SLIDE 1
Factors that control the phase behavior of a meat-starch extruded system illustrated on a state diagram
C.I. Moraru, T.C. Lee, M.V. Karwe and J.L. Kokini Department of Food Science and Center for Advanced Food Technology, Rutgers University
7th Conference of Food Engineering, Reno, 2001
SLIDE 2 Objectives of the Research
v To study the phase behavior of a complex meat-starch extruded system and to illustrate it on a state diagram. v To study the effects of plasticizers (water and glycerol)
- n the glass transition of the system.
SLIDE 3
Background
v Understanding the phase behavior of complex food systems can help predict and control their texture and storage stability (Kokini et al., 1994). v Carbohydrate-protein mixtures are commonly used for the production of snack foods by extrusion. v The properties of complex systems are not just a sum of their componentsÕ properties. v The interactions of proteins and carbohydrates with water, with the other minor components and with each other govern the structure-property relationships of foods (Matveev et al., 2000).
SLIDE 4
Glass Transition Temperature (Tg)
v Tg is a critical parameter for amorphous food matrices, which controls their processability, properties, stability and safety (Levine and Slade 1993, Roos 1995). v Most foods are mixtures of proteins and carbohydrates, which in many cases are immiscible and retain their own Tg. v Tg can be depressed by the addition of plasticizers.
SLIDE 5
Plasticization of Biopolymers
v Plasticizers increase the workability and flexibility of polymers (Sears & Darby 1982) and decrease their Tg by shielding macromolecular interactions, facilitating segmental motion and decreasing internal friction (Matveev et al., 2000). v Water is the most effective plasticizer for food systems (Roos & Karel 1991, Lillie & Gosline 1993, Brent et al., 1997). v Glycerol is frequently used to plasticize food biopolymers (Lourdin et al., 1997, DiGioia et al., 1998, Forssell et al., 1999, Moates et al., 2001). v If a low molecular compound acts as a plasticizer for each components of a mixed system, both TgÕs are depressed (Matveev et al., 2000).
SLIDE 6
Formulations
v Blends of meat mix and potato granules (1.48/1) with m.c. of 36.5±1%, were prepared (beef jerky analogs). v Meat mix = low fat ground beef (87.99%), oat fiber (5.28%), salt (3.96%), jerky spice mix (1.65%), oil mix (0.48%), liquid smoke (0.48%), sodium tripolyphosphate (0.22%), ascorbyl palmitate (0.04%) and sodium nitrate (0.01%), mixed and cooked for 45min. v 2% and 4% glycerol was added to the mixtures before extrusion. v Starch extrudates were obtained from potato granules.
SLIDE 7
Sample Preparation
Extrusion
v ZSK-30 co-rotating, intermeshing twin-screw extruder, in a high shear screw configuration (W&P, Ramsey, NJ) v Temperature profile: 25-35-90-135-100-105°C (hopper to die). v Screw speed = 100rpm and specific mechanical energy input of ≈ 1000kJ/kg.
Sample equilibration
v In dessicators over supersaturated solutions of salts, at water activity (aw) values between 0 and 0.84.
SLIDE 8
Analytical Methods
v Mechanical Spectroscopy: Rheometrics ARES II (Rheometrics Scientific, Piscataway, NJ) v Differential Scanning Calorimetry - TA 4000 System with DSC 30- S Cell, and a TC11 TA Processor (Mettler Instrument Inc., Highstown, NJ). Samples were inserted in medium pressure stainless steel crucibles and scanned at a heating rate of 5C/min.
SLIDE 9 Tg Analysis by Mechanical Spectroscopy
14.0 46.0 78.0 110.0 108 10
9
10
10
1011 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 Temp [¡C] G' (dyn/cm2) G" (dyn/cm2) ) tan_delta Endset Onset Midpoint
Onset of relaxation:
Midpoint of relaxation : GÓ peak Endset of relaxation : Tan δ peak
Example of dynamic temperature sweep test (Extruded potato granules, aw=0.84)
SLIDE 10
Tg Analysis by DSC
DSC thermogram showing an endothermic event and a Tg (extruded potato granules, aw=0.26)
SLIDE 11 Transition identification for the complex biopolymer matrix
v Identification of transitions was made by comparing thermo-mechanical spectra and DSC plots of extruded starch and extruded S-P matrix
0.0 20.0 40. 60.0 80.0 100.0 120.0 10 8 0.0 0.05 Temp [Á C] G' ( bQ ) [dyn/cm 2 ] tan_delta ( bQ ) [ ]
Extruded S-P Extruded starch
Comparative temperature sweeps Comparative DSC thermograms
SLIDE 12 Mechanical relaxations of the matrix
v Two major relaxations (Tg1, Tg2) and two secondary relaxations were
v The major relaxations were influenced by moisture content/aw.
10.0 30.0 50.0 70.0 90.0 110.0 130.0 150.0 0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Temp [¡C] tan_delta tan_delta aw=0.57 aw=0.32 aw=0.17 aw=0.0 7 aw=0.21 Tg2 Tg1 Sub Tg2 relaxation
aw<0.58
10.0 30.0 50.0 70.0 90.0 110.0 0.1 0.15 0.2 0.25 0.3 0.35 0.1 0.15 0.2 0.25 0.3 0.35 Temp [¡C] tan_delta tan_delta
aw=0.75 aw=0.84 aw=0.88
Tg1 Ice melting
aw=0.90
Tg2
aw>0.67
SLIDE 13 Moisture had a depressing effect on both major relaxations
Tg1 Ð meat proteins Tg2 Ð starch
y = -91.65x + 150.57, R2 = 0.96 y = -70.68x + 106.92, R2 = 0.92
20 40 60 80 100 120 140 160 0.2 0.4 0.6 0.8 1 aw Temperature, C
Tan delta(endset) G' onset y = -86.08x + 46.86,R2 = 0.98 y = -86.09x + 15.13, R2 = 0.88
10 20 30 40 50 0.2 0.4 0.6 0.8 1 aw Temperature of Tg2, C
Tandelta peak(endset) G' onset
SLIDE 14 The magnitude of the relaxations was influenced by moisture
v Tan δ peak increased with increased moisture content for Tg of proteins - typical for polar polymers (Kalichevsky et al.1993). v For starch, the decrease of relaxation magnitude could be explained by increased crystallinity.
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.2 0.4 0.6 0.8 1 Aw Tan delta, Tg2 y = 0.1688x + 0.0648 R
2 = 0.9934
0.05 0.1 0.15 0.2 0.25 0.2 0.4 0.6 0.8 1 Aw Tan delta, Tg1
Protein Tg Starch Tg
SLIDE 15 The secondary relaxations were not influenced by moisture
v Moisture content did not change the location of the sub Tg relaxation and ice melting
10 20 30 40 50 60 70 80 90 0.2 0.4 0.6 0.8 1 Aw Temperature of transition 3, C Tan delta peak (endset) G' onset Sub Tg relaxation Ice melting
SLIDE 16 State diagram of the extruded system
v Immiscibility of the two biopolymers is highlighted.
20 40 60 80 100 120 140 160 0.2 0.4 0.6 0.8 1
aw
Temperature, C
Starch Tg Protein Tg
G l a s s + I c e G l a s s y s t a t e Flow state+chemical degradation Rubbery texture
SLIDE 17 v Glycerol decreased the modulus and increased the magnitude of the relaxations
30.0 70.0 110.0 150.0 109 1010 1011 0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Temp [ÁC] G' ( bQ ) [dyn/cm2 ] tan_delta ( bQ ) [ ]
Tan delta
0%gly 2%gly 4%gly 4%gly 0%gly 2%gly
[dyn/cm
2
]
GÕ
Effect of glycerol on the thermo- mechanical properties of the matrix
SLIDE 18 Glycerol depressed slightly both TgÕs at low moisture content / aw
y = -86.08x + 46.86, R2 = 0.98 y = -67.74x + 32.25, R2 = 0.94 y = -86.14x + 42.77, R2 = 0.90
10 20 30 40 50 0.2 0.4 0.6 0.8 1 aw Temperature of Tg1, C Reference 2% glycerol 4% glycerol
y = -91.648x + 150.57, R
2 = 0.9603
y = -83.381x + 141.67, R
2 = 0.9036
y = -72.910x + 136.64, R2 = 0.8722 60 70 80 90 100 110 120 130 140 150 160 0.2 0.4 0.6 0.8 1 Aw Temperature of Tg2, C Reference 2% glycerol 4% glycerol
Tg1 Ð meat proteins Tg2 Ð starch
SLIDE 19
Practical conclusions
v In the studied system, starch and meat proteins were immiscible and retained their own Tg. v Water was found to be the major plasticizer for both components of the system. v Glycerol had also a plasticizing effect on the matrix.
SLIDE 20 Fundamental conclusion
v Complex food systems show similar transitions and relaxations as synthetic polymers, but their interpretation is complicated due to multiple,
SLIDE 21 References
Anderson S.L., Grulke E.A., DeLassus E.A., Smith P.B., Kocher C.W., Landes B.G. 1995. Macromolecules 28(8):2944-2954 Brent J.L., Mulvaney S.J., Cohen C. and Bartsch J.A. 1997. Journal of Cereal Science 26:301-312 Di Gioia L., Cuq B. and Guilbert S. 1998. Cereal Chemistry 75(4):514-519 Forssell P.M., Hulleman S.H.D., Myllarinen P.J., Moates G.K. and Parker R. 1999. Carbohydrate Polymers 39:43-51 Lillie M.A. and Gosline J.M. 1993. In: The Glassy State in Foods. Editors: Blanshard J.M.V., Lillford P.J., Nottingham UK, Nottingham University Press Kalichewsky M.T., Blanshard J.M.V., Marsh R.D.L. 1993. In: The Glassy State in Foods. Editors: Blanshard J.M.V., Lillford P.J., Nottingham UK, Nottingham University Press Kapsalis J.G., Walker J.E., Wolf M. 1970. Journal of Texture Studies I:464-483 Kokini J.L. 1994. Trends in Food Science & Technology Sept. 1994 (5):281-288 Lourdin D., Ring S.G. and Colonna, P. 1998. Carbohydrate Research 306:551-558 Mano JF, Lanceros-Mendez S. 2001. Journal of Applied Physics, 89: (3) 1844-1849 Matveev Yu.I, Grinberg V.Y. and Tolstoguzov V.B. 2000. Food Hydrocolloids 14:425-437 Roos Y. and Karel M. 1991. Journal of Food Science 56(6):1676-1681 Sears J.K. and Darby J.R. 1982. The Technology of Plasticizers. John Wiley & Sons, New York
