expansion characteristics of the east african highland banana (matooke) flour

THE EAST AFRICAN HIGHLAND

BANANA

PRESENTED BYENG KIBUUKA RONALD

SSEMPEBWA PhD GUEST RESEARCHER

KARLSRUHE INSTITUTE OF TECHNOLOGY,GERMANY

A deeper understanding of the complex expansion

mechanism, which leads to the pore structure, is

crucial to control expansion product properties.

Expansion is caused by flash vaporization of water,

due to the high pressure drop at the die exit, and

subsequent formation and growth of vapor bubbles

(Kokini et al. 1992).

ABSTRACT

MATERIALS AND METHODSRaw Material

East African banana flour (Matooke) was produced by

peeling fresh fruit and slicing into thin slices, which were

then placed in a 0.2% solution of sodium meta-bisulphite

for about 5 minutes to prevent browning. The slices were

then dried in ITDG (batch) fuel energy drier before

extruding using a co-rotating twin screw extruder.

Nandigobe

(AAA-AE)

Bukumu

(AAA-AE)

Embururu

(AAA-AE)

Moisture Content 9.6 8.1 8.8

Starch 81.8 82.5 82.9

Protein 4.71 5.1 4.01

Fat 0.87 ND 0.56

Crude Fiber 1.25 ND 1.33

Ash 4.34 3.58 4.1

Calcium (Ca) 0.0058 0.0044 0.0052

Potassium (K) 1.9 1.82 1.84

Magnesium (Mg) 0.09 0.09 0.01

Tannin (Abs at 500nm) 0.111 0.181 0.012

CHEMICAL COMPOSITION OF BANANA (MATOOKE ) FLOUR

The original moisture content of the banana flour (Matooke) was 8% wet weight basis. The composition of the Raw material was 100% East African banana Flour with the chemical composition as stated in the table above.[Muranga,2007]

EXTRUSION Extrusion trials were conducted on a co-rotating twin

screw extruder (Coperion Werner & Pfleiderer ZSK 26Mc) with a screw diameter of 25.5 mm. The extruder barrel has an overall length of 769 mm (barrel length-to-diameter ratio is 29) and is divided into seven sections.

East African Banana flour(Matooke) and water were fed into the first barrel by a gravimetrically controlled feeder (Hess,Brabender DDW-DDSR 40) and a water feed pump (TrueDos, Alldos Eichler GmbH, Pfinztal, Germany), respectively.

VARIED EXTRUSION PARAMETERS

The mass flow rate was set to 10 kg/ h.

The moisture content was varied between 6 and 17 %

wet weight basis (w.b.).

The screw speed was varied between 300 and 700

rpm.

The barrel temperature were 40,60,100,100,100,and

100oC, screw speed and feed water content were

suggested by extrusion process engineers according

to the extruder capabilities.

EXTRUDER OPERATION PROCEDUREA typical extrusion run involved a calibration step, an initial warm-up

period, steady state conditions, and a warm-down period.

The calibration step consisted of the standardization of the solid feeder and of the water pump and in bringing the barrel temperatures of zones 3.4 and 5 to, or close to, the final working temperatures.

In the warm-up period, starch was fed into the extruder; initially in small amounts and gradually increasing the feed rate until the target feed rate setting was reached.

Simultaneously, the water feed was started with high flow rates and then

was decreased gradually to the desired setting. Moreover, in this period the barrel temperatures were gradually brought

to the working temperature.

SAMPLE TAKING AND RECORDING DURING EXTRUSION

Once the extrusion response parameters, such as screw torque, die temperature and die pressure, were constant for at least 15 min, Die and barrel pressures, torque, barrel temperatures and moisture contents measurements were made and extrudate samples collected with respect to the set screw speed at every change in the Process Variables.

The picked samples are dried for ten minutes in the dryer before storage, to stabilize the water activity hence increasing the shelf stability.

EXTRUDATE SAMPLE ANALYSIS

The extrudates were crushed using a laboratory mill to particles with a diameter less than 0.5mm. The resultant banana (Matooke) extrudate flour was subjected to all the lab tests below:

MOISTURE CONTENT WATER SOLUBILITY AND ABSOPTION INDEX LONGITUDINAL AND SECTIONAL EXPANSION INDEX SPECIFIC MECHANICAL ENERGY ANALYSIS EXPANSION RATIO BULK DENSITY

RESULTS AND DISCUSSION

The results are shown from the measurement of local and final SEI and LEI, respectively, and moisture content, specific mechanical energy as well as temperature of the expanding extrudate. The results are evaluated and the contributions of the parameters to the mechanisms of expansion are discussed.

TABLE A. EXTRUSION PROCESS PARAMETERS

SAMPLE NUMBER

SCREW SPEED (rpm)

MOISTURE CONTENT

(Kg/h)WATER CONT

%THROUGH PUT

(Kg/h)BARREL TEMPERATURE

(°C)

1 300 1.3 15.8 16.3 40,60,100,100,100,100

2 300 1.4 16.4 16.4 43,60,100,100,100,100

3 300 1.6 17.9 16.6 44,60,100,100,97,99

4 400 1.2 15.4 16.3 42,60,100,101,100,100

5 400 1.4 16.5 16.4 42,60,100,100,100,100

6 400 1.6 17.9 16.6 42,100,100,100,100

7 500 1.6 17.9 16.6 42,60,100,100,100,100,

8 500 1.4 16.7 16.4 43,60,100,100,101,101

9 500 1.2 15.5 16.2 43,60,100,101,101,100

MAIN PROCESS CONDITIONS OBTAINED DURING THE EXTRUSION PROCESS

SAMPLE NUMBER

PRODUCT TEMPERATURE

(°C)TORQUE

%PRESSURE

(bar)SME

( Wh/Kg)

1 146 42 52 135.1

2 145 42 50 142.3

3 145 40 51 132.0

4 136 32 36 137.2

5 143 37 39 163.1

6 143 36 39 155.4

7 147 32 30 166.1

8 149 31 31 161.4

9 154 39 29 218.1

EXTRUSION PRODUCT RESULTS OBTAINED FROM EXTRUDATE ANALYSIS

SAMPLE NUMBER LEI LEI STD SEI SEI STD VEI WSI WSI STD WAI WAI STD

1 16.7 0.8 11.36 0.02 190.2 48.507 1.6032 2.1 0.13

2 16.3 0.9 10.33 0.06 168.2 73.4 0.38 1.8 0.04

3 15.3 1 9.61 0.15 146.8 67.4 0.79 2.2 0.01

4 17.3 0.8 7.09 0.02 122.5 96 1.07 1.3 0.04

5 18.4 1.6 8.14 0.05 149.4 95.7 1.04 1.2 0.01

6 17.3 1 7.4 0.05 127.7 95 0.72 1.5 0.03

7 21.3 0.8 5.7 0.08 121.3 70.1 1.85 1.8 0.13

8 22.5 2.2 7.16 0.04 161.2 77.7 0.23 1.4 0.05

9 31.8 2.3 6.47 0.04 205.5 78.587 1.1982 1.6 0.14

SME INCREASES WITH INCREASE IN SCREW SPEED

CONSTANT•Barrel Temp•Feed Matrix

INCREASE IN SCREW SPEED REDUCES DIE PRESSSURE


INCREASE IN SCREW SPEED INCREASES PRODUCT TEMPERATURE


INCREASE IN SCREW SPEED INCREASES LONGITUDINAL EXPANSION OF EXTRUDATES


WSI HAS A TENDENCY TO INCREASE WITH INCREASE IN SME AT REGULATED MOISTURE CONTENTS


WAI HAS A TENDENCY TO DECREASE WITH INCREASE IN SCREW SPEED


SEI DECREASES WITH INCREASE IN SME AT REGULATED MOISTURE CONTENTS


LEI INCREASES WITH INCREASE IN SCREW SPEED AT REGULATED MOISTURE CONTENTS


SEI DECREASES WITH INCREASE IN PRODUCT TEMPERATURE AT REGULATED MOISTURE CONTENTS


RESULTS ANALYSIS

The extrudates were crushed using a laboratory mill to

particles with a diameter less than 0.5mm. The resultant

banana (Matooke) extrudate flour was subjected to all the lab

tests and Table B above displays the major results that are

varied with respect to the extrusion parameters to attain the

Graphic interpretations below.

CONCLUSIONIn twin-screw extruders SME decreases when the screw

speed decreases (Meuser et al., 1982, Fletcher et al., 1985, Della Valle et al., 1989). Tsao et al. (1978) and Della Valle (1989) observed that SME increased at higher screw speeds.

SME is usually directly related to the expansion of expanded extrudates, in that case high expanded extrudates have high SME, since the energy spent during the extrusion process creates highly expanded extrudates which in turn is responsible for the puffed texture that is typical of expanded extrudates.

As a result, it was reasonable that the extruded flour in this study should be highly dispersed in water giving a high WSI. The WAI at 30°C of extruded flour was also higher than that of raw flour due to the swelling of highly degraded starch [Whalen 1999]

Water absorption index values of all extruded samples were significantly higher compared to non-extruded corn grits. Extrusion resulted in decrease of peak, hot and cold viscosity of all samples. Starch damage significantly increased and resistant starch [RS] content decreased after extrusion.

expansion characteristics of the east african highland banana (matooke) flour

Technology