Abstract
The effect of cooking water on both textural and cooking properties of spaghetti was investigated for spaghetti samples, which differ in protein content. The samples were analysed after cooking in deionised, laboratory tap water, deionised water with 2.5% salt and deionised water with 5.0% salt. Brands A, B, and C were usual durum wheat spaghetti and brand D was spaghetti enriched with bran. Regardless of the cooking water used, brand D had higher hardness and lower adhesiveness than other spaghetti samples and required longer cooking time to achieve optimum cooking. It was found that samples cooked deionised water had lower hardness and adhesiveness values as compared to samples cooked in salty water. It can be concluded that a certain amount of salt in the cooking water improves textural characteristics of cooked pasta.
INTRODUCTION
Pasta and its products are major constituents of most diets. Determination of the textural parameters after pasta cooking is of great importance from the point of product acceptability by the consumers. Generally, pasta is consumed within a short period after cooking. Good quality pasta is defined as having high degree of firmness and elasticity, which is mainly, termed as “al dente.”[Citation1,Citation2] Proper evaluation of pasta cooking quality requires consideration of a number of factors including elasticity, firmness, surface stickiness, cooking tolerance, water absorption, and loss of solids to cooking water. Taste panels can be used to estimate pasta cooking quality, but they are time consuming and impractical when sample size is limited or large numbers of samples are to be evaluated.[Citation3] Therefore, rapid instrumental methods that consider a number of textural factors have been developed.[Citation4] A very popular one is the texture profile analysis based on the recognition of texture as a multi parameter attribute. The test consists of compressing bite size pieces of food two times in a motion that simulates the action of jaw, and extracting from the resulting force time curve a number of textural parameters. These can be divided into the primary parameters of hardness, cohesiveness, springiness and adhesiveness and the secondary parameters of fracturability, chewiness and gumminess.[Citation5,Citation6] In Durum wheat pasta, starch gelatinization and protein coagulation cause the major structural changes during cooking. Both transformations occur at approximately the same temperature and moisture level. There are several factors that affect the characteristics of cooked pasta such as semolina protein quality and quantity, drying conditions and composition of cooking water.[Citation7]
It was shown previously that increased water hardness increased stickiness values and caused higher cooking losses.[Citation8] It was also declared that high levels of calcium and magnesium in the cooking water can adversely affect spaghetti cooking quality.[Citation9] Some workers also mentioned about pH level of cooking water. Alary et al.[Citation10] found that at pH levels of 6.0 spaghetti cooking quality peaked and on either side of this pH range it declined. To the author's knowledge, there is little information regarding to the effect of cooking water on cooking properties of spaghetti. Previous researchers[Citation7,Citation8] have shown that the cooking water has influence on cooking quality of spaghetti, especially on parameters like cooking loss, water absorption, hardness, and stickiness. Therefore, this study was carried out to determine the effects of cooking water composition on spaghetti cooking quality. From this point of view, textural properties of cooked spaghetti were analysed after cooking in deionised, tap, and 2.5 and 5.0% salt levels.
MATERIALS AND METHODS
Sample Preparation
Four different spaghetti brands (A, B, C, and D) were supplied commercially. Brand A, B, and C were regular durum wheat spaghetti varying in protein content and brand D was enriched with bran. The degree of cooking, water absorption and texture were measured as they were cooked 6, 8, 10, 12, 14, 16, and 20 min in laboratory tap water (pH = 8.09), deionized water (pH = 5.45) containing 0, 2.5% salt (pH = 6.81) and 5% (pH = 7.96) salt (wt NaCl/ wt H2O). All cooking tests were performed in duplicate. Spaghetti (10 g of 10 cm strands) was added to 250 ml rapidly boiling water.[Citation11] Boiling was kept at this level for the entire cooking period. Cooked spaghetti samples were drained in a sieve and rinsed with distilled water. Excess moisture on the spaghetti surface was removed by lightly patting the strands between paper towels and the samples were used immediately for analysis.
Analytical Methods
Protein content
The protein content was determined according to standard Kjehldahl method as described in Egan et al.[Citation12]
Water absorption
Water absorption capacity of spaghetti samples was determined after drying the samples in an oven for 2 h and the result was expressed as percent water absorption.
Instrumental Methods
Degree of cooking
Cross-sectioned images of spaghetti samples were placed on the glass plate of a scanner (HP Scanjet 4200C) with a non reflecting black paper sheet. Images were analyzed by quantifying the uncooked area (Ao) and total area (At). The results were expressed as Ao/At.
Texture profile analysis
Texture profile analysis (TPA) were done by TA.XT2i texture analyser (Texture Technologies Corp., Stable Micro Systems, UK) equipped with a Texture Expert software program (v 2.03). TPA of each spaghetti sample was measured as a function of cooking time in each of the four cooking water by using pasta stickiness rig. The test consists of compressing a bite size of food two times in a reciprocating motion that imitates the action of the jaw and extracting from the resulting force-time curve a number of textural parameters such as; hardness, stickiness, cohesiveness, chewiness and resilience. The test was done with a pre-test speed of 3 mm/s, test and post speeds were 1 mm/s. The test distance was set to 1 mm with a trigger force of 0.05 N.
Sensory analysis
Sensory analysis was carried out to find out the correlation with instrumental measurements. Brand C was selected for sensory analysis and cooked in deionised, laboratory tap, deionised + 2.5% salt and deionised + 5.0% salt cooking waters for 12 min. The cooked samples were analysed by seven trained panellists (4 female and 3 male, 25–35 years old). The parameters of interest were hardness, adhesiveness, cohesiveness, resilience, and chewiness. The following textural parameters were evaluated: hardness, the resistance of cooked pasta to compression by the teeth, was measured by compressing the spaghetti strand against the palate with the tongue. Adhesiveness was evaluated by placing the spaghetti in the mouth, pressing it against the palate and determining the force required to remove it with the tongue. Chewiness was measured as the number of chews to masticate a known amount of sample at a constant rate of force application to reduce it to a consistency ready for swallowing. Cohesiveness was meaured as the rate at which the spaghetti strands disintegrate under mechanical action. Springness was measured as the degree to which the product returns to its original shape after partial compression (without failure) between the tongue and palate or teeth. Each of these five parameters were evaluated on a scale ranging from 0 to 9. The panellists were asked to define which spaghetti sample cooked in various cooking waters they liked the best and state the reason.
Statistical analysis
Correlation analysis and Analysis of Variance (ANOVA) were carried out using Statgraphics plus for windows.
RESULTS AND DISCUSSION
Degree of Cooking
presents the degree of cooking values obtained from cooking spaghetti brands in each of the four different cooking waters. The cooking time taken as the time required for the white core in the spaghetti to disappear. It was seen that spaghetti samples coked in deionised water had lower cooking time and then increased in the order of deionised, tap, 2.5 and 5.0% salt. Brand A had the lowest cooking time compared to other brands and brand D had the highest. Optimum cooking time is mainly affected by the rate of water migration and resulting starch gelatinisation. It was also clear that as the salt concentration increased in cooking water, the spaghetti samples required longer cooking time to achieve optimum cooking. NaCl had a kind of limiting effect on water migration, which also limits starch gelatinisation.
Table 1 Mean values and standard deviations of degree of cooking values of cooked spaghetti samples
Water Absorption
presents the change in water absorption of spaghetti brands cooked in various cooking waters. The protein content in brand A, B, C and D were 11.67 ± 0.09, 11.98 ± 0.08, 12.46 ± 0.04, and 12.90 ± 0.03, respectively. It was found that as protein content increased water absorption of cooked spaghetti samples decreased. Strongly formed gluten network limited water diffusion to the starch granules, which also limited swelling. As cooking time increased, there was a decline in water absorption capacity after 12 min cooking. Samples cooked in tap water exhibited higher water absorption values as compared to samples cooked in deionized water. This can be related to the alkaline pH of tap water. Alkaline pH of tap water was found to be related with the increase in water absorption. In alkaline pH few interactions develop between protein and starch making the structure. As salt concentration increased water absorption of cooked spaghetti samples were found to decrease. NaCl has a tendency to bind water as a result water cannot migrate into inner layers of spaghetti sample.
Table 2 Water absorption (%) of spaghetti samples during cooking
Multifactor ANOVA results for water absorption showed that the effect of cooking time and cooking water on water absorption during cooking was significant (P < 0.05). On the other hand the effect of brands, which differ in protein content were found to be insignificant (P > 0.05).
Texture Profile Analysis
It is generally accepted that the main criterion for overall cooking quality of pasta is based on evaluation of texture. Cooked pasta is desired to be not sticky or mushy when eaten and exhibit some firmness to the bite. In fact sensory evaluation is the most reliable method in measuring quality of pasta it is time consuming so mechanical tests are preferred. From this point of view TPA by the use of a texture analyser is quite advantageous since it is more economic and time saving.
During pasta processing, gluten proteins present as irregular globular structures that build a three-dimensional network when the flour is mixed with water. After kneading gluten can be considered to be a network composed of layers of thin films, which can only be penetrated by the starch granules. The surface of freshly extruded pasta is a continuous protein film, while the inner portion is a compact structure of starch granules embedded in an amorphous protein matrix aligned in layers parallel to the protein film. When cooking durum wheat pasta, starch gelatinisation and protein coagulation cause major structural changes and hence influence the final texture.[Citation4] During cooking good quality pasta, the protein absorbs water and swells more rapidly than does starch. Hydration of the protein fraction of pasta before the beginning of starch gelatinisation appears to be important to produce a firm, good quality pasta.
Firmness and Adhesiveness
Firmness and adhesiveness are the most important textural parameters in cooked spaghetti quality. illustrates the change in firmness of spaghetti samples with cooking time and cooking water. Changes in adhesiveness of samples were presented in . Spaghetti cooked in deionised water was found to have higher firmness values than spaghetti cooked in tap water. The finding that as the hardness of the cooking water increased, the spaghetti became stickier and less firm was consistent with literature.[Citation13] It is obvious that Ca level of tap water is higher than deionised water. This is significant that Ca lowered pH during cooking. At an acidic pH, protein molecules are positively charged and starch molecules are negatively charged. Under these conditions, electrostatic interactions between proteins and gelatinised starch readily occur, enhancing starch-protein interactions. In a basic medium, both protein and starch are negatively charged; therefore, few interactions may develop.[Citation14]
Figure 1 Change in hardness values of spaghetti samples cooked in deionized water, tap water, deionized water + 2.5% salt, and deionized water + 5.0% salt.
Figure 2 Change in adhesiveness values of spaghetti samples cooked in deionized water, tap water, deionized water + 2.5% salt, and deionized water + 5.0% salt.
Firmness and adhesiveness values were found to be negatively correlated. At lower pH values cooking water favours starch protein interactions, preventing the leaching of starch into the cooking medium. As expected, spaghetti which has low protein content was found to be stickier and soft. Spaghetti samples with low protein content were found to be prone to deteriorate rapidly and became soft with over cooking. Cooked spaghetti firmness was mainly affected by the protein fraction. Spaghetti with lower protein content absorbed higher water, which resulted in high stickiness and low firmness. In other words, higher firmness correlated with lower adhesiveness. Although stickiness decreased as protein content increased, protein content appeared to play a limited role in determining spaghetti stickiness compared to cooking water quality. The stickiness or surface state of cooked spaghetti is due to the amylopectin that escapes during the cooking phase from the protein network which envelops the gelatinised starch granules.[Citation15]
Adhesiveness of spaghetti brands A, B, C, D decreased sharply up to 12 min cooking time in all cooking waters. This decrease, however, was more critical for samples cooked in deionised water containing 5.0% salt (). NaCl is a nonchatropic salt, which stabilizes protein structure. Salts that stabilize proteins enhance hydration of proteins and bind weakly. Weak gluten protein solubility decrease at high salt levels (>0.5 M).[Citation16] At 2.5% salt concentration (gr salt/100 ml solution) (0.43 M) adhesiveness was found to be lower than that of 5.0% salt concentration (0.86 M). At 5.0% salt concentration protein solubility is lower than 2.5% salt concentration. Decrease in protein solubility caused a decrease in unfolding of protein. Protein network became weak causing starch to leach into cooking water, which increased stickiness. After 12 min, stickiness values continued decreasing but not as sharply as before.
Firmness of spaghetti brands increased as salt concentrations increased (). Migration of water into inner layers of spaghetti became slower causing a decrease in starch gelatinisation. The faster the starch swells, the slower the protein-protein interaction and the weaker the protein-network. When the interaction of the coagulating protein with itself is more rapid than the starch swelling and gelatinisation, and the protein network is strong and elastic enough to prevent breakages, the cooked pasta will be firm.
According to multifactor ANOVA results for hardness it was found that the effect of cooking time and cooking water on hardness during cooking was significant (P < 0.05). One-way ANOVA results for hardness in tap water, 2.5 and 5.0% salt indicated that the effect of brands on hardness was not significant (P > 0.05). Similar results were found for adhesiveness of spaghetti brands.
Chewiness
shows the change in chewiness of cooked spaghetti brands in various cooking waters. During cooking, the microstructure of pasta greatly changes. While raw pasta is relatively uniform, cooked pasta has a structure, which changes continually from the surface to the core. The changes are greatest at the surface, which has been subjected to the effects of cooking for the longest period.
Figure 3 Change in chewiness values of spaghetti samples cooked in deionized water, tap water, deionized water + 2.5% salt, and deionized water + 5.0% salt.
Chewiness is basically related with the elastic strength of protein matrix. As the protein concentration increased between the four brands of spaghetti chewiness increased (). Spaghetti samples cooked in tap water had lower chewiness values than the spaghetti samples cooked in deionized water. Calcium decreases the hydration ability of water causing gelatinized forms of starch. This result encompasses with the increase in chewiness in deionized water. Chewiness values of spaghetti samples were not affected by pH of cooking water used. As salt concentration of cooking water increased from 2.5 to 5.0% chewiness of all spaghetti brands were found to increase.
From the multifactor ANOVA results for chewiness, the effect of cooking time and cooking water on chewiness during cooking was found to be significant (P < 0.05). One-way ANOVA results for chewiness in deionised water, tap water, 2.5 and 5.0% salt indicated that the effect of brands on chewiness was significant (P < 0.05).
Cohesiveness
Cohesiveness, which is related with tensile strength, was measured as the rate at which the material disintegrates under mechanical action. presents the change in cohesiveness values of spaghetti brands. Cohesiveness is an indication of how the sample holds together on cooking. In the literature, cohesiveness was found to be related with gluten quantity and quality. Gluten network formed during cooking entraps starch. If a gluten network does not develop, starch granules swell and disperse during cooking, the structure of pasta became weaker leading to a less cohesive material. Gluten can modify the availability of water to the starch with reduction of both granule swelling and starch leaching.[Citation17]
Figure 4 Change in cohesiveness values of spaghetti samples cooked in deionized water, tap water, deionized water + 2.5% salt, and deionized water + 5.0% salt.
All spaghetti samples cooked in deionised water were found to have higher cohesiveness values than tap water. With increasing salt concentration cohesiveness values were found to decrease. Because of the water binding capacity of salt, cooking water can not diffuse into spaghetti easily; as a result gluten network does not open its structure. Consequently, starch leaches away leading to a less cohesive product. As cooking time increased cohesiveness values increased. After 12 min, overcooking of spaghetti occurred resulting in a product that was soft, sticky and less cohesive. Water can migrate from sites where it is bound more strongly to sites where it is more weakly bound. Riva et al.[Citation18] claimed that water is more tightly bound to proteins than to the starch which limited water for starch granules .The effect of cooking time and cooking water on cohesiveness during cooking was significant (P < 0.05). One-way ANOVA results for cohesiveness in tap water, 2.5 and 5.0% salt indicated that the effect of brands on cohesiveness was not significant (P > 0.05).
Instrumental versus Sensory Measurement
Instrumental measurement of cooked spaghetti texture can be a reliable and convenient alternative to the sensory panel. In fact sensory evaluation of spaghetti eating quality is a direct method for determining the quality of cooked spaghetti it is quite laborious and expensive. Objective methods are quicker and give more accurate results but an objective method without any correlation to sensory judgement makes no sense. From this point of view Pearson correlation analysis was performed on cooked spaghetti samples to compare objective and subjective evaluations. The results of texture profile analysis correlated well with the sensorial judgement of hardness, and adhesiveness (). There was a strong correlation between instrumental chewiness-sensory hardness, instrumental resilience-sensory chewiness, and instrumental cohesiveness-sensory resilience. Panellists specially had difficulties in sensing resilience, chewiness and cohesiveness values. The other factors assessed in the sensory results and TPA parameters did not give significant correlations. The panellists indicated that they liked spaghetti samples cooked in cooking water that contains 2.5% salt more than the other samples regarding to textural properties.
Table 3 Correlation coeffcients between the sensory and instrumental parameters of spaghetti texture for brand C
CONCLUSIONS
Cooking water is quite important for the textural characteristics of cooked spaghetti. The extremes of this change are mainly affected by the protein content of spaghetti. Spaghetti with higher protein content had higher adhesiveness and lower firmness values. Hardness and adhesiveness parameters were found be negatively correlated with each other. Both hardness and chewiness values increased with increase in salt concentration of cooking water however chewiness values decreased. Water absorption (%) of spaghetti samples were found to increase with cooking time, which showed how they respond to cooking. Presence of salt in the cooking water limited water uptake, which resulted an extension to achieve optimum cooking. A sensorial panel was performed to make a correlation between instrumental and sensorial measurements. It was found that there was a strong correlation between instrumental chewiness-sensory hardness, instrumental resilience-sensory chewiness, and instrumental cohesiveness-sensory resilience.
REFERENCES
- Antognelli , C. 1980 . The manufacture and application of pasta as a food and as a food ingredient: a review . Journal of Food Technology , 15 : 125 – 145 .
- Pomeranz , Y. 1987 . Wheat Chemistry and Technology , Vol. 1 , 47 – 95 . St. Paul, Minnesota : American Association of Cereal Chemists, Inc. .
- Edwards , N.M. , Izydorczyk , M.S. , Dexter , J.E. and Biliaderis , C.G. 1987 . Cooked pasta texture: Comparison of dynamic viscoelastic properties to instrumental assessment of firmness . Cereal Chemistry , 70 : 122 – 126 .
- Smewing , J. 1997 . Analyzing the texture of pasta for quality control . Cereal Foods World , 42 : 8 – 12 .
- Bourne , M.C. 1978 . Texture profile analysis . Food Technology , 32 : 62 – 66 . 72
- Szcesniak , A.S. 1963 . Classification of textural characteristics . Journal of Food Science , 28 : 385 – 389 .
- Cunin , C. , Handschin , S. , Walther , P. and Escher , F. 1995 . Structural changes of starch during cooking of during wheat pasta . Lebensmittel-Wissenschaft und Technologie , 28 : 323 – 328 .
- Malcolmson , L.J and Matsuo , R.R. 1993 . Effects of cooking water composition on stickiness and cooking loss of spaghetti . Cereal Chemistry , 70 ( 3 ) : 272 – 275 .
- Oh , N.H. , Seib , P. , Deyoe , C.W. , Ward , A.B. and Noodles II . 1985 . The surface firmness of cooked noodles from soft and hard wheat flours . Cereal Chemistry , 62 : 431 – 436 .
- Alary , R. , Abecassis , J. , Kobrehel , K. and Feillet , P. 1980 . Effects of cooking water type and pH on the characteristics of pasta products . Tecnica-Molitoria , 31 : 776 – 784 .
- Dexter , J. E. , Matsuo , R. R. and Morgan , B. C. 1983 . Spaghetti stickiness: some factors influencing stickiness and relationship to other cooking quality characteristics . Journal of Food Science , 48 : 1545 – 1551 . 1559
- Egan , H. , Kirk , S.R. and Sawyer , R. 1981 . Pearson's Chemical Analysis of Foods , New York : Churchill Livingston .
- Kruger , J.E , Matsuo , R.B. and Dick , J.W. 1996 . Pasta and Noodle Technology , 13 – 15 . St. Paul, MN : American Associaton of Cereal Chemists, Inc. .
- Delcour , J.A. , Vansteelandt , J. , Hythier , M.C. and Abecassis , J. 2000 . Fractionation and reconstitution experiments provide insight into the role of starch gelatinization and pasting properties in pasta quality . Journal of Agriculture and Food Chemistry , 48 : 3774 – 3778 .
- Bhattacharya , M. , Zee , S.Y. and Corke , H. 1999 . Physicochemical properties related to quality of rice noodles . Cereal Chemistry , 76 : 861 – 867 .
- Shih , Y.C. , Prausnitz , J.M. and Blanch , H.W. 1992 . Some characteristics of protein precipitation by salts . Biotechnology and Bioengineering , 40 : 1155 – 1164 .
- Dexter , J.E. , Kilborn , R.H. , Morgan , B.C. and Matsuo , R.R. 1983 . Grain research laboratory compression tester: Instrumental measurement of cooked spaghetti stickiness . Cereal Chemistry , 60 : 139 – 142 .
- Riva , M. , Fessas , D. and Schiraldi , A. 2000 . Starch retrogradation in cooked pasta and rice . Cereal Chemistry , 77 : 433 – 438 .