation" Polysaccharides 6, no. 3: 81. https://doi.org/10.3390/polysaccharides6030081

APA Style

González-Mendoza, M. E., Martínez-Bustos, F., Castaño-Tostado, E., Cortez-Trejo, M. d. C., & Amaya-Llano, S. L. (2025). Microwave–Assisted OSA–Faba Bean Starch Production for Probiotic Microencapsulation. Polysaccharides, 6(3), 81. https://doi.org/10.3390/polysaccharides6030081

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