oat protein as an alternative protein source for semi ... protein as an alternative protein source...
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Oat protein as an alternative protein source for semi-solid foodsMonika Brückner-Gühmann and Stephan Drusch
Department of Food Technology and Food Material Science, TU Berlin, Germany
OATPRO - Engineering of oat proteins
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Project aim: Valorization of an oat protein side stream
The specific objectives are:
• Characterization of the functionality of oat protein concentrates with
different degree of purity in relation to their applicability in different model
food categories
• Analysis of consumer preferences
• Development of high protein food prototypes with good texture and
flavor
• Study the environmental effects associated with the production of protein
enriched foods and their adaptation in the human diet through life cycle
analysis
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OATPRO structure
VTT: VTT Technical Research Centre of Finland (Finland),
MTT: Natural Resources Institute Finland (Finland),
AU: Aarhus University (Denmark)
IBA: National Institute of Research & Development for Food Bioresources Bucharest (Romania)
TUB: Technical University Berlin (Germany),
Protein functionality
Structure, Conformation
Techno-functionality,
Physico-chemical
functionality
Nutritional properties
Physiological properties
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Intrinsic factors
Extrinsic factors
Processing
Molecular characteristics of oat protein
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pI MW (kDa) Proportion
(%)
Albumin 4-7.5 14-47 1-20.1
Globulin 12 S
α-subunit
β-subunit
5.5 and 8-10
5.9-7.2
8.7-9.2
322
31.7-37.5 up to 42
19-25
45-80
3S - 15-21
7S - 55-65
Prolamin 5-9 15-36 4-15
Gluteline 4.5-6.5 and 9-10 9-18 5-10
Similar to soy
glycinin and
other legumin-
like (11S)
storage
proteins
Peterson, 1978; Brinegar and Peterson, 1982; Burgess et al., 1983; Robert et al., 1983; Ma
and Harwalkar, 1984; Welch, 1995; Lasztity, 1996; Klose and Arendt, 2012
Properties of oat protein on a molecular level
• Main protein fraction 12S globulin
• subunit A acidic polypeptide
• subunit B basic polypeptide
• Under physiological conditions (pH 7) most of the
12S globulin is associated in its hexameric form
• Very heat-stable
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SDS-PAGE profile of OPC ,
non-reducing conditions
Protein functionality
Structure, Conformation
Techno-functionality,
Physico-chemical
functionality
Nutritional properties
Physiological properties
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Surface or interface Hydrodynamic Bioactivity
Solubility Viscosity Enzyme
Wettability Thickening Hormone
Dispersability Gelation Antimicrobial
Foaming Coagulation Antihypertensive
Emulsification Film formation Immunmodulatory
Fat binding Antioxidant
Flavour binding Opoid
Selected parameter and their influence on
solubility
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• A homogenization step improves
the protein solublility
• A heat-treatment improves the
protein solubility at neutral pH
Solubility of oat proteins
• limited around neutral and slightly
acidic pH range
• limited use as a functional food
ingredient in liquid/semi-solid food
matrices
Concentration of soluble protein versus pH Protein solubility of an OPC suspension (4% w/v)
before and after homogenization (300 bar, 2
cycles)
Food with interfaces
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Dispersed Phase
Co
nti
nu
ou
sP
hase
Gas Liquid Solid
Gas - Aerosol Smoke
Liquid Foam(beer foam, milk
foam, whipped cream)
Emulsion(mayonnaise, milk)
Dispersion (fermented,
acidic
beverages)
Solid Solid foam(baked products,
bread)
Solid emulsion,
gel(cheese, processed
meat products)
Mixtures(chocolate)
Interfacial properties of proteins
Most proteins are surface-active
Protein unfolds at interface and decreases
interfacial tension
Proteins in dispersions cause lowering of
surface tension at the water–air interface,
thus creating foaming capacity.
A lowering of surface tension at the
oil/water–air interface creates
emulsification capacity.
SURÓWKA, K. & FIK, M. Studies on the recovery of proteinaceous
substances from chicken heads. I. An application of neutrase to the
production of protein hydrolysate. Int. J. Food Sci. Technol. 27, 9–20
(1992).
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2 3 4
Interface
Air or oil
Water
1 Diffusion
2 Adsorption
3 conformational changes
4 network formation
Proteins at interfaces – schematic presentation
of the behavior
Interfacial properties of oat protein
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Surface tension [mN/m] of OPC 50, OPC
60 and OPI against oil after 30 min of
drop formation
Surface tension [mN/m] of OPC 50, OPC
60 and OPI against air after 30 min of
drop formation
• Oat protein is surface-acitve and able to reduce the surface tension
Emulsification
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Schematic presentation of the
homogenizer valve
http://gaulinhomogenizer.com/images/thumb/b/b
c/Homogenizer_valve_assembly.png/270px-
Homogenizer_valve_assembly.png
OPC
5 %
Extraction
(1 h in 10 mM pH 4 or pH 6
buffer)
Centrifugation
(10.000 g, 10 min)
Protein extract
(supernatant)
Pre-Emulsification with ultra
turrax
(72 g extracts, 10 % oil)
Emulsification
300 bar, 1 cycle
OPC emulsion
@TUB
Emulsification
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Z average of diluted emulsions Long-term stability of emulsions (1 week)
• No differences have been detected for the EAI
• Problem: low solubility of the OPC and consequently low
protein content in the extracts
Foaming
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Foaming device DFA 100, Krüss GmbH (left) with brightness distribution of a foam sample (middle), OPC
foam and OPC caramell ice cream (right)
A: Foaming; B: Foam collapse
Number 1 represents the foaming speed, 2 describes the cumulative drainage after 1 min, and 3 gives the
liquid proportion at the point of maximum foam hight
Brightness distribution: median and width
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BDm after 100 and 1800 s
BDw after 100 and 1800 s
• BDm is a measure for transmitted light
• Foam coarseness increases time-
dependent
• OPC samples at pH 7 are coarser
• BDw is a measure for foam
inhomogeneity
• No major differences detected
Problem: low solubility of the OPC
especially under acidic conditions
Foaming of OPC is comparable to milk protein
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• At pH 4: OPC not foamable
• At pH 7: foaming properties comparable to WPI
Foam made of 0.14 % (w/v) OPC at pH 7, foam at the beginning in the DFA (left),
brightness profile (middle), foam in the DFA after 1800 s (right)
Foam made of 0.14 % (w/v) WPI at pH 7, foam at the beginning in the DFA (left),
brightness profile (middle), foam in the DFA after 1800 s (right)
Cultured fermented dairy products
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• Cold-set after heat treatment Acidificaion (yoghurt)
Milk yoghurt fortified with OPC @TUB
Mechanism of structure development
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Heat treatment of15% (w/v) OPC suspension at neutral pH
Gelatinization ofstarch and increasein protein solubility
Addition of starterculture
Production of lacticacid and reductionof pH
Acid-induced aggregationof the protein due todecreased solubility and charge neutralization
Formation of a proteinnetwork throughhydrophobic and electrostatic interactions
Set-style oatyoghurt
Set-style milk yoghurt fortified with OPC @TUBCourse of storage modulus G´, loss modulus
G`` and pH during fermentation of Lactobacillus
delbrückii ssp. Bulgaricus and Streptococcus
thermophilus at 45 °C
Modification
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OPC
(1:6 in destilled water)
Extraction
pH 9.2
Protein extract
(supernatant)
OPI
83 % protein
Freeze-drying
OPI suspensions
pH adjustment pH 8.0
Tempering (45°C)
Hydrolysis pH stat
(alcalase or trypsin)
Hydrolyzed OPI
Enzyme inactivation
(78°C, 30 min)
Cooling to room temperature
Freeze-drying
Modification: enzymatic hydrolysis
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SDS polyacrylamide gel electrophoresis of
0.14% OPI-, OPA- and OPT- solutions at pH
7 (DH3)
• Limited enzymatic hydrolysis with
trypsin and alcalase alters peptide
profile
• Alcalase (endoprotease): strong effect
on the dimer and the 12SA band (it
disappeared)
• Trypsin: very specific towards its
substrate
Protein solubility of OPI, OPA and OPT at
different pH
• At pH 8: hydrolysis has a negative
effect on protein solubility
• At pH 4.5: hydrolosys improves
protein solubility
• The higher the rate of enzymatic
degardation the better the protein
solubility
Modification: tailored functionality
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Foam made of 0.14 % (w/v) OPI at pH 4, foam at the beginning in the DFA (left), brightness profile (middle), foam in the DFA after 1800 s (right)
Foam made of 0.14 % (w/v) OPT at pH 4, foam at the beginning in the DFA (left), brightness profile (middle), foam in the DFA after 1800 s (right)
Trypsin hydrolized oat protein has
improved foam stability at pH 4
Take-home message
• Oat protein has a low solubility at food-relevant pH
• It is surface-active but low solubility restricts functional properties under
acidic conditions
• Aggregation behavior supports structure in acidified products
• Modification by tryptic hydrolysis improves the solubility at pH 4
• Tryptic hydrolyzates have imrpoved foaming properties at pH 4
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The project is part of the ERA-NET SUSFOOD “OATPRO, Engineering of oat proteins: Consumer
driven sustainable food development process”. Thanks to the German Ministry of Education and
Science (BMBF) Projektträger Jülich for the financial support (project no. 031A661).
Special thanks to project partners Technical Research Centre of Finland (Finland), Natural Resources
Institute Finland (Finland), Aarhus University (Denmark) and National Institute of Research &
Development for Food Bioresources Bucharest (Romania).
More information:
Dr. Monika Brückner-Gühmann
Department of Food Technology and Food Material Science
Institute of Food Technology and Food Chemistry
Technische Universität Berlin
Please visit our website:
www.oatpro.eu
Acknowledgments & Contact
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