Characterization of Cereals and Flours G. Kaletunc, K. Breslauer (Marcel Dekker, 2003) WW

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.In Figure7A, the thermogram for the pretzel dough, prior to caustic-bath treatment, canbe seen to resemble quite closely the one for flour in Figure 4A.The reason forthis was alluded to earlier: It is simply that a pretzel dough is, in essence (i.e.,aside from a bit of fat and a few other minor ingredients that need not concernus here), a flour-water dough.Thus, the major biphasic endotherm with a peakT of 69�C can be assigned without question to Ap (as verified, in part, by theexpected appearance of the immediate rescan), and its peak area, correspondingto a delta Q of 4.22 J/g, can be taken to represent 100% native Ap structure.Applying the fingerprint analysis to the DSC thermograms in Figure 7, wesee in Figure 7B that, as a consequence of the caustic-bath treatment, the Appeak area (2.26 J/g) was reduced to 53.6% of its original value for native Apstructure for the in-process sample of dough taken prior to baking.For the finishedproduct, after both caustic-bath treatment and baking, the area of the Ap peak(0.33 J/g) in Figure 7C demonstrated that the remaining native Ap structure hadreached a final value of 7.8%, in reasonable agreement with the value of 7.3%from Figure 6B for a different sample of the pretzel with good eating quality.Figure 7 Typical DSC curves for representative samples (1:1 mixtures with water) of:(A) a commercial pretzel dough before caustic-bath treatment scan and immediaterescan; (B) the same pretzel dough after caustic-bath treatment but before baking; and(C) the same pretzel dough after caustic-bath treatment and baking, representing a finishedproduct of good eating quality.(From Ref.13.)Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.We also note that the Am L peak in Figure 7C (in its characteristic location above100�C) is slightly larger in area than the Ap peak (this time, the delta Qs aregiven in the figure, showing the Am L peak to be 8% larger), as was also thecase for the good-textured product represented in Figure 6B.The DSC thermograms in Figure 8 reveal how the prototype pretzel, withpoor texture and eating quality, had been subjected to a presumably less-than-optimal process of starch conversion (i.e., combination of gelatinization andannealing), via a processing path that contrasted significantly with the one fol-lowed by the pretzels (Figs.6B and 7C) with good eating quality.Again, byapplying the fingerprint approach to the DSC results in Figure 8, in order tocompare them to the corresponding results in Figure 7, we see that, as a conse-quence of the progression from untreated dough (Fig.8A) to dough after caustic-bath treatment but before baking (Fig.8B) to finished product after caustic treat-ment and baking (Fig.8C), the percentage remaining native Ap structure, asreflected by the Ap peak area, decreased from 100% (4.30 J/g) to 61.8% (2.66J/g) to 15.8% (0.68 J/g), with the last value of 15.8% again being in reasonableagreement with the earlier value of 14.4% obtained from Figure 6A for a differentsample of these same poor-eating-quality pretzels.The values of 61.8% (Fig.8B)and 15.8% (Fig.8C) can be said to contrast significantly with the respectivevalues of 53.6% and 7.8% obtained from Figures 7B and 7C.[That is, if we caninfer a measure of significance from the reproducibility (actually, of one sampleof commercial product to another) of experimental results compared earlier7.3 vs.7.8% and 14.4 vs.15.8%.] Thus, we are led to surmise that the inferiorpretzel (represented in Fig.8) had been subjected to too little starch conversionin the caustic bath, possibly resulting from (a) too short a residence time, (b) toocool a bath, and/or (c) too low an NaOH concentration.Was this the direct andsole cause of its poor texture and eating quality? It seems clear from the DSC fingerprints that the caustic-bath treatment was certainly a critical processingstep that distinguished the good and bad products, in terms of their starch struc-ture thermal property relationships, on the one hand, and their starch functionalcharacteristics and concomitant finished-product quality attributes, on the otherhand.But what about what happened during baking? Interestingly, the DSC fingerprint results revealed that the extent of starch conversion caused by bak-Figure 8 Typical DSC curves for representative samples (1:1 mixtures with water) of:(A) a prototype pretzel dough before caustic-bath treatment; (B) the same pretzel doughafter caustic-bath treatment but before baking; and (C) the same pretzel dough aftercaustic-bath treatment and baking, representing a finished product of poor eating quality.(From Ref.13.)Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.ing was essentially the same for the good and bad products; i.e., the change inpercentage native Ap due to baking was 45.8% for the good product (53.67.8% Figs.7B and 7C) vs.46.0% for the bad product (61.8 15.8% Figs.8Band 8C).However, as noted earlier with regard to the thermogram in Figure 6Arepresenting the other sample of bad product, the Am L peak in Figure 8C issmaller (this time, obviously much smaller) than the Ap peak, which again con-trasts with the situation for the good product, as illustrated in Figure 7C [ Pobierz całość w formacie PDF ]

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