3.2. Effect of lipid phase on dough rheologyThe effect of type and content of the lipid phasewas evaluated inthose formulations that presented the best textural behavior inSection 3.1, i.e. those with xanthan/guar and xanthan/HPMCmixtures.Table 1 shows the maximum forces in puncture (FP) and elongation(FE) tests for all the assayed formulations and also theextensibility or deformation at the breaking point (D). Texturalanalyses did not detected any significant differences (P < 0.05)between both hydrocolloid combinations used, regardless of thelipid type and concentration.When margarine was used, the increase in fat contentproduced doughs with higher resistance to puncture, while theopposite effect was found using sunflower oil. Both type and lipidcontent also affected FE and D significantly (P< 0.05). Margarineprovided ductility to the dough; more markedly in the case of theindustrial margarine which contained higher solid fat content(46.8%) than the retail (‘‘all purpose’’) one (24.7%). The formulationwith high sunflower oil content showed the lowest FP FE, andD, values, making it the least suitable for industrial handling(Fig. 2 and Table 1).The effect of lipid phase on the viscoelastic characteristics of thedoughs was analyzed using the Friedrich and Heymann theory(Friedrich and Heymann, 1988; Lorenzo et al., 2008). According tothis theory, complex viscosity (h*) could be expressed ash* ¼G*u¼pffiGffiffiffi0ffi2ffiffiffiþffiffiffiffiffiGffiffiffi0ffi0ffi2ffiffiuzAauða1Þ (1)where a is the order of the relaxation function and Aa the materialstrength parameter, related to the rigidity of the network.Equation (1) was fitted to the frequency sweep curves andaverage values of the material strength parameter obtained for eachformulation are listed in the last column of Table 1. A markedincrement of Aa with the solid fat content of the lipid phase isobserved. When the matrix contained higher solid content(industrial margarine) it showed more elastic behavior, which wasreflected in an increase in Aa (Aa(IM) > Aa(RM)). Additionally, type ofhydrocolloids significantly affected the material strength of thedough (P < 0.05). When HPMC replaced guar gum in thehydrocolloid mixture, the decrease in Aa valuewas more noticeablein the doughs containing industrial margarine. The order of therelaxation function (a) was lower than 0.2 for all formulations,indicating the pronounced elastic character of the doughs, typicallyobserved in gel-like samples (Doublier et al., 1992; Steffe, 1996).However, a was significantly higher for those formulations containingoil (a¼ 0.19) than those values corresponding to doughsmade with margarine, either retail or industrial (a¼ 0.15), sincea liquid lipid phase decreased the solid characteristics of the matrix.3.3. Storage3.3.1. Refrigerated storage of dough disksThe 20% sunflower oil or 30% industrial margarine showed thehighest values for maximum breaking forces (FP and FE) as well asthe highest deformation at break but did not differ significantlyamong themselves; thus, formulations with the lower lipid content(healthier formulations), i.e. XGSO20 and XHSO20 (Table 1) , werechosen to analyze the effect of refrigerated storage (4 C). Theirrheological and textural behaviorwas evaluated in dough disks at 1,5, 8, 12, 16, and 20 days.FP (364 mN), FE (290 mN), remained constant during refrigeratedstorage for both formulations and significant differences werenot detected between them (P < 0.05). G0, and G00 did not changeeither during the storage time. However, the mixture of xanthan/guar (G0 ¼1.41$105 Pa, SEM ¼ 7.0$103 Pa; G00 ¼ 2.30$104 Pa,SEM¼ 7.7$102 Pa at 1 Hz) produced a more elastic dough than thexanthan/HPMC formulation (G0 ¼ 9.88$104 Pa, SEM ¼3.1$103 Pa;G00 ¼1.92$104 Pa, SEM¼ 7.7$102 Pa at 1 Hz).The deformation at breaking point in the elongation tests (D)remained constant for the formulation containing HPMC. On theother hand, XGSO20 presented a decrease of the extensibility as isshown in Fig. 3.The capability to retain water of hydroxyl groups present inHPMC could probably be responsible for the longer keepability ofthe dough. A similar trend was observed in wheat bread whenHPMC was added (Collar et al., 1998).3.3.2. Frozen storage of ready-to-bake ‘‘empanadas’’The effect of frozen storage of ready-to-bake ‘‘empanadas’’ onthe microstructure and textural behavior of the baked final productwas evaluated. Three formulations: XGSO20, XHSO20, and XHIM30(Table 1) were tested. The formulation with industrial margarinewas included to examine whether a significant difference would bedetected after the baking process.Baking irreversibly alters the structural nature of doughconstituents through a series of physical, chemical and biochemicalreactions (Pyler, 1988). Temperature, humidity, and duration ofbaking influence the final product. Oven heat is responsible for theformation of an enveloping crust, coagulation of proteins, gelatinizationof starch, and the stabilization of the colloidal doughsystem (Freeman and Shelton, 1991). Microscopic observationsrevealed that the crust appeared as a continuous sheet of proteinsand hydrocolloids with embedded starch granules, which were notgelatinized because of the rapid dehydration of the surface at theoven temperature (Fig. 4a). The inner structure of the doughshowed both intact and gelatinized granules (Fig. 4b and c). Whengoing from the crust to the interior of the dough, less intact starchgranules were observed (Fig. 4b). Near the filling, gelatinization ismore complete and a distinction cannot be made between starchand the hydrocolloid matrix (Fig. 4c), while in the middle region ofthe dough (between crust and filling), starch granules are stillrecognizable. The limited water content of the dough may accountfor these differences. Fig. 4d presents a photograph of the finalbaked product.The maximum puncture force of the baked specimens did notpresent significant differences (P< 0.05) between the control(unfrozen) and frozen samples. Besides, FP was not affected by thestorage time in any of the three tested compositions. This effect is inagreement with Sanderson (1981) who has stated that xanthangum induced cooking and cooling stability of wheat flour-basedproducts and improved the freeze–thaw stability of starch-thickenedfrozen foods. This result implies an important technologicaladvantage since the product could be frozen without changing itstextural quality.3.4. Sensory assessmentThe forty experienced panelists evaluated the appearance,texture, flavor and overall acceptability of the formulations thathave been stored for ten days at 4 C. A formulation developed withxanthan gum/HPMC mixture and 20% sunflower oil (XHSO20) wascompared with a commercial gluten-free dough.There were no significant differences in flavor, texture andoverall acceptability between both formulations (P <0.05). Theappearance of the commercial dough was perceived as significantlyworse by the panel, which was related with the notorious cracksthat appeared in these products during baking.The observations were classified into three perception sensorialgroups, the first one corresponded to those that disliked the
product (scores 1 to 4, dislike extremely to slightly), the second one
was indifferent (scores 5), and the third group expressed that they
liked the samples (scores 6 to 9, like slightly to like extremely).
More than 70% of the panelists liked all the attributes of the
products. In particular, over 94% of the panelists liked the formulation
containing xanthan/HPMC mixture and sunflower oil. Two
thirds of the panelists preferred formulation XHSO20 over the
commercial dough (Table 2) (P< 0.05). It is important to remark
that none of the formulations developed in the present work
showed signs of rupture during baking. Meanwhile, more than 90%
of the commercial gluten-free disks presented this problem, which
is an important parameter to consider since crust rupture produces
a low quality product.
4. Conclusion
Textural and rheological behavior of non-fermented gluten-free
doughs, a product intended for celiac people, was studied. The
study of different hydrocolloid mixtures revealed that formulations
containing xanthan gum exhibited the best elasticity and resistance
to puncture regardless of the other hydrocolloids present in the
dough (guar or HPMC). Formulations containing only HPMC were
the least suitable for industrial production of ‘‘empanadas’’ or piecrusts.
When margarine was used, the increase in fat content produced
doughs with higher resistance to puncture, while the opposite
effect was found using sunflower oil. Margarine for industrial uses
(with higher solids content) provided greater elasticity to the
dough than the retail margarine rendering it more ductile.
Doughs were stored at 4 C for twenty days without any
significant changes in rheological properties. Frozen storage did not
affect textural characteristics of baked dough either. The panel
accepted the xanthan/HPMC dough with a 75/90 score and it was
significantly preferred over a commercial gluten-free dough.
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