Water Sorption Kinetics of Gluten-added Wheat Noodle

Abstract

Noodles were prepared using wheat flour with 0 – 20% (w/w) added powdered gluten, and the transient changes in their moisture content during cooking were measured. Kinetic analysis of the water sorption process during cooking indicated that the process occurred in two distinct stages for all of the noodles. Water diffusion and consequent starch gelatinization predominantly controlled water sorption during the early stage, while relaxation of the gluten network structure was rate-limiting for the water sorption process during the latter stage. The moisture content, at which the rate-limiting factor for the water sorption process changed, was lower for the wheat noodles having a higher gluten content. Thus, it was suggested that the change in the gluten network structure induced by the addition of gluten to wheat flour affected the water sorption behavior of wheat noodles.

Introduction

Noodles made with wheat flour are commonly consumed in many countries and regions. Udon, or Japanese white salted noodles, is a type of wheat noodle popularly consumed in Japan. Prior to eating, udon is cooked in boiling water to improve its textural and digestive properties via water sorption; the texture of cooked udon plays an important role in its palatability (Konik and Miskelly, 1992). The texture of cooked noodles, such as udon and pasta, is affected by the state of the starch granules (Lai and Hwang, 2004), the swelling properties of those granules (Crosbie, 1991), the moisture distribution in the noodle (Kojima et al., 2001; Irie et al., 2004), and the addition of modified starch to wheat flour (Eguchi et al., 2014). The state of the starch granules and moisture distribution in the noodles depend on the overall moisture content, which changes with cooking time (Liu and Thompson, 1998; Kojima et al., 2001; Lai and Hwang, 2004). Therefore, understanding the water sorption behavior is important to control the quality of wheat noodles.

Gluten is one of the major components in wheat flour. The content (Del Nobile et al., 2005) and composition (Kovacs et al., 1995) of gluten in wheat flour significantly affect the quality of wheaten food, such as noodles and breads, as well as the thermal stability (Kovacs et al., 2004) and degree of polymerization (Pareyt et al., 2015) of gluten. Addition of gluten to wheat flour is prevalent in the food industry to improve the quality of wheaten food (Day et al., 2006). Gluten added to wheat flour forms a network structure that increases the firmness and tensile strength of cooked wheat noodles (Park and Baik, 2009). The network structure in the noodles affects their water sorption behavior and the hydrolysis of starch by amylase as well as the textural characteristics. The starch granules are embedded in the gluten network in the noodle (Sekiyama et al., 2012), and water sorption of the noodle is governed by the relaxation of this gluten network during its overcooking stage (Del Nobile and Massere, 2000). A tight structure of the gluten network decelerates enzymatic hydrolysis of starch in the flour (Zou et al., 2015). However, the effect of adding gluten to wheat flour on the water sorption behavior during cooking has been insufficiently investigated, and hence, the water sorption mechanism of gluten-added wheat noodles has not yet been elucidated.

In this study, wheat noodles were prepared using wheat flour with different added gluten contents, 0 – 20% (w/w), and their moisture content was measured for a long duration in order to understand the phenomena occurring during cooking in boiling water. The change in the moisture content with cooking time was analyzed to examine the kinetic effects of the added gluten on the water sorption behavior of wheat noodles.

Materials and Methods

Materials    Wheat flour, the protein and ash contents of which were respectively 8.6 and 0.35 wt% on a wet basis, suitable for udon preparation was supplied by Nisshin Seifun Group, Inc., Tokyo, Japan. Powdered wheat gluten was purchased from Wako Pure Chemical Industries, Osaka, Japan.

Preparation of wheat noodles    Powdered wheat gluten was added to wheat flour to produce mixtures with a gluten weight fraction of 0, 5, 10, 15, and 20% (w/w). Tap water (150 g) was intermittently added to each mixture (500 g) of wheat flour and powdered wheat gluten while kneading with a KSM 150 mixer (KitchenAid, U.S.A.) over 20 min. The resultant wheat dough was put into a pasta-making machine (Magica, Bottene, Italy) equipped with a vacuum pump (DTC-60, Ulvac Kiko, Miyazaki, Japan) and extruded through a 2.25-mm opening die made of Teflon at 31.3 to 41.3 kPa (abs) to produce wheat noodles.

Water sorption    The wheat noodles were cut to 8-cm long pieces. Distilled water (45 mL) contained in a 50-mL polypropylene culture tube (VIO-50R, As One, Osaka) was heated to 98°C or higher by immersing the tube in boiling water. The wheat noodles were added to the tube and kept there for different lengths of time (up to 180 min) to sorb water. The noodles were then removed from the tube and blotted with Kimwipe (Nippon Seishi Cresia, Tokyo) to remove excess water on the noodle surface. The noodles were weighed before and after drying at 135°C for 5 h in a DN-400 oven (Yamato Scientific, Tokyo). The dry moisture content of the wheat noodle, Xt, was calculated using Eq. (1).

  

where W₁ and W₂ are the weights of water-sorbed and born-dried noodles, respectively. The measurement for each sample was repeated in triplicate.

Results and Discussion

Water sorption process    Figure 1 shows the water sorption curves at 98°C for wheat noodles containing 0, 5, 10, 15, and 20% (w/w) powdered gluten. The curves in the figure were drawn to connect smoothly the experimentally determined data points for each noodle. The moisture content of the wheat noodles decreased with increasing gluten content. A possible reason for this decrease in moisture content may be related to the difference in the equilibrium moisture content between gelatinized starch and gluten as observed by our previous study (Ogawa et al., 2014). We found that the equilibrium moisture content of spaghetti prepared from durum semolina wheat flour was much higher than that of spaghetti-like noodle prepared by only gluten isolated from the durum semolina flour.

Fig. 1.

Water sorption by wheat noodles containing 0 (●), 5 (◊), 10 (□), 15 (△), and 20% (w/w) (○) powdered gluten. The curves were drawn to connect smoothly the experimentally determined data points for each noodle. The error bars indicate the standard deviation for three independent measurements.

Kinetic analysis of the water sorption process    A hyperbolic equation has been conveniently applied to describe the water sorption processes for pasta (Cunningham et al., 2007; Ogawa et al., 2011), wheat noodles (Roppongi et al., 2014) and cereal grains (Sopade et al., 1992), although the equation is not derived from any theoretical assumptions. We applied the equation to describe the water sorption process of each wheat noodle in this study. The equation fits the overall water sorption data fairly well, but it did not fit the water sorption data during the early stages (data not shown), similar to the water sorption data for spaghetti (Yoshino et al., 2013).

Next, we assumed that the water sorption process obeyed first-order kinetics for the difference between the moisture content at equilibrium, X_e, and the moisture content at an arbitrary sorption time, X_t (Eq. (2)).

  

where k is the rate constant. According to Butterworth et al. (2012), Eq. (2) can be rewritten as Eq. (3).

  

where X₀ is the initial moisture content of the wheat noodle. Equation (3) is useful to estimate the X_e value. Therefore, the parameters X_e and k can be estimated by plotting the water sorption rate, dX_t/dt, against the cooking time, t, on a semi-logarithmic scale.

For the water sorption process of each wheat noodle, the dX_t/dt values were evaluated by graphical differentiation and plotted against t on a semi-logarithmic scale, as shown in Fig. 2. Irrespective of the amount of added gluten, the ln(dX/dt) value decreased with the water sorption time. The plots during the early (5 to 40 min) and latter (60 to 180 min) stages lie on two separate lines. This indicates that the water sorption process of wheat noodles occurred in two distinct stages and that the noodle sorbed water via two different mechanisms. The intersection of the two lines indicates the point where the faster early stage transmutes to the slower latter stage. Similar phenomena were observed in the hydrolysis of raw starch by α-amylase. The hydrolytic process was analyzed assuming two different stages, each of which obeyed first-order kinetics (Butterworth, et al., 2012; Patel et al., 2014).

Fig. 2.

The moisture content X_t (○) and ln(dX_t/dt) (●) values as a function of sorption time for wheat noodles with (a) 0% (w/w), (b) 5%, (c) 10%, (d) 15%, and (e) 20% added powdered gluten. The solid curve was drawn by substituting the estimated k₁, k₂, X_e1, and X_2e values into Eqs. (6) and (7).

Starch granules existing in the interior of pasta are embedded in a gluten network (Sekiyama et al., 2012). Water sorption behavior is affected by the diffusion of water through the noodle matrix, melting of crystalline starch, and relaxation of the gluten network. The first two factors play important roles in the sorption during the early stage of cooking, while the last factor controls the sorption during the latter overcooking stage (Del Nobile and Massera, 2000). Water sorption causes swelling of the starch granules and relaxation of the gluten network. Because the gelatinized starch granules sorb water quickly, a rapid increase in the moisture content during the early stage would reflect the water sorption by starch granules until the effect of the gluten network on the sorption process becomes significant. On the other hand, because relaxation of the gluten network progresses slowly, it would govern the water sorption process during the latter stage. That is, the rate-limiting factor for water sorption by wheat noodles would change at a certain moisture content. The two lines in Fig. 2 would reflect the rapid uptake of water by starch granules and slow relaxation of the gluten network during the early and latter stages, respectively, and the intersection of the lines indicates the change in the rate-limiting factor. Therefore, we assumed that the water sorption process obeys first-order kinetics during both the early and latter stages. The water sorption rate during the early stage (from the beginning of cooking to the time at the intersection, t_c) is expressed by Eq. (4).

  

where k₁ is the rate constant and X_1e is the hypothetical equilibrium moisture content during the rapid water sorption process. The water sorption rate during the latter stage (cooking times longer than t_c) is expressed by another first-order equation (Eq. (5)).

  

where k₂ is the rate constant for the latter stage and X_2e is also the hypothetical equilibrium moisture content during the slow sorption process. The initial conditions for Eqs. (4) and (5) are X_t = X₀ at t = 0 and X_t = X_c at t = t_c, respectively. The moisture content X_t is given by Eqs. (6) and (7) for the early and latter stages, respectively.

  

  

The parameters t_c and X_c were evaluated from the intersection of the two lines in Fig. 2 for each wheat noodle. The parameters for the early and latter stages, k₁ and X_1e, and k₂ and X_2e, were determined from the slopes and intercepts of their respective lines. The solid curves in Fig. 2 were drawn by substituting the estimated k₁, k₂, X_1e, and X_2e values into Eqs. (6) and (7), and they well represented the experimental results for all the tested noodles (R² = 0.996 to 0.999).

Effect of gluten addition on the water sorption kinetics    Figure 3 illustrates the k₁, k₂, X_1e, and X_2e values for the wheat noodles with different gluten contents. Irrespective of the gluten content, the k₂ value was approximately one-tenth of the k₁ value, indicating that the relaxation of the gluten network restricted water-sorption-induced swelling of starch granules during the latter stage. Both X_1e and X_2e values decreased with increasing gluten content. This can be ascribed to the reduced equilibrium moisture content of the wheat noodle because the equilibrium moisture content of gluten was lower than that of starch. In this manner, the gluten content seemed to scarcely affect the rate process for water sorption, such as water diffusion in the noodle, but to affect the equilibrium moisture content, X_e, reflecting the structure.

Fig. 3.

The dependence of k₁ (○), k₂ (△), X_1e (●), and X_2e (▲) values on the gluten content of wheat noodles.

Figure 4 shows the t_c and X_c values for the wheat noodles with different gluten contents. Both the t_c and X_c values were smaller for the noodles with higher gluten content, and the transition from the rapid water sorption during the early stage to the slow water sorption during the latter stage occurred at a shorter cooking time and lower moisture content for the noodles containing more gluten. The addition of gluten to wheat flour made the gluten network structure in the wheat noodles firmer (Park and Baik, 2009). Because the gluten network structure surrounding the starch granules was changed by the addition of gluten to the flour, the moisture content, which regulates the water sorption rate, shifted toward a lower value. The X_c value ranged from 2 to 3 kg-H₂O/kg-d.m., which was almost the same as the moisture content in the peripheral region of the cooked wheat noodle (Fukuzawa et al., 2016). Therefore, it can be suggested that the water sorption in the peripheral region of wheat noodles is controlled by the relaxation of the gluten network (Ogawa et al., 2014), and that the moisture content-dependent change of the factor controlling the water sorption contributes to the change in the moisture distribution in the interior of noodle.

Fig. 4.

The dependence of t_c (○) and X_c (●) values on the gluten content of wheat noodles.

Acknowledgement    This study was carried out during the project of the Cereal Science Consortium by the Graduate School of Agriculture, Kyoto University, Gifu University, and the Nissin Seifun Group, Inc.

References

•  Butterworth,  P.J.,  Warren,  F.J.,  Grassby,  T.,  Patel,  H., and  Ellis,  P.R. (2012). Analysis of starch amylolysis using plots for first-order kinetics. Carbohydr. Polym., 87, 2189-2197.
•  Crosbie,  G.B. (1991). The relationship between starch swelling properties, paste viscosity and boiled noodle quality in wheat flour. J. Cereal Sci., 13, 145-150.
•  Cunningham,  S.E.,  McMinn,  W.A.M.,  Magee,  T.R.A., and  Richardson,  P.S. (2007). Modelling water absorption of pasta during soaking. J. Food Eng., 82, 600-607.
•  Day,  L.,  Augustin,  M.A.,  Batey,  I.L., and  Wrigley,  C.W. (2006). Wheat-gluten uses and industry needs. Trends Food Sci. Technol., 17, 82-90.
•  Del Nobile,  M.A.,  Baiano,  A.,  Conte,  A., and  Mocci,  G. (2005). Influence of protein content on spaghetti cooking quality. J. Cereal Sci., 41, 347-356.
•  Del Nobile,  M.A. and  Massera,  M. (2000). Modeling of water sorption kinetics in spaghetti during overcooking. Cereal Chem., 77, 615-619.
•  Eguchi,  S.,  Kitamoto,  N.,  Nishinari,  K., and  Yoshimura,  M. (2014). Effects on esterified tapioca starch on the physical and thermal properties of Japanese white salted noodles prepared partly by residual heat. Food Hydrocoll., 35, 198-208.
•  Fukuzawa,  S.,  Ogawa,  T.,  Nakagawa,  K., and  Adachi,  S. (2016). Moisture profiles of wheat noodles containing hydroxypropylated tapioca starch. Int. J. Food Sci. Technol., in press.
•  Irie,  K.,  Horigane,  A.K.,  Naito,  S.,  Motoi,  H., and  Yoshida,  M. (2004). Moisture distribution and texture of various types of cooked spaghetti. Cereal Chem., 81, 350-355.
•  Kojima,  T.I.,  Horigane,  A.K.,  Yoshida,  M.,  Nagata,  T., and  Nagasawa,  A. (2001). Change in the status of water in Japanese noodles during and after boiling observed by NMR micro imaging. J. Food Sci., 66, 1361-1365.
•  Konik,  C.M. and  Miskelly,  D.M. (1992). Contribution of starch and non-starch parameters to the eating quality of Japanese white salted noodles. J. Sci. Food Agric., 58, 403-406 (1992).
•  Kovacs,  M.I.P.,  Howes,  N.K.,  Leisle,  D., and  Zawistowski,  J. (1995). Effect of two differential low molecular weight glutenin subunits on durum wheat pasta quality parameters. Cereal Chem., 72, 85-87.
•  Kovacs,  M.I.P.,  Fu,  B.X.,  Woods,  S.M., and  Khan,  K. (2004). Thermal stability of wheat gluten protein: its effect on dough properties and noodle texture. J. Cereal Sci., 39, 9-14.
•  Lai,  H.M. and  Hwang,  S.C. (2004). Water status of cooked white salted noodles evaluated by MRI. Food Res. Int., 37, 957-966.
•  Liu,  Q. and  Thompson,  D.B. (1998). Effects of moisture content and different gelatinization heating temperatures on retrogradation of waxy-type maize starches. Carbohydr. Res., 314, 221-235.
•  Pareyt,  B.,  Steertegem,  B.V.,  Brijs,  K., and  Delcour,  J.A. (2015). The role of gluten proteins in production and quality of a yeast leavened sugar and fat rich wheat based food model system — 2. Impact of redox agents. Food Res. Int., 67, 169-174.
•  Ogawa,  T.,  Kobayashi,  T., and  Adachi,  S. (2011). Water sorption kinetics of spaghetti at different temperatures. Food Bioprod. Process., 89, 135-141.
•  Ogawa,  T.,  Hasegawa,  A., and  Adachi,  S. (2014). Effects of relaxation of gluten network on rehydration kinetics of pasta. Biosci. Biotechnol. Biochem., 78, 1930-1934.
•  Park,  S.J. and  Baik  B.K. (2009). Quantitative and qualitative role of added gluten on white salted noodles. Cereal Chem., 86, 646-652.
•  Patel,  H.,  Day,  R.,  Butterworth,  P.J., and  Ellis,  P.R. (2014). A mechanistic approach to studies of the possible digestion of retrogradation starch by α-amylase revealed using a log of slope (LOS) plot. Carbohydr. Polym., 113, 182-188.
•  Roppongi,  T.,  Ogawa,  T., and  Adachi,  S. (2014). Water sorption kinetics of wheat noodle with different diameters. Food Sci. Technol. Res., 20, 241-246.
•  Sekiyama,  Y.,  Horigane,  A.K.,  Ono,  H.,  Irie,  K.,  Maeda,  T., and  Yoshida,  M. (2012). T2 distribution of boiled dry spaghetti measured by MRI and its internal structure observed by fluorescence microscopy. Food Res. Int., 48, 374-379.
•  Sopade,  P.A.,  Ajisegiri,  E.S., and  Badau,  M.H. (1992). The use of Peleg's equation to model water absorption in some cereal grains during soaking. J. Food Eng., 15, 269-283.
•  Yoshino,  M.,  Ogawa,  T., and  Adachi,  S. (2013). Properties and water sorption characteristics of spaghetti prepared using various dies. J. Food Sci., 78, E520-525.
•  Zou,  W.,  Sissons,  M.,  Gidley,  M.J.,  Gilbert,  R.G., and  Warren,  F.J. (2015). Combined techniques for characterising pasta structure reveals how the gluten network slows enzymic digestion rate. Food Chem., 188, 559-568.