Physico-chemical and functional properties of Resistant starch prepared from red kidney beans (Phaseolus vulgaris.L) starch by enzymatic method

Advancements in enhancing resistant starch type 3 (RS3) content in starchy food and its impact on gut microbiota: A review

Resistant starch type 3 (RS3), often found in cooked starchy food, has various health benefits due to its indigestible properties and physiological functions such as promoting the abundance of gut beneficial microbial flora and inhibiting the growth of intestinal pathogenic bacteria. However, it is challenging to develop starchy food with high RS3 content. This review aims to provide a detailed overview of current advancements to enhance RS3 content in starchy food and its effects of RS3 on gut microbiota. These approaches include breeding high-amylose cereals through gene editing techniques, processing, enzyme treatments, storage, formation of RS3 nanoparticles, and the incorporation of bioactive compounds. The mechanisms, specific conditions, advantages, and disadvantages associated with each approach and the potential effects of RS3 prepared by different methods on gut microbiota are summarized. In conclusion, this review contains important information that aims to provide guidelines for developing an efficient RS3 preparation process and promote the consumption of RS3-enriched starchy foods to improve overall health outcomes.

Synthesis and Functions of Resistant Starch

Resistant starch (RS) has become a popular topic of research in recent years. Most scholars believe that there are 5 types of RS. However, accumulating evidence indicates that in addition to starch-lipid complexes, which are the fifth type of RS, complexes containing starch and other substances can also be generated. The physicochemical properties and physiologic functions of these complexes are worth exploring. New physiologic functions of several original RSs are constantly being discovered. Research shows that RS can provide health improvements in many patients with chronic diseases, including diabetes and obesity, and even has potential benefits for kidney disease and colorectal cancer. Moreover, RS can alter the short-chain fatty acids and microorganisms in the gut, positively regulating the body's internal environment. Despite the increase in its market demand, RS production remains limited. Upscaling RS production is thus an urgent requirement. This paper provides detailed insights into the classification, synthesis, and efficacy of RS, serving as a starting point for the future development and applications of RS based on the current status quo.

Effects of Debranching Conditions and Annealing Treatment on the Formation of Starch Nanoparticles and Their Physicochemical Characteristics

Starch nanoparticles (SNPs) have unique attributes that make them suitable for specific applications. In this study, we assessed the optimum conditions for the fabrication of SNPs from the rice starches of low- (TCSG2) and medium-amylose rice lines (TK11) using pullulanase debranching combined with annealing treatment and evaluated their physicochemical and digestion properties. The highest crystalline SNP percent recoveries of 15.1 and 11.7% were obtained from TK11 and TCSG2, respectively, under the following debranching conditions: 540-630 NPUN/g, pH 5.0, 60 °C, and 12 h. The percent recovery of the crystalline SNPs by the combined modification of the debranching and the annealing treatment with an extended annealing incubation prepared from TK11 and TCSG2 was significantly increased to 25.7 and 23.8%, respectively. The modified starches from TK11 had better percent recovery of the crystalline SNPs than those from TCSG2. They exhibited a higher weight-average molecular weight (Mw) and a broader/bimodal molecular weight distribution with a higher polydispersity (PDI) (Mw = 92.76-92.69 kDa; PDI = 4.4) than those from TCSG2 (Mw = 7.13-7.15 kDa; PDI = 1.7). Compared to the native counterparts, the color analyses showed that the modified starches from TK11 and TCSG2 exhibited decreased brightness (L*)/whiteness index (WI) values with marked color difference values (∆E) ranging between 6.32 and 9.39 and 10.67 and 11.32, respectively, presumably due to the protein corona formed on the surface of SNPs which induced the browning reaction during the treatments. The pasting properties revealed that the modified starches displayed restricted swelling power with extremely low pasting viscosities, reflecting that they were highly thermally stable. The modified starches, especially those treated with an extended annealing incubation, exhibited marked decreases in the rate and extent of digestion and estimated glycemic index due to the honeycomb-like agglomerates comprising an assembly of densely packed SNPs. The results could provide helpful information for the preparation and characterization of the crystalline SNPs for potential applications such as emulsion stabilizers for Pickering emulsion and health-promoting ingredients.

Pullulanase: unleashing the power of enzyme with a promising future in the food industry

Pullulanases are the most important industrial group of enzymes in family 13 glycosyl hydrolases. They hydrolyze either α-1,6 and α-1,4 or both glycosidic bonds in pullulan as well as other carbohydrates to produce glucose, maltose, and maltotriose syrups, which have important uses in food and other related sectors. However, very less reports are available on pullulanase production from native strains because of low yield issues. In line with the increasing demands for pullulanase, it has become important to search for novel pullulanase-producing microorganisms with high yields. Moreover, high production costs and low yield are major limitations in the industrial production of pullulanase enzymes. The production cost of pullulanase by using the solid-state fermentation (SSF) process can be minimized by selecting agro-industrial waste. This review summarizes the types, sources, production strategies, and potential applications of pullulanase in different food and other related industries. Researchers should focus on fungal strains producing pullulanase for better yield and low production costs by using agro-waste. It will prove a better enzyme in different food processing industries and will surely reduce the cost of products.

Increase of resistant starch content by hydrolysis of potato amylopectin and its microstructural studies by 2D and 3D imaging

The effect of amylopullulanase treatment on recrystallization behaviour and the formation of resistant starch crystals have been investigated. Extracted potato starch (Solanum tuberosum) has been subjected to the enzymatic assisted bioprocessing without any physical or chemical treatment, where 120 min of incubation, 7 % (v/v) of enzyme and 8 mL/g of water content were found to be optimum to increase the resistant starch content by 41.88 %. The resistant starch crystals showed the characteristic behaviour of B-type allomorph with an increase in 21.32 % crystallinity. The modified crystals portrayed less reduction in actual weight when assessed by thermo-gravimetric analysis. The compact linear arrangement of the linear amylose chains within the crystallized granule of starch has been evidenced by Bright Field Microscopy. The microstructure of the resistant starch crystals showed 33.18 % reduction in porosity when the 3-dimensional structural form was analysed by X-ray micro-Computed Tomography.

Effect of Pullulanase Debranching Time Combined with Autoclaving on the Structural, Physicochemical Properties, and In Vitro Digestibility of Purple Sweet Potato Starch

The effects of pullulanase debranching combined with autoclaving (PDA) at various debranching times (0 h, 5 h, 10 h, 15 h, 20 h, and 25 h) and 121 °C/20 min of autoclave treatment on the structural and physicochemical characteristics of purple sweet potato (Jinshu No.17) starch were investigated. The results indicated that the native starch (NS) was polygonal, round, and bell-shaped with smooth surfaces. After debranching treatment, the surface of the starch samples became rough and irregular. The molecular weight became smaller after treatments. X-ray diffraction C-type pattern was transformed into a B-type structure in treated samples with increased relative crystallinity. ¹³C NMR indicated an increased propensity for double helix formation and new shift at C1, 3, 5 region compared to NS. The apparent amylose content was 21.53% in the NS. As the swelling power decreased, the percentage of soluble solids increased and different thermal properties were observed. A higher yield of the resistant starch (RS) was observed in all treated starch except PDA 25 h. The findings of our study reveal that a combination of pullulanase debranching time (15 h) and autoclaving (121 °C for 20 min) is a great technique that can be used to produce a higher amount of resistant starch in the Jinshu No.17 starch.

The effects of fermentation of Qu on the digestibility and structure of waxy maize starch

The fermentation of Qu (FQ) could efficiently produce enzymatically modified starch at a low cost. However, it is poorly understood that how FQ influences the waxy maize starch (WMS) structure and the digestion behavior. In this study, WMS was fermented by Qu at different time and starches were isolated at each time point, and its physico-chemical properties and structural parameters were determined. Results showed that the resistant starch (RS), amylose content (AC), the average particle size [D(4,3)] the ratio of peaks at 1,022/995 cm-1, and the onset temperature of gelatinization (T o ) were increased significantly after 36 h. Conversely, the crystallinity, the values of peak viscosity (PV), breakdown (BD), gelatinization enthalpy (ΔH), and the phase transition temperature range (ΔT) were declined significantly after 36 h. It is noteworthy that smaller starch granules were appeared at 36 h, with wrinkles on the surface, and the particle size distribution was also changed from one sharp peak to bimodal. We suggested that the formation of smaller rearranged starch granules was the main reason for the pronounced increase of RS during the FQ process.

Optimization of Corn Resistant Starch Preparation by Dual Enzymatic Modification Using Response Surface Methodology and Its Physicochemical Characterization

Corn starch was dually modified using thermostable α-amylase and pullulanase to prepare resistant starch (RS). The concentration of starch liquid, the amount of added thermostable α-amylase, the duration of enzymatic hydrolysis and the amount of added pullulanase were optimized using RSM to increase RS content of the treated sample. The optimum pretreatment conditions were 15% starch liquid, 3 U/g thermostable α-amylase, 35 min of enzymatic hydrolysis and 8 U/g pullulanase. The maximum RS content of 10.75% was obtained, and this value was significantly higher than that of native corn starch. The degree of polymerization (DP) of the enzyme-modified starch decreased compared with that of native starch. The scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were performed to assess structural changes in native and pretreated starch. The effect of dual enzyme pretreatment on the structure and properties of corn starch was significant. Unlike the untreated one, the pretreated corn starch showed clear pores and cracks. Significant differences in RS contents and structural characterization between starch pretreated and untreated with dual enzymes demonstrated that the dual enzyme modification of corn was effective in enhancing RS contents.

Verification of autoclaving-cooling treatment to increase the resistant starch contents in food starches based on meta-analysis result

Autoclaving-cooling is a common starch modification method to increase the resistant starch (RS) content. The effect of this method varies depending on the type of crop and treatment condition used. The objectives of this study were to verify the autoclaving-cooling treatment based on a meta-analysis result and to evaluate the physicochemical properties of modified starches. The meta-analysis study used 10 articles from a total of 1,293 that were retrieved using the PRISMA approach. Meta-analysis showed that the optimal treatments of autoclaving-cooling process that increase the RS content significantly, was in starch samples from the cereal group (corn, oats, rice) (SMD: 19.60; 95% CI: 9.56–29.64; p < 0.001), with water ratio 1:4 (SMD: 13.69; 95% CI: 5.50–21.87; p < 0.001), using two cycles of autoclaving-cooling (SMD: 16.33; 95% CI: 6.98–25.67; p < 0.001) and 30 min of autoclaving heating (SMD: 12.97; 95% CI: 1.97–23.97; p < 0.001) at 121°C (SMD: 12.18; 95% CI: 1.88–22.47; p < 0.001). Verification using corn flour and corn starch showed a significant increase in RS contents from 15.84 to 27.78% and from 15.27 to 32.53%, respectively, and a significant decrease in starch digestibility from 67.02 to 35.74% and from 76.15 to 28.09%, respectively. Treated sample also showed the pasting profile that was stable under heating and stirring.

Production of buckwheat starch-myristic acid complexes and effect of reaction conditions on the physicochemical properties, X-ray pattern and FT-IR spectra

In this study, the effect of reaction parameters on complex index (CI%) value of complexes formed between buckwheat starch (BS) and myristic acid (MA) was investigated. The temperature (60-90 °C) and MA to BS ratio (0.1-0.8 mmoL/g) were determined as the most effective parameters and their effect on CI% was evaluated using response surface methodology. The MA to BS ratio, temperature, and interaction between them had an influence on CI%. The CI% of BS-MA complexes increased with increasing MA ratio until a certain level of MA. Principal component analysis (PCA) was used for correlation analysis between parameters. Swelling power and paste clarity of BS decreased with complex formation while syneresis increased. Peak and final viscosity values of the BS-MA complexes were significantly lower than those of BS. FT-IR revealed the complex formation led to change in starch structure. The XRD confirmed the BS-MA complex formation but the BS-MA produced using 0.1 mmoL/g at 60 °C was not detected by XRD due to having low crystallinity, and expectedly, the lowest relative crystallinity value was achieved with this sample among complex samples. All results showed that the buckwheat might be an alternative starch source for starch-lipid complex formation.

Beneficial Effect of Kidney Bean Resistant Starch on Hyperlipidemia-Induced Acute Pancreatitis and Related Intestinal Barrier Damage in Rats

Accumulating attention has been focused on resistant starch (RS) due to its blood-lipid-lowering activities. However, reports on the potential bioactivities of RS for preventing hyperlipidemia acute pancreatitis (HLAP) are limited. Therefore, in this study, an acute pancreatitis model was set up by feeding a hyperlipidemia diet to rats, and subsequently evaluating the anti-HLAP effect of RS in kidney beans. The results show that the IL-6, IL-1β, and TNF-α of serum in each RS group were decreased by 18.67-50.00%, 7.92-22.89%, and 8.06-34.04%, respectively, compared with the model group (MOD). In addition, the mRNA expression of tight junction protein ZO-1, occludin, and antibacterial peptides CRAMP and DEFB1 of rats in each RS group increased by 26.43-60.07%, 229.98-279.90%, 75.80-111.20%, and 77.86-109.07%, respectively. The height of the villi in the small intestine and the thickness of the muscle layer of rats were also increased, while the depth of the crypt decreased. The present study indicates that RS relieves intestinal inflammation, inhibits oxidative stress, and prevents related intestinal barrier damage. These results support the supplementation of RS as an effective nutritional intervention for HLAP and associated intestinal injury.

A review of starch biosynthesis in cereal crops and its potential breeding applications in rice (Oryza Sativa L.)

Starch provides primary storage of carbohydrates, accounting for approximately 85% of the dry weight of cereal endosperm. Cereal seeds contribute to maximum annual starch production and provide the primary food for humans and livestock worldwide. However, the growing demand for starch in food and industry and the increasing loss of arable land with urbanization emphasizes the urgency to understand starch biosynthesis and its regulation. Here, we first summarized the regulatory signaling pathways about leaf starch biosynthesis. Subsequently, we paid more attention to how transcriptional factors (TFs) systematically respond to various stimulants via the regulation of the enzymes during starch biosynthesis. Finally, some strategies to improve cereal yield and quality were put forward based on the previous reports. This review would collectively help to design future studies on starch biosynthesis in cereal crops.

Effects of Auricularia auricula-judae polysaccharide on pasting, gelatinization, rheology, structural properties and in vitro digestibility of kidney bean starch

Auricularia auricula-judae polysaccharide (AP) has unique molecular structures and multiple bioactivities with excellent gel-forming property and thermal tolerance. However, few researches focus on the interactions between AP and legume starches. In this study, the effects of AP on the pasting, gelatinization, rheology, microstructure, and in vitro digestibility of kidney bean starch (KBST) were evaluated. The pasting, gelling and structural properties of AP-KBST mixtures were characterized by rapid visco analyzer, rheometry, texture analyzer, laser particle analyzer, low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. And an in vitro method was employed to measure the digestibility of AP-KBST composites. The pasting viscosity, swelling degree of starch granules, viscoelasticity, gel strength, cold storage stability and water-retention capacity of KBST were enhanced with increasing AP concentration. The combination of AP and KBST exhibited a higher short-range ordered and a firmer and denser structure than that of KBST alone. Moreover, AP increased the contents of resistant starch and slowly digestible starch, which were positively correlated with the storage modulus and the degree of order, thereby suggesting that the formation of strong and ordered gel network structure by synergistic interactions between AP and KBST was responsible for the reduced starch digestibility.

Efficacy of fermentation parameters on protein quality and microstructural properties of processed finger millet flour

The present study aims to explore the outcome of processing methods such as fermentation; treatments using lemon juice (T1), sodium chloride (T2), lemon juice followed by sodium chloride (T3) and fermentation followed by treatment-T3 on the quality characteristics of processed finger millet flour to develop a specialized low protein food supplement for a protein-related inborn error of metabolic disorders. The clean dirt-free finger millet grains were made into slurry subjected to treatment T1 (FMFT1), T2 (FMFT2), T3 (FMFT3), fermentation for 8-36 h with 4 h intervals using yoghurt as starter culture (FFMF) and fermentation (8-36 h) followed by treatment T3 (FFMFT3). The acidity of the finger millet slurry significantly increased with the increase in fermentation time when compared to control. The IVPD was found to be 89% in FFMF (20 h) sample which was significantly higher than the IVPD of control sample flour (27%). However, the crude protein content (%), the protein fractions and the IVPD of FFMFT3 (8-36 h) samples were found to be lesser than the FFMF (8-36 h) samples. The findings were further ensured by the results of scanning electron microscopic images and FT-IR spectra which showed the morphological and chemical modifications caused by the processing methods. The setback and breakdown viscosity of control (945 cP and 664 cP respectively) approximately reduced to two-third in FFMF (20 h) samples and one-third for FFMFT3 samples (303 cP and 286 cP respectively). From the study, it is evident that the processing method of fermentation followed by treatment-T3 could be utilized in the development of low protein food supplements.

Influence of freeze-drying and fresh cooking on starch morphology and physicochemical and thermal properties of various tropical tubers

Flours and starches extracted from the tropical tubers underwent freeze-drying and cooking in comparison with fresh cooking. Freeze-dried and cooked starch (FDS) granules were found to have different shapes and collapsed arrangement whereas freshly cooked starch (FCS) granules had the least varied structures. The freeze-dried flours had larger structures compared to freshly cooked flours. The physicochemical parameters were high in Dioscorea esculenta (DE)-FDS, followed by Amorphophallus paeoniifolius (AP)-FDS and other samples whereas D. alata (DA)-FCS had the lowest, whereas flours followed similar trend. FDS (42.1%) had the highest solubility index and swelling power whereas FCS (11.1%) showed the lowest. The syneresis and light transmittance levels were higher in FDS and FDF. The freeze dried flour and starch showed higher onset (T₀), peak (T_P), and conclusion (T_C) temperature than fresh cooked samples. The variations in IR spectra, thermal properties, and crystalline index were termed as differential function of physicochemical characteristics, structural changes that resulted from freeze drying, and cooking treatment employed.

Evaluation of Various Starchy Foods: A Systematic Review and Meta-Analysis on Chemical Properties Affecting the Glycemic Index Values Based on In Vitro and In Vivo Experiments

The chemical properties that serve as major determinants for the glycemic index (GI) of starchy food and recommended low-GI, carbohydrate-based foods have remained enigmatic. This present work performed a systematic assessment of linkages between chemical properties of foods and GI, and selected low-GI starchy foods. The data were sourced from literature published in various scientific journals. In total, 57 relevant studies and 936 data points were integrated into a database. Both in vitro and in vivo studies on GI values were included. The database was subsequently subjected to a meta-analysis. Meta-analysis from in vitro studies revealed that the two significant factors responsible for the GI of starchy foods were resistant starch and phenolic content (respectively, standardized mean difference (SMD): -2.52, 95% confidence interval (95%CI): -3.29 to -1.75, p (p-value) < 0.001; SMD: -0.72, 95%CI: -1.26 to -0.17, p = 0.005), while the lowest-GI crop type was legumes. Subgroup analysis restricted to the crop species with significant low GI found two crops, i.e., sorghum (SMD: -0.69, 95%CI: -2.33 to 0.96, p < 0.001) and red kidney bean (SMD: -0.39, 95%CI: -2.37 to 1.59, p = 0.001). Meta-analysis from in vivo studies revealed that the two significant factors responsible for the GI of starchy foods were flavonoid and phenolic content (respectively, SMD: -0.67, 95%CI: -0.87 to -0.47, p < 0.001; SMD: -0.63, 95%CI: -1.15 to -0.11, p = 0.009), while the lowest-GI crop type was fruit (banana). In conclusion, resistant starch and phenolic content may have a desirable impact on the GI of starchy food, while sorghum and red kidney bean are found to have low GI.

Starch-gelatin film as an alternative to the use of plastics in agriculture: a review

BACKGROUND

The technological advances in agriculture, driven by the increased demand for food attributed to population growth, have led to the search for technologies that allow greater control over the variables that interfere in crop yield. Several techniques stand out for optimizing yield capacity, including cultivation in a protected environment, mulching and low tunneling. To expand the use of these techniques, synthetic petroleum-based polymers are employed due to their low cost, easy processing, and lightness. However, they take a long time to degrade, and, since they are discarded at the end of each cycle of cultivation, end up accumulating in the environment causing irreversible damage.

RESULTS

The use of biodegradable films, made of starch and/or a protein source such as gelatin, has been studied as a promising alternative. Both stand out because of their film-forming ability, and because they come from abundant sources and are biodegradable.

CONCLUSION

This study aimed to review the current findings on starch and gelatin films that can be used as alternatives to conventional plastics in agricultural crops. © 2019 Society of Chemical Industry.

The preparation, formation, fermentability, and applications of resistant starch

Resistant starch (RS) cannot be digested in the small intestine but can be fermented by microflora in the colon. To meet the demand for RS, effective methods and advanced equipment for preparing RS have emerged, but further development is needed. RS contents are affected by different prepared methods, starch source and certain nutrients such as protein, phenols, and hydrocolloids interacted with RS. As a beneficial fermentation substrate, RS modifies and stabilizes the intestinal flora to balance the intestinal environment and improve intestinal tract health and function. RS is also a kind of ingredient with potential physiological function, even better than that dietary fiber, but also in terms of providing various health benefits. RS has good food-processing characteristics as well and can thus be widely used in the food industry.

Comparative study on the chemical composition, anthocyanins, tocopherols and carotenoids of selected legumes

Twenty-nine legumes were assessed for their nutritional and phytochemical compositions. Soybean and black soybean had the highest protein contents (34.05-42.65 g/100 g DW, dry weight of legumes), particularly being a rich source of lysine (1.78-2.23 g/100 g DW. Soybean and black soybean had the highest fat contents (14.13-22.19 g/100 g DW). Broad beans had the highest unsaturated fatty acids (83.57-89.01 g/100 g fatty acid), particularly rich in α-linolenic and linoleic acid. The highest and the lowest dietary fiber were found in red kidney beans (35.36 g/100 g DW) and mung beans (22.77 g/100 g DW), respectively. Except for soybean and white kidney bean, 6 major anthocyanins in the legumes samples were identified. The soybean contained the highest total tocopherols content (90.40-120.96 μg/g dry weight of beans), followed by black soybean (66.13-100.76 μg/g DW). The highest carotenoids were found in lentils (4.53-21.34 μg/g DW) and red kidney beans (8.29-20.95 μg/g DW).

Pullulanase treatments to increase resistant starch content of black chickpea (Cicer arietinum L.) starch and the effects on starch properties

This study aimed to increase resistant starch (RS) content of black chickpeas (Cicer arietinum L.) by using pullulanase enzyme. Physicochemical and functional properties of enzyme treated starch (NE) was compared with that of enzyme-treated and gelatinized starch (GE) and the retrograded control starch (RC). RS contents for native black chickpea starch (NS) and black chickpea flour (NF) were measured as 15.2% and 5.0%, respectively. While for NE and GE, were found as 16.4% and 12.3%, respectively. Treatments made on the NS, increased the amount of RDS and reduced the amount of SDS significantly (p < .05). When the effect of enzyme application-autoclaving and retrogradation were compared, 41.3% increase in RS content was measured. In this study; RS3 production from black chickpea starch by a pullulanase enzyme was successfully performed. Enzymatic applications also improved the functional properties such as water absorption capacity, water solubility index value, fat binding capacity and emulsifying capacity. This enzyme treated black chickpea starch samples, being functionally improved, will possibly help to produce different products with desired quality parameters. Therefore, instead of native starch, pullulanase treated black chickpea starch may be used as a functional ingredient for increasing the amount of RS in food formulations.

Changes in protein and starch digestibility in sorghum flour during heat-moisture treatments

BACKGROUND

Heat-moisture treatment (HMT) has been used to modify properties of sorghum starches. However, information is limited on the effects of HMT on the digestibility of starch and the concurrent changes in protein in sorghum flour. The objectives of this research were to identify heat-moisture conditions to increase the resistant starch (RS) content of sorghum flour and investigate changes in sorghum proteins and starch structure.

RESULTS

Sorghum flours with different moisture contents (0, 125, 200, and 300 g kg^-1 w.b.) were heated at three temperatures (100, 120 and 140 °C) and times (1, 2 and 4 h). HMT of sorghum flour increased its RS level. The flour treated at 200 g kg^-1 moisture and 100 °C for 4 h had a high RS content (221 g kg^-1 vs. 56 g kg^-1 for the untreated flour). Starch was not gelatinized when sorghum flours heated at moisture content of 200 g kg^-1 or below. Sorghum protein digestibility and solubility decreased during HMT. The increase in RS of sorghum flour upon HMT was attributed to enhanced amylose-lipid complexes and heat induced structural changes in its protein fraction.

CONCLUSION

HMT can be used to increase RS content in sorghum flour without gelatinizing its starch, thereby providing sorghum flour with unique food applications. © 2017 Society of Chemical Industry.

Investigation of debranching pattern of a thermostable isoamylase and its application for the production of resistant starch

Debranching enzymes contribute to the enzymatic production of resistant starch (RS) by reducing substrate molecular weight and increasing amylose yield. In the present study, the action pattern of a thermostable isoamylase-type debranching enzyme on different types of starch was investigated. The molecular weight distribution, glycosidic bond composition and contents of oligosaccharides released were monitored by various liquid chromatography techniques and nuclear magnetic resonance spectroscopy (NMR). These analyses showed that the isoamylase could specifically and efficiently attack α-1,6-glucosidic linkages at branch points, leaving the amylose favored by other amylolytic enzymes. Its ability to attack side chains composed of 1-3 glucose residues differentiates it from other isoamylases, a property which is also ideal for the RS preparation process. The enzyme was used as an auxiliary enzyme in the hydrolytic stage. The highest RS yield (53.8%) was achieved under the optimized conditions of 70 °C and pH 5.0, using 7 U isoamylase per g starch and 2 NU amylase per g starch. These data also help us better understand the application of isoamylase for preparation of other products from highly branched starch materials.