Eur Food Res Technol (2003) 218:44–48DOI 10.1007/s00217-003-0818-9

O R I G I N A L P A P E R

E. Gallagher · A. Kunkel · T. R. Gormley ·E. K. Arendt

The effect of dairy and rice powder addition on loafand crumb characteristics, and on shelf life (intermediateand long-term) of gluten-free breads stored in a modified atmosphereReceived: 29 July 2003 / Published online: 25 October 2003� Springer-Verlag 2003

Abstract Many commercially available gluten-freebreads are inferior in quality to their gluten-containingcounterparts. They also have a relatively short shelf life.The current study investigated the effects of 3% milkprotein isolate and 3% novel rice starch addition to agluten-free bread formulation, and on the intermediate(8 days) and long-term (43 days) staling profile of bothgluten-free bread formulations, packed in an 80%CO2\20% N2 atmosphere. Dairy protein and rice starchaddition increased loaf volume and the loaves werepreferred to a control sample by an untrained panel. Themost notable changes in crumb hardness occurred in theearly days of the testing periods for the control gluten-freebread in both the intermediate and long-term studies.

Keywords Gluten-free bread · Loaf volume · Imageanalysis · Staling · Modified atmosphere

Introduction

Coeliac disease, or in the U.S., celiac disease, is acondition where the sufferer’s body reacts to the proteinfraction gluten [1]. The avoidance of wheat, rye, barleyand oats and all products made from these grains is theonly treatment for coeliac disease [2]. Treatment with agluten-free diet results in significant improvement of theintestinal mucosa and its absorptive function. Gluten is

the main structure-forming protein in flour, responsiblefor the elastic and extensible properties needed to producegood quality bread. Currently, many gluten-free breadsavailable on the market are of a low quality, exhibiting adry crumbling crumb, resulting in poor mouthfeel andflavour [3].

The incorporation of dairy ingredients is long estab-lished in the baking industry [4, 5]. Dairy proteins arehighly functional ingredients, and can be readily incor-porated into many food products. They may be used inbread for both nutritional and functional benefits includ-ing flavour and texture enhancement, and storage im-provement [6, 7, 8]. Dairy powders used in gluten-freebread formulations resulted in improved volume, appear-ance and sensory aspects of the loaves [3].

The shelf life of bread is mainly influenced by loss ofmoisture, staling and microbial deterioration [9]. Of these,staling is the main shelf life-limiting factor. The bread-making process, including dough recipe, method ofmixing and proofing, temperature of the dough duringbaking, and the final packaging, affect staling of breadloaves. The actual staling mechanism is complex; crumbfirmness increases, the crust becomes softer, and thebread loses its fragrance, assuming a stale flavour [10].The retrogradation of starch is significantly involved inthe staling process, whereby changes in the amylopectinwithin the starch granule occur over time. However, it hasbeen widely documented that bread firming is notsynonymous with starch recrystallisation; it has beensuggested that bread firming may be due to starch gluteninteractions, where gluten is crosslinked by gelatinisedstarch [11, 12]. It has been cited that changes in thefirming rate of bread are due to hydrogen bondingbetween gluten and starch granules. In one study, breadsbaked from lower (10.4%) protein flours staled at a fasterrate than those from higher (13.1%) protein flours, and itwas concluded that the flour component primarilyresponsible for the shelf life of bakery products was, infact, gluten [13].

Many authors have reported the staling characteristicsof white wheat bread stored under modified atmosphere

E. Gallagher ()) · T. R. GormleyTeagasc, The National Food Centre,Ashtown, Dublin 15, Irelande-mail: egallagher@nfc.teagasc.ieTel.: +353-1-8059500Fax: +353-1-8059550

A. KunkelUniversity of Applied Sciences, Nutrition,Food Business and Home Economics, Fulda, Germany

E. K. ArendtDepartment of Food Science, Technology and Nutrition,National University of Ireland, Cork, Ireland

conditions. Knorr and Tomlins (1985) [14] and Avital etal. (1990) [15] found that white wheat bread stored in aCO2 atmosphere over 10–14 days had a softer crumb thanbread stored either in N2 or in atmospheric air. Rasmussenand Hansen (2001) [16] found that packaging in atmo-spheres with increased levels of CO2 did not affect thestaling rate of white bread and used their results as a basisfor extending the microbial shelf life of bread withoutaffecting the staling rate.

Little published work is available on the staling profileof gluten-free breads, stored either in air or in a modifiedatmosphere. It is only in recent years that the prevalenceof coeliac disease, and the need for research anddevelopment on the quality of gluten-free products hasbeen identified [17]. It has also been stated that glutenpresent in wheat bread slows down the movement ofwater by forming an extensible protein network, thuskeeping the crumb structure together [18]. Therefore, theabsence of gluten should increase the movement of waterfrom the bread crumb to crust, resulting in a firmer crumband a softer crust. The objective of the present study wastwofold: (1) to study the effects of addition of 3% milkprotein isolate and 3% rice starch to a wheat-starch-basedgluten-free bread formulation, and (2) to examine theintermediate (8-day) and long-term (43-day) stalingprofile of both gluten-free bread formulations, packed inan 80% CO2\20% N2 atmosphere.

Materials and methods

The control gluten-free formulation contained commercial wheatstarch (Codex Alimentarius) gluten-free flour (Odlum Group,Dublin, Ireland), fresh yeast (Yeast Products, Dublin, Ireland),vegetable oil (Crest Foods Ltd., Dublin, Ireland) and DATEM(Quest Ingredients, Holland). In the trials this was supplementedwith a dairy powder (3%) (milk protein isolate) obtained fromKerry Ingredients (Listowel, Co. Kerry, Ireland), and 3% of a novelrice starch obtained from Leckpatrick Dairies (Strabane, Co.Tyrone, Northern Ireland). The batter recipe (based on flourweight) was 100% gluten-free flour, 87% water at 35 �C, 2.7%fresh yeast, 1% oil and 0.5% DATEM. The blended liquidingredients were added to the dry ingredients and mixed for atotal of 3.5 min in a three-speed mixer, (Model A120, Hobart, UK);450 g of batter was scaled into 1-lb tins and placed in a proofer for45 min (40 �C, 80% RH). The batter was baked at 230 �C for25 min in a reel oven (Henry Simon, UK). The loaves were cooledto room temperature and placed in polyethylene bags. They werethen packed in an atmosphere of 80% CO2\20% N2 using an A300CVP packaging machine (CVP Systems Ltd., UK) and left at roomtemperature until tested. The test breads are referred to as CRDbreads [i.e. control formula (C) supplemented with rice starch (R)and dairy powder (D)] for convenience in this paper.

Tests on the loaves

For each analysis, three loaves from each batch were used. Specificvolume was measured using rapeseed displacement. Crust andcrumb colour was measured using a Minolta Chromameter(Minolta CR-100, Osaka, Japan). L*, a*, b* and L*/b*, wererecorded, each value being the average of six measurements. Crust(penetration, cylindrical probe; 6 mm diameter) and crumb (textureprofile analysis, cylindrical probe; 20 mm diameter) characteristicswere assessed using a texture analyser (TAXT2i, Stable Micro

Systems, Surrey, UK). Loaf moisture was measured by the AOACtwo-stage drying method.

Images of the sliced breads were captured using a flatbedscanner (Sharp, JX-330, Japan). The images were scanned full scaleat 300 dots per inch and analysed in grey scale. A 60�60-mmsquare field of view (FOV) was evaluated for each image. ThisFOV captured the majority of the crumb area of each slice. Twelvedigital images were processed and analysed for each batch, giving atotal of 60 images. Image analysis was performed by the methoddescribed by Crowley et al. (2000) [19].

Two paired comparison assessments (sessions 1 and 2) wereconducted by taste panels on the control and CRD breads. One loaffrom each batch was kept whole while the second loaf was cut intoslices. This allowed the panellists to assess the volume, colour andappearance of the crust and the crumb (session 1), and then to eat thebreads and rate them for overall preference (session 2). Thepanellists were untrained and 13 males and 17 females took part ineach session. The samples were uniform in size, were served at roomtemperature, and were randomly presented with three-digit coding.

(a) Intermediate-term analysisTesting took place on days 0 (day of baking), 2, 4 and 8. Thetrials were replicated three times [2 breads (control andcontrol+rice starch+dairy powder [CRD])x4 testing daysx3replications].

(b) Long-term analysisTesting took place on days 0, 9, 23 and 43. The trials werereplicated three times [2 breadsx4 testing daysx3 replications].

Results were analysed using one way analysis of variance(ANOVA) using SAS (Version 6.12, SAS Institute Inc., Cary, NC,USA) as 2 treatmentsx4 testing days (for both intermediate andlong-term trials)x3 replicates.

The visual assessment and taste panel responses were analysedaccording to British Standard Methods for sensory analysis of food(1982) [20].

Results and discussion

Effects of rice starch and diary powder additionon the baking characteristics of gluten-free breads

Loaf volume

Addition of rice starch and dairy powder resulted in anincrease in loaf volume. However, the effect was notsignificant when compared to the control (975 versus1,101 cm3). Similar increases due to dairy ingredientaddition in a wheat bread formulation have also beenfound [6, 21, 22]. It should be noted, nonetheless, that thegluten-free breads with the additional ingredients (CRD)in the current study had a better external appearance, andresembled wheat-bread loaves more closely than thegluten-free control. Conflicting opinions have been citedas to the relevance of loaf volume on the rate of staling ofbread loaves. Axford et al. (1968) [22] concluded that alower specific volume increased the staling rate. However,Pronte et al. (1962) [23] found no significant correlationbetween bread staling rate and bread volume. Loavesbaked in larger loaf tins were initially softer and remainedsofter during storage than loaves baked in smaller tins, butthe staling rates were essentially the same [13].

45

Crust and crumb colour

The CIE L* values gives a darkness to lightness indicatorfor products (0=black, 100=white). The CRD loaves hadlower crust L* values than the control (Fig. 1, P<0.01).This is to be expected as the dairy powder contained asmall amount of lactose, which was involved in Maillardbrowning and caramelisation reactions; these reactionsare influenced by the distribution of water and thereaction of reducing sugars and amino acids [24], thusresulting in a darker crust colour. Crumb colour (L*, L*/b*) was not significantly influenced by either dairypowder or rice starch addition.

Image analysis/visual assessment/sensory analysis

Examples of images from each bread type (control; CRD)are shown in Fig. 2. The total number of cells decreased(P<0.05) with addition of the powders to the gluten-freeformula. (1583-control versus 1229-CRD). Thus thenumber of cells/cm2 was 44.0 (control) and 34.1 (CRD).The results for the CRD loaf were similar to those foundby Crowley et al. (2000) [19] in studies with wheat breadloaves, in that the number of small cells in the range 0.05–4 mm2 decreased by approximately 25% after addition of

the dairy and rice powders (1358 versus 1006, P<0.05).The CRD loaves had a more open structure, compared tothe typical cake-like tight structure/appearance of somegluten-free breads.

In the visual assessment, the overall preference was forthe CRD loaves (P<0.01). Panellists commented that thisbread “looked more like real bread”, that the crumb was“more even and more airy than the control”, and that theloaves had “better volume and crust colour, like wheatbread”. Of the 30 assessors in the tasting trial, 16 showeda preference for the CRD, and 14 for the control, i.e. nosignificant difference was found.

Effects of rice starch and diary powder addition,and MAP (80% CO2, 20% N2) on the intermediateand long-term shelf life of gluten-free breads

Crust and crumb texture

Movement of water from crumb to crust over the testingperiods was apparent (i.e. crust hardness decreased, whilecrumb texture became harder). The CRD loaves had asofter crust on day 0 than the control (P<0.05), andthereafter throughout the 8-day staling trial (Fig. 3).

Fig. 1 Influence of rice starch (R) and dairy powder (D) additionon the crust colour (L*) of gluten-free breads

Fig. 2 Sample images of60�60-mm field of view ofgluten-free breads. A Controland B control with rice starchand dairy powder added (CRD)

Fig. 3 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crust hardness ofgluten-free breads stored over an 8-day period

46

However, the rate of decrease of crust hardness waslargely unaffected by the addition of the rice starch anddairy powder, i.e. these loaves remained softer than thecontrol, but staled at a similar rate. An overall significantdecrease in crust hardness (P<0.01) was found for theintermediate and long-term trials for these breads. Withinthe modified atmosphere package, it appeared that crusthardness reached a minimum after 2 days, and furthertesting beyond this revealed no significant changes to thecrusts of either the control or the CRD loaves (Fig. 4).

The most notable changes in crumb characteristics, i.e.hardness (P<0.001) and springiness (P<0.005) occurredduring the first 23 days of the testing period for bothgluten-free bread formulations in the intermediate and

long-term staling studies (Figs. 5 and 6). The hardnessvalues were lower for the CRD loaves (P<0.05), but nosignificant difference was found for the rate of stalingbetween the two formulations. Between days 0 and 9,crumb hardness increased linearly with time (P<0.001)reaching a maximum value after 23 days, and nosignificant increase occurred between testing days 23and 43 (Fig. 6). These findings agree with those ofRasmussen and Hansen (2001) [16], where maximumcrumb firmness of MAP wheat bread was attained at35 days.

No significant differences were found for crumb springfrom the two formulations, and the trends were similarover the intermediate and long-term testing periods(Figs. 7 and 8). Crumb spring decreased (P<0.001)between days 0 and 9, but no further changes in crumbspring occurred thereafter. (It should be noted that nomould was present at the end of the 43-day testingperiod.)

A negative correlation was found between loaf volumeand crumb hardness (R2=0.76). This signifies that smallerloaves (as in the case of the control) were more dense andhad a tightly packed crumb structure, resulting in highercrumb hardness readings. Similar findings were obtainedby Axford et al. (1968) [21] in wheat breads.

Fig. 4 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crust hardness ofgluten-free breads stored over a 43-day period

Fig. 5 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crumb hardness ofgluten-free breads stored over an 8-day period

Fig. 7 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crumb spring of gluten-free breads stored over an 8-day period

Fig. 8 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crumb spring of gluten-free breads stored over a 43-day period

Fig. 6 Influence of rice starch (R) and dairy powder (D) addition,plus modified atmosphere packaging on the crumb hardness ofgluten-free breads stored over a 43-day period

47

Conclusions

The addition of milk protein isolate and a novel ricestarch to a gluten-free bread formulation resulted inloaves with an increased volume and better appearanceand acceptability than the control. These loaves also hadsofter crust and better crumb characteristics but ultimate-ly, loaves from both formulations staled at a similar rate.The most notable changes to crust characteristics occurredwithin the first 9 days. Peak crumb hardness values wereattained between days 23 to 43; however, no statisticallysignificant change was found between the day 23 and day43 values.

References

1. Cooke WT, Asquith P (1974) Clinics in gastroenterology. WBSaunders, London, pp 3–9

2. Taylor SL (1999) Prospects for the future: Conference onInternational Food Trade Beyond 2000: Science-Based Deci-sions, Harmonization, Equivalence and Mutual Recognition,Melbourne, Australia, pp 11–15

3. Gallagher E, Gormley TR, Arendt, EK (2003) J Food Eng56:153–161

4. Stahel N (1983) Cereal Foods World 28:453–4545. Zadow JG, Hardham JF (1981) Aust J Dairy Technol 36:60–63

6. Kenny S, Wehrle K, Auty M, Arendt EK (2001) Cereal Chem78:458–463

7. Mannie E, Asp EH (1989) Cereal Foods World 44:143–1468. Cocup RO, Sanderson WB (1987) Food Technol 41:102–1049. Willhoft EMA (1971) J Sci Food Agric 22:176–180

10. Schiraldi A, Fessas D (2001) In: Chihachoti P, Vodovotz Y(eds) Bread staling. CRC Press, New York, pp 1–17

11. Martin ML, Zelenak KJ, Hoseney RC (1991) Cereal Chem68:498–502

12. Martin ML, Zelenak KJ, Hoseney RC (1991) Cereal Chem68:503–507

13. Maleki M, Hoseney RC, Mattern PJ (1980) Cereal Chem57:138–140

14. Knorr D, Tomlins RI (1985) J Food Sci 50:1172–117315. Avital Y, Mannheim CH, Miltz J (1990) J Food Sci 55:413–41616. Rasmussen PH, Hansen A (2001) Lebens Wiss Techol 34:487–

49117. Fasano A, Catassi C (2001) Gastroenterol 120:636–65118. Roach RR, Hoseney RC (1995) Cereal Chem 72:578–58219. Crowley P, Grau H, Arendt EK (2000) Cereal Chem 77:370–

37520. Erdogdu-Arnoczky N, Czuchzjowska Z, Pomeranz Y (1996)

Cereal Chem 73:309–31621. Kadnahrmestan C, Baik BK, Czuchajowska Z (1998) Cereal

Chem 75:762–76622. Axford DWE, Colwell KH, Cofor JJ, Elton JAH (1968) J Sci

Food Agric 19:9523. Pronte JG, Titcomb ST, Cotton RH (1962) Cereal Chem 39:43724. Kent NL, Evers AD (1994) Technology of cereals. Pergamon,

Oxford, p 215

48