Published paper in journal of food processing and technology

Keywords: Sweet potato starch; Sung bean starch; Cooking quality; Starch noodles Abbreviation: SPS: Sweet Potato Starch; SPS_N: Sweet Potato Starch Noodle; SP1_W_YR: White skin and Yell

http://www.omicsonline.org/jfpthome.ph p

Chris Sommers, Eastern Regional Research Center, USA

Rogers E Harry-OKuru, National Center for Agricultural Utilization Research, USA

Shiowshuh Sheen, Microbial Food Safety Research Unit, USA

Tony Jin, Eastern Regional Research Center, USA

C J Boushey, Purdue University, USA

Regis Stentz, Institute of Food Research Park- Colney, UK

Chalat Santivarangkna, Technical University of Munich, Germany

Yin Li, North Dakota State University, Fargo

Ghufran bin redzwan, Universiti Malaya, Kuala Lumpur

Jozef Kokini, Director, Illinois Agricultural Experiment Station, USA

Noureddine Benkeblia, UWI Mona Campus, JAMAICA

Fabio Mencarelli, University of Viterbo, Italy Steven Pao,

Virginia State University, Petersburg

Toru Matsui, Univ of the Ryukyus, Japan

Mohamed Fawzy Ramadan Hassanien, Zagazig university, Egypt

Daniel St-Gelais, Food Research and Development Centre, Canada

Federico Harte, The University of Tennessee, USA

Marie Yeung, California Polytechnic State University, USA

Dike O Ukuku, Philadelphia

F ood Processing and Technology

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ISSN: 2157-7110

Keywords: Sweet potato starch; Sung bean starch; Cooking quality;

Starch noodles

Abbreviation: SPS: Sweet Potato Starch; SPS_N: Sweet Potato

Starch Noodle; SP1_W_YR: White skin and Yellow-Red flesh color

Sweet Potato variety; SP2_P_P: Purple skin and Purple flesh color

Sweet Potato variety; SP3_P_Y: Purple skin and Yellow flesh color

Sweet Potato variety; SP4_OP_O: Orange-Purple skin and Orange flesh

Sweet Potato variety; MBS: Mung Bean Starch; MBS_N: Mung Bean

Starch Noodle; 1S_9M_N: Noodles made from 10% SPS and 90% MBS;

2S_8M_N: Noodles made from 20% SPS and 80% MBS; 3S_7M_N:

Noodles made from 30% SPS and 70% MBS; 4S_6M_N: Noodles made

from 40% SPS and 60% MBS; 35S65WN: Noodles made from 35%

starch and 65% Water; 40S60WN: Noodles made from 40% starch and

60% Water; 45S55WN: Noodles made from 45% Starch and 55% Water

Introduction

Starch noodles or cellophane noodles are popular staple foods in

many Asian countries in which China is the largest production and

consuming country Unlike the other types of noodles such as wheat

noodles or pasta in which gluten protein is responsible for forming the

network to integrate other components to form visco-elastic dough

[1], starch noodles are made only from free-gluten starches and water,

therefore the starch properties are essential for noodle processing and

final product quality The starch noodles can be produced by dropping,

cutting or extruding method The common characteristics of these

methods are heat treatment starch dough or slurry which are boiling

or steaming to gelatinize the starch and cooling or freezing to accelerate

retro gradation process which fixes noodle structure [2].Nevertheless,

cooling is preferred to freezing in noodle production because more

time and cost are required for freezing treatment [3] Noodle qualities

are usually defined by visual attributes of the dry and cooked noodles

The dry starch noodles should be high transparence, high glossiness,

inexistence of discoloration and straightly fine threads The most

important characteristics for cooked starch noodles are texture and

mouth feel, they should remain firmness, not sticky after cooking, high

tensile strength, short cooking time and low cooking loss [2,3] The

quality of starch noodles usually is measured by three different aspects,

namely sensory evaluation, cooking quality, and textures [2,4-7]

Mung bean starch traditionally was ideal material for noodle production because its starch showed high amylose content, restricted swelling and a C-type Bra bender viscosity pattern which indicated no pasting peak but rather a very high viscosity which remained constant

or else increased during cooking and it provided the favorite texture and appearance of cooked noodles [2,4,5] However, due to low yield and tediousness in starch isolation procedure, together with expensive price; mung bean starch cannot meet the increasing demand of starch noodles in recently years [4,8]; therefore looking for other starch materials, which are abundant and cheaper price, substitute mung bean starch partially or totally will be valuable The sweet potato starch is one of the promising substitutes for mung bean starch in noodle production The sweet potato is relatively easy to grow, high productivity, high starch content (6.9-30.7%) in which amylose content

is 8.5-38% depending on variety [4] The Asian countries contributed more than 80% of total world production of sweet potato In China, Vietnam, Indonesia, Thailand and India, sweet potatoes are important food crops grown throughout country However, noodles made from sweet potato starch are not much preferred by customers, and their qualities are significantly inferior to mung bean starch noodle qualities The sweet potato starch noodles are dull, opaque, moderately elastic, and high cooking loss and swelling as cooking [2,4,5,9] Therefore, the blending SPS with MBS for noodle production needs to be investigated

to combine both advantage attributes of mung bean and sweet potato starch

The purposes of this study were: (1) to investigate and compare the

*Corresponding author: Ho Minh Thao, Food Technology Deparment, An Giang

University, Vietnam, Fax: +84 76 3842560; E-mail: hmthao@agu.edu.vn

Received January 24, 2011; Accepted February 19, 2011; Published February

27, 2011

Citation: Thao HM, Noomhorm A (2011) Physiochemical Properties of Sweet

Potato and Mung Bean Starch and Their Blends for Noodle Production J Food Process Technol 2:105 doi:10.4172/2157-7110.1000105

Copyright: © 2011 Thao HM, et al This is an open-access article distributed under

the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Physiochemical properties of four types of sweet potato starch (SPS) and mung bean starch (MBS), and their blends for noodle production were accessed The results indicated that MBS was significantly higher in

amylose content (40.69%), gel hardness, hot paste stability and cold paste viscosity; but substantially lower

in protein, lipid, ash content, and gel stickiness than those of all sweet potato starches Among all sweet potato

varieties, the white skin and yellow-red flesh color sweet potato variety (SP1_W_YR) was the most suitable

for noodle production due to its the highest starch yield (17%) and starch purity as well as the best starch color

The MBS noodle quality was superior to SPS noodle quality, and blending SPS with MBS for noodle production

resulted in markedly reducing quality However, the quality of noodles made from mixture of 20% SPS and 80%

MBS was not significant difference to that of MBS noodles The increase of solid content of starch slurry resulted

in considerable increasing in cooking time, cooking loss, rehydration and tensile of noodles while aging time only

markedly affected cooking loss and tensile For noodles prepared from mixture of 20% SPS and 80% MBS, the

Physiochemical Properties of Sweet Potato and Mung Bean Starch and Their Blends for Noodle Production

Ho Minh Thao 1 and Athapol Noomhorm 2

1 Food Technology Deparment, An Giang University, Vietnam

2 Food Engineering and Bioprocess Technology, School of Environment, Resources and Development, Asian Institute of Technology, Pathumthani, Klong Luang 12120,

Citation:Thao HM, Noomhorm A (2011) Physiochemical Properties of Sweet Potato and Mung Bean Starch and Their Blends for Noodle Production

J Food Process Technol 2:105 doi:10.4172/2157-7110.1000105

Page 2 of 9 physiochemical properties of starches isolated from four common Thai

sweet potato varieties and mung bean starch, (2) to evaluate qualities

of noodles prepared from mixture of SPS and MBS and (3) to access

effects of processing parameters on noodle quality

Materials and Methods

Raw materials

Four types of sweet potato varieties namely, white skin and

yellow-red flesh color (Kratai cultivar) (SP1_W_YR), purple skin and purple

flesh color (Torpuag cultivar) (SP2_P_P), purple skin and yellow

flesh color (Kaset cultivar) (SP3_P_Y) and orange- purple skin and

orange flesh color (Khai cultivar) (SP4_OP_O); and mung bean starch

produced by SitThiNan Co., Ltd were purchased from Thailand All

used chemicals and reagents were in analytical grade

Starch isolation

The sweet potato roots were washed thoroughly, peeled, cut

into small pieces (4x4x4mm) that were then soaked in 0.2% sodium

metabisulfite solution with ratio of 1:2 (w/w) for 15 minutes and

ground in a blender for 5 min The slurry was filtrated through a fabric

filter to remove fibers and other components before passing through

a 100 mesh sieve The filtrate was allowed to undisturbed stand for 3

hrs The collected starch re suspended with tap water, settled down and

removed water This process was repeated in three times to remove any

pigment residue The obtained starches were dried in hot air oven at

50°C for 12 hrs until about 10% MC (wet basis) Then, it was finely

ground and packaged in polyprolene bags and kept at cold room (4°C)

until further analysis

Starch yield (%)

The starch yield (%) obtained from sweet potato root could be

calculated by following formula:

Extractd starch

Total amount of raw sweet potato root×

Proximate compositions of starches

Apparent amylose content (%) was determined by colorimetric

iodine assay index method, following Juliano [10] The moisture,

protein, lipid and ash content in starch were determined using

procedure of AACC method [11]

Starch color

The color of starches in terms of L*, a* and b* values were measured

by Hunter lab Colorimeter (Color flex, USA) The whiteness value was

obtained by following equation:

1

Whiteness=100 (100− −L) + +a b  (2.2)

Light microscopy observation

The shape and size of starch granule were determined by using

BX40 Microscope (MBL2100, Germany) interfaced to digital camera

(DCM 300, 3M pixels) Placing a drop of starch suspension (0.1g

starch in 10ml water and stirring thoroughly) onto the glass plate and

cover with cover slit and observing under microscopic Granule size

was measured using a microscope fitted with a calibrated eyepiece to

calculate the range and average of the granular size [4]

Gel texture

Gel texture was determined by using Instron TA.XT2 Plus, uniaxal

compression (Stable Micro System, USA) as reported by Pons [12]

Starch gel was made by heating and stirring continuously 10% starch slurry at 85°C for 20 minutes Then, it was poured into in PVC pipe (3/4inch diameter) After sealing with covers at both two ends, the tubes were kept overnight at 4ºC The height of gel obtained was 25mm The gel was compressed at 1mm/s to distance of 10mm by using stainless steel punch probe (P/35) The gel hardness and stickiness were obtained from the peaks of force-time curve

Pasting properties

Rapid Visco Analyzer (RVA, Mode l4D, Newport Scientific, Australia) was used to determine the starch pasting properties [11] Amylogram profile showed RVA parameters in terms of pasting temperature (Ptemp), peak viscosity (PV), trough viscosity (TV), breakdown (BD = PV-TV), final viscosity (FV) and setback viscosity (SB = FV-TV)

Noodle preparation

The procedure for starch noodle making was followed according to Lee and Hormdok and Noomhorm [5,13] with a slight modification The SPS were well mixed to MBS to form starch mixture in which SPS accounted for 0, 10, 20, 30, 40 and 100% The water was added into starch mixture to obtain starch slurry with solid content of 35, 40 and 45% The starch slurry was equilibrated at room temperature for 1hr before pouring into stainless plate (150x160mm), then spread to form sheet in 1mm thickness After steaming at 92.5°C until complete gelatinization, the samples were cooled at room temperature for 10minutes and then covered with aluminum foil and aged in a refrigerator (4°C) for 1, 10 and 20hr After that, the starch gel was cut into thin-noodle strands (2mm in width) by cutting knife The noodle strands were dried in an air oven at 40°C until about 12% of final MC To simplify the experiment,

as studying effects of a processing condition on starch noodle quality, other processing conditions were kept constant The best processing condition from previous step was chosen for the next step The quality

of both dried and cooked noodles was evaluated by following methods

Color of starch noodles: The color of both dry and cooked starch

noodles was determined by Hunter lab Colorimeter (Colorflex, USA)

in terms of L*, a* and b* values

Cooking quality of starch noodles: The cooking time of the starch

noodles measured by cooking 5g noodles (2-3cm long) in 200ml distillated water, every 30second the noodle strands were removed and pressed between two pieces of watch glass Optimum cooking time was achieved when the center of the noodles was fully hydrated [2] Cooking loss (CL) and % rehydration (RE) starch noodles were determined by the method introduced by Hormdok and Noomhorm [13] CL was calculated based on the dry weight of noodles The RE was calculated as the percentage increase in weight of the cooked noodle compared to the weight of dried noodle

Extension of starch noodles: The extension of a single strand of

cooked noodles was measured by using Instron TA.XT2 Plus, (Stable Micro System, USA), following method of Chen [4] with the test speed was 1mm/s The extension modulus (E,MPa) and the relative extension (re) were calculated from the following equations: E = (F/∆L)(L/A) and re = ∆L/L Where F is the extension force (g force), A is the cross sectional area of starch noodle (mm2), ∆L is the increased length (mm) and L is the original length of starch noodle (mm)

Sensory evaluation of starch noodles: Multiple comparison tests

were used for sensory evaluation the quality of both dry and cooked starch noodles The cooked noodles were prepared by cooking in

boiling water for 1minute more than cooking time and cooling in cold

water for 5 minutes before evaluation The twelve panelists (seven men

and five women whose their age was from 27 to 40 year olds), who

were familiar to products, were asked comparing each of all samples

to the reference sample made from pure mung bean starch in terms of

appearance, texture, flavor and overall acceptability by using 9-point

scale They were informed the method evaluation and terminology of

quality attribute before evaluation

Data analysis

All experiments and analysis were performed in three replications

The data were subjected to statistical one-way ANOVA test and Fisher’s

Least Significant Difference (LSD) test or Duncan Multiple Range Test

(DMRT) to compare among treatments at the 5% significant level by

using SPSS version 16

Results and Discussions

Starch yield (%)

The SP1_W_YR variety showed the highest extracted starch with

about 17.52%, following by SP2_P_P cultivar with 15.54% The isolated

starch content from both SP3_P_Y and SP4_OP_O roots was not

significant difference, holding 12.38% and 12.55% respectively (Figure

1) This may be explained that starch content in SP1_W_YR and

SP2_P_P roots was much higher than that in SP3_P_Y and SP4_OP_O

roots However, the roots with higher starch content was not necessarily

higher percentage of extracted starch, almost there was no relationship

between starch content in roots and isolated starch [14] The reason

for that difference can be the structure of cell wall of SP3_P_Y and

SP4_OP_O varieties seem to be much thicker than that of the other

sweet potato varieties, resulting in hindering starch isolation from

chloroplast, resulting in low starch yield

Chemical compositions

The starches from all SPSs were high in apparent amylose content

ranging from 28.06% to 34.52%, but much lower than that in MBS which

was 40.36% (Table 1) These results were in agreement with the previous

reports, amylose content in SPSs ranged from 8.5% to 37.4% depending

on Amylose content in starch was one of important factors influencing

to starch pasting and the strength of starch gel due to its quick retro

gradation, association and interaction to lipids and amylopectin to

form helical complex giving strong gel structures Starches with high amylose content were desired for manufacture of starch noodles [2,18] However, Kim [3] found that amylase content was no significant correlation to noodle hardness and suggested that next to a amylose threshold level, other starch properties were more important than amylose content Tam [19] found that high amylose corn starch was not suitable for noodle making because it was not sufficiently gelatinized

at atmosphere condition, leading to almost no amylose molecules released to participate into the noodle structure formation The starch with high amount of protein, lipid and ash content indicated low purity The protein content in starches from all sweet potato cultivars, which ranged from 0.15 to 0.23% db, were slightly higher than that in mung bean starch which was 0.16% db; while the ash content in SPSs (0.110

- 0.282%) was markedly greater comparing to that in MBS (0.053%) (Table 1) The lipid content in SP2_P_P and SP3_P_Y starches, which was 0.084% and 0.061% respectively, was considerable higher than that

in SP1_W_YR, SP4_OP_O and MBS, which was 0.031%, 0.039% and 0.038% respectively High lipid content can reduce in clarity of starch paste and hinder the swelling of starch granule because of high rate formation of amylose-lipid complex [4,8] Nevertheless, the protein and lipid played important role in retention of amylose in starch noodles during cooking, resulting in minimizing cooking loss [3]

Light microscopy analyses

The microscopic images of mung bean and sweet potato starch granules are shown in Figure 2 For all sweet potato varieties, the

Figure 1: The starch yield (%) in all sweet potato roots.

12.38 c 12.55 c

15.54 b 17.52 a

0 2 4 6 8 10 12 14 16 18 20

SP3_P_Y SP4_OP_O SP2_P_P SP1_W_YR

Sample

Chemical composition, % db (*)

- Moisture 09.97a(0.50) 10.14a(0.29) 10.03a(0.10) 09.79a(0.63) 10.13a(0.09)

- Protein 0.21 b (0.021) 0.15 a (0.018) 0.21 b (0.017) 0.23 b (0.028) 0.16 a (0.019)

- Lipid 0.031 c (0.0073) 0.084 a (0.0027) 0.061 b (0.0026) 0.039 c (0.0079) 0.038 c (0.0054)

- Ash 0.137 b (0.0238) 0.282 d (0.0480) 0.110 b (0.0221) 0.221 c (0.0353) 0.053 a (0.0055)

Apparent amylose content (%) (*) 31.50 c (0.81) 29.34 d (0.56) 28.06 d (1.11) 34.52 b (1.18) 40.36 a (0.59)

Granule size (µm) (**)

(*) All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the va lues with different letters are significant difference at p < 0.05 by LSD test.

(**) All values are means of three determinations For each determination, the value was average of fifty particles

Table 1: Comparison of the chemical composition and granule size among all sweet potato starch and mung bean starches.

Citation:Thao HM, Noomhorm A (2011) Physiochemical Properties of Sweet Potato and Mung Bean Starch and Their Blends for Noodle Production

J Food Process Technol 2:105 doi:10.4172/2157-7110.1000105

Page 4 of 9 starch granule shapes were heterogeneous and no noticeable difference,

including small or largely polygonal and circle-shaped particles It

therefore was very difficult to distinguish these sweet potato varieties on

the basis of starch granule shapes The mung bean starch granule shapes

were more homogeneous, consisting of small, round-shaped and large,

kidney-shaped particles Some of large granules in both sweet potato

and mung bean starches had centered fissures, while small ones almost

no had this phenomenon

The granule size range of all sweet potato starch was not clearly

different from that of mung bean starch Nevertheless, the starch

granule average size of all sweet potatoes was significant smaller than

that of mung bean The mean length of SPS granules ranges from 14

to 17µm while granule length of MBS was about 24µm (Table 1) This

could be explained that the ratio of large particles to small ones for all sweet potato starches was nearly equal whereas for mung bean starch the large granules account for a larger proportion Granule size and particle size distribution influenced on water binding capacity, swelling power and paste clarity as well as applicable ability of starches in food processing [4]

Starch color

The desired starches for noodle production should be high value for lightness and low value for chroma [2] The color of starches extracted from SP1_W_YR and SP3_P_Y varieties was no significant difference to that of MBS in terms of lightness (L*), yellowness (b*) However, due to slight difference in greenness (a*) resulted in small difference in whiteness (Table 2) While the SP2_P_P and SP4_OP_O

Note:

SP1_W_YR: White skin and yellow-red flesh color SP2_P_P: Purple skin and purple flesh color SP3_P_Y: Purple skin and yellow flesh color SP4_OP_O: Orange-purple skin and orange flesh MBS: Mung bean starch

SP2_P_P SP1_W_YR

SP3_P_Y SP4_OP_O

MBS

Figure 2: Light microscopy (40X) of starch granules of sweet potatoes and mung bean.

varieties contained a higher amount of pigments, polyphenol oxidase

and phenolic compounds which are easily undergo denaturalization or

browning during starch isolation and drying process, lead to inferior

starch color [4]

Gel texture

The gel texture of MBS was significant higher in hardness, which

was about 1.2 kg forces, than that of all SPSs which ranged from 0.13 to

0.26kg force depending on varieties, but markedly lower in gel stickiness

The gels obtained from SP1_W_YR and SP4_OP_O starches were more

firmness than the other SPSs although there were no considerable

differences in stickiness (Table 3) The mechanical properties of starch

gel depended on the amylose content and amylopectin structure The

starches which exhibited higher gel firmness seem to have higher

amylose content and longer amylopectin chains [2,20] The soluble

amylose served as main materials for forming the network which binds

and entraps the unabsorbed water, or links intact granules or fragments

together, thus providing additional strength to network [21] The

textural parameters of the gels were found to well correlate with actual

noodle textures [22]

Pasting properties

The pasting temperature for sweet potato starches ranged from

80.1°C (SP4_OP_O starch) to 82.3°C (SP1_W_YR starch), while this

temperature for MBS only was about 76.83°C (Table 4) These results

were similar to the results reported by Moorthy in which pasting

temperature of sweet potato starches varied from 61.5°C to 86.3°C

[17] But these results were much higher than findings of Katayama

in which pasting temperature of sweet potato starches ranged from

64.35°C to 73.8°C, depending on variety [23] The differences in pasting

temperature were affected by changes in interior structure of starches

which can occur in both amorphous and crystallize regions [23] or by

starch granule size [4] The peak time for sweet potato starches, ranging

from 4.15min (SP2_P_P) to 4.40min (SP1_W_YR), was markedly lower

than that for MBS (4.49 min) This indicated that sweet potato starches

required longer time to gelatinize than mung bean starch The pasting temperature and peak time could have implications for the stability of components in formulated food, and also indicated energy costs [14] The peak viscosity of all sweet potato starches ranged from 403.06 RVU for SP1_W_YR starch to 473.63 for SP4_OP_O starch that of mung bean starch was in the middle of that range about 427.31 RVU (Table 4 and Figure 3) The peak viscosity found in this research for sweet potato starches appeared in the range with the findings of Collado and Corke [15], in which the peak viscosity of sweet potato starches were from 377 RVU to 428 RVU They also reported that peak viscosity have negative correlation with amylose content because the amylose restricted the starch granules swelling, resulting in low peak viscosity This seems to be not comparable to the results in this study The differences in peak viscosity may partly result from differences in phosphorous content [4] differences in size and shape of starch granules [14] or difference in size and branching chain length of amylopectin [20,24] Starches with higher in phosphorous content exhibited a higher peak viscosity due to increasing hydration of starch by weakening the degree of bonding within the crystalline region [25] The very long branch chains of amylopectin mimiced amylose to form helical complexes with lipids and interlink with other branch chains to hold the integrity of starch granules during heating and shearing, resulting

in low peak viscosity [18] Larger granules had a lower surface area to volume ratio and therefore the association between hydrogen bond and granules were very weak, hence enhanced swelling [26]

The results in Table 4 indicated that mung bean starch withstands shear much better and higher temperature than all sweet potato starches due to very low breakdown value, which was about 94.97 RVU,

SP1_W_YR 96.21 ac (0.96) -1.54 a (0.14) 3.89 ac (0.68) 94.34 b (0.28)

SP2_P_P 94.80 b (0.29) -1.75 b (0.12) 4.59 bc (0.61) 92.78 c (0.46)

SP3_P_Y 96.64 a (0.12) -1.75 b (0.06) 3.59 a (0.28) 94.73 ab (0.27)

SP4_OP_O 95.49 bc (0.64) -1.46 a (0.04) 4.86 b (0.59) 93.20 c (0.04)

MBS 96.78 a (0.04) -1.62 a (0.03) 3.39 a (0.16) 95.05 a (0.09)

All values are mean of three replications Data in the parenthesis are standard

deviation Within the same column, the values with different letters are significant

difference at p < 0.05 by LSD test.

Table 2: The color values of sweet potatoes and mung bean starches.

Samples Hardness, kg force Stickiness, kg force

SP1_W_YR 0.259 b (0.043) 0.0276 a (0.0031)

SP2_P_P 0.133 c (0.015) 0.0275 a (0.0006)

SP3_P_Y 0.131 c (0.030) 0.0276 a (0.0031)

SP4_OP_O 0.266 b (0.053) 0.0268 a (0.0021)

All values are mean of three replications Data in the parenthesis are

standard deviation Within the same column, the values with different letters are

significant difference at p < 0.05 by LSD test.

Table 3: Gel texture of sweet potato and mung bean starches.

Figure 3: RVA pasting profiles of four types of sweet potato and mung bean

starches.

0 10 20 30 40 50 60 70 80 90 100 110

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Time, min

Temperature

MBS

SP4_OP_O SP1_W_YR SP3_P_Y SP2_P_P

Pasting properties SP1_W_YR SP2_P_P SP3_P_Y Samples (*) SP4_OP_O MBS Ptemp (oC) 82.30 a (0.52) 80.82 C (0.06) 81.67 b (0.03) 80.10 d (0.00) 76.83 e (0.03) Ptime (min) 4.40 b (0.00) 4.15 C (0.04) 4.18 b (0.04) 4.37 b (0.03) 4.49 a (.08)

PV (RVU) 403.06 C (1.14) 420.53 e (2.83) 415.33 d (3.47) 473.63 a (3.54) 427.31 b (0.94)

TV (RVU) 199.36 C (0.55) 199.67 C (1.89) 178.06 d (3.06) 252.29 b (1.46) 332.33 a (.04)

BD (RVU) 203.69 C (0.97) 222.86 b (2.07) 237.28 a (2.89) 221.33 b (5.00) 94.97 d (0.75)

FV (RVU) 268.86 C (2.58) 27.97 d (1.58) 240.06 e (6.71) 349.29 b (1.04) 599.69 a (7.90)

SB (RVU) 69.50 C (2.40) 60.31 d (1.23) 62.00 cd (3.96) 97.00 b (2.50) 267.36 a (7.57)

Table 4: Pasting properties of four types of sweet potato and mung bean starches.

All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference at p < 0.05 by LSD test Ptemp : pasting temperature, Ptime : pasting time, PV : peak viscosity, TV : trough viscosity, BD : breakdown (BD = PV-TV), FV: final viscosity, and SB : setback viscosity (SB = FV-TV).

Citation:Thao HM, Noomhorm A (2011) Physiochemical Properties of Sweet Potato and Mung Bean Starch and Their Blends for Noodle Production

J Food Process Technol 2:105 doi:10.4172/2157-7110.1000105

Page 6 of 9 comparing to that for sweet potato starches, ranging from 203.69 RVU

(SP1_W_YR) to 237.28 RVU (SP3_P_Y) Among sweet potato starches,

SP1_W_YR starch was the most stable to temperature and shear

treatment, followed by SP4_OP_O, SP2_P_P and SP3_P_Y starches in

descending order

The tendency of starch retrogradation can be predicted by using

setback ratio obtained from RVA curve Higher setback value indicates

higher rate of retrogradation Setback value in Table 4 indicated that

the retro gradation rate of mung bean starch was higher approximately

three times than that of all sweet potato starches The starches with

higher amylose content exhibited higher setback value, more hardness

and less stickiness Therefore, the setback was considered as another

important criterion for starch selection for many food industries such

as noodles [14,22]

The pasting profiles can be used for evaluation of suitability for

starch noodles The firmness of starch noodles was positively significant

correlation to final viscosity [15] This final viscosity for mung bean

starch was about 599.69 RVU, much higher than those for all sweet

potato starch (240.06-349.29 RVU) Starches with high trough viscosity

generally exhibited superior eating quality and low cooling loss while

that with high final viscosity related to high shear resistance [22]

The above presented properties indicated that the mung bean

starch was the best material for noodle production, the SP1_W_YR

and SP4_OP_O starches were more suitable for making noodle than

the SP2_P_P and SP3_P_Y starches However, the isolated starch of

SP4_OP_O variety had low starch yield and purity of starch, together

with output limitation; the SP1_W_YR starch was chosen for blending

with mung bean starch in noodle production

Correlation among sweet potato starches properties

The results of correlation among property parameters of sweet potato starches shown in Table 5 that the ash content was well negative correlated to starch whiteness (r = -0.94, P < 0.01) This indicated that starches with high ash content had low in whiteness because ash expressed the fine fibers or pigments remaining in starch after isolation which could be browned after drying A significantly positive correlation was observed between amylose content and trough viscosity (r = 0.91, P < 0.01), final viscosity (r = 0.92, P < 0.01), setback viscosity (r

= 0.89, P < 0.05) and gel hardness (r = 0.82, P < 0.05) Moreover, highly positive relationship also was found between peak and final viscosity (r

= 0.91, P < 0.01) These relations can be explained that higher amylose content led to higher rate of amylose leaching into free water, resulting

in greater peak viscosity This associated with greater degree of starch swelling could be to increase in final viscosity, more viscous network and high rate of retrogradation upon cooling [7,22]

Effects of substituted ratios of SPS for MBS on starch noodle quality

Noodle colors: For both forms of dry and cooked noodles, the

MBS_N were much more lightness and greatly less yellowness and greenness than SPS_N (Table 6) The different color between MBS_N and SPS_N could be due to difference of starch color (Table 2) or due

to difference of degree integrity and association of starch chain after pasting [4] The transparency was the most important appearance attribute of noodles The transparent noodles were perceived as high quality product by customers [2] The increase of substituted ratio

of SPS for MBS resulted in reducing in lightness but increasing in yellowness and greenness of noodles, resulting in decrease of noodle quality Nevertheless, the color of both dry and cooked noodles with 20% SPS was not significantly different to that of MBS_N

1 Amylose

5 FV 0.92** 0.91** 0.99** -0.23

6 SB 0.89* 0.88* 0.95** -0.17 0.98**

8 Ptemp -0.48 -0.87* -0.72 -0.31 0.68 -0.58 0.10

9 Length -0.65 0.41 -0.66 0.57 -0.60 -0.47 -0.41 0.45

10 Diameter -0.47 -0.67 -0.66 0.00 -0.58 -0.42 0.07 0.86* 0.73

11 Protein 0.43 0.26 0.29 -0.08 0.36 0.47 0.58 0.04 0.35 0.36

12 Lipid -0.59 -0.20 -0.42 0.52 -0.49 -0.61 -0.88* -0.26 0.13- 0.36 -0.60

13 Ash 0.23 0.39 0.39 -0.01 0.32 0.18 -0.25 -0.63 -0.72 -0.85* -0.37 0.32

14 Hardness 0.82* 0.41 0.70 -0.66 0.73 0.76 0.93** -0.05 -0.50 -0.04 0.14 -0.79 -0.04

15 Stickness 0.25 0.12 0.18 -0.13 0.16 12 0.23 -0.08 -0.10 -0.23 0.47 -0.13 -0.06 0.02

16 White ness -0.30 0.50 -0.52 0.06 -0.45 -0.30 0.15 0.70 0.77 0.89* 0.28 -0.25 -0.94** -0.04 0.03

= Amylose = Amylose Content, 2 = PV = peak viscosity; 3 = TV = trough viscosity; 4 = BD = breakdown; 5 = FV = Final viscosity; 6 = SB = setback, 7 = Ptemp = temperature

at which peak viscosity was reached; 8 = Ptime = time from onset of pasting to peak viscosity; 9 = Length = average length of polygonal-shaped particles, 10 = Diameter

= average diameter of sphere-shaped particles; 11 = Protein = Protein content, 12 = Lipid = lipid content, 13 = Ash = Ash content, 14 = Hardness = Gel hardness, 15 = Stickiness = Gel stickiness; 16 = starch whiteness;*, ** were significant at P < 0.05, P < 0.01, respectively.

Table 5: Correlation among property parameters of sweet potato starche.

MBS_N 57.99 a (0.67) -1.35 a (0.21) 5.41 f (0.20) 55.67 a (0.02) -1.84 d (0.02) -3.97 d (0.24)

1S_9M_N 57.19 a (0.41) -1.26 a (0.06) 7.39 e (0.06) 55.49 a (0.28) -1.87 d (0.06) -3.89 d (0.16)

2S_8M_N 57.05 a (1.18) -1.25 a (0.05) 8.84 d (0.35) 54.95 a (0.41) -1.92 d (0.07) -1.86 c (0.47)

3S_7M_N 56.80 a (0.15) -1.22 a (0.09) 11.18 c (0.30) 53.64 b (0.70) -2.21 c (0.06) 0.62 b (0.46)

4S_6M_N 54.13 b (0.04) -1.18 a (0.04) 12.41b(0.53) 53.12 b (0.59) -2.49 b (0.10) 0.24 b (0.15)

SPS_N 48.62 c (0.44) 0.72 b (0.08) 16.83 a (0.40) 51.62 c (0.28) -2.78 a (0.03) 3.93 a (0.33)

Table 6: The color of dry and cooked noodles at different ratios of SPS and MBS.

All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference

at p < 0.05 by LSD test.

Cooking quality: Three important factors standing for cooking

quality namely cooking time, cooking loss and rehydration shown in

Table 7 indicated that cooking quality of MBS_N was superior to that of

SPS_N, and the blending SPS with MBS would reduce cooking quality

of noodles in the ways of increasing in cooking loss and rehydration

but reducing in cooking time The differences in cooking time and

rehydration between MBS_N (10.33min and 215.22% respectively)

and SPS_N (8.67min and 285.99% respectively) could be differences

in swelling and solubility of starch, and noodle inside structures The

starches with higher swelling power resulted in higher rehydration and

shorter cooking time of noodles [3] The MBS noodles had a compact

structure while inside structure of SPS noodles was loose and porosity

Therefore, SPS_N absorbed more water and faster than MBS_N, leading

to shorter cooking time [2] The slow water absorption of MBS_N in the

first 0.5hr was good eating quality because cooked noodles were usually

consumed within 0.5hr [4]

Although amylose content in SPS was significant lower than that of

MBS (Table 1), the cooking loss for SPS_N (3.68%) was nearly threefold

than that for MPS_N (1.44%) These results were in agreement with

findings of Chen [4] and conclusions of Kim [3] in which there was

negatively significant correlation between cooking loss of starch

noodles and amylose content The desired noodles should have short

cooking time and less cooking loss [13] The cooking loss of all noodles

was still accepted according to Chinese Agriculture Trade Standards

and Thai Standards for starch noodles in which cooking loss should

be less than 10 and 9% respectively [2] The cooking quality of the 20%

SPS containing noodles could be comparable to that of MBS noodles

Noodle texture: The extension modulus (E), which is a measurement

of stretch-hardness of cooked noodles, and the relative extension

(re), which expresses the stretch-ability of cooked noodles, shown in

Table 7 revealed that the extension modulus and relative extension

of MBS_N (51.40 MPa and 1.80 respectively) were markedly higher

than those of SPS_N (28.42 MPa and 1.21 respectively) These results were in the line with the findings reported by Chen and Kasemsuwan [4,8] The tensile strength of MBS_N in this study which was 51.40 MPa was slight lower than that of mung bean starch noodles prepared from 50% dry starch and 50% gelatinized starch by dropping method which was about 54 MPa [8] The differences in cooked noodles texture between MBS_N and SPS_N could be different about the leaching-out amylose content, swelling power and solubility of starch [6] Besides, the inside structure of SPS_N was loose and existed many small pores, resulted in low tensile strength comparing to that of MBS_N which was compact structure The desired starch noodles should be high tensile strength [2,3,9] They should remain in a noodle strand and withstand

to turbulences and mixing during cooking or frying The addition of SPS to MBS affected significantly the noodle extension However, the extension of noodles prepared from 30% SPS and 70% MBS was not significant in comparison to that of MBS_N

Sensory evaluation: The results of sensory evaluation shown

in Table 8 indicated that appearance of both dry and cooked SPS_N, which was yellowish, were lower than that of reference sample High transparent noodle was considered as high quality product

by customers [2] The transparence of noodles highly depended on starch physiochemical properties and phosphorus content [3] In some extent, there was no significant change in appearance as until 20% SPS replaced for MBS in dry noodles and 40% SPS replaced for MBS

in cooked noodles in comparison to that of reference (Figure 4) The off-flavor of noodles could be as results of adding bleaching chemicals

or degradation by microorganism, etc Therefore, the starch noodles should be no off-flavor From the results of sensory evaluation, all samples were absence of off-flavor Among noodle properties, texture could be the most important property The dry SPS_N was high hardness and easy to break during transportation and delivery; while cooked SPS_N was high stickiness, and the adhesiveness each other among strands, together with low in elasticity, resulted in breaking into small strands during mixing or other mechanical impacts The changes in texture of dry and cooked noodles were not recognized by panelists as about 30% of SPS replaced for MBS in comparison to pure MBS noodles Although there was high deviation in results evaluation among panelists, the evaluation results for appearance and texture

of noodles were well correlation with the results of color and texture measured by instruments (Table 6 and 7)

Overall, the blending MBS with 20% SPS for noodle production almost did not cause any significant changes in appearance, cooking quality, texture and sensory evaluation in comparison to those of pure MBS noodles

Effects of solid content of starch slurry on noodle quality

The transparency was the most important appearance attribute

Samples

Cooking quality Tensile characteristics Cooking time

(min) Rehydration (%) Cooking loss (%) E (MPa) re

MBS_N 10.33 a (0.29) 215.22 c (7.23) 1.44 e (0.13) 51.40 a (2.24) 1.80 a (0.05)

1S_9M_N 10.17 ab (0.29) 217.66 c (8.50) 1.55 de (0.09) 50.77 a (0.64) 1.68 ab (0.13)

2S_8M_N 9.83 abc (0.29) 223.87 bc (9.89) 1.64 d (0.13) 47.93 ab (1.18) 1.53 bc (0.15)

3S_7M_N 9.67 bc (0.29) 228.63 bc (4.03) 2.05 c (0.11) 45.22 bc (1.39) 1.44 c (0.11)

4S_6M_N 9.33 bc (0.29) 234.57 b (5.30) 2.52 b (0.10) 42.78 c (3.97) 1.35 cd (0.06)

SPS_N 8.67 d (0.29) 285.99 a (6.70) 3.68 a (0.08) 28.42 d (0.69) 1.21 d (0.04)

All values are mean of three replications Data in the parenthesis are standard

deviation Within the same column, the values with different letters are significant

difference at p < 0.05 by LSD test.

Table 7: The cooking quality and tensile characteristics of noodles made from

different ratios of SPS and MBS.

Table 8: Average scores of sensory evaluation for noodles made from various SPS ratios.

(*) Appearance : transparence and glossiness, Hardness : broken degree, Elasticity : stretching it until they broke; Stickiness : attaching two noodle strands to each other and pulling them apart All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference at p < 0.05 by LSD test.

SAMPLE Dry NoodlesAppearance Hardness(*) Overall Cooked Noodles

Acceptability Appearance Stickness Elasticity Flavour Overall Acceptability MBS_N

(reference

sample) 5.00

SPS_N 1.92 e (0.83) 2.17 d (0.67) 2.08 d (0.67) 2.92 d (0.51) 2.00 d (0.74) 2.83 d (0.72) 3.75 b (0.87) 2.25 c (0.45) 1S_9M_N 4.58 ab (0.67) 4.58 a (0.67) 4.67 ab (0.65) 4.58 ab (0.67) 4.50 ab (0.80) 4.50 abc (0.67) 4.67 a (0.49) 4.67 a (0.78) 2S_8M_N 4.42 a (0.67) 4.67 a (0.65) 4.50 ab (0.80) 4.50 bc (0.67) 4.42 ab (0.79) 4.58 ab (0.79) 4.58 a (0.51) 4.75 ab (0.45) 3S_7M_N 3.92 c (0.51) 3.92 c (0.51) 4.42 bc (0.79) 4.08 bc (0.67) 4.25 bc (0.87) 4.33 bc (0.78) 4.75 a (0.45) 4.58 ab (0.67) 4S_6M_N 3.33 d (0.49) 3.25 c (0.75) 3.92 c (0.67) 4.17 c (0.39) 3.75 c (0.62) 4.00 c (0.60) 4.67 a (0.65) 4.17 b (0.58)

Citation:Thao HM, Noomhorm A (2011) Physiochemical Properties of Sweet Potato and Mung Bean Starch and Their Blends for Noodle Production

J Food Process Technol 2:105 doi:10.4172/2157-7110.1000105

Page 8 of 9

of noodles The transparent noodles were perceived as high quality

product by customers [2] The color of noodles at various solid contents

was significant difference (Table 9) As increasing solid content of

starch slurry, it was likely to reduce lightness (L*) of noodles, especially

for dry noodles The high solid content of starch slurry could lead to

insufficient water for starch completely gelatinization, the presence of

incompletely gelatinized starch granules in noodles could affect noodle

color or transparence

The cooking time, rehydration and cooking loss of starch noodles

considerable increased with increasing of solid content of starch slurry

(Table 10) The water content in starch slurry can become inadequate

for starch gelatinization as starch concentration in starch slurry was

too high [3,15] The excess presence of incompletely gelatinized starch

granules in noodle matrix promoted starch solubility into cooking

water, resulting in high cooking loss and long cooking time

The results in Table 10 indicated that as increase of solid content

of starch slurry resulted in markedly increasing of extension modulus

(E) and relative extension (re) of cooked noodles These findings were similar to results obtained for rice and mung bean starch vermicelli produced by extrusion method [7,27] and sweet potato starch noodles produced by cutting method [3] The amount of swollen starch granules and leaching-out amylose could be not enough for forming a continuous matrix at low starch concentration The slurry starch with higher solid content offered sufficient leaching-out amylose amount to speed up gel formation [7] Moreover, solid content greatly affected to retrogradation rate which was believed to highly impact on gel formation and strength

As increasing of solid content, retrogradation rate might continuously increase, resulting in more stretch hardness noodle texture [3] From all above results, at 45% of solid content resulted in difficulty

in sheet formation, reducing in cooking quality of noodle, raising noodle cost and very high extension modulus or stretch hardness Therefore, solid content of 35-40% was found to suitable for producing good quality noodles However, with aims to reduce noodle cost, 35%

of solid content was chosen for next experiment in which effects of aging time at 4°C were evaluated

Effects of aging time of gelatinized starch on starch noodle quality

The aging time was not significantly influence on color of dry noodle, except to yellowness which was decrease with increasing aging time; cooking time; rehydration and relative extension (Table

11 and 12) However, it was considerable effect lightness, cooking loss and extension modulus of cooked noodles These results could be comparable to those of Kim [3] in which aging time was markedly effect

to cooking loss and noodle texture The starch retro gradation occurred during aging and effectively stabilized the starch chains in the gel matrix [15] Therefore, as prolong aging time of gelatinized starch, there were more amylose or short-chain amylopectin molecules participated

in retro gradation process, resulting in highly impact to noodle strength and cooking loss [2,3]

Conclusions

The results of this study revealed that MBS was the ideal material

35S65WN 6.17 c (0.29) 184.20 b (9.97) 1.31 c (0.12) 40.51c (1.37) 1.31b (0.01)

40S60WN 9.83 b (0.29) 223.87 a (9.89) 1.64 b (0.13) 47.93b (1.18) 1.53ab(0.15)

45S55WN 10.67 a (0.29) 231.01 a (3.34) 2.51 a (0.10) 59.68a (1.66) 1.63a (01.2)

All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference

at p < 0.05 by LSD test.

Table 10: The cooking quality and tensile characteristics of noodles at different solid content.

Figure 4: Starch noodles made from various ratios of SPS and MBS.

(1) (2) (3) (4) (5) (6)

1) : Noodles from pure sweet potato starch, (2) : Noodles from 40% of SPS and

60% of MBS, (3) : Noodles from 30% of SPS and 70% of MBS, (4) : Noodles

from 20% of SPS and 80% of MBS, (5) : Noodles from 10% of SPS and 90% of

MBS, (6) : Noodles from pure MBS

All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference at p < 0.05 by LSD test.

Table 9: The color of dry and cooked noodles at different solid content

35S65WN 57.53 a (0.14) -1.54 c (0.06) 9.68 a (0.13) 56.95 a (0.88) -2.23 a (0.18) -0.43 b (0.20)

40S60WN 57.05 ab (1.18) -1.25 a (0.05) 8.84 b (0.35) 54.95 b (0.41) -1.92 b (0.07) -1.86 a (0.47)

45S55WN 55.98 b (0.33) -1.66 b (0.03) 9.44 a (0.03) 55.73 b (0.40) -2.05 ab (0.10) -0.54 b (0.04)

All values are mean of three replications Data in the parenthesis are standard deviation Within the same column, the values with different letters are significant difference

at p < 0.05 by LSD test

Table 11: The color of dry and cooked noodles at different aging time.

1 57.53 a (0.14) -1.54 a (0.06) 9.68 a (0.13) 56.95 b (0.88) -2.23 a (0.18) -0.43 b (0.20)

10 57.92 a (0.45) -1.44 b (0.03) 7.67 b (0.22) 59.37 a (0.27) -1.91 b (0.06) -0.48 b (0.16)

20 57.90 a (0.45) -1.44 b (0.01) 5.83 c (0.03) 59.73 a (0.3) -2.22 a (0.02) -1.82 a (0.17)

for noodle production due to high amylose content, high hardness

and low stickiness of gel, and high hot paste stability and cold paste

viscosity Among four types of sweet potato varieties, SP1_W_YR

starch was the most suitable for noodle production Contrary to MBSN

which was most preferred by customers due to high transparence, high

tensile, low cooking loss; SPSN was dull, opaque, moderately elastic,

high cooking loss, and high hardness of dry noodles which could be

easy to break during transportation and delivery The blending MBS

with SPS for noodle production resulted in markedly reducing its

quality However, the quality of noodles made from mixture of 20% SPS

and 80% MBS was not significant difference to that of MBS noodles

The increase of solid content of starch slurry resulted in considerable

increasing in cooking time, cooking loss, rehydration and tensile of

noodles while aging time only markedly affected to cooking loss and

tensile of noodles For noodles prepared from mixture of 20% SPS and

80% MBS, the most suitable initial solid content and aging time at 4oC

were 35% and 10-20 hrs respectively

Acknowledgements

The authors thanks to Food Engineering and Bioprocess Technology, Asian

Institute of Technology, Thailand for supplying all needed equipments and thanks to

UNEP (United Nations Environment Program) Organization for financial supporting

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