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JFS S: Sensory and Nutritive Qualities of Food

Relationships Between Sensory Flavor Evaluation and Volatile and Nonvolatile Compounds in Commercial Wheat Bread Type Baguette J. QU´ıLEZ, J.A. RUIZ, AND M.P. ROMERO

T

Introduction

he quality of bread is normally defined according to its volume, texture, color, and flavor. However, the characteristic aroma of bread is undoubtedly one of the most important parameters influencing its acceptance by consumers. The flavor of bread is composed of a large number of compounds, the majority of them with different olfactive characteristics. The volatile and nonvolatile compounds that contribute to the flavor of bread include acids, alcohols, aldehydes, esters, ethers, ketones, furans, hydrocarbons, lactones, pyrazines, pyrroles, and sulfur compounds. More than 540 compounds have been described in the complex aromatic fraction of bread. Not all these compounds have the same degree of influence on the flavor, but there is a series of key odorants that have a marked influence on both crust and crumb (Grosch and Schieberle 1997). Apart from ethanol, which is the majority volatile compound, several key odorants in the crumb have been cited, including 3-methylbutanol (isoamyl alcohol), 2-phenylethanol, 2,3-butanedione (diacetyl), hexanal, 2-nonenal, and 2,4-decadienal (Schieberle and Grosch 1991; Gassenmeier and Schieberle 1995), and different acids, such as acetic, butyric, 2-methylpropanoic (isobutyric), and 3methylbutanoic (isovaleric) (Richard-Molard 1994). The main nonvolatile compounds that affect the flavor are salt and lactic acid (Calvel 2001). The flavor of bread is a result of the interaction of many factors: on the one hand, the type of flour and other ingredients (Chang and others 1995), and on the other, the type of fermentation, with distinctive characteristics depending on whether this is by yeasts MS 20050677 Submitted 11/11/2005, Accepted 4/11/2006. Authors Qu´ılez and Ruiz are with Dept. de Tecnologia. Europastry, S.A., Ctra. de Sarral a Barberà, s/n. 43424-Sarral, Spain. Author Romero is with Food Technology Dept., Univ. of Lleida, Alcalde Rovira Roura, 177. 25198-Lleida, Spain. Direct inquiries to author Qu´ılez (E-mail: [email protected]).

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Institute of Food Technologists doi: 10.1111/j.1750-3841.2006.00053.x

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(Saccharomyces), or lactic acid bacteria (Mart´ınez-Anaya and others 1990a, 1990b). Finally, the production process also has a vital influence on the flavor (Galey and others 1994; Mart´ınez-Anaya 1996). All this means that the aromatic profile is a fingerprint that enables a comparison of different types of bread or the control of process conditions (Schieberle, 1996). Due to economic requirements, current methods of industrial production are often forced to alter the traditional methods of bread production, leading to significant changes in the texture, shelf life, and flavor. This is important because in Europe over the last few years, there has been a large increase in the industrial production of French-type bread, such as frozen or prebaked baguettes. Different studies relate some aspects of bread with its sensory characteristics. Baardseth and others (2000) analyzed different methods for producing baguettes and reached the conclusion that 40% of the differences in quality were due to variations in the process, whereas 16% were due to the flour used. Other studies investigated the relationship between biochemical aspects and different quality parameters (Mart´ınez-Anaya and others 1990a, 1990b; Rouzaud and Mart´ınez-Anaya 1997), and the evaluation of the shelf life by consumers compared with instrumental measures (Gámbaro and others 2004). However, there is very little information relating to the aromatic profile in the sensorial evaluation of bread (Hironaka 1986). Furthermore, there are no studies that compare this profile with acceptance by consumers. One of the disadvantages of performing this type of study is that, to date, the methods used to isolate the volatile compounds of bread for later analysis have been very complex and expensive. However, headspace analysis by solidphase microextraction (SPME) offers a fast and easy way of quantifying the volatile compounds in the bread crumb (Ruiz and others 2003). The purpose of this study was sensorial analysis of the flavor in baguettes by a consumer panel. This information was then related Vol. 71, Nr. 6, 2006—JOURNAL OF FOOD SCIENCE

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S: Sensory & Nutritive Qualities of Food

ABSTRACT: A sensorial evaluation was carried out on the flavor of wheat bread using a test of consumer acceptance for this type of product. The 5 samples evaluated corresponded to prebaked baguettes from the main brands marketed in Spain. At the same time, headspace analysis using a solid-phase microextraction (SPME) method was used to assess the volatile components of the bread crumb as well as other components, such as salt, lactic acid, and total titratable acidity (TTA), which could affect the flavor. The results of the sensorial analysis indicate that there are no significant differences between the samples. Nevertheless, the content of volatile and nonvolatile compounds shows certain variations that correlate with the flavor scores. In general, the alcohol, ketone, and salt contents are considered positive, whereas the aldehyde and acid contents, including lactic acid, are considered negative. The main conclusions obtained were that for this type of bread, consumers tend to prefer products with a greater degree of fermentation by yeasts, without secondary fermentation by lactic acid bacteria. However, considering the geographic differences regarding these preferences, it will be necessary to perform further tests to establish the acceptance of different types of bread. Keywords: bread, flavor, sensory evaluation, volatile compounds

Bread flavor evaluation and volatiles . . . to the contents in volatile compounds, as well as other nonvolatile compounds capable of influencing the flavor of bread. The type of bread used was prebaked baguettes manufactured and marketed in Spain. This bread is eaten on a daily basis, and therefore there is wide taste awareness among consumers.

Materials and Methods Samples

The column used was TR-WAX (Tecknokroma, San Cugat del Valles, Spain) with a 0.25-μm film thickness, 60 m × 0.25 mm i.d. The temperature program was 35 ◦ C maintained for 5 min, then increased by 5 ◦ C/min to 50 ◦ C, where it was held again for 5 min, then increased by 5.5 ◦ C/min to 230 ◦ C, where it was held again for 5 min. The carrier gas was helium, with a column flow of 2.0 mL/min. The injector was at 300 ◦ C in splitless mode for 5 min using an inlet of 0.75 mm i.d. The quantified compounds were ethanol, isobutyl alcohol, isoamyl alcohol, 1-hexanol, benzyl alcohol, 2-phenylethanol, hexanal, furfural, benzaldehyde, 2-nonenal, 2,4-decadienal, acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, diacetyl, and 3-hydroxy-2-butanone (acetoin). Moreover, 47 other volatile compounds were determined but not quantified.

Five samples of prebaked frozen baguettes, acquired in commercial distributors from the main brands on the Spanish market, were defrosted for 15 min, and baked at 190 ◦ C for 15 min in a commercial convection oven (Salva, Barcelona, Spain). The bread was cooled at room temperature. For the chemical determinations and volatile compound analysis, the crumb was separated 1 cm from crust. Fi- Statistical analyses The statistical analyses were performed with the statistical softnally, the crumb was frozen with liquid nitrogen and ground with an analytical grinding device (Ika, Labortechnik, Germany) to give ware SYSTAT 10 for Windows (SPSS Inc., Chicago, Ill., U.S.A.). The a powder, which was stored at −20 ◦ C until it was analyzed. Each means between groups in sensory analysis were compared by the Friedman test (Meilgaard and others 1999). The relationships besample was analyzed in triplicate. tween variables were tested using Pearson’s correlation and by factorial analysis for all variables, except humidity, protein, and fat. Sensory evaluation Cluster analysis was used to estimate the distances between the samA sensory test was carried out in a test room (IRANOR 1979). ples, also taking into account all variables except humidity, protein, One hundred untrained panelists (50 males and 50 females) were and fat. For this analysis, the data were standardized by standard selected considering age, sex, and frequency of use. All panelists deviation to avoid the excessive weight of some variables, such as were staff or students in the Agronomy Faculty at the Univ. of Lleida. ethanol. Experienced panelists consider that untrained panelists cannot evaluate more than 3 samples of bread in 1 sitting, and so a balanced Results and Discussion incomplete block (BIB) design-ranking test was applied. Each judge able 1 shows the results of the sensorial analysis of the flavor in was randomly assigned 1 of the 10 groups of 3 samples according the 5 samples of baguettes analyzed. There are no significant to the BIB design from Cochran and Cox (1957). Therefore, each differences between the results because of the width of the consample was evaluated by 60 panelists. fidence intervals, common in acceptance tests. Nor are there any Experimental samples were prepared 2h before serving and kept significant differences after segmenting the data by sex or age (data at room temperature (20 ◦ C). The baguettes were sliced into 10- not shown). Nevertheless, some tendencies can be observed when cm-long portions. The baguette ends were not used. Samples were analyzing the frequencies corresponding to the positions obtained presented in random order and identified with 3-digit codes. The in this test (Table 1). Sample 3 was only better evaluated on 24% score sheets required the judges to rank their 3 samples from least of the occasions (score = 3), and on 42% of the times, it was con(= 1) to most (= 3) pleasant flavor. sidered the worst of the group (score = 1). In samples 1 and 5, the

T

Proximate and acidity parameters Protein was determined by the Kjeldahl method (N × 6.25). Total fat was determined by the Soxhlet method. Salt was analyzed as chloride by the Volhard method after burning the sample in a furnace device at 525 ◦ C for 5 h. Lactic acid was determined enzymatically by a UV method with a commercial L/D-Lactic acid kit (RocheBiopharm, Darmstadt, Germany). Total titratable acidity (TTA) was measured using the method described by Mart´ınez-Anaya and others (1990b).

Volatile compounds


The volatile compounds were analyzed according to the method in Ruiz and others (2003). A 0.25 g of bread crumb powder was weighed into a 20-mL vial. Then, 9.9 mL of a 20% NaCl solution (pH = 3 with 0.05 M citric acid) and 0.1 mL of internal standard solution (4-methyl-2-pentanol and 2-ethylbutyric acid at 0.2 and 6 ppm, respectively) were added to the vial. Then, the vial, previously sealed with silicone septa, was immersed in a water bath at 50 ◦ C, and the SPME fiber (75 μm Carboxen/polydimethylsiloxane) was exposed to the headspace for 60 min. The sample was continuously shaken with a magnetic stirring bar during the extraction process. Afterward, the fiber was inserted into the GC–MS chromatograph (Shimadzu GC17A/QP5050A Mass Spectrometer, Kyoto, Japan) injector port for thermal desorption of the extracted volatiles for 5 min. S424

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situation is quite the opposite as sample 5 was considered the best in its group on 42% of the occasions it was tasted, and this was also true for sample 1 on 38% of the occasions. Table 2 shows the results for the main parameters and those related to acidity. Although there are variations, the former are the expected results for baguette-type bread. Furthermore, the results for fat show that there are no lipids added to any of the samples, as these could alter the flavor and affect the results of the sensorial analysis. Also with variations, the parameters for acidity show certain homogeneity except in sample 3, where the values for TTA and lactic acid are higher and stand out above the other samples. This implies a distinctive characteristic as it indicates that, apart from the Table 1 --- Sensory evaluation of commercial prebaked baguettes Sample n = 60 Flavor score Meana SD Sum First position (%) Second position (%) Third position (%) a

1

2

3

4

5

2.08 0.81 125 38 27 35

1.93 0.78 116 29 32 39

1.83 0.65 110 24 34 42

2.00 0.84 120 34 31 35

2.15 0.84 129 42 27 31

No significant difference was found between samples. URLs and E-mail addresses are active links at www.ift.org

Bread flavor evaluation and volatiles . . . main fermentation by yeasts, there is also a secondary fermentation by lactic acid bacteria. The results for the volatile compounds are shown in Table 3. More variability is observed in these parameters, although sample 3 is also outstanding compared with the others because of its high concentration in alcohols and acids, mainly acetic, propionic and butyric, confirming fermentation by lactic acid microorganisms. Other unquantified acids, such as hexanoic or heptanoic, also show a high presence in this sample. The contents of some alcohols indicate the intensity of the fermentation by yeasts. This means that, apart from the ethanol, it was observed that the content in 2-phenylethanol and isoamyl alcohol significantly increases with the fermentation time (Frasse and others 1993). Therefore, according to the results obtained, the degree of alcoholic fermentation would be headed by sample 3, followed by samples 5 and 1 and, at the bottom, by samples 4 and 2. The first approximation between the flavor score and the different parameters analyzed is shown by the correlation coefficients in Table 4 (all samples column). The results obtained are different and difficult to compare with those cited previously (Hironaka 1986), as there are strongly negative correlations for flavor with ethanol and isobutyl alcohol, and positive associations with several aldehydes. In our study, there is a clear positive relationship between flavor and pH (inverse with TTA), salt content and ketones, as well as a negative relationship with acids, alcohols, and aldehydes. Apart from

Table 2 --- Proximate and acidity analysis of commercial prebaked baguettes Sample Variables (%) Humidity Protein Total fat NaCl PH TTAa Lactic acid (μg/g) a

1

2

3

4

5

32.0 8.54 0.26 1.42 6.30 1.53 46.0

27.5 9.93 0.29 1.38 5.58 2.30 39.1

33.7 9.02 0.20 1.29 5.57 3.17 100.2

31.6 9.67 0.18 1.23 5.68 2.03 54.1

29.4 9.60 0.23 1.48 6.02 1.77 54.3

the volatile compounds, salt is also an important element in the perception of flavor, it having been shown that a concentration of less than 1% has a negative effect on the bread flavor (Salovaara and others 1982). Conner and others (1988) place the ideal salt content in wheat bread at about 1.43%, and so it seems reasonable for there to be a positive correlation with salt content, especially considering that the results found are close to, or slightly below, this value. A combined increase of all the variables is shown in the factor analysis of Figure 1. Isovaleric acid, although located in the same Table 4 --- Correlation coefficients between the different parameters analyzed and sensory evaluation Flavor score

Humidity Protein Total fat Salt pH TTA Lactic acid Ethanol Isobutyl alcohol Isoamyl alcohol 1-Hexanol Benzyl alcohol 2-Phenylethanol Hexanal Furfural Benzaldehyde 2-Nonenal 2,4-Decadienal Acetic acid Propionic acid Isobutyric acid Butyric acid Isovaleric acid Diacetyl Acetoin

All samples (n = 5)

Without #3 (n = 4)

−0.311 −0.042 0.314 0.663 0.798 −0.915 −0.612 −0.307 −0.337 −0.303 −0.394 0.263 −0.505 −0.702 −0.486 −0.916 −0.349 −0.690 −0.891 −0.362 −0.245 −0.793 0.025 0.553 0.733

0.375 −0.463 0.027 0.609 0.776 −0.823 0.645 0.965 0.431 0.699 0.186 0.806 0.990 −0.530 0.344 −0.898 −0.664 −0.886 −0.770 0.221 0.141 −0.776 −0.415 0.760 0.822

mL NaOH 0.1 N/10 g bread.

Table 3 --- Volatile compounds in commercial prebaked baguettes Sample 1

Alcohols Ethanol 1001 Isobutyl alcohol 0.939 Isoamyl alcohol 1.547 1-Hexanol 0.081 Benzyl alcohol 0.039 2-Phenylethanol 1.696 Aldehydes Hexanal 0.071 Furfural 0.029 Benzaldehyde 0.030 2-Nonenal 0.043 2,4-Decadienal 0.022 Acids Acetic acid 212.4 Propionic acid 2.970 Isobutyric acid 2.600 Butyric acid 0.473 Isovaleric acid 2.026 Ketones Diacetyl 0.069 Acetoin 20.32

2

3

226 1932 0.448 1.520 0.825 2.249 0.069 0.093 0.033 0.078 1.488 2.433

4

5

539 1037 1.227 0.915 0.453 1.325 0.037 0.062 0.029 0.110 1.544 1.789

0.094 0.037 0.051 0.052 0.025

0.093 0.054 0.050 0.046 0.023

0.045 0.028 0.035 0.077 0.022

0.055 0.043 0.029 0.030 0.021

275.4 1.920 2.377 0.701 2.550

396.8 3.092 2.700 5.192 1.582

193.6 2.424 2.744 0.888 1.412

188.2 1.999 2.487 0.422 1.814

0.056 12.60

0.059 10.72

0.033 4.56

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Figure 1 --- Factor analysis. Plot values of the two principal factors for all samples (n = 5). LAC = lactic; ET = ethanol; IBU = isobutylic; IAM = isoamylic; HOL = hexanol; BEN = benzylic; 2-PE = 2-phenylethanol; HAL = hexanal; FUR = furfural; BEA = benzaldehyde; 2-NO = 2-nonenal; 2,4-D = 0.091 2,4-decadienal; ACT = acetic; PRO = propionic; IBUT = isobutyric; BTC = butyric; IVAL = isovaleric; DAT = di31.22 acetyl; ATN = acetoin. Vol. 71, Nr. 6, 2006—JOURNAL OF FOOD SCIENCE

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(μg/g)

Bread flavor evaluation and volatiles . . . quadrant, does not follow the same tendency as the other acids. This and isobutyric acid have been related to the mixing intensity and therefore oxidation of the dough (Richard-Molard and others 1978). In view of the results obtained, this should therefore have no important influence on the flavor of this type of bread. However, in Factor 3 (21.4% of total variance explained, not shown), isovaleric acid is clearly distant from the flavor coordinates. This is quite different from the case of aldehydes and, more specifically, hexanal, 2-nonenal, and 2,4-decadienal, which appear as a result of fat oxidation and especially the oxidation of linoleic acid (Ullrich and Grosch 1987; Luning and Roozen 1991). In general, they are present in flour and their concentration is reduced in the dough by the yeast and later fermentation (Frasse and others 1993). They have a high odor activity value (OAV) and are related to disagreeable nuances of flavor (Schieberle and Grosch 1991; Gassenmeier and Schieberle 1995), and this would confirm the results obtained. Apart from the aldehydes quantified, sample 3 also has higher octanal, nonanal, decanal, and 2-decenal aldehydes contents than the others. The fact that diacetyl and acetoin correlate positively with flavor leads to the possibility of a masking effect in sample 3. Indeed, just like alcohols, the concentration of acetoin increases during fermentation (Frasse and others 1993), and so the correlation coefficients between the flavor score and the other variables were recalculated without sample 3 (Table 4, without sample 3 column). As can be seen, the majority of tendencies are maintained (salt, pH, TTA, aldehydes, and ketones). On the other hand, the alcohols now have a positive correlation, which is especially high in the case of ethanol and 2-phenylethanol. In the case of the acids, including lactic acid, there are uneven individual responses, although acetic acid and TTA maintain their close negative relationship with flavor. On the other hand, the presence of acetic acid in sourdoughs is positively valued, as it has the function of strengthening the flavor (Lönner and PreveAkesson 1989; Richard-Molard 1994). The factor analysis of Figure 2 shows the new distribution of the variables excluding sample 3, and shows the positive effect of the greater intensity of fermentation by yeasts. In order to provide a general estimate of the degree of similarity or difference between the samples considered, a cluster analysis was carried out as shown in Figure 3. The greatest proximity (distance = 0.84) is found between samples 5 and 1, the latter also having the highest score in the sensorial analysis. Samples 4 and 2 coincide on a second level (distance = 1.17), corresponding to the intermediate scores for sensorial analysis. Finally, sample 3 (distance = 1.56) is in last place. This classification coincides, although in a different order, with that regarding fermentation intensity, and leads to the conclusion that the samples studied all proceeding from commercially available products correspond to 3 different types of industrial processes. The most notable difference would be the degree of alcoholic fermentation of the doughs, as well as the presence or absence of secondary fermentation by lactic acid bacteria.

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Conclusions

Figure 2 --- Factor analysis. Plot values of the two principal factors without the sample #3 (n = 4). The legend is the same as in Figure 1.

Figure 3 --- Cluster analysis. Data standardized by standard deviation.


this is associated with low-intensity mixing processes. The higher degree of fermentation may be achieved by increasing the time in the straight dough process or including naturally leavened starter sponge in the recipe (Calvel 2001). At the same time, the inclusion of lactic fermentation processes, the base of breads of the sourdough or levain type, seems to have less acceptance in our case. Nevertheless, further studies are necessary to be able to establish consumers’ acceptance of different types of bread; and consideration should also be given to the geographic differences associated with these preferences. The availability of fast techniques for the analysis of volatile compounds, such as SPME, related to sensorial evaluation, should make it possible to obtain more information in this regard and enable a more precise adjustment of industrial processes to consumer preferences.

ensorial analysis of prebaked baguettes available on the Spanish market shows that there are no significant differences between the brands studied. Nevertheless, based on an analysis of their components, including the volatile part, it is possible to discern the production process that would allow us to obtain bread better adapted Acknowledgment to consumer preferences. From the analysis of the data obtained in Supported by Europastry S.A., St. Cugat del Vallés, Barcelona, Spain. our study, there is a tendency toward a preference for products with a greater degree of fermentation by yeasts, an aspect that has tended References to be reduced in modern industrial bread production processes. A P, Kvaal K, Lea P, Ellekjaer PM, Faergestad EM. 2000. The effects of bread high level of alcohols and ketones is positively valued, and this is Baardseth making process and wheat quality on French baguettes. J Cereal Sci 32:73–87. compatible with a low content in acids and aldehydes, especially if Calvel R. 2001. The taste of bread. Gaithesburg, MD: Aspen Publishers.

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