Nutritional and potential health benefits of konjac glucomannan,a promising polysaccharide of elephant foot yam,Amorphophallus konjac K. Koch: A review

Amorphophallus konjac (konjac) is one among the major vegetable (tuber) crops grown in Asian countries. In China and Japan, it has been used as food and a food additive for more than 1000 years. Over the last few decades, the purified konjac flour, commonly known as konjac glucomannan (KGM), a dietary fiber hydrocolloidal polysaccharide, has been introduced as a food additive as well as a dietary supplement in many Asian and European countries. The present article reviews the literature (up to January 2015) covering the development of various functional foods, food additives from KGM and their derivatives, Also, this review deals with global nutritional aspects and value added products of konjac corm. The bioprocessing techniques such as preparation, purification, and extraction of KGM from konjac flour and methods to improve quality of KGM are discussed.

Abbreviations: ¹³C NMR: carbon-13, nuclear magnetic resonance spectroscopy; CHD: coronary heart disease; CKF: crude konjac flour; CVD: cardiovascular disease; DA: degree of acetylation; DMSO: dimethyl sulfoxide; DOB: degree of branching; EC: European Commission; EFSA: European Food Safety Authority; EFY: elephant foot yam; FCC: Food Chemical Codex; FDA: Food and Drug Administration; GM: glucomannan; KG: konjac gel; KGM: konjac glucomannan; KGMOS: KGM octenyl succinate; KM: konjac mannan; OSA: octenyl succinic anhydride; PKF: purified konjac flour; SEM: scanning electron microscopy; USDA: United States Department of Agriculture; WHO: World Health Organization; WVP: water vapor permeability     

Effect of non-starch polysaccharides on the in vitro digestibility and rheological properties of rice starch gel

The starch digestibility and rheological properties of gels were evaluated in the presence of three non-starch polysaccharides (agar, xanthan gum and konjac glucomannan) with rice starch. Each polysaccharide was added to 30% (w/w) rice starch suspension at defined concentrations and starch gels were prepared. The extent of starch gel digestibility was determined by an in vitro method and rheological properties by a dynamic oscillatory test and a compression test. The added polysaccharides suppressed starch hydrolysis in the gels compared with the control, and a concentration dependency of this suppressive effect was observed. Adding agar and xanthan gum increased the storage shear modulus (G′) of starch gels, while adding konjac glucomannan decreased G′ values. The results indicate that the suppressive effect of non-starch polysaccharides on starch digestibility appears to be not only due to the rigidity of the gel, but also the interaction between starch and non-starch polysaccharides.     

食用胶对虾蛄中磷酸化肌原纤维蛋白凝胶特性的影响

将魔芋胶、卡拉胶、黄原胶分别添加到虾蛄磷酸化肌原纤维蛋白中,在不同食用胶、三聚磷酸钠添加量及不同温度下形成凝胶,研究食用胶对磷酸化蛋白凝胶特性的影响。结果表明：随着三聚磷酸钠添加量的增加,3 种食用胶形成的蛋白凝胶强度和保水性均提高;随着食用胶添加量的增加,卡拉胶与黄原胶形成的蛋白凝胶强度和保水性提高,魔芋胶添加量为0.1%时,其蛋白凝胶强度最高;随着温度的升高,魔芋胶与卡拉胶均对蛋白凝胶强度和保水性有显著性影响（P＜0.05）,但黄原胶对凝胶强度和保水性无显著影响（P＞0.05）。     

Sweetening power of aspartame in hydrocolloids gels: Influence of texture

Equivalent sweetness of aspartame relative to two sucrose concentrations (10% and 20% w/w) were determined in water and in hydrocolloids gels. The influence of the texture of three hydrocolloids gelled systems—gellan gum, κ-carrageenan, and κ-carrageenan/locust bean gum (LBG)—at two gums concentrations (0.3% and 1.2% w/w) on the equivalent sweetness of aspartame were then studied. For the three gelled systems, the increase in hydrocolloid concentration produced a significant increase in the true rupture stress and in the deformability modulus values. For both κ-carrageenan and mixed gels the true rupture strain values increased when increasing hydrocolloid concentration while for gellan gels, decreased. For the same hydrocolloid concentrations the κ-carrageenan/LBG gels showed the largest strain at rupture and gellan gels the smallest (most brittle). For both soft (0.3% gum) and hard (1.2% gum) gellan gels and κ-carrageenan gels, the concentrations of aspartame needed to deliver a sweetness intensity equivalent to that of gels with 10% sucrose (0.079–0.087% w/w) were similar to those obtained for aqueous solutions (0.084% w/v). For hard κ-carrageenan/LBG gels the corresponding concentration of aspartame was slightly lower. For all gelled systems the concentrations of aspartame needed to deliver a sweetness intensity equivalent to that of gels with 20% sucrose were higher for soft gels than for hard gels.     

The potential use of hydrolysed konjac glucomannan as a prebiotic

Konjac glucomannan hydrolysate was derived enzymatically from konjac flour under optimal conditions. A number of culture strains of lactobacilli and bifidobacteria were grown on De Man, Rogosa and Sharpe (MRS) media supplemented with the hydrolysate. This hydrolysate stimulated the growth of all strains examined. Colony sizes of those strains grown on konjac hydrolysate were significantly (P = 0.001) bigger than those grown on pectin or xylan hydrolysates. Bacterial growth profiles were also conducted on nutrient agar (MRS or modified MRS agar containing konjac hydrolysate) using single strains of lactobacilli or bifidobacteria (Lactobacillus acidophilus, Lactobacillus casei or Bifidobacterium adolescentis), single pathogen cultures (Escherichia coli or Listeria monocytogenes) or mixed bacterial cultures (from chicken breast extract). Although the growth of lactobacilli inhibited the growth of pathogens (single or mixed culture) the pathogens could not grow on the konjac hydrolysate as a sole carbon source. Microbial growth profiles using konjac hydrolysate or inulin in UHT milk were also investigated. The results showed that the numbers of colony forming units (cfu) obtained from milk containing the konjac hydrolysate were significantly (P = 0.01) higher than those containing inulin. It is suggested that the unique properties of konjac hydrolysate make it universally valuable as a prebiotic which can be applied to a wide range of foods, feeds and healthcare/pharmaceutical products. Copyright © 2007 Society of Chemical Industry     

魔芋葡甘聚糖/κ-卡拉胶复合凝胶制备条件的优化

为了优化κ-卡拉胶-魔芋葡甘聚糖复合凝胶制备条件,以期改善以魔芋葡甘聚糖为原料的复合凝胶质产品,使其具备较佳的特性黏度。本研究以κ-卡拉胶(KC)、魔芋葡甘聚糖(KGM)为实验对象,以复合胶液黏度作为指标,在单因素实验的基础上,通过建立三因素三水平响应面优化设计实验,对水浴温度、搅拌时间及底物配比工艺参数进行优化分析。结果表明:水浴温度、搅拌时间及底物配比是复合胶液黏度的显著影响因子(p<0.05),各因素间交互作用对复合胶液的黏度影响效果显著(p<0.05);当水浴温度为76 ℃,搅拌时间为1.5 h及底物配比(KGM:KC)为5:3时,实验所得复合胶液黏度值为68.87 Pa·s,与模型预测值69.1397 Pa·s接近,误差为0.39%<1%,说明经过优化所得的最佳工艺参数可靠合理。     

Effect of antioxidants in combination of VCO nanoemulsion on gel properties and storage stability of refrigerated sardine surimi gel

Impacts of β-glucan–virgin coconut oil (VCO) nanoemulsion containing epigallocatechin gallate (EGCG) and α-tocopherol at levels of 0–3.0 g kg⁻¹ on properties and storage stability of surimi gel were investigated. Augmented breaking force, deformation and fracture constant were obtained in gels containing 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol (P < 0.05). Expressible moisture content increased as EGCG levels were more than 2.0 g kg⁻¹. Smoother microstructure was observed in gels containing 2.0 g kg⁻¹ EGCG. Whiter gels were obtained when β-glucan–VCO nanoemulsion was incorporated. No change in protein pattern of gels was observed regardless of antioxidant incorporation. Viscoelastic moduli decreased as β-glucan–VCO nanoemulsion was added; however, incorporation of 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol lowered the decrease in G'. β-glucan–VCO nanoemulsion containing gels had higher likeness scores than the control (P < 0.05). Gels containing EGCG and α-tocopherol at selected levels had the improved oxidative stability and lowered microbial loads.     

精制对魔芋葡甘聚糖及其与κ-卡拉胶复配凝胶性质的影响

本论文主要研究魔芋葡甘聚糖（Konjac glucomannan,KGM）的精制条件及精制前后的KGM与κ-卡拉胶复配凝胶的理化性质和结构表征,并进一步解析KGM的理化性质与其复配体系凝胶特性之间的相关性。结果表明,KGM的最佳精制条件为:乙醇浓度为60%,溶胀时间为2 h,溶胀温度为50 ℃;在此精制条件下的KGM的葡甘聚糖含量、粘度、亮度和白度分别增加了34.43%、128.55%、17.94%和28.29%,其与κ-卡拉胶复配体系的凝胶强度、硬度、咀嚼性和胶着性分别显著提高了47.39%、60.47%、55.44%和45.87%（P < 0.05）,复配体系的氢键作用力增强,凝胶网络结构更加平滑紧密;相关性分析结果表明,精制后KGM的葡甘聚糖含量、粘度、色泽、气味是提高复配体系凝胶特性等品质的关键因素。本论文为开发高凝胶强度的KGM与卡拉胶复配凝胶的研究提供了一种高效简单的精制KGM的方法,并为后续精制KGM的工业化生产奠定了理论基础。     

魔芋葡甘聚糖机械力化学降解研究

研究了魔芋葡甘聚糖在超微粉碎过程中的机械力化学降解效应.结果表明,在超微粉碎过程强烈的机械力作用下,魔芋葡甘聚糖发生了机械力化学降解,随粒度细化,溶胶粘度、分子量和葡甘聚糖含量呈显著下降趋势,并产生大量魔芋低聚糖.与粗于80目粉相比,细于600目粉粘度下降93.06%,分子量下降68.45%,葡甘聚糖含量下降9.02%,魔芋低聚糖的含量为7.56%.     

Differential scanning calorimetric studies of Philippines natural grade κ-carrageenan

Using differential scanning calorimetry, the gel-sol transition temperatures were compared for KCl-precipitated κ-carrageenan and Philippines natural grade (PNG) κ-carrageenan. The latter contains cellulose, which is associated with the carrageenan in seaweed. This leads to lower gel-sol transition temperatures. More heat absorption (-ΔH_m = 79 kJ/mol) is required for the formation of junction zones for the PNG κ-carrageenan than the KCl-precipitated κ-carrageenan (-ΔH_m = 40 kJ/mol). This behaviour can be attributed to the cellulose interspersing between κ-carrageenan aggregates in the PNG κ-carrageenan gels.     

Thermodynamic incompatibility between denatured whey protein and konjac glucomannan

The current study investigated the effect of a neutral polysaccharide, konjac glucomannan, on the heat-induced gelation of whey protein isolate (WPI) at pH 7. Oscillatory rheology (1 rad/s; 0.5% strain), differential scanning calorimetry and confocal laser scanning microscopy were used to investigate the effect of addition of konjac in the range 0-0.5% w/w, on the thermal gelation properties of WPI. The minimum gelling concentration for WPI samples was 11% w/w; the concentration was therefore held constant at this value. Gelation of WPI was induced by heating the samples from 20 to 80 °C, holding at 80 °C for 30 min, cooling to 20 °C, and holding at 20 °C for a further 30 min. On incorporation of increasing concentrations of konjac the gelation time decreased, while the storage modulus (G′) of the mixed gel systems increased to ∼1450 Pa for 11% w/w WPI containing 0.5% w/w konjac gels, compared to 15 Pa for 11% w/w WPI gels (no konjac). This increase in gel strength was attributed to segregative interactions between denatured whey proteins and konjac glucomannan.     

Rheological characterisation of yolk-based gels and Staphylococcus growth

Model yolk-based (10% v/v) gels with different concentrations of κ-carrageenan (0–2% w/w) were characterised employing rheological measurements, textural analysis and scanning electron microscopy. Additionally, the effect of the microstructure of the model gels on the growth rate of Staphylococcus was also evaluated. In all cases, the nature of the gel was dominated by the elastic component, specifically, 1.5, 1.75 and 2% κ-carrageenan samples can be described as ‘true gels’ (tan δ < 0.1). Maximum strength of the interactions between rheological units (A) was observed with 1.75% κ-carrageenan (4.74 ± 0.38 kPa), which indicates that the strength of interactions was determined not only by κ-carrageenan concentration, but also by the amount of yolk. Finally, an inverse linear correlation was found between the maximum specific growth rate of Staphylococcus and rheological data (R² > 0.99).     

魔芋葡甘聚糖基抗菌活性包装膜的研究进展

魔芋葡甘聚糖是一种天然高分子,具有成膜性、生物相容性、可降解和可再生等特性,来源广泛,价格低廉。在众多以魔芋葡甘聚糖为基质的复合材料研究中,魔芋葡甘聚糖基抗菌活性包装膜的研究受到广泛关注,在食品包装领域表现出广阔的应用前景。本文主要从魔芋葡甘聚糖的结构、性能与复合膜的制备方法,以及不同种类魔芋葡甘聚糖基抗菌膜的制备、功能特性、抗菌效果等方面综述了魔芋葡甘聚糖基抗菌活性包装膜的研究进展。     

Techniques for localisation of konjac glucomannan in model milk protein–polysaccharide mixed systems: Physicochemical and microscopic investigations

The effect of conjugating konjac glucomannan with fluorescein isothyocyanate (FITC) via covalent labelling on selected physicochemical properties of FITC and konjac was investigated using spectrophotometry, rheometry, and size exclusion chromatography (SEC). The binding of the lectin concanavalin A (ConA) to sugar residues of konjac was investigated using SEC. Covalent conjugation of konjac with FITC led to a shift in the absorbance spectrum peak of FITC to a lower wavelength and a decrease in the average molecular weight distribution of konjac. Furthermore, covalently labelled konjac showed reduced apparent viscosity compared to unlabelled konjac. ConA bound to the sugar residues in konjac. The potential of konjac–FITC covalent labelled conjugate or konjac–lectin labelled ConA complexes as fluorescent markers for localisation of konjac in a phase separated micellar casein–konjac mixture was investigated using confocal laser scanning microscopy. Results indicated that covalently labelled konjac has microscopic phase behaviour similar to that of un-labelled konjac and are therefore suitable for localising konjac glucomannan in a phase-separated micellar casein–konjac system.     

Elastic gels based on flaxseed gum with konjac glucomannan and agar

Food Science and Biotechnology - In this study, we prepared hydrocolloid gels in which flaxseed gum (FSG), konjac glucomannan (KGM), and agar (AG) were blended in different ratios for use as a...     

Structure and rheology of the κ-carrageenan/locust bean gum gels

The structure and interaction of κ-carrageenan and locust bean gum (LBG) has been studied using rheology, cryo-SEM, conductivity and syneresis characterization. The rheological behaviour of the binary system has been characterized using both compression and shear measurements. Elimination of slip in the shear measurements yields G′ values of the order 10,000–30,000 Pa for a 1% κ-carrageenan gel in 0–0.2 M added KCl. These values are higher than previously reported. No synergistic peak was found with the addition of LBG as has been previously reported. The measured modulii for these gels yields a Poisson's ratio of 0.5. Compression rupture stress and strain were also monitored. The rupture measurements do show a synergistic peak indicating that the interaction does occur and is important at high strain amplitudes. The gel points as determined by conductivity for these systems show a decrease in temperature with increasing LBG concentration, which is consistent with rheological measurements. Syneresis results are reported for the range of κ-carrageenan/LBG ratios. The syneresis shown by the mixtures is the same as that shown by the same concentration of κ-carrageenan. Structures of the gels as determined by cryo-SEM are also reported. Characteristic length scales in these systems are of the order of tens of microns and show little change with LBG concentration. The reduction in the characteristic length scale with increasing LBG concentration is discussed in terms of the rheological behaviour.     

β-甘露聚糖酶产生菌的筛选及魔芋低聚糖制备工艺的研究

以魔芋粉为唯一碳源,从种植魔芋土壤中定向筛选一株高产胞外β-甘露聚糖酶的菌株,进行形态观察、生理生化试验和16S rDNA序列分析鉴定,并研究了该β-甘露聚糖酶水解魔芋胶制备魔芋低聚糖的工艺。结果表明,筛选出一株高产胞外β-甘露聚糖酶的菌株,编号为G1,被鉴定为枯草芽孢杆菌（Bacillus subtilis）。确定魔芋低聚糖制备的酶解条件为酶添加量50 U/g魔芋葡甘聚糖（KGM）,酶解pH值 6.5,酶解温度55 ℃;当KGM质量浓度为10 g/L,酶解时间2 h时,还原糖转化率为51.6%;当KGM质量浓度为30 g/L,酶解时间4 h时,还原糖转化率仍可达到46.9%,表明该酶具有较高的催化效率。利用薄层层析（TLC）定性分析酶解产物主要为三糖及三糖以上的低聚糖。该研究为实现酶法制备魔芋低聚糖的工业化生产奠定了基础。     

Phase behaviour,rheology and microstructure of mixture of meat proteins and kappa and iota carrageenans

The phase behaviour of mixtures of salt soluble meat proteins, kappa (κ) and iota (ι) carrageenan in non-gelling conditions (45 °C) were determined at pH 5.6, 6.2 and 7.1. The concentration of meat proteins ranged from 0.1 to 1.0 percent and that of κ-carrageenan and ι-carrageenan from 0.02 to 0.3 percent in the mixtures. Mixtures separated under gravity to form soluble/liquid and gelled/complex phases. For meat proteins- κ-carrageenan mixtures, phase separations at all meat protein/carrageenan ratios were observed. For meat protein-ι-carrageenan mixtures, soluble complexes were formed at low meat protein to ι-carrageenan ratios and gels at higher ratios. The yield of the complex/gels increased with the increase in the concentration of the meat proteins and carrageenans and decreased with increase in the pH of the initial mix. The complex/gels formed became stronger with the increase in carrageenan in the mix and with κ-carrageenan compared to ι-carrageenan. Chemical analyses and scanning electron and phase contrast microscopy indicated that in phase separated mixtures, the bulk of the meat proteins and carrageenan were found in the gel compared to the liquid phase; and that meat protein interacted with carrageenan in the gel and formed soluble complexes with carrageenan in the liquid phase. SDS-PAGE showed that the meat proteins that interacted to form the complex/gels with carrageenan included myosin heavy chain, α-actinin, actin, myosin light chains and proteins with molecular weights around 150 and 50 kD. The outcomes of the present study could be used in the formulation of multi-component foods with a range of consistencies containing meat proteins.     

Differential scanning calorimetric studies of Philippines natural grade κ-carrageenan

Using differential scanning calorimetry, the gel-sol transition temperatures were compared for KCl-precipitated κ-carrageenan and Philippines natural grade (PNG) κ-carrageenan. The latter contains cellulose, which is associated with the carrageenan in seaweed. This leads to lower gel-sol transition temperatures. More heat absorption (-ΔH_m = 79 kJ/mol) is required for the formation of junction zones for the PNG κ-carrageenan than the KCl-precipitated κ-carrageenan (-ΔH_m = 40 kJ/mol). This behaviour can be attributed to the cellulose interspersing between κ-carrageenan aggregates in the PNG κ-carrageenan gels.     

Effect of konjac glucomannan addition on aroma release in gels containing potato starch

The present study aimed to measure the retention of aroma compounds (ethyl acetate, ethyl hexanoate and carvacrol) in dispersions based on konjac glucomannan and/or potato starch, and to highlight the influence of konjac glucomannan on the mechanisms involved in aroma retention. Publications on the effect of konjac glucomannan on aroma release are scarce. Konjac glucomannan is a polysaccharide used as a food additive for its viscous and emulsifying properties. Retention of aroma compounds in dispersions was calculated from partition coefficients which were measured using the phase ratio variation method. This method, consisting of analyses of the headspace at equilibrium, enables the determination of the partition coefficient of volatile compounds in a gas/liquid system without external or internal calibration. The three aroma compounds chosen for this study behave differently toward amylose. Prior to the release study, the complexing behavior of carvacrol with starch, hitherto unknown, was investigated by X-ray diffraction: V_6III amylose complexes were formed with carvacrol. Our results showed no specific interaction between ethyl hexanoate and potato starch or konjac glucomannan. Ethyl acetate retention seemed to be due to trapping in the complex network of polysaccharides and to the density of this network. Retention of carvacrol was influenced by the nature of polysaccharides present in the dispersion, and was mainly governed by specific interaction with starch. Additionally, the addition of konjac glucomannan to potato starch dispersions decreased the retention of volatile compounds complexing starch, but had little effect on the retention of the other aroma compounds.