Viscosity reduction of tapioca starch by incorporating with molasses hydrocolloids

Xin Wan,Hui Jiang,Zhen Ye,Hang Zhou,Yimin Ma,Xuanrui Miao,Xun He,Kequan Chen

State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical, Nanjing Tech University, Nanjing 210009, China

Keywords:Biomass Molasses Tapioca starch Blend Starch gelatinization Polymer processing

ABSTRACT As a low cost non-staple food resource,the high-viscosity paste and poor gel-forming ability of tapioca starch limit its industrial application.Herein,molasses hydrocolloids that is a by-product of the sugar refining process was applied as a blending modifier to reduce the viscosity of tapioca starch paste.The test results of paste and rheological properties show that molasses hydrocolloids exhibited a good physical viscosity-reducing effect on tapioca starch paste.The irregular network structure and high K+/Ca2+ion contents of molasses hydrocolloids exerted wrapping,adhesion,barrier,and hydration effects on starch,leading to the reduction of viscosity.The scanning electron microscope images and textural analysis demonstrated that this strategy also improve the structure of tapioca starch gel and enhanced its puncture strength by 75.46%.This work shows the great potential of molasses hydrocolloids as a lowcost and desirable material for the viscosity reduction of tapioca starch.

1.Introduction

Various starches for crops (e.g.,tapioca,wheat,potato,and maize) can be used as a raw material for the fabrication of edible films and gum.As a non-staple food resource,tapioca starch is widely used in industrial fields due to its low cost and highly availability.However,its high-viscosity paste and poor gel-forming ability tend to cause high production energy consumption,low material performance and high equipment loss,limiting its industrial applications.Therefore,the modification of tapioca starch to improve its gelation properties and expand its applications has become a popular research area in starch science [1,2].

To date,various chemical and physical strategies have been applied to address the above shortcomings.Chemical denaturation methods,such as hydroxypropylation and cross-linking,are reported to possess the ability of the paste viscosity reduction and gel stability enhancement [3,4].Blending with polymers(i.e.,physical modification),such as hydrophilic colloids,can also improve the rheological properties of starch paste[5].For example,gum arabic weakened the hydrogen bonds between starch molecules and inhibited the binding of starch molecules by forming barriers against the starch granules in the spatial structure,which ultimately reduced the paste’s viscosity[6].The physical properties of hydrophilic colloids can be utilized for starch modification.For instance,nonionic guar gum increased the viscosity of negatively-charged potato starch paste,while negatively-charged xanthan gum significantly decreased the viscosity of this potato starch paste [7].Negatively-charged hydrocolloids can create repulsive forces with negatively-charged phosphate groups of the potato starch,delaying the pasting and gelatinization of starch granules,leading to a lower viscosity.In addition,hydrophilic colloids have good water solubility and will compete with starch for water molecules.The lack of water will cause the starch to slowly form a paste.In general,only a small amount of hydrophilic colloids can effectively change the properties of starch via blending process [8-10].However,the complexity of chemical methods and the high cost of commercial hydrocolloids allow more new strategies to be explored.

Molasses is a by-product of the sugar refining process and a common biocatalytic substrate.It contains 7%-25% colloids,with hydrocolloids accounting for 20%-90% of the total colloids,which mainly consist of sugars and their derivatives [11-13].Molasses colloids are often discarded directly at the molasses pretreatment stage because they inhibit the biotransformations of molasses[14].These characteristics show its potential as an ideal low-cost raw material obtained from food wastes for the blending modification of starch;even so,its application in starch-based materials has never been reported.

Inspired by the above consideration,the present study investigated the feasibility of using molasses hydrocolloids as blending modifiers to reduce the viscosity of tapioca starch paste.Firstly,the physical properties of molasses hydrocolloids,such as charge distribution,morphology,and viscosity,were characterized.Then,the effects of molasses hydrocolloids on the paste,static/dynamic rheological,textural,and gel properties of starch were comprehensively determined.The possible blending modification mechanism of molasses hydrocolloids and tapioca starch was also speculated by comparing with a commonly used commercial hydrocolloid(i.e.,gum arabic).This work provided a new facile and low-cost strategy for the viscosity reduction of tapioca starch,which also broadens the application fields of molasses hydrocolloids.

2.Materials and Methods

2.1.Materials

Molasses was obtained from Shandong Jinan Sugar Co.,Ltd.(Shandong,China) and stored at room temperature.The metal ion concentration determination in molasses was performed by the Physical and Chemical Testing Center of Jiangsu Province.The total carbohydrate concentration was analyzed using the phenol/-sulfuric acid method.The contents of monosaccharides and disaccharides were analyzed using high-performance liquid chromatography with an evaporative light scattering detector(2000ES,Alltech,USA) [10].

Industrial-grade gum arabic was purchased from Hebei Dongtai Wax Products Co.,Ltd.(Hebei,China).Tapioca starch (starch content 78.25% ± 1.01%) was purchased from a local supermarket in Nanjing,China.All other chemicals were of analytical grade.

2.2.Hydrocolloids preparation

Molasses hydrocolloids were separated from molasses step-bystep.The supernatant of the molasses was subjected to centrifugation and ultrafiltration,and the retention liquid and supernatant were obtained.The middle-layer gel was obtained by liquid extraction using petroleum ether.The middle-layer gel and intercept liquid were mixed,and crude colloids were obtained by ethanol precipitation.Then,crude colloids were repeatedly washed with 95% ethanol to remove free sugar molecules to obtain molasses hydrocolloids.The complete removal of free sugars was determined by Molisch’s test.The free proteins in molasses hydrocolloids were removed by the Sevag method to obtain deproteinized molasses hydrocolloids.

Commercially available gum arabic and synthetic Maillard reaction products were used as controls.The Maillard reaction conditions were described that casein (5 g) and glucose (10 g) were dissolved in pure water so that the total concentration of casein and glucose was 20%(mass to volume ratio).The mixture was controlled at pH 12 using sodium hydroxide (5 mol·L-1) and hydrochloric acid (1 mol·L-1).It was then heated to reflux in an oil bath with stirring (102 °C,10 min,14000 g) in a 250 ml three-neck round-bottom flask.The residual solution was cooled in an ice bath,then stirred,and centrifuged with 95% ethanol at room temperature.The obtained solid precipitate was the Maillard reaction products [15].

2.3.Combination of tapioca starch and hydrocolloids

Molasses hydrocolloids,gum arabic,and synthetic Maillard reaction products were added separately to the tapioca starch suspension (100 ml).The compounding ratios of tapioca starch and hydrocolloids were 9.5:0.5,9.0:1.0,8.5:1.5,and 8.0:2.0 (by dry matter mass).Stirring was performed at room temperature to uniformly disperse the tapioca starch in the mixture suspension.

2.4.Combination of tapioca starch and metal ions

Different concentrations of calcium chloride,magnesium chloride,manganese chloride,and potassium chloride solutions were prepared separately.The volume of each salt solution was 100 ml.Tapioca starch was slowly added to each salt solution so that the concentration of tapioca starch in the suspension was 6%(mass to volume ratio).Stirring was performed at room temperature to uniformly disperse the tapioca starch in the mixture suspension.

2.5.Starch pasting

Pasting characteristics were analyzed using a rheometer (MCR 302,Anton Paar GmbH,Austria).The heating and cooling program was as follows: after holding at 50 °C for 2 min,the temperature was increased to 95 °C at the rate of 5 °C·min-1and then held for 6 min,before finally being decreased to 50 °C at the rate of 5 °C·min-1,and finally held for 2 min.The rotation speed was 1000 r·min-1for the first 20 s,and then it was maintained at a constant speed of 200 r·min-1until the end of the experiment.

2.6.Rheological property analysis

The static rheological properties and dynamic viscoelastic properties of tapioca starch and tapioca starch-hydrocolloids mixture were analyzed immediately after gelatinization.

The rheological analysis parameters were a diameter,gap,and temperature of 4 cm,0.1 cm,and 25 °C,respectively.The change in the shear stress of samples at shear rates of 0-300 s-1was studied.

Dynamic viscoelastic parameters,including the diameter,gap,temperature,and strain,were 4 cm,0.1 cm,25 °C,and 1%,respectively.The storage modulus (G′),loss modulus (G′′),and loss tangent (tanδ) were recorded by frequency sweep tests ranging from 0.1 to 10 Hz.

2.7.Scanning electron microscopy (SEM)

Neat tapioca starch paste/gel and starch/molasses (8:2) mixed system paste/gel were fixed on conductive double-sided adhesive and then sprayed with a thin layer of gold,before being observed by a scanning electron microscope (SEM,JSM-5900,Japan).The paste and gel samples were thoroughly freeze dried to obtain the dry gel.

2.8.Surface charge

A mixture of molasses hydrocolloid and the aqueous solution was prepared,and the surface potential of molasses hydrocolloids was determined using a zeta potential analyzer (Zetasizer,Malvern,UK).

2.9.Viscosity analysis

A mixture of molasses hydrocolloids and the aqueous solution was prepared,and the sample viscosity was determined using a Tec Master rapid viscosity analyzer (Perten Instruments,Sweden).The procedure was as follows:hold at 50°C for 1 min;heat to 95°C at 6°C·min-1for 5 min;cool to 50°C at 6°C·min-1for 2 min;stir at 960 r·min-1from 0-10 s;stir at 160 r·min-1for viscosity testing.

2.10.Textural characteristics

Samples were stored at 4°C for 24 h,and then the textural characteristics of the gels were measured by a TMS-PRO Texture analyzer (FTC,USA).The measured parameters were as follows:starting force 0.05 N;puncture distance 5 mm;test speed 60 mm·min-1.The measured parameters were gel hardness,puncture displacement at maximum hardness,work done by puncturing the gel,and maximum modulus.Data were analyzed by the software provided with the instrument.

2.11.Thermogravimetric (TG) analysis

Samples were stored at 4 °C for 24 h.Thermogravimetric (TG)analysis was performed with a Synchronous Thermal Analyzer(STA449F3,NETZSCH,Germany) under a nitrogen atmosphere.The mass of each gel sample was 9-10 mg,the heating rate was 10 °C·min-1,and the scanning temperature range was from room temperature to 800 °C.

3.Results and Discussion

3.1.Properties of molasses hydrocolloids

The properties of the molasses hydrocolloids are shown in Table 1.When the concentration of molasses hydrocolloids was 5%,the pH of the mixture was 6.38,and the corresponding ξ-potential value was -20.30 mV.When the pH was adjusted to 4.0 or 9.54,the corresponding ξ-potential was -6.33 or-32.2 mV.These results indicated that molasses hydrocolloids were negatively charged and could create repulsive forces with the negatively-charged phosphate groups of tapioca starch.Molasses hydrocolloids contained 80.48%polysaccharides,indicating that they could adhere to the surface of tapioca starch granules.In addition,the viscosities of the 1% (mass to volume ratio)molasses hydrocolloids aqueous solutions were in the range of 1.52-1.87 mPa·s,while those of commercially-available gum arabic,guar gum,and xanthan gum-aqueous solutions at the same concentrations were in the ranges of 1-20 mPa·s,1000-6000 mPa·s,and 500-800 mPa·s,respectively [16,17].The viscosity of guar gum and xanthan gum increased gradually upon increasing the temperature,while temperature had no significant effect on the viscosity of gum arabic and molasses hydrocolloids.

Table 1 The properties of molasses hydrocolloids and commercially available hydrocolloids

3.2.Viscosity curve

The viscosity curve can reflect the pasting properties of tapioca starch and its viscosity profile (Fig.1).Tapioca starch showed a sharp viscosity peak,but the tapioca starch mixed with molasses hydrocolloids exhibited a lower viscosity peak.It can also be seen from Fig.1 that the viscosity of the molasses hydrocolloids was very low and unaffected by temperature.Notably,starch modification influenced the starch pasting properties,especially the pasting temperature and peak viscosity (Table 2).The pasting parameters,including the pasting temperature,peak viscosity breakdown,and final viscosity were 72.2 °C,193.70,126.90,and 114.00 mPa·s,respectively.When crude colloids,molasses hydrocolloids,and deproteinized molasses hydrocolloids were compounded with tapioca starch at a ratio of 8:2,the pasting temperatures of these mixed systems increased by 5.1,4.3,and 4.6 °C,respectively,and the peak viscosity also decreased by 13.37%,17.45%,and 17.50%,respectively.The solution values decreased by 5.83%,6.93%,and 7.98%,respectively,and the final viscosity decreased by 21.23%,38.51%,and 38.33%,respectively.Moreover,the viscosityreducing effect of molasses hydrocolloids and deproteinized molasses hydrocolloids on tapioca starch was stronger than that of crude colloids.The pasting parameters were closely related to the interaction between starch molecules and other molecules in the aqueous solution.Molasses hydrocolloids were obtained by removing free sugar molecules,such as sucrose,glucose,and fructose,from crude colloids.The hydroxyl groups in these smallmolecule sugars formed hydrogen bonds with adjacent water molecules,which decreased amylose dissolution [18].Moreover,as a bridging molecule,sugar molecules formed strong sugar-starch interactions with starch chains,thus stabilizing the molecular structure of starch and increasing the pasting temperature and viscosity [19,20].

Table 2 Effects of molasses hydrocolloids on the gelatinization of tapioca starch

Fig.1.Viscosity curve of tapioca starch.

When the tapioca starch-to-molasses hydrocolloids ratio was 8:2,the peak viscosity of the mixed system was 17.45%lower than that of single tapioca starch.The peak viscosity of the mixed system was only 7.95% lower than that of single tapioca starch(Table 2).The molecular weight range of the Maillard reaction products prepared from glucose and tyrosine was only 3000-5000 Da [15],which was much lower than that of the molasses hydrocolloids,which displayed stronger phase separation.On the other hand,when the ratio of tapioca starch to gum arabic gum was 9:1,the peak viscosity of the mixed system of tapioca starch and gum arabic was 20.75% lower than that of single tapioca starch,which was similar when the ratio of molasses hydrocolloids was 8:2 (Table 2).These results indicate that when the amount of molasses hydrocolloids was about twice that of gum arabic,the viscosity-reducing effect was similar to that of gum arabic.

The molasses hydrocolloids contained xylose gum,gum arabic,and pectin [11].Gum arabic is a natural biomacromolecular polyanionic gum with a highly-branched structure that forms a low-viscosity solution and whose typical colloid has a high concentration and low viscosity.When gum arabic was compounded with starch,the anion of gum arabic and starch molecules underwent charge interactions.The multi-branched structure of gum arabic was interspersed between hydrated starch molecules to exert a barrier effect that hindered the chain entanglement between starch molecules and reduced the content of gum arabic due to electrostatic repulsion between particles [16],which decreased the peak viscosity.

The effects of salt ions on starch and its mixed system were closely related to the salt type and salt concentration[21].The effects of metal ions(Ca2+,K+,Fe2+,Mn2+)in the molasses hydrocolloids on the pasting of tapioca starch were investigated(Table 3).When K+(0.5 g·L-1) or Ca2+(0.2 g·L-1) were mixed with tapioca starch,the pasting temperature increased by 1.2 and 1.4°C,the retrogradation values increased by 8.47%and 18.64%,the peak viscosity decreased by 13.47% and 16.77%,and the final viscosity decreased by 7.01%and 20.08%,respectively.Low concentrations of metal ions had no significant effects on the pasting properties of tapioca starch.It can also be seen from Table 3 that under the same concentrations of K+and Ca2+,Ca2+had a greater impact on the breakdown,final viscosity,and setback of tapioca starch than K+.The mechanism by which metal ions affected the pasting properties of starch included two effects: the phosphate radical group of starch was vulnerable to the dissociated metal ions,and dissociated metal ions reduced the exudation of starch.These effects prevented the destruction of the crystal structure [22];therefore,the addition of metal ions inhibited the pasting of starch,and the pasting temperature gradually increased upon increasing the metal ion concentration.The reason for the significant decrease in the tapioca starch peak viscosity was that the added chloride salt added is a strong electrolyte that can dissociate into a cation and anion in water,which affects the hydrogen bonds between starch and water.This makes starch difficult to gelatinize,thus significantly decreasing the peak viscosity [21].

Table 3 Effects of metal ions on the gelatinization of tapioca starch

3.3.Static rheological properties

Fig.2(a) shows the relationship between the shear stress and shear rate of tapioca starch,in which the ratios of tapioca starch and molasses hydrocolloids were 10:0,9.5:0.5,9:1,and 8:2,respectively.Under the same shear rate,the required shear stress values of tapioca starch blended with molasses hydrocolloids were much lower than those of single tapioca starch.This indicated that the flow resistance of the mixed system was lower than that of the single tapioca starch system.Meanwhile,the required shear stress of the single tapioca starch system increased rapidly upon increasing the shear rate,while the required shear stress of the mixed system increased slowly.Although the network structure of the mixed system was disrupted by shear,the thixotropic ring area decreased when the shear rate decreased,indicating that the structure of the mixed system easily recovered after removing the stress.This phenomenon can be described as a synergistic viscosity behavior caused by the molecular interaction (hydrogen bonding) betweenstarch and molasses hydrocolloids,which was also reported in the static shear rheological properties of the corn starch-gum arabic mixed system [16].

Fig.2.Static rheological properties of the mixed systems containing tapioca starch and molasses hydrocolloids.

The mixed system was initially determined to be a shearthinning fluid (pseudoplastic fluid) based on the lgτ-lgγ linear fit to the increasing shear rate (upward line,Fig.2(b)).The Ostwaldde Waele power-law model(Eq.(1))was used to fit the flow curve.

By using Eq.(1) to fit the data in Fig.2,it was found that the Ostwald-de Waele power-law model had high fitting accuracy for the mixed system,with correlation coefficientsR2all above 0.995 and curve fluid indicesnall less than 1 (Table 4),which indicated proved that the mixed system was a typical pseudoplastic fluid[23].This may also be due to steric hindrance because the entanglement points of the molecular structure were reduced,which decreased the apparent viscosity [24].The consistency coefficientK(upward and downward curves)of the mixed system decreased,and the value ofnincreased,indicating that the molasses hydrocolloids had a significant viscosity-reducing effect on tapioca starch.

Table 4 Rheological parameters of mixed systems of tapioca starch and molasses hydrocolloids

3.4.Dynamic viscoelasticity

The dynamic modulus and tanδ of tapioca starch and molasses hydrocolloids under different compounding ratios and tanδ change curves are shown in Fig.3.The dynamic viscoelasticity of a starch paste gel system is directly related to its practical applications.The storage modulus (G’) represents energy storage and recoverable elastic properties,while the loss modulus (G") represents the viscous energy dissipation [25].G’ ＞G" indicates that the sample shows gel characteristics of a viscoelastic solid,andG’ ＜G" indicates that the sample shows characteristics of a viscoelastic liquid.The greater tanδ,the greater the viscosity ratio and the stronger the fluidity of the test system (tanδ=G’/G’’),and the greater the elastic ratio [26].From Fig.3,upon increasing the test frequency,theG’andG"values of single tapioca starch and the mixed system gradually increased.AllG’values were always greater thanG",and all tanδ values were always less than 1.Ikeda and Nishinari [27]demonstrated that these were typical properties of weak gels,so the mixed systems consisting of tapioca starch and molasses hydrocolloids in any ratio were weak gels.TheG’ andG′′values of the mixed systems were much lower than those of single tapioca starch,but all tanδ values were slightly higher than those of the single tapioca starch.These results were similar to those of gum arabic and starch.Thus,there may be branched structures in molasses hydrocolloids components that hindered the gelation of tapioca starch,so that the gel strength of the mixed systems of tapioca starch and molasses hydrocolloids was weak.

Fig.3.Dynamic viscoelasticity for the mixed systems containing tapioca starch and molasses hydrocolloids.

3.5.Textural characteristics

The textural characteristics of tapioca starch gels were measured by a physical analyzer at 4°C for 24 h,including the gel hardness,maximum hardness displacement,and maximum modulus.The results are shown in Table 5.The hardness of the single tapioca starch gel was 0.216 N,and the addition of molasses hydrocolloids increased the tapioca starch gel strength to 0.223-0.379 N,an increase of 3.25%-75.46%.When the amount of molasses hydrocolloids increased from 10.0:0 to 9.5:0.5,the strength of the tapioca starch gels did not change significantly,but when the amount increased to 9.0:1 and 8.5:1.5,the gel strength of the mixed system was 10.19%and 57.41%higher than that of the single tapioca starch gel,respectively.When dextran and tapioca starch were mixed in a ratio of 16:1,the puncture strength of the mixed-system gel increased by 10.88% [28].The strength of the tapioca starch gel itself was low.Polysaccharides were blended with tapioca starch by wrapping,adhesion,or embedding to form a denser spatialstructure than single starch gels,which increased the gel strength of the mixed system.

Table 5 Effects of molasses hydrocolloids on the texture characteristics of tapioca starch gels

The maximum hardness of the single tapioca starch gel was 2.81 mm.When the molasses hydrocolloids were added,the displacement of the maximum hardness increased to 2.83-3.04 mm,an increase of 0.71%-8.19%,reflecting the flexibility and toughness of the starch gel.

When the amount of water-soluble molasses colloid increased from 10.0:0 to 9.0:1,the maximum hardness of the mixed systems did not change significantly.When the amount of molasses in the water-soluble colloid increased to 8.5:1.5,the maximum hardness of the mixed system was 7.12%higher than that of the single tapioca starch.

3.6.TG curve

The TG curves in Fig.4 showed that the mass of tapioca starch gels decreased upon increasing the temperature.The mass reduction in the temperature range of 25-120 °C was caused by water evaporation,which represents the moisture content in the samples.The single tapioca starch gels had no significant mass loss in the temperature range of 120-280°C,while the mass loss curves of the mixed system gels were smooth because of the dehydration of organic molecules or the loss of small-molecule substances.The mass of both single tapioca starch gels and gels of the mixed system decreased significantly at 280 °C,indicating organic macromolecules began to break down at this stage.As shown in Fig.4,the decomposition temperature of the mixed system was lower than that of single tapioca starch,indicating that the mixed system had worse thermal stability than single tapioca starch.The addition of guar gum also led to the same result [17].Moreover,all tested samples exhibited the same two concave peaks at 100 °C and 280 °C,indicating the absence of new component formation,and thus the non-chemical modification (i.e.,physical modification)may responsible for the viscosity-reducing effect of molasses hydrocolloids.

Fig.4.TG curves of the mixed systems containing tapioca starch and molasses hydrocolloids.

3.7.SEM

The SEM images of the tapioca starch gels are shown in Fig.5.The surface of the single tapioca starch gel was rough,but the gel surface of the mixed system was smooth.This was consistent with the modification of starch structure by polysaccharides such as pullulan.The single tapioca starch gel had an irregular spongy mesh structure,and its mesh size,pore wall thickness,and mesh profile were non-uniform,and many small pores appeared on the pore walls.The molasses hydrocolloids in the mixed system covered the surface of tapioca starch or were embedded in the mesh structure of starch,which made the gel structure of the mixed system dense.

Fig.5.Effects of molasses hydrocolloids on the surface morphology of tapioca starch gels:(a)tapioca starch paste,(b)the mixed systems paste,(c)tapioca starch gel,(d)gels of the mixed systems.

3.8.Mechanism

The main component of molasses hydrocolloids is anionic macromolecular sugars,which have low aqueous solution viscosity.The temperature had no significant effect on the viscosity of aqueous solutions containing molasses hydrocolloids.Therefore,changes in the paste characteristics in the mixed system were due to changes in the paste properties of tapioca starch.The dissolution and pasting of tapioca starch in the aqueous solution containing molasses hydrocolloids occurred,and the whole process was divided into three stages.In the first stage,tapioca starch granules were dispersed and slightly swollen in the aqueous solution containing molasses hydrocolloids,and this swelling phenomenon was reversible during drying.In the second stage,tapioca starch granules were heated in the aqueous solution containing molasses hydrocolloids,allowing them to absorb water and swell.However,some tapioca starch granules may have been wrapped or adhered to by molasses hydrocolloids,isolating the starch granules from each other,which in turn hindered the swelling and gelation ofstarch granules.In addition,the starch granules that underwent swelling gradually occupied more space and had an extrusion effect on the starch granules that adhered to or were wrapped by the molasses hydrocolloids.Then,the normally swollen tapioca starch granules lost their integrity and disintegrated into fragments,as shown in the third stage.The disintegration of the swollen tapioca starch granules caused them to also become wrapped or adhered to and separated by molasses hydrocolloids.More importantly,as the content of branched starch increased,more starch granules may have been wrapped and undergo limited swelling by molasses hydrocolloids,which explains the viscosityreducing effect of molasses hydrocolloids on tapioca starch.The microstructure of the starch pasting system was closely related to its rheological properties,and significant changes in the microstructure led to different rheological properties between the mixed system and the single tapioca starch.

4.Conclusions

In this study,a method for preparing high-strength tapioca starch by adding molasses hydrocolloids was proposed.The molasses hydrocolloids had a significant viscosity-reducing effect,implying its retrogradation retarding capacity.The mixed system consisting of tapioca starch and molasses hydrocolloids was a typical non-Newtonian pseudoplastic fluid.Compared with the single tapioca starch,the shear stress required during the flow of the mixed system was reduced,and the curve curvature was decreased,indicating a lower resistance to flow in this mixed system.For the preparation of starch gels with a higher puncture strength and better flexibility,the gel surface of the mixed system was smoother and more compact than that of the single tapioca starch gel.The TG curves showed that no new substances formed during the bleeding modification process,indicating that the modification was a physical process.

Data Availability

Data will be made available on request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (U21B2097),the National Key Research and Development Program of China (2018YFA0901500) and the Jiangsu Postdoctoral Research Foundation (2019K242).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2023.03.003.