Chapter 32
Chain Length and Functional Group Impact on Flavor Retention during Extrusion
Thermally Generated Flavors Downloaded from pubs.acs.org by AUBURN UNIV on 03/01/19. For personal use only.
C. H. Kim and J. A. Maga Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523
A series of C , C and C acids, alcohols and aldehydes were added to high amylose corn starch, the mixture adjusted to 24% moisture and extruded at 115°, 125° or 135°C using a 3:1 compression screw operating at 100 rpm. Residual added volatiles were extracted from the extrudates and analyzed using gas chromatography. Total retention was greatest for alcohols and lowest for aldehydes. For all compound classes, total retention increased with increasing chain length. 6
8
10
The flavoring of extruded foods has traditionally been a problem due to the limited stability of some flavorants during extrusion and their volatility upon exiting the die (7). Surprisingly few studies have specifically addressed this important issue (2-7). Consequently, the major objective of this study was to add a series of compounds varying in chain length and functional group to a high amylose starch and to extrude at increasing temperature. The anticipated outcome was that this information would be useful in providing a better understanding of flavor compound retention during extrusion. Materials and Methods Materials. High amylose corn starch (Hylon V , National Starch and Chemical Corp., Bridgewater, NJ) was used as the base material. Hexanol, octanol, decanol, hexanal, octanal, decanal, and hexanoic, octanoic and decanoic acids were commercially obtained (Sigma Chemical Co., St. Louis, MO). Theramyl 120L was used for enzymatic starch digestion and was obtained from Novo Laboratories, Wilton, CT. Feed Material Preparation. Each alcohol, aldehyde and acid was added at a level of 200 ppm to the starch and manually blended for 10 min. The moisture content of the starch was determined and then adjusted to 24% with tap water. The resulting mixture of flavor compound, starch and water was manually blended for an additional 10 min., transferred to moisture- proof containers, and stored at 22°C for eight hours
0097-6156/94/0543-0380$06.00/0 © 1994 American Chemical Society
32. KIM & MAGA
Flavor Retention during Extrusion
381
to insure equilibrium. Blending was performed at 4°C to minimize volatile compound losses. Extrusion. A Brabender Plasticorder Model P L V500 single screw laboratory extruder with a barrel length-to-diameter ratio of 20:1 was used. It was equipped with a 4.80 mm die opening and a 3:1 compression screw operating at 100 rpm. Dough temperature just before the die exit was maintained at 115°, 125° or 135°C. The ratio of measured extrudate diameter to the die diameter resulted in expansion ratio values. In addition, a series of control samples, without added flavorants, were obtained at each of the three extrusion temperatures. Compound Extraction. Extrudates were permitted to air dry at room temperature for 24 hours, then were frozen and ground to pass through a 0.5 mm screen. Two 0.5 g ground samples of each extrudate were placed in screw cap culture tubes and suspended in 4 mL of deionized water. No enzyme was added to one set of tubes while enzyme was added to the other set. Both sets of tubes were sealed and incubated at 50°C for one hour in a vibrating water bath. The tubes were permitted to cool to room temperature and then extracted with 4 mL of ether. The extraction was repeated twice, and the ether extracts were combined and concentrated under a stream of nitrogen. The set of tubes with no added enzyme represented the "free" volatiles that were not bound to starch. The second set of tubes represented the "total" volatiles that were released by the enzyme. The "bound" volatiles were represented by the difference between the "free"" and "total" volatiles. Preliminary informal subjective analysis demonstrated that the starch/water mixture remaining after extraction contained no detectable amount of added flavorants. Gas Chromatographic Analysis. A Hewlett Packard Model 5830A gas chromatograph was used to separate and quantitate the added compounds. A 2 m glass column packed with 5% Carbowax 20M on 80/100 mesh GasChrom Ρ was used. Known quantities of the added compounds were used for identification/quantitation purposes. All quantitation data were converted to percent extrudate retention. Statistical Design and Analysis. A complete factorial design involving all variables was used. A l l extrusion runs were repeated and all analyses were performed in duplicate for each of the two runs. A l l resulting data were then combined and averaged. Results and Discussion One could argue that the degree of expansion that an extrudate undergoes immediately after exiting the extruder die can influence volatile retention with the greater the expansion, the larger the surface area that would be available for volatilization. Extrudate Expansion. As can be seen in Figure 1, extrusion temperature and type of added flavor compounds apparently did influence extrudate expansion. As expected, overall expansion increased from 115° to 125°C, where maximum expansion occurred. However, at the higher extrusion temperature (135°C), dough viscosity was not ideal to promote optimum expansion.
382
THERMALLY GENERATED FLAVORS 2.5
•CONTROL EaALCOHOLS
EALDEHYDES •ACIDS
0 115
125
135
EXTRUSION TEMP. °C
Figure 1. Extrudate expansion as influenced by extrusion temperature and functional group additions. When added compound functional groups are compared to a no-additive control, temperature also displayed significant interaction. At a low extrusion temperature (115°C), it can be seen in Figure 1 that alcohols and acids did not influence extrudate expansion, but the presence of aldehydes actually increased extrudate expansion. However, at the highest extrusion temperature (135°C), it can be seen that the addition of all compounds resulted in lower expansion ratios than a no-additive control, with aldehydes and acids resulting in less expansion than alcohols. Alternatively, at 125°C, it can be seen that acid additions did not influence extrudate expansion, whereas alcohols and aldehydes also lowered extrudate expansion. The data clearly demonstrate that most of these compounds can apparently interact with starch during extrusion, thereby influencing expansion. Standard deviation data are not shown in Figure 1 since the maximum noted deviation was less than 7%. Compound Retentions. As can be seen in Figures 2, 3 and 4, overall compound retention increased as compound chain length increased. This is probably best explained on the basis of volatility, with shorter chain compounds in a homologous series having more volatility than longer chain ones. It can also clearly be seen in Figures 2, 3 and 4 that the ratio of "free" to "bound" compound retention was influenced by functional group. In the case of added acids, (Figure 2) most of the retention was in the "free" form. In fact, at the highest extrusion temperature (135°C), no "bound" C or C acids were found. These data indicate that under the conditions of this experiment acids do not bind to starch during extrusion. However, in the case of alcohols (Figure 3), more binding regardless of chain length can be noted. Aldehydes (Figure 4) behaved more like acids, 6
8
32. KIM & MAGA
Flavor Retention during Extrusion
115 120
ι
EXTRUSION TEMR °C 125 •
383
135
i
Figure 2. Retention of added acids as a function of chain length and extrusion temperature. 115
120 I
EXTRUSION TEMP. °C 125 ;
135
;
Figure 3. Retention of added alcohols as a function of chain length and extrusion temperature.
384
THERMALLY GENERATED FLAVORS
115 80
î
EXTRUSION TEMP. °C 125 135 ; j
Figure 4. Retention of added aldehydes as a function of chain length and extrusion temperature.
especially at the two higher extrusion temperatures, since the "bound" form of the compounds was quite low. If one looks at the total amount of added compounds retained, it can be seen that at all extrusion temperatures, alcohols had the greatest retention (85-98%) while aldehydes had the least (60-68%). Total retention of added acids was also relatively high ranging from approximately 85 to 98%. The presence of "free" and "bound" flavor compounds in extruded products are both quite important in that in theory the "free" compounds can influence product acceptability before actual product ingestion, while "bound" compounds can modify product acceptability during product mastication. Conclusion This study demonstrates that compounds of the same chain length but possessing different functional groups behave differently relative to their retention during extrusion processing. Literature Cited 1. 2. 3. 4. 5. 6.
Blanchfield, J. R.; Ovenden, C. Food Mfg. 1974, 49, 27-28, 51. Packert, P. E.; Fagerson, I. S. J. Food Sci. 1980, 45, 526-528, 533. Delache, R. GretreideMehl.Brot. 1982, 36, 246-248. Lane, R. P. Cereal Foods World 1983, 28, 181-183. Lazarus, C. R.; Renz, Κ. H. Cereal Foods World 1985, 30, 319-320. Mariani, M.; Scotti, Α.; Colombo, E. In Progress in Flavor Research; Adda, J., Ed.; Elsevier: Amsterdam. 1985; pp 549-562. 7. Chen, J.; Reineccius, G. Α.: Labuza, T. P. J. Food Technol. 1986, 21, 365-383. RECEIVED
July 13, 1993
