Long-term retrogradation properties of rice starch modified with transglucosidase

Insight to starch retrogradation through fine structure models: A review

The retrogradation of starch is crucial for the texture and nutritional value of starchy foods products. There is mounting evidence highlighting the significant impact of starch's fine structures on starch retrogradation. Because of the complexity of starch fine structure, it is a formidable challenge to study the structure-property relationship of starch retrogradation. Several models have been proposed over the years to facilitate understanding of starch structure. In this review, from the perspective of starch models, the intricate structure-property relationship is sorted into the correlation between different types of structural parameters and starch retrogradation performance. Amylopectin B chains with DP 24-36 and DP ≥36 exhibit a higher tendency to form ordered crystalline structures, which promotes starch retrogradation. The chains with DP 6-12 mainly inhibit starch retrogradation. Based on the building block backbone model, a longer inter-block chain length (IB-CL) enhances the realignment and reordering of starch. The mathematical parameterization model reveals a positive correlation between amylopectin medium chains, amylose short chains, and amylose long chains with starch retrogradation. The review is structured according to starch models; this contributes to a clear and comprehensive elucidation of the structure-property relationship, thereby providing valuable references for the selection and utilization of starch.

Two-step modification of pullulanase and transglucosidase: A novel way to improve the gel strength and reduce the digestibility of rice starch

The multiscale structure, gel strength and digestibility of rice starch modified by the two-step modification of pullulanase (PUL) pretreatment and transglucosidase (TG) treatment for 6, 12, 18 and 24 h were investigated. The debranching hydrolysis of PUL produced some linear chains, which rearranged to form stable crystalline structures, reducing the digestible starch content, but weakening the gel strength. TG treatment connected some short chains to longer linear chains via α-1,6-glycosidic bonds, generating the structures of linear chain with fewer branches. The short branches promoted the interaction between starch molecules to form a more compact three-dimensional gel network structure, showing higher hardness and springiness. Moreover, these chains could form more stable crystals, reducing the digestible starch content, and the increase of branching degree inhibited digestive enzyme hydrolysis, reducing the digestion rate. The multiscale structure of starch tended to stabilize after TG treatment for 18 h, which could form a gel with stronger strength and lower digestibility than native starch gel. Therefore, the two-step modification of PUL and TG was an effective way to change the structure of rice starch to improve the gel strength and reduce the digestibility.

Synergistic effect of enzymatic pre-treatment and amylose-lipid complex construction on the physicochemical properties of maize starch

In this study, the effects of maltogenic amylase (MAA) pre-treatment and starch-fatty acid complex construction on the physicochemical properties of maize starch (MAS) were investigated. The average chain length of MAA-modified MAS was found to decrease from 18.15 to 14.92. Moreover, MAA pre-treatment of starch induced the formation of a V-type complex. This behaviour was demonstrated by the higher diffraction intensity, enzymatic resistance and short-range ordering of the samples pre-treated with MAA compared with unmodified samples. X-ray diffraction and rheological analysis revealed that the re-crystallisation peak intensities and storage modulus of MAA-MAS-lauric acid (LA)/stearic acid (SA) complexes were lower than those of MAA-starches, MAS-LA/SA complexes and control. The rate of starch re-crystallisation was effectively decreased by the combination of MAA pre-treatment and V-type complex construction. The anti-retrogradation (long-term) characteristics of the tested samples were in the following order: MAA-MAS-LA/SA complexes > MAA-starches > MAS-LA/SA complexes > control.

Designing a Specific Pretreatment on Corn Starch to Facilitate Enzymatic Rearrangement of Glycosidic Bonds for Efficiently Reducing Starch Digestibility

Bacterial 1,4-α-glucan branching enzymes (GBEs) provide a viable strategy for glycosidic bond rearrangement in starch and regulation of its digestion rate. However, the exponential increase in paste viscosity during starch gelatinization has a detrimental effect on the catalytic action of GBEs, thereby limiting productivity and product performance. Here, we designed an enzymatic treatment on corn starch granules by the GBE from Rhodothermus obamensis STB05 (Ro-GBE) prior to the glycosidic bond rearrangement of gelatinized starch catalyzed using the GBE from Geobacillus thermoglucosidans STB02 (Gt-GBE). Specifically, a moderate amount of Ro-GBE was required for the pretreatment stage. The dual GBE modification process enabled the treatment of more concentrated starch slurry (up to 20%, w/w) and effectively reduced starch digestibility. The resulting product contained a rapidly digestible starch fraction of 66.0%, which was 11.4% lower than that observed in the single Gt-GBE-modified product. The mechanistic investigation showed that the Ro-GBE treatment promoted swelling and gelatinization of starch granules, reduced starch paste viscosity, and increased the mobility of water molecules in the starch paste. It also created a preferable substrate for Gt-GBE. These changes improved the transglycosylation efficiency of Gt-GBE. These findings provide useful guidance for designing an efficient process to regulate starch digestibility.

Unveiling the retrogradation mechanism of a novel high amylose content starch-Pouteria campechiana seed

The research of starch retrogradation have been attracting interest. Thereby, the long-term retrogradation mechanism (0-21 days) of Pouteria campechiana seed starch (PCSS) was investigated. The results showed that crystal type was changed from A- to B + V-type during retrogradation. The retrogradation PCSS (RPCSS) exhibited faster retrogradation rate and more compact internal ultra-structure compared to rice, wheat and maize starch. Pearson correlation indicated that, as retrogradation days increased, values of α-1,4-glycosidic bond, A chains, double helix, V-type polymorphism, Mw, relative crystallinity (Rc) and short-range order gradually significantly increased, and B1 chains, B3 + chains values gradually significantly dropped (p < 0.05). These inferred an increasing peak temperature and compactness of morphology with increasing retrogradation days. Compared to native starch, RPCSS α-1.4-glycosidic bond was increased, which indicated that its quick molecules degradation including decreased Mw, B3 + chains, Rc, semicrystalline order, and ΔH. These might provide a theoretical direction for preparation of starch-basis food.

Pulsed electric field-assisted esterification improves the freeze-thaw stability of corn starch gel by changing its molecular structure

The influence of pulsed electric field (PEF) combined with octenyl succinic anhydride (OSA) on the freeze-thaw stability of corn starch gel was investigated. After five freeze-thaw cycles, the syneresis value of OSA starch treated with PEF-assisted esterification for 15 min was lower by 29.5 %, while that of OSA starch without PEF treatment was lower by 10.17 %, compared to that of native starch. Low-field nuclear magnetic resonance data showed that the introduction of OSA groups greatly increased the water-holding capacity of starch. Results from differential scanning calorimetry (DSC) and X-ray diffraction (XRD) showed that the PEF-assisted esterification markedly hindered the re-formation of the helical structure of starch during freeze-thaw cycles. Moreover, PEF-assisted esterification improved the viscoelastic properties of the starch gel. It is found that the freeze-thaw stability of the PEF-modified starch depends not only on the degree of substitution but also on the starch molecular fine structure. PEF-assisted OSA starch with a high degree of substitution, a low content of amylose, and a high content of short amylopectin chains were found to have high freeze-thaw stability. This study shows that PEF-assisted esterification is a promising technique that should be used for preserving the quality of frozen foods.

Effect of modification by maltogenic amylase and branching enzyme on the structural and physicochemical properties of sweet potato starch

Sweet potato starch (SPSt) was treated sequentially with the combination of maltogenic amylase (MA) and branching enzyme (BE) (MA → BE) or BE and MA (BE→MA) to modify its structural and physicochemical properties. Following the MA → BE and BE→MA modifications, the degree of branching was increased from 12.02 % to 44.06 %; whereas, the average chain length decreased from 18.02 to 12.32. Fourier-transform infrared spectroscopy and digestive performance analysis indicated that the modifications reduced hydrogen bonds and increased resistant starch in SPSt. Rheological analysis revealed that the storage and loss moduli of the modified samples were lower than those of the control samples, except for starch treated with MA alone. X-ray diffraction measurements suggested that the re-crystallisation peak intensities of the enzyme-modified starches were lower than those of the untreated sample. The retrogradation resistance ability of the analysed samples followed the order: BE→MA-starches > MA → BE-starches > untreated starch. The relationship between the crystallisation rate constant and short branched chains (DP_6-9) was well described by linear regression. This study provides a theoretical foundation for retarding the retrogradation of starch, which can improve food quality and extend the shelf-life of enzymatically modified starchy foods.

Structural, physicochemical and digestive properties of rice starch modified by preheating and pullulanase treatments

The structural, physicochemical and digestive properties of rice starch modified by the combination of different temperature (60, 70, 80, 90 and 100 °C) preheating and pullulanase (PUL60, PUL70, PUL80, PUL90 and PUL100) treatments were investigated. The PUL60 treatment mainly modified the surface layer of starch granules, which increased the amylose content and damaged some ordered structures, resulting in slight decreases of gel strength and estimated glycemic index (eGI). With the increase of preheating temperature, PUL could act on more enzymatic sites to release a large amount of linear chains, reduce the ordered degree, and transform the A-type crystalline structure into B-type. The low molecule interaction strength between linear chains weakened the gel network structure, and some stable crystal structures formed by longer chains resisted the enzyme digestion. The gel strength and eGI value of PUL70 starch decreased significantly, and the properties of PUL80-100 starches tended to be stable, showing a further significant decrease of gel strength and a slight reduction of eGI value. Therefore, the preheating treatments at 60, 70 and 80 °C were suitable for the PUL modification of rice starch to obtain strong, medium and weak gel strength respectively, and the digestibility decreased with increasing preheating temperature.

The relationship between molecular structure and film-forming properties of thermoplastic starches from different botanical sources

To illustrate the correlations between molecular structures and the film-forming properties of thermoplastic starch from various botanical sources, starches from cereal, tuber and legume were modified by thermoplastic extrusion and the corresponding thermoplastic starch films were prepared including thermoplastic corn starch (TCS), thermoplastic rice starch (TRS), thermoplastic sweet potato starch (TSPS), thermoplastic cassava starch (TCAS) and thermoplastic pea starch (TPES) films. TPES film displayed a higher tensile strength (6.28 MPa) and stronger water resistance, such as lower water solubility (15.70 %), water absorption (42.35 %), and water vapor permeability (0.285 g·mm·h-1·m-2·kPa-1) due to higher contents of amylose and B1 chains. TCAS showed a smoother and more amorphous film due to higher amylopectin content, resulting higher elongation at break and larger opacity. TCS film was the most transparent due to a compacter network and more ordered crystallinity structure, which was suit for the packaging of fresh vegetables and aquatic products, whereas TCAS film was the opaquest, which protected package foods from light such as meat products, etc. The outcome would provide an innovative theory to regulate accurately the functional properties of thermoplastic starch films for different food needs.

Self-healing properties of retrograded starch films with enzyme-treated waxy maize starch as healing agent

Waxy maize starch (WMS) was modified using sequential α-amylase and transglucosidase to create enzyme-treated waxy maize starch (EWMS) with higher branching degree and lower viscosity as an ideal healing agent. Self-healing properties of retrograded starch films with microcapsules containing WMS (WMC) and EWMS (EWMC) were investigated. The results indicated that EWMS-16 had the maximum branching degree of 21.88 % after transglucosidase treatment time of 16 h, and A chain of 12.89 %, B1 chain of 60.76 %, B2 chain of 18.82 % and B3 chain of 7.52 %. The particle sizes of EWMC ranged from 2.754 to 5.754 μm. The embedding rate of EWMC was 50.08 %. Compared to retrograded starch films with WMC, water vapor transmission coefficients of retrograded starch films with EWMC were lower, while tensile strength and elongation at break values of retrograded starch films were almost similar. Retrograded starch films with EWMC had higher healing efficiency of 58.33 % as compared to that Retrograded starch films retrograded starch films with WMC was 44.65 %.

The relationship between linear chain length distributions of amylopectin and the functional properties of the debranched starch-based films

The relationship between linear chain length distributions and the functional properties of the starch-based films after pullulanase debranching treatment of corn (CS), rice (RS) and wheat (WS) were investigated. The results indicated that the film thickness was negatively correlated with A chains content (r = -0.939) and apparent amylose content (r = -0.926), and was positively correlated with B3 chains content (r = 0.847). The tensile strength of the debranched starch-based films were positively correlated with apparent amylose content (r = 0.813), and the elongation at break were inversely proportional to B3 chains content (r = -0.817). The hydrophobicity of the starch-based films was positively and negatively correlated with the proportions of linear chains with DP 6-12 (r = 0.892) and DP 25-36 (r = -0.863), respectively. On the contrary, no significant correlation was noticed between chain length distribution of amylopectin and transparency and thermal stability.