The Effect of Tempering Time on the Immediate Texture of Sugar Cookies. Anna Rose Alsman, F&N 453 Individual Project

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1 The Effect of Tempering Time on the Immediate Texture of Sugar Cookies 1 of 11 Anna Rose Alsman, F&N 453 Individual Project Abstract Tempering refers to a step in many cereal and pasta processes which involves the product being held at a constant temperature and moisture content for an extended period of time. This common process unit operation had been seldom studied in complex systems until recently a Purdue University study involving the retrogradation of starch (amylose and amylopectin) in corn grits during the flaking process on corn flakes (Gonzalez et. al., 2005). The retrogradation of starch in these systems may also be influenced by other ingredients, such as proteins, sugars, and fats. A short time (45 minute) tempering study was done on simple sugar cookies by holding the cookies at constant temperature and moisture after baking and measuring the hardness (with a texture analyzer) and water activity of the finished food. The hardness of the cookie increased with increased tempering time. However, further study is necessary to definitively conclude that the increased hardness was or was not due to starch retrogradation. Introduction Starch is an a-d-glucose polymer that constitutes a major food reserve material for higher plants (Langley and Miller, 1971). Starch is composed of two chemically distinguishable entities: amylose and amylopectin. Amylose is considered to be a mixture of essentially linear polymers. Amylopectin is a mixture of highly branched polymers. Starch is a used as a thickening agent in many foods. Starch will gelatinize in the presence of heat and water. This means that the starch granules will swell, gelatinize, and paste and the starch granule will be disrupted (Atwell et. al, 1988). After gelatinization, the starch will retrograde. Retrogradation (analogous to physical aging in polymer chemistry) is the spontaneous reassociation of the starch chains into a more ordered structure (Perera, 2003). Retrogradation begins with the irreversible retrogradation of amylose. Amylopectin reversibly retrogrades more slowly, over the course of days. An example of retrogradation (specifically amylopectin) is the staling of bread. Wheat flour is composed of 23-27% amylose and has a gelatinization temperature of (Lineback, 1984). Also, wheat flour is composed of protein. The protein in wheat flour will form gluten, which is responsible for much of the elasticity in baked goods such as cookies and breads. Because retrogradation of starch is the target of this study, cookie flour will be used because cookie flour is wheat flour with less protein. Less protein will limit the effect of the protein on the water uptake and retrogradation of starch and thus on the objective texture measurements. Tempering in this study refers to a step in many cereal or pasta processes involving the product being held at a constant temperature and moisture for an extended period of time. Tempering is a common processing step associated with starch retrogradation for which little literature exists in complex food systems. The molecular mechanisms of water sorption and the subsequent effects on the structure (and dynamics) on the carbohydrate matrix (or retrograded starch structure) are relatively unknown (Kilburn et. al., 2005). Until recently, the only mechanism that was thought to occur during tempering was moisture migration. However, research currently being done at Purdue University is showing that tempering also involves retrogradation of starch (amylose and amylopectin) (Gonzalez et. al., 2005).

2 2 of 11 This means that not only is moisture migrating to the surface of the food, but the starch molecules are reassociating (or retrograding) at the same time. Cookies were chosen as a complex system in this study because cookies are a familiar food item made with starch that sensory panels will readily recognize. The ultimate purpose of this study is to test the changes in cookie texture, as a result of starch retrogradation, when cookies are tempered after cooking. The tempering temperature, 79.44ºC, was chosen due to the limitations from the maximum allowable temperature of the broadband oscillatory squeezing flow probe that may be used in future studies on this food. Gaining an understanding of the changes that occur in the tempering process, specifically with relation to starch retrogradation, will allow food companies to increase the quality of product by implementing tempering steps that allow for maximum or minimum retrogradation patterns (depending on which is favorable). This could, in turn, lead to economic benefits due to a decrease in time or thermal energy or time necessary to the tempering step of a process. Also, an understanding of the retrogradation patterns at low tempering temperatures may give insight into the effect of increased temperatures during storage of finished product in a constant moisture environment (e.g. in the packaging). Therefore, this study is based on maintaining baked cookies at constant temperature and moisture for varying short periods of time in order to observe a change (or lack-there-of) in hardness of the cookie as a result of the retrogradation of starch. Methods I. Sugar Cookie Recipe Scaled to 20 Cookies (Weaver and Daniels, 2003) A. Ingredients g Cookie Flour g Hydrogenated Fat g Sugar ml Milk g Blended Whole Egg g Salt g Baking Soda g S.A.S. Baking Powder ml Vanilla B. Baking Procedure 1. Three trials of cookie batches were prepared in Stone Hall Room Variables other than tempering time were controlled by keeping every detail constant. This means when cookies were mixed, the same ingredients and masses will be used. The same mixing times, speeds, and number of strokes were used for each replication. The same oven was used at the same temperature, the cookie sheet placed on the same rack, cookies placed on the same cookie sheet, and baked for the same length of time for each replication. 3. The flour, salt, soda, and baking powder were sifted together on paper. 4. The fat, vanilla, and sugar were mixed together in a bowl. Add the egg and milk. Stir well. 5. All ingredients were mixed and stirred with an electric mixer until the ingredients are well blended (2 minutes).

3 3 of g portions of the dough were weighed, formed into uniform balls, and placed onto cookie sheets 2' apart. 7. Cookies were baked at ºC for 8 minutes. 8. After baking, the cookies were allowed to cool until an internal temperature of 79.44ºC was reached by placing a temperature probe inside a random cookie. (This was done to ensure that the cookies did not sweat or lose moisture out of the cookie that clung to the wrapping during the tempering process). 9. Immediately after the proper temperature was reached, the cookies were wrapped in an inner layer of plastic cling wrap (saran plastic wrap) and an outer layer of laboratory stretch wax to ensure that the moisture content stayed as constant as possible. 10. All cookies but the fresh cookie samples were placed in a second convection oven with a temperature set point of 79.44ºC. Samples were taken randomly off the pan and placed in different random groups corresponding to each tempering time variable. II. Objective Evaluation Methods A. Texture Analyzer 1. The texture of the fresh cookies was taken after the cookies had cooled by use of a cone probe was used and the computer file C:/foodchem/cookie on the Stable Micro Systems Texture Analyzer (TA) in Stone Hall Room 227. The texture of fresh cookies at 79.44ºC was not taken during this study because of logistical reasons (other students using the TA, time required for wrapping subsequent samples, etc.). 2. The remaining cookies were held at in a convection oven for 15 minutes, 30 minutes, and 45 minutes. When the tempering time for each variable had finished, the cookies were removed from the oven. The cookies were allowed to cool to room temperature before the texture measurement was taken. B. Water Activity The water activity of each variable was measured by use of a Water Activity System machine after the sample was cooled to room temperature. Two replicate water activity measurements were done per variable for 3 trials. C. Subjective Evaluation Methods 1. Subjective evaluation for cookies held at constant temperature for 15 minutes, 30 minutes, 45 minutes, and fresh cookies were done by a 9-point hedonic scale sensory panel of students in F&N 453L who were also conducting experiments. Six sensory panelists were used for each trial (total of 18 sensory data points collected). 2. Cookies were prepared, cooled, and served on identical plates each time sensory panels were conducted. Cookie samples were displayed so that no cookie was favored or disfavored by panelists as a result of the display. This meant that each cookie will be on uniform size, placed on the same type of plate, arranged similarly on the plate, and was served in the same environment. 3. The sensory scorecard is appended to this report. Note that the order of samples given to panelists was varied from week to week, as did the numbers. On the appended scorecard, the following 3 digit numbers are indicative of associated time variable.

4 a. Fresh Cookie b. 15 Minute Tempered Cookie c. 30 Minute Tempered Cookie d. 45 Minute Tempered Cookie of 11 Results/Discussion Table 1 Average Hardness (g) of Cookies at Increasing Tempering Time at 79.44ºC per Trail and Overall Average as Obtained from Peak of Texture Profile Analysis Curves Fresh 15 Minutes 30 Minutes 45 Minutes Trial Trial Trial Overall Average Overall Standard Deviation Average values were calculated according to the formula below. Average = (TA Peak Force)/Number of Data Points For example, the trial 2, fresh average was calculated as follows: (92.7g+106.1g+103.8g+100.6g+127.0g+205.1g)/6 = g Hardness (g) Fresh 15 min 30 min 45 min Tempering Time (Minutes) Figure 1 Overall Average Hardness of Cookies at Increasing Tempering Times at 79.44ºC

5 5 of 11 As indicated on Figure 1 and in Table 1, overall, the hardness (or increased force required to penetrate the cookie) increased with increased tempering time. This is consistent with the literature indicated expectations (Gonzalez et. al., 2005). The hardness of the sample was expected to increase with increased retrogradation of starch at increased temperatures. This indicates that some change within the structure of the cookie was happening over the tempering time. Table 2 Water Activity of Cookies at Increasing Tempering Time at 79.44ºC per Trail Fresh 15 Minutes 30 Minutes 45 Minutes Trial Trial Trial Overall Average Overall Standard Deviation Water Activity Fresh 15 min 30 min 45 min Tempering Time (Minutes) Figure 2 Overall Average Water Activity of Cookies at Increasing Tempering Times at 79.44ºC The average water activity (a w ) was calculated according to the following formula. Also, an example is given for the average water activity calculation for trial 1, 15 minutes. Average = (Water Activity)/Number of Data Points ( )/3 = Analysis of the water activity data recorded in Table 2 and Figure 2 leads to the conclusion that the water activity from sample to sample is relatively constant. The average value range is units. Therefore, the water activity can be assumed to be reasonably constant throughout the study.

6 6 of 11 For an ideal solution, the water activity of a food is equal to the mole fraction of water (x w ) in the food, which is represented by the following equation: m w a w x w m w + Where m w molar concentration of water and m s,i is the sum of the molar concentrations of solutes. High molecular weigh solutes (like starch) have very little effect on x w and water insoluble components have no effect at all (Walstra, 2003). Cookies are not an ideal solution, but this assumption is not unreasonable for purposes of determining if moisture content of the cookies is constant. Because the molar concentration of solute (any ingredient other than water) is the same for each cookie tested and also does not change over time, the moisture content must be the same for each cookie tested. Table 3 9-Point Hedonic Scale Sensory Results of Cookies at Increasing Tempering Times at 79.44ºC i m s, i Fresh 15 Minutes 30 Minutes 45 Minutes Tenderness Texture Moistness Palatability Average Score Standard Deviation Average Score Standard Deviation Average Score Standard Deviation Average Score Standard Deviation Tenderness Texture Moistness Palatability 7 Average Sensory Score Fresh 15 min 30 min 45 min Tempering Time (Minutes) Figure 3 Scores from 9-Point Hedonic Scale Sensory Panel

7 Figure 3 and Table 3 indicate that the sensory panelists perceived that the cookies became harder, crunchier, drier, and less palatable with increased tempering time. 7 of 11 Table 4 Statistical Significance of Differences between Sensory Characteristics of Cookies at Increasing Tempering Times at 79.44ºC as Determined by Paired t-tests (t differemce = 2.567) Sensory Characteristic Tenderness Texture Moisture Palatability Compared Tempering Times t-value Significant Difference (yes or no) Fresh/ no Fresh/ no Fresh/ yes 15/ no 15/ yes 30/ yes Fresh/ no Fresh/ no Fresh/ yes 15/ no 15/ yes 30/ yes Fresh/ no Fresh/ no Fresh/ yes 15/ yes 15/ yes 30/ yes Fresh/ no Fresh/ no Fresh/ yes 15/ yes 15/ yes 30/ no The paired t-test calculations were conducted according to the following method. The example calculation is that of the test for the significance of the difference in palatability between the fresh and 15 minute variables. Mean Difference µ = ( difference)/n µ = ( )/18

8 µ = of 11 Standard Deviation σ = ( difference 2 - (difference 2 /n))/(n-1) In this equation, n is the number of data points and difference is the arithmetic difference between corresponding sample data points (data points from the same trial and same panelist). Experimental t-value σ = ( /18 ( ))/(18-1) σ = 1.58 t = µ/(σ/ n) t = 0.83/(1.58/ 18) t = 2.24 A probability level of 99.9% was chosen for the t-test. This means that the significance level to read off the chart is α = From Percentage Points t α,υ of the t-distribution chart (where α is the significance value and υ is n-1 or the number of degrees of freedom) (Montgomery and Runger, 2002) t table = The two sets of data are significantly different if t experimental > t table. Because 2.24 < 2.567, the difference in palatability between the fresh and 15 minute variables was not significant. As indicated by Table 4, there were no significant differences in tenderness, texture, moistness, or palatability between the fresh and 15 minute and the fresh and 30 minute samples throughout the experiments. Significant differences were noted in all four categories between fresh and 45 minute and 15 minute and 45 minute samples. The texture and tenderness categories had the same significant difference results throughout the study also. In general, significant differences do not exist between samples tempered for very short times (fresh and 15 minutes), but do exist between samples tempered at short times and longer times (fresh and 45 minutes, 15 minutes and 45 minutes). In summary, the results of this study has shown that statistically significant sensory differences exist between samples tempered for short times and longer times (fresh and 45 minutes, 15 minutes and 45 minutes), the hardness of samples increases with tempering time, and the water activity (and hence moisture content) stays constant when properly wrapped to ensure moisture does not escape. Sources of error in this experiment include human error and equipment error. Human error could be a factor in the exact tempering time, reproducing the ingredient measurements and mixing methods, and

9 9 of 11 misuse of equipment. Equipment error could come from the scale used to weigh ingredients, the water activity meter, or texture analyzer malfunctions. Although this study has shown that significant changes in texture occur over short periods of time during tempering at constant moisture, it does not show what the cause of the texture change was. The cause hypothesized initially was starch retrogradation. Starch retrogradation is likely to be a part of the cause of the increase in hardness over short tempering times, but other factors may also contribute, such as protein coagulation (after denaturation by heat during cooking) or sugar binding water and limiting the swelling of starch granules and the amount of retrogradable amylose released. Further studies are necessary to determine the exact method of the increase in hardness of cookies as a result of tempering time. X-ray crystallography could be done on samples taken at each tempering time to record the structure of the molecules at each stage. This may show the degree of retrogradation of the starch. Retrogradation is also frequently measured by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and Raman spectroscopy (Lii and His-Mei Lai, 1998, Li-Chan, 1996). Also, changes in ingredients may be made to see the effect on hardness. Wheat flour may be substituted with starch to see the effect of no protein on the hardness of the cookie. Also, the amount of protein may be varied to see the same results. The effect of sugar may bee seen by varying the sugar content or using alternative sweeteners. In conclusion, significant texture changes occur in cookies held at constant moisture for extended heating periods and further work must be done to conclude the mechanism by which the textural changes occur. References Atwell, W.A., L.F. Hood, D.R. Lineback, E. Varriano-Marston, and H.F. Zobel The terminology and methodology associated with basic starch phenomena. Cereal Foods World 33: Daniel, J. and Weaver, C Food Chemistry Laboratory Manual. 2: Gonzalez, D.C., Mert, B, Campanella, O.H., and Okos, M.R A Novel Non-Invasive Method to Measure Visco-Elastic Properties of Cereal Grains during Processing. Kilburn, D., Claude, J., Schweizer, T., Alam, A., and Ubbnik, J Carbohydrate Polymers in Amorphous States: An Integrated Thermodynamic and Nanostructural Investigaiton. Biomacromolecules. 6: Langley, R.W., and B.S. Miller Note on the relative effects of monoglycerides on the gelatinization of wheat starch. Cereal Chemistry 48:81-85 Li-Chan, E.C.Y The applications of Raman spectroscopy in food science. Trends in Food Science & Technology. 7(11): Lii, C.Y. and Hsi-Mei Lai, S.T.J O NMR and DSC for studying quality of taro past as affected by processing and storage. Lebensmittel-Wissenschaft und-technologie. 31(1):57-63.

10 10 of 11 Lineback, D.R The starch granule organization and properties. Bakers' Digest 58(3): Jameson, K Food Science Laboratory Manual Montgomery, D.C., and Runger, G.C Applied Statistics and Probability for Engineers. Ed. 3. John Wiley & Sons, Inc. New York, NY. 3: , 656. Perera, Dan Y Physical ageing of organic coatings. Progress in Organic Coatings. 47: Walstra, P Physical Chemistry of Foods. Marcel Dekker, Inc. New York, NY. 1: Appendix Raw Data Sheets Sensory Panel Scorecard

11 11 of 11 Sugar Cookie Texture Sensory Panel Scorecard Please rank the following attributes of the sugar cookies you taste on a 9 point hedonic scale with 1 indicating very soft, chewy, moist, or extremely palatable and 9 indicating hard, crunchy, dry, or unpalatable. Sample Tenderness (1=very soft, 9=very hard) Texture (1=very chewy, 9=very crunchy) Moistness (1=very moist, 9=very dry) Palatability (1=extremely palatable, 9=unpalatable) Comments Tenderness Texture Moistness Palatability Comments Thank you very much for your time and have a nice day!

Lipid-Based Fat Replacer in Cookies: The Effect On Taste and Texture. Meagan Moyer 20 November 2006 F&N 453 Individual Project Report

Lipid-Based Fat Replacer in Cookies: The Effect On and Meagan Moyer 20 November 2006 F&N 453 Individual Project Report Abstract Dietary fats are an important topic in today s American society. High fat