Elsevier

Food Hydrocolloids

Volume 103, June 2020, 105653
Food Hydrocolloids

A novel low-alkali konjac gel induced by ethanol to modulate sodium release

https://doi.org/10.1016/j.foodhyd.2020.105653Get rights and content

Highlights

  • Ethanol promoted the gelation of KGM at a low alkali concentration of 0.02 wt%.

  • The mechanical properties of KGM gels were remarkably changed by ethanol.

  • A more compact network structure could be found in KGM gels with ethanol.

  • KGM alcogels presented lower swelling ratio and higher turbidity in appearance.

  • KGM alcogels could be potentially used for the rapid release of Na+.

Abstract

Alcogels have attracted many attentions recently due to their versatile functions and potential applications in developing innovative semi-solid alcohol-containing products. In this study, comparisons were made in the aspect of rheology, physicochemical properties and sodium release between the conventional alkali konjac glucomannan (KGM) gels and alkali KGM alcogels prepared by mixing ethanol with KGM aqueous solution at 0.02 wt%, 0.04 wt% or 0.08 wt% Na2CO3. 20% (v/w) Ethanol could promote the formation of a rigid yet brittle alcogel of KGM with lower dependence of rheological response on frequency and temperature at as low as 0.02 wt% Na2CO3. KGM alcogels were more opaque and constructed by small highly-connected pores, which are 30% smaller in average than those of their counterparts, examined by turbidity and microstructure measurements. Although the swelling ratio of KGM alcogel was only about one third of that of conventional alkali-induced gel, there was about fourfold rise in the amount of Na+ released from alcogels. The release of Na+ could be probably regulated by fine-tuning the macro-properties of alcogels through controlling the alkali concentrations.

Introduction

When food is chewed, the flavor substances are released in mouth and subsequently transported to the taste buds from the food matrix (Busch, Yong, & Goh, 2013). Flavor release is a crucial step in taste perception as the flavor substances have to be dissolved in saliva in order to be detectable by flavor receptors (Scherf, Pflaum, Koehler, & Hofmann, 2015) and rapid release of flavor substances has great potential for applications in functional foods, such as low-sodium foods (Busch et al., 2013). The release rate of flavor substances is highly dependent on structural diversity and related mechanical properties of foods (Cook, Woods, Methven, Parker, & Khutoryanskiy, 2018), since the specialty in migration and diffusion behaviors of substances might be originated from a subtle but substantial microscopic structural rearrangement. Gel, one common structural element, constitutes an important part of food products (Hu et al., 2019; Kyomugasho et al., 2016) and has unique advantages in the controlled release of flavor substances (Boland, Delahunty, & Van Ruth, 2006; Kohyama, Hayakawa, Kazami, & Nishinari, 2016). The formulation of gel-based food products should be based on the knowledge of their mechanical and physical properties (Sala & Stieger, 2013). The accelerated release of tastants and volatiles is related with the greater exposure of fresh surfaces upon the fracture of brittler gels under chewing (Boland et al., 2006; Koliandris, Lee, Ferry, Hill, & Mitchell, 2008).

The term “alcogel” is used for the gel of which the solvent is alcohol or at least partially alcohol. Alcogels have attracted many attentions recently due to their versatile functions and great potential in the rapid release of flavor and the protection of heat-sensitive substances (Kim, Jeong, Kim, Kim, & Jung, 2019; Koliandris et al., 2008; Sala & Stieger, 2013) in developing innovative semi-solid alcohol-containing products (Cassanelli, Norton, & Mills, 2017; Sason & Nussinovitch, 2018). The formation of alcogels normally requires the aqueous solution of a certain gelling agent to be mixed with alcohol or binary aqueous system containing alcohol. It is known that gelation could possibly happen at low solubility. The combination of an antisolvent, such as alcohol, and an aqueous solution containing a solute poorly soluble in water, such as polysaccharide, would result in the rapid precipitation of the solute or in some special cases gelation. It was previously demonstrated that alcogels could be formed by gelling agents such as alginate, κ-carrageenan, xanthan, guar gum, gellan gum, pectin and xyloglucan (Cassanelli et al., 2017; Sason & Nussinovitch, 2018; Tkalec, Knez, & Novak, 2015; Yamanaka et al., 2000; Yang, Yang, & Yang, 2018). Cassanelli et al. (2017) assumed the study of alcogels could be extended to a wider range of gelling agents. Umemura and Yuguchi (2009) described the role of alcohol in the gelation of xyloglucan as a promotor of the aggregation of xyloglucan chains in some domain by adhering to xyloglucan and slowing the swelling-shrink motion of xyloglucan. Use of ethanol could promote gelation at a lower temperature and change gel properties (Sason & Nussinovitch, 2018; Uzun, Kim, Leal, & Padua, 2016; Yamanaka et al., 2000; Yang et al., 2018). It was reported that the ethanol addition would lead to alteration of water network, which irreversibly affected the gel properties at both molecular and macroscopic scales (Cassanelli et al., 2017).

Konjac glucomannan (KGM) is extracted from the tuber of the Amorphophallus konjac C. plant and often used as gelling agent in food industry. Chemically, KGM is composed of β-(1 → 4) linked d-mannose and d-glucose in a molar ratio of 1.6:1 or 1.4:1 (He et al., 2019; Luo, He, & Lin, 2013). There are some acetyl groups attached to the suger units, which are scattered randomly along the chain with an occurrence of approximately 1 per 19 residues (Tang, Wang, Li, & Dong, 2019; Zhang, Han, Yao, Pang, & Luo, 2013), contributing to the solubility and gel properties of KGM (Du, Li, Chen, & Li, 2012; Luo et al., 2013). Effects of alkali on facilitating the deacetylation and decreasing the solvation of KGM are crucial for the thermally irreversible gelation of KGM (Williams et al., 2000). The complete gelation of KGM is composed of an induction process corresponding to deacetylation and a two-stage gelling process: the first stage is the partial unfolding of the packed loose structure of slightly dehydrated KGM; the second stage involves the conformational transition from random coils to self-assembling filament networks and the formation of junction zones essentially composed of acetyl-free portions (Zhou, Jiang, Perkins, & Cheng, 2018). The intermolecular aggregation of KGM chains is not only regarding to hydrogen bonding, but also related to hydrophobic interactions (Du et al., 2012; Zhou et al., 2018). Commercial KGM food gels are produced at a high KGM concentration above 3 wt% under alkaline condition, normally pH 11–13. However, almost all KGM food gels prepared in the presence of alkali exhibit obvious defects, such as a high syneresis rate and undesirable alkaline taste, etc (Herranz, Tovar, Solo-de-Zaldívar, & Borderias, 2013; Wang, Jiang, Lin, Pang, & Liu, 2016), which can be alleviated by acid-wash for several hours or multiple times. Besides, KGM food gels should be preserved in alkaline solutions, making them costly for transportation and storage. An alternative method for preparing KGM gels is required to overcome these problems brought by alkali.

Therefore, the main purpose of this work was to prepare a novel low-alkali konjac alcogel and investigate its physicochemical and mechanical properties at macroscopic level. Elucidating the preliminary relationship between gel properties and Na+ release could help to explore the its potential application in low-sodium foods.

Section snippets

Materials

The purified konjac glucomannan (KGM) (>95.1 wt%, dry basis) was purchased from the Hubei Yizhi Konjac Biotechnology Co., Ltd. (Hubei, China). The contents of moisture and crude protein were 8.2 wt% and 0.76 wt%, respectively. The average molecular weight was around 2.59 × 103 kDa determined by gel permeation chromatography (GPC) using a dilute aqueous solution of KGM. All chemicals used were analytical grade and supplied by the Beijing Chemical Reagent Co., Ltd. (Beijing, China).

Sample preparation

The purified

Time sweep

The evolution of both storage modulus G′, loss modulus G″ with time and loss tangent (tan δ) at 30 min are shown in Fig. 1. The storage modulus G′ characterizes the elastic energy absorbed by the solid component of samples, while the loss modulus G″ characterizes the viscous energy dissipated due to internal shear stress by the liquid component. We can also judge the sol-gel status of samples by tan δ (tan δ = G"/G′), which is shown in Fig. S1.

The G′ was initially lower than the G″ for A1-A3,

Conclusions

A rigid but brittle alcogels of KGM could be obtained at a low alkali concentration of 0.02 wt% even without heating, which exhibited lower dependence on frequency and temperature than conventional KGM gels induced only by alkali. The rheological responses and mechanical properties of KGM alcogels are largely dependent on alkali concentrations given a certain ethanol addition amount. Compact network structures with highly restricted swelling ratio are evident for KGM alcogels, which are much

CRediT authorship contribution statement

Yun Zhou: Conceptualization, Methodology, Writing - original draft, Writing - review & editing, Project administration, Funding acquisition. Liangliang Wu: Methodology, Validation, Formal analysis, Investigation, Data curation, Writing - original draft, Visualization. Yuan Tian: Formal analysis, Visualization. Rui Li: Investigation, Validation. Chongyang Zhu: Investigation, Formal analysis. Guohua Zhao: Supervision, Project administration, Funding acquisition. Yongqiang Cheng: Supervision,

Declaration of competing interest

No conflict of interest exits in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part.

Acknowledgements

This work has been supported by the grant from the National Science Foundation of China (31571791), Fundamental Research Funds for the Central Universities (XDJK2020C051), the Venture & Innovation Support Program for Chongqing Overseas Returnees (cx2019119) and Development and Research Center of Sichuan Cuision (CC18Z13).

References (66)

  • X. Du et al.

    Effect of degree of deacetylation on physicochemical and gelation properties of konjac glucomannan

    Food Research International

    (2012)
  • J. Gong et al.

    The rheological and physicochemical properties of a novel thermosensitive hydrogel based on konjac glucomannan/gum tragacanth

    Lebensmittel-Wissenschaft und -Technologie

    (2019)
  • B. Herranz et al.

    Influence of alkali and temperature on glucomannan gels at high concentration

    Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology

    (2013)
  • Y. He et al.

    Interaction between konjac glucomannan and tannic acid: Effect of molecular weight, pH and temperature

    Food Hydrocolloids

    (2019)
  • Y. Hu et al.

    Partial removal of acetyl groups in konjac glucomannan significantly improved the rheological properties and texture of konjac glucomannan and κ-carrageenan blends

    International Journal of Biological Macromolecules

    (2019)
  • W. Jian et al.

    Effects of pH and temperature on colloidal properties and molecular characteristics of Konjac glucomannan

    Carbohydrate Polymers

    (2015)
  • W. Jin et al.

    Analysis of deacetylated konjac glucomannan and xanthan gum phase separation by film forming

    Food Hydrocolloids

    (2015)
  • G.M. Kavanagh et al.

    Rheological characterisation of polymer gels

    Progress in Polymer Science

    (1998)
  • C. Kim et al.

    Cyclodextrin functionalized agarose gel with low gelling temperature for controlled drug delivery systems

    Carbohydrate Polymers

    (2019)
  • K. Kohyama et al.

    Sucrose release from agar gels and sensory perceived sweetness

    Food hydrocolloids

    (2016)
  • A. Koliandris et al.

    Relationship between structure of hydrocolloid gels and solutions and flavour release

    Food Hydrocolloids

    (2008)
  • K.K. Kundan et al.

    Vibration assisted puncturing of a soft brittle solid

    Extreme Mechanics Letters

    (2019)
  • C. Kyomugasho et al.

    Evaluation of cation-facilitated pectin-gel properties: Cryo-SEM visualisation and rheological properties

    Food Hydrocolloids

    (2016)
  • K.Y. Lee et al.

    Characterization of gellan/gelatin mixed solutions and gels

    Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology

    (2003)
  • A.K. Lele et al.

    Energetically crosslinked transient network (ECTN) model: Implications in transient shear and elongation flows

    Journal of Non-newtonian Fluid Mechanics

    (1998)
  • M.A. Lenji et al.

    Experimental study of swelling and rheological behavior of preformed particle gel used in water shutoff treatment

    Journal of Petroleum Science and Engineering

    (2018)
  • J. Liang et al.

    Measuring microgel swell ratio by cryo-SEM

    Polymer

    (2017)
  • X. Liu et al.

    Effects of sodium carbonate and potassium carbonate on colloidal properties and molecular characteristics of konjac glucomannan hydrogels

    International Journal of Biological Macromolecules

    (2018)
  • T. Li et al.

    Effect of ε-polylysine addition on κ-carrageenan gel properties: Rheology, water mobility, thermal stability and microstructure

    Food Hydrocolloids

    (2019)
  • X. Luo et al.

    The mechanism of sodium hydroxide solution promoting the gelation of Konjac glucomannan (KGM)

    Food Hydrocolloids

    (2013)
  • C. Mao et al.

    A kinetic model of the gelation of konjac glucomannan induced by deacetylation

    Carbohydrate Polymers

    (2017)
  • H.M. Moreno et al.

    Effect of high pressure treatment on the structural, mechanical and rheological properties of glucomannan gels

    Food Hydrocolloids

    (2016)
  • K. Nishinari et al.

    Recent advances in the understanding of heat set gelling polysaccharides

    Trends in Food Science & Technology

    (2004)
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