Key structural factors that determine the in vitro enzymatic digestibility of amylose-complexes.

The effects of complexing conditions on the formation of amylose-lipid-protein complexes and relationships between structure and digestion of amylose-lipid and amylose-lipid-protein complexes were poorly understood. The objective of this study was to investigate the effects of complexing time (0, 0.5, 2, 4 and 6 h) and temperature (60, 70, 80, 90 and 100 °C) on the structure and in vitro amylolysis of amylose-lauric acid (AM-LA) and amylose-lauric acid-ß-lactoglobulin (AM-LA-ßLG) complexes, and to understand the relationships between structure and in vitro digestiblity of these complexes. Longer complexing time and higher complexing temperature promoted the formation of greater amounts of the more stable type II crystallites than type I crystallites in both AM-LA and AM-LA-ßLG complexes, which in turn decreased the rate and extent of the complexes digestion to a greater extent. Correlation analyses between parameters for structure and digestion kinetics showed that both the quantity of AM-LA and AM-LA-ßLG complexes and the quality of their arrangement into V-type crystallites influenced their rate and extent of digestion. This study demonstrates that AM-LA and AM-LA-ßLG complexes can be prepared with designed structural and functional properties tailored for various applications.

Simple Method for Preparing Starch Inclusion Complexes with Enhanced Amylolysis Resistance and Antioxidant Properties.

Slow-digesting starch with bioactive functionality has been attracting much interest with the increasing incidence of type-2 diabetes and other diet-related illnesses. The present study demonstrates a simple method for preparing a starch inclusion complex with reduced enzymic digestion and enhanced antioxidant activities using debranched pea starch (PS) and 10-gingerol (10G). Enzymically debranched starch complexed more 10G and formed more structurally ordered starch-10G complexes compared to PS that had not been debranched. Debranching for 6 h resulted in starch with better complexing ability for 10G than starches debranched for longer times. The debranched starch-10G complexes had higher antioxidant activities and a much slower in vitro enzymic digestion profile (rate and hydrolysis extent) than the 10G complex prepared with starch that was not debranched. Our study demonstrates that debranched pea starch-10G complexes with slow-digesting and antioxidant properties are likely to be of interest for developing ingredients for healthier food choices.

Structural Factors That Determine the Amylolytic Properties of Starch-Lipid Complexes.

Structural factors that determine the amylolysis of starch-lipid complexes have remained unclear. Understanding the relationship between the structure and amylolysis of starch-lipid complexes is important for the design and preparation of complexes with predictable digestibility. In this study, the multiscale structures and amylolytic properties of complexes formed under different conditions between debranched high-amylose starch (DHAMS) and lauric, myristic, palmitic, and stearic acids were investigated. Higher complexing temperatures facilitated the formation of DHAMS-fatty acid (FA) complexes, especially the more stable type II crystallites. Longer complexing times also promoted the formation of complexes and the type II crystallites, except for DHAMS-lauric acid (LA). Molecular dynamics simulations showed that the binding free energy for the formation of DHAMS-LA complexes (10 kJ/mol) was lower than those for the other three DHAMS-FA complexes (20-50 kJ/mol), accounting for the lower stability of DHAMS-LA complexes at longer complexing times. The rate and extent of enzymatic digestion of the DHAMS-FA complexes were much lower in comparison to those of gelatinized HAMS. Correlation analyses showed that the rate and extent of enzymic digestion of DHAMS-FA complexes were mainly determined by the degree of crystallite perfection of the complexes.

Novel Type of Slowly Digested Starch Complex with Antioxidant Properties.

With the increasing number of diabetic patients in the world, there is an urgent requirement to reduce the incidence of diabetes. It is considered that a viable prophylactic treatment for type 2 diabetes mellitus is to reduce starch digestibility and oxidative stress. In this study, a novel type of slowly digested starch [pea starch (PS)-gingerol complex] was fabricated to evaluate its in vitro enzymatic digestibility and antioxidant activities. Theoretical and experimental analyses showed that PS can encapsulate gingerols with long alkyl chains to form starch-gingerol complexes, which are further stacked into a mixture of V6- and V7-crystallites. These complexes, in particular the PS-10-gingerol complex, showed high resistance to amylolysis and good antioxidant activities. This study demonstrates that these novel starch-gingerol complexes have the potential to deliver antioxidants encapsulated in starch with slow-digesting properties and reduce oxidative stress. Moreover, this new type of slowly digested starch with antioxidant properties showed great potential in the prevention of type 2 diabetes.

A novel method for quantifying the short-range order in non-crystalline starch by Raman spectroscopy.

A quantitative method was developed to characterize the short-range order in non-crystalline starch by Raman spectroscopy. The Raman spectra of three forms of non-crystalline starches (just-gelatinized starch, which was heated to the point of having just lost its long-range order but still retaining essentially all of its short-range order, gelatinized starch and amorphous starch) were resolved into subspectra to calculate the short-range ordered phases. By deducting the spectra of amorphous starch using a subtraction technique, the areas of subspectra for short-range ordered phases in just-gelatinized and gelatinized starches were obtained. The ratio of the area for short-range ordered phases in gelatinized starch relative to that in just-gelatinized starch was negatively correlated with water content for gelatinization. Based on this, we propose that this ratio of areas provides a quantitative measure for assessing the short-range order in non-crystalline starch. This study provides an alternative and simpler method to an X-ray diffraction protocol proposed previously.

Molecular Mechanisms Underlying the Effects of Small Intestinal Fermentation on Enhancement of Prebiotic Characteristics of Cellulose in the Large Intestine.

Knowledge about the prebiotic characteristics of cellulose by in vitro fermentation is not complete due to the neglect of small intestinal fermentation. This study investigated the effects of small intestinal fermentation on the prebiotic characteristics of cellulose in the large intestine and potential mechanisms through an approach of combined in vivo small intestinal fermentation and in vitro fermentation. The structural similarity between cellulose in feces and after processing by the approach of this study confirmed the validity of the approach employed. Results showed that small intestinal fermentation of cellulose increased both acetate and propionate content and enriched Corynebacterium selectively. Compared to in vitro fermentation after in vitro digestion of cellulose, the in vitro fermentation of cellulose after in vivo small intestinal fermentation produced higher contents of acetate and propionate as well as the abundance of probiotics like Ruminococcaceae_UCG-002, Blautia, and Bifidobaterium. The changes in the structural features of cellulose after in vivo small intestinal fermentation were more obvious than those after in vitro digestion, which may account for the greater production of short-chain fatty acids (SCFAs) and the abundance of probiotics. In summary, small intestinal fermentation enhanced the prebiotic characteristics of cellulose in the large intestine by predisrupting its structure.

The influence of short-range molecular order in gelatinized starch on the formation of starch-lauric acid complexes.

A model system of gelatinized wheat starch (GWS) and lauric acid (LA) was used to examine the effect of residual short-range molecular order in GWS on the formation of starch-lipid complexes. The extent of residual short-range molecular order, as determined by Raman spectroscopy, decreased with increasing water content or heating duration of gelatinization. The enthalpy changes, crystallinity, short-range molecular order and the in vitro enzymic digestion of GWS-LA complexes increased initially to a maximum and then declined as the short-range molecular order in GWS decreased, showing that there was an optimal amount of residual short-range molecular order in GWS for maximizing GWS-LA complexes formation. Below this optimum amount, the limited disruption of short-range molecular order may constrain the mobility of amylose chains for complexation with LA, whereas with excessive disruption above this amount the amylose chains may be too disorganized or entangled to form complexes with LA. The susceptibility of GWS-LA complexes to enzymatic hydrolysis was influenced by both long- and short-range structural order, and to a lesser extent the amounts of complexes. This study showed clearly the role of short-range molecular order in gelatinized starch in influencing the formation of GWS-LA complexes.

The structure and in vitro starch digestibility of wheat starch-glycerol monopalmitin complexes: the effect of heating conditions and water content.

The effects of the heating conditions and water content on the structure and digestibility of wheat starch (WS)-glycerol monopalmitin (GMP) complexes were investigated. The results showed that the higher water content and the heating conditions of 90°C for 60 min after 100°C for 10 min favor the formation of more WS-GMP complexes with the greater short-range order, although the thermal transition temperatures of GWS-GMP-100 complexes are not significantly affected by the water content. Only the type I complexes were formed under the heating conditions of 90°C for 60 min. The heating conditions of 90°C for 60 min after 100°C for 10 min facilitates the formation of type II complexes, and the amounts of type II complexes increased with increasing water content. The digestion rates of WS-GMP complexes decreased slightly with increasing water content, and the extent of starch amylolysis of WS-GMP complexes significantly decreased after heating further at 90°C compared with that only heating at 100°C. The digestibility of complexes is mainly related to structural order rather than the number of complexes. This study is helpful to further understand starch-lipid complexes by showing that heating conditions and water content influence the formation of WS-GMP complexes.

Revisiting the Formation of Starch-Monoglyceride-Protein Complexes: Effects of Octenyl Succinic Anhydride Modification.

Starch-lipid-protein complexes are attracting increasing attention due to their unique structure and low enzymatic digestibility. However, the mechanisms underlying the formation of these ternary complexes, especially those with monoglycerides as the lipid component, remain unclear. In the present study, potato starch or octenyl succinic anhydride (OSA)-modified potato starch (OSAPS), various monoglycerides (MGs), and beta-lactoglobulin (ßLG) were used in model systems to characterize the formation, structure, and in vitro digestibility of the respective ternary complexes. Colorimetry and live/dead staining assays demonstrated that the OSAPS had good biocompatibility. Experimental data and molecular dynamics simulations showed that both unmodified potato starch and OSAPS formed starch-lipid-protein complexes with MGs and ßLG. Of the two types of starch, OSA formed a greater amount of the more stable type II V-crystallites in complexes, which had greater resistance to in vitro enzymic digestion. This study demonstrated for the first time that starch can interact with MGs and ßLG to form ternary complexes and that OSA esterification of starch promoted the formation of more complexes than unmodified starch.

Effects of different sources of proteins on the formation of starch-lipid-protein complexes.

In the present study, the influence of different sources of proteins on the formation of complexes with starch and lipid were investigated. A model system containing wheat starch (WS), palmitic acid (PA) and four proteins (whey protein isolate, egg white protein, soy protein isolate and pea protein isolate) was used to prepare the complexes by Rapid Visco Analyzer. The addition of PA in the pasted WS-protein systems resulted in higher cooling viscosity compared to the pasted WS-PA systems, which was interpreted as being due to the formation of WS-PA-protein complexes. Analyses from differential scanning calorimetry, X-ray diffraction and Raman spectroscopy showed that more complexes were formed in WS-PA-protein systems than in WS-PA systems, especially in the WS-PA-whey protein isolate. The better emulsifying action of whey protein isolate was proposed to be accountable for the greater amounts of complexes formed compared to other three proteins. This study provides important information about the formation of starch-lipid-protein complexes in regard to the selection of proteins for food processing.

Prior interaction of protein and lipid affects the formation of ternary complexes with starch.

The effects of prior interaction between ß-lactoglobulin (ßLG) and lauric acid (LA) on their formation of ternary complexes with wheat starch (WS) was studied. Firstly, the interaction between ßLG and LA after they were heated at different temperatures between 55 and 95 °C was characterized by fluorescence spectroscopy and molecular dynamics simulation. This showed that a greater degree of ßLG-LA interaction occurred after heating at higher temperatures. The WS-LA-ßLG complexes formed subsequently were analyzed by differential scanning calorimetry, X-ray diffraction, Raman and FTIR spectroscopy, which showed that as interaction of ßLG and LA increased there was an inhibitory action on the formation of ternary complex with WS. Hence, we conclude that there is competition in the ternary systems between the protein and starch to interact with the lipid, and that stronger interaction of the protein and lipid may hinder the formation of ternary complexes with starch.

Inhibition of In Vitro Amylolysis of Wheat Starch by Gluten Peptides.

The effect of gluten peptides (GPs) isolated from a gluten proteolysate on in vitro amylolysis of gelatinized wheat starch was investigated. GPs in a pepsin hydrolysate were fractionated into fractions with molecular weights (MWs) of 500-3000, 3500-7000, 10-17, and 35-48 kDa. The fractions containing peptides with MW > 10 kDa had a strong inhibitory effect on enzyme activity and amylolysis of starch, whereas GPs with MW <10 kDa had no inhibitory effect. Binding constants estimated by surface plasmon resonance showed that peptides in the fractions with MW > 10 kDa bound more strongly to α-amylase, in contrast to peptides of MW <10 kDa. Significant correlations were observed between digestion parameters and equilibrium binding affinity. We conclude that peptides with MW >10 kDa in a pepsin digest of gluten have a strong inhibitory effect on in vitro enzymatic hydrolysis of starch due to their strong binding affinity to α-amylase.

Novel Approach for Quantitative Characterization of Short-Range Molecular Order in Gelatinized Starch by X-ray Diffraction.

A novel quantitative method was developed to characterize short-range molecular order in gelatinized wheat and potato starches using X-ray diffraction (XRD). Gelatinized starches with different amounts of short-range molecular order and amorphous starches with no short-range molecular order were prepared and characterized by the intensity and area of Raman spectral bands. The degree of short-range molecular order in the gelatinized wheat and potato starches decreased with increasing water content used for gelatinization. By comparing XRD patterns of gelatinized and amorphous starch, the XRD peak at 33° (2θ) was shown to be typical of gelatinized starch. The relative peak area (RPA), intensity, and full width at half-maximum (FWHM) of the XRD peak at 33° (2θ) decreased with the increase in water content for gelatinization. We propose that the RPA of the XRD peak at 33° (2θ) can be used to quantify the amount of short-range molecular order in gelatinized starch. The method developed in this study will help to explore and understand the relationship between the structure and functionality of gelatinized starch in food and nonfood applications.

Methods for characterizing the structure of starch in relation to its applications: a comprehensive review.

Starch is a major part of the human diet and an important material for industrial utilization. The structure of starch granules is the subject of intensive research because it determines functionality, and hence suitability for specific applications. Starch granules are made up of a hierarchy of complex structural elements, from lamellae and amorphous regions to blocklets, growth rings and granules, which increase in scale from nanometers to microns. The complexity of these native structures changes with the processing of starch-rich ingredients into foods and other products. This review aims to provide a comprehensive review of analytical methods developed to characterize structure of starch granules, and their applications in analyzing the changes in starch structure as a result of processing, with particular consideration of the poorly understood short-range ordered structures in amorphous regions of granules.

Mechanisms Underlying the Formation of Amylose- Lauric Acid-ß-Lactoglobulin Complexes: Experimental and Molecular Dynamics Studies.

The aim of the present study was to reveal the mechanisms underlying the formation of ternary complexes with a model system of amylose (AM), lauric acid (LA), and ß-lactoglobulin (ßLG) using experimental studies and molecular dynamics (MD) simulations. Experimental analyses showed that hydrophobic interactions and hydrogen bonds contributed more than electrostatic forces to the formation of the AM-LA-ßLG complex. MD simulations indicated that interactions between AM and ßLG through electrostatic forces and hydrogen bonds, and to a less extent van der Waals forces, and interactions between AM and LA through van der Waals forces, were mostly responsible for complex formation. The combination of experimental results and MD simulations has provided new mechanistic insights and led us to conclude that hydrophobic interactions, van der Waals forces between AM and LA, and van der Waals forces and hydrogen bonds between AM and ßLG were the main driving forces for the formation of the AM-LA-ßLG complex.

Effect of Debranching and Differential Ethanol Precipitation on the Formation and Fermentation Properties of Maize Starch-Lipid Complexes.

The objective of this study was to investigate the effect of starch debranching followed by differential ethanol precipitation on the formation and in vitro fermentation of starch-lipid complexes. Three groups of linear glucan chains, with a degree of polymerization (DP) of 383∼2950, 37∼75, and 3∼8, were obtained after debranched maize starch (DMS) was fractionated by differential ethanol precipitation. The glucan fraction with DP 383∼2950 formed only type IIb complexes with lauric acid (LA), whereas the fraction with DP 37∼75 formed predominantly type Ia complexes. The glucan faction with DP 8∼32 did not form V-complexes with LA. In vitro fermentation of the type IIb complexes with human fecal samples promoted the proliferation of butyrate-producing bacteria Megamonas, Blautia, and Megasphaera and resulted in a larger amount of butyrate and total short-chain fatty acids being produced than in similar fermentations of the maize starch-LA complex, DMS-LA complex, and fructo-oligosaccharides. This study showed that starch-lipid complexes with a more stable type IIb crystallite resulted in a greater production of butyrate.

Green synthesis of acetylated maize starch in different imidazolium carboxylate and choline carboxylate ionic liquids.

This work demonstrates that acetylated maize starches (AMS) with varied degree of substitution (DS, 0.26-2.63) was synthesized in ionic liquids (ILs) (imidazolium chloride, imidazolium carboxylate and choline carboxylate) at 85 °C without catalyst. The DS of AMS and reaction efficiency increased with decreasing alkyl chain length of cations or anions, while decreased as the choline cation replaced the imidazolium cation and the chloride anion replaced the acetate anion. The AMS synthesized in imidazolium-based ILs exhibited much higher hydrophobicity and thermal stability than the native starch. Rheological properties of ILs and ATR-FTIR analysis of acetic anhydride/ILs mixtures indicated that a shorter alkyl side chain or the combination of an imidazolium cation and an acetate anion gave ILs lower viscosities and weaker interactions between acetic anhydride molecules, which favored the acetylation of starch. These findings provide insights into the design of green processes to modify starch and the application of acetylated starch.

Octenyl Succinate Modification of Starch Enhances the Formation of Starch-Lipid Complexes.

The present study investigated the effect of octenyl succinic anhydride (OSA) modification of starch on the formation of starch-lipid complexes. The complexing index (CI) showed that native maize starch (NMS) formed more complexes with monopalmityl glycerol (MPG) than with palmitic acid (PA), whereas dipalmityl glycerol (DPG) was not effective in forming complexes with NMS. After OSA modification, the complexation between OSA-starch and lipids was greatly enhanced, especially for PA and DPG, and the CI values increased from 79.6 to 93.3% for OSA-starch-PA and from 80.3 to 93.2% for OSA-starch-DPG complexes with increasing DS of OSA-starch. Structural analyses showed that OSA-starch-lipid complexes had higher degrees of long- and short-range molecular orders than the corresponding NMS-lipid complexes. This study showed for the first time that DPG can form complexes with OSA-starch, which was attributed to the increased dispersion of DPG in water by the emulsifying ability of OSA-starch. The finding is of great significance for a better understanding of the formation of starch-lipid complexes.

Dissolution of Cellulose in Ionic Liquid-DMSO Mixtures: Roles of DMSO/IL Ratio and the Cation Alkyl Chain Length.

The dissolution behavior of cellulose in the mixtures of dimethyl sulfoxide (DMSO) and different ionic liquids (ILs) at 25 °C was studied. High solubility of cellulose was reached in the mixtures of ILs and DMSO at mole fractions of 1:2, 1:2, and 1:1 for 1-butyl-3-methylimidazolium acetate, 1-propyl-3-methylimidazolium acetate, and 1-ethyl-3-methylimidazolium acetate, respectively. At high DMSO/IL molar ratios (10:1-2:1), a longer alkyl chain of the IL cation led to higher cellulose solubility. However, shorter cation alkyl chains favored cellulose dissolution at 1:1. Rheological, Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) measurements were used to understand cellulose dissolution. It was found out that the increase of the DMSO ratio in binary mixtures caused higher cellulose solubility by decreasing the viscosity of systems. For cations with longer alkyl chains, stronger interaction between the IL and cellulose and higher viscosity of DMSO/IL mixtures were observed. The new knowledge obtained here could be useful to the development of cost-effective solvent systems for biopolymers.

Mechanisms Underlying the Effect of Tea Extracts on In Vitro Digestion of Wheat Starch.

The effect of extracts from four types of tea made from Camelia sinensis (green, white, black, and oolong) on in vitro amylolysis of gelatinized starch and the underlying mechanisms were studied. Of the four extracts, black tea extract (BTE) gave the strongest inhibition of starch digestion and on α-amylase activity. Fluorescence quenching and surface plasmon resonance (SPR) showed compounds in BTE bound to α-amylase more strongly than those in the green, white, and oolong tea extracts. Individual testing of five phenolic compounds abundant in tea extracts showed that theaflavins had a greater inhibitory effect than catechins on α-amylase. SPR showed that theaflavins had much lower equilibrium dissociation constants and therefore bound more tightly to α-amylase than catechins. We conclude that BTE had a stronger inhibitory effect on in vitro enzymatic starch digestion than the other tea extracts, mainly due to the higher content of theaflavins causing stronger inhibition of α-amylase.