Flour Particle Size, Starch Damage, and Alkali Reagent: Impact on Uniaxial Stress Relaxation Parameters of Yellow Alkaline Noodles D. W. Hatcher,1,2 G. G. Bellido1 and M. J. Anderson1 ABSTRACT
Cereal Chem. 86(3):361–368
Three patent flours, each possessing three different levels of starch damage were prepared from a single hard white spring wheat. Each flour was sieved to yield three flours with different particle size distributions (85–110, 110–132, 132–183 μm). Raw alkaline noodles were prepared from the nine flours using either 1% w/w kansui (sodium and potassium carbonates in 9:1 ratio) or 1% w/w sodium hydroxide. Uniaxial stress relaxation parameters percent stress relaxation (SR%), initial rate of relaxation (k1) and the extent of relaxation (k2) were measured on the raw noodles immediately after production (t = 0 min) and at 60 min. Raw noodles after resting for 60 min were optimally cooked and stress relaxation parameters were measured. Raw noodles at t = 0 min exhibited SR%, k1, and k2 that were significantly (P < 0.0001) influenced by both the
degree of starch damage and the type of alkaline reagent used. Flour particle size only influenced SR% and k1 (P < 0.025) but had no impact on k2. In raw noodles aged for 60 min, both SR% and k2 were significantly influenced by alkaline reagent, particle size, and starch damage (P < 0.01) while k1 was only affected by the degree of starch damage (P < 0.0001). Cooked noodle SR parameters were all significantly (P < 0.0001) influenced by alkaline reagent, particle size, and the degree of starch damage. Cooked noodles prepared from starch with low damaged flours within any given particle size range, regardless of the type of alkali employed, yielded the most rheologically elastic-like (firmer) noodles. Two potential mechanisms by which the degree of starch damage influences noodle elastic like texture are discussed.
While bread and bread products are the major uses of wheat flour in most Asian countries, noodle production is very significant, representing 35–40% of flour consumption (Hatcher 2001). The majority of these noodles (alkaline Chinese and Cantonese noodles) use flour, water, an alkaline reagent and, where appropriate for taste, sodium chloride. Sodium and potassium carbonates are the most prevalent salts of the alkaline reagent (Moss et al 1986) although in some countries such as Malaysia, sodium hydroxide is used (Hatcher 2001). Alkaline reagent-wheat flour interactions during noodle manufacturing are complex (Terada et al 1978; Miskelly and Moss 1985; Moss et al 1986), with both the ratio and concentration of alkali significantly influencing cooked noodle texture (Hatcher and Anderson 2007). Recently, Hatcher et al (2008a) showed that cooked noodles prepared using 1% (w/w) sodium hydroxide had a greater volumetric expansion upon cooking (i.e., became thicker) than corresponding noodles prepared using 1% (w/w) kansui reagent. However, the molecular basis by which alkaline reagents interact with wheat flour biopolymers is poorly understood. Part of the research problem is that these interactions are influenced by flour quality parameters such as the wheat flour cultivar, degree of starch damage, and flour particle size (Hatcher et al 2008a), which are traditionally not monitored in noodle studies (Terada et al 1978; Miskelly and Moss 1985; Moss et al 1986; Oh et al 1986). Oh et al (1986), for example, found that empirical noodle texture properties, previously correlated with sensory evaluation (Oh et al 1983), were influenced by particle size and starch damage. Their data, however, was difficult to interpret as they used flours from different wheat classes and variable protein content. Hatcher et al (2002) demonstrated that particle size and starch damage influenced white salted noodle quality independently of protein content; flours with fine particle size yielded noodles with better textural attributes compared with those made with coarser flour particles. Starch damage significantly increased leaching losses during cooking and decreased the cooked noodle water uptake, whereas no consistent effect was observed between the degree of starch damage and cooked noodle texture.
Empirical instrumental measurements of cooked noodle texture (Hatcher et al 2008a) derived from a single wheat source demonstrated that type of alkaline reagent exerted a significant influence on maximum cutting stress (MCS), resistance to compression (RTC), recovery (REC), chewiness (CHE), and springiness (SPR). The same textural parameters were also significantly influenced by flour particle size and starch damage, although their influence was dependent on alkaline reagent. In general, noodles prepared with kansui exhibited an increase in these texture parameters with increasing starch damage while noodles formulated with NaOH displayed an inverse relationship, declining with increasing starch damage. Additionally the impact of particle size was most noticeable on noodles prepared with NaOH as they exhibited a general decline in their texture parameters as the particle size of the flours became larger. Addition of kansui toughened the texture of raw noodle dough based on rheological studies (Terada et al 1978; Edwards et al 1996; Shiau and Yeh 2001, 2004; Wu et al 2006). Using the extensigraph, Terada et al (1978) demonstrated that the ratio of resistance to extension/extensibility (an index of elasticlike behavior) of dough with kansui was significantly larger than that of dough with neutralized kansui, therefore attributing these changes to the alkalinity of the kansui. They proposed that kansui influences wheat flour dough rheology by promoting formation of disulfide linkages through mild oxidation of the gluten proteins. This hypothesis was subsequently supported by the work of Shiau and Yeh (2004), who demonstrated using small strain shear oscillatory rheology that kansui significantly increased solid-like behavior in dough. Edwards et al (1996), using shear oscillatory rheology as well, measured the time-dependent effects of alkaline reagents and found that sodium hydroxide increased raw noodle dough stiffness more than kansui initially, and stiffness continued to increase over a 24-hr period. Kansui showed only a milder effect and no significant effect over 24 hr. Alkaline noodles are normally prepared using minimal water (32–36%) (Hatcher 2001). Addition of kansui or sodium hydroxide to noodle dough has been proposed to increase competition between wheat protein and starch for limited water, resulting in delayed protein hydration and matrix development (Wu et al 2006). Light microscopy analyses of noodle dough after roll sheeting processing revealed that dough containing 1% sodium hydroxide appeared to have a less smooth surface appearance in comparison to noodle dough containing 1% kansui (Moss et al 1986). Noodles prepared using 1% sodium hydroxide did not exhibit as contin-
1 Canadian
Grain Commission, Grain Research Laboratory, 1404-303 Main St. Winnipeg, Manitoba, Canada R3C 3G8. Paper #1010. 2 Corresponding author. E-mail:
[email protected] doi:10.1094 / CCHEM-86-3-0361 © 2009 AACC International, Inc.
Vol. 86, No. 3, 2009
361
uous or as uniform a protein network as the kansui noodles, presumably due to inadequate development and stretching of gluten protein (Moss et al 1986). Furthermore, while no differences in starch granule appearance was found due to the type of alkaline reagent, Moss et al (1986) attributed the difference in protein network formation to the low water absorption level (30%) present in the dough system. However, after cooking, the extent of swelling of starch granules in noodles prepared with sodium hydroxide was significantly greater than when prepared with kansui. In fact, the authors noted, starch swelling was so accentuated in noodles prepared with sodium hydroxide that granules became grossly distorted and burst. Moss et al (1986) attributed this behavior to poorer protein development in the NaOH which allowed greater water availability for the granules. They also indicated that the action of sodium hydroxide on the starch granules themselves could also be responsible for the observed distortions. The purpose of this study was to use recently reported uniaxial stress relaxation measurements (Singh et al 2006; Hatcher et al 2009), based upon Peleg (1979), to characterize the influence of particle size, starch damage, and type of alkali reagent employed to prepare yellow alkaline noodles, on the rheological parameters of both raw and cooked noodles. MATERIALS AND METHODS Flour A commercial sample of Canada Prairie Spring White (CPSW) wheat, AC Vista, was used to generate all flours. The wheat was conditioned to 16.5% moisture content and ground using the first three break roll passages of the Grain Research Laboratory (GRL) tandem Bühler (Uzvil, Switzerland) laboratory pilot mill (Martin and Dexter 1991). Purified farina was reduced in three different ways to produce flour with various levels of starch damage (low, medium, and high) using roll stands from the GRL 25-cm research mill as described by Hatcher et al (2008a). Flour of low starch damage was produced using fluted rolls (Allis sharp, 12.6 corrugations/cm) set dull-to-dull at a roll differential of 1.77:1 and a roll gap of 0.076 mm. Medium and high starch damage flours were prepared using smooth frosted rolls at a differential of 2:1. Medium starch damage flour was obtained by reducing the farina at a roll gap of 0.065 mm and then sieving over 202 Nitex (202 μm aperture) and 183 Nitex clothing. High starch damage flour was produced in a similar manner, but the initial roll gap was narrowed to 0.051 mm, and subsequent reduction of material held on 183 Nitex was at a roll gap of 0.038 mm (Hatcher et al 2008a). The low, medium, and high starch damaged flours were subsequently sieved over 188 Nitex, 132 Nitex (132 μm aperture), 110 Nitex (110 μm aperture), and 85 Nitex (85 μm aperture) clothing. The trace amount of material held on 188 Nitex was discarded while material held on 132, 110, and 85 Nitex were designated coarse, intermediate and fine granulation flour, respectively and used for the production of YAN. Analytical Methods Protein content (% N × 5.7) was determined by combustion nitrogen analysis (CNA) (model FP-248, Dumas CNA analyzer, LECO Corp., St. Joseph, MI) calibrated with EDTA. Ash content, amylograph peak viscosity, and starch damage were determined using Approved Methods 08-01, 22-10, and 76-31, respectively (AACC International 2000), and expressed on a 14.0% moisture basis. Wet gluten was determined by Standard Method 137 (ICC 1980). Noodle Preparation Previous research (Hatcher et al 2008a) had determined that optimum water absorption was 37% for all flours and formulas, based upon dough feel and sheeting properties. Flour (50 g) and 362
CEREAL CHEMISTRY
water containing either dissolved kansui (9:1 sodium to potassium carbonates) or dissolved sodium hydroxide (1% w/w basis) were mixed for 30 sec at 3,000 rpm using an asymmetrical speed mixer (model DAC 150 FV, FlackTec, Landrum, SC) in a Pin Max 80 bowl according to the method of Hatcher and Preston (2004). The high gravitational forces to which the dough crumb is subjected during the quick mixing procedure duplicated the traditional texture properties of noodles prepared using a Hobart mixer (5.5 min). In addition, this procedure dramatically improved dough crumb hydration such that no streaking was observed for the resulting dough sheet. The dough was sheeted on a laboratory noodle machine (Ohtake, Tokyo, Japan) with an initial gap setting of 3.0 mm, folded longitudinally, and resheeted to simulate the lamination process employed by commercial noodle manufacturers. The resulting sheet underwent seven further reductions at successive gap settings of 3.0, 2.55, 2.15, 1.85, 1.57, 1.33, and 1.1 mm, incorporating a 45-sec delay between each pass. The dough sheet was passed through a B12 cutter and cut into noodles for texture measurement (Hatcher et al 2008a). Noodle Texture Measurement Stress relaxation measurements were performed on raw noodles (three strands/test) immediately after production (t = 0 min) as well as t = 60 min after resting in a sealed plastic container maintained at room temperature (22°C). Additional raw noodles, aged for 60 min, were optimally cooked and allowed to rest for 10 min before undergoing stress relaxation testing. The initial rate of relaxation (k1) and the extent of relaxation (k2) were determined by the method of Singh et al (2006) with minor modification (Hatcher et al 2009) using a texture analyzer (TA-XT2i, Texture Technologies, Scarsdale, NY) fitted with a 1-cm wide flat compression fixture. A 20% engineering strain was capable of differentiating the texture of noodles prepared from different wheat flour cultivars (Hatcher et al 2009). This engineering strain level was consistent with the level recommended by Safari-Ardi and Phan-Thien (1998) using dynamic oscillatory rheology, who demonstrated that a strain level of 22–29% was required to discriminate the stress relaxation responses of wheat doughs of varying strength. In the current study, percent stress relaxation was calculated as in Hatcher et al (2008b) %SR = [σ0 – σ(t = 20)/σ0] × 100%
where σ0 denotes initial stress (Pa) after the sample was brought to a constant deformation and σ0 = (t = 20) denotes the stress (Pa) 20 sec after the initial strain was achieved. A pretest crosshead speed of 0.5 mm/sec was employed to achieve the desired strain level and force measurements. Data were captured at 200 points/sec over a 50-sec period. Transformation of the force versus time measurements were achieved as in Singh et al (2006), using the macro provided with proprietary software of the TX-XT2i unit. Noodle Cook Time Optimum cooking time for all noodles was determined during preliminary testing and was based upon the loss of a visible core when pressed between two sheets of plexiglass. Noodles were cooked in boiling water for 5 min and, subsequently, five noodle strands were withdrawn at 30-sec intervals. The noodles were immediately immersed in cool water (20°C) for 1 min, rinsed, placed between two sheets of plexiglass, and gently squeezed. Optimal cook time was achieved when four of the five noodles displayed no visible core. Optimally cooked noodles were rinsed and allowed to sit in a sealed plastic container for 10 min before testing. Stress relaxation measurements were initiated exactly 10 min after the rinse stage. Cooked noodle thickness was determined by subtracting
the distance the fixture had travelled when 2 g of force was recorded on the TX-XT2i unit from the initial 5-mm blade height. Experimental Design Noodles were prepared to investigate the effect of the various treatments on three separate days using a randomized design. Texture measurements of raw or cooked noodles were conducted five times on sets of three noodle strands for each day’s treatment and the results averaged. The daily mean of each treatment was analyzed using statistical software (v.9.1, SAS Institute, Cary, NC). Analysis of variance (ANOVA), with all combinations of the main effects (reagent, particle size, and starch damage, plus corresponding interaction terms) were determined using Proc GLM. Pairwise comparisons of treatment group means were accomplished using Fisher’s least significant difference (LSD) test. Significance was assigned when P < 0.05 unless stated otherwise. RESULTS Flour Characterization The particles of the larger, coarser (≤183 μm and held on 132 μm), medium (≤132 μm and held on 110 μm), and finer (≤110 μm and held on 85 μm) flours had the majority (>79%) of the size distributions within the specified range (Hatcher et al 2008a). Though flours with high starch damage were slightly finer than the medium and low starch damage flours, the degree of starch damage within each category was consistent within any given particle size group. Flour protein content, wet gluten content, and amylograph peak viscosity exhibited a very narrow range as would be expected from a single wheat source (Table I). Raw Noodle Texture The raw noodles stress relaxation parameter (SR%) immediately after sheeting (t = 0 min) was determined by ANOVA to be significantly influenced by the type of alkali (P < 0.0001), particle size (P = 0.0058), and the degree of starch damage (P < 0.0001). Only the alkali type by starch damage interaction term had a significant effect (P = 0.0452) on SR% values. Noodles prepared using low starch damage flours, regardless of particle size and or alkali, consistently displayed the highest SR% values (Fig. 1A,B). However, even though noodles prepared with kansui displayed significant declines in SR% values with each increase in starch damage, noodles prepared using NaOH did not display this behavior to the same extent. SR% for NaOH moderate starch damaged flour noodles were not significantly distinct from low starch damage flour noodles for either fine (85–110 μm) or medium (112–132 μm) noodles (Fig. 1B). Noodles incorporating NaOH generally displayed significantly larger SR% values than their kansui counterparts, with the largest differences being evident for noodles prepared with the highest levels of starch damage for a given particle size.
Analysis of the k1 values at t = 0 min indicated that the type of alkali, starch damage (P < 0.0001 each), and particle size (P = 0.0018) exerted a significant influence on k1 as well. As observed previously, only the interaction term alkali type by starch damage also exhibited a significant influence (P = 0.0247) on k1. Noodles prepared with either kansui or NaOH from high starch damaged flours consistently displayed significantly larger k1 values than either medium or lower starch damaged flours of the same particle size (Fig. 1C,D). Noodles prepared with kansui displayed significantly larger k1 values (P < 0.0001) than corresponding noodles prepared with NaOH. There was no significant difference observed in k1 values for either kansui or NaOH noodles between low and moderate starch damaged flours within a given particle size. The k2 values at t = 0 min were significantly influenced by alkaline reagent type and degree of starch damage (P < 0.0001 each) (Fig. 1E,F). Particle size did not influence (P = 0.0833) k2 values, nor did any of the interaction terms. Noodles prepared with kansui generally had greater asymptotic residual stress values (= 1 – [1/k2]) or equivalently greater elasticlike behavior as defined by Peleg and Pollak (1982) than noodles made using NaOH (Fig. 1E,F). Examples of the asymptotic residual stress for noodles prepared using the low starch damage, 85–110 μm flour were 0.255 for kansui and 0.243 when using NaOH. In all cases, the high starch damage flours displayed the largest k2 values within any given particle size. A general increase in k2 values was observed in noodles prepared from any one particle size and alkali reagent with increasing starch damage. However, raw noodles prepared with the coarsest flour particle size, regardless of the type of alkaline reagent, displayed a significant increase in each k2 value with each incremental increase in the degree of starch damage. The k2 values for noodles prepared with NaOH and with a high degree of starch damage were almost identical, irrespective of particle size, but were significantly lower (P < 0.0001) than those for noodles prepared with kansui. Allowing the raw noodles to rest for 60 min at 22°C before measurement resulted in similar SR% trends (Fig. 2A,B) as those observed at t = 0 min (Fig. 1A,B). All three main effects, type of alkali (P = 0.0007), starch damage (P < 0.0001), and particle size (P = 0.0038) remained significant influencers of SR% although no interaction term was significant. Relative to SR% at t = 0, a significant increase (P < 0.0001) in SR% was observed after 60 min of resting time in all nine kansui flour noodles, while noodles prepared with NaOH showed a general significant (P < 0.0001) decline in SR% after the same resting time (Fig. 2A,B). The lowest SR% values, corresponding to the firmest raw noodles, were observed when noodles were prepared from flours with a high degree of starch damage, regardless of flour particle size or alkaline reagent. SR% increased (firmness decreased) regardless of particle size when noodles were made from flours exhibiting the lowest degree of starch damage. Maximum SR% values were observed with all low starch damage flour within a given particle size for both kansui and NaOH.
TABLE I Characterization of the Canada Prairie Spring White Wheat Flours Used for Noodle Productiona Particle Size >85–110 μm >110–132 μm >132–183 μm
a
Starch Damage
Protein (%)
Wet Gluten (%)
Ash (%)
Grade Color (SIU)
Starch Damage (MU)
Amylograph Viscosity (BU)
Low Medium High Low Medium High Low Medium High
10.1 10.1 10.1 9.8 10.0 10.0 9.9 10.1 10.1
28.0 27.3 27.5 27.3 27.2 26.4 27.0 27.8 27.3
0.35 0.39 0.37 0.34 0.40 0.38 0.40 0.43 0.41
–4.7 –3.8 –3.9 –4.5 –3.4 –3.4 –3.2 –2.4 –2.3
4.9 6.7 8.2 4.4 6.2 8.1 4.2 6.1 7.8
430 450 475 485 460 485 440 400 430
SIU, Satake international units; MU, Megazyme units; BU, Brabender units. Vol. 86, No. 3, 2009
363
Aging (60 min) of the raw noodles resulted in only starch damage exerting a significant effect (P < 0.0001) on the raw noodle k1 value. All other main effects (flour particle size and type of alkaline reagent) and their interaction terms did not have a significant effect on k1, even at the P = 0.10 level. Regardless of particle size and alkaline reagent, the maximum k1 values were observed when kansui noodles were prepared from flour with the highest starch damage level (Fig. 2C,D), a response that was similar to that displayed in unrested noodles (t = 0 min) (Fig. 1C,D). It is worth noting that for high starch damage kansui noodles, the k1 values dropped from values of 3.5–3.0 to 3.0–2.5. Thus, noodles adopted a more elasticlike mechanical behavior after 60 min of aging. Examination of k2, extent of relaxation, of the raw noodles after aging for 60 min reflected the same trends as the (t = 0) unrested noodles; that is to say that this parameter was significantly influ-
Fig. 1. Stress relaxation parameters of raw noodles immediately after production (t = 0 min). Stress relaxation (SR %) (A, kansui; B, NaOH); k1 (C, kansui; D, NaOH); k2 (E, kansui; F, NaOH) as a function of flour particle size (85–110 μm, 110–132 μm, and 132–183 μm); flour starch damage L M H (low, medium, and high); and type of alkaline reagent (kansui vs. NaOH). 364
CEREAL CHEMISTRY
enced by the type of alkaline reagent (P < 0.001), degree of starch damage (P < 0.0001), and flour particle size (P = 0.0019) (Fig. 2E,F). As observed at t = 0, no interaction term had a significant effect on the k2 values in the uncooked noodles at t = 60 min. Both kansui and NaOH noodles prepared with high starch damage flour, regardless of flour particle size, displayed the maximum k2 value (Fig. 2E,F). The k2 discriminated the effect of starch damage better but not completely for any given particle size, on the mechanical properties of the noodles when prepared with kansui as compared to NaOH. Compared to unrested (t = 0) noodles, the kansui k2 values declined upon aging, whereas the reverse trend was observed in noodle prepared using NaOH. Cooked Noodle Stress Relaxation Parameters ANOVA of the cooked noodle stress relaxation parameters indicated that the type of alkali (P < 0.0001), particle size (P < 0.0001), and degree of starch damage (P < 0.0001) had significant
Fig. 2. Stress relaxation parameters of raw noodles aged for 60 min after production. Stress relaxation (SR %) (A, kansui; B, NaOH); k1 (C, kansui; D, NaOH); k2 (E, kansui; F, NaOH) as a function of flour particle size (85–110 μm, 110–132 μm, and 132–183 μm); flour starch damage L M H (low, medium, and high); and type of alkaline reagent (kansui vs. NaOH).
influences on SR%. Additionally, the alkali type by starch damage interaction was highly significant (P < 0.0001), as was the alkali type by particle size interaction term. However, the starch damage by particle size interaction term was not significant. The SR% values of the cooked noodles were about half of their raw counterparts (Fig. 3A,B). In all cases, SR% for cooked noodles prepared with kansui exhibited significantly larger values (P < 0.0001) than their NaOH counterparts (Fig. 3A,B), indicating they were less elastic (firm). For both types of alkali, for any given particle size, the low starch damaged flours displayed the lowest SR%. Increasing the degree of starch damage in the flour resulted in noodles with higher SR%. Measurements of the initial rate of relaxation of cooked noodles (k1) indicated that this parameter was significantly influenced by the type of alkali (P < 0.0001), particle size (P < 0.0001), and degree of starch damage (P < 0.0001). The interaction terms, type of alkali by starch damage (P < 0.0001), as well as type of alkali by particle size (P = 0.0122) interactions, significantly affected k1. Cooking the alkaline noodles had a very significant effect on k1 values (Fig. 3C,D) as they were nearly twice those observed for corresponding raw noodles at either resting time (0 or 60 min). The magnitude of influence that the type of alkali exerted on k1 is evident in Fig. 3C,D, as all of the k1 values of kansui noodles were significantly lower (P < 0.0001) than corresponding NaOH noodles. In none of the kansui noodles did k1 exceed a value of 7.25 while those prepared with NaOH all exceeded this value. Because the initial rate of relaxation and the magnitude of k1 are inversely related (initial rate of relaxation = 1/k1) (Peleg and Pollak 1982), the experimental results showed that noodles prepared with NaOH had slower initial rates of relaxation and, hence, exhibited a greater elasticlike (firmer) behavior than noodles made with kansui. Cooked noodles prepared from either alkali had maximum k1 values when prepared with flour with a low degree of starch damage and finer particle size. There was a general decline in k1 observed in both alkaline noodle types as particle size increased. The decrease in k1 for NaOH noodles, progressing from low to moderate starch damage for any given particle size, was greater than that detected in the corresponding kansui noodles. In both types of alkaline noodles, no significant difference was found between moderate and high starch damaged flours within a given particle size. ANOVA of the extent of relaxation (k2) for cooked noodles showed that this texture parameter was significantly influenced (P < 0.0001 in all cases) by all main effects (type of alkali, degree of starch damage, and particle size), much like SR% and k1 were influenced by the same parameters. The interaction term type of alkali by degree of starch damage displayed a highly significant influence (P < 0.0001) as did type of alkali by particle size to a lesser extent (P = 0.0464). The k2 values increased by ≈40% when the noodles were cooked compared with the 60-min rested raw counterparts. In both alkaline noodle types, the low starch damaged flours within a given particle size displayed the highest k2 value, hence the more elasticlike behavior, although those noodles prepared with kansui (Fig. 3E) were significantly lower than noodles formulated with NaOH (Fig. 3F). Correlations with Flour Parameters Previous research (Hatcher et al 2008b,c) had found that significant correlations existed among cooked noodle SR%, k1, and k2 with RVA pasting parameters confirming the involvement of starch in the overall noodle texture (Ross et al 1997; Crosbie et al 1999). Our results (Table II) showed that raw noodle parameters SR% and k2 exhibited significant correlations with peak viscosity, trough and breakdown; however, no such correlations were detected in the cooked noodles. This may be due to the fact that, unlike the previous studies, all of the flours for this study were
derived from a single wheat sample and it was only through milling that differences in the degree of starch damage and flour particle size were introduced. The ANOVA results indicated a strong, significant (P < 0.0001) influence due to starch damage on the rheological parameter k2 for raw and cooked noodles alike. It is likely that the correlations detected between the raw samples is due to the overriding influence of the starch damage because strong, significant correlations were detected for all RVA parameters and starch damage (r = –0.68 to –0.92, P < 0.0001 to P = 0.0020) with the exception of setback. DISCUSSION Effects of Degree of Starch Damage and Particle Size on Noodle Texture Because the degree of starch damage in the experimental flours was manipulated through milling, the events taking place during
Fig. 3. Stress relaxation parameters of noodles, aged for 60 min after production and optimally cooked. Stress relaxation (SR %) (A, kansui; B, NaOH); k1 (C, kansui; D, NaOH); k2 (E, kansui; F, NaOH) as a function of flour particle size (85–110 μm, 110–132 μm, and 132–183 μm); flour starch damage L M H (low, medium, and high); and type of alkaline reagent (kansui vs. NaOH). Vol. 86, No. 3, 2009
365
this processing operation provide valuable information to establish a link between the structure of starch granules and the properties of noodles. During milling, as the particle size of wheat endosperm is gradually reduced into flour, the structural integrity of intact starch granules is damaged, resulting in starch granules that are fractured, shattered, chopped, or otherwise modified (Chen and D’Appolonia 1986). Accordingly, an increase in the degree of starch damage in the flours was an indication of a higher number of physically broken starch granules. The degree of starch damage is affected by wheat hardness; hard wheat, such as the CPSW used in this experiment (AC Vista) with a particle size index (PSI) of 48–50 resulted in more breakage of starch granules during milling than that occurring in soft wheat. These differences in physical damage to the starch granules are thought to be due to stronger particle-matrix adhesion between the starch granules and the protein matrix of strong wheats (Chen and D’Appolonia 1984; Dobraszczyk 1994). Note that the wheat sample used in this study is unusually hard. Canadian common hard spring wheat normally exhibit PSI values 52–57, while soft wheat fall in the range of 70–72. Experimental results from the current study showed that using flour with increasing amounts of starch damage resulted in noodles with increased elasticlike behavior, as evidenced by lower SR%, slower initial rates of stress relaxation (1/k1), and higher residual stress (1 – [1/k2]). These trends did not change when the uncooked noodles were rested for 60 min, regardless of the flour particle size covered in this study. Clearly, the degree of starch damage had a strong influence on the material properties of the noodles, with an overall stiffening of the noodle texture as starch damage levels increased. A central event by which starch granules and the concomitant damage affected the mechanical properties of noodles is through an increase in the specific surface area of starch granules (Lelievre et al 1987; Edwards et al 2002). Two mechanisms have been identified by which an increase in the specific starch granule surface area may have affected noodle mechanical properties. One potential mechanism is related to changes in water availability for hydration of starch and protein biopolymers. As the degree of starch damage and the specific starch granule surface area increases, so does the water hydration capacity of starch granules, which results in increased competition between starch granules and gluten proteins for available water. Reduced water availability for hydration of the gluten molecules would have a negative effect on gluten development and hence viscoelastic behavior. This would explain the reduced stiffness of uncooked noodle doughs prepared from wheat flour with a higher degree of starch damage.
Another potential mechanism, central to the findings here, is related to an increase in the number-density of interactions between starch granules and the gluten protein matrix due to an increase in specific surface area of damaged starch granules. These increased interactions would also cause stiffening of the resulting uncooked noodle product. Recently, in a thorough study of the effects of starch particle size on dough strength, Edwards et al (2002) observed the positive effect of small starch granules on dough strength and on elasticlike behavior. In the field of polymer science, inclusion of small particulates to composite materials reinforces the material properties (Ahmed and Jones 1990). Such an effect may also be responsible for the stiffening effect of small starch granules (relative to larger ones) on the mechanical properties of noodle dough. The findings of Amemiya and Menjivar (1992) are consistent with this study’s uniaxial rheological parameters. Employing an alternative method consisting of small and large deformation rheological testing, they demonstrated that starch-starch and starchprotein interactions contribute to the elastic properties of dough by storing potential energy upon deformation, provided that strains remain 25%, Amemiya and Menjivar (1992) asserted that longer range protein-protein interactions would dominate dough viscoelastic behavior. Hence, at the strains used in this study (20%), starch granules through starch-starch and starch-protein interactions are expected to play an important role in noodle dough viscoelasticity. An additional benefit derived from this current investigation is that previous studies used dough systems that were developed using a dough mixer (Lelievre et al 1987; Edwards et al 2002). Such dough systems entrap a considerable number of gas bubbles, resulting in a significant effect on the dough mechanical properties (Chin et al 2005; Bellido et al 2006). In comparison, the present study had the benefit of using much lower water absorption levels with roll sheeting as the primary means to develop the experimental doughs. This reduced the contributions of the gas bubbles to the dough mechanical properties such that it was possible to clarify the effects of the degree of starch damage. Cooked Noodle Texture and Mechanisms of Action of Alkaline Solutions Although the elasticlike (firmer) behavior was greatest for the uncooked noodle prepared with the highest degree of starch damage (Figs. 1 and 2), the opposite effect was observed when noodles were cooked (Fig. 3). The most pronounced elasticlike behavior (lowest SR% and highest k1 and k2 values) was observed in cooked noodles prepared with the lowest degree of starch damage. The opposite mechanical behavior observed in uncooked and
TABLE II Correlations Between Flour Characteristics and Stress Relaxation Parametersa Raw Noodle t = 0 min Protein Gluten Ash Agtron Starch damage Peak viscosity Trough Breakdown Final viscosity Setback a
Cooked Noodle
k2
k1
SR%
k2
k1
SR%
k2
k1
ns ns ns 0.56 0.0167 –0.82 0.0001 0.62 0.0057 0.56 0.0156 0.70 0.0013 ns ns
ns ns ns –0.56 0.0158 0.86 0.0001 –0.65 0.0032 –0.58 0.0108 –0.73 0.0005 ns ns
ns ns ns ns
ns ns ns 0.64 0.0039 –0.86 0.0001 0.66 0.0026 0.61 0.0073 0.75 0.0003 ns ns
ns ns ns –0.66 0.0030 0.86 0.0001 –0.68 0.0016 –0.63 0.0050 –0.77 0.0002 ns ns
ns ns ns ns
ns ns ns
ns ns ns
ns ns ns
ns, Not significant at P = 0.05.
366
Raw Noodle t = 60 min
SR%
CEREAL CHEMISTRY
0.61 0.0068 ns ns –0.48 0.0429 ns ns
0.65 0.0030 ns
ns ns
–0.48 0.0431 ns
ns ns
ns
ns
ns
ns
–0.47 0.0466 ns ns
ns
ns
ns
ns ns
ns ns
ns ns
cooked noodles can also be explained in terms of the two hypotheses put forward. For the hypothesis based on increased competition for water hydration, it can be argued that flour with a higher degree of starch damage gave rise to cooked noodles of lower stiffness values because, upon cooking, the integrity of the gluten protein network was likely disrupted to a greater extent by an excessive swelling of starch granules, which had been preferentially hydrated during dough preparation. Moss et al (1986) proposed a similar hypothesis to explain the effect of NaOH on noodle texture. Using light microscopy, Moss et al (1986) found that starch damage (from use of NaOH) hindered protein development during noodle preparation and that, upon cooking, excessive swelling of damaged starch was more pronounced in alkaline noodle than in the control (alkaline-free) noodle. The fact that amylograph viscosity increased proportionally with the degree of starch damage only in the flour with the finest particle size (Table I), however, suggested that undue disruption of the gluten protein network upon cooking only partly explained the mechanical behavior observed in the experimental noodle samples. The second mechanisms proposed to explain the mechanical behavior of noodles made from flour with varying degrees of starch damage was related to changes in the number-density of starch-starch and starch-protein interactions. While increased starch-starch and starch-protein interactions elicited greater elastic responses in the uncooked material made with high starch damage flour, it can be argued that the influence of these interactions is largely diminished upon cooking. On cooking, longer range interactions between gluten protein chains would likely dominate over shorter range interactions due to thermal transition reactions causing melting of starch granules. Once starch granules undergo gelatinization, they are unable to contribute to the elastic behavior of noodles and can no longer restore mechanical energy applied to the cooked noodle during the loading phase of stress relaxation testing (Amemiya and Menjivar 1992). Hence, while in an uncooked noodle, starch granules with a greater degree of physical damage reinforced mechanical structure, they contributed little to viscoelastic behavior in the cooked noodle and yet they were more likely to undergo gelatinization than their counterparts, intact starch granules. This mechanism would explain the opposite mechanical behavior observed in uncooked and cooked noodles made from flour with varying degrees of starch damage. A confounding factor influencing mechanical properties of noodles was the addition of alkaline reagents, not discussed hitherto. Because noodles are prepared using a limited amount of water (32–36%), alkaline reagents would mainly exert influence on gluten protein development through influence on protein hydration (Wu et al 2006). Gluten hydration allows the unfolding of the aggregated glutenin and gliadin polymeric proteins which is essential for subsequent interactions through disulfide bonding, hydrogen bonding, hydrophobic interactions, and electrostatic and van der Waals forces. Although the kansui (pH 11.1) and NaOH (pH 13.2) solutions would influence gluten protein hydration through the effect on dough pH, the strong buffering properties of gluten proteins cause these two alkaline agents to elevate the pH to comparable values (pH ≈10). At this pH level, the gluten ionizable amino acids would be negatively charged as the isoelectric point of gluten proteins is ≈6.5 (Eliasson and Larsson 1993). Under this condition, it seems more plausible that the alkaline salts exerted the specified influence on gluten protein hydration (and hence development) mainly through lyotropic effects. When the milieu in which bicarbonate anions are dissolved has a pH ≈10, bicarbonate species are mainly present as carbonate anions (Hoseney 1998), which are considered nonchaotropic species (Calligaris and Nicoli 2006). Nonchaotropic species can be regarded as water-structure builders (Eliasson and Larsson 1993), with the ability to increase the molecular order of water around protein molecules in the dough (Preston 1981). Due to the structuring of water, hydrophobic interactions among protein polypeptide chains
are favored in the unfolded proteins. This will impair protein disaggregation during dough development and thus hinder the formation of the gluten protein network (Preston 1981; Kinsella and Hale 1984). These events would explain how carbonate anions may have reduced hydration of gluten proteins. By contrast, the hydroxyl anions liberated by the NaOH alkali, although capable of elevating the dough pH, lacked the lyotropic effects of carbonate anions and hence were unable to influence protein development in the same fashion as carbonate anions from kansui. This hypothesis is in line with experimental results showing that cooked noodles prepared with NaOH showed a significantly more pronounced elasticlike behavior than those prepared from kansui (Fig. 3). Consistent with this hypothesis, Hatcher et al (2008a) found that compared with a control noodle (no alkaline solution added), noodles made with kansui became stiffer (higher MCS, RTC, REC, CHE, and SPR), whereas NaOH had the opposite effect, with such effects being more pronounced with increasing starch damage. Furthermore, Hatcher and Anderson (2007) demonstrated that by increasing the concentration of kansui from 1 to 5% w/w, significant deleterious reductions in empirical texture measurements (MCS, RTC, and REC) were observed (they rendered noodles more compliant or less firm). It is important to note that microphotographic evidence presented in another report using light microscopy conflicts with the above hypothesis. Moss et al (1986) observed that noodle dough containing 1% sodium hydroxide had a protein network which was not as continuous or as uniform as a dough containing 1% kansui due to inadequate development and stretching of the gluten protein. This observation is difficult to reconcile with our hypothesis and therefore the exact mechanism of action of kansui and NaOH on noodle rheology remains complex and its precise elucidation warrants further investigation. CONCLUSIONS The degree of flour starch damage, particle size, and the nature of the alkaline reagent used to prepare yellow alkaline noodles significantly affected the three rheological parameters measured by uniaxial stress relaxation. Clear and distinct differences were observed in both the raw noodles at resting times of 0 or 60 min, as well as in the cooked products. For uncooked noodles, the greatest elasticlike (firmer) behavior was observed when flour with the greatest degree of starch damage was used in the noodle formulation. The magnitude of the changes observed when assessing the cooked products, particularly k2 and k1, were significantly greater than those observed in the raw noodles, underlining the increase in noodle firmness brought about by thermal transitions of the starch and gluten protein components. Results showed that starch damage had a positive effect on noodle elastic behavior, possibly due to an increase in the specific surface area of starch granules which was hypothesized to increase interactions between starch granules and gluten proteins and to promote competition for water between starch granules and proteins molecules. These events appeared to have hindered the development of a strong gluten network upon cooking, resulting in noodles with reduced elastic behavior upon cooking. A mechanism of action of kansui and NaOH in gluten protein development was considered. ACKNOWLEDGMENTS We gratefully acknowledge the assistance of H. Facto and J. Dexter of the Canadian Grain Commission Grain Research Laboratory for their assistance in preparation of the flours and noodles. LITERATURE CITED AACC International. 2000. Approved Methods of the American Association of Cereal Chemists, 10th Ed. Methods 08-01, 22-10, 54-21, and 76-31. The Association: St. Paul, MN. Vol. 86, No. 3, 2009
367
Ahmed, S., and Jones, F. R. A review of particulate reinforcement theories for polymer composites. J. Mater. Sci. 25:4933-4942. Amemiya, J. I., and Menjivar, J. A. 1992. Comparison of small and large deformation measurements to characterize the rheology of wheat flour doughs. J. Food Eng. 16:91-108. Bellido, G. G., Scanlon, M. G., and Page, J. H. 2006. The bubble size distribution in wheat flour dough. Food Res. Int. 39:1058-1066. Calligaris, S., and Nicoli, M. C. 2006. Effect of selected ions from lyotropic series on lipid oxidation rate. Food Chem. 94:130-134. Chen, J., and D’Appolonia, B. L. 1986. Effect of starch damage and oxidizing agents on alveogram properties. Pages 117-129 in: Fundamentals of Dough Rheology. H. Faridi and J. M. Faubion, eds. AACC International: St. Paul. MN. Chin, N. L., Martin, P. J., and Campbell, G. M. 2005. Dough aeration and rheology. 3. Effect of the presence of gas bubbles in bread dough on measured bulk rheology and work input rate. J. Sci. Food Agric. 85:2203-2212. Crosbie, G. B., Ross, A. S., Moro, T. and Chiu, P. C. 1999. Starch and protein requirements of Japanese alkaline noodles (ramen). Cereal Chem. 76:328-334. Dobraszczyk, B. J. 1994. Fracture mechanics of vitreous and mealy wheat endosperm. J. Cereal Sci. 19:273-282. Edwards, N. M., Dexter, J. E., and Scanlon, M. G. 1996. Starch participation in durum dough linear viscoelastic properties. Cereal Chem. 79:850-856. Edwards, N. M., Scanlon, M. G., Kruger, J. E. and Dexter, J. E. 2002. Oriental noodle dough rheology: Relationships to water absorption, formulation and work input during dough sheeting. Cereal Chem. 73:708-711. Eliasson, A., and Larsson, K. 1993. Physicochemical behavior of the components of wheat flour. Pages 77-78 in: Cereals in Breadmaking: A Molecular Colloidal Approach. Marcel Dekker: New York. Hatcher, D. W. 2001. Asian noodle processing. Pages 131-157 in: Cereals Processing Technology. G. Owens, ed. Woodhead Publishing: Cambridge, UK. Hatcher, D. W. and Anderson, M. J. 2007. Influence of alkaline formulation on oriental noodle color and texture. Cereal Chem. 84:253-259. Hatcher, D. W., and Preston, K. R. 2004. Investigation of small-scale asymmetric centrifugal mixer for the evaluation of Asian noodles. Cereal Chem. 81:303-307. Hatcher, D. W., Anderson, M. J., Desjardins, R. G., Edwards, N. M., and Dexter, J. E. 2002. Effects of flour particle size and starch damage on processing and quality of white salted noodles. Cereal Chem. 79:64-71. Hatcher, D. W., Edwards, N. M., and Dexter, J. E. 2008a. Effects of particle size and starch damage of flour and alkaline reagent on yellow alkaline noodle characteristics. Cereal Chem. 85:425-432. Hatcher, D. W., Bellido, G. G., Dexter, J. E., Anderson, M. J., and Fu, B. X. 2008b. Investigation of uniaxial stress relaxation parameters to characterize the texture of yellow alkaline noodles made from durum and common wheats. J. Texture Stud. 39:695-708. Hatcher, D. W., Bellido, G. G., Dexter, J. E., Anderson, M. J., and Fu, B. X. 2009. Effect of hard white wheat blending on the quality of yellow
alkaline durum noodles. Food Chem. 113:980-988. Hoseney, R. C. 1998. Soft wheat products. Pages 275-305 in: Principles of Cereal Science and Technology, 2nd Ed. AACC International: St. Paul. MN. ICC. 1980. International Association for Cereal Science and Technology. Standard 137/1, Mechanical Determination of the Wet Gluten Content of Wheat Flour (Glutomatic). The Association: Vienna. Kinsella, J. E., and Hale, M. L. 1984. Hydrophobic associations and gluten consistency: Effects of specific anions. J. Agric. Food Chem. 32:1054-1056. Lelievre, J., Lorenz, K., Meredith, P., and Baruch, D. W. 1987. Effects of starch particle size and protein concentration on breadmaking performance. Starch 39:347-352. Martin, D. G., and Dexter, J. E. 1991. A tandem Buhler laboratory mill: Its development and versatility. AOM Bull. 5855. Miskelly, D. M., and Moss, H. J. 1985. Flour quality requirements for Chinese noodle manufacture. J. Cereal Sci. 3:379-387. Moss, H. J., Miskelly, D. M., and Moss, R. 1986. The effect of alkaline conditions on the properties of wheat flour dough and Cantonese style noodles. J. Cereal Sci. 4:261-268. Oh, N. H., Seib, P. A., Finney, K. F., and Pomeranz, Y. 1986. Noodles. V. Determination of optimum water absorption of flour to prepare oriental noodles. Cereal Chem. 63:93-96. Peleg, M. 1979. Characterization of the stress relaxation curves of solid foods. J. Food Sci. 44:277-281. Peleg, M., and Pollak, M. 1982. The problem of equilibrium conditions in stress relaxation analysis of solid foods. J. Texture Stud. 13:1-11. Preston, K. R. 1981. Effects of neutral salts upon wheat gluten protein properties. I. Relationship between the hydrophobic properties of gluten proteins and their extractability and turbidity in neutral salts. Cereal Chem. 58:317-324. Ross, A. S., Quail, K. J., and Crosbie, G. B. 1997. Physicochemical properties of Australian flours influencing the texture of yellow alkaline noodles. Cereal Chem. 74:814-820. Safari-Ardi, M., and Phan-Thien, N. 1998. Stress relaxation and oscillatory tests to distinguish between doughs prepared from wheat flours of different varietal origin. Cereal Chem. 75:80-84. Shiau, S.-Y., and Yeh, A.-I. 2001. Effects of alkali and acid on dough rheological properties and characteristics of extruded noodles. J. Cereal Sci. 33:27-37. Shiau, S.-Y., and Yeh, A.-I. 2004. On-line measurement of rheological properties of wheat flour extrudates with added oxido-reductants, acid and alkali. J. Food. Eng. 62:192-202. Singh, H., Rockall, A., Martin, C. R., Chung, O. K., and Lookhart, G. L. 2006. The analysis of stress relaxation data of some viscoelastic foods using a texture analyzer. J. Texture Stud. 37:383-392. Terada, M., Minami, J., and Yamamoto, T. 1978. Some rheological properties of dough alkalified and neutralized. Agric. Biol. Chem. 42:365369. Wu, J., Beta, T., and Corke, H. 2006. Effects of salt and alkaline reagents on dynamic rheological properties of raw oriental wheat noodles. Cereal Chem. 83:211-217.
[Received August 7, 2008. Accepted February 2, 2009.]
368
CEREAL CHEMISTRY
