Effect of controlled gelatinization in excess water on digestibility of waxy maize starch

An aqueous dispersion of waxy maize starch (5%, w/w) was controlled gelatinized by heating at various temperatures for 5 min. The treated samples were analysed using in vitro Englyst assay, light microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. When heated, SDS and RS levels were decreased inversely with RDS. A high SDS content (>40%) was kept prior to the visible morphological and structural changes (before 60 °C). Swelling factor began to increase slightly at 50–60 °C and continued to maximum value at 80 °C. A large decrease in ΔH, crystallinity, and ratio of 1047/1022 cm⁻¹ attributed to partially dissociation of crystalline clusters and double helices occurred at 65–80 °C. These changes showed that controlled gelatinized starch with slow digestion property occurred in the molecular rearrangement process before granule breakdown and SDS mainly consists of amorphous regions and a small portion of less perfect crystallites.     

Impact of mild acid hydrolysis on structure and digestion properties of waxy maize starch

In this study, the molecular structure of acid-treated waxy maize starch residues was investigated, and the in vitro digestibility of the residues with 2.2 N HCl at 35 °C for different time periods, was assessed. The granular appearance of waxy maize starch was destroyed and small fractions formed aggregates. A change in chain-length distribution profiles occurred with the degradation of shortest A chains and long B chains in amylopectin. The rise in the ratio of absorbance height at 1047 cm⁻¹ to the height at 1022 cm⁻¹, the intensities of major peaks, X_c, T_p, T_c, and ΔH were observed during mild acid hydrolysis, but the X-ray diffraction patterns displayed A-type for all starches. The amount of rapidly digestible starch increased, whereas the amounts of slowly digestible and resistant starch decreased. These results demonstrate that the amorphous regions of starch granules, including the shortest A chains and long B chains, are preferentially hydrolysed and affect the slow digestion and resistance properties of waxy maize starch.     

Study on structural changes of microwave heat-moisture treated resistant Canna edulis Ker starch during digestion in vitro

Microwave heat-moisture treated Canna edulis Ker starch has been applied to study structural changes in vitro using porcine α-amylase, pancreatin and amyloglucosidase. The structures at different digestion stages were characterized using scanning electron microscopy (SEM), polarized optical microscopy (POM), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), Fourier transforms infrared (FT-IR) spectroscopy and solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy. The increase in molecular order was observed with increasing digestion time and reflected in higher scattering intensity measured by SAXS, higher crystallinity observed by XRD, the increase of the double helix order obtained by solid state ¹³C NMR spectroscopy, and corresponding changes in the measurement of FT-IR, in favour of increasing resistant starch content. SAXS reveals a single peak around 0.6335 nm⁻¹, suggesting that the enzyme may erode the special site of granule surface and catalyze whole hydrolysis reaction through pitted canals. In the process of digestion, amorphous region of starch granule is susceptible to the attack of enzyme. Moreover, the result also demonstrates that the resistance to enzymatic digestion may mainly depend on specific structure in the treated starches.     

Nutritionally important starch fractions in cereal based Indian food preparations

Recent research studies have invalidated the earlier assumptions regarding the rate of digestion of carbohydrates. Hence, in the present study the rate and extent of starch digestion in vitro was measured in 10 cereal-based Indian food preparations (with/without accompaniments). The selected foods included chapathi, dosa, idli, pongal, poori, ragi roti, rice roti, rice flakes upma, semolina idli and upma and the accompaniments — cooked dhal, chutney and potato palya. In view of the nutritional importance of starch, the major starch fractions viz., rapidly digestible starch, slowly digestible starch (SDS) and resistant starch as defined by Englyst [Englyst, H. N., Kingman, S. M., & Cummings, J. H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal Clinical Nutrition, 46(2), 333–350] were measured, by using controlled enzymic hydrolysis with pancreatin and amyloglucosidase. In addition, rapidly available glucose (RAG) was measured and a starch digestion index was derived. Dietary fiber components (soluble and insoluble fiber) were measured by the enzymatic method [Asp, N. G., Johansson, C. G., Hallmer, H., & Siljestrom, M. (1983). Rapid enzymatic assay of insoluble and soluble dietary fiber. Journal of Agricultural Food Chemistry, 31, 476–482]. The results indicate that the course of starch hydrolysis was not only characteristic for each food but also appears to be affected by the addition of accompaniment. Also, while the correlation between RAG and SDS did not attain significance in foods with accompaniment, a significant inverse correlation (r=−0.68, P<0.05) was seen in foods without accompaniment. It is evident that starch digestibility in Indian foods is influenced by the accompaniment rather than the cereal base.     

In vitro starch digestion kinetics of diets varying in resistant starch and arabinoxylan compared with in vivo portal appearance of glucose in pigs

The current study was undertaken to investigate the relationship between the in vitro starch digestion kinetics and the in vivo portal glucose appearance in pigs used as models for humans. In vivo data were obtained from a previous study where the portal glucose appearance was obtained from six catheterised pigs equipped with permanent catheters in an artery and the portal vein and with a flow probe attached to the portal vein for monitoring the blood flow rate. Three experimental diets were studied — a low dietary fibre (DF), western-style diet (WSD) and two high-DF diets containing resistant starch (RSD) or arabinoxylan (AXD). A modified Englyst-assay involving gradual glucose hydrolysis over a time frame of 6 h was used in vitro. The in vitro starch digestion kinetics was modelled using a mechanistic growth model (R² > 0.995), whereas the in vivo data were better described by a sigmoid Gompertz model (R² > 0.997). The estimated plateau values were higher in vitro than in vivo but the diets were similarly ranked; ~ 95% for AXD and WSD and 81.8% for RSD in vitro and ~ 86% and 76.6% for the same diets in vivo. The rate of glucose release in vitro was much faster than the portal glucose appearance in vivo (0.0347–0.0705 versus 0.0136–0.0197% starch/min) with the starch in RSD being the most slowly degradable. This difference was most likely an effect of gastric retention. In conclusion, the in vitro method ranked the three diets in a similar relative manner as in vivo but the rate of glucose release was much faster in vitro than in vivo. It was only when the starch structure set the limit for the starch hydrolysis, however, that similar relative results were obtained.     

Physicochemical changes in barley starch during malting

The objective of this work was to study the physicochemical modifications of starch during the malting of barley. The results showed that malting modifies the physicochemical properties of the starch over time by the action of barley enzymes. The gelatinisation temperature of starch increased as a function of the malting time owing to the selective enzymatic attack. The viscosity of starch decreased through malting. During germination, scanning electron microscopy showed that the enzymes degrade some starch granules which exhibited micro‐holes on the surface. X‐ray diffraction showed an apparent increase in the crystallinity during the first three days of germination, reflecting the consumption of amorphous regions. Such changes have not been previously reported. Infrared spectroscopy (1200–1500 cm^?1) showed the unfolding of carbohydrates as a result of enzymatic action. Such changes in the physicochemical properties of starch indicate that the amorphous area is consumed in the early stages of malting. © 2018 The Institute of Brewing & Distilling     

In vitro digestibility of starch in cooked potatoes as affected by guar gum: Microstructural and rheological characteristics

Potatoes from different New Zealand cultivars (Nadine, Moonlight, Red Rascal, Agria) were analysed for starch digestibility in vitro (under simulated gastric and small intestinal conditions). The extent of starch hydrolysis (%) for all the potato cultivars ranged between 85% and 95% at the end of in vitro digestion. Nadine potatoes, which were waxy in texture, showed higher starch hydrolysis (%) whereas these levels did not differ significantly among the other three cultivars. Confocal laser scanning microscopy and scanning electron microscopy were performed on the digests in order to study the microstructural changes occurring during digestion in cooked potatoes. The micrographs clearly showed that starch was quickly hydrolysed by the enzymes present in simulated intestinal fluid (SIF) whereas the cell walls remained intact during simulated digestion process. Addition of guar gum (0.5%) to cooked potatoes reduced their starch hydrolysis (%) by ∼15% during the in vitro digestion. Online viscosity measurements were also performed on the cooked potatoes during simulated small intestinal digestion using a dynamic rheometer. Cooked potato viscosity dropped considerably upon the action of enzymes from SIF on starch as the digestion progressed. The presence of 0.5% guar gum facilitated the cooked potato matrix to maintain viscosity similar to undigested cooked potato sample throughout the in vitro digestion, which might have resulted in lower starch hydrolysis (%).     

Original article: In vitro starch digestion and potassium release in sweet potato from Papua New Guinea†

Twenty samples of sweet potato from Papua New Guinea, made up of cultivars 3‐mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1‐mun from three provinces, three farmers, and three locations, were subjected to an in vitro starch digestion procedure. Digestion of starch was studied by glucometry, while potassium release was monitored using electrochemistry. The potassium content of the nondigested samples ranged from 4 to 17 mg g^?1 dry solids, while the starch content was from 47 to 80 g per 100 g dry solids and independent of G × E effects. In vitro starch digestibility (2–75 g digested starch per 100 g dry starch) significantly (P < 0.05) varied with time in a nonlinear manner with biphasic digestograms. Potassium release was independent of time in in vitro gastric and pancreatic regions, but more potassium was released during pancreatic than gastric digestion. Results suggest differences in resistant starch and bioavailability of (micro)nutrients that could influence utilisation of sweet potato.     

Effects of wheat and rye bread structure on mastication process and bolus properties

Chemical composition, baking process and structure of breads influence their degradation in digestion leading to different postprandial responses. Rye bread has a very different structure as compared to wheat bread, and rye breads are known to induce lower postprandial insulin responses than wheat bread. The aim of this study was to find out potential differences in mastication and initial starch hydrolysis rate of rye and wheat breads. Three rye breads (wholemeal rye, endosperm rye and endosperm rye with gluten) and wheat bread were masticated by fifteen participants and the process was monitored using electromyography. The particle size distribution and initial in vitro starch hydrolysis of the bread boluses were analysed. Specific volume correlated negatively and closed porosity of breads correlated positively with work required for mastication. When compared to wheat bread, wholemeal rye bread required more work for mastication process (p = 0.004). Rye breads were degraded to smaller particles than wheat bread during mastication. There was a trend (p = 0.098) towards slower in vitro starch hydrolysis rate in rye bread boluses than in wheat bread boluses. The results indicate that the digestion process of rye breads differs from that of wheat bread already in the early phase of digestion. This may be one reason behind the unique postprandial responses reported for rye breads.     

In vitro digestibility,structural and functional properties of starch from pigeon pea (Cajanus cajan) cultivars grown in India

Starches isolated from two pigeon pea cultivars (AL-15 and AL-201) were evaluated for their in vitro digestibility, structural and functional properties. Both the cultivars exhibited a characteristic C-type diffraction pattern with relative crystallinity values of 31.9% and 34.2%, for AL-15 and AL-201, respectively. The structural characterization obtained using high performance size exclusion column chromatography revealed that molecular weight of amylopectin and amylose was higher for AL-201 (396 and 3.92 × 10⁶ g/mol, respectively) in comparison to AL-15 starch (354 and 3.31 × 10⁶ g/mol, respectively). AL-201 exhibited higher values for transition temperatures, enthalpy of gelatinization, pasting temperature and percentage retrogradation in comparison to AL-15 starch. Slowly digestible starch, readily digestible starch and resistant starch contents of AL-15 and AL-201 cultivars were observed to be 31.0, 8.1 and 60.9% and 29.6, 5.2 and 65.2%, respectively. The hydrolysis index and RS values indicated that pigeon pea starches were highly resistant to digestion.     

Multi‐scale structural and digestion properties of wheat starches with different amylose contents

The physicochemical and digestion properties of three wheat starches with different amylose contents were studied. Scanning electron microscopy (SEM) showed they displayed a spherical disc‐like form, a lenticular shape and an irregular morphology, respectively. Compared with waxy and normal wheat starches, high‐amylose wheat starch (HAWS) was characterised by the presence of lower molecular weight amylose fraction, and its granules demonstrated the highest resistance to the cooking. The changes in the IR ratio 1022/999–1047/1022 cm^?1 following the gel storage suggested the molecules of HAWS are more readily to re‐associate and re‐organise into a more organised status than other two starches. The determination of glucose release showed that HAWS had the lowest digestion kinetics (P < 0.001), and this difference in the digestion properties between HAWS and the other two starches might imply that starch molecular structure, in particular amylose structure is another key factor for manipulating starch digestion property rather than amylose content alone.     

SDS-Sulfite Increases Enzymatic Hydrolysis of Native Sorghum Starches

The sodium dodecyl sulfate (SDS) starch isolation procedure is often used to remove efficiently the surrounding and surface protein of starch granules in order to obtain a pure starch sample. In this study the changes in enzymatic hydrolysis of sorghum starch granules due to SDS-sulfite solution treatment were investigated. As SDS-sulfite solution soak time increased, enzymatic hydrolysis rate increased and the Michaelis-Menten pattern of enzymatic reaction did not change. The degree of this effect differed among starches from three sorghum cultivars. The effect of SDS-sulfite solution treatment on enzymatic hydrolysis became negligible after the treated starch samples were partially hydrolyzed. The adsorption of α-amylase onto the starch granules also increased with SDS-sulfite solution treatment and was highly correlated with hydrolysis rate. The different effects of SDS-sulfite solution on enzymatic hydrolysis of the three sorghum starches were related to the properties of the amorphous regions in starch granules.     

Evolutions of rheology,microstructure and starch hydrolysis of pumpkin-enriched bread during simulated gastrointestinal digestion

In this study, the influences of pumpkin flour additions to breadmaking on evolutions of microstructure, rheology and starch hydrolysis during simulated gastrointestinal digestion were investigated. Compared to white bread (PB₀), the bread supplemented with 20% pumpkin flour (PB₂₀) showed more continuous and fibrous gel network structure with most starch granules encapsulated in the network throughout the in vitro digestion. Due to the dilution of digestive fluids and enzymatic hydrolysis, the digesta moduli and viscosity remarkably decreased as time progressed, but PB₂₀ presented significantly higher rheology compared to PB₀ in each digestion phase. At the end of intestinal phase, the in vitro starch digestibility was 69.9% for PB₀, significantly higher than that for PB₂₀ (55.4%). This is presumably attributed to the abundant dietary fibre in pumpkin flour, contributing to the increased digesta viscosity and the formation of more compact and stable gel networks that would hinder the contact of starch granules with α-amylase. In addition, the pumpkin-added breads gave satisfactory results in terms of sensory acceptability. This study has suggested promising potential of incorporating pumpkin flour in the production of functional bakery products with reduced starch digestibility while maintaining good sensory characteristics.     

Optimisation of porous starch preparation by ultrasonic pretreatment followed by enzymatic hydrolysis

Porous starch granules were formed by the partial hydrolysis of starch using amylase. Fungal amylase and corn starch were chosen as the original amylase and substance from different sources, respectively. Ultrasonic technique as an assistant of enzymatic hydrolysis was used to pretreat raw starch. Scanning electron microscopy was used to examine the structure of native and treated starch, revealing the size of the pores in each occasion. The extent of enzymatic hydrolysis (y%) was markedly enhanced by statistical optimisation of enzymatic conditions. A significant influence of amount, temperature and pH of enzyme has been noted with Plackett–Burman design. It was then revealed with response surface methodology (RSM) that 503.26 U (g substance)^?1 amount of enzyme, temperature of 55 °C and pH of 5.1 were optimum. This optimisation strategy led to the enhancement of y% from 53.4% to 61.38%.     

Digestibility of common native starches with reference to starch granule size,shape and surface features towards guidelines for starch-containing food products

Influence of diverse botanical sources (wheat, maize, waxy maize, cassava, potato, rice or waxy rice) on in vitro native starch digestibility has been investigated. Physicochemical properties (chemical composition, particles size and shape, surface features) of starch granules were determined with a view to explaining digestibility differences between samples. Rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) contents were measured according to Englyst method. Potato starch was shown to be composed of large rounded granules having smooth surfaces, which explains its slow enzymatic breakdown. Potato starch displayed the highest RS (86%) content and the lowest RDS content (9.9%). Since RS positively influences health and SDS may result in cell, tissue and/or organ damages, potato starch is an ideal starch nutrient. Conversely, waxy rice starch was rich in amylopectin and displayed small diameters and angular shapes, which are both known to facilitate enzymatic starch hydrolysis. It exhibited a near-zero RS content (0.9%) and a high RDS fraction (60%). According to this study, potato starch exhibited the best nutrient profile, followed up in this order by cassava, waxy maize, wheat, maize and waxy rice starches.     

Impacts of acid-methanol treatment and annealing on the enzymatic resistance of corn starches

Normal corn, Hylon V and Hylon VII starches were acid-methanol-treated at 25 °C for 1–30 days in methanol containing 0.36% HCl, and then annealing at 50 °C for 72 h in excess water. The rapid digestible starch (RDS), slow digestible starch (SDS) and resistant starch (RS) contents of starch before and after treatments were determined. The molecular structure, thermal properties, double helix content and relative crystallinity of starch were observed for elucidating the impacts of acid-methanol treatment and annealing, as well as the molecular structure, on the enzymatic resistance of starch. Results showed that the weight-average degree of polymerization of acid-methanol-treated corn starches ranged from 884 × 10³ to 404, 778 × 10³ to 299 and 337 × 10³ to 250 anhydrous glucose units for normal corn, Hylon V and Hylon VII starches, respectively. Annealing increased the RS content of starch, and the increment of RS increased with decreasing molecular size of starch. Furthermore, the change in RS content after treatments depended on the content and weight-average chain length of amylose fraction of starch. The RS content of starch after treatments increased from 19.2 to 56.2%, 69.9 to 86.1%, and 73.1 to 89.1% for normal corn, Hylon V and Hylon VII starches, respectively. The gelatinization peak temperature and double helix content of starch increased after acid-methanol treatment or annealing. Results demonstrate that the degradation of starch, causing by acid-methanol treatment, enhances the mobility and realignment of starch chains in molecules during treatments and further increases the enzymatic resistance of starch granules.     

湿热及酶解处理对糯米粉体外消化特性和血糖生成指数的影响

目的 研究酶解处理、湿热处理和湿热复合酶解处理对糯米粉体外消化特性和血糖生成指数(glycemic index, GI)的影响。方法 采用体外消化法测定了不同处理糯米粉的水解度和血糖生成指数值, 并通过X-射线衍射和激光共焦拉曼光谱实验测定了不同处理糯米的淀粉晶体结构。结果 3种处理的水解度和抗性淀粉(resistant starch, RS)相对含量增加, 慢消化淀粉(slowly digestible starch, SDS)相对含量降低; 其中湿热复合酶解处理条件下, RS相对含量最高, 为71.31%; 酶解处理条件下, RS相对含量最低, 为67.66%。酶解处理、湿热处理和湿热复合酶解处理的GI值分别为79.1、76.0和70.6。3种处理后糯米淀粉的晶体结构发生改变, 3种处理均使分子短程有序度与结晶度增加, 其中湿热复合酶解处理条件下, 结晶度最高, 为34.41%。 结论 湿热复合酶解处理后的糯米粉抗消化特性增强且GI值降低, 湿热复合酶解工艺可能通过影响糯米粉的体外消化率来降低GI值。     

In vitro digestibility and physicochemical properties of Arenga pinnata starch-chitosan following heat-moisture treatment

In vitro digestibility and physicochemical properties of chitosan (CS)-modified Arenga pinnata starch (APS) after heat-moisture treatment (HMT) were evaluated. HMT would limit the enzymatic hydrolysis of APS and the digestion rate of HMT-APS-CS was further reduced with the decrease of CS molecular weight. CS and HMT inhibited the solubility (SOL) and swelling power (SP) of APS, and the inhibition effect was more obvious with the decrease in CS molecular weight. Changes in the pasting properties of the CS-modified APS indicated that the initial structure of the APS granules was destroyed with the formation of a denser structure. The increase of the relative crystallinity and the aggregation of the APS granules were related to starch cross-linking confirmed by Fourier transform infrared. The interactions between CS and APS granules after HMT greatly altered granular morphology and internal structure of APS. Therefore, the improvements of SDS and RS of HMT-APS-CS were mainly related to CS covering the surface of the APS granules, granule aggregation and HMT-induced changes in the internal structure of the starch granule.     

Physicochemical,structural, and digestibility properties of enzymatic modified plantain and mango starches

The effect of two enzymatic treatments (increasing the branch density of starch and shortening of AP and amylose chains) on the fraction of slowly digestible starch (SDS) and resistant starch (RS) of plantain (Musa paradisiaca L.) and mango (Mangifera indica L.) starches was investigated. The enzymatic modifications were carried out using β‐amylase (β‐AMY) and β‐amylase‐transglucosidase (β‐AMY‐TGs), in gelatinized starches. Plantain starch showed an increase from 10.9 to 18.5% of SDS, when it was modified by β‐AMY‐TGs, while the treatment with β‐AMY alone showed reduction from 10.9 to 7.1% in SDS. RS content increased with both treatments. On the other hand, mango starch showed an increase in SDS from 6.3 to 22.3% using β‐AMY treatment and from 6.3 to 11.7% using β‐AMY‐TGs treatment. The latter treatment also increased RS content. The enzyme modified starches showed a reduction in the values of molar mass and gyration radius compared with the native starch. The content of short chains of AP, particularly in the DP range 5–12, increased, the percentage of crystallinity decreased in treated starches, and ¹H NMR spectra showed a significant increase of α‐(1 → 6) linkages in the starches modified with β‐AMY‐TGs. These characteristics were related to an increase in the slow and resistant digestion properties of plantain and mango starches.     

Preparation of products rich in slowly digestible starch (SDS) from rice starch by a dual-retrogradation treatment

In this work, a dual-retrogradation treatment (gelatinization–retrogradation–gelatinization–retrogradation) was designed for preparing slowly digestible starch (SDS) products from rice starch. The results showed that a maximum SDS yield in the tested samples increased from 39.3% to 56.7% by the dual retrogradation with the time interval of 36 h. The dual retrogradation also seemed to increase with the melting temperature range (T_c–T_o) of the SDS products. This increase indicated that more imperfect crystallites were formed during the dual-retrogradation treatment. Furthermore, compared to the single retrogradation, the dual retrogradation generated larger cavities and more solid connection parts in the SDS products. This internal microstructure could result in the increase of slow digestibility. These findings suggest that the dual retrogradation can be used in starchy products to increase the yield of SDS.