Interfacial Catalysis during Amylolytic Degradation of Starch Granules: Current Understanding and Kinetic Approaches

Mechanism analysis for the differences in multi-level structure, enzyme accessibility and pasting properties of starch granules caused by different hydrolysis pathways of maltogenic α-amylase

The effect of pores distribution on the multi-scale structure, enzyme accessibility, and pasting properties of the waxy maize starch granules with the same degree of hydrolysis were examined. Increased maltogenic α-amylase (MA) dosage obviously increased the shallow pores number and the roughness, whereas extended time increased the holes depth. Despite achieving the same hydrolysis degree and specific surface area, samples with numerous shallow holes exhibited a higher mass fractal dimension, a lower, peak viscosity, final viscosity and setback. Besides, increased dosage prompted a sustained decrease in the number of short chains with DP 10-17; whereas prolonging time encouraged the continuous catalyzation in the same chains. Enzymatic probe profiles showed MA was more accessible to the amorphous region on the periphery of starch granules, rather than the inside. This finding provides a more valuable understanding of the catalytic mechanism for MA in heterogeneous systems and an accurate guidance for the industrial production.

Potential of Process-Induced Modification of Potato Starch to Modulate Starch Digestibility and Levels of Resistant Starch Type III

Starch digestibility and the content of resistant starch (RS) play a crucial role in human health, particularly in relation to glycemic responses, insulin sensitivity, fat oxidation, and satiety. This study investigates the impact of processing methods on potato starch digestibility and RS content, focusing on two modification techniques: autoclaving and high hydrostatic pressure (HHP), followed by retrogradation at different temperatures. The research employs a comprehensive approach to characterize structural changes in starch samples using X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and scanning electron microscopy (SEM). In turn, semi-dynamic in vitro digestion experiments based on the INFOGEST protocol were conducted to assess starch digestibility, while RS content was evaluated through enzymatic digestion of the non-RS fraction. SEM, XRD, and FTIR measurements reveal thermal processing appreciably affected starch architectures while HHP had a marginal effect. Further, the FTIR 1045/1022R ratio was found to be correlated with RS content measurements while reducing rapidly digestible starch (RDS). The findings led to the stipulation that thermal processing facilitates amylose leaching and granular disruption. In turn, retrogradation enabled the deposition of the amylose onto the disrupted structures which delineated their subsequent liability to enzymatic digestion. Conversely, HHP had minimal effects on granular architectures and amylose leaching. Overall, this research provides valuable insights for processing starch-based food products with the goal of increasing RS content, which may have significant implications for the food industry and nutritional science.

Metabolic pathways associated with Firmicutes prevalence in the gut of multiple livestock animals and humans

Dynamic interspecific interactions and environmental factors deeply impact the composition of microbiotic communities in the gut. These factors intertwined with the host's genetic background and social habits cooperate synergistically as a hidden force modulating the host's physiological and health determinants, with certain bacterial species being maintained from generation to generation. Firmicutes, one of the dominant bacterial phyla present across vertebrate classes, exhibits a wide range of functional capabilities and colonization strategies. While ecological scenarios involving microbial specialization and metabolic functions have been hypothesized, the specific mechanisms that sustain the persistence of its microbial taxa in a high diversity of hosts remain elusive. This study fills this gap by investigating the Firmicutes metabolic mechanisms contributing to their prevalence and heritability in the host gut on metagenomes-assembled bacterial genomes collected from 351 vertebrate samples, covering 18 food-producing animals and humans, specific breeds and closely-related species. We observed that taxa belonging to Acetivibrionaceae, Clostridiaceae, Lachnospiraceae, Ruminococcaceae, and the not well understood CAG-74 family were evolutionarily shared across all hosts. These prevalent taxa exhibit metabolic pathways significantly correlated with extra-host survival mechanisms, cell adhesion, colonization and host transmission, highlighted by sporulation, glycan biosynthesis, bile acid metabolism, and short-chain fatty acid encoded genes. Our findings provide a deeper understanding of the ecological foundations governing distinct transmission modes, effective colonization establishment, and maintenance of Firmicutes, offering new perspectives on both well-known and poorly characterized species.

Applying the Sabatier Principle to Decipher the Surface-Structure-Dependent Catalysis of Different Starch Granules by Pullulanase

Interfacial enzyme catalysis is widespread in both nature and industry. Granular starch is a sustainable and abundant raw material for which a rigorous correlation of the surface structure with enzymatic degradation is lacking. Here pullulanase-catalyzed debranching of 12 granular starches varying in amylopectin contents and branch chain contents and lengths is shown to present a biphasic relationship characteristic of the Sabatier principle. Introducing normalization of the specific rate (v 0/E 0) by a substrate-dependent constant C, related to the Arrhenius prefactor of k cat, reveals that optimal activity according to the Sabatier principle occurs at moderate substrate binding strength. The density of pullulanase attack sites (kinΓmax), determined using combined conventional and inverse Michaelis-Menten kinetics, was increased by branching enzyme treatment. Medium kinΓmax and branch chain length conferred the highest activity depending on substrate load. Correlation analysis demonstrated that starch granular crystallinity, surface order, and average branch chain length influence the enzymatic degradation by affecting the C constant. Therefore, C should be considered together with the enzyme binding strength to understand the degradation of starch granules. The Sabatier principle could serve as a diagnostic tool to characterize enzyme performance on substrates having different surface structures and guide rational modification of granular starches for specific purposes.

Investigation of the physicochemical factors affecting the in vitro digestion and glycemic indices of indigenous indica rice cultivars

Rice (Oryza sativa) is a vital food crop and staple diet for most of the world's population. Poor dietary choices have had a significant role in the development of type-2 diabetes in the population that relies on rice and rice-starch-based foods. Hence, our study investigated the in vitro digestion and glycemic indices of certain indigenous rice cultivars and the factors influencing these indices. Cooking properties of rice cultivars were estimated. Further, biochemical investgations such as amylose content, resistant starch content were estimated using iodine-blue complex method and megazyme kit respectively. The in vitro glycemic index was estimated using GOPOD method. The rice cultivars considered in our study were classified into low-, intermediate-, and high-amylose rice varieties. The rice cultivars were subjected to physicochemical characterization by using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) techniques. FTIR spectral analysis revealed prominent bands at 3550-3200, 2927-2935, 1628-1650, 1420-1330, and 1300-1000 cm-1, which correspond to -OH groups, C=O, C=C, and C-OH stretches, and H-O-H and -CH bending vibrations, confirming the presence of starch, proteins, and lipids. Additionally, the FTIR ratio R(1047/1022) confirmed the ordered structure of the amylopectin. DSC analysis revealed variations in the gelatinization parameters, which signifies variations in the fine amylopectin structures and the degree of branching inside the starch granules. The percentage of resistant starch (RS) ranged from 0.50-2.6%. The swelling power (SP) of the rice flour ranged between 4.1 and 24.85 g/g. Furthermore, most of the rice cultivars are classified as having a high glycemic index (GI) based on the estimated in vitro GI (eGI), which varies from 73.74-90.88. The cooking properties of these materials were also investigated. Because the amylose content is one of the key factors for determining the cooking, eating, and digestibility properties of rice, we investigated the relationships between the amylose content and other biochemical characteristics of rice cultivars. The SP and GI were negatively correlated with the amylose content, whereas the RS had a positive relationship. The findings of our study can be beneficial in illustrating the nutritional profile and factors affecting the digestibility of traditional rice cultivars which will promote their consumption, cultivation, and contributes to future food security.

Are cellulases slow? Kinetic and thermodynamic limitations for enzymatic breakdown of cellulose

Cellulases are of paramount interest for upcoming biorefineries that utilize residue from agriculture and forestry to produce sustainable fuels and chemicals. Specifically, cellulases are used for the conversion of recalcitrant plant biomass to fermentable sugars in a so-called saccharification process. The vast literature on enzymatic saccharification frequently refers to low catalytic rates of cellulases as a main bottleneck for industrial implementation, but such statements are rarely supported by kinetic or thermodynamic considerations. In this perspective, we first discuss activation barriers and equilibrium conditions for the hydrolysis of cellulose and how these parameters influence enzymatic turnover. Next, we propose a simple framework for kinetic description of cellulolytic enzyme reactions and show how this can pave the way for comparative biochemical analyses of cellulases acting on their native, insoluble substrate. This latter analysis emphasizes that cellulases are characterized by extraordinarily low off-rate constants, while other kinetic parameters including specificity constants and rate constants for association and bond cleavage are quite like parameters reported for related enzymes acting on soluble substrates.

Comparative analysis of granular starch hydrolysis and multi-structural changes by diverse α-amylases sources: Insights from waxy rice starch

Three cultivars of waxy rice starch with different multi-scale structures were subjected to α-amylase hydrolysis to determine amylopectin fine structure, production of oligosaccharides, morphology, and crystallinity of the partially hydrolyzed starch granules. α-amylases hydrolyzed the amylopectin B2 chain during the initial stage of hydrolysis, suggesting that it is primarily located in the outer shell of the granules. For waxy rice starch with loose structure, α-amylases attacked the crystalline and amorphous regions simultaneously in the initial stage, while for starch granules with compact structure, the outer shell blocklet (crystalline structure) can be a hurdle for α-amylases to proceed to hydrolysis of the internal granule structure. The ability of α-amylases from porcine pancreatic α-amylases to attack the outer shell crystalline structure was lower than that of α-amylases from Bacillus amyloliquefaciens and Aspergillus oryzae. These results show that α-amylase source and rice cultivar combinations can be used to generate diverse structures in degraded waxy rice starch.

Unravelling carbohydrate binding module 21 (CBM21) dynamics of interaction with amylose

The carbohydrate binding module 21 (CBM21) from Rhizopus oryzae is a dual-site CBM proposed to disrupt polysaccharide structures. Additionally, it serves as a purification tag in industry. CBM21 crystal structure features a Glc residue in an unusual 1S3 conformation, whose relevance for the CBM mechanism of action is unclear. In this context, we seek to contribute for the understanding of CBM21 mechanism of action by: i) investigating the role of the 1S3 conformation on carbohydrate recognition, and ii) characterize the protein-carbohydrate binding dynamics using molecular dynamics and metadynamics simulations at MM and QM/MM levels. Results indicate the 1S3 Glc conformation is unlikely to occur under biological conditions, being originated from the crystallographic environment. CBM21 binding to small ligands appears transient and unstable, while protein dimerization and polysaccharide chain size influence complex stability. In interactions with amylose, CBM21 exhibits a repeated unbinding followed by re-binding, while simultaneously alternating between binding sites I and II. These results suggest that CBM21 acts through transient interactions, directing carbohydrates to the catalytic center rather than forming strong and long-lasting bonds with carbohydrates. Accordingly, we expect such atomistic depiction of CBM21 mechanism could aid in CBM design targeting biotechnological applications.

Functional Roles of N-Terminal Domains in Pullulanase from Human Gut Lactobacillus acidophilus

Pullulanases are multidomain α-glucan debranching enzymes with one or more N-terminal domains (NTDs) including carbohydrate-binding modules (CBMs) and domains of unknown function (DUFs). To elucidate the roles of NTDs in Lactobacillus acidophilus NCFM pullulanase (LaPul), two truncated variants, Δ41-LaPul (lacking CBM41) and Δ(41+DUFs)-LaPul (lacking CBM41 and two DUFs), were produced recombinantly. LaPul recognized 1.3- and 2.2-fold more enzyme attack-sites on starch granules compared to Δ41-LaPul and Δ(41+DUFs)-LaPul, respectively, as measured by interfacial kinetics. Δ41-LaPul displayed markedly lower affinity for starch granules and β-cyclodextrin (10- and >21-fold, respectively) in comparison to LaPul, showing substrate binding mainly stems from CBM41. Δ(41+DUFs)-LaPul exhibited a 12 °C lower melting temperature than LaPul and Δ41-LaPul, indicating that the DUFs are critical for LaPul stability. Notably, Δ41-LaPul exhibited a 14-fold higher turnover number (kcat) and 9-fold higher Michaelis constant (KM) compared to LaPul, while Δ(41+DUFs)-LaPul's values were close to those of LaPul, possibly due to the exposure of aromatic by truncation.