Formation of Volatile Compounds from Extruded Corn-Based Model

Chapter 47 Formation of Volatile Compounds from Extruded Corn-Based Model Systems

Downloaded by UNIV LAVAL on April 14, 2016 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0409.ch047

Chi-Tang Ho, Linda J . Bruechert, May-Chien Kuo, and Mark T. Izzo Department of Food Science, New Jersey Agricultural Experiment Station, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903 Volatile compounds generated by model systems of zein, corn amylopectin and corn o i l extruded at barrel temepratures of 120°C and 165°C were analyzed by GC and GC/MS. The largest quantities of lipid oxidation products were detected in systems containing a l l three components. In each system, the quantity of 2,4-decadienal was low relative to the quantities of hexanal, heptanal and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pentylpyrazine, 2-methyl-3(or 6)-hexylpyrazine and 2,5-dimethyl-3-pentylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines. 4-Methylthiazole was identified as a major decomposition product of thiamin when corn meal containing 0.5% thiamin was extruded at a final temperature of 180°C. L i p i d oxidation and the M a i l l a r d reaction are s i g n i f i c a n t sources of flavors and o f f - f l a v o r s i n processed foods. Thermal processing such as extrusion cooking of foods accelerates l i p i d oxidation and i n creases the potential for interactions between l i p i d s , proteins and carbohydrates, and t h e i r breakdown products. When foods are ex truded, variables such as shear force and pressure, i n addition to the expected time and temperature thermal processing variables, also influence these reactions. The flavor of extruded foods i s further complicated by the loss of v o l a t i l e s at the end of the extruder. Although the flavor of many extruded grain products, e s p e c i a l l y snack products, i s highly dependent on the flavor contributed by the base grain (1), only a few papers have been published i n this area. Fagerson (2) has reported some q u a l i t a t i v e e f f e c t s of extrusion on the retention of v o l a t i l e s i n textured vegetable protein, and Chen et a l . (3) have studied the loss of v o l a t i l e s during extrusion of a corn-based product. As a part of a larger cooperative e f f o r t to increase the cur rent understanding of extrusion processing, the v o l a t i l e compounds produced by extruded and baked zein samples were compared. Zein i s a 0097HS156/89/0409-0504$06.00/0 o 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Volatile Compounds from Corn-Based Model Systems 505

major storage protein of corn and constitutes at least 50% of the t o t a l endosperm protein. It i s the most hydrophobic protein known among the prolamines. The v o l a t i l e compounds generated from the degradation of thamine during extrusion cooking were also studied i n a model system.


Materials and Methods Extruded Model System. For this investigation, 100 parts zein, 40 parts corn amylopectin and 5 parts corn o i l were blended thoroughly, and water was added at 30% of the t o t a l dry weight. V o l a t i l e s c o l lected from extruded samples of this model system were compared to v o l a t i l e s from the same system heated i n an oven for 30 minutes at 120°C or 180°C and to v o l a t i l e s from extruded samples of zein with 30% added water. The extruded samples were prepared on a C. W. Brabender single-screw extruder, type 2003, with a barrel diameter of 1.9 cm and an L/D r a t i o of 20:1. The f i r s t heating zone of the barrel was held at 60°C, and the second was set at either 120°C or 165°C. The die diameter was 6.5 cm. One hundred grams of each sample were ground to a powder and extracted with a t o t a l volume of 1000 mL r e d i s t i l l e d ethyl ether i n two aliquots. O i l , carotenoids and other nonvolatile ether-extractable materials were removed from the extract by a modified Nickerson-Likens procedure (4). The r e s u l t i n g d i s t i l l a t e was dried with anhydrous sodium sulfate and concentrated with a spinning band s t i l l to a f i n a l volume of lOOuL. The concentrated extracts were stored in a freezer at -40°C to reduce further reactions or decompositions. A Varian 3400 gas chromatograph equipped with a flame ioniza t i o n detector and a nonpolar fused s i l i c a c a p i l l a r y column (60 m x 0.25 mm i . d . ; 0.25 um thickness, SPB-1, Supelco, Inc.) was used to analyze the v o l a t i l e compounds from the model systems. The injector temperature was 250°C, and the detector temperature was 260°C. The flow rate of the helium c a r r i e r gas was 1 mL/min and the s p l i t r a t i o was 50:1. The temperature program consisted of a 10 min isothermal period at 35°C, temperature increases of 2°C/min from 35°C to 120°C and of 4°C/min from 120°C to 235°C, and a 40 min. isothermal period at 235°C. The chromatograms were plotted and integrated on a Varian 4270 integrator. Linear retention indices for the v o l a t i l e compounds were calculated using n-paraffin standards (C6-C25; A l l t e c h Associ ates) as references according to the method of Majlat and co-workers (5). The concentrated samples were also analyzed by GC/MS using a Varian 3400 gas chromatograph coupled to a Finnigan MAT 8230 high resolution mass spectrometer. Spectra were recorded on a Finnigan MAT SS 300 Data System. GC conditions were the same as described above. Extruded Corn Meal with Thiamin Added. Degerminated yellow corn meal with 0.5% thiamin HC1 was extruded on a Werner P f l e i d e r e r ZSK30 co-rotating twin-screw extruder. The five heating zones of the barrel were held at 50°C, 76°C, 100°C, 134°C and 172°C, respectively. The product temperature was 180°C, the torque was 46% at 200 RPM and the pressure was 130-172 p s i . The extrudate was allowed to cool to room temperature, then stored i n glass vessels under nitrogen at 4°C.

Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


506

THERMAL GENERATION OF AROMAS

For purge-and-trap analysis, a portion of the extrudate was ground and 15 g were placed i n a two-necked sample flask with 30 g of NaCl and 100 ml of d i s t i l l e d water. Headspace components were collected on activated Tenax TA by purging nitrogen gas through the sample suspension at a flow rate of 400 mL/min for 2 hours. The collected v o l a t i l e s were desorbed from the Tenax TA at 260°C using a modified GC packed-column injector. A 25 G, 2.5 inch needle at one end of the injector was inserted through the GC sep tum, and the Tenax sample tube was placed into the injector through a screw cap at the other end. The desorbed v o l a t i l e s were carried through the injector by a flow of helium and were trapped as a sharp band at the beginning of the GC column by maintaining the GC oven temperature at -40°C with dry ice for the 15 min desorption period. The helium c a r r i e r gas supplied by the GC was turned o f f as long as the needle of the desorption unit was inserted into the GC. A Varian 3400 gas chromatograph equipped with a flame ioniza tion detector and a fused s i l i c a c a p i l l a r y column (60 m X 0.32 mm I.D., df = 1.0 urn, DB-1, J&W S c i e n t i f i c , Folsom, CA) was used to analyze the trapped v o l a t i l e s . The injector temperature was 270°C and the detector temperature was 300°C. The flow rate of the helium c a r r i e r gas was 1 mL/min, and the i n j e c t i o n was s p l i t l e s s . The oven temperature increased from -40°C to 40°C at 10°C/min and from 40°C to 260°C at 2°C/min. V o l a t i l e s isolated by the purge-and-trap method were analyzed by GC-MS using a Varian 3400 gas chromatograph coupled to a Finnigan MAT 8230 high resolution mass spectrometer equipped with an open s p l i t interface. Mass spectra were obtained by electron ionization at 70 eV and an ion source temperature of 250°C. The filament emission current was 1 milliampere and spectra were recorded on a Finnigan MAT SS 300 Data system. Results and Discussion Comparison of V o l a t i l e Compounds i n Extruded and Baked Model Systems. V o l a t i l e s from the extruded zine and zein/corn amylopectin/corn o i l and the baked zein/corn amylopectin/corn o i l samples were separated on a nonpolar SPB-1 c a p i l l a r y column. The quantities of the vola t i l e s from the extruded zein and the extruded and the baked zein/ corn amylopectin/corn o i l samples are l i s t e d i n Table I. Larger quantities of v o l a t i l e s were detected i n the baked samples than i n the extruded samples, and more v o l a t i l e s were generated during ex trusion at 165°C than 120°C. These data suggest that the actual amount of v o l a t i l e s generated i n the samples extruded at 165°C i s much larger than the amount detected. I t i s expected that reactions to produce flavors during extrusion w i l l increase at higher tempera tures, but also that products extruded at higher temperatures w i l l experience more extreme drops of temperature and pressure as they emerge from the die. The rapid expansion and rapid moisture loss that result contribute to an increased loss of v o l a t i l e compounds. In addition, flavors that are formed i n or added to the extruded product should be more susceptible to thermal degradation and sec-

Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

47. HOETAL.

Volatile Compounds from Corn-Based Model Systems

Table I. Quantitation of V o l a t i l e Compounds i n Extruded and Baked Zein/Corn Amylopectin/Corn Samples


Z

Quantitation (ppb) Extruded Z+O+A

120 165 (°c) Compounds From Lipids t t* Hexanal 6 2 2-Heptanone 18 Benzaldehyde 5 t t 2-Octanone 1 3 3,5-0ctadien-2-one 2 t 2,4-Decadienal t t 2-Methyl-3-phenyl2-propenal From Carotenoids t t Toluene t 6-Methyl-5-hepten-3-one t 28 8 Isophorone 1 3 a-Ionone t t 8-Ionone t t 6,10-Dimethyl-5,9undecadien-2-one From Proteins and Carbohydrates 40 12 2,5-Dimethylpyrazine 6 2 2-Methyl-5-ethylpyrazine 2 t 2,5-Dimethyl-3ethylpyrazine From L i p i d s , Proteins and Carbohydrates 1 t 2-Methyl-3(or 6)pentylpyrazine t t 2-Methyl-3(or 6)hexylpyrazine t t 2,5-Dimethyl-3pentylpyrazine *Trace Amount

120

165

Formation of Volatile Compounds from Extruded Corn-Based Model

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