This is a review on resistant starch (RS), resistant dextrin (RD), and polydextrose (PDX), focusing on their similarities and differences. RS refers to the starch (or a portion of) that cannot be digested in the small intestine, but can be partially fermented in the colon. The enzyme resistance of RS is mainly due to either its crystalline/granular structure or its interaction with other components. RD is produced by pyrodextrinization of starch, while PDX is produced by polycondensation of glucose and sorbitol. Both RD and PDX contain glycosidic linkages that are not digestible by the enzymes in the small intestine. RS is not soluble in water, whereas RD and PDX are soluble, mainly due to their molecular structures and other structural features. The major health benefits of RS, RD, and PDX are quite similar, including gut health, prebiotic effects, glycemic control, weight management, and prevention of cardiovascular disease. However, the efficacies can be different among them, for example, the degree and rate of gut fermentation. This review compares the definitions, functional properties, and health benefits of RS, RD, and PDX with the underlying mechanisms, which can be useful for their incorporation in food formulations to improve human health and wellness.

Background and Objective Due to the rapid digestibility, cooked starch can cause a high postprandial blood glucose response (hyperglycemia), one of the risk factors for metabolic diseases, such as obesity and diabetes. The objective was to understand the properties of starch that provided slow digestibility in low-moisture baked goods. Buckwheat (Fagopyrum esculentum Moench) starch was used to prepare biscuits with slowly digestible starch and was compared with wheat (Triticum aestivum) starch. Findings Buckwheat starch had higher gelatinization temperature and smaller breakdown viscosity (in pasting curve) than wheat starch. Slower starch digestion rate and higher amount of undigested starch were observed when 60% (w/w) wheat flour in biscuits was substituted by buckwheat starch than by wheat starch. The biscuits containing buckwheat starch or wheat starch also showed a structure with lower firmness than the control biscuits. Conclusion Buckwheat starch was more resistant to gelatinization and breakage during baking, and thus was less susceptible to enzyme digestion in biscuits than wheat starch. Significance and Novelty This is the first study utilizing a starch having a normal amylose content without any modification, except partial gelatinization during baking, as a source of slowly digestible starch in biscuits. Buckwheat starch not only provided slow digestibility, but also improved the palatability of the biscuits, creating a smoother and less firm texture than those made using whole grain flour.

Low-GI biscuits are commonly produced using whole-grain flour, bran, or soluble dietary fibers, giving an undesirable texture. New low-GI biscuits containing dietary fibers and with improved palatability were formulated by substituting 60% of wheat flour (WF) with a native starch (ST) and 15% of WF with a resistant dextrin (RD), a source of dietary fibers. The botanical source of ST was common buckwheat (Fagopyrum esculentum Moench). Biscuits were also made with a single substitution by ST or by RD at the same level for comparison. The firmness of the biscuits was increased with the single substitution by RD due to its small average molecular size and high hygroscopicity, while it was decreased with the single substitution by ST. The double substitution by ST and RD not only produced the texture with the lowest firmness and brittleness, but also led to the lowest in vitro starch digestion rate and total starch digestibility. The human trial confirmed that the biscuits with the double substitution had a low GI of 47. The results indicated the additive or synergistic effects of ST and RD on the properties of the biscuits, demonstrating that low-GI biscuits can be produced with a substantial dietary fiber content without jeopardizing their palatability.

AbstractDocosahexaenoic acid (DHA) is the predominant omega‐3 long‐chain polyunsaturated fatty acid found in human brain and eyes. There are a number of studies in the literature showing the health benefits of DHA. It is critical throughout all life stages from the need for fetal development, the prevention of preterm birth, and the prevention of cardiovascular disease to the improvements in the cognitive function and the eye health of adults and elderly. These benefits might be related to the modulation of gut microbiota by DHA. In addition, there are some discrepancies in the literature regarding certain health benefits of DHA, and this review is intended to explore and understand these discrepancies. Besides the variations in the DHA contents of different supplement sources, bioavailability is crucial for the efficacy of DHA supplements, which depends on several factors. For example, DHA in phospholipid and triglyceride forms are more readily to be absorbed by the body than that in ethyl ester form. In addition, dietary lipids in meals and emulsification of DHA oil can increase the bioavailability of DHA. Estrogens stimulated the biosynthesis of DHA, whereas testosterone stimulus induced a decrease in DHA. The roles of DHA through human lifespan, the sources, and its recommended daily intake in different countries are also discussed to provide a better understanding of the importance of this review.

In this study, shrimp feed was substituted with a dried alga, Schizochytrium sp., at five levels (0, 10, 20, 40, and 60% of compound feed) to yield protein/energy (P/E) ratios of 22.72, 19.75, 16.71, 13.72 and 10.75 mg protein/KJ, respectively. The effects of this substitution on the specific growth rate (SGR), survival rate, fatty acid composition, digestive enzyme activities and biochemical composition of the sera in postlarval white shrimp (Litopenaeus vannamei) were evaluated. Four replicates, each consisting of 5,000 postlarval shrimp in a single cage, were performed at each substitution level. The postlarval shrimp were randomly distributed to 20 cages, and the duration of the trial was 50 d. The results showed that the best performance was obtained with a diet containing 40% dried Schizochytrium. The survival rate of the 40% trial group was 24% higher than that of the shrimp fed a control diet (p < 0.05). The final body weight gain and SGR peaked at a substitution level of 40% dried Schizochytrium (p < 0.05). The feed conversion ratios (FCRs) of the 20% and 40% trial groups were significantly lower than that of the control group (p < 0.05). The muscle protein and ash contents of the shrimp fed diets containing 20% and 40% dried algae were higher than those of the shrimp fed the control diet (p < 0.05). Although the level of dried Schizochytrium was associated with a decrease in the protease specific activity, an increase in the lipase activity was observed. The serum biochemical composition of the shrimp was significantly affected by the level of dried Schizochytrium in the diet (p < 0.05). In summary, when the feed content of dried Schizochytrium ranged from 20 to 40%, an optimal P/E ratio of 13.72-16.71 mg protein/KJ was achieved. Thus, such supplementation could increase the amount of highly unsaturated fatty acids (HUFAs) and decrease the required level of protein in the production of high-quality feed.

Amylose has a small but significant number of long-chain branches. Two-dimensional size-exclusion chromatography is used to obtain the first measurement of the average number of branches per amylose molecule (from potato tubers) as a function of molecular size. Molecular weight dispersity, average chain length and average amylose molecular weight all increase with increasing size. However, the average number of branches of amylose molecules is weakly, if at all, dependent on size, with 2-4 per molecule except perhaps for the very largest molecules, although for these, the data may suffer from artifacts. Differences in the sizes of amylose molecules is mostly ascribed to variations in chain length. This observation is consistent with the postulate that most branching events occur in the early stage of amylose synthesis, and afterwards the branches are further elongated by granule-bound starch synthases. This gives improved mechanistic understanding of amylose biosynthesis.

Pullulanase is a starch debranching enzyme involved in starch biosynthesis, but its function in starch biosynthesis is not fully established. This study aims to understand its function by analyzing a sorghum variety (SbPUL-RA) with increased pullulanase activity (67% higher than wild-type). The results demonstrate that increased pullulanase activity has little or no effect on crystalline structure or amylose content; however, it increases the total amount of starch, and produces amylose with longer chains. The changed amylose structures results in slightly decreased starch gelatinization temperatures. These results indicate a hitherto unconsidered role for pullulanase during amylose biosynthesis: it removes shorter amylose branches, which further facilitate the elongation of existing amylose chains.

The effects of molecular and crystalline structures on the tensile mechanical properties of thermoplastic starch (TPS) films from waxy, normal, and high-amylose maize were investigated. Starch structural variations were obtained through extrusion and hydrothermal treatment (HTT). The molecular and crystalline structures were characterized using size-exclusion chromatography and X-ray diffractometry, respectively. TPS from high-amylose maize showed higher elongation at break and tensile strength than those from normal maize and waxy maize starches when processed with 40% plasticizer. Within the same amylose content, the mechanical properties were not affected by amylopectin molecular size or the crystallinity of TPS prior to HTT. This lack of correlation between the molecular size, crystallinity and mechanical properties may be due to the dominant effect of the plasticizer on the mechanical properties. Further crystallization of normal maize TPS by HTT increased the tensile strength and Young's modulus, while decreasing the elongation at break. The results suggest that the crystallinity from the remaining ungelatinized starch granules has less significant effect on the mechanical properties than that resulting from starch recrystallization, possibly due to a stronger network from leached-out amylose surrounding the remaining starch granules.

The objective of the present study is to understand the changes in starch structures during digestion and the structures contributing to slow digestion properties. The molecular, crystalline, and granular structures of native waxy maize, normal maize, high-amylose maize, and normal potato starch granules were monitored using SEC, XRD, DSC, and SEM. The amylose and amylopectin molecules of all four starches were hydrolyzed to smaller dextrins, with some having linear molecular structure. Neither the A- nor B-type crystallinity was resistant to enzyme hydrolysis. Starch crystallites with melting temperature above 120°C appeared in waxy and normal maize starches after digestion, suggesting that the linear dextrins retrograded into thermally stable crystalline structure. These crystallites were also observed for high-amylose maize starch before and after digestion, contributing to its low enzyme digestibility. On the contrary, the enzyme-resistant granular structure of native normal potato starch was responsible for its low susceptibility to enzyme hydrolysis.

This study examines the relationships between genetics (single nucleotide polymorphisms (SNPs) in GBSSI and SSIIa genes), starch structure (amylose and amylopectin fine structures), and starch properties (relating to gelatinization). GBSSI and SSIIa SNPs did not alter the starch content of rice grains. GBSSI SNPs can affect the amylose content, but they are incapable of altering the chain-lengths of amylopectin and amylose. The amounts of both long and short amylose branches changed with the same trend as amylose content, and they appeared to affect starch gelatinization properties. SSIIa synthesizes intermediate single-lamella amylopectin chains (DP 16-21), and consequently impacts the gelatinization temperature. Mathematical modelling suggests that the reduction in SSIIa activity significantly increases the activity of SBEII, resulting in a decreased activity ratio of SS to SBE in the enzyme set governing an appropriate chain-length distribution range. This application of the genetics-structure-property paradigm provides selection strategies to produce rice varieties with improved qualities.

Starch granules both isolated from plants and used in foods or other products have typically been dried. Common food laboratory and industry practices include oven (heat), freeze, and ethanol (solvent-exchange) drying. Starch granules isolated from maize (A-type polymorph) and potato (B-type polymorph) were used to understand the effects of different dehydration methods on starch structure and in vitro digestion kinetics. Oven and ethanol drying do not significantly affect the digestion properties of starches compared with their counterparts that have never been dried. However, freeze-drying results in a significant increase in the digestion rate of potato starch but not maize starch. The structural and conformational changes of starch granules after drying were investigated at various length scales using scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction, FTIR spectroscopy, and NMR spectroscopy. Freeze-drying not only disrupts the surface morphology of potato starch granules (B-type polymorph), but also degrades both short- and long-range molecular order of the amylopectin, each of which can cause an increase in the digestion rate. In contrast to A-polymorphic starches, B-polymorphic starches are more disrupted by freeze-drying, with reductions of both short- and long-range molecular order. We propose that the low temperatures involved in freeze-drying compared with oven drying result in greater chain rigidity and lead to structural disorganization during water removal at both nanometer and micrometer length scales in B-type polymorphic starch granules, because of the different distribution of water within crystallites and the lack of pores and channels compared with A-type polymorphic starch granules.

This work describes the first investigation of starch degradation during extrusion occurring at multiple structural levels and explains the effects of the thermal and mechanical energy of extrusion. Investigated samples comprised starches with a range of amylose contents and of glycerol/water plasticizer contents. Structural analysis was performed using size-exclusion chromatography, XRD and light microscopy. The (branch) chain length distribution did not show apparent changes upon either thermal or mechanical energy treatment. Statistical analysis showed that mechanical energy played a dominant role in reducing starch molecular size and degree of starch crystallinity, while thermal energy only partially gelatinized starch granules with negligible effect on molecular size. The rigid crystallites of amylopectin in starch granules are more susceptible to shear degradation than the flexible amorphous amylose. Previous studies did not draw quantitative conclusions as to the relative importance of these two types of energy in extrusion on starch structural degradation. This mechanistic understanding from multi-level characterization is helpful to design the processing of starch-based biopolymers with improved functional properties.

Starches with different amylopectin contents and different molecular sizes prepared using acid hydrolysis were hydrophobically modified using octenylsuccinic anhydride (OSA). The OSA-modified starches were used as surfactants to stabilize emulsions of β-carotene and canola oil dispersed in water. The objective of this study is to investigate the relationship between starch molecular structure and the chemical stability of the emulsified β-carotene, as well as the colloidal stability of emulsion droplets during storage. The oil droplet size in emulsions was smaller when starch had (a) lower hydrodynamic volume (Vh) and (b) higher amylopectin content. The oxidative stability of β-carotene was similar across samples, with higher results at increased amylopectin content but higher Vh. Steric hindrance to coalescence provided by adsorbed OSA-modified starches appears to be improved by more rigid molecules of higher degree of branching.

Two-dimensional (2D) structural distributions based on macromolecular size and branch chain-length are obtained for three maize starches with different amylose contents (one normal and two high-amylose varieties). Data were obtained using an analytical methodology combining chemical fractionation, enzymatic debranching, and offline 2D size-exclusion chromatography with multiple detection. The 2D distributions reveal novel features in the branching structure of high-amylose maize starches. Normal maize starch shows well-resolved structural topologies, corresponding to the amylopectin and amylose macromolecular populations. However, high-amylose maize starches exhibit very complex topologies with significant features between those of amylose and amylopectin, showing the presence of distinct intermediate components. These have the macromolecular size of amylose but similar branching structure to amylopectin, except for a higher proportion of longer branches. These structural features of the intermediate components can be related to a less tightly controlled biosynthesis of the branching structures in high-amylose maize starch mutants, which may prevent these molecules from maturing into full-size amylopectin. This altered macromolecular branched architecture of high-amylose starches probably contribute to their better nutritional properties.

The germination of barley grains is an important step in malt production for beer brewing. This study examines the changes in starch molecular structure in barley grains under optimal conditions for sprouting. Two barley varieties were tested: Schooner and Grimmett, which are low and moderate dormancy grains, with >90 and <5% of grains germinating within two days in sprouting conditions, respectively. The barley grains were germinated in humid conditions after being soaked in excess water for 24 h. The grain weight and starch content of Schooner decreased significantly (P < 0.05) with germination time, whereas those of Grimmett showed no significant changes (P > 0.05). The starch chain-length distributions, analyzed from enzymatically debranched starch molecules with size-exclusion chromatography, indicated that the shorter amylopectin branches of Schooner were degraded at a faster rate than its longer amylopectin branches, which was also confirmed by the decreasing degree of branching with germination time. The changes in starch molecular structure of Grimmett grains were less apparent. The results of this study showed that barley grains containing shorter starch chains can produce sugars more quickly, which indicates that starch structure can serve as one of the specifications when selecting barley grains for brewing.

The effects of variety and growth location on grain composition and starch structures were investigated using three rice (Oryza sativa L.) cultivars (Phka Romduol, Sen Pidao and IR66) with different amylose contents. All the three cultivars were planted in three different agro-climatic zones (Phnom Penh, Coastal and Plateau) of Cambodia. The protein content of polished grains increased when rice was planted at a location with higher average temperature, but their lipid content decreased. The amylose content and degree of branching were not greatly affected by the minor temperature differences among the growing locations. Starch fine structures characterized by the chain-length distribution were significantly different among the cultivars, but not significantly among different locations. The results suggested that protein and lipid biosyntheses were more sensitive to the environmental temperature than that of starch in rice grains.

The molecular structures of amylose and amylopectin have an impact on functional properties of starch-containing food. This is the first study comparing amylose size distributions from various plant sources. Chain-length distributions (CLDs) of amylose and amylopectin branches (“fine structure”) are characterized using size-exclusion chromatography [sometimes termed gel permeation chromatography (GPC)] and parametrized by both biosynthesis-based and empirical fits, to understand the starch biosynthesis mechanism and identify associations with starch digestibility. All starches show bimodal amylose weight CLDs, varying with plant sources, with potato tuber and sweet potato root starch having relatively longer branches than the others. The digestograms of all starches fit first-order kinetics. Unlike what has been seen in cooked grains/flours, amylose and amylopectin fine structures have no association with the digestibility of freshly gelatinized starch. This suggests that the observed effect in cooked grains/flours arises from a secondary interaction between amylose fine structure and higher order structural features.