The structural characteristics of amylosucrase-treated waxy corn starch and relationship between its in vitro digestibility

Assessing Amylose Content with Iodine and Con A Methods, In Vivo Digestion Profile, and Thermal Properties of Amylosucrase-Treated Waxy Corn Starch

In this study, waxy corn starch was modified with 230 U or 460 U of amylosucrase (AS) from Neisseria polysaccharea (NP) to elongate the glucan. The amylose content of the AS-modified starches was determined using iodine and concanavalin A (Con A) methods, and their in vivo digestion, thermal, swelling, and pasting properties were evaluated. The amylose content of AS-treated starches was not significantly different (p > 0.05) when using the Con A method but was significantly higher than that of non-AS-treated samples when using the iodine method. In vivo, rats fed AS-treated starch had significantly lower blood glucose levels at 15 min than other rats; rats fed 460 U AS had lower blood glucose levels at 30 and 60 min than non-AS-treated rats. DSC analysis revealed that AS-treated starches exhibited higher initial, melting, and completion temperatures. Minimal volume expansion was observed by swelling factor analysis, while a Rapid Visco Analyzer assessment revealed that they had higher pasting onset temperatures, lower peak viscosities, and no trough viscosity compared to native starch. The elongated glucans in AS-treated starch reinforced their crystalline structure and increased slowly digestible and enzyme-resistant starch content. Overall, AS-treated starch showed unique thermal properties and a reduced blood glucose index upon administration. This distinctive characteristic of NPAS-treated starch makes it a good candidate food or non-food material for cosmetic products, medical materials, and adhesives.

Effects of maltogenic α-amylase on physicochemical properties and edible quality of rice cake

Maltogenic α-amylase (MA) are commercially used in the baking industry to retard starch retrogradation. However, whether MA can be used to modify rice flour during the fermentation process to improve the quality of rice flour remains unclear. In this study, MA was introduced during rice cake (RC) processing, and the modification effect and underlying mechanism were explored. Mn showed a decreasing trend except for 4.0 × 10-3 U/g sample. Chain length distribution data showed that MA effectively hydrolyzed long chains in amylopectin and increased the concentration of amylopectin chain length with a degree of polymerization of ≤ 9. High-performance liquid chromatography results suggested that the maltose content increased to 3.14% at an MA concentration of 9.5 × 10-3 U/g, which affected the fermentation effect of MA-treated RC. MA effectively reduced the viscosity of RC, and the gelatinization enthalpy of RC changed to 0.835 mJ/mg. MA also reduced the hardness and chewiness of RC after storage for 7 d. Moreover, rapidly digestible starch and slowly digestible starch contents of MA-treated RC decreased and increased, respectively, and resistant starch contents were remained unchanged. These results indicate that MA exerts a significant and effective antiretrogradation effect on RC. Combining the above results with sensory evaluation findings, an MA concentration of 4.0 × 10-3 U/g was the best supplemental concentration for obtaining RC with better edible quality. These findings suggest that MA treatment to rice flour during the fermentation process not only preserved the edible quality of RC but also retarded its retrogradation, thus, providing a novel processing method for the industrial production of RC.

Enhancing gel strength of Thermoproteus uzoniensis 4-α-glucanotransferase modified starch by amylosucrase treatment

4-α-glucanotransferase is used to produce thermoreversible starch gels to alleviate limitations to use of starch gels in repetitively heat-processed foods. However, the gel strength was weakened after this enzyme modification. In the present study, treatment by amylosucrase (NpAS) of corn starch and sucrose was applied to retain the gel thermoreversibility and eliminate the shortcoming caused by 4-α-glucanotransferase (TuαGT). Changes in molecular structure, rheological and retrogradation properties of modified starch were investigated after NpAS and TuαGT sequential and one-pot treatment, respectively. The apparent amylose content was reduced and increased by sequential and one-pot treatments, respectively, compared to single TuαGT modification. Chain length profiles showed higher proportion of degree of polymerization (DP) ≥ 13 by sequential treatment, whereas DP 6-12 was higher after one-pot treatment. All modified starches had reduced molecular weight. G' and G" increased by dual enzyme compared to single TuαGT treatment having little effect on retrogradation. Interestingly, starch subjected to 3 h one-pot treatment caused G' and G" temperature curves to cross-over, improving thermoreversible properties. The results indicate that NpAS treatment compensated for loss of starch gel strength caused by TuαGT and offered possibility to provide a wider range of thermoreversible starches.

New Techniques in Structural Tailoring of Starch Functionality

Inherent characteristics of native starches such as water insolubility, retrogradation and syneresis, and instability in harsh processing conditions (e.g., high temperature and shearing, low pH) limit their industrial applications. As starch properties mainly depend on starch composition and structure, structural tailoring of starch has been important for overcoming functional limitations and expanding starch applications in different fields. In this review, we first introduce the basics of starch structure, properties, and functionalities and then describe the interactions of starch with lipids, polysaccharides, and phenolics. After reviewing genetic, chemical, and enzymatic modifications of starch, we describe current progress in the areas of porous starch and starch-based nanoparticles. New techniques, such as using the CRISPR-Cas9 technique to tailor starch structures and using an emulsion-assisted approach in forming functional starch nanoparticles, are only feasible when they are established based on fundamental knowledge of starch. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Development changes in multi-scale structure and functional properties of waxy corn starch at different stages of kernel growth

Waxy corn starch is widely used in food and papermaking industries due to its unique properties. In this work, the structural and functional properties of starch isolated from waxy corn at different stages of kernel growth were investigated and their relationships were clarified. The results showed that with kernel growth, the surface of starch granules became smooth gradually, and the inner growth rings and the porous structure grew and became clear. Meanwhile, the weight-average molecular mass (M_w), root mean square radius (R_g), and average particle size increased while the amylose content decreased, which should account for the decreased pasting temperature (from 71.37 to 67.44 °C) and increased peak viscosity (1574.2 to 1883.1 cp) and breakdown value observed. Besides, the contents of slowly digestible starch (SDS) and resistant starch (RS) in waxy corn starch decreased significantly (from 44.01% to 40.88% and from 16.73% to 9.80%, respectively, p < 0.05) due to decreases in the double helix content, crystallinity, and structural order, and increases in the semi-crystalline lamellae thickness and the amorphous content. This research provides basic data for the rational utilization of waxy corn starch at different stages of kernel growth.

The Influence of Starch Modification with Amylosucrase Treatment on Morphological Features

Amylosucrase (AS) is a starch-modifying enzyme from Neisseria polysaccharea used to produce low-glycemic starches such as slowly digestible starch (SDS) and resistant starch (RS). The morphology of native, control, and AS-modified waxy corn starches (230 and 460 U) was examined using a particle size analyzer and field-emission scanning electron microscopy (FE-SEM). AS modification of the starch elongated the glucose and resulted in higher SDS and RS contents. The mean particle sizes of the control, 230 U-AS-, and 460 U-AS-treated starches were 56.6 µm, 128.0 µm, and 176.5 μm, respectively. The surface of the 460 U-AS-treated starch was entirely porous and coral-like, while the 230 U-AS-treated starch had a partial dense and flat surface which did not react with AS. FE-SEM of the granule cross section confirmed that the center contained a dense and flat region without any evidence of AS reaction to either of the AS-treated starches. It was assumed that the particle size and porous and sponge-like particle features might be related to the SDS and RS fractions.

Starch nanoparticles prepared by enzymatic hydrolysis and self-assembly of short-chain glucans

Enzymatic hydrolysis and self-assembly are considered promising methods for preparation of starch nanoparticles (SNPs) because they are environmentally friendly, and time- and cost-effective. These methods are based on the self-assembly of short-chain glucans released from the α-1,6 bonds in amylopectin. Since their discovery, many studies have described the structural and physicochemical properties of self-assembled SNPs. Self-assembled SNPs can be prepared by two methods: using only the soluble portion containing the short-chain glucans, or using the whole hydrolyzate including both insoluble and soluble fractions. Although the structural and physical properties of self-assembled SNPs can be attributed to the composition of the hydrolyzates that participate in self-assembly, this aspect has not yet been discussed. This review focuses on SNPs self-assembled with only soluble short-chain glucans and addresses their characteristics, including formation mechanisms as well as structural and physicochemical properties, compared with SNPs prepared with total hydrolyzates.

Enrichment of Polyglucosylated Isoflavones from Soybean Isoflavone Aglycones Using Optimized Amylosucrase Transglycosylation

Isoflavones in soybeans are well-known phytoestrogens. Soy isoflavones present in conjugated forms are converted to aglycone forms during processing and storage. Isoflavone aglycones (IFAs) of soybeans in human diets have poor solubility in water, resulting in low bioavailability and bioactivity. Enzyme-mediated glycosylation is an efficient and environmentally friendly way to modify the physicochemical properties of soy IFAs. In this study, we determined the optimal reaction conditions for Deinococcus geothermalis amylosucrase-mediated α-1,4 glycosylation of IFA-rich soybean extract to improve the bioaccessibility of IFAs. The conversion yields of soy IFAs were in decreasing order as follows: genistein > daidzein > glycitein. An enzyme quantity of 5 U and donor:acceptor ratios of 1000:1 (glycitein) and 400:1 (daidzein and genistein) resulted in high conversion yield (average 95.7%). These optimal reaction conditions for transglycosylation can be used to obtain transglycosylated IFA-rich functional ingredients from soybeans.

Comparison of the Structural Properties and Nutritional Fraction of Corn Starch Treated with Thermophilic GH13 and GH57 α-Glucan Branching Enzymes

Two thermophilic 1,4-α-glucan branching enzymes (GBEs), CbGBE from Caldicellulosiruptor bescii and PhGBE from Pyrococcus horikoshii, which belong to the glycoside hydrolase family 13 and 57 respectively, were cloned and expressed in Escherichia coli. Two GBEs were identified to have α-1,6 branching activity against various substrates, but substrate specificity was distinct. Starch was modified by two GBEs and their in vitro digestibility and structural properties were investigated. Short-branched A chains with a degree of polymerization (DP) of 6–12 increased with CbGBE-modified starch, increasing the proportion of slow digestible and resistant starch (RS) fractions. PhGBE-modified starch resulted in an increase in the RS fraction only by a slight increase in part of A chains (DP, 6–9). Compared to the proportion of control not treated with GBE, the proportion of α-1,6 linkages in CbGBE- and PhGBE-modified starch increased by 3.1 and 1.6 times. ¹³C cross polarization/magic angle sample spinning (CP/MAS) NMR and XRD pattern analysis described that GBE-modified starches reconstructed double helices but not the crystalline structure. Taken together, CbGBE and PhGBE showed distinct branching activities, resulting in different α-1,6 branching ratios and chain length distribution, and double helices amount of starch, ultimately affecting starch digestibility. Therefore, these GBEs can be used to produce customized starches with controlled digestion rates.

Amylosucrase as a transglucosylation tool: From molecular features to bioengineering applications

Amylosucrase (EC 2.4.1.4, ASase), an outstanding sucrose-utilizing transglucosylase in the glycoside hydrolase family 13, can produce glucans with only α-1,4 linkages. Generally, on account of a double-displacement mechanism, ASase can catalyze polymerization, isomerization, and hydrolysis reactions with sucrose as the sole substrate, and has transglycosylation capacity to attach glucose molecules from sucrose to extra glycosyl acceptors. Based on extensive enzymology research, this review presents the characteristics of various ASases, including their microbial metabolism, preparation, and enzymatic properties, and exhibits structure-based strategies in the improvement of activity, specificity, and thermostability. As a vital transglucosylation tool of producing sugars, carbohydrate-based bioactive compounds, and materials, the bioengineering applications of ASases are also systematically summarized.