Some Studies on Starch Gelation

Investigating the effect of natural fermentation in modifying the physico-functional, structural and thermal characteristics of pearl and finger millet starch

BACKGROUND

In recent years, millets are often considered an emerging crop for sustainable agriculture. Therefore, millets can be exploited as an alternative source of starch which has many applications ranging from food, packaging, bioplastics, and others. However, starch is seldom used in its native form and is more often modified to enhance its functional properties. In literature, many traditional millet-based food recipes often incorporate a fermentation step before cooking. Therefore, using this traditional knowledge fermentation has been explored as a potential method for modifying millet starch.

RESULTS

Pearl millet (PM) and finger millet (FM) flour were allowed to naturally ferment for 24 h followed by starch extraction. Compared to native (N) starch, water/oil holding capacity and least gelation concentration of fermented (F) starch decreased with no significant change in swelling power. The solubility, paste clarity and in vitro digestibility of starch were significantly affected by fermentation. X-ray diffraction (XRD) data indicates that after fermentation, crystallinity increased while the A-type crystalline structure remained intact. Fourier-transform infrared (FTIR) spectra showed no deletion or addition of any new functional groups. Thermal characterization by differential scanning calorimetry (DSC) showed that the enthalpy of gelatinization of PM starch decreased while that of FM starch increased after fermentation.

CONCLUSION

The results indicate that 24 h natural fermentation had a significant impact on functional properties of starch without altering the structural architecture of starch granules. Therefore, fermentation can be further explored as a low-cost alternative for starch modification. © 2023 Society of Chemical Industry.

Development of Novel Cornstarch Hydrogel-Based Food Coolant and its Characterization

The food, pharmaceutical, and supply transport storage chain is seeking coolants that come with plastic-free packaging, are nontoxic, environmentally friendly, robust, reusable, and reduce water waste. To meet this demand, a new food coolant based on cornstarch hydrogel was developed and tested using the regeneration method. This study investigated the reusability, water retention, rehydration, and surface cleanliness of the hydrogel, along with its application in freshness retention for fruits. The results of the gel strength and differential scanning calorimetry (DSC) analysis showed that the ideal concentration of cornstarch hydrogel was 8%. Freezing and thawing experiments demonstrated that the hydrogel had the potential to be used as a cooling medium for refrigerated fresh foods. Moreover, the gel strength, scanning electron microscopy images (SEM), DSC, and thermogravimetric analysis (TG) revealed that the freeze-thaw reuse only slightly affected its freezable water content and that its gel strength gradually increased during reuse. Water retention and rehydration tests showed that the hydrogels could be better preserved at -20 °C compared to 4 °C, and the water lost during reuse could be replenished through rehydration. The flexibility in terms of shape and size also allows the hydrogel ice to be used as a customized coolant for various food shapes, as demonstrated by preservation experiments. Additionally, washing the hydrogel after each use can result in a significant reduction in Escherichia coli, Salmonella, and Staphylococcus aureus concentrations by 3.03, 3.47, and 2.77 log CFU/hydrogel, respectively. Overall, the new cornstarch hydrogel coolant is a promising alternative to conventional ice, with the potential to serve as a food coolant.

Effect of steam explosion on nutritional components, physicochemical and rheological properties of brown rice powder

Brown rice powder is underutilized mainly due to its lower starch digestibility and poor processing performance. The present study investigated the potential of steam explosion on the improvement of nutritional and physicochemical characteristic in brown rice powder and rheological property of paste. Compared with native brown rice powder, steam explosion at 0.5 MPa for 7 min increased the water-extractable arabinoxylans (5.77%), reducing sugar content (21.04%), and iodine blue value (30.38%), which indicated steam explosion that destroyed the intact cells of brown rice. Later the crystalline structure of brown rice powder was destroyed into an amorphous structure by steam explosion. Steam explosion enhanced the degree of gelatinization (4.76~351.85%) and solvent retention capacity (SRC) of brown rice powder, compared with native sample. The effect on the intact cells and starch structure of brown rice caused the starch digestibility enhancement remarkable. Viscoelastic profiles confirmed that steam explosion weakened the paste strength and elasticity corresponded with hardness and cohesiveness by increasing the loss factor (tanδ). This work provided important information for brown rice powder modified by steam explosion (0.5 MPa, 7 min) with good nutritional property (nutrients and digestibility) and processability (SRC, textural, and rheological property). Steam exploded brown rice powder (0.5 MPa, 7 min) could serve as a potential ingredient widely used in food products.

Processing, digestion property and structure characterization of slowly digestible gorgon nut starch

Slowly digestible gorgon nut starch (GN-SDS) was prepared by heating-cooling treatment (HCT), meanwhile its morphological and structural features were characterized in detail by SEM, DSC, XRD and IR detection. The optimized parameters of GN-SDS processing were as following: starch milk (20%) was heated at 100 °C for 20 min, and then cooled under 4 °C for 24 h. Under the optimized parameters, the SDS content increased from 20.49 to 61.74%. GN-SDS showed typical SDS characteristics in in vivo digestion with a low postprandial blood glucose. SEM images suggested that GN-S particles changed from uniform regular polyhedron with smooth surface to irregular gravel-like particles with coarse surface and obvious layered structure inside after HCT. The results of SEM, DSC, XRD and IR determination indicated that HCT changed the granule morphology, interior structure, gelatinization temperature and crystal type (A to B-type) of GN-S, and therefore made it hard to be digested accordingly.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10068-021-01007-6.

Effect of starch concentration and resistant starch filler addition on the physical properties of starch hydrogels

Corn starch-based hydrogels are safe and biodegradable polymers with a wide array of applications in food science. The aim of this study was to investigate the effects of starch and natural filler resistant starch type 2 (RS2) particles concentration on the textural properties of corn starch hydrogels. Native starch (NS) hydrogels of 8%, 10%, 12%, and 15% w/v were prepared; in each of these dispersions, part of the NS was substituted with RS2 to a concentration of 2% or 10%. NS hydrogels with the highest concentrations had the maximum hardness, cohesiveness, and gumminess values, whereas the addition of RS2 particles did not affect gel textural properties. Native and substituted RS2 hydrogels showed close similarities in their rheological and textural characteristics. Water-holding capacity greatly decreased with increasing starch concentration, suggesting that the hydrogels with the highest NS concentration had the densest network as depicted by SEM micrographs. Subsequently, hardness, gumminess, and consistency coefficient were linearly correlated to starch concentration and storage time. Fluid release was exponentially dependent on starch concentration. The degree of crystallinity by X-ray diffraction (XRD) indicated that by increasing starch concentration and substitution level, crystallinity increased. Consequently, NS concentration determined the textural properties of corn starch hydrogels. On the other hand, RS2 substitutions did not affect any of these parameters, indicating their potential role as inactive fillers with a beneficial effect on the maintenance of normal blood glucose levels. Therefore, the consistency of a food gel can be optimized by changing the ratio of inactive filler to starch gel matrix.

Insights into the relationship between structure and rheological properties of starch gels in hot-extrusion 3D printing

This work investigated the relationship between structure, rheological properties and 3D printability of starch. For this purpose, the structural evolution of various starch gels at different concentrations and printing temperatures was systematically studied. The mechanical strength (G', τ_y) and extrudability (τ_f) of CS and RS gels were used to determine its 3D printability. Furthermore, G', τ_y and τ_f were closely related to the structure of starch and starch gel network. Ascribing to compact and stable gel network, CS samples with 20% concentration at 70-75 °C printing temperature and RS samples with 15-20% concentration at 75-80 °C printing temperature displayed preferable printing values (G', τ_y and τ_f), indicating the suitability for HE-3DP. RS samples exhibited higher mechanical strength than CS samples and were more suitable to print owing to the formation of new crystal structure. Overall, this work provided important information for HE-3DP based foods with good printability.

Effect of Initial Conformation on the Starch Biopolymer Film Formation Studied by NMR

The formation of a rigid porous biopolymer scaffold from aqueous samples of 1% w/v (suspension) and 5% w/v (gel) corn starch was studied using optical and nuclear magnetic resonance (NMR) techniques. The drying process of these systems was observed using a single-sided NMR scanner by application of the Carr-Purcell-Meiboom-Gill pulse sequence at different layer positions. The echo decays were analyzed and spin-spin relaxation times (T₂) were obtained for each layer. From the depth dependent T₂ relaxation time study, it was found that the molecular mobility of water within the forming porous matrix of these two samples varied notably at different stages of film formation. At an intermediate stage, a gradual decrease in mobility of the emulsion sample towards the air-sample interface was observed, while the gel sample remained homogeneous all along the sample height. At a later stage of drying, heterogeneity in the molecular dynamics was observed in both samples showing low mobility at the bottom part of the sample. A wide-angle X-ray diffraction study confirmed that the structural heterogeneity persisted in the final film obtained from the 5% corn starch aqueous sample, whereas the film obtained from the 1% corn starch in water was structurally homogeneous.

Influence of Fiber Addition on White Sauces Made with Corn Starch: Effect on Their Freezing/Thawing Stability

Fiber-enriched white sauces with apple (AF401), potato (KF200), and microcrystalline cellulose (MCC) were selected among six white sauces, all of them elaborated by replacing corn starch and milk with 3% of different dietary fibers. It was investigated the freezing/thawing (F/T) stability of these three enriched white sauces studying their physico-chemical (color, syneresis percentage, total soluble solids content), rheological (viscoelastic and steady measurements), and sensorial properties before and after a freezing/thawing treatment. White sauce with MCC resulted in being the most like the control (without fiber) showing a higher elasticity and a heat stability. Moreover, the sauce elaborated with MCC has a sensorial profile as a traditional corn starch sauce with high "creaminess" and lower "heterogeneity" after the F/T treatment. Therefore, the properties provided by MCC make this product interesting in food design, and MCC sauce could be used as an industrial frozen fiber-enriched white sauce. PRACTICAL APPLICATION: These days, there is an increase in the demand of precooked frozen dishes due to current lifestyles and because the use of fiber exhibits many proven health benefits. A béchamel sauce made from corn starch and enriched with different fibers was elaborated, frozen and thawed in microwave. Both fresh and frozen/thawed microcrystalline cellulose (MCC) sauces exhibited very similar rheological and sensorial properties to an industrial and traditional frozen white sauce without fiber. Therefore, MCC-enriched white sauce resulted to be a feasible strategy to produce a white sauce suitable for frozen dishes with good functional properties and sensorial quality.

Determination of thermal transitions of gluten-free chestnut flour doughs enriched with brown seaweed powders and antioxidant properties of baked cookies

A protocol for determining the characteristic temperatures of thermomechanical transitions on gluten-free flour doughs is proposed. This protocol is based on the mathematical analysis of experimental curve of storage modulus (G′) vs temperature obtained by means of Dynamic Mechanical Thermal Analysis (DMTA) technique. Doughs at constant consistency of chestnut flour with different levels (3, 6 and 9% flour basis, f.b.) of brown seaweed (Bifurcaria bifurcata, Fucus vesiculosus and Ascophyllum nodosum) powders addition, 2% f.b. of guar gum and 1.8% f.b. of salt with different water absorption were used to test the proposed protocol. The ranges of temperatures corresponding to starch gelatinization (59–97 °C), amylopectin crystallites melting (82–101 °C), reversible dissociation of lipid-amylose complexes (107–128 °C) and amylose melting (133–171 °C) showed a strong dependence with water absorption of samples. Doughs with the same water absorption submitted to starch gelatinization during mixing were also analysed to corroborate the protocol suitability. Total polyphenols content and radical scavenging activity of extracts from chestnut flour-seaweed powder blends and seaweed-enriched chestnut cookies baked at 180 °C were determined. Extraction assisted with ultrasounds was carried out employing acetone-water (70:30 v/v) solution as solvent during 4 min with a liquid/solid ratio of 30 w/w. Seaweed powder addition had a positive effect on antioxidant properties of doughs before baking. However, the seaweed powder addition effect on baked products (cookies) is not clear due to antioxidant activity is overlapped by Maillard's products generated during baking.

Characteristics of pea, lentil and faba bean starches isolated from air-classified flours in comparison with commercial starches

This study aimed to isolate starches of a high purity from starch-rich pea, lentil and faba bean flours and to characterize and compare the isolated starches with important commercial starches. Isolated pulse starches had a purity of 94.8-97.9% and contained only 0.9-1.1% damaged starch. The isolated pulse starches showed amylose contents and amylopectin branch-chain-length distributions similar to those of commercial pea starch. Therefore, the granular morphologies, crystalline structure, thermal properties, pasting properties, gelling ability and in vitro digestibility of the isolated pulse starches were comparable to those of commercial pea starch but different from those of commercial maize and tapioca starches. The desirable functionality of the pulse starches (e.g., strong gelling ability) renders them suitable for some specific industrial applications, and further modifications can be utilized to enhance their functionality for broader use. This research provided the fundamental knowledge required for future efforts to promote value-added utilization of pulse starches.

Settling volume and morphology changes in cross-linked and unmodified starches from wheat, waxy wheat, and waxy maize in relation to their pasting properties

Normal wheat, waxy wheat and waxy maize starches were cross-linked with 0.01, 0.03 and 0.06% (sb) phosphorus oxychloride. The objective of this study was to correlate the morphology changes and settling volume to the pasting properties of those cross-linked and unmodified starches. Pasting and microscopic data for waxy maize starch and its cross-linked products was similar to waxy wheat starch, except changes occurred at ∼5 °C higher in temperature. At 6% solids, waxy wheat starch cross-linked with 0.01% POCl₃ had a greater settling volume and a higher pasting viscosity than the cross-linked waxy maize starch, but at 7 and 8% solids, waxy maize starch cross-linked with 0.03% and 0.06% POCl₃ had a higher pasting viscosity. At 6% starch solids, particle volume fraction appeared to be the dominant factor controlling consistency, but at higher starch solids contents, the deformability (rigidity) of swollen granules became important in controlling viscosity.

Pasting, rheological, and retrogradation properties of low-amylose rice starch with date syrup

Effects of date syrup on pasting, rheological, and retrogradation properties of low-amylose rice starch were investigated using three levels of date syrup (starch:syrup 1:1, 1:2, or 1:3). Measurements were carried out using HR-2 Discovery Rheometer equipped with a pasting cell and parallel plate geometry. The pasting measurements showed that the peak viscosity of the control is significantly higher than the samples with date syrup (p < 0.05), while the final viscosity increases with increased date syrup levels. Addition of date syrup increases the solid-like behavior of the gel in reverse order with increased date syrup levels. Low-amylose starch gel used in this study showed minor changes in elastic modulus (G') during one week cold storage indicting that low-amylose rice starch is resistant to retrogradation. Addition of date syrup slightly resulted in increased retrogradation compared to the control.

Polysaccharide based superabsorbent hydrogel from Mimosa pudica: swelling–deswelling and drug release

Polysaccharide based stimuli responsive, superporous and superabsorbent hydrogel for sustained drug release.

Polysaccharides based superabsorbent hydrogel from Linseed: Dynamic swelling, stimuli responsive on-off switching and drug release

Swelling properties of Linseed hydrogel (LSH) were studied in deionized water and different physiological pH values, i.e., 1.2, 6.8 and 7.4. Analysis of the kinetics drawn from swelling data has revealed that swelling of LSH followed second order kinetics. The results indicated that swelling of LSH is greatly affected by different concentration of salts. Stimuli responsive on-off switching of LSH was studied in water/normal saline, water/ethanol and basic/acidic environment and found reversible. LSH swells maximum in water and at pH 7.4 while deswells abruptly in ethanol and at pH 1.2. The elongated porous structures uniformly organized in layers were observed in FE-SEM. LSH was used as a sustained release material for tablet formulation of diclofenac sodium. Drug release study followed non-Fickian diffusion. LSH sustained the release of drug even better than a commercially available formulation of diclofenac sodium.