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The effect of gellan gum addition on corn grits extrusion
Food Hydrocolloids Yol.5 no.5 pp.435-441, 1991
The effect of gellan gum addition on corn grits extrusion Joseph A.Maga, Chin Hong Kim and Carol Lynn Wolf l Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523 and 1 Kelco Division of Merck and Co., Inc., PO Box 23576, San Diego, CA 92123, USA Abstract. The addition of 0,0.01,0.1 and 0.5% gellan gum was evaluated in 15 and 25% moisture corn grits that were extruded using either 1/1, 3/1 or 5/1 compression screws operating at 100 r.p.m, through both large and small dies at dough temperatures of either 100, 150 or 200°C. Resulting extruder torque and extrudate yield (Y), density (D), expansion ratio (ER), breaking strength (BS) and water absorption index (WAI) were measured. Gellan addition was found to not significantly influence Y, D, ER and BS. However, as gellan gum addition increased, so did WAI. Also, under certain specific formulation and extrusion combinations at both high and low dough temperatures, the addition of gellan significantly reduced extruder torque.
Introduction The influence of numerous hydrocolloids on various extruder/extrudate properties has been reported (1-9). Most ofthese studies centered on the potential of added hydrocolloids to lower extruder torque, which in turn can increase product throughput and decrease power requirements during extrusion processing. In addition, hydrocolloid inclusion can be expected to influence extrudate breaking strength and water absorption (6). However, the role of gellan gum, a new high-molecular-weight extracellular anionic heteropolysaccharide derived from the fermentation of Pseudomonas elodea (10), on extruder/extrudate properties has not been reported. Structurally, gellan gum consists of a linear tetrasaccharide repeating unit comprising 1,3-I3-D-glucose, 1,4-I3-D-glucuronic acid, l,4-I3-D-glucose, and 1,4-a-L-rhamnose (11,12). The major objective of this study was to evaluate the addition of increasing amounts of gellan gum to corn grits under a wide range of extrusion conditions and measure extruder performance relative to torque and yield as well as extrudate expansion, density, breaking strength and water absorption. Materials and methods
Materials Commercially available (Evans Milling, Indianapolis, IN 96222) dehulled and degerminated yellow corn grits were used as the base material. A laboratory sample of KELCOGEL gellan gum was obtained from Kelco, Division of Merck and Co., San Diego, CA 92123.
Pre-extrusion blending The moisture content of the corn grits was determined and 0,0.01,0.1 or 0.5% (w/w) gellan gum was dry blended with the corn grits for 10 min using a 435
J.A.Maga, C.H.Kim and C.L.Wolf
Patterson-Kelly Model LB-P8 twin shell blender. Based on the initial moisture content, either 15 or 25% total moisture was obtained in the blended corn gritl gum mixture by slowly adding the appropriate amount of 20°C tap water. The mixture was then blended for an additional 20 min. The batches were placed in moisture-proof plastic bags and stored at room temperature for 14 h to permit equilibrium before extrusion. Extrusion conditions
All runs were performed on a Brabender Model PL-V500 single screw laboratory extruder. The unit had a barrel diameter of 19.05 mm with a 20:1 length to diameter ratio and was rifled with eight 0.79 X 3.18 mm longitudinal grooves. Runs were made at 100 r.p.m. using screws having compression ratios of 1:1, 3:1 and 5:1. The barrel was equipped with electrically heated, compressed air cooled collars. A thermocouple accurate to ±2°C was inserted just before the die exit to be in direct contact with the dough and the unit operated to obtain dough temperatures of 100, 150 or 200°C. Die size openings of either 3.175 or 4.750 mm were used. Measurements
Torque was read directly from a digital torque indicator attached to the extrusion unit. Yield was determined by collecting each sample for 2 min and dividing throughput by two after permitting the extrudate to air dry at room temperature for 48 h. Measuring the volume displaced by a known weight of extrudate using a laboratory rapeseed displacement meter gave extrudate density. The extrudate breaking strength was measured using a Wamer-Bratzer shear press. The expansion ratio was the ratio of the cross-sectional diameter of the extrudate, which was manually measured, to the die exit diameter. The method of Anderson et al. (13) was used to measure the extrudate water absorption index. Experimental design and statistical evaluation
All experimental combinations represented a total of 154 individual extrusion runs . Three separate batches of feed material were prepared and randomly extruded over a 3 week period. Therefore, a total of 462 extrusion runs were performed. All of the formulation and processing variables evaluated are summarized in Table I. Torque data for the three replicate runs were averaged while all analytical measurements were performed in duplicate, averaged and subjected to analysis of variance utilizing the SPSSX statistical package. Results and discussion General considerations
The overall statistical significance, as determined by one-, two-, and three-way analysis of variance, of the formulation and extrusion variables evaluated is 436
The effect of gellan gum on corn grits
Table I. Formulation and extrusion variables evaluated and measurements taken Base material Gellan gum levels Feed moisture Screw Screw speed Dough temperature Die size Measurements
corn grits 0,0.01,0.1,0.5% w/w 15 or 25% total moisture 1/1, 3/1 or 5/1 compression ratio constant at 100 r.p.m. 100, 150 or 200°C 3.175 or 4.750 mm torque, yield, density, expansion ratio, breaking strength, water absorption index
Table II. Statistical significance of variables evaluated Variable
Screw compression ratio (screw) Die size (die) Extrusion temperature (temp.) Dough moisture (moist.) Gum level (gum) Screw x die Screw x temp. Screw x moist. Screw x gum Die x temp. Die x moist. Die x gum Temp. x moist. Temp. x gum Moist. x gum Screw x due x temp. Screw x die x moist. Screw x die x gum Screw x temp. x moist. Screw x temp. x gum Screw x moist. x gum Die x temp. x moist. Die x temp. x gum Die x moist. x gum Temp. x moist. x gum
Torque
•• NS
••
••
NS NS NS
••
NS NS NS
•• ••
NS NS NS NS NS NS
••
NS NS NS NS
Yield
**
Expansion ratio
•• ••
Density
Breaking Water strength absorption index
NS
NS
•
••
NS NS NS NS
••
•• ••
NS NS NS
NS NS' NS
NS NS NS NS
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
••
••
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
••
NS NS NS NS NS NS NS NS NS NS NS NS
••
•• ••
NS NS
..
NS NS NS NS
•
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
NS NS
••
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
• Significant at the 0.05% level; "significant at the 0.01% level; NS, not significant.
summarized in Table II. It can be seen that the screw compression ratio, extrusion temperature and dough moisture content all had a major influence on most of the properties measured. This was expected because of the wide range of conditions evaluated. Also, the interaction between screw compression ratio and dough moisture content significantly influenced most measured properties while the majority of the other two- and three-way interactions were not found to be significant. Since the major objective of this study was to evaluate the influence of gellan
437
J.A.Maga, C.n.Kim and C.L.Wolf
gum addition, at this point gum addition relative to the measured properties will be discussed.
Torque It is evident from Table II that the addition of gellan gum did directly influence extruder torque. This is especially important in light of the fact that if torque, a mea surement of extruder power consumption, can be reduced , processing costs will also be reduced. Maga and Fapojuwo (5) reported that certain hydrocolloids were effective in lowering torque but only at low extrusion temperatures, whereas other hydrocolloids had no influence on torque under any extrusion conditions evaluated. With reference to gellan gum, a summary of its influence on torque over a wide range of formulation and extrusion conditions is shown in Table III. These data follow the same general trends as previously reported for other hydrocolloids (5), namely that, dependent upon formulation and extrusion conditions, either increases, decreases or no significant change in torque were observed. Therefore , clearly defined conditions need to be established for significant torque reduction to become apparent. Torque reduction results from the presence of a less viscous dough which in turn is influenced by the degree of hydrocolloid rehydration and interaction before starch gelatinization occurs. The degree of starch gelatinization in turn is influenced by factors such as dough moisture and extrusion temperature. In light of the above discussion, there were several extrusion conditions where gellan gum addition exhibited superior torque reduction capabilities than previously reported hydrocolloids (5). One such condition was with a low screw compression ratio (1/1), small die , low extrusion temperature , high dough moisture situation similar to conditions employed for pasta production . Here the 0.5% gellan gum addition was extremely effective in reducing torque. Torque went from 480 Nm in the no gum control to 180 Nm with 0.5% gellan . As mentioned previously, other hydrocolloids have been shown to be effective in reducing extrusion torque under the same conditions evaluated in the present study (5) but only at low extrusion temperatures , which severely limits their application in expanded snack food extrusion systems since these are usually performed at higher temperatures (150-200°C). However, in the present study several extrusion conditions at medium (150°C) and high (200°C) temperatures were noted where gellan gum addition effectively reduced extruder torque. Interestingly, these conditions all represented low moisture dough systems, which are preferred in the extruded, expanded snack industry since better expansion can usually be obtained in lower moisture systems. Also, lower moisture doughs require higher torque to extrude since they are usually higher in viscosity and thus torque reduction becomes even more important. Therefore, it would appear that gellan gum has an advantage over other hydrocolloids in that it is more effective in reducing extruder torque in low moisture dough systems similar to those preferred for the manufacture of expanded snacks. The actual reason for the observed reduction in torque under certain extrusion 438
Table III. Effect of gellan gum addition on the torque (Nm) and standard deviation of corn grits extruded at different moistures, screw compression ratios, dough temperatures and die sizes
Treatment
Dough temperature 0.01
o1 2 3 4 5 6 7 8 9 10 11 12
300(10) 820(20) 990(10) 580(15) 820(15) 770(15) 480(10) 380 (5) 420(10) 210 (5) 390(10) 390(10)
460(15)b 780(15)" 860(15)< 440(10)< 830(15) 770(10) 260 (5t 380 (5) 420(10) 200 (5) 380 (5) 390(10)
= 100°C 0.1
0.5
Dough temperature 0 0.01
470(15)b 760(15)< 840(20)< 410(10)< 830(15) 740(10)< 240 (5)C 380 (5) 420(10) 200 (5) 370 (5)< 400(10)
480(IW 730(15)< 800(15)< 380(10)< 830(15) 710(15)< 180 (5) 380 (5) 410(10) 190 (5)" 350 (5)< 400(10)
350(10) 480(10) 590(10) 640(10) 530(10) 500(10) 190 (5) 200 (5) 260 (5) 200 (5) 220 (5) 210 (5)
430(10)b 450(10)" 540(10)< 580(10)< 520(10) 480(10)< 180 (5) 210 (5) 260 (5) 200 (5) 220 (5) 230 (5)b
= 150°C 0.1
0.5
Dough temperature 0.01 0
460(1O)b 440(10)< 540(10)" 440(10)< 520(10) 470(10)< 180 (5) 210 (5) 260 (5) 210 (5) 240 (5)b 240 (5)b
540(15)b 420(lOt 530(10)< 430(10)" 510(10)< 470(10) 180 (5) 210 (5) 260 (5) 220 (5? 240 (5)b 240 (5)b
320(10) 310 (5) 370 (5) 250 (5) 320 (5) 330 (5) 120 (5) 170 (5) 160 (5) 170 (5) 180 (5) 160 (5)
= 200°C 0.1
320(10) 310 (5) 310(10) 310 (5) 350(10)< 340(lOt 290(1O)b 300(l0)b 310(10) 310(10) 320 (5) 320(10) 120 (5) 120 (5) 150 (5)< 160 (5) 180 (5)b 170 (5) 160 (5) 160 (5) 170 (5) 170 (5) 170 (5) 170 (5)
0.5 300(10)" 320(10) 310(10)< 320(1O)b 300(10)< 300(10)< 110 (5) 150 (5)< 190 (5)b 160 (5) 170 (5) 170 (5)
1: 15% moisture , 1/1 screw. 3.175 mm die; 2: 15% moisture, 3/1 screw, 3.175 mm die; 3: 15% moisture, 5/1 screw, 3.175 mm die; 4: 15% moisture, 1/1 screw, 4.750 mm die; 5: 15% moisture, 3/1 screw, 4.750 mm die; 6: 15% moisture , 5/1 screw, 4.750 mm die; 7: 25% moisture , 111 screw, 3.175 mm die ; 8: 25% moisture , 3/1 screw , 3.175 mm die; 9: 25% moisture, 5/1 screw, 3.175 mm die ; 10: 25% moisture , 1/1 screw, 4.750 mm die; 11: 25% moisture, 3/1 screw , 4.750 mm die; 12: 25% moisture , 5/1 screw , 4.750 mm die. a_% gellan . "Significant increase in torque over 0% gellan at same dough temperature (P < 0.05).
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J.A.Maga, C.n.Kim and C.L.Wolf
conditions evaluated in this study involving gellan and soy protein is not directly understood. However, earlier researchers (14) have reported that during the extrusion of soy protein with alginate, water is formed during the thermal reaction. This water in turn would be available to reduce torque. Apparently, a similar reaction can occur with gellan.
Yield In this study the addition of gellan gum was shown not to significantly increase or decrease product yield over a wide range of extrusion conditions (data not shown). This contrasts with a significant reduction in yield with the use of Methocel derivatives at low extrusion temperatures (5). However, Maga and Fapojuwo (5) found that numerous other hydrocolloids (locust bean, agar, guar, alginate, tragacanth, carrageenan, xanthain, pectin and gelatin) also did not significantly influence yield.
Expansion The influence of gum additions on product expansion was not previously reported by Maga and Fapojuwo (5,6), but it is apparent from this study that gellan did not influence product expansion (data not shown). Therefore, its inclusion in expanded snacks should not be detrimental to the expansion.
Density The inclusion of gellan gum was found not to significantly influence product density (data not shown). This is drastically different to the performance of other hydrocolloids (6), which have been reported, in general, to actually increase product density. The se current data would indicate that the use of gellan gum can produce expanded snacks of more uniform density than other hydrocolloids, thus resulting in overall better product quality .
Breaking strength Previous data (6) have shown that product breaking strength can be significantly increased or decreased depending upon the specific hydrocolloid used along with the extrusion conditions employed. Therefore, if extrusion conditions are changed, the type of hydrocolloid used may also have to be changed to maintain the desired breaking strength. In contrast, the use of gellan gum was not found to influence product breaking strength significantly (data not shown). This, in turn, would result in a more uniform expanded product relative to breakability during packaging and product distribution.
Water absorption index (WAI) Maga and Fapojuwo (6) reported that hydrocolloid addition in general increased product WAr. When using gellan gum, it was also found that, dependent upon the specific extrusion conditions, as the amount of gellan gum utilized was 440
The effect of gellan gum on corn grits
increased, the WAI also increased (data not shown). The WAI is a functionality test evaluating the amount of free water a product is capable of absorbing under standardized conditions. Therefore, an increase in the WAI would indicate that the hydrocolloid is still capable of absorbing water and thus has maintained its functionality throughout the extrusion process. This is an especially important property relative to low temperature extrusion conditions, typified by pasta extrusion processes. The resulting cooked pasta, with hydrocolloid addition, can absorb increased amounts of cooking water, thereby increasing cooked weight yield. Conclusions
Under certain low and high temperature conditions, the addition of gellan gum can significantly reduce extruder torque. This would have direct applications in pasta and expanded snack production. The WAI increased with gellan gum addition, which would in turn increase cooked pasta yield. Extrudate yield, density and breaking strength were not significantly influenced by the addition of gellan gum, and therefore its use would not detract from product quality. The extrusion process is a complex form of processing where many interactions can occur, and under certain combinations of formulation and extrusion conditions, the addition of gellan gum is beneficial. References 1. Berrington,D., Imeson, A., Ledward,D.A., Mitchell,J.R. and Smith,A.J. (1984) Carbohydr. Polym., 4, 443-460. 2. Boison,G., Taranto,M.V. and Cheryan,M. (1983) J. Fd Technol., 18, 719-730. 3. Ganz,A.J. (1973) US Patent no. 3,769,029. 4. Glicksman,M. (1984) In Phillips,G.O., Wedlock,D.J. and Wiliiams,P.A. (eds), Gums and Stabilizers ,for the Food Industry, Vol. 2. Applications of Hydrocolloids. Pergamon Press, Oxford, pp, 315-345. 5. Maga,J.A. and Fapojuwo,O.O. (1986) J. Fd Technol., 21, 61-66. 6. Maga,J.A. and Fapojuwo,O.O. (1988) Int. J. Fd Sci. Technol., 23, 49-56. 7. Mitchell,J.R., Berrington,D. and Oliver,J. (1986) In Phillips,G.O., Wedlock,D.J. and Williams, P.A. (eds), Gums and Stabilizers in the Food Industry, Vol. 3. Elsevier, London, pp. 204-236. 8. Smith,J., Mitchell,J.R. and Ledward,D.A. (1982) Prog. Fd Sci. Nutr., 6, 139-147. 9. KUhn,M., Elsner,G. and Graber.S, (1989) Starke, 41, 467-471. 10. Kelco (1987) Research Communication no. 105, San Diego, CA 92123. 11. Jansson,P.E., Linderg,B. and Sandford,P.A. (1983) Carbohydr. Res., 124, 135-139. 12. O'Neill,M.A., Selvendran,R.R. and Morris,V.J. (1983) Carbohydr. Res., 124, 123-133. 13. Anderson,R.A., Conway,H.F. and Peplinski,A.J. (1970) Starke, 22, 130-134. 14. Oates,C.G., Ledward,D.A., Mitchell,J.R. and Hodgson,!. (1987) Int. J. Fd Sci. Technol., 22, 477-483.
Received on May 14, 1991; accepted on July 30, 1991
441
The effect of gellan gum addition on corn grits extrusion Joseph A.Maga, Chin Hong Kim and Carol Lynn Wolf l Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523 and 1 Kelco Division of Merck and Co., Inc., PO Box 23576, San Diego, CA 92123, USA Abstract. The addition of 0,0.01,0.1 and 0.5% gellan gum was evaluated in 15 and 25% moisture corn grits that were extruded using either 1/1, 3/1 or 5/1 compression screws operating at 100 r.p.m, through both large and small dies at dough temperatures of either 100, 150 or 200°C. Resulting extruder torque and extrudate yield (Y), density (D), expansion ratio (ER), breaking strength (BS) and water absorption index (WAI) were measured. Gellan addition was found to not significantly influence Y, D, ER and BS. However, as gellan gum addition increased, so did WAI. Also, under certain specific formulation and extrusion combinations at both high and low dough temperatures, the addition of gellan significantly reduced extruder torque.
Introduction The influence of numerous hydrocolloids on various extruder/extrudate properties has been reported (1-9). Most ofthese studies centered on the potential of added hydrocolloids to lower extruder torque, which in turn can increase product throughput and decrease power requirements during extrusion processing. In addition, hydrocolloid inclusion can be expected to influence extrudate breaking strength and water absorption (6). However, the role of gellan gum, a new high-molecular-weight extracellular anionic heteropolysaccharide derived from the fermentation of Pseudomonas elodea (10), on extruder/extrudate properties has not been reported. Structurally, gellan gum consists of a linear tetrasaccharide repeating unit comprising 1,3-I3-D-glucose, 1,4-I3-D-glucuronic acid, l,4-I3-D-glucose, and 1,4-a-L-rhamnose (11,12). The major objective of this study was to evaluate the addition of increasing amounts of gellan gum to corn grits under a wide range of extrusion conditions and measure extruder performance relative to torque and yield as well as extrudate expansion, density, breaking strength and water absorption. Materials and methods
Materials Commercially available (Evans Milling, Indianapolis, IN 96222) dehulled and degerminated yellow corn grits were used as the base material. A laboratory sample of KELCOGEL gellan gum was obtained from Kelco, Division of Merck and Co., San Diego, CA 92123.
Pre-extrusion blending The moisture content of the corn grits was determined and 0,0.01,0.1 or 0.5% (w/w) gellan gum was dry blended with the corn grits for 10 min using a 435
J.A.Maga, C.H.Kim and C.L.Wolf
Patterson-Kelly Model LB-P8 twin shell blender. Based on the initial moisture content, either 15 or 25% total moisture was obtained in the blended corn gritl gum mixture by slowly adding the appropriate amount of 20°C tap water. The mixture was then blended for an additional 20 min. The batches were placed in moisture-proof plastic bags and stored at room temperature for 14 h to permit equilibrium before extrusion. Extrusion conditions
All runs were performed on a Brabender Model PL-V500 single screw laboratory extruder. The unit had a barrel diameter of 19.05 mm with a 20:1 length to diameter ratio and was rifled with eight 0.79 X 3.18 mm longitudinal grooves. Runs were made at 100 r.p.m. using screws having compression ratios of 1:1, 3:1 and 5:1. The barrel was equipped with electrically heated, compressed air cooled collars. A thermocouple accurate to ±2°C was inserted just before the die exit to be in direct contact with the dough and the unit operated to obtain dough temperatures of 100, 150 or 200°C. Die size openings of either 3.175 or 4.750 mm were used. Measurements
Torque was read directly from a digital torque indicator attached to the extrusion unit. Yield was determined by collecting each sample for 2 min and dividing throughput by two after permitting the extrudate to air dry at room temperature for 48 h. Measuring the volume displaced by a known weight of extrudate using a laboratory rapeseed displacement meter gave extrudate density. The extrudate breaking strength was measured using a Wamer-Bratzer shear press. The expansion ratio was the ratio of the cross-sectional diameter of the extrudate, which was manually measured, to the die exit diameter. The method of Anderson et al. (13) was used to measure the extrudate water absorption index. Experimental design and statistical evaluation
All experimental combinations represented a total of 154 individual extrusion runs . Three separate batches of feed material were prepared and randomly extruded over a 3 week period. Therefore, a total of 462 extrusion runs were performed. All of the formulation and processing variables evaluated are summarized in Table I. Torque data for the three replicate runs were averaged while all analytical measurements were performed in duplicate, averaged and subjected to analysis of variance utilizing the SPSSX statistical package. Results and discussion General considerations
The overall statistical significance, as determined by one-, two-, and three-way analysis of variance, of the formulation and extrusion variables evaluated is 436
The effect of gellan gum on corn grits
Table I. Formulation and extrusion variables evaluated and measurements taken Base material Gellan gum levels Feed moisture Screw Screw speed Dough temperature Die size Measurements
corn grits 0,0.01,0.1,0.5% w/w 15 or 25% total moisture 1/1, 3/1 or 5/1 compression ratio constant at 100 r.p.m. 100, 150 or 200°C 3.175 or 4.750 mm torque, yield, density, expansion ratio, breaking strength, water absorption index
Table II. Statistical significance of variables evaluated Variable
Screw compression ratio (screw) Die size (die) Extrusion temperature (temp.) Dough moisture (moist.) Gum level (gum) Screw x die Screw x temp. Screw x moist. Screw x gum Die x temp. Die x moist. Die x gum Temp. x moist. Temp. x gum Moist. x gum Screw x due x temp. Screw x die x moist. Screw x die x gum Screw x temp. x moist. Screw x temp. x gum Screw x moist. x gum Die x temp. x moist. Die x temp. x gum Die x moist. x gum Temp. x moist. x gum
Torque
•• NS
••
••
NS NS NS
••
NS NS NS
•• ••
NS NS NS NS NS NS
••
NS NS NS NS
Yield
**
Expansion ratio
•• ••
Density
Breaking Water strength absorption index
NS
NS
•
••
NS NS NS NS
••
•• ••
NS NS NS
NS NS' NS
NS NS NS NS
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
••
••
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
••
NS NS NS NS NS NS NS NS NS NS NS NS
••
•• ••
NS NS
..
NS NS NS NS
•
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
NS NS
••
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
• Significant at the 0.05% level; "significant at the 0.01% level; NS, not significant.
summarized in Table II. It can be seen that the screw compression ratio, extrusion temperature and dough moisture content all had a major influence on most of the properties measured. This was expected because of the wide range of conditions evaluated. Also, the interaction between screw compression ratio and dough moisture content significantly influenced most measured properties while the majority of the other two- and three-way interactions were not found to be significant. Since the major objective of this study was to evaluate the influence of gellan
437
J.A.Maga, C.n.Kim and C.L.Wolf
gum addition, at this point gum addition relative to the measured properties will be discussed.
Torque It is evident from Table II that the addition of gellan gum did directly influence extruder torque. This is especially important in light of the fact that if torque, a mea surement of extruder power consumption, can be reduced , processing costs will also be reduced. Maga and Fapojuwo (5) reported that certain hydrocolloids were effective in lowering torque but only at low extrusion temperatures, whereas other hydrocolloids had no influence on torque under any extrusion conditions evaluated. With reference to gellan gum, a summary of its influence on torque over a wide range of formulation and extrusion conditions is shown in Table III. These data follow the same general trends as previously reported for other hydrocolloids (5), namely that, dependent upon formulation and extrusion conditions, either increases, decreases or no significant change in torque were observed. Therefore , clearly defined conditions need to be established for significant torque reduction to become apparent. Torque reduction results from the presence of a less viscous dough which in turn is influenced by the degree of hydrocolloid rehydration and interaction before starch gelatinization occurs. The degree of starch gelatinization in turn is influenced by factors such as dough moisture and extrusion temperature. In light of the above discussion, there were several extrusion conditions where gellan gum addition exhibited superior torque reduction capabilities than previously reported hydrocolloids (5). One such condition was with a low screw compression ratio (1/1), small die , low extrusion temperature , high dough moisture situation similar to conditions employed for pasta production . Here the 0.5% gellan gum addition was extremely effective in reducing torque. Torque went from 480 Nm in the no gum control to 180 Nm with 0.5% gellan . As mentioned previously, other hydrocolloids have been shown to be effective in reducing extrusion torque under the same conditions evaluated in the present study (5) but only at low extrusion temperatures , which severely limits their application in expanded snack food extrusion systems since these are usually performed at higher temperatures (150-200°C). However, in the present study several extrusion conditions at medium (150°C) and high (200°C) temperatures were noted where gellan gum addition effectively reduced extruder torque. Interestingly, these conditions all represented low moisture dough systems, which are preferred in the extruded, expanded snack industry since better expansion can usually be obtained in lower moisture systems. Also, lower moisture doughs require higher torque to extrude since they are usually higher in viscosity and thus torque reduction becomes even more important. Therefore, it would appear that gellan gum has an advantage over other hydrocolloids in that it is more effective in reducing extruder torque in low moisture dough systems similar to those preferred for the manufacture of expanded snacks. The actual reason for the observed reduction in torque under certain extrusion 438
Table III. Effect of gellan gum addition on the torque (Nm) and standard deviation of corn grits extruded at different moistures, screw compression ratios, dough temperatures and die sizes
Treatment
Dough temperature 0.01
o1 2 3 4 5 6 7 8 9 10 11 12
300(10) 820(20) 990(10) 580(15) 820(15) 770(15) 480(10) 380 (5) 420(10) 210 (5) 390(10) 390(10)
460(15)b 780(15)" 860(15)< 440(10)< 830(15) 770(10) 260 (5t 380 (5) 420(10) 200 (5) 380 (5) 390(10)
= 100°C 0.1
0.5
Dough temperature 0 0.01
470(15)b 760(15)< 840(20)< 410(10)< 830(15) 740(10)< 240 (5)C 380 (5) 420(10) 200 (5) 370 (5)< 400(10)
480(IW 730(15)< 800(15)< 380(10)< 830(15) 710(15)< 180 (5) 380 (5) 410(10) 190 (5)" 350 (5)< 400(10)
350(10) 480(10) 590(10) 640(10) 530(10) 500(10) 190 (5) 200 (5) 260 (5) 200 (5) 220 (5) 210 (5)
430(10)b 450(10)" 540(10)< 580(10)< 520(10) 480(10)< 180 (5) 210 (5) 260 (5) 200 (5) 220 (5) 230 (5)b
= 150°C 0.1
0.5
Dough temperature 0.01 0
460(1O)b 440(10)< 540(10)" 440(10)< 520(10) 470(10)< 180 (5) 210 (5) 260 (5) 210 (5) 240 (5)b 240 (5)b
540(15)b 420(lOt 530(10)< 430(10)" 510(10)< 470(10) 180 (5) 210 (5) 260 (5) 220 (5? 240 (5)b 240 (5)b
320(10) 310 (5) 370 (5) 250 (5) 320 (5) 330 (5) 120 (5) 170 (5) 160 (5) 170 (5) 180 (5) 160 (5)
= 200°C 0.1
320(10) 310 (5) 310(10) 310 (5) 350(10)< 340(lOt 290(1O)b 300(l0)b 310(10) 310(10) 320 (5) 320(10) 120 (5) 120 (5) 150 (5)< 160 (5) 180 (5)b 170 (5) 160 (5) 160 (5) 170 (5) 170 (5) 170 (5) 170 (5)
0.5 300(10)" 320(10) 310(10)< 320(1O)b 300(10)< 300(10)< 110 (5) 150 (5)< 190 (5)b 160 (5) 170 (5) 170 (5)
1: 15% moisture , 1/1 screw. 3.175 mm die; 2: 15% moisture, 3/1 screw, 3.175 mm die; 3: 15% moisture, 5/1 screw, 3.175 mm die; 4: 15% moisture, 1/1 screw, 4.750 mm die; 5: 15% moisture, 3/1 screw, 4.750 mm die; 6: 15% moisture , 5/1 screw, 4.750 mm die; 7: 25% moisture , 111 screw, 3.175 mm die ; 8: 25% moisture , 3/1 screw , 3.175 mm die; 9: 25% moisture, 5/1 screw, 3.175 mm die ; 10: 25% moisture , 1/1 screw, 4.750 mm die; 11: 25% moisture, 3/1 screw , 4.750 mm die; 12: 25% moisture , 5/1 screw , 4.750 mm die. a_% gellan . "Significant increase in torque over 0% gellan at same dough temperature (P < 0.05).
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conditions evaluated in this study involving gellan and soy protein is not directly understood. However, earlier researchers (14) have reported that during the extrusion of soy protein with alginate, water is formed during the thermal reaction. This water in turn would be available to reduce torque. Apparently, a similar reaction can occur with gellan.
Yield In this study the addition of gellan gum was shown not to significantly increase or decrease product yield over a wide range of extrusion conditions (data not shown). This contrasts with a significant reduction in yield with the use of Methocel derivatives at low extrusion temperatures (5). However, Maga and Fapojuwo (5) found that numerous other hydrocolloids (locust bean, agar, guar, alginate, tragacanth, carrageenan, xanthain, pectin and gelatin) also did not significantly influence yield.
Expansion The influence of gum additions on product expansion was not previously reported by Maga and Fapojuwo (5,6), but it is apparent from this study that gellan did not influence product expansion (data not shown). Therefore, its inclusion in expanded snacks should not be detrimental to the expansion.
Density The inclusion of gellan gum was found not to significantly influence product density (data not shown). This is drastically different to the performance of other hydrocolloids (6), which have been reported, in general, to actually increase product density. The se current data would indicate that the use of gellan gum can produce expanded snacks of more uniform density than other hydrocolloids, thus resulting in overall better product quality .
Breaking strength Previous data (6) have shown that product breaking strength can be significantly increased or decreased depending upon the specific hydrocolloid used along with the extrusion conditions employed. Therefore, if extrusion conditions are changed, the type of hydrocolloid used may also have to be changed to maintain the desired breaking strength. In contrast, the use of gellan gum was not found to influence product breaking strength significantly (data not shown). This, in turn, would result in a more uniform expanded product relative to breakability during packaging and product distribution.
Water absorption index (WAI) Maga and Fapojuwo (6) reported that hydrocolloid addition in general increased product WAr. When using gellan gum, it was also found that, dependent upon the specific extrusion conditions, as the amount of gellan gum utilized was 440
The effect of gellan gum on corn grits
increased, the WAI also increased (data not shown). The WAI is a functionality test evaluating the amount of free water a product is capable of absorbing under standardized conditions. Therefore, an increase in the WAI would indicate that the hydrocolloid is still capable of absorbing water and thus has maintained its functionality throughout the extrusion process. This is an especially important property relative to low temperature extrusion conditions, typified by pasta extrusion processes. The resulting cooked pasta, with hydrocolloid addition, can absorb increased amounts of cooking water, thereby increasing cooked weight yield. Conclusions
Under certain low and high temperature conditions, the addition of gellan gum can significantly reduce extruder torque. This would have direct applications in pasta and expanded snack production. The WAI increased with gellan gum addition, which would in turn increase cooked pasta yield. Extrudate yield, density and breaking strength were not significantly influenced by the addition of gellan gum, and therefore its use would not detract from product quality. The extrusion process is a complex form of processing where many interactions can occur, and under certain combinations of formulation and extrusion conditions, the addition of gellan gum is beneficial. References 1. Berrington,D., Imeson, A., Ledward,D.A., Mitchell,J.R. and Smith,A.J. (1984) Carbohydr. Polym., 4, 443-460. 2. Boison,G., Taranto,M.V. and Cheryan,M. (1983) J. Fd Technol., 18, 719-730. 3. Ganz,A.J. (1973) US Patent no. 3,769,029. 4. Glicksman,M. (1984) In Phillips,G.O., Wedlock,D.J. and Wiliiams,P.A. (eds), Gums and Stabilizers ,for the Food Industry, Vol. 2. Applications of Hydrocolloids. Pergamon Press, Oxford, pp, 315-345. 5. Maga,J.A. and Fapojuwo,O.O. (1986) J. Fd Technol., 21, 61-66. 6. Maga,J.A. and Fapojuwo,O.O. (1988) Int. J. Fd Sci. Technol., 23, 49-56. 7. Mitchell,J.R., Berrington,D. and Oliver,J. (1986) In Phillips,G.O., Wedlock,D.J. and Williams, P.A. (eds), Gums and Stabilizers in the Food Industry, Vol. 3. Elsevier, London, pp. 204-236. 8. Smith,J., Mitchell,J.R. and Ledward,D.A. (1982) Prog. Fd Sci. Nutr., 6, 139-147. 9. KUhn,M., Elsner,G. and Graber.S, (1989) Starke, 41, 467-471. 10. Kelco (1987) Research Communication no. 105, San Diego, CA 92123. 11. Jansson,P.E., Linderg,B. and Sandford,P.A. (1983) Carbohydr. Res., 124, 135-139. 12. O'Neill,M.A., Selvendran,R.R. and Morris,V.J. (1983) Carbohydr. Res., 124, 123-133. 13. Anderson,R.A., Conway,H.F. and Peplinski,A.J. (1970) Starke, 22, 130-134. 14. Oates,C.G., Ledward,D.A., Mitchell,J.R. and Hodgson,!. (1987) Int. J. Fd Sci. Technol., 22, 477-483.
Received on May 14, 1991; accepted on July 30, 1991
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