Advancements in enhancing resistant starch type 3 (RS3) content in starchy food and its impact on gut microbiota: A review

Resistant starch type 3 (RS3), often found in cooked starchy food, has various health benefits due to its indigestible properties and physiological functions such as promoting the abundance of gut beneficial microbial flora and inhibiting the growth of intestinal pathogenic bacteria. However, it is challenging to develop starchy food with high RS3 content. This review aims to provide a detailed overview of current advancements to enhance RS3 content in starchy food and its effects of RS3 on gut microbiota. These approaches include breeding high-amylose cereals through gene editing techniques, processing, enzyme treatments, storage, formation of RS3 nanoparticles, and the incorporation of bioactive compounds. The mechanisms, specific conditions, advantages, and disadvantages associated with each approach and the potential effects of RS3 prepared by different methods on gut microbiota are summarized. In conclusion, this review contains important information that aims to provide guidelines for developing an efficient RS3 preparation process and promote the consumption of RS3-enriched starchy foods to improve overall health outcomes.

Metal ion-mediated modulation of morphology, physicochemical properties, and digestibility of type 3 resistant starch microparticle

Short-chain glucan (SCG) derived from debranched amylopectin has emerged as a promising candidate for the production of resistant starch particle (RSP) due to its controllable self-assembly features. Here, we investigated the effect of metal cations with different valencies and concentrations on the morphology, physicochemical properties, and digestibility of RSP formed by the self-assembly of SCG. The effect of cations on the formation of RSP followed the valency in the following order: Na⁺, Ka⁺, Mg²⁺, Ca²⁺, Fe³⁺, and Al³⁺, of which 10 mM trivalent cations increased the particle size of RSP over 2 μm and considerably decreased the crystallinity by 49.5 % ~ 50.9 %, which were significantly different from that of mono- and divalent ones. Importantly, RSP formed with divalent cations switched the surface charge from -18.6 mV to 12.9 mV, which significantly increased the RS level, indicating that metal cations would be useful for regulating physicochemical properties and digestibility of RSP.

Debranching facilitates malate esterification of waxy maize starch and decreases the digestibility

In this study, the debranching followed by malate esterification was employed to prepare malate debranched waxy maize starch (MA-DBS) with a high degree of substitution (DS) and low digestibility using malate waxy maize starch (MA-WMS) as the control. The optimal esterification conditions were obtained using an orthogonal experiment. Under this condition, the DS of MA-DBS (0.866) was much higher than that of MA-WMS (0.523). A new absorption peak was generated at 1757 cm^-1 in the infrared spectra, indicating the occurrence of malate esterification. Compared with MA-WMS, MA-DBS had more particle aggregation, resulting in an increase in the average particle size from scanning electron microscopy and particle size analysis. The X-ray diffraction results showed that the relative crystallinity decreased after malate esterification, in which the crystalline structure of MA-DBS almost disappeared, which was consistent with the decrease of decomposition temperature by thermogravimetric analysis and the disappearance of the endothermic peak by differential scanning calorimeter. In vitro digestibility tests showed an order: WMS > DBS > MA-WMS > MA-DBS. The MA-DBS showed the highest content of resistant starch (RS) of 95.77 % and the lowest estimated glycemic index of 42.27. In a word, pullulanase debranching could produce more short amylose, promoting malate esterification and improving the DS. The presence of more malate groups inhibited the formation of starch crystals, increased particle aggregation, and enhanced resistance to enzymolysis. The present study provides a novel protocol for producing modified starch with higher RS content, which has potential application in functional foods with a low glycemic index.

Preparation and characterization of debranched starches: Influence of botanical source and debranching time

The influence of botanical source (waxy corn, glutinous rice, tapioca and potato), either based on crystallization or morphology, and the debranching time (6-48 h) on the physicochemical properties of debranched starches (DBSs) were systematically investigated. The divergence of depolymerization among different botanical sources within same hydrolysis time suggested that the debranching treatment was not only depending on the molecular profile and crystalline structure, but also related with the granular size and morphology of native starches. Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) suggested that long-term debranching reaction produced DBSs with improved degree of crystallization and reduced iodine binding capacity. Simulated in-vitro digestion assay showed that the proportion of digestive fractions from different botanical originated DBSs differed greatly. Additionally, prolonging the debranching time yielded increased level of resistant starch. The study may provide guidance for exploring DBSs with various molecular weight to fulfill their tailored applications.

Multiscale structure and precipitation mechanism of debranched starch precipitated by different alcohols

Alcohol solution is a cheap, simple, and effective precipitating solvent frequently used for separating debranched starch (DBS), yet little is known about the precipitation mechanism of DBS by different alcohols. This study precipitated DBS from pullulanase-hydrolyzed starch using ethanol, n-butanol, and isopentanol. The multiscale structures of DBS were characterized, including chain length, single/double helix, and crystalline. The chain conformation and precipitation mechanism of DBS in different alcohols was investigated using molecular dynamics (MD) simulation. DBS precipitated by n-butanol contained the largest proportion of short chain (DP6-24, 83.2 %), the highest V-type crystallinity (21.1 %), and the largest single-helix content (24.7 %). A single helix conformation of DBS chain was determined in alcohols, where alcohol molecules entered the helix cavity. Intra/inter-molecular hydrogen bonds stabilized the helix, with a large number of hydrogen bonds leading to strong molecular interaction and stable helical structure. The solvent accessible surface area of DBS chain decreased by 7.88-19.32 % in alcohols, and the radial distribution function revealed that the first solvent layer of DBS chain at 0.29 nm was closely related to hydrogen bonding. This study provides a basis for the choice of precipitation solvent for preparing DBS with different chain lengths and physicochemical properties.

Reinvention of starch for oral drug delivery system design

Starch is a polysaccharide with varying amylose-to-amylopectin ratios as a function of its biological sources. It is characterized by low shear stress resistance, poor aqueous/organic solubility and gastrointestinal digestibility which limit its ease of processing and functionality display as an oral drug delivery vehicle. Modulation of starch composition through genetic engineering primarily alters amylose-to-amylopectin ratio. Greater molecular properties changes require chemical and enzymatic modifications of starch. Acetylation reduces water solubility and enzymatic digestibility of starch. Carboxymethylation turns starch acid-insoluble and aggregative at low pHs. The summative effects are sustaining drug release in the upper gut. Acid-insoluble carboxymethylated starch can be aminated to provide an ionic character essential for hydrogel formation which further reduces its drug release. Ionic starch can coacervate with oppositely charged starch, non-starch polyelectrolyte or drug into insoluble, controlled-release complexes. Enzymatically debranched and resistant starch has a small molecular size which confers chain aggregation into a helical hydrogel network that traps the drug molecules, protecting them from biodegradation. The modified starch has been used to modulate the intestinal/colon-specific or controlled systemic delivery of oral small molecule drugs and macromolecular therapeutics. This review highlights synthesis aspects of starch and starch derivatives, and their outcomes and challenges of applications in oral drug delivery.

Modulation of the self-assembly kinetics and digestibility of type 3 resistant starch particles by co-crystallization with amino acid

The effect of eight different l-amino acids (L-AA) on type-3 resistant starch particles (rSPs) derived from short chain glucan (SCG) was investigated. The L-AA were categorized based on their charge and polarity. The results reveal that positively charged L-AA, such as lysine and arginine, decreased the nucleation and growth rate of rSPs, while non-charged L-AA have negligible effects. Negatively charged L-AA, such as glutamic acid and aspartic acid, had a significant impact on the morphology and crystallinity of the rSPs, resulting in particle size of around 3 μm and crystallinity of around 35%. This implies that charged L-AA influence the arrangement of SCG double helices in the particles. Furthermore, the complexation of SCG with charged L-AA reduced the level of RS in rSPs, indicating that L-AA could be useful in modulating the physical properties and digestibility of rSPs.

Physicochemical Characterizations, Digestibility, and Lipolysis Inhibitory Effects of Highland Barley Resistant Starches Prepared by Physical and Enzymatic Methods

This study aimed to investigate the differences in the physicochemical and structural characteristics, digestibility, and lipolysis inhibitory potential in vitro of highland barley resistant starches (HBRSs) prepared by autoclaving (HBSA), microwave-assisted autoclaving (HBSM), isoamylase (HBSI) and pullulanase (HBSP) debranching modifications. Results revealed that the resistant starch content of native starch was significantly elevated after modifications. HBSA and HBSM showed distinctly higher swelling power and water-binding capacities along with lower amylose amounts and solubilities than those of HBSI and HBSP (p < 0.05). Fourier transform infrared spectroscopy and X-ray diffraction exhibited that HBSP displayed the highest degree of the ordered crystalline region and crystallinity with a mixture of C_B- and V-type polymorphs. Meanwhile, HBSA and HBSM were characterized by their high degree of the amorphous region with a mixture of B- and V-type polymorphs. Physical and enzymatic modifications resulted in different functionalities of HBRSs, among which HBSP showed the lowest digestibility and HBSM exhibited the highest inhibitory activity on lipolysis due to their structure and structure-based morphology and particle size. This study provided significant insights into the development of native starch from highland barley as an alternative functional food.

Characterization of Cationic Modified Short Linear Glucan and Fabrication of Complex Nanoparticles with Low and High Methoxy Pectin

In this study, we chemically modified the short linear glucan (SLG) using the 3-chloro-2-hydroxypropyl trimethylammonium chloride to introduce a positive surface charge via cationization (CSLG). We then prepared CSLG-based binary nanocomplex particles through electrostatic interactions with low and high methoxyl pectin. The two new types of binary nanocomplex were comprehensively characterized. It was found that the nanocomplex particles showed a spherical shape with the particle size of <700 nm, smooth surface, homogeneous distribution, and negative surface charge. Fourier transform infrared spectroscopy (FTIR) revealed that the driving forces to form nanocomplex were primarily electrostatic interactions and hydrogen bonding. In addition, increasing the CSLG concentration in the nanocomplex significantly enhanced both thermal stability and digestive stability. By comparing the two complex nanoparticles, the HMP-CSLG has a larger particle size and better stability under the GI condition due to the high content of the methoxy group. Additionally, the HMP-CSLG nanoparticle has a higher encapsulation efficiency and slower release rate under simulated gastrointestinal fluid for tangeretin compared with the LMP-CSLG. These results provide new insights into designing the CSLG-based nanocomplex as a potential oral delivery system for nutraceuticals or active ingredients.

Preparation of rutin-loaded microparticles by debranched lentil starch-based wall materials: Structure, morphology and in vitro release behavior

Different treatments of autoclaving, pullulanase debranching and/or ultrasound were applied to prepare debranched lentil starch (DBLS). Their fine structures can affect the retrogradation patterns of DBLSs, which consequently could affect their potential use as delivery carrier of sensitive bioactive compounds. An attempt was made to use these DBLSs as wall materials to encapsulate rutin, aiming to improve the bioaccessibility, meanwhile to enhance the aqueous solubility and stability of rutin molecules. Their encapsulation efficiency, structural characteristics, thermal stability, morphological features, antioxidant activity and in vitro release behavior under simulated upper gastrointestinal tract environment were evaluated. The results suggested that rutin was dispersed in the DBLS polymer matrix, showing the amorphous nature that further authenticates the encapsulation and entrapment of rutin. The structural analyses of microparticles revealed that rutin could interacted with DBLS biopolymer chains by hydrogen bonds, making the starch molecular chains less susceptible to interact with themselves for reordering. The encapsulation efficiency was found to be in an opposite trend with those values obtained for relative crystallinity, melting enthalpy, degree of order/double helices of DBLS wall materials before encapsulation. The release rate results indicated that DBLS carrier with lower M_w, DP_n and higher molecular order was beneficial for the slower release of rutin encapsulated in the microparticles.

Preparation of starch-based drug delivery system through the self-assembly of short chain glucans and control of its release property

Here, we report a starch-based carrier system for the delivery of insoluble bioactive compound via oral route. We utilized the intrinsic characteristics of debranched amylopectins that self-assemble into a spherical microparticle in aqueous environment to encapsulate guest molecules. Upon complexation with β-cyclodextrin, the model bioactive compound, curcumin (CUR), was effectively incorporated into the starch microparticles (SMPs) to form CUR-CD@SMPs during the self-assembly reaction. The stability of encapsulated curcumin against environmental stresses, such as photodegradation and chemical oxidation, was greatly enhanced upon encapsulation. The size of CUR-CD@SMPs could be precisely controlled from 0.3 μm to 2 μm by modulating the rate of debranching reaction. A change of release profiles from concave-downward to sigmoidal form was observed upon increasing the size of CUR-CD@SMPs, suggesting that the release site could be controlled by modulating the crystallinity or size of the carrier microparticles.

Characterization of Cationic Modified Debranched Starch and Formation of Complex Nanoparticles with κ-Carrageenan and Low Methoxyl Pectin

The functional modifications of debranched starch (DBS) has been attracting the interest of researchers. This study marks the first time that DBS was modified by cationization through the use of (3-chloro-2-hydroxypropyl) trimethylammonium chloride with the introduction of cationic functional groups. The physicochemical properties and structural characteristics of cationized debranched starch (CDBS) were systematically assessed. The results demonstrate that the maximum degree of substitution (DS) value obtained was as high as 1.14, and the corresponding CDBS exhibited significantly higher zeta potential values: approximately +35 mV. The minimal inhibitory concentration values of the CDBS of DS 1.14 against Escherichia coli and Staphylococcus aureus were 6 and 8 mg mL^-1, respectively. In addition, nanoparticles were successfully prepared with a combination of CDBS and low methoxyl pectin (LMP) and a combination of CDBS and κ-carrageenan (CRG). The maximum encapsulation efficiency of nanoparticles for (-)-epigallocatechingallate can reach 87.8%.

Investigation of debranching pattern of a thermostable isoamylase and its application for the production of resistant starch

Debranching enzymes contribute to the enzymatic production of resistant starch (RS) by reducing substrate molecular weight and increasing amylose yield. In the present study, the action pattern of a thermostable isoamylase-type debranching enzyme on different types of starch was investigated. The molecular weight distribution, glycosidic bond composition and contents of oligosaccharides released were monitored by various liquid chromatography techniques and nuclear magnetic resonance spectroscopy (NMR). These analyses showed that the isoamylase could specifically and efficiently attack α-1,6-glucosidic linkages at branch points, leaving the amylose favored by other amylolytic enzymes. Its ability to attack side chains composed of 1-3 glucose residues differentiates it from other isoamylases, a property which is also ideal for the RS preparation process. The enzyme was used as an auxiliary enzyme in the hydrolytic stage. The highest RS yield (53.8%) was achieved under the optimized conditions of 70 °C and pH 5.0, using 7 U isoamylase per g starch and 2 NU amylase per g starch. These data also help us better understand the application of isoamylase for preparation of other products from highly branched starch materials.

Preparation and characterization of essential oil-loaded starch nanoparticles formed by short glucan chains

Essential oils (EOs), including menthone, oregano, cinnamon, lavender, and citral, are natural products that have antimicrobial and antioxidant activities. However, extremely low water solubility, and easy degradation by heat, restrict their application. The aim of this work was to evaluate the enhancement in antioxidative and antimicrobial activities of EOs encapsulated in starch nanoparticles (SNPs) prepared by short glucan chains. For the first time, we have successfully fabricated menthone-loaded SNPs (SNPs-M) at different complexation temperatures (30, 60, and 90°C) by an in situ nanoprecipitation method. The SNPs-M displayed spherical shapes, and the particle sizes ranged from 93 to 113nm. The encapsulation efficiency (EE) of SNPs-M increased significantly with an increase in complexation temperature, and the maximum EE was 86.6%. The SNPs-M formed at 90°C had high crystallization and thermal stability. The durations of the antioxidant and antimicrobial activities of EOs was extended by their encapsulation in the SNPs.