PACKAGING TECHNOLOGY AND SCIENCE VOL 9 29-42 (1996)

The Effect of Ethanol and Oxygen Absorption on the Shelf-Life of Packed Sliced Rye Bread

A. Salminen,t K. Latva-Ka1a.S K. Randell,* E. Hurme,S P. Linkot and R. Ahvenainen*,S tHelsinki University of Technology, Department of Chemical Engineering, Laboratory of Biotech- nology and Food Engineering, FIN-021 50 Espoo, Finland; *VTT Biotechnology and Food Research, PO Box 1500, FIN-02044 VTT, Finland

The effect of ethanol emitters, 1% (v/v) ethanol-containing gases and oxygen absorbers on the shelf-life o f whole grain rye bread was investigated in t w o 6 week storage experiments. The bread slices (21 5 g) were packed in 500 ml plas- t i c containers with headspace volumes o f 240 ml. The biggest ethanol emitters (2 and 36) extended the microbial shelf-life of rye bread from 8-12 t o 26-27 days in the t w o experiments, and oxygen absorbers correspondingly t o the end o f the storage period (42 days). Small ethanol emitters (0.6 and 1 G) and 1% (v/v) ethanol-containing gases had no influence on the microbial shelf- life. Ethanol and oxygen absorbers had no effect on changes in texture and moisture during storage. The overall sensory quality of the samples without microbial growth was evaluated as rather good at the end o f the storage per- iod. The flavour of ethanol was discovered not t o prevent the use of ethanol for the preservation o f bread, since ethanol was detected only a f ew times in the panellist sensory evaluation

Keywords: ethanol emitter; oxygen absorber; active packaging; modified atmosphere packaging; bakery products; rye bread

INTRODUCTION

Rye bread has a very important role in the Finnish diet. The dietary fibre content of Finnish rye bread is high and in Finland the average daily intake of rye fibre was 6.5 g in 1990, comprising 50% of the total daily intake of cereal dietary fibre.' Recent studies suggest that consumption of wholemeal products from rye can have positive effects on human health by inhibiting hormone-related cancers via the lignans present in rye.* Finnish bakeries are interested in exporting rye bread, therefore, a longer shelf-life for rye bread is needed. Conventional preservation methods, like freezing and the use of additives, will preferably be replaced. *To whom correspondence should be addressed.

CCC 0894-3214/96/010029- 14 0 1996 by John Wiley & Sons, Ltd.

Received 5 November 199s Accepted 8 November 1995

30 A. SALMINEN ET AL.

The use of ethanol as a disinfectant in the medical field is well known.3 Similarly, it is well appreciated that the alcohol created during the preparation of fermented foods and drinks has a preservative function. However, it is only comparatively recently that the beneficial affects of the deliberate addition of low concentrations of ethanol as a means of preventing microbial spoilage, e.g. prolonging the shelf-life of packaged foods, has been recognized. The effect of ethanol as a preservative is based on etha- nol’s ability to lower water activity and function as an antimicrobial agent! Ethanol has been shown to extend the shelf life of many bakery products, for example pita breads, apple turnovers and Madeira It is also suggested that ethanol prevents staleness by delaying firming in flour-based product^.^ In recent years, the use of ethanol emitters in particular, from which ethanol vapour is released into the package headspace, has been studied.

Commercial oxygen absorbers remove the oxygen present in the headspace by chemical reaction.’ The anaerobic conditions created serve to inhibit the growth of aerobic microorganisms and prevent oxidative changes in the food during storage. Oxygen absorbers can maintain the residual oxygen level at 0.01 %, whereas vacuum and gas packaging rarely achieve a 0.5% level.’

In the literature, no research information regarding the effect of ethanol and oxygen absorbers on the shelf-life of rye bread is available. In the present study, the effects of ethanol and oxygen absorbers on the shelf-life of sliced wholemeal rye bread was investigated in two storage experiments.

MATERIALS A N D METHODS

Sample preparation and storage

The effect of ethanol emitters and oxygen absorbers on the shelf-life of rye bread was examined in two storage experiments. The wholemeal rye bread with whole grains (a, 0.94) was obtained from a commercial supplier (Fazer Oy, Vantaa) 1 day after baking. Ethanol emitters Antimold@ (Freund Industrial Co. Ltd, Japan) of size 0.6, 1 ,2 and 3 G and gases containing 1 % (v/v) ethanol (Oy Aga Ab, Espoo) in air or nitrogen were employed as an ethanol source. Ethanol emitters of sizes 0.6 and 2 G contained vanilla aroma, which was not noticed until the moment of packaging. Because of the limited amount of the ethanol emitters, part of the ethanol emitters had to be replaced with ethanol contained on cotton-wool in sachets. Sachets of PE film of size 3 x 4 cm were heat sealed and a piece of cotton wool was inserted into the sachet. Cotton wool for a 1 G ethanol emitter weighed 0.2 g on average, for a 2 G emitter 0.4 g and for a 3G emitter 0.6g. The amount of ethanol corresponding to the amount in Anti- mold@ ethanol emitters was added to the sachets before closing the bread containers. Oxygen absorbers ATCO@ (Standa Industrie, France) with an oxygen absorbing capacity of 100 ml were used in a portion of the samples to remove oxygen from packages. The samples in the storage experiments are listed in Table 1.

The bread slices were packed in HDPE containers (500 ml). Oxygen absorbers and ethanol emitters were placed on the uppermost bread slice and the packages were heat

RYE BREAD SHELF-LIFE 31

Table 1. Samples in storage experiments

Experiment Experiment 2

Sample Abbreviation Sample Abbreviation

Air-packed control Control Air-packed control 0.6 G ethanol emitter 0.6 G Oxygen absorber OA 1 G ethanol emitter 0.6 G ethanol emitter and 0.6 G + OA oxygen absorber

1 G ethanol emitter of cotton wool

2 G ethanol emitter of cotton wool 2 G ethanol emitter of cotton wool and oxygen absorber 3 G ethanol emitter of cotton wool Gas mixture of 1 % ethanol and 99% air Gas mixture of 1 % ethanol and 99% nitrogen

Control 1 G 1 G EE 2G 2G+OA

3 G l%+air

1%+N2

sealed with a PET/PE-PA-PE laminate cover using Dyno 462 VGA (Dyno, Germany). Samples packed in ethanol-containing gases were first vacuum packed and then flushed with the gas mixture. The packages contained 215 g of bread with a headspace volume of 240ml and were stored at 20°C and 50% RH for 6 weeks. For sensory evaluation, control bread slices were packed in PE pouches and frozen at -20°C. Before evaluation the bread slices were thawed at +5"C overnight.

During storage, samples were monitored for changes in microbial growth, head- space ethanol, 0 2 and C02 concentrations, moisture, texture and sensory quality. During the first 2 weeks of storage, quality of changes were monitored twice a week and during the rest of the storage once a week. Four packages of each sample were employed for the analysis mentioned for each quality check.

Microbial growth

Inspection for visible microbial growth on bread slices was done daily through the unopened packages. The microbial shelf-life was considered as the time period from packaging to the day when visible microbial growth was detected in any sample for the first time.

Headspace gas analysis

Headspace 0 2 and CO2 concentrations were checked throughout the storage with two parallel samples each time using new, unapplied packages, using Servomex 570 A (0, concentrations) and Servomex PA 404 (COz concentrations) gas analysers. Headspace ethanol content was analysed in experiment 2 with a gas chromatography HP 5870

32 A. SALMINEN ET AL.

equipped with a FID. The HP-FFAP column (25 m x0.32 mm) operated at 60°C with a helium flow rate of lml/min. Ethanol concentrations were reported as volume percent ages.

Moisture measurement

Bread slices were crushed by mixer and 5 g of crushed bread were added to a small vessel. Samples of two parallel packages were dried in an oven (130°C) for 1 h, after which they were cooled in an exicator. Moisture contents are given on a wet weight basis.

Texture measurement

TPA (Texture Profile Analysis) parameters, hardness and springiness, were measured by compressing the bread slices in a TA.XT2 Texture Analyser (Stable Microsystems, UK). Two bread slices were set one upon another under a compressor plunger of 20 mm diameter. They were compressed to 25% of their original height at a compres- sion speed of 1.7 mm/s. Ten bread slices of each sample were used for the measure- ments.

Sensory eva I uat i o n

Sensory quality was evaluated by a trained 10 member panel with proven skills. From each sample, half of the bread slices were served on white, odourless, disposable plates. The order of the samples was randomized, including the frozen control. In the second storage experiment, samples were evaluated in two sessions to avoid too many samples being evaluated in one session. Samples were scored for appearance, odour, flavour, texture and overall quality using a scale from 0 (unfit) to 5 (excel- lent). Samples with scores of <2 were regarded as unacceptable for sale, and with scores of < 1.5 unacceptable for human consumption. Panellists were also asked to describe any defects noticed in sensory quality. Scores were analysed by analysis of variance and where significant effects were detected the Newman-Keuls’ test was applied. Samples were evaluated until half of the samples had been spoilt by micro- organisms.

RESULTS AND DISCUSSION

The .biggest ethanol emitters (2 and 3G) and the oxygen absorbers significantly extended the microbial shelf-life of rye bread (Tables 2 and 3). In samples containing oxygen absorbers, no microbial growth was observed during the total storage period (42 days). In samples with ethanol emitters 2 or 3 G, microbial growth was observed

RYE BREAD SHELF-LIFE 33

~

Table 2. Effect of ethanol and oxygen absorption on visible microbial growth in bread during storage in experiment 1

The no. of microbiologically spoilt packageshhe total no. of packages

Storage period (days) Control (n = 43)t %

0.6 G (n = 43) %

OA (n=41) %

0.6 G + OA (n = 43) %

7 10 14 21 28 35 42 Shelf-life (days)

0/33 0 4/29 14

14/25 56 12/20 60 16/16 100 12/12 100 10/10 100

a

1/33 1/29 9/25

13/20 1511 6 11/12 1011 0

6

3 3

36 65 94 92

100

0/31 0 0.27 0 0/23 0 0.19 0 0/15 0 0/11 0

0.9 0 2 42

0/33 0 0.29 0 0/25 0 0.21 0 0.17 0 0.13 0 0/11 0 2 42

t n =original no. of packages

for the first time after 26 or 27 days of storage. The microbial shelf-life of the air- packed bread (control) was 8 days in experiment 1, and 11 days in experiment 2. In addition to this, the amount of microbially spoilt control samples increased more slowly in experiment 2 than in experiment 1. It is supposed that in experiment 2 circum- stances were not favourable for microbial growth, because of cool and dry winter weather during packaging. Small ethanol emitters and ethanol-containing gas mixtures did not improve the microbial shelf-life of bread as compared to control samples.

Headspace ethanol concentrations were highly correlated with the amount of ethanol added to the packages (Figure 1). After 2 weeks of storage the ethanol level was 0.30% (v/v) in packages containing a 3 G ethanol sachet, 0.22% (v/v) with a 2 G sachet and 0.15% (v/v) with a 1 G sachet. Ethanol concentrations in the control sample and in packages containing an ethanol gas mixture were around 0.08% (v/ v). Comparing samples containing a 2 G ethanol emitter and an oxygen absorber to 2G samples without an oxygen absorber, the oxygen absorber seemed to slow the secretion of ethanol into the package headspace at the beginning of the storage. In general, the final ethanol levels in the headspace were reached a week after packa- ging. Ethanol-containing cotton wool sachets were observed to operate as well as commercial ethanol emitters.

The ethanol concentration in bread slices was also estimated. It was presumed that all the ethanol was secreted from the ethanol emitter into the headspace and the bread slices. The total amount of ethanol in the headspace was only 1.5 mg in samples with the 3 G ethanol emitter while the total amount in a 3 G emitter is 1.65 g. Presuming the total ethanol amount is absorbed into the bread, the ethanol concentration of bread in packages containing a 3 G ethanol emitter should be 0.77%, with 2 G 0.51%, with 1 G 0.26% and with 0.6G 0.15%. The amount of ethanol inserted into packages with

Tab

le 3

. Eff

ect o

f et

han

ol a

nd

oxy

gen

ab

sorp

tio

n o

n v

isib

le m

icro

bia

l gro

wth

in b

read

du

rin

g s

tora

ge

in

exp

erim

ent

2 Th

e no

. of

mic

robi

olog

ical

ly s

poilt

pac

kage

slth

e to

tal n

o. o

f pa

ckag

es

__

~

Con

trol

1

G E

E 1

G

2G

2

G+

OA

3

G

l%+

air

1

%+

N2

(n

= 4

2)

(n =

42)

(n

= 4

2)

(n =

42)

(n

= 4

2)

(n =

42)

(n

= 4

2)

(n =

42)

S

tora

ge p

erio

d (d

ays)

%

%

%

%

%

%

%

%

7 10

14

21

28

35

42

She

lf-lif

e (d

ays)

0130

0

01

26

0

6/26

23

8/

21

38

6/17

35

8/

13

62

619

67

11

0/3

0

0

0130

0

01

26

0 01

26

0 1/

26

4 3/

26

12

6/21

29

6/

22

27

7/17

41

8/

18

44

6/13

46

7

/14

50

51

9 56

5/

10

50

13

7

0130

0

1/2

6

4 01

26

0

0/22

0

4/18

22

2/

13

15

21

8 25

26

0130

0

01

30

0

0124

0

01

26

0 01

26

0 01

20

0 01

26

0 01

26

0 3

/20

1

5

0.22

0

Of2

2 0

5/15

33

0/

18

0 1/

18

6 5/

11

45

0114

0

2/14

14

31

7 43

0.10

0 2/

10 2

0 21

4 50

< 4

2 27

1

2

0122

0

01

18

0

3/18

17

6/

14

43

6/10

60

41

6 67

21

3 67

13

P

RYE BREAD SHELF-LIFE 35

0.5

- 0.4 s h

a. Y

0.3 I. p 0.2

4 I 0.1

I - *.- .. I I.....

0.0 j I I I I I 1 I I I I

1 I I I , I I 1

0 4 8 12 16 20 24 28 32 36 40

Storage time (d)

-Control -..+-. 1 G

- - -& - - 1 % + & ...).. 2G -3G - -. - lGEEi

-A-- 1 % + N 2 - - E - 2G+OA

Figure 1 .Headspace ethanol concentrations during storage in experiment 2. Keys are explained in Table 1.

ethanol-containing gas mixtures was as low as 0.0045 g, which is < 1 % of the ethanol in a 1 G ethanol emitter.

In microbiologically spoilt samples, the headspace oxygen concentrations decreased and carbon dioxide concentrations increased up to 18% (v/v), due to micro- bial growth. In samples with an oxygen absorber, the oxygen concentration decreased to below the detection limit (0.1 %) within a few days of packaging.

Neither ethanol emitters nor oxygen absorbers had an influence on moisture and texture changes in rye bread during storage. The moisture content was maintained at N 40% throughout the storage period. The hardness increased from 2 to 5 kg during the 6 weeks of storage (Figure 2). In these experiments, ethanol was observed not to prevent hardening and thus staleness of the bread slices, in contrast to observa- tions by Vora and Sidhu" and Cencic et ul." for wheat bread. The opposite results may be due to different parameters used in texture measurements. The springiness increased only slightly during storage (Figure 3).

According to sensory evaluation, neither the amount of ethanol used nor the oxygen absorbers affected changes in the sensory quality of bread, as long as microbial spoilage was prevented (Tables 4 and 5). Impairment of sensory quality was most marked at the beginning of storage, after which the quality decreased slowly and steadily. The total sensory quality of rye bread packed with an oxygen absorber alone or in conjunction with ethanol emitters was evaluated with mean scores of 2.7-3.1

36

I

A. SALMINEN ET AL.

5.5

h

8 4.5

1 3 . 5

2.5

1.5

(b) 6.5

5.5

8 4.5 e 3.5

2.5

I

I , I I , I I I I I I I

I 1 I

0 4 8 12 16 20 24 28 32 36 40 Storage time (a)

--w- Control ~--+--- 0,6 G -..).. OA - +- -0.6 G + OA

1.5 0 4 8 12 16 20 24 28 32 36 40

S totpge ti me (a) ,-++- Control ...*.. 1G

- + - 1 % + a i r ...).. 2 G ...+.. 3G - - a - l G E E

--t 1 % + N 2 - - W - 2 0 + O A Figure 2. Effect of ethanol and oxygen absorption on the hardness of sliced rye bread during storage: (a) experiment 1 and (b) experiment 2. Keys are explained in Table 1.

RYE BREAD SHELF-LIFE 37

-n- Control --c- 0,6 G -. .m -. OA - + -0.6 G + OA

38 A. SALMINEN ET AL.

Table 4. The effect of ethanol and oxygen absorption on the sensory quality of sliced rye bread during the storage (Experiment 1 ) Sample Storage time (days)

1 3 7 10 15 21 28 35 42

(a) Appearance Frozen R 4.9 4.0 4.5 4.0 3.9

SX 0.2 1.2 0.6 0.4 0.7 X 4.9 4.1 4.3 3.8 3.7

control Control

S X 0.2 0.9 0.9 0.9 0.7 0.6 G P 5.0 4.1 4.4 3.9 3.8

SX 0.1 1.2 0.5 0.4 0.9 OA X 4.9 4.3 4.2 3.8 3.9

SX 0.2 0.8 0.8 0.5 0.7 0.6 G + OA X 5.0 4.3 4.2 3.9 3.7

S X 0.1 0.8 0.7 0.6 0.8

3.9 0.7

3.8 0.7

4.2 3.9 0.6 0.8

3.9 1 .o 3.8 0.7

3.6 0.6 3.4 0.6

3.8 3.4 0.6 0.7 3.7 3.5 0.9 0.5

Frozen X 4.8 3.8 4.0 (b) Odour

SX 0.3 1 .o 0.6 X 4.7 3.9 3.8

control Control

3.6 3.6 0.7 0.8 3.6 3.6 1 .o 0.5 3.5 3.3 0.5 0.6 3.5 3.5 0.5 0.5 3.6 3.6 0.8 0.6

3.6 0.7

3.1 1.3

3.9 3.5 0.8 0.8

SX 0.5 0.8 0.7 0.6 G X 4.7 3.8 3.8

SX 0.5 1 .o 0.6 OA R 4.9 4.0 3.8

SX 0.3 0.9 0.8 0.6 G + OA R 4.8 3.8 3.8

SX 0.4 1.2 0.6

3.6 0.6 3.5 0.5

3.6 0.7 3.3 0.7

3.6 3.3 0.7 0.8 3.6 3.5 0.9 0.5

(c) Taste Frozen P 4.9 4.2 4.0 3.7 3.9

SX 0.2 0.7 0.6 0.6 0.8 X 4.9 4.1 3.8 3.5 3.4

control Control

SX 0.1 0.7 0.5 0.9 0.8 0.6 G X 4.9 4.0 4.0 3.6 3.3

SX 0.3 0.9 0.6 0.70 0.6 OA X 5.0 4.2 3.7 3.6 3.4

SX 0.1 0.6 1.1 0.6 0.7 0.6 G + OA R 4.9 4.1 3.5 3.5 3.4

SX 0.2 0.7 0.8 0.8 0.6

Frozen X 4.9 4.0 4.1 3.8 3.9 (d) Texture

control SX 0.2 1.1 0.8 0.8 0.8 Control R 5.0 3.9 3.8 3.6 3.2

SX 0.1 0.8 0.5 0.9 0.5 0.6 G R 4.9 3.8 4.0 3.7 3.5

3.6 3.1 4.0A 3.8 0.8 1.3 0.4 0.9

3.4 3.4 3.1b 3.2 0.5 0.6 0.7 0.5

0.5 0.6 0.5 0.3 3.5 3.3 3.4b 3.4

4.1 a 3.0a 0.6 0.7

4.0a 4.1a 0.8 0.9

S X 0.2 1 .o 0.7 0.7 0.7 OA R 5.0 4.1 4.1 3.7 3.5 3.1b 3.18b

0.4 0.7 3.4b 3.08b 0.5 0.8

3.1b 2.7b 0.7 0.9 3.3b 2.gb 0.6 0.6

SX 0.2 0.9 0.9 0.6 0.8 0.6 G + OA X 5.0 4.1 3.6 3.8 3.3

SX 0.1 1.2 0.7 0.8 0.6

Frozen X 4.8 3.9 4.0 (e) Overall quality

control SX 0.2 1 .o 0.7 Control R 4.8 3.9 3.7

SX 0.2 0.7 0.6 0.6 G X 4.7 3.8 3.9

SX 0.4 0.9 0.6 OA R 4.9 4.2 3.5

SX 0.2 0.6 1 .o 0.6G + OA X 4.9 4.2 3.5

SX 0.2 0.6 0.7

-

3.6 3.7 3.6 3.1 3.ga 3.7a 0.6 0.7 0.7 1.2 0.6 1.0 3.5 3.3 1 .o 0.5 3.6 3.3 0.5 0.6 3.4 3.3 3.2 3.1 3.0b 2.9"9b 0.5 0.5 0.5 0.5 0.6 0.7 3.4 3.3 3.4 3.2 3.1 3.1 0.7 0.7 0.4 0.6 0.5 0.3

Asterisks denote samples were not evaluated by the sensory panel because of visible microbial growth. Different letters (a-b) indicate significant statistical differences (p < 0.05) between samples on the same evaluation day. Sample codes are ex- plained in Table 1.

RYE BREAD SHELF-LIFE 39

Table 5. The effect of ethanol and oxygen absorption on the sensory quality of sliced rye bread during the storage (Experiment 2) Sample Storage (days)

2 7 14 21 28 35 42

Frozen control Control

1 G EE

1G

2G

2G+OA

3G

1%+N2

l%+air

X

SX X

3.9 0.9 4.0 0.9 3.9 1 .o 4.0 0.8 3.9 0.9 3.7 0.9 4.0 0.9 4.0 0.9 4.1 0.8

3.9 0.6 4.0 0.7 4.2 0.5 4.0 0.8 4.2 0.5 4.1 0.7 3.9 0.8 4.1 0.7 4.2 0.8

3.9 0.8 3.9 0.6 3.8 0.6 3.8 0.6 3.8 0.8 4.0 0.6 4.0 0.7 3.9 0.5 3.8 0.6

3.3 1.1

~

3.7 0.6

2.ga 0.8

3.3 1 .o

SX

sx X

X

3.6b 0.6 3.6b 0.4

0.6 3.7b

3.5 0.7

3.5 0.6

3.2 0.6

3.7 0.7 3.6 0.7

3.7 0.8

3.6 0.5 3.4 0.7

3.6 0.9

(b) Odour Frozen control Control

1 G EE

1G

2G

2G+OA

3G

1%+N2

l%+air

4.1 0.5 4.0 0.6 3.6 0.7 4.0 0.7 3.9 0.7 3.8 0.7 3.8 0.6 4.0 0.6

0.6 3.8

4.0 0.4 3.8 0.6 3.9 0.8 4.1 0.8 4.0 0.3 3.5 0.6 3.5 0.8 3.9 0.8 3.9 0.8

3.9 0.8 3.9 0.4 3.4 0.6 3.6 0.8 3.7 0.5

R SX x SX R

3.7 0.5

3.8 0.6

3.8 0.8

3.5 0.8

SX X

3.4 0.7

3.3 0.7

3.5 0.8 3.4 1.1 3.4 0.9

2.8 0.7

3.2 0.6

3.1 0.5

3.2 0.6

2.8 0.9

3.6 0.6 3.6

3.4 0.5

3.3 0.8

3.3 1 .o

0.5 3.7 0.5

SX x SX

(c) Taste Frozen control Control

1 G EE

4.0 3.7 0.6 0.4 4.1 3.6 0.5 0.6 3.8 4.0 1.2 0.8 3.8 3.9 1 .o 0.8 4.0 3.7 0.7 0.6 3.7 3.7 0.7 0.4 3.6 3.4

3.7 0.7

0.4 3.6 0.6 3.7 0.6 3.8 0.5 3.4

3.8

3.8

0.8

3.5 0.7

3.7 0.8

3.7 3.4 0.3 0.7

1G

2G

2G+OA

3G

3.2 0.9

2.8 0.4 3.0 0.5 3.1

3.2 3.0 0.8 0.7 3.4 2.8 0.9 0.9 3.2 3.2

3.1 0.6 3.2

SX 0.9 0.7 0.7 0.6 0.7 0.8 1 .o 1%+N2 x 3.9 3.8 3.5

SX 0.9 0.9 0.6 l%+air x 3.9 3.8 3.6

SX 0.8 0.8 0.6

40 A. SALMINEN ET AL.

Table 5 continued

X 4.1 3.8 3.7 3.6 3.7' 3.7 3.6 (d) Texture Frozen control Control

1 G EE

1G

2G

2G+OA

3G

1%+"2

l%+air

SX R SX x SX X

SX ii SX R SX

SX ii

X

SX ii SX

0.8 3.8 0.7 3.9 1 .o 4.0 0.8 3.9 0.9 3.8 0.9 3.9 0.8 3.8 0.8 3.9 0.9

0.5 3.8 0.5 4.0 0.7 3.9 0.8 4.0 0.4 3.9 0.5 3.6 0.7 3.9 0.8 3.9 0.6

0.9 3.8 0.8 3.4 0.7 3.8 0.4 3.7 0.6 3.7 0.5 3.8 0.6 3.4 0.5 3.6 0.5

0.8

3.3 0.4 3.3 0.3 3.2 0.6

0.8

2.8b 0.4 3.0b 0.5 3.1 a,b 0.7

0.4

3.0 0.8 3.4 0.9 3.1 0.7

0.6

2.8 0.6 2.9 0.8 3.1 1.3

(e) Overall quality Frozen R control SX Control X

SK 1 G EE R

SK 1G x

SX 2G R

SX 2G+OA x

S X

3G R

3.9 0.8 3.9 0.6 3.6 1.1 3.9 0.8 3.8 0.9 3.7 0.8 3.8

3.7 0.4 3.7 0.6 3.9 0.8 3.8 0.9 3.8 0.4 3.6 0.6 3.3

3.6 0.7 3.6 0.6 3.4 0.5 3.7 0.4 3.6 0.6 3.3 0.6 3.7

3.3 3.5' 3.6 3.4 0.5 0.6 0.5 0.7

3.2 2.gb 3.1 2.9 0.6 0.3 0.7 0.6 3.2 3.0b 3.3 2.7 0.5 0.5 0.9 0.8 3.2 2.gb 3.1 3.0

SX 0.7 0.8 0.7 0.5 0.5 0.7 1.1 1%+N2 R 3.8 3.7 3.5

SX 0.8 0.9 0.4 l%+air X 3.8 3.7 3.6

S X 0.6 0.7 0.6

Asterisks denote that samples were not evaluated by the sensory panel because of visible microbial growth. Different letters (a*b indicate significant statistical differences (P < 0.05) between samples on the same evaluation day. Sample codes are explained in Table 1.

after 6 weeks of storage (Table 4e). For overall quality, stored samples without visible microbial growth differed statistically from the frozen control sample in experiment 1 only during the last two evaluations (35 and 42 days) and in experiment 2 a month after packaging (Tables 4e and 5e).

Panelists detected the flavour of ethanol in very rare cases, although the flavour of ethanol is often considered to prevent its use for food products. According to Seiler? at ethanol concentrations of > 2.0%, the alcoholic flavour is likely to be noted. In these experiments, the maximum ethanol concentration of the bread, if all ethanol has been secreted from the emitter to the bread, was 0.77%. The critical factor for sensory quality was rather the characteristics resulting from staleness, like hardening and loss of moistness. After 2 weeks of storage, breads were often described as dry and hard. Also, according to scores, texture was evaluated as the poorest quality property (Tables 4d and 5d). No anti-staling effect of ethanol was observed in sensory

RYE BREAD SHELF-LIFE 41

evaluation: changes in texture took place whether ethanol was added or not. Vanilla aroma was mentioned only a few times by the panelists.

The comparative poor quality of the frozen bread was considered to be due to the unsuitability of rye bread of this type for freezing: the edges of the bread darkened, flavour richness was lost and the texture of the bread crumbled. Taste and odour migration from the plastic bag into the bread during freezing also impaired the quality of the control bread.

CONCLUSIONS

The shelf-life of rye bread was extended considerably using ethanol emitters and oxygen absorbers. The shelf-life of bread stored with small ethanol emitters was restricted by microbial spoilage, while in the case of oxygen absorbers and the biggest ethanol emitters, the shelf-life was restricted because of the loss of sensory quality of the bread. The size of ethanol emitters was observed to be an important factor for preservation: the bigger the size of the emitter, the more reliably the shelf-life of the bread was extended. Oxygen absorbers prevented microbial spoilage without excep- tion in either of the bread types. Whether or not ethanol emitters prevent microbial spoilage reliably without use in conjunction with oxygen absorbers in the case of rye bread cannot be determined from the results of this study. Examination with bigger ethanol emitters is needed. Additionally, further studies with longer storage times are needed in order to determine if oxygen absorbers and ethanol emitters have any synergistic effect. The optimal size of the headspace volume when using ethanol emitters and oxygen absorbers should also be examined.

On the strength of texture measurements and sensory evaluation, ethanol was observed to have no anti-staling effects on bread. It is probable that the use of ethanol emitters and oxygen absorbers hold potential benefits, especially for products which go stale slowly and which have a naturally rather strong flavour.

The use of ethanol-containing gases did not prove to be an advantageous method because gas mixtures with an ethanol concentration > 1% were not available: the ethanol concentration of the gas mixtures was too low to have any positive influence on the shelf-life of the bread. Because of only a 1 atm pressure in the gas bottles, the use of ethanol-containing gas mixture was troublesome, and packaging was costly.

Acknowledgements

We wish to thank the group responsible for the arrangement of the sensory evaluations and Ms Heli Nykanen for her help in the packaging procedure. We also wish to thank Freund Industrial Co. Japan for the Ethicap samples and Fazer Oy Finland for the bread.

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42 A. SALMINEN ET AL.

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