Interactions among macronutrients in wheat flour determine their enzymic susceptibility

The evolution of granular surface structure and functional properties in rice starch during grain filling

The developmental changes in the granular surface structure and functional properties of starch during the entire grain filling period of rice (around 40 days) were investigated. The specific surface area of rice starch significantly decreased firstly then stabilized during growth due to increasing granular size. The pore volume decreased from 5.40 cm3/g at 6th day after anthesis (DAA-6) to 3.02 cm3/g (DAA-46). More starch granule-associated proteins (SGAPs) accumulated on the surface and in channels. Swelling power decreased by 46 %, whereas the flow behavior index (n) decreased by 32 % in upward curve during starch development from DAA-6 to DAA-30. Tan δ first dropped then remained steady at DAA 22-34 and lightly rebounded at the final stage, indicating that starch in the middle stage tended to have greater viscoelastic gel behavior at all sweeps. Mature starch showed lower in vitro hydrolysis rate and exhibited stronger enzymatic resistance. The results showed that granular surface features of rice starch may be an essential factor in determining rheological behavior and resistance to hydrolysis.

Lauric acid improved the quality of fresh noodles with/without sodium bicarbonate by altering physical properties and structure of wheat starch

To know the influence of lauric acid (LA) on wheat flour fresh noodles (WFN) quality and the latent mechanism, the effect of LA on cooking properties, digestibility and structure of WFN with/without sodium bicarbonate (SB) and the properties of wheat flour (WF) with/without SB were studied. The results indicated that LA reduced cooking loss and digestibility of WFN with SB and slightly decreased water adsorption and increased the free water binding ability and hardness of WFN without SB. Furthermore, LA increased the degree of short- and long-range order and molecular weight of starch in cooked WFN with/without SB and it had greater effect on the degree of short- and long-range order and molecular weight of starch in cooked WFN with SB than that without SB. Differential scanning calorimeter (DSC) and rapid viscosity analysis (RVA) displayed that WFN with LA and SB formed more starch-LA or/and starch-LA-protein complexes than WFN with LA. Additionally, the impact of LA on WFN quality and WF properties was influenced by SB concentration. This study will provide theoretical basis and new thoughts for the design of high-quality fresh noodles with low digestibility, low cooking loss and high hardness.

Effects of crystallization temperature on structure and digestibility of spherulites formed from debranched high-amylose maize starch

High-amylose maize starch (69.3 % amylose) was debranched to increase the level of linear molecules and enhance the formation of spherulites. Debranched high-amylose maize starch (25 %, w/w) was heated to 180 °C in a Parr reactor followed by crystallization at different temperatures between 25 and 150 °C. The objectives of this study were to investigate the effects of crystallization temperature on the yield, morphology, structure, crystallinity, and digestibility of the spherulites formed. When the crystallization temperature was 150 °C, spherulites with negative birefringent sign were formed. High crystallization temperature caused molecular degradation and the degree of degradation was severe at 150 °C, resulting in relatively short chain amylose (DP < 150). When crystallized at 25 to 120 °C, spherulites with strong positive birefringence were produced. The long chain amylose was attributed to the positive birefringence. All spherulites had a predominant B-type crystalline structure. The spherulites with negative birefringence showed a lower degree of crystallinity and lower resistance to enzyme digestion, but all the spherulites with positive birefringence had a high resistant starch content (89-94 %). α-Amylase was not able to penetrate inside the spherulites as revealed by the confocal laser scanning microscopic images.

Study of starch molecular structure-property relations provides new insight into slowly digested rice development

White rice consumption has been regarded as a potential risk factor for non-communicable diseases including obesity and type 2 diabetes. Thus, increasing attention has been paid to develop slowly digested rices with acceptable palatability. As the most abundant component of rice kernels, the fine molecular structure of starch controls not only the texture & aroma, but also the digestion properties of cooked rice. A large number of studies have been conducted to see what molecular structural features control the digestibility and palatability of cooked rice, which further could be connected to starch biosynthesis to enable rices with targeted functionalities to be chosen in non-empirical ways. Nonetheless, little progress has been made because of improper experimental designs. For example, the effects of starch fine molecular structure on cooked rice digestibility and palatability has been rarely studied within one study, resulting to various digestion results. Even for the same sample, it is hard to obtain consistent conclusions and sometimes, the results/coclusions are even controversy. In this review paper, starch fine molecular structural effects on the texture, aroma and starch digestion properties of cooked white rice were summarized followed by a detailed discussion of the relations between the fine molecular structures of amylopectin and amylose to deduce a more general conclusion of starch molecular structure-cooked rice property relations. It is expected that this review paper could provide useful information in terms of how to develop slowly digested rices with acceptable palatability.

Role of pea protein isolate in modulating pea starch digestibility: insights from physicochemical and microstructural analysis

BACKGROUND

Understanding the interactions between protein and starch is crucial in revealing the mechanisms by which protein influences starch digestibility. The present study investigated the impact of different contents of pea protein isolate (PPI) on the physicochemical properties and digestibility of pea starch (PS).

RESULTS

The results demonstrated that as the content of PPI increased from 0% to 12%, and the digestion of PS decreased by 12.3%. Rheological analysis indicated that PPI primarily interacted with molecular chains of PS through hydrogen bonds. Increasing the content of PPI resulted in a 30.6% decrease in the hardness of the composite gels, accompanied by a 10% reduction in the short-ordered structure of PS. This hindered the formation of molecular aggregation and resulted in a loose and disordered gel network structure. The microstructure confirmed that the attachment of PPI to PS served as a physical barrier, impeding starch digestibility.

CONCLUSION

In summary, the primary mechanism by which PPI inhibited PS digestion involved steric hindrance exerted by PPI and its interaction with PS via hydrogen bonds. These findings contribute to a better understanding of the interaction mechanisms between PS and PPI and offer insights for the optimal utilization of pea resources. © 2024 Society of Chemical Industry.

Micro-encapsulation of garlic oil using esterified-wheat porous starch and whey protein isolate: Physicochemical properties, release behavior during in vitro digestion

The study aimed to inhibit the stimulating impact of garlic oil (GO) on the stomach and attain high release in the intestine during digestion. So, wheat porous starch (WPS) was modified with octenyl succinic acid (OSA) and malic acid (MA) to obtain esterified WPS, OWPS and MWPS, respectively. The differences in physicochemical, encapsulation, and digestive properties of two GO microcapsules, WPI/OWPS/GO and WPI/MWPS/GO microcapsules produced by using OWPS and MWPS as variant carrier materials and whey protein isolate (WPI) as the same coating agent, were compared. The results found that OWPS had greater amphiphilicity, while MWPS had better hydrophobicity and anti-digestive ability than WPS. Encapsulation efficiency of WPI/OWPS/GO (94.67 %) was significantly greater than WPI/MWPS/GO (91.44 %). The digestion inhibition and low GO release (approximately 23 %) of WPI/OWPS/GO and WPI/MWPS/GO microcapsules in the gastric phase resulted from the protective effect of WPI combined with the good adsorption and lipophilicity of OWPS and MWPS. Especially, WPI/OWPS/GO microcapsule was relatively stable in the gastric phase and had sufficient GO release (67.24 %) in the intestinal phase, which was significantly higher than WPI/MWPS/GO microcapsule (56.03 %), benefiting from the adsorption and digestive properties of OWPS, and resulting in a total cumulative GO release rate of 90.86 %.

Effect of non-starch components on the structural properties, physicochemical properties and in vitro digestibility of waxy highland barley starch

Highland barley (HB) endosperm with an amylose content of 0-10 % is called waxy HB (WHB). WHB is a naturally slow-digesting grain, and the interaction between its endogenous non-starch composition and the WHB starch (WHBS) has an important effect on starch digestion. This paper focuses on the mechanisms by which the components of β-glucan, proteins and lipids affect the molecular, granular, crystalline structure and digestive properties of WHBS. After eliminating the main nutrients except for starch, the estimated glycemic index (eGI) of the samples rose from 62.56 % to 92.93 %, and the rapidly digested starch content increased from 60.81 % to 98.56 %, respectively. The resistant starch (RS) content, in contrast, dropped from 38.61 % to 0.13 %. Comparatively to lipids, β-glucan and protein contributed more to the rise in eGI and decline in RS content. The crystalline characteristics of starch were enhanced in the decomposed samples. The samples' gelatinization properties improved, as did the order of the starch molecules. Protein and β-glucan form a dense matrix on the surface of WHBS particles to inhibit WHBS digestion. In summary, this study revealed the mechanism influencing the digestibility of WHBS from the perspective of endogenous non-starch composition and provided a theoretical basis to develop slow-digesting foods.

Enrichment of resistant starch in starch-protein hydrolysate binary matrix by modulating pH during thermal processing

Controlling the digestion features of starch-based food matrices following thermal processing plays vital roles in reducing risks of metabolic diseases such as obesity and type II diabetes. To date, it remains largely unclear how regulating the pH during thermal processing alters the microstructure and digestion features of starch-based matrix including protein hydrolysates. Considering this, corn starch (CS) and soybean protein isolate (SPI) (or its hydrolysates (SPIH)) were used to prepare thermally-processed CS-SPI and CS-SPIH binary matrices under different pH values (3 to 9), followed by inspection of changes in the structures and digestibility using combined methods. It was found that including SPI (especially SPIH) caused structural changes of those binary systems, such as reduced network sizes, increased V-crystals and reduced nanoscale structures, which could allow more resistant starch (RS). This phenomenon was especially true when including SPIH with regulated pH value. For instance, SPIH inclusion at pH 5 caused the highest RS content (about 20.30%), presumably linked to the reduced molecule size of SPIH with strengthened aggregation at pH 5. In contrast, the acidic (pH 3) and alkaline (pH 9) conditions allowed reduced short-range orders and tailored porous networks and thus less RS (ca. 17.46% at pH 3 and 16.74% at pH 9).

Modulating the glycemic response of starch-based foods using organic nanomaterials: strategies and opportunities

Traditionally, diverse natural bioactive compounds (polyphenols, proteins, fatty acids, dietary fibers) are used as inhibitors of starch digestive enzymes for lowering glycemic index (GI) and preventing type 2 diabetes mellitus (T2DM). In recent years, organic nanomaterials (ONMs) have drawn a great attention because of their ability to overcome the stability and solubility issues of bioactive. This review aimed to elucidate the implications of ONMs in lowering GI and as encapsulating agents of enzymes inhibitors. The major ONMs are presented. The mechanisms underlying the inhibition of enzymes, the stability within the gastrointestinal tract (GIT) and safety of ONMs are also provided. As a result of encapsulation of bioactive in ONMs, a more pronounced inhibition of enzymes was observed compared to un-encapsulated bioactive. More importantly, the lower the size of ONMs, the higher their inhibitory effects due to facile binding with enzymes. Additionally, in vivo studies exhibited the potentiality of ONMs for protection and sustained release of insulin for GI management. Overall, regulating the GI using ONMs could be a safe, robust and viable alternative compared to synthetic drugs (acarbose and voglibose) and un-encapsulated bioactive. Future researches should prioritize ONMs in real food products and evaluate their safety on a case-by-case basis.

The impact of the soluble protein fraction and kernel hardness on wheat flour starch digestibility

Wheat is the staple crop for 35% of the world's population, providing a major source of calories, mainly in the form of starch. The digestibility of wheat starch varies between different flours and products. Wheat products that are rapidly digested elicit large post-prandial glucose peaks associated with metabolic disorders. We investigated the impact of protein on starch digestion in three commercial flours with different grain hardness. A soluble extract of wheat proteins reduced starch digestion, even following gastric proteolysis. This extract was enriched in proteinaceous α-amylase inhibitors which were partially degraded during gastric proteolysis. Starch digestion kinetic analysis was carried out for flour samples pre-treated with different pepsin activities. The rate of starch digestion was altered following pepsin pre-digestion, and the extent of starch digestion increased in response to pepsin pre-digestion. We conclude that soluble proteinaceous alpha-amylase inhibitors present in wheat can escape gastric digestion and significantly contribute to reducing starch digestion in the small intestine.

Investigation of the mechanism of different 3D printing performance of starch and whole flour gels from tuber crops

This study aims to reveal the variation in 3D printing performance of whole flour and starch gels as derived from different varieties of tuber crops including cassava, potato, and yam, along with its mechanism. The whole flour of the same tuber crops showed a higher branching degree, average molecular weight (R¯_h), and the proportion of AM chains for 100 < X ≤ 1000 than its starch. Due to the higher degree of branching, the crystallinity of whole flour reached a higher level. In this circumstance, G2' of the dispersion system decreased, which facilitated smooth extrusion of ink from the nozzle, thus improving the precision of printing for the final product. Besides, a higher R¯_h and the percentage of AM chains for 100 < X ≤ 1000 made it easier for the material to extrude, thus enhancing the printing accuracy of the product. The higher short-range ordered structure of whole flour also enhanced the printing performance of 3D printed products. This research contributes an effective solution to the selection of starch and whole flour for food 3D printing.

Effect of protein-starch interactions on starch retrogradation and implications for food product quality

Starch retrogradation is a consequential part of food processing that greatly impacts the texture and acceptability of products containing both starch and proteins, but the effect of proteins on starch retrogradation has only recently been explored. With the increased popularity of plant-based proteins in recent years, incorporation of proteins into starch-based products is more commonplace. These formulation changes may have unforeseen effects on ingredient functionality and sensory outcomes of starch-containing products during storage, which makes the investigation of protein-starch interactions and subsequent impact on starch retrogradation and product quality essential. Protein can inhibit or promote starch retrogradation based on its exposed residues. Charged residues promote charge-dipole interactions between starch-bound phosphate and protein, hydrophobic groups restrict amylose release and reassociation, while hydrophilic groups impact water/molecular mobility. Covalent bonds (disulfide linkages) formed between proteins may enhance starch retrogradation, while glycosidic bonds formed between starch and protein during high-temperature processing may limit starch retrogradation. With these protein-starch interactions in mind, products can be formulated with proteins that enhance or delay textural changes in starch-containing products. Future work to understand the impact of starch-protein interactions on retrogradation should focus on integrating the fields of proteomics and carbohydrate chemistry. This interdisciplinary approach should result in better methods to characterize mechanisms of interaction between starch and proteins to optimize their food applications. This review provides useful interpretations of current literature characterizing the mechanistic effect of protein on starch retrogradation.

Advances in isolation, characterization, modification, and application of Chenopodium starch: A comprehensive review

The Chenopodium genus includes >250 species, among which only quinoa, pigweed, djulis, and kaniwa have been explored for starches. Chenopodium is a non-conventional and rich source of starch, which has been found effective in producing different classes of food. Chenopodium starches are characterized by their smaller granule size (0.4-3.5 μm), higher swelling index, shorter/lower gelatinization regions/temperature, good emulsifying properties, and high digestibility, making them suitable for food applications. However, most of the investigations into Chenopodium starches are in the primary stages (isolation, modification, and characterization), except for quinoa. This review comprehensively explores the major developments in Chenopodium starch research, emphasizing isolation, structural composition, functionality, hydrolysis, modification, and application. A critical analysis of the trends, limitations, and scope of these starches for novel food applications has also been provided to promote further scientific advancement in the field.

Increasing the pH value during thermal processing suppresses the starch digestion of the resulting starch-protein-lipid complexes

To date, how the pH conditions of thermal processing tailor the structure and digestibility of resulting starch-based complexes remains largely unclear. Here, indica rice starch (IRS), stearic acid (SA), and a whey protein isolate (WPI) were used as materials. Increasing the pH value from 4 to 8 during thermal processing (pasting) mainly suppressed the starch digestion of starch-WPI-SA complexes rather than starch-SA counterparts. The starch-SA complexes showed moderate structural changes as the pH value rose, and there was less rapidly digestible starch (RDS) only at pH 8. For the starch-WPI-SA complexes, an increased pH value allowed larger nonperiodic structures and more V-type starch crystallites, with almost unchanged short-range orders but apparently collapsed networks at pH 8. Such ternary complexes displayed more resistant starch (RS) as the pH value rose. The ternary sample at pH 8 contained ca. 29.87% of the RS fractions.

Effect of Endogenous Lipids and Proteins on the Antioxidant, in vitro Starch Digestibility, and Pasting Properties of Sorghum Flour

This study evaluated the effect of endogenous lipids and proteins on the antioxidants, starch digestibility, and pasting properties of sorghum (Sorghum bicolor) flour (SF). Endogenous lipids and/or proteins were removed from different portions of SF to obtain defatted (DF), deproteinized (DP), and defatted and deproteinized (DF-DP) flours. Bioactive constituents (total phenolics, tannins, flavonoids, saponins, and anthocyanins), antioxidant activities [2,2-Azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation (ABTS*+) and 2, 2-Diphenyl-2-picrylhydrazyl radical (DPPH*) scavenging activities, reducing power, and Fe2+ chelating capacity], starch, amylose, starch hydrolysis index (HI), estimated glycemic index (eGI), and pasting properties of treated and control (untreated) flours were determined. The control flour (SF) had significantly higher (p < 0.05) levels of all the bioactive constituents and antioxidant activity tested than the DF, DP, and DF-DP flours, while the DF-DP flour had the least levels of bioactive constituents and antioxidant activity. In contrast, the starch, amylose, HI, and eGI were consistently in the order of DF-DP > DF > DP > control flour (p < 0.05). The control flour had the highest (p < 0.05) peak viscosity, and the least peak time and pasting temperature, while the DF flour had the highest final viscosity. Therefore, endogenous lipids and proteins contribute to the antioxidant, starch digestibility, and pasting properties of sorghum flour.

Utilizing Hydrothermal Processing to Align Structure and In Vitro Digestion Kinetics between Three Different Pulse Types

Processing results in the transformation of pulses’ structural architecture. Consequently, digestion is anticipated to emerge from the combined effect of intrinsic (matrix-dependent) and extrinsic (processed-induced) factors. In this work, we aimed to investigate the interrelated effect of intrinsic and extrinsic factors on pulses’ structural architecture and resulting digestive consequences. Three commercially relevant pulses (chickpea, pea, black bean) were selected based on reported differences in macronutrient and cell wall composition. Starch and protein digestion kinetics of hydrothermally processed whole pulses were assessed along with microstructural and physicochemical characteristics and compared to the digestion behavior of individual cotyledon cells isolated thereof. Despite different rates of hardness decay upon hydrothermal processing, the pulses reached similar residual hardness values (40 N). Aligning the pulses at the level of this macrostructural property translated into similar microstructural characteristics after mechanical disintegration (isolated cotyledon cells) with comparable yields of cotyledon cells for all pulses (41–62%). We observed that processing to equivalent microstructural properties resulted in similar starch and protein digestion kinetics, regardless of the pulse type and (prolonged) processing times. This demonstrated the capacity of (residual) hardness as a food structuring parameter in pulses. Furthermore, we illustrated that the digestive behavior of isolated cotyledon cells was representative of the digestion behavior of corresponding whole pulses, opening up perspectives for the incorporation of complete hydrothermally processed pulses as food ingredients.

Effects of whey protein on the in vitro digestibility and physicochemical properties of potato starch

The aim of this study was to examine the effect of whey protein isolate (WPI) on the digestibility and physicochemical properties of potato starch (PS) after heat treatment. WPI reduced the digestibility of PS and increased the order and aggregation structure of gelatinized PS. Examination of the rheological properties of the PS-WPI mixed system before and after adding different chemicals (sodium chloride, urea, and sodium dodecyl sulfate) indicated an involvement of hydrogen bonds and hydrophobic interactions in the PS-WPI gelatinization system. The pasting properties, swelling power, and thermal properties indicated that WPI suppressed the swelling and gelatinization of PS. The addition of WPI reduced the amylose leaching rate from the starch granules, indicating that the presence of exogenous protein could prevent amylose diffusion from the starch granules. Native WPI and its hydrolysate also inhibited amyloglucosidase activity. These findings indicated that the mechanism by which WPI reduces PS digestion involves hydrophobic interactions and hydrogen bonding between WPI and PS, as well as enzyme activity inhibition.

Effects of degree of milling on the starch digestibility of cooked rice during (in vitro) small intestine digestion

Effects of degree of milling on starch digestibility of cooked rice during (in vitro) small intestine digestion were investigated. By fitting starch digestograms to the logarithm of slope plot and combination of parallel and sequential digestion kinetics model, two starch fractions with distinct digestion rate constants were identified. Results from scanning electronic microscope and confocal laser scanning microscope showed that the rapidly digestible starch fraction (RDF) was mainly composed of gelatinized starch, while the slowly digestible starch fraction (SDF) was consisted of relatively intact starch granules, protein matrix encapsulated starch and starch-protein binary complex. The cooked rice with milling treatment had more loosely packed and larger network cells compared to that for brown rice. Consequentially, the RDF content was decreased, while that for SDF was increased by the milling treatment. These results could help the rice processing industry to develop healthy rice products with desirable starch digestibility.

Starch-lipid interaction alters the molecular structure and ultimate starch bioavailability: A comprehensive review

Starch bioavailability which results in eliciting postprandial glycaemic response, is a trait of great significance and is majorly influenced by the physical interaction among the matrix components governed by their molecular structure as well as dynamics. Among physical interactions limiting starch bioavailability, starch and any guest molecules like lipid interact together to alter the molecular structure into a compact V-type arrangement endorsing the processed crystallinity, thus limiting carbolytic enzymatic digestion and further bioavailability. Considering the importance of starch-lipid dynamics affecting bioavailability, intensive research based on endogenous (internal lipids which are embedded into the food matrix) as well as exogenous (those are added from outside into the food matrix during processing like cooking) lipids have been carried out, endorsing physical interactions at colloidal and microstructural levels. The shared insights on such binary (starch-lipid) interactions revealed the evolution of characterization techniques as well as their role on altering the functional and nutritional value. It is very much vital to have a thorough understanding about the mechanisms on the molecular level to make use of these matrix interactions in the most efficient way, while certain basic questions are still remaining unaddressed. Do starch - lipid complexation affects the ultimate starch bioavailability? If so, then whether such complexation ability depends on amylose - fatty acid/lipid content? Whether the complexation is influenced further by fatty acid type/concentration/chain length or saturation? Further comprehending this, whether the altered bioavailability by binary (starch-lipid) could further be affected by ternary (starch-lipid-protein) and quaternary (starch-lipid-protein-phenolics) interactions are also discussed in this comprehensive review.

The effect of baking conditions on protein digestibility, mineral and oxalate content of wheat breads

Different baking conditions were used in order to evaluate its effects on bread aspects. Doughs were baked at 160, 190 and 220 °C, during 9, 12, 15 and 20 min, and characterized in relation to color change, oxalate and mineral concentration, and protein digestibility. The higher the baking temperature and time, the higher the crust color change, the lower the oxalate concentration, and the higher the amount of some macro minerals. Protein digestibility may also be favored, however it does not follow a linear correlation. Although it is not possible to obtain a condition that favors the content of all minerals, protein digestibility and reduces oxalate content, the use of high temperatures and times is important as it can reduce oxalate and thereby prevent its associated problems. Understanding how to optimize it during baking could be used to produce breads with a higher mineral bioavailability, an important strategy for food industry and also when using alternative flours.

Effects of endogenous proteins on rice digestion during small intestine (in vitro) digestion

Rices with higher protein contents are nutritionally desirable. This study investigates the effects of endosperm proteins on starch in vitro digestibility in cooked and uncooked rice, and the mechanisms underlying any changes. The composition of rice endosperm proteins and the morphologies of proteins and starch granules were determined by SDS-PAGE and confocal microscopy. Starch molecular fine structure was examined using size-exclusion chromatography. In vitro digestion showed that the digestion rate coefficients (k) of cooked rice flour were significantly lower than those of isolated starch or of a starch-protein mixture. (e.g for samples from SWR4, k is 9.6, 12.9 and 11.6 × 10^-2 min^-1 for cooked rice flour, isolated starch and starch-protein mixture, respectively). For uncooked samples, digestion rate coefficients were 1.4, 1.5 and 1.8 × 10^-2 min^-1 for flour, starch-protein mixture and starch, respectively. The digestion rates in cooked samples were higher than those in uncooked samples. This suggests that, in cooked samples, starch digestion rates are more affected by the protein physical barrier than by some chemical effect (e.g. hydrogen bonding between protein and starch), while in uncooked samples, a chemical effect from protein is more pronounced than a physical barrier from protein.

Protein-starch matrix plays a key role in enzymic digestion of high-amylose wheat noodle

Wheat flour, consisting of a complex matrix of starch and protein, is used as a representative model of whole food here to investigate the binary interaction in relation to amylose level and hydrothermal treatment in noodles as a food exemplar. Noodle made of high-amylose wheat (HAW) flour showed an eight-fold higher resistant starch content, compared to the wild type. Protein removal under simulated intestinal digestion conditions resulted in higher starch digestion rate coefficients in raw and cooked flours. In cooked flours, the substrate becomes similarly accessible to digestive enzymes regardless of protein removal. The results indicate that the increased protein content in native HAW flour and thermal stability of starch in HAW noodles lead to higher food integrity and consequently enhance the resistance against α-amylase digestion. Overall, the study suggests that a diversity of starch-protein interactions in wheat-based food products underlies the nutritional value of natural whole foods.

In vitro starch and protein digestion kinetics of cooked Bambara groundnuts depend on processing intensity and hardness sorting

When pulse seeds from a single batch are cooked, considerable variability of hardness values in the population is usually observed. Sorting the seeds into hardness categories could reduce the observed diversity and increase uniformity. Therefore, we investigated the effect of processing intensity whether or not combined with sorting into hardness categories on the in vitro starch and protein digestion kinetics of cooked Bambara groundnuts (cooking times 40 min and 120 min). The average hardness values were 89 ± 32 N and 42 ± 20 N for 40 min and 120 min cooking time, respectively. The high standard deviation of hardness for each cooking time revealed a high level of diversity amongst the seeds. Individual cells were isolated from (non-)sorted seeds before simulating digestion. The estimated lag phase describing the initial phase of starch digestion was not significantly different despite the processing intensity or the hardness category, implying that cell wall barrier properties for these samples were not majorly different. However, the rate constants and the extents of starch digestion of samples cooked for 40 min were significantly higher for the low hardness (50-65 N) compared to the high hardness (80-95 N) category (0.71 vs 1.02 starch%/min and 63 vs 77%, respectively). Kinetic evaluation of digested soluble protein (after acid hydrolysis of the digestive supernatant) showed that low hardness samples were digested faster than high hardness samples (0.037 vs 0.050 min^-1). The faster protein hydrolysis in the low hardness samples was accompanied by faster starch digestion, indicating the possible role of the protein matrix barrier. Individual cells of comparable hardness obtained from the two different processing times had similar starch and protein digestion kinetics. Our work demonstrated that, beyond cooking time, hardness is a suitable food design attribute that can be used to modulate starch and protein digestion kinetics of pulse cotyledon cells.