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

Monika.brueckner@tu-berlin.de

Please visit our website:

www.oatpro.eu

Acknowledgments & Contact

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