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Bread Baking Potential of UHT-Milk
Can. Insl. food Sci. Technol. J. Vol. 19, No.5, pp. 231·234, 1986
RESEARCH
Bread Baking Potential of UHT-Milk W. Zellen ' , B. Lau and V.F. Rasper Department of Food Science University of Guelph Guelph, Ontario NIG 2WI Canada
Abstract The effects of UHT-treated liquid milk on the physical quality of milk-supplemented bread doughs were evaluated by farinography, extensigraphy, maturography and test baking. In comparison with pasteurized milk and scalded milk, the UHT-treated milk tended to give doughs with farinograph absorptions lower than those recorded with the other tested milk doughs, but the doughs appeared stronger and gave better baking results. In addition to lower loaf volume depression, the UHT-treated milk seemed to exhibit a more favourable effect on the crumb firming during storage than the other two heat-treated milks.
Resume
Materials and Methods
On a evalue les effets des laits UHT sur la qualite physique des pates boulangeres enrichies de lait Ii I'aide de farinographie, extensographie, maturographie et de cuisson. Par rapport au lait pasteurise et au lait sterilise, Ie lait UHT eut tendance Ii produire des pates dont les absorptions au farinographe etaient plus faibles que celles obtenues avec les autres laits. Par contre, les pates ont semble plus fortes et furent plus aptes Ii la cuisson. En plus de prevenir davantage la depression volumetrique des pains, Ie lait UHT a semble favorise mieux Ie raffermissement de la croilte au cours du stockage que les deux autres laits.
Introduction For a long time, preheating of milk has been recognized as essential for its good baking quality. Dough from unheated milk has a slack consistency and yields bread with a poor loaf volume. Factors responsible for the dough softening and the loaf volume depressing effects of unheated milk have been the subject of many investigations (Stamberg and Bailey, 1942; Larsen et at., 1949; Gordon et al., 1954; Swanson and Sanderson, 1967; Volpe and Zabik, 1977). Some of these studies attributed the poor baking quality of unheated milk to the sulfhydryl groups present in the milk protein and tried to relate the quality improvement upon heating to changes in these groups. The contribution of the sulfhydryl groups to the rheological properties of wheat dough has been well established (Bloksma, 1972). During the ultra-high-temperature treatment of milk, these groups within the milk protein undergo Jpresent address: Robin Hood Multifoods Ltd., Rexdale, Ontario M9W 5Z1 Copyright
©
changes which surpass effects of other conventional heat processes (Watanabe and Klostermeyer, 1976; Aboshama and Hansen, 1977). It is unlikely that UHT milk in its liquid form will be used by large commercial bakers. Nevertheless, a quantitative evaluation of the effects of this milk on the bread dough baking performance in comparison with other conventionally heated liquid milks may be of interest for further elucidation of the relationship between the milk heat treatment and baking quality.
A preheated (52°C) skimmed milk, supplied by a local dairy processor was subjected to three different heat treatments: a) Batch pasteurization by heating at 62-64°C for 30 min (UNIVAT®, Cherry Burrell Corp., Chicago, Illinois); b) Scalding by heating to 75°C with a 5-min holding period in the same equipment; c) UHT-treatment at 141°C for 4 to 5 s in a No-Bac Unitherm IV indirect tubular heat exchanger (Cherry Burrell, Cedar Rapids, Iowa). Each treatment was followed by immediate cooling to 27-28°C. The treatments were carried out in the Department of Food Science, University of Guelph. Total solids content of the heat treated milks, determined by the Cenco moisture balance method, was in the range of 10.0 to 10.1010. In all tests involving milk supplemented wheat flour doughs, the liquid milk was added to replace 6% of the flour solids with milk solids. Flour used was a commercially milled and treated bread flour (13.7% protein, 0.36% ash, both on 14% m.b.) supplied by a local flour mill. The effects of the tested milks on the dough mixing properties were evaluated by farinography following the AACC constant flour weight method 54-21 (AACC, 1983) and using a Brabender farinograph (Brabender Instruments Inc., South Hackensack, NJ) with a 50-g stainless steel mixing bowl. Liquid milk was added to flour prior to mixing in a quantity required to obtain the above milk solids/flour solids replacement. Additional water was added to flour by titration until a maximum development consistency of
1986 Canadian Institute of Food Science and Technology
231
Table I. Farinogram data of doughs prepared with differently treated milk. Farinograph Arrival Sample absorption time (on 14070 m.b.) % min A. Wheat flour 64.78 No milk (control) 2.75b M.50a 2 Pasteurized milk 3.5a Scalded milk M.40a 3.0ab UHT-treated milk 64.00 2.0 B. Wheat flour + salt
Dough development time min
Dough stability
5.8 7.5a 7.25a 8.0a
17.5a 18.0ab 19.0b 19.5b
min
(2%)
No milk (control) 61.54 2.0 5.0 Pasteurized milk 65.66a 1O.75a 6.0a Scalded milk 65.49a 1O.75a 5.25a UHT-treated milk 4.5 65.06 1O.75a C. Wheat flour + salt + sugar + yeast I No milk (control) 65.94 1.0a 2.5 Pasteurized milk 68.36 6.0a 2.5 Scalded milk 68.16a 5.5a 1.25a UHT-treated milk 68.06a 6.0a 1.0a I Ingredients used in the same proportions as in the baking formula. 2AII results are means of triplicate determinations. Values in vertical columns for the individual sets of test (A., B. and C.) not followed by the same letter are significantly different using Duncan's multiple range test (P 0::;0.05).
500 Brabender units (B.U.) was reached. In calculating the farinograph absorption, both the water quantity present in the liquid milk and water added were taken into account. The tests were run in triplicate on flour /milk mixtures only as well as on mixtures containing all other ingredients used in the preparation of dough for maturography or for test baking. Stretchability tests on unfermented doughs were according to the AACC method 54-10 (AACC, 1983) using a strain-gauge equipped extensigraph (Engineering Research Service, Canada Agriculture, Ottawa). Maximum resistance of the tested dough to extension and its extensibility at the point of maximum resistance were recorded in units of force (N) and time (s), respectively. All tests were run in quadruplicate. For testing the fermenting doughs, maturograph tests were performed according to the Instruction Manual for the Brabender Maturograph (Brabender OHG, Duisburg, West Germany). The following indices were read from the recorded maturograms: a) "Final proof time" (min) indicating time required for a maximum rise of the dough under the conditions of the test; b) "dough level" (M.U. - maturogram units), a measure of the volume of dough at the final proof time; c) "stability" (min) measured as time for which the dough retains its maximum volume, and; d) "elasticity" (M.U.) which gives information on the dough potential to recover from a temporary deformation. A straight dough pup-loaf procedure was used for baking tests. All doughs contained 100 g flour (14070 m.b.), 50 mL milk, 4 g sugar, 2 g salt and 1.5 g reconstituted active dry yeast. An appropriate amount of water was added in order to adjust the water content in each individual mixture to a level corresponding to its farinograph absorption. Doughs were mixed to optimum consistency and fermented at 30 ± 0.5°C and 85070 R.H. for 180 min with punches at 105 and 232 / ZeBen et al.
155 min. After 55-min proofing, the loaves were baked at 215°C for 18 min. One hour after baking, loaf weights and volumes were determined. Unsliced loaves were stored at 25°C in sealed polyethylene bags. Crumb compressibility was measured after one and three d of storage with a Precision penetrometer (Precision Scientific Co., Chicago, IL) using a flat circular plunger (diameter 30 mm, weight 30.5 g, with an additional load of 20.0 g). The depth of penetration into a 2.5 cm thick slice after a 5-s compression period was recorded in 1/10 mm.
Results and Discussion Data summarized in Table 1 indicate the effects of the tested milks on the farinograph absorption of wheat flour dough and on the rate of dough development during mixing. While a slight reduction in the absorption resulted from replacing water with milk in the plain wheat flour dough, a marked increase was observed when either salt alone or all baking ingredients in addition to milk became part of the dough formula. The interaction between milk and salt appeared to have the most pronounced effect. However, regardless of the absence or presence of ingredients other than milk, a consistenJ trend in the relationship between the farinograph absorption and the type of milk became evident. Among the milkdoughs, those which contained the UHT-treated milk gave consistently the lowest absorption values. A similar trend was observed with the arrival time data which are primarily a reflection of the flour hydration rate during the early stages of dough mixing. A considerable increase in arrival time over the control was measured with doughs containing the pasteurized and the scalded milk. This increase was most noticeable in the presence of 2070 salt in the mixture. The flour-salt mixture was also the only one which reacted to the presence of the UHT-treated milk by a significantly J. [nsf. Can. Sci. Techno!. Aliment. Vol. 19. No.5, 1986
Table 2. Extensigram data of doughs with differently treated milk. Resistance (N) Sample Control With pasteurized milk With scalded milk With UHT-treated milk
Resting period (min) 45 90 135 51.4 59.9 57.8 (2.5) (3.0) (5.5) 39.2a 1 56.8a 67.3a (1.8) (4.3) (4.7) 37.7a 55.0a 63.8a (2.3) (4.0) (6.9) 55.0 74.0 72.0 (3.6) (4.2) (6.4)
Extensibility (s) Resting Period (min) 45 90 135 19.3a 14.8a 12.3a (0.5) (0.9) (1.5) 21.8 l4.3a 13.la (0.8) (1.3) (0.9) 19.1a 13.8a 11.6a (1.2) (1.1) (0.6) 17.1 11.0 9.6 (0.5) (1.0) (1.1)
Resistance/Extensibility (N/s) Resting period (min) 45 90 135 2.7 3.6b 4.7b (0.2) (0.7) (0.8) 1.8a 4.0ab 5.lab (0.1) (0.5) (0.3) 2.0a 3.la 5.5a (0.1) (0.6) (0.6) 3.2 6.8 7.4 (0.3) (1.4) (0.7)
IAII data are means (standard deviation) of four determinations. Values in vertical columns not followed by the same letter are significantly different (P :s 0.05) using Duncan's multiple range test.
(P :5 0.05) increased value of this farinogram index. Plain wheat flour and flour mixed with the other ingredients in addition to the UHT-treated milk behaved in a similar way like the no-milk control. Despite the differences in arrival time, the type of heat treatment of milk did not seem to have any significant effect on the time required to attain the maximum dough consistency during the process of dough development during mixing, generally referred to as dough development time. Although this time increased considerably with all doughs containing milk, data were practically identical regardless of the type of milk. The term dough stability indicates the resistance of dough to get overmixed and to lose its consistency upon prolonged mixing beyond the point of its maximum development. Doughs prepared from wheat flour without any ingredients other than water or milk were the only ones which were subjected to this test. A significant (P :5 0.05) improvement in dough stability over the control resulted from the incorporation of the scalded or UHT-treated milk; the latter tended to be somewhat more efficient in enhancing this quality. Dough containing ingredients other than water or milk were mixed to the point of their maximum development after which they were used for further testing by means of extensigraph and maturograph. Stretchability tests by means of the extensigraph provided results from which the differences in the effects of the tested milks on the functionality of nonfermented doughs emerged even more noticeably than from farinography (Table 2). Doughs containing the pasteurized or the scalded milk when allowed to rest for 45 min after the end of mixing, showed a reduction in the resistance to extension compared to the no-
milk control. After longer periods of resting (90 and 135 min), the resistance increased and eventually exceeded that of the control, a behaviour clearly demonstrating the well recognized 'tightening' effect of milk on the physical condition of dough. Unlike the resistance to extension, the extensibility of these doughs, measured as time to reach the maximum resistance under a constant rate of extension (1.45 cm/s), did not significantly (P :5 0.05) differ from the control value. Likewise, there was no significant difference in the resistance/extensibility ratio, a parameter usually taken as an approximate measure of work required to stretch the dough. Doughs containing the UHT-treated milk behaved differently. There was an increase in resistance to extension even after the shortest period of resting (45 min) with a simultaneous decrease in extensibility. Both the resistance and the resistance/extensibility ratio of these doughs were consistently higher than the corresponding data characterizing the other tested doughs. Differences between the UHT-treated milk and the other two tested milks were further revealed by maturograph tests on fermenting doughs (Table 3). Doughs containing the UHT-treated milk were found to be the closest to the control no-milk dough with respect to all evaluated maturogram indices. On the other hand, a considerable reduction in the values of these indices resulted from the use of either the pasteurized or scalded milk. The results of the maturograph tests on fermenting doughs were found to be in good agreement with data obtained by test baking (Table 4). All tested milks exhibited a loaf volume depressing effect under the given conditions of test. Nevertheless, it may be noticed that the smallest depression was
Table 3. Maturogram data of doughs prepared with differently treated milk. Doug 'Elasticity' level Stability Proofing time M.U.\ M.U.2 Sample min min 295 (5.5)a Control 46.0 (1.6)a 840 (Il)a 8.5 (0.5)ab 271 (8.3)b With pasteurized milk 41.3 (2.0)b 722 (16)b 7.1 (l.5)b 275 (9.5)b With scalded milk 41.3 (2.2)b 720 (l9)b 7.5 (1.4)b 295 (9.8)a With UHT-treated milk 842 (26)a 9.0 (1.2)a 45.0 (1.8)a IMaturograph units. 2AlI data are means (standard deviation) of six determinations. Means in vertical columns not followed by the same letter are significantly different (P :s 0.05) using Duncan's multiple range test. Can. Ins!. Food Sci. Techno!. J. Vol. 19. No.5. 1986
Zellen et al. / 233
Table 4. Results of baking tests with differently treated milk. Sample
Specific loaf volume mUg
Crumb compressibility, 1/10 mm Uncorrected
Corrected I
After 24 h After 72 h After 24 h After 72 h Control 4.69 (0.09) 46.6 (2.78) 46.6 (2.78)a 31.2 (4.45)a 31.2 (4.45)a With pasteurized milk 4.16 (0.05)a 2 38.1 (4.13)a 25.6 (3.42)b 42.9 (4.27) 28.9 (3.57) 23.8 (4.4I)b 26.3 With scalded milk 4.24 (0.09)a 40.8 (4.09)a 45.1 (4.2I)a With UHT-treated milk 4.38 (0.03) 42.2 (4.94) 29.0 (4.15)a 45.2 (5.03)a 31.1 (4.27)a lCalculated for the specific volume of the control sample. 2All data are means (standard deviation) of results obtained with six loaves. Means in the vertical columns not followed by the same letter are significantly different (P :5 0.05) using Duncan's multiple range test.
caused by the UHT-treated milk. Breads containing this milk not only were characterized by loaf volume values closest to the control but they, more than any other of the tested milk breads, resembled the no-milk control in their crumb compressibility properties. The similarities in the rate of firming upon storage became even more evident when the compressibility measurements were recalculated on the control loaf-volume basis in order to eliminate any interference from the varying crumb porosity (Axford et al., 1986).
Conclusions The intensity of milk heat treatment is well known to be qualitatively related to milk baking quality. The data presented provide quantitative evidence for comparing the effects of the UHT-treated milk with the effects other thermal treatments usually applied in processing liquid milk. When compared with doughs containing pasteurized or scalded milk, the UHTtreated milk doughs appeared 'stronger' in the strechability tests and gave better results of test baking, while their absorption as measured by farinography displayed a tendency towards lower values than those measured with the other milk doughs. Acknowledgement The authors acknowledge the financial support from the Ontario Ministry of Agriculture and Food which made this work possible.
234 / ZeBen et al.
References AACC. 1983. Approved Methods of the American Association of Cereal Chemists. The Association, St. Paul, MN. Aboshama, K. and Hansen, A.P. 1977. Effect of ultra high temperatures steam injection processing on' sulphurcontaining amino acids in milk. J. Dairy Sci. 60: 1374. Axford, D.W.E., Colwell, K.H., Corford, S.J. and Elton, G.A.H. 1968. Effect of loaf specific volume on the rate and extent of staling in bread. J. Sci. Food Agric. 19:95. Bloksma, A.H. 1972. The relation between the thiol and disulfide contents of dough and its rheological properties. Cereal Chern. 49:104. Gordon, A.L., Jenness, R. and Geddes, W.F. 1954. The baking behaviour of casein and whey prepared from skim milk by various procedures. Cereal Chern. 31: I. Larsen, R.A., Jenness, R, and Geddes, W.F. 1949. Effect of heat treatment of separated milk on the physical and baking properties of doughs enriched with dry milk solids. Cereal Chern. 26:189. Stamberg, O.E. and Bailey, C.H. 1942. The effect of heat treatment of milk in relation to baking quality as shown by polarograph and farinograph studies. Cereal Chern. 19:507. Swanson, A.M. and Sanderson, W.B. 1967. Milk proteins responsible for deleterious effects in continuous mix bread. Cereal Sci. Today 12:363. Volpe, T. and Zabik, M.E., 1977. A whey protein contributing to loaf volume depression. Cereal Chern. 52:188. Watanabe, K. and Klostermeyer, H. 1976. Heat-induced changes in sulphydryl and disulphide levels of 13-lactoglobulin A formation of polymers. J. Dairy Res. 43:411. Submitted July 29, 1985 Revised April 28, 1986 Accepted July 19, 1986
J. InSf. Can, Sci. Technol. Aliment. Vol. 19. No.5, 1986
RESEARCH
Bread Baking Potential of UHT-Milk W. Zellen ' , B. Lau and V.F. Rasper Department of Food Science University of Guelph Guelph, Ontario NIG 2WI Canada
Abstract The effects of UHT-treated liquid milk on the physical quality of milk-supplemented bread doughs were evaluated by farinography, extensigraphy, maturography and test baking. In comparison with pasteurized milk and scalded milk, the UHT-treated milk tended to give doughs with farinograph absorptions lower than those recorded with the other tested milk doughs, but the doughs appeared stronger and gave better baking results. In addition to lower loaf volume depression, the UHT-treated milk seemed to exhibit a more favourable effect on the crumb firming during storage than the other two heat-treated milks.
Resume
Materials and Methods
On a evalue les effets des laits UHT sur la qualite physique des pates boulangeres enrichies de lait Ii I'aide de farinographie, extensographie, maturographie et de cuisson. Par rapport au lait pasteurise et au lait sterilise, Ie lait UHT eut tendance Ii produire des pates dont les absorptions au farinographe etaient plus faibles que celles obtenues avec les autres laits. Par contre, les pates ont semble plus fortes et furent plus aptes Ii la cuisson. En plus de prevenir davantage la depression volumetrique des pains, Ie lait UHT a semble favorise mieux Ie raffermissement de la croilte au cours du stockage que les deux autres laits.
Introduction For a long time, preheating of milk has been recognized as essential for its good baking quality. Dough from unheated milk has a slack consistency and yields bread with a poor loaf volume. Factors responsible for the dough softening and the loaf volume depressing effects of unheated milk have been the subject of many investigations (Stamberg and Bailey, 1942; Larsen et at., 1949; Gordon et al., 1954; Swanson and Sanderson, 1967; Volpe and Zabik, 1977). Some of these studies attributed the poor baking quality of unheated milk to the sulfhydryl groups present in the milk protein and tried to relate the quality improvement upon heating to changes in these groups. The contribution of the sulfhydryl groups to the rheological properties of wheat dough has been well established (Bloksma, 1972). During the ultra-high-temperature treatment of milk, these groups within the milk protein undergo Jpresent address: Robin Hood Multifoods Ltd., Rexdale, Ontario M9W 5Z1 Copyright
©
changes which surpass effects of other conventional heat processes (Watanabe and Klostermeyer, 1976; Aboshama and Hansen, 1977). It is unlikely that UHT milk in its liquid form will be used by large commercial bakers. Nevertheless, a quantitative evaluation of the effects of this milk on the bread dough baking performance in comparison with other conventionally heated liquid milks may be of interest for further elucidation of the relationship between the milk heat treatment and baking quality.
A preheated (52°C) skimmed milk, supplied by a local dairy processor was subjected to three different heat treatments: a) Batch pasteurization by heating at 62-64°C for 30 min (UNIVAT®, Cherry Burrell Corp., Chicago, Illinois); b) Scalding by heating to 75°C with a 5-min holding period in the same equipment; c) UHT-treatment at 141°C for 4 to 5 s in a No-Bac Unitherm IV indirect tubular heat exchanger (Cherry Burrell, Cedar Rapids, Iowa). Each treatment was followed by immediate cooling to 27-28°C. The treatments were carried out in the Department of Food Science, University of Guelph. Total solids content of the heat treated milks, determined by the Cenco moisture balance method, was in the range of 10.0 to 10.1010. In all tests involving milk supplemented wheat flour doughs, the liquid milk was added to replace 6% of the flour solids with milk solids. Flour used was a commercially milled and treated bread flour (13.7% protein, 0.36% ash, both on 14% m.b.) supplied by a local flour mill. The effects of the tested milks on the dough mixing properties were evaluated by farinography following the AACC constant flour weight method 54-21 (AACC, 1983) and using a Brabender farinograph (Brabender Instruments Inc., South Hackensack, NJ) with a 50-g stainless steel mixing bowl. Liquid milk was added to flour prior to mixing in a quantity required to obtain the above milk solids/flour solids replacement. Additional water was added to flour by titration until a maximum development consistency of
1986 Canadian Institute of Food Science and Technology
231
Table I. Farinogram data of doughs prepared with differently treated milk. Farinograph Arrival Sample absorption time (on 14070 m.b.) % min A. Wheat flour 64.78 No milk (control) 2.75b M.50a 2 Pasteurized milk 3.5a Scalded milk M.40a 3.0ab UHT-treated milk 64.00 2.0 B. Wheat flour + salt
Dough development time min
Dough stability
5.8 7.5a 7.25a 8.0a
17.5a 18.0ab 19.0b 19.5b
min
(2%)
No milk (control) 61.54 2.0 5.0 Pasteurized milk 65.66a 1O.75a 6.0a Scalded milk 65.49a 1O.75a 5.25a UHT-treated milk 4.5 65.06 1O.75a C. Wheat flour + salt + sugar + yeast I No milk (control) 65.94 1.0a 2.5 Pasteurized milk 68.36 6.0a 2.5 Scalded milk 68.16a 5.5a 1.25a UHT-treated milk 68.06a 6.0a 1.0a I Ingredients used in the same proportions as in the baking formula. 2AII results are means of triplicate determinations. Values in vertical columns for the individual sets of test (A., B. and C.) not followed by the same letter are significantly different using Duncan's multiple range test (P 0::;0.05).
500 Brabender units (B.U.) was reached. In calculating the farinograph absorption, both the water quantity present in the liquid milk and water added were taken into account. The tests were run in triplicate on flour /milk mixtures only as well as on mixtures containing all other ingredients used in the preparation of dough for maturography or for test baking. Stretchability tests on unfermented doughs were according to the AACC method 54-10 (AACC, 1983) using a strain-gauge equipped extensigraph (Engineering Research Service, Canada Agriculture, Ottawa). Maximum resistance of the tested dough to extension and its extensibility at the point of maximum resistance were recorded in units of force (N) and time (s), respectively. All tests were run in quadruplicate. For testing the fermenting doughs, maturograph tests were performed according to the Instruction Manual for the Brabender Maturograph (Brabender OHG, Duisburg, West Germany). The following indices were read from the recorded maturograms: a) "Final proof time" (min) indicating time required for a maximum rise of the dough under the conditions of the test; b) "dough level" (M.U. - maturogram units), a measure of the volume of dough at the final proof time; c) "stability" (min) measured as time for which the dough retains its maximum volume, and; d) "elasticity" (M.U.) which gives information on the dough potential to recover from a temporary deformation. A straight dough pup-loaf procedure was used for baking tests. All doughs contained 100 g flour (14070 m.b.), 50 mL milk, 4 g sugar, 2 g salt and 1.5 g reconstituted active dry yeast. An appropriate amount of water was added in order to adjust the water content in each individual mixture to a level corresponding to its farinograph absorption. Doughs were mixed to optimum consistency and fermented at 30 ± 0.5°C and 85070 R.H. for 180 min with punches at 105 and 232 / ZeBen et al.
155 min. After 55-min proofing, the loaves were baked at 215°C for 18 min. One hour after baking, loaf weights and volumes were determined. Unsliced loaves were stored at 25°C in sealed polyethylene bags. Crumb compressibility was measured after one and three d of storage with a Precision penetrometer (Precision Scientific Co., Chicago, IL) using a flat circular plunger (diameter 30 mm, weight 30.5 g, with an additional load of 20.0 g). The depth of penetration into a 2.5 cm thick slice after a 5-s compression period was recorded in 1/10 mm.
Results and Discussion Data summarized in Table 1 indicate the effects of the tested milks on the farinograph absorption of wheat flour dough and on the rate of dough development during mixing. While a slight reduction in the absorption resulted from replacing water with milk in the plain wheat flour dough, a marked increase was observed when either salt alone or all baking ingredients in addition to milk became part of the dough formula. The interaction between milk and salt appeared to have the most pronounced effect. However, regardless of the absence or presence of ingredients other than milk, a consistenJ trend in the relationship between the farinograph absorption and the type of milk became evident. Among the milkdoughs, those which contained the UHT-treated milk gave consistently the lowest absorption values. A similar trend was observed with the arrival time data which are primarily a reflection of the flour hydration rate during the early stages of dough mixing. A considerable increase in arrival time over the control was measured with doughs containing the pasteurized and the scalded milk. This increase was most noticeable in the presence of 2070 salt in the mixture. The flour-salt mixture was also the only one which reacted to the presence of the UHT-treated milk by a significantly J. [nsf. Can. Sci. Techno!. Aliment. Vol. 19. No.5, 1986
Table 2. Extensigram data of doughs with differently treated milk. Resistance (N) Sample Control With pasteurized milk With scalded milk With UHT-treated milk
Resting period (min) 45 90 135 51.4 59.9 57.8 (2.5) (3.0) (5.5) 39.2a 1 56.8a 67.3a (1.8) (4.3) (4.7) 37.7a 55.0a 63.8a (2.3) (4.0) (6.9) 55.0 74.0 72.0 (3.6) (4.2) (6.4)
Extensibility (s) Resting Period (min) 45 90 135 19.3a 14.8a 12.3a (0.5) (0.9) (1.5) 21.8 l4.3a 13.la (0.8) (1.3) (0.9) 19.1a 13.8a 11.6a (1.2) (1.1) (0.6) 17.1 11.0 9.6 (0.5) (1.0) (1.1)
Resistance/Extensibility (N/s) Resting period (min) 45 90 135 2.7 3.6b 4.7b (0.2) (0.7) (0.8) 1.8a 4.0ab 5.lab (0.1) (0.5) (0.3) 2.0a 3.la 5.5a (0.1) (0.6) (0.6) 3.2 6.8 7.4 (0.3) (1.4) (0.7)
IAII data are means (standard deviation) of four determinations. Values in vertical columns not followed by the same letter are significantly different (P :s 0.05) using Duncan's multiple range test.
(P :5 0.05) increased value of this farinogram index. Plain wheat flour and flour mixed with the other ingredients in addition to the UHT-treated milk behaved in a similar way like the no-milk control. Despite the differences in arrival time, the type of heat treatment of milk did not seem to have any significant effect on the time required to attain the maximum dough consistency during the process of dough development during mixing, generally referred to as dough development time. Although this time increased considerably with all doughs containing milk, data were practically identical regardless of the type of milk. The term dough stability indicates the resistance of dough to get overmixed and to lose its consistency upon prolonged mixing beyond the point of its maximum development. Doughs prepared from wheat flour without any ingredients other than water or milk were the only ones which were subjected to this test. A significant (P :5 0.05) improvement in dough stability over the control resulted from the incorporation of the scalded or UHT-treated milk; the latter tended to be somewhat more efficient in enhancing this quality. Dough containing ingredients other than water or milk were mixed to the point of their maximum development after which they were used for further testing by means of extensigraph and maturograph. Stretchability tests by means of the extensigraph provided results from which the differences in the effects of the tested milks on the functionality of nonfermented doughs emerged even more noticeably than from farinography (Table 2). Doughs containing the pasteurized or the scalded milk when allowed to rest for 45 min after the end of mixing, showed a reduction in the resistance to extension compared to the no-
milk control. After longer periods of resting (90 and 135 min), the resistance increased and eventually exceeded that of the control, a behaviour clearly demonstrating the well recognized 'tightening' effect of milk on the physical condition of dough. Unlike the resistance to extension, the extensibility of these doughs, measured as time to reach the maximum resistance under a constant rate of extension (1.45 cm/s), did not significantly (P :5 0.05) differ from the control value. Likewise, there was no significant difference in the resistance/extensibility ratio, a parameter usually taken as an approximate measure of work required to stretch the dough. Doughs containing the UHT-treated milk behaved differently. There was an increase in resistance to extension even after the shortest period of resting (45 min) with a simultaneous decrease in extensibility. Both the resistance and the resistance/extensibility ratio of these doughs were consistently higher than the corresponding data characterizing the other tested doughs. Differences between the UHT-treated milk and the other two tested milks were further revealed by maturograph tests on fermenting doughs (Table 3). Doughs containing the UHT-treated milk were found to be the closest to the control no-milk dough with respect to all evaluated maturogram indices. On the other hand, a considerable reduction in the values of these indices resulted from the use of either the pasteurized or scalded milk. The results of the maturograph tests on fermenting doughs were found to be in good agreement with data obtained by test baking (Table 4). All tested milks exhibited a loaf volume depressing effect under the given conditions of test. Nevertheless, it may be noticed that the smallest depression was
Table 3. Maturogram data of doughs prepared with differently treated milk. Doug 'Elasticity' level Stability Proofing time M.U.\ M.U.2 Sample min min 295 (5.5)a Control 46.0 (1.6)a 840 (Il)a 8.5 (0.5)ab 271 (8.3)b With pasteurized milk 41.3 (2.0)b 722 (16)b 7.1 (l.5)b 275 (9.5)b With scalded milk 41.3 (2.2)b 720 (l9)b 7.5 (1.4)b 295 (9.8)a With UHT-treated milk 842 (26)a 9.0 (1.2)a 45.0 (1.8)a IMaturograph units. 2AlI data are means (standard deviation) of six determinations. Means in vertical columns not followed by the same letter are significantly different (P :s 0.05) using Duncan's multiple range test. Can. Ins!. Food Sci. Techno!. J. Vol. 19. No.5. 1986
Zellen et al. / 233
Table 4. Results of baking tests with differently treated milk. Sample
Specific loaf volume mUg
Crumb compressibility, 1/10 mm Uncorrected
Corrected I
After 24 h After 72 h After 24 h After 72 h Control 4.69 (0.09) 46.6 (2.78) 46.6 (2.78)a 31.2 (4.45)a 31.2 (4.45)a With pasteurized milk 4.16 (0.05)a 2 38.1 (4.13)a 25.6 (3.42)b 42.9 (4.27) 28.9 (3.57) 23.8 (4.4I)b 26.3 With scalded milk 4.24 (0.09)a 40.8 (4.09)a 45.1 (4.2I)a With UHT-treated milk 4.38 (0.03) 42.2 (4.94) 29.0 (4.15)a 45.2 (5.03)a 31.1 (4.27)a lCalculated for the specific volume of the control sample. 2All data are means (standard deviation) of results obtained with six loaves. Means in the vertical columns not followed by the same letter are significantly different (P :5 0.05) using Duncan's multiple range test.
caused by the UHT-treated milk. Breads containing this milk not only were characterized by loaf volume values closest to the control but they, more than any other of the tested milk breads, resembled the no-milk control in their crumb compressibility properties. The similarities in the rate of firming upon storage became even more evident when the compressibility measurements were recalculated on the control loaf-volume basis in order to eliminate any interference from the varying crumb porosity (Axford et al., 1986).
Conclusions The intensity of milk heat treatment is well known to be qualitatively related to milk baking quality. The data presented provide quantitative evidence for comparing the effects of the UHT-treated milk with the effects other thermal treatments usually applied in processing liquid milk. When compared with doughs containing pasteurized or scalded milk, the UHTtreated milk doughs appeared 'stronger' in the strechability tests and gave better results of test baking, while their absorption as measured by farinography displayed a tendency towards lower values than those measured with the other milk doughs. Acknowledgement The authors acknowledge the financial support from the Ontario Ministry of Agriculture and Food which made this work possible.
234 / ZeBen et al.
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J. InSf. Can, Sci. Technol. Aliment. Vol. 19. No.5, 1986