VOLUME EXPANSION OF CAKE DURING BAKING AND ITS INFLUENCE ON CAKE QUALITIES.

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1 VOLUME EXPANSION OF CAKE DURING BAKING AND ITS INFLUENCE ON CAKE QUALITIES. Mchèle Marcotte. Food Research and Development Centre, Agrculture and Agr-Food Canada, 3600 Casavant Blvd West. St. Hyacnthe, Quebec, J2S 8E3, ABSTRACT Located at the end of the processng lne, bakng s essental n the manufacturng of starchy products (e.g. breads, cookes, cakes). The operaton leads to products wth typcally mportant technologcal macroscopc propertes (e.g. mosture content, proper dmensons or yeld, desred and appealng color, texture and taste). Durng bakng, bochemcal consttuents undergo physco-chemcal changes at mcroscopc level (e.g. phase transton, modfcaton of structural propertes etc.). Results of these changes are apprecable. As an example durng bakng, the dough/batter of starchy products ncreased and the macroscopc volume s expandng from the effect of the ar ncorporaton (mxng), the producton of CO 2 ether by the chemcal agent or by fermentaton (proofng) and the water vaporzaton. For all starchy products, typcal knetc profles are usually obtaned: an ncrease up to around 2/3 to 2/4 of the bakng tme then a decrease to some extent. Wthout quantfyng the relatonshp between the cellular structure and the molecular forces that govern ts creaton and stablzaton, there s lttle hope of developng the process scence that wll permt us to control the formaton of these man-made cellular solds (.e. a sold matrx wth an assocated gaseous phase. The objectve of the study was to analyze the man factors responsble for the generaton of the expanded or porous structure durng bakng. More specfcally, the amount (X) of a typcal leavenng agent (0, 1X and 2X) and 5 levels of constant bakng temperatures (0, 225, 250, 275, 300 o C) were studed for ther effect on volume expanson, color and texture (nstrumental and sensory). Increasng the quantty of leavenng agents dd not necessarly result n a sgnfcant effect on volume expanson but the frmness of the resultng products was decreased. As expected, a slght ncrease of the temperature resulted n an ncrease of the volume expanson but an mportant elevaton of the temperature resulted n a decrease of the volume accompaned by an ntense surface color and an ncrease of the hardness. INTRODUCTION Cellular solds are structures comprsed of a sold matrx and an assocated flud. If the flud s gaseous, cellular solds have low denstes. Many foods are cellular solds, ether because nature made them so (fruts and vegetables), or manly because they are processed nto them (e.g., bread, cookes, cakes) to obtan desred or appealng textural propertes. Cellular solds are alternatvely named bubble foods. The prncples for studyng the structure and propertes of cellular solds were lad out by Gbson and Ashby (1997) and by Weare and Hutzler (1999). A relatonshp was establshed between the Young s modulus (an ndcaton of the hardness of the structure) and the densty as well as between the falure stress and the densty as: * * ε ρ = C ε and ε ρ * * σ ρ = C σ (1) σ ρ Where C s the parameter characterzng the mcrostructure, the * ndcates the property of the cellular sold whereas the absence of * ndcates only the property of the solds wthout bubbles. At frst, food technologsts appled these prncples to develop consstent strateges for creatng and controllng cellularty n extruded starch foams (Waterburton et al, 1990). To

2 demystfy structure-property relatonshps of cereal products, Emehd et al. (03) used the same prncples. It s nterestng to pont out that the volume fracton occuped by gas bubbles n a fnal bread product may represent more than 50% of the total loaf volume (Scanlon and Zghal, 01). However, the majorty of the rheologcal studes on starchy products (Bloksma and Bushuk, 1988) have not vewed the presence of gas bubbles as an mportant area of nvestgaton, despte ther mportance to the rheologcal propertes of the processed dough/batter. Alternatvely, Campbell et al. (1999) are vewng starchy product makng as a seres of aeraton stages wth publshed detaled results on number, sze and dstrbuton of bubbles durng the proofng of bread. In ther recent study, Babn et al. (04) have shown that the Gbson and Ashby model could not explan satsfactorly the great dsperson of expermental data for extruded starches. The dfference of mechancal propertes for samples of same densty could be explaned by ther nherent mcrostructure (number of bubbles, sze and dstrbuton). Other models were developed to descrbe volume expanson n other areas of research (Ramesh et al., 1991), for expanson of extruded products (Fan et al., 1994) and for bread bakng (Fan et al., 1999). In these models, macroscopc volume expanson s related to the ncrease of the volume of ndvdual gas bubbles nsde the cellular sold. It s possble to descrbe the rate of bubble expanson as a functon of the pressure dfference between gas bubbles and the contnuous phase takng nto account the surface tenson of the bubble and the product vscosty. It s well recognzed n the lterature that there s not only a strong relatonshp between the formulaton (choce and quantty of ngredents) and fnal product propertes but also between processng condtons and fnal product propertes (Bak et al., 00ab). Moreover, the propertes are nfluenced by the structure that may be evolvng durng processng. Due to a lack of knowledge, most of the research on these relatonshps s specfc to a partcular operaton and product, and the relatonshps are establshed usng a tral and error approach. The processng of a typcal bakery product requres several steps ncludng usng the approprate flour (the major ngredent that may change from year to year due to varyng weather condtons, orgn of the gran, cultural practces, gran mllng processes etc.), addng other ngredents (e.g., sugar, fat, leavenng agents, water etc.) by mxng (ncorporaton of ar), formng, proofng (e.g. bread fermentaton for CO 2 producton) and fnal bakng (e.g., ar temperature, humdty and velocty n varous ovens, mosture evaporaton wthn the product) at the ndustral plant. Varatons at any of these steps (e.g., flour gran producton, mllng factory, bakery plant etc.) can affect one s ablty to manufacture a bakery product of the fnal structure wth desred macroscopc physcal characterstcs (e.g., consstent dmenson, densty, mosture content, surface color and texture). Industral varablty s experenced qute frequently (e.g., uncontrolled thckness of cookes, undesrable cake volcanoes, textural varatons makng the resultng cookes more brttle and fragle, bread or cooke dough stckng to the equpment durng the formng process etc.). A typcal bakery plant would lke to control the product yeld (.e., the rato of a gven mass of product to ts volume). On one hand, t s relatvely easy to control the mass of product. Ths s performed on a routne bass as a qualty control measurement. However, snce the volume of a typcal bakery product wll expand sgnfcantly (4-10 tmes) upon processng (e.g., proofng, bakng etc.), controllng the volume expanson (.e., the yeld) stll remans an mportant dffculty. Currently, troubleshootng of these recurrng varablty problems s not an easy task and requres n-depth, hands-on practcal experence. Because of a lack of basc understandng of the mechansms nvolved, solutons are normally found usng a tral and error approach that s qute tme consumng and expensve (because of the quantty of raw materals needed), and wll result n consderable product waste. Understandng the effect of ngredent selecton and quantty and processng condtons on the resultng structure and propertes durng mxng, proofng

phenomenon. MATERIALS AND METHODS Cake Batter Formulaton A typcal AACC (Amercan Assocaton of Cereal Chemsts) model formulaton for whte cake was used: water (870g, 31.3%), sugar (840g, 30.

3 and bakng s therefore a key ssue. The objectve of ths study was to quantfy the volume expanson whle varyng bakng temperatures and leavenng agent concentraton smultaneously n order to get a better understandng of the volume expanson phenomenon. MATERIALS AND METHODS Cake Batter Formulaton A typcal AACC (Amercan Assocaton of Cereal Chemsts) model formulaton for whte cake was used: water (870g, 31.3%), sugar (840g, 30.3%); flour (600g, 21.6%); shortenng (300g, 10.8%); skmmed mlk powder (72g, 2.6%); whte egg powder (54g, 1.9%), leavenng agents (22.37g, 0.8%) and salt (18g, 0.7%). Cake Batter Preparaton The cake was prepared usng a Hobart Mxer n 3 steps. At frst, all ngredents were mxed wth 522 g of water. The second and thrd steps conssted of addng 174 g of water. At every step, 4 pulses were appled. The frst pulse was performed at the frst speed level for 30 mn. The subsequent pulses were performed for tme duraton of 4 mn at the second speed level. Between every step, the bowl was swept usng a hand scraper. Bakng Condtons and Oven Fve bakng temperatures were appled (0, 225, 250, 275 and 300 C) and three amount of leavenng agents (C) (.e. wthout leavenng agen or 0X, the recommended AACC amount or 1X, twce the AACC recommendaton or 2X) were vared smultaneously for a total of 15 expermental condtons. Experments were performed n duplcates. For each batch of batter, 16 molds (Cup Cake type) were flled. Molds were entered nto a constant temperature batch oven (Fgure 1) mounted on a scale. Weght losses were recorded contnuously durng bakng. A typcal value of cake batter ntal mosture content was 33%. Bakng tmes for each oven temperature condtons were determned to reach a fnal mosture content of 23-24% as beng: 1) 1800 s at 0 o C; 2) 1340 s at 225 o C; 3) 1160 s at 250 o C; 4) 940 s at 275 o C and fnally 5) 800 s at 300 o C. For verfcaton, the fnal mosture content was determned at 23% and results were not sgnfcantly dfferent for each bakng tme-temperature condtons at 5% level. Fgure 1: Bakng Oven

Measurement of qualty parameters Yeld & Volume Index Measured Color Volume expanson Color Measurements of heght cake durng bakng L a b system measurement Volume ndex VI = a + b + c + b1 + a1 L :

5286 * VI( mm) Yeld = Weght( g) ΔE ΔE = (L 2 + a 2 + b 2 ) 1/2 Surface Frst measurement at Centre Second measurement at border Thrd measurement at bottom Texture parameters measured (chewness,

4 Measurement of qualty parameters Yeld & Volume Index Measured Color Volume expanson Color Measurements of heght cake durng bakng L a b system measurement Volume ndex VI = a + b + c + b1 + a1 L : lghtness from black to whte (0 to 100%) a : Color scale from green to red (-1 to +1) b : Color scale blue to yellow (-1 to +1) * VI( mm) Yeld = Weght( g) ΔE ΔE = (L 2 + a 2 + b 2 ) 1/2 Surface Frst measurement at Centre Second measurement at border Thrd measurement at bottom Texture parameters measured (chewness, gummness, hardness) Texture (1) Texture (2) Texture propertes measured usng a TA-XT2 A double compresson procedure (TPA) was used at a speed of 0.8 mm/s at room temperature. Sample sze Φ=25 mm H= mm Hardness (Ha): maxmum force of the frst compresson Sprngness (Sp): dstance of the sample recovered n heght after the frst compresson Cohesveness (Co): rato of the A46 to A13 under the compresson curves Chewness (Ch) Ha X Sp X Co Gummness (Gu) Ha X Co Frst compresson A13 A12 A23 Second compresson A46 A45 A56 Sensory Evaluaton A lmted sensory evaluaton was performed for texture n mouth specfcally for the hardness. A statstcal analyss, a Fredman rankng test usng 24 judges, was performed usng the software FIZZ (verson 1.30, Bosystemes, Couternon, France) at a level of sgnfcance of 5%. RESULTS AND DISCUSSION Volume Expanson Knetcs Fgure 2 shows the volume expanson knetcs at varous temperatures. A typcal ncrease was observed to reach a maxmum volume. Then the cake volume decreased sgnfcantly. The heght of the cake as well as the rate of ncrease s greatly affected by the bakng temperature. These profles are typcally obtaned for other bakery products such as bread (Kusunose et al., 1999) or cookes and are even smlar to those obtaned by for extruded products (Fan et al, 1994). A vsual observaton of the bakng process demonstrated that the volume expanson ceased as soon as there s a sgnfcant crust formaton at the surface. As well, the vscous batter s gradually becomng an elastc cellular sold. Bubbles expanson s reduced by the soldfcaton of the structure.

5 40 38 Heght at Centre (mm) Bakng at 0 C Bakng at 225 C Bakng at 250 C Bakng at 275 C Bakng at 300 C Tme (s) Fgure 2: Volume expanson profle Usng a smplfed model presented at the ASAE-CSAE meetng n Ottawa (Marcotte and Chen, 04), smulatons of macroscopc volume expanson were performed. The shape of the cake was assumed to be a cylnder. Modeled phenomena ncluded: heat transfer, mosture transfer, gaseous producton and cake volume expanson. Heat and mosture transfer phenomena were well descrbed by Fourer s law of conducton wth approprate boundary condtons. Major assumptons ncluded: 1) a unform ntal temperature and mosture for oven and cake; 2) a constant temperature and mosture durng bakng; 3) ndvdual bubbles were lumped nto a macro bubble; 4) gases nsde the bubble followed the deal law; 5) CO 2 producton was assumed to follow a frst order reacton knetcs and an Arrhenus type of behavour for the effect of temperature. Volume changes were related to changes n temperature and pressure as: PV 1 T 1 1 P V T 2 2 = [2] 2 The pressure (P) nsde the bubble was assumed dependent on CO 2 pressure (P c ) and on vapour pressure (P v ). A Kelvn model, comprsng both an elastc and a vscous element, was used to descrbe the volume expanson usng the pressure dfference. Fgure 3 shows that predcted volume expanson was n accordance to expermental data at both 0 o C and 225 o C and that t was possble to predct very well the macroscopc volume expanson durng the ncreasng part of the curve but t was not possble to descrbe the plateau and the decrease of curve. Heght (mm) Predcted 225 C Expermental 0 C Bakng process tme (s) Fgure 3: Predcted and expermental volume expanson

6 Volume Index Fgure 4a shows the volume ndex of varous cakes as a functon of bakng temperatures and quanttes of the leavenng agent (0X, 1X and 2X). The volume ndex ncreased whle addng leavenng agents. Therefore t can be concluded that not only the water evaporaton nether the ar ncorporaton n the batter was suffcent to generate the desred volume although t resulted n a small ncrease of the volume. There s a lmt n the amount of leavenng agents that can be added to the batter as doublng the concentraton dd not result n a sgnfcant ncrease of the volume. An ncrease of the bakng temperature dd not necessarly result n an ncrease of the volume expanson. There seems to be an optmal value of bakng temperature. Ths phenomenon mght have also been lnked to the crust formaton (earler at hgher bakng temperatures). In terms of volume expanson, best results were obtaned for cakes (1X) baked at relatvely low temperatures (0 C and 255 C). A maxmum volume expanson was observed. As expected there was a strong nteracton between the leavenng agent concentraton and the bakng temperature. Usng the fve measurement pont of the volume ndex (a, b, c, a1 and b1), t was possble to evaluate the surface profle of the volume expanson and hence to dentfy any major defect that could occur durng bakng as seen n Fgure 4b. A hgh bakng temperature resulted n a reduced fnal heght of cakes characterzed by a flat shape. Ths phenomenon was even more mportant for cakes contanng twce the concentraton of the leavenng agent Volume Index (mm) g g f f f cd a ab bcd bc bcd bcd de cd e 0oC 225oC 250oC 275oC 300oC Heght (mm) T0-0X T225-0X T250-0X T275-0X T300-0X T0-1X T225-1X T250-1X T275-1X T300-1X T0-2X T225-2X T250-2X T275-2X T300-2X 100 W/O leavenng agent (0X) AACC (1X) AACC (2X) a b c b1 a1 Fgure 4a: Global volume ndex Fgure 4b: Local volume ndex Color Measurement As observed n Fgure 5, globally, an elevaton of the bakng temperature resulted n a decrease of the average ΔE. The presence or absence of the leavenng agent dd not affect sgnfcantly the fnal surface color of cakes. Increasng the concentraton of the leavenng agent resulted n a decrease of ΔE. Ths phenomenon s probably due to the degradaton of sodum bcarbonate that accompaned an ncrease of the ph that resulted n a darker cake. Vsual observaton revealed that t was most unform and typcal of ndustral caked whle products were baked at lower temperatures.

7 70 ΔE a ab bcd cd d ab ab b cd d bcd d c e f 0oC 225oC 250oC 275oC 300oC 10 0 W/O leavenng agent AACC (1X) AACC (2X) Fgure 5: Average ΔE of cakes at varous bakng temperatures Texture parameters Hardness decreased as the concentraton of the leavenng agent ncreased due to the ncrease of porosty (Fgure 6). Sgnfcant dfferences were obtaned wth respect to temperature for the AACC recommended concentraton. Hgher bakng temperatures resulted n harder cakes. For a concentraton of leavenng agent that was doubled, bakng temperatures dd not have any sgnfcant effect on the hardness of cakes c d a b b 2400 Force (g) h g f e e 0oC 225oC 250oC 275oC 300oC W/O leavenng agent (0X) AACC (1X) AACC (2X) Fgure 6: Hardness of a cake for varous bakng temperatures Sensory Evaluaton Sensory evaluaton s normally performed usng a lmted number of samples (3-5). From the results of hardness measurement usng a TA-XT2, only samples wth the AACC recommended concentraton of leavenng agents were presented. Snce there was no sgnfcant dfference between the hardness at 275 and 300 o C, judges evaluated only 4 samples baked at 0 C, 255 C, 250 C and 275 C. The performance of the judges s demonstrated n Fgure 7. They were able to dfferentate cakes cooked at 225 C, 250 C and 275 C based on ther hardness but could not dstngush statstcallycakes baked at 0 C and 225 C. Ffteen and 7 judges ranked cakes baked at 0 C and 225 C as beng less frm (rank 1) where 9 and 12 judges ranked cakes baked at 0 o C and 225 o C as beng second (rank 2) n terms of hardness. Cakes baked at 275 C were found to be the hardest (rank 4) by 19 judges and 16 judges were able to rank cakes baked at 250 C as the thrd (rank 3) n terms of hardness. Results were well correlated wth those obtaned wth the nstrumental analyss (TA-XT2) as harder cakes were found f baked at hgher

8 temperatures. Preferred samples were those baked at 0 C and 225 C. Panellsts were found to be qute senstve for the cake texture evaluaton c b a Number of people c Bakng at 0 C Bakng at 225 C Bakng at 250 C Bakng at 275 C 0 Rank 1 Rank 2 Rank 3 Rank 4 Fgure 7: Sensory evaluaton performance of judges (24) for cakes. CONCLUSIONS A certan amount of leavenng s necessary to obtan an approprate volume expanson. Increasng the amount of leavenng agent dd not nfluence postvely the volume expanson. It resulted n some shape defect and surface color darkenng. A slght ncrease of the bakng temperature had a postve effect on the volume expanson but an mportant ncrease resulted n a decrease of the volume expanson. An elevaton of the bakng temperature resulted n a decrease of the average ΔE. A strong nteracton was found between bakng temperature and concentraton of leavenng as for ther effect not only on cake volume expanson but also on nstrumental analyss of the cake hardness. The sensory evaluaton of hardness was correlated to the nstrumental measurements. Expermental data of the volume expanson knetcs matched predcted volume expanson data for the frst ascendng part of the curve usng an n-house smplfed model. However, t was not possble to descrbe the entre volume expanson knetcs. REFERENCES [1] Babn et al. (04) X Ray Tomography Investgatons of Extruded Starches: Relatonshps between Process, Structure and Propertes. Poster presented at the 9 th Internatonal Conference on Engneerng and Food. March Montpeller. [2] Bak et al. (00a) Food Res. Intl. 33: 587. [3] Bak et al. (00b) Food Res. Intl. 33: 599. [4] Bloksma et al Wheat: Chemstry and Technology. Vol. II:131. [5] Campbell et al. (1999). Bubbles n Food. Eagan Press. St. Paul Mnnesota, USA. [6] Elmehd et al. (03). J. Cereal Sc. 38: [7] Fan et al. (1994) J. Food Eng. 23:337. [8] Fan et al. (1999). J. Food Eng., 41: 69. [9] Gbson, L.J., Ashby, M.F. (1997). Cellular Solds: Structure and Propertes. 2 nd Edton. Unversty Press. New York. [10] Kusunose C., Fuj T., Matsumoto H Role of starch granules n controllng expanson of dough durng bakng. Cereal Chemstry, 76(6), [11] Marcotte, M., Chen, C.R. 04. A Computer Smulaton Program for Cake Bakng n a Contnuous Industral Oven. Oral Presentaton. Sesson: 303/610 Mathematcal Modelng n Food Process Engneerng. 04 ASAE/CSAE Annual Internatonal Meetng. Ottawa, Ontaro. August 1-4. [12] Ramesh, N. S., Rasmussen, D. H., and Campbell, G. A. (1991). Numercal and expermental studes of bubble growth durng the mcrocellular process. Polym. Eng. Sc., 31 : [13] Scanlon and Zghal, 01. Food Res. Intl 34(10: 841. [14] Waterburton et al., J. Mater. Sc. 25:4001 [15] Weare, D.L., Hutzler, S. (1999). The Physcs of Foams. Clarendon Press. New York.

1 Basic concepts for quantitative policy analysis

1 Basic concepts for quantitative policy analysis 1 Basc concepts for quanttatve polcy analyss 1.1. Introducton The purpose of ths Chapter s the ntroducton of basc concepts of quanttatve polcy analyss. They represent the components of the framework adopted