Meral KILI, Ph'D'

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FACTORS AFFECTING TEXTURAL PROPERTIES OF AYRAN

• Meral KILIÇ, Ph.D.
• Istanbul Technical University
• Department of Food Engineering

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Content

• Definition of ayran
• Rheological properties and serum separation of
  ayran
• Effects of added water and salt levels
• Effects of stabilizers
• Effects of ropy cultures
• Conclusions

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Ayran

• Fermented milk drink
• Traditional
• yoghurt diluted with salty water
• Industrial
• diluted milk fermented
• mixed and further diluted with salty water

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Ayran (TGK, 2001)
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Texture of ayran

• 1. Homogeneous texture with high enough
  viscosity (consistency)
• 2. No serum separation

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Rheological properties of ayran

• Non-Newtonian fluid
• Shear thinning
• Reduction in viscosity with increasing shear rate
• Power law model
• Thixotropy
• Viscosity reduction with time at constant shear
  rate

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Rheological properties of ayrans sold at retail
Power law
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Rheological properties and serum separation of
ayrans sold at retail
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Serum separation in ayran
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Added water and salt levels(Köksoy and Kiliç,
2003)

• Ayrans produced by diluting yoghurt with salty
  water
• Water level 30, 50
• Salt level 0.0, 0.5, 1.0

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Effects of water and salt levels
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Effects of water and salt levels

• Increasing water and salt levels
• Change in flow behaviour
• Non-Newtonian to Newtonian
• Increase in serum separation
• Reduction in thixotropy

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Textural stabilization of fermented milk drinks

• Stabilizers
• High methoxyl pectin
• Ropy cultures
• Exopolysaccharide (EPS) producing cultures

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Stabilizers (Koksoy and Kilic, 2003)

• Stabilizers high methoxyl pectin, gelatine,
  locust bean gum, guar gum
• 0.10, 0.25
• added with salty water to yoghurt
• 8.7 dry matter
• 1 salt

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Stabilizers (Koksoy and Kilic, 2003)
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Stabilizers (Koksoy and Kilic, 2003)

• HMP and Gelatine affected flavor
• Guar gum provided undesirable oily mouthfeel
• Locust bean gum at 0.1 level reduced serum
  separation without affecting flavor

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Culture type

• Ropy and nonropy cultures
• Model ayrans
• nonfat milk powder
• 6.6 dry matter
• 0.0016 culture
• 1.3 salt

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Culture type
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Culture type

• Ropy culture did not improve properties of ayran
  compared to nonropy culture
• Specific properties of the ropy culture used
• low EPS production
• short time for fermentation
• Effect of EPS on casein interactions
• reduction in interactions between caseins by EPS
• Presence of salt in ayran
• shielding of charges between EPS-EPS and between
  casein-casein
• Stirring of ayran
• Low dry matter in ayran compared to yoghurt

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Effect of salt in ayran (Schkoda et al., 1999)
pH 6.7
no salt pH 4.3
salt pH 4.3
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Effect of polysaccharides in ayran
salt pH 4.3
LBG
EPS
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Conclusions

• Optimum levels of dry matter and salt must be
  used
• Stabilizers can prevent serum separation
• Effects of salt and stirring should be
  investigated

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Exopolysaccharides

• Two types of EPS
• Capsular
• Rope

• Polysaccharides excreted outside the cell
  membrane are called
• exopolysaccharides (EPS)

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• 1. Homopolysaccharides
• ?-D-glucans, ?-D- glucans, Fructan Polygalactans
• 2. Heteropolysaccharides
• Glucose, galactose, ramnose, N-acetylglucosylamine
  ,
• N-acetylgalactosamine, glucuronic acid

• Lactic acid bacteria

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• EPS cultures
• Increase in viscosity (Schellhaass and Morris,
  1985, Cerning et al., 1986 Rawson and Marshall,
  1997 Jaros et al., 2002)
• Increase in thixotropy (Jaros ve dig., 2002)
• Reduction in serum separation (Schellhaass and
  Morris, 1985, Cerning et al., 1986)

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• Schellhaass and Morris (1985)
• Acid milk gel
• Ropy and nonropy cultures
• Incubation T 32, 37, 45oC
• As T increases
• Increase in viscosity
• Increase in serum separation
• Less production of EPS

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• Skriver et al. (1993)
• Ropy culture
• Incubation T 32, 43oC
• Increase in T
• Increase in shear stress
• Shaker et al. (2001)
• set yoghurt, 40, 45, 48oC
• Min viscosity at 40oC, maximum at 48oC

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• Haque et al. (2001)
• Incubation T 37oC46oC
• Increase in T
• Increase in viscosity
• Hydrophobic interactions between casein micelles

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• Beal et al. (1999)
• yoghurt
• pH 4.4, 4.8
• Decrease in pH
• Increase in viscosity
• Increase in EPS production
• Interaction of EPS with caseins should be
  considered.

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• Schkoda et al. (1999)
• Acid milk gel
• Decrease in pH
• Increase in viscosity
• Increase in water holding capacity
• Increase in positive charges on casein micelles,
  reduction in electrostatic attractions and less
  compaq gel at low pH

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• Effects of manufacturing parameters on textural
  properties of ayran
• Culture type ropy, nonropy
• Incubation T 40, 43C
• Final pH 4.3, 4.6

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Farkli üretim parametrelerinde üretilen
ayranlarin yapisal özellikleri1
1 P?0,05 Ayni sütunda farkli harflerle
gösterilen degerler birbirinden farklidir.
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• Nonropy culture
• Higher viscosity
• Lower flow behaviour index
• Higher thixotropy
• No effect of culture type on serum separation

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• Increase in incubation T
• Higher viscosity
• Lower flow behaviour index
• Higher thixotropy
• Lower serum separation

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• According to Shaker et al. (2001)
• In yoghurt, intermolecular disulphide bonds and
  coil formation of protein strands
• Haque et al. (2001)
• Increase in hydrophobic interactions

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• Decrease in pH
• Increase in viscosity
• Lower flow behaviour index
• Higher thixotropy
• Lower serum separation

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• EPS producing culture might have reduced
  interactions between casein particles and
  weakened protein network
• Low dry matter, agitation during manufacture
  might have caused differences in the results
  compared to studies done with yoghurt
• The ropy culture used in this study might have
  produced low amount of EPS
• More studies required for EPS producing cultures

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• To increase in viscosity in ayran
• Nonropy culture / 43oC / pH 4.3
• Nonropy culture / 43oC / pH 4.6
• Ropy culture / 43oC / pH 4.6
• T is important

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• To reduce serum separation
• 43 C / pH 4.3
• But to prevent it, stabilizers should be used.