Starch granule size: Does it matter?

Nature has developed starch granules varying in size from less than 1 µm to more than 100 µm. The granule size is an important factor affecting the functional properties and the applicability of starch for food and non-food applications. Within the same botanical species, the range of starch granule size can be up to sevenfold. This review critically evaluated the biological and environmental factors affecting the size of starch granules, the methods for the separation of starch granules and the measurement of size distribution. Further, the structure at different length scales and properties of starch-based on the granule size is elucidated by specifying the typical applications of granules with varying sizes. An amylopectin cluster model showing the arrangement of amylopectin from inside toward the granule surface is proposed with the hypothesis that the steric hindrance for the growth of lamellar structure may limit the size of starch granules.

Mashing performance as a function of malt particle size in beer production.

Significant innovations have occurred over the past 50 years in the malting and brewing industries, focused on optimization of the beer mashing, boiling and fermentation processes. One of the challenges faced in beer brewing has been in the malting process to obtain the desired malt and wort quality to produce high-quality beer products. The hydrolytic enzymes produced during grain germination are mostly entrapped inside the cellular matrices of the grain. The intra-grain diffusion of enzymes for in-situ hydrolysis, as well as diffusion of enzymes to wort, depends upon the malt size and malt size fractions obtained after milling. This review investigates the relationship between varying barley grain particle size distribution and the efficiency of the malting and mashing processes. Recommended ideal particle size of barley grain before and after milling are proposed based on the review of existing literature. Each brewing batch of grains with a proportion of >80% plump grains (>2.5 mm in size) is suggested to be the optimal size before milling, whereas the optimum grain particle size after milling ranged between 0.25 and 0.5 mm. The current review will summarize the theoretical aspects for malt milling and the particle size characteristics for optimizing the brewing process.

Enhancing enzymatic resistance of starch through strategic application of food physical processing technologies.

The demand for clean-label starch, perceived as environmentally friendly in terms of production and less hazardous to health, has driven the advancement of food physical processing technologies aimed at modifying starch. One of the key objectives of these modifications has been to reduce the glycaemic potency and increase resistant starch content of starch, as these properties have the potential to positively impact metabolic health. This review provides a comprehensive overview of recent updates in typical physical processing techniques, including annealing, heat-moisture, microwave and ultrasonication, and a brief discussion of several promising recent-developed methods. The focus is on evaluating the molecular, supramolecular and microstructural changes resulting from these modifications and identifying targeted structures that can foster enzyme-digestion resistance in native starch and its forms relevant to food applications. After a comprehensive search and assessment, the current physical modifications have not consistently improved starch enzymatic resistance. The opportunities for enhancing the effectiveness of modifications lie in (1) identifying modification conditions that avoid the intensive disruption of the granular and supramolecular structure of starch and (2) exploring novel strategies that incorporate multi-type modifications.

Complexation of starch and phenolic compounds during food processing and impacts on the release of phenolic compounds.

Phenolic compounds can form complexes with starch during food processing, which can modulate the release of phenolic compounds in the gastrointestinal tract and regulate the bioaccessibility of phenolic compounds. The starch-phenolic complexation is determined by the structure of starch, phenolic compounds, and the food processing conditions. In this review, the complexation between starch and phenolic compounds during (hydro)thermal and nonthermal processing is reviewed. A hypothesis on the complexation kinetics is developed to elucidate the mechanism of complexation between starch and phenolic compounds considering the reaction time and the processing conditions. The subsequent effects of complexation on the physicochemical properties of starch, including gelatinization, retrogradation, and digestion, are critically articulated. Further, the release of phenolic substances and the bioaccessibility of different types of starch-phenolics complexes are discussed. The review emphasizes that the processing-induced structural changes of starch are the major determinant modulating the extent and manner of complexation with phenolic compounds. The controlled release of complexes formed between phenolic compounds and starch in the digestive tracts can modify the functionality of starch-based foods and, thus, can be used for both the modulation of glycemic response and the targeted delivery of phenolic compounds.

Camel milk-derived probiotic strains encapsulated in camel casein and gelatin complex microcapsules: Stability against thermal challenge and simulated gastrointestinal digestion conditions.

Probiotics have received increased attention due to their nutritional and health-promoting benefits. However, their viability is often impeded during food processing as well as during their gastrointestinal transit before reaching the colon. In this study, probiotic strains Lactobacillus rhamnosus MF00960, Pediococcus pentosaceus MF000967, and Lactobacillus paracasei DSM20258 were encapsulated within sodium alginate, camel casein (CC), camel skin gelatin (CSG) and CC:CSG (1:1 wt/wt) wall materials. All 3 strains in encapsulated form showed an enhanced survival rate upon simulated gastrointestinal digestion compared with free cells. Among the encapsulating matrices, probiotics embedded in CC showed higher viability and is attributed to less porous structure of CC that provided more protection to entrapped probiotics cells. Similarly, thermal tolerance at 50°C and 70°C of all 3 probiotic strains were significantly higher upon encapsulation in CC and CC:CSG. Scanning electron microscope micrographs showed probiotic strains embedded in the dense protein matrix of CC and CSG. Fourier-transform infrared spectroscopy showed that CC- and CSG-encapsulated probiotic strains exhibited the amide bands with varying intensity with no significant change in the structural conformation. Probiotic strains encapsulated in CC and CC:CSG showed higher retention of inhibitory properties against α-glucosidase, α-amylase, dipeptidyl peptidase-IV, pancreatic lipase, and cholesteryl esterase compared with free cells upon exposure to simulated gastrointestinal digestion conditions. Therefore, CC alone or in combination with CSG as wall materials provided effective protection to cells, retained their bioactive properties, which was comparable to sodium alginate as wall materials. Thus, CC and CC:CSG can be an efficient wall material for encapsulation of probiotics for food applications.

Intact cells: "Nutritional capsules" in plant foods.

Macronutrients of pulses or cereals are stored in the cotyledon or endosperm cells with protection from intact cell walls. However, pulses and cereals are generally processed into fine particles during food production. For example, after milling, the macronutrients enclosed in the intact cells are released and are easily accessible to digestive enzymes in the gastrointestinal tract, leading to high metabolic responses. Therefore, studies on the health effects of intact cells and developing an alternative ingredient with a higher proportion of intact cells are areas of emerging interest. In this review, we highlighted the smallest unit of whole grain, an individual cell, as "nutritional capsules" and elucidated the structure-function of the nutritional capsules, followed by isolation techniques, as a potential novel functional ingredient and food. The polysaccharides' monomeric composition, secondary structure, and interactions determine the cell wall properties including the cell detachment during isolation and isolated cell properties. The intact cellular structure is retained after mild food processing and digestion, thereby, contributing to a lower extent/rate of digestion of entrapped macronutrients. Furthermore, the excursed intact capsules in the colonic environment modulate the population and diversity of microbiota, favouring the increased production of the short-chain fatty acids (SCFAs). The structural schematic model of Type-I and Type-II cells is developed together with the schematics of the cell wall isolation process. The review provides a critical summary of the recent trends in intact plant cells as a functional-nutritional food. It paves the way for the industrial production of intact cells as a novel food ingredient.

High-Amylose Starches to Bridge the "Fiber Gap": Development, Structure, and Nutritional Functionality.

Although high-amylose starches are not a recent innovation, their popularity in recent years has been increasing due to their unique functional properties and enhanced nutritional values in food applications. While high-amylose maize, barley, and potato are commercially available, high-amylose variants of other main crops such as wheat and rice have once been developed more recently and will be available commercially in the near future. This review summarizes the development, structure, and nutritional functionality of high-amylose starches developed and reported so far. The range of biotechnological strategies utilized are reviewed, as are the consequent effects on structural properties at different length scales, as well as sensory aspects of foods containing high-amylose starch (HAS). This review identifies the molecular and microstructural features contributing to digestive enzyme resistance not only in native HAS but also in forms of relevance to food processing. During heat treatment, HAS tends to retain or form dense molecular structures that resist amylase degradation through the retention of the granular structure as well as helices (type-2 resistant starch [RS]), reassociation of glucan chains (type-3 RS), and formation of lipid-amylose complexes (type-5 RS). The review also identifies opportunities for food manufacturers and consumers to incorporate HAS in food products and diets for better nutritional outcomes.

Mechanisms of starch digestion by α-amylase-Structural basis for kinetic properties.

Recent studies of the mechanisms determining the rate and extent of starch digestion by α-amylase are reviewed in the light of current widely-used classifications for (a) the proportions of rapidly-digestible (RDS), slowly-digestible (SDS), and resistant starch (RS) based on in vitro digestibility, and (b) the types of resistant starch (RS 1,2,3,4…) based on physical and/or chemical form. Based on methodological advances and new mechanistic insights, it is proposed that both classification systems should be modified. Kinetic analysis of digestion profiles provides a robust set of parameters that should replace the classification of starch as a combination of RDS, SDS, and RS from a single enzyme digestion experiment. This should involve determination of the minimum number of kinetic processes needed to describe the full digestion profile, together with the proportion of starch involved in each process, and the kinetic properties of each process. The current classification of resistant starch types as RS1,2,3,4 should be replaced by one which recognizes the essential kinetic nature of RS (enzyme digestion rate vs. small intestinal passage rate), and that there are two fundamental origins for resistance based on (i) rate-determining access/binding of enzyme to substrate and (ii) rate-determining conversion of substrate to product once bound.

Multilevel Structure of Wheat Starch and Its Relationship to Noodle Eating Qualities.

Although the processing and eating qualities of noodles are largely related to the quality and quantity of wheat protein (gluten), the importance of starch, a major ingredient of wheat flour, is often overlooked. Recent developments on the multilevel structural model of starch have brought new insights into the role of starch for better processing and noodle eating qualities. With critical analysis and discussion, this review outlines the comprehensive relationships between the multilevel (molecular, crystalline, and granular) starch structure, noodle eating qualities, and related physicochemical properties. Further, the major and minor structural features of wheat starch and their contributions toward noodle quality are summarized and presented as a schematic diagram, which shows the effects of starch structure on cooked noodles. These features provide new insights for the scientific community, as well as industry, into the role of starch, along with gluten, on the quality of noodles.

Flaking of millets and its impact on bioactivity, pasting, digestibility, structural and thermal properties.

Five different millets (foxtail, little, barnyard, kodo and browntop) with and without sprouting were subjected to flaking. Phytic acid and phenolic content tends to decrease significantly, whereas antioxidant activity increased up to 77.32% on flaking of millets. A significant decrease in peak and final viscosity was observed in millet flakes. A-type diffraction pattern was predominant for unsprouted millets whereas the flaked millets showed V-type crystallinity. The protein digestibility significantly increased up to 37.77% in flakes made from sprouted millets. The mineral bioavailability upon flaking of millets increased, especially Ca (88.22% for little), Fe (43.04% for barnyard) and Zn (61.77% for kodo), which is attributed to the reduction in phytic acid. Flaking, however, led to an increase in rapidly and slowly digestible starch with a corresponding decrease in resistant starch. Among the unsprouted and sprouted millet flakes, foxtail received the highest sensory scores for overall acceptability.

Sonication-mediated modulation of macronutrient structure and digestibility in chickpea.

Ultrasound processing is an emerging green technology that has the potential for wider application in the food processing industry. While the effects of ultrasonication on isolated macromolecules such as protein and starch have been reported, the effects of physical barriers on sonication on these macro-molecules, for example inside whole seed, tissue or cotyledon cells, have mostly been overlooked. Intact chickpea cells were subjected to sonication with different ultrasound processing times, and the effects of sonication on the starch and protein structure and digestibility were studied. The digestibility of these macronutrients significantly increased with the extension of processing time, which, however was not due to the molecular degradation of starch or protein but related to damage to cell wall macro-structure with increasing sonication time, leading to enhanced enzyme accessibility. Through this study, it is demonstrated that ultrasound processing has least effect on whole food structure, for example, whole seeds but can modulate the nutrient bioavailability without changing the properties of the macronutrients in seed fractions e.g. intact cells, offering new scientific knowledge on effect of ultrasound in whole foods at various length scales.

Leaching of Phytochemicals from Beans during Hydration, Kinetics, and Modeling.

In the current era, there is a growing emphasis on the circular economy and the valorization of waste products. Bean processing industries generate substantial nutrient-rich waste laden with valuable phytochemicals. Understanding the leaching patterns and kinetics of major phytochemicals is key to designing better processes leading to increased sustainability. This review investigates phytochemical leaching mechanisms and kinetic modeling methods. Firstly we lay the foundation with a broad theoretical framework, and later deal with kinetic modeling approaches and promising areas for future research. Currently, the composition of industrial-scale bean wastewater remains undocumented in the open literature. Nonetheless, drawing from existing studies and general bean composition knowledge, we proposed a multi-phase leaching process. We hypothesize three distinct phases: initial leaching of phytochemicals from the outer seed coat, followed by a second phase involving polysaccharides, and concluding with a third phase wherein phenolic acids within the cotyledons leach into the hydration water. This review aims to shed light on the complex process of phytochemical leaching from common beans during hydration. By combining theoretical insights and practical modeling strategies, this work seeks to enhance our understanding of this phenomenon and ultimately contribute to the optimization of food processing methods with reduced environmental impact.

Gallic acid forms V-amylose complex structure with starch through hydrophobic interaction.

This study aimed to investigate the role of amylose and amylopectin in the formation of starch-polyphenol complex and elucidate the interaction mechanisms. Gallic acid (GA) was used to complex with maize starch with various amylose contents. Results showed GA formed V-type crystals with normal maize starch (NMS) and high amylose maize starch (HAMS), while higher relative crystallinity was exhibited in HAMS-GA complexes than NMS counterparts. Molecular structure analysis revealed more amylose in GA-starch complexes than in treated starch counterparts without GA, and this was more apparent in HAMS than NMS, implying amylose is preferred to complex with GA than amylopectin. FTIR detected higher R1047/1022 value in starch-GA complexes than their starch counterparts without GA, suggesting increased short-range ordered structrure of complexes. Typical signatures of hydrophobic interactions were further revealed by isothermal titration calorimetry, indicating the complexation of GA to starch is mainly through hydrophobic bonds. More binding sites were observed for HAMS (72.50) than NMS (11.33), which proves the preferences of amylose to bind with GA. Molecular dynamics simulated the complexation of GA to amylose, and confirmed hydrophobic bond is the main interaction force. These findings would provide guidance for precise design and utilization of starch-polyphenol complexes in functional foods.

Structural changes and degradation mechanism of type 3 resistant starch during in vitro fecal fermentation.

The colonic fermentation metabolites of resistant starch (RS) are recognized to have various health benefits. However, the relationship between the structural variation of RS and the colonic fermentation properties, remains inadequately studied, especially for type 3 resistant starch. The in vitro fecal fermentation properties with multi-structure evolution of A- and B-type polymorphic resistant starch spherulites (RSS) were investigated. Both polymorphic types of RSS showed similar fermentation rate and total short-chain fatty acid profiles, while the butyrate concentration of the A-type RSS subjected to 24 h of fermentation was significantly higher compared to B-type RSS. In the case of recrystallized starch spherulites, irrespective of the polymorphic type, gut bacteria preferentially degraded the intermediate chains and crystalline regions, as the local molecule-ordered area potentially serves as suitable attachment sites or surfaces for microbial enzymes.

Synergistic and antagonistic effects of α-Amylase and amyloglucosidase on starch digestion.

The influence of biomacromolecular physical structure on the kinetics of degradation with exo-acting or a mixture of endo- and exo-acting enzymes was studied using three physical forms of maize and potato starch, amyloglucosidase (exo-acting) and α-amylase (endo-acting) as exemplars. For starch in granular form, there was synergism between the enzymes in the production of glucose. In contrast, endo- and exo-acting enzymes showed antagonistic effects in digestion of cooked starches. Antagonism was ascribed to the rapid production of low molecular weight oligomers by α-amylase, which are less efficiently digested by amyloglucosidase than polymeric substrates. The rates of digestion of swollen granule ghosts cooked under low shear conditions were slower than starches cooked under high shear conditions that prevent granule ghost formation. There was also an enzyme-resistant fraction present in granule ghosts, in contrast to high shear cooked starches that were fully digested under the conditions used.

Bioactive Nutrient Retention during Thermal-Assisted Hydration of Lupins.

Lupin, an arid pulse, is gaining popularity as a super food due to its superior nutritional properties. However, it has not been considered for large scale thermal processing, e.g., canning. The present work evaluated the best time/temperature combination to hydrate lupins for canning with minimum losses of bioactive nutrients, pre-biotic fibre, and total solids during hydration. The two lupin species showed a sigmoidal hydration behaviour, which was adequately modelled by the Weibull distribution. The effective diffusivity, Deff, increased from 7.41 × 10-11 to 2.08 × 10-10 m2/s for L. albus and 1.75 × 10-10 to 1.02 × 10-9 m2/s for L. angustifolius with increasing temperature, namely, from 25 °C to 85 °C. The lag phase decreased from 145 min to 56 min in L. albus and 61 min to 28 min in L. angustifolius. However, based on the effective hydration rate, reaching the equilibrium moisture, minimum loss of the solids, and prebiotic fibre and phytochemicals, 200 min hydration at 65 °C can be regarded as the optimum temperature of hydration. The findings are thus relevant for designing the hydration protocol to achieve the maximum equilibrium moisture content and yield with the minimum loss of solids (phytochemicals and prebiotic fibres) for L. albus and L. angustifolius.

Degradation of starch in pasta induced by extrusion below gelatinization temperature.

The structural deformation of starch during pasta extrusion leads to varied effects on pasta quality. We investigated the impact of shearing force on the starch structure of pasta and pasta quality by varying the screw speed (100, 300, 500 and 600 rpm) with a temperature range of 25 to 50 ℃ in increments of 5 ℃, from the feeding zone to the die zone. The higher screw speeds were associated with more specific mechanical energy input (157, 319, 440, and 531 kJ/kg for pasta produced at 100, 300, 500 and 600 rpm, respectively), resulting in a lower pasting viscosity (1084, 813, 522 and 480 mPa·s for pasta produced at 100, 300, 500 and 600 rpm, respectively) in the pasta due to the loss of starch molecular order and crystallinity. Size-exclusion chromatography revealed that pasta produced at 600 rpm screw speed had a lower amylopectin size distribution which indicated molecular breakdown during extrusion. Pasta produced at 600 rpm had higher in vitro starch hydrolysis (both raw and cooked) than the pasta made at 100 rpm. The research provides relationship of how the screw speed can be manipulated to design pasta with varied texture and nutritional functionality.

Structural and Thermal Characterization of Protein Isolates from Australian Lupin Varieties as Affected by Processing Conditions.

Proteins from the full and defatted flours of L. angustifolius cv Jurien and L. albus cv Murringo were prepared using alkaline extraction and iso-electric precipitation. Isolates were either freeze dried or spray dried or pasteurized at 75 ± 3 °C/5 min before freeze-drying. Various structural properties were investigated to elucidate the varietal and processing-induced effect on molecular and secondary structure. Irrespective of processing, isolated proteins had a similar molecular size, with α-conglutin (412 kDa) and ß-conglutin (210 kDa) being principal fractions for the albus and angustifolius variety, respectively. Smaller peptide fragments were observed for the pasteurized and spray dried samples, indicating some degree of processing-induced changes. Furthermore, secondary structure characterization by Fourier-transform-infrared and circular dichroism spectroscopy showed ß-sheet and α-helical structure being the dominant structure, respectively. Thermal characterization showed two denaturation peaks corresponding to ß-conglutin (Td = 85-89 °C) and α-conglutin (Td = 102-105 °C) fractions. However, the enthalpy values for α-conglutin denaturation were significantly higher for albus species, which corroborates well with higher amounts of heat stable α-conglutin present. Amino acid profile was similar for all samples with limiting sulphur amino acid. In summary, commercial processing conditions did not have a profound effect on the various structural properties of lupin protein isolates, and properties were mainly determined by varietal differences.

Hard-to-cook phenomenon in common legumes: Chemistry, mechanisms and utilisation.

Future dietary protein demand will focus more on plant-based sources than animal-based products. In this scenario, legumes and pulses (lentils, beans, chickpeas, etc.) can play a crucial role as they are one of the richest sources of plant proteins with many health benefits. However, legume consumption is undermined due to the hard-to-cook (HTC) phenomenon, which refers to legumes that have high resistance to softening during cooking. This review provides mechanistic insight into the development of the HTC phenomenon in legumes with a special focus on common beans and their nutrition, health benefits, and hydration behaviour. Furthermore, detailed elucidation of HTC mechanisms, mainly pectin-cation-phytate hypothesis and compositional changes of macronutrients like starch, protein, lipids and micronutrients like minerals, phytochemicals and cell wall polysaccharides during HTC development are critically reviewed based on the current research findings. Finally, strategies to improve the hydration and cooking quality of beans are proposed, and a perspective is provided.

The microbiota and metabolites during the fermentation of intact plant cells depend on the content of starch, proteins and lipids in the cells.

Intact cells, as the smallest unit of whole foods, were isolated from three legume crops and fermented with human faecal inoculum to elucidate the effect of food macro-nutrients compositional difference (starch, proteins and lipids) on in vitro colonic fermentation profiles. After 48 h of fermentation, the highest production of short-chain fatty acids (SCFAs) were observed for the pea cells, abundance in starch (64.9 %, db). In contrast, branch chain fatty acids (BCFAs) were the major metabolites for protein-enriched soybean cells (protein content 56.9 %, db). The peanut cells rich in lipids (49.2 %, db) has the lowest fermentation rate among the three varieties. Correspondingly, pea cells favoured the growth of Bifidobacterium, whereas soybean and peanut cells promoted an abundance of Bacteroides and Shigella, respectively. Furthermore, except the intact pea cells promoting the abundance of butyrate producer Roseburia, a similar fermentation pattern was found between intact and broken cells suggesting that macro-nutrient types, rather than structure, dominate the production of metabolites in colonic fermentation. The findings elucidate how the food compositional difference can modulate the gut microbiome and thus provide the knowledge to design whole food legumes-based functional foods.