SHELF-LIFE STABILITY OF OAT GROATS

PROCESSED WITH SUPERHEATED STEAM D. Head1, S. Cenkowski1, S. Arntfield2 K. Henderson3

1Biosystems Engineering, UofM, Winnipeg, MB 2Food Science, UofM, Winnipeg, MB 3Can-Oat Milling, Portage la Prairie, MB

Presentated at the CSBE/SCGAB 2008 Annual Conference Vancouver, BC, July 13 - 16, 2008

Oats are heat processed

• to enhance stability (high lipid content, 5-7%)• to develop characteristic flavour

Routine industrial process includes:

•Roasting, steaming and drying to

inactivate the fat splitting enzymes

Roasting at 88-115C for 90-104 min (up to 80% inactivation)then steaming at 100-104C for 8-10 min

Grain is dried and…processed toCommercial products (flour, bran, rolled oats)

Limiting factors for storage and handling

• Degradation of lipids via enzymatic hydrolysis followed by oxidation leading to rancidity and off-flavours development

• Prevention:– Hydro-thermal inactivation of the lipolytic enzymes– The kiln drying operation is difficult to control, lengthy and

not energy efficient– Risk of grain cross-contamination with microorganisms

present in the air used for cooling of the grain after kiln drying

• Superheated steam drying and processing is an attractive technology offering variety of advantages over the kiln drying

Objective

• to determine the shelf-life stability of oat groats processed with the optimum superheated steam

parameters and stored at 21C

Optimum SS processing conditions were established in previous studies:

• steam temperature of 110C• steam velocity of 1 m/s• processing time of 10 and 14 min

Materials and methods

• Groats standard kilned at a commercial plant A and B• SS processed groats at 110C at 1m/s for 10 and 14 min

(SS10 and SS14)• Storage at 21C for 6 months+ and measured:

– Moisture content– Pasting viscosity at 64C (Rapid Visco Analyzer)– Hexanal and free fatty acids content– Sensory evaluation (flavour: oaty, toasted, raw, bitter, rancid)– Color determination (L, a, b values)

Results

3000

4000

5000

6000

7000

0 30 60 90 120 150 180 210 240 270 300 330 360 390

Storage Time (days)

Fin

al V

isco

sity

at 6

4o C (

cP)

Plant APlant B

SS10SS14

Fig. 1 Storage time effect on the final viscosity (at 64C (commercial plant A & B) or processed with superheated steam (SS)

Storage at 21CCommercial plants

110C, 10min and 14 min

Plant A

Plant B

0

2

4

6

8

10

12

0 30 60 90 120 150 180 210 240 270 300 330 360 390

Storage Time (days)

Moi

stur

e C

onte

nt (

% w

b)

Plant A

Plant B

SS10

SS14

Fig. 2 Moisture content of oat groats processed commercially (Plant A and B) or with SS at 110C and 1 m/s for 10 and 14 min.

Storage at 21C

Commercial plants

110C, 10min and 14 min

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 30 60 90 120 150 180 210 240 270 300 330 360

Storage Time (days)

Fre

e F

atty

Aci

ds (

g/10

0g f

at)

Plant APlant BSS10SS14

Storage at 21C

Fig. 3 The effect of storage time on free fatty acids content of oat groats processed commercially or with superheated steam (SS) at 110C

Commercial plants

110C, 10min and 14 min

0

1

2

3

4

5

6

7

8

9

0 30 60 90 120 150 180 210 240 270 300 330 360

Storage Time (days)

Hex

anal

(pp

m)

Plant APlant BSS10SS14

Fig. 4 The effect of storage time on level of hexanal released from oat groats processed commercially (Plant A and B) or with superheated steam (SS) at 110C

Commercial plants

110C, 10min and 14 min

Storage at 21C

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

Storage Time (days)

Sen

sory

Scr

ore

(0-1

0)

Plant APlant BSS10SS14

Oaty Flavour

Storage at 21C

Fig. 5 The effect of storage time on intensity of oaty flavour of oat groats processed commercially or with superheated steam (SS) at 110C

Commercial plants

110C, 10min and 14 min

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

Storage Time (days)

Sen

sory

Sco

re (

0-10

)

Plant APlant B

SS10SS14

Toasted Flavour Commercial plants

110C, 10min and 14 minStorage at 21C

Fig. 6 The effect of storage time on intensity of toasted flavour of oat groats processed commercially or with superheated steam (SS) at 110C

0.0

0.4

0.8

1.2

1.6

2.0

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420

Storage Time (days)

Sen

sory

Sco

re (

0-10

)

Plant APlant BSS10SS14

Rancid Flavour Commercial plants

110C, 10min and 14 min

Storage at 21C

Fig. 9 The effect of storage time on intensity of rancid flavour of oat groats processed commercially or with superheated steam (SS) at 110C

45

48

51

54

57

60

0 30 60 90 120 150 180

Storage Time (days)

L v

alue

Plant A Plant B SS10 SS14

Fig.10 The effect of storage time on L value (lightness) of oat groats processed commercially or with superheated steam (SS) at 110C

Commercial plants 110C, 10min and 14 min

Storage at 21C

Summary

• The shelf-life stability of oat groats processed with superheated steam at 110C for 10 and 14 min, and stored at 21C was acceptable and exceeded the intended storage time period of 6 months