Oat protein as an alternative protein source for semi-solid foods

Transcription

1 Oat protein as an alternative protein source for semi-solid foods Monika Brückner-Gühmann and Stephan Drusch Department of Food Technology and Food Material Science, TU Berlin, Germany

2 OATPRO - Engineering of oat proteins 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 1

3 OATPRO structure VTT: MTT: AU: IBA: TUB: VTT Technical Research Centre of Finland (Finland), Natural Resources Institute Finland (Finland), Aarhus University (Denmark) National Institute of Research & Development for Food Bioresources Bucharest (Romania) Technical University Berlin (Germany), 2

4 Protein functionality Technofunctionality, Physicochemical functionality Intrinsic factors Extrinsic factors Processing Structure, Conformation Physiological properties Nutritional properties 3

5 Molecular characteristics of oat protein pi MW (kda) Proportion (%) Albumin Globulin 12 S α-subunit β-subunit 5.5 and S S up to Prolamin Gluteline and Similar to soy glycinin and other leguminlike (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,

6 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 SDS-PAGE profile of OPC, non-reducing conditions 5

7 Protein functionality Technofunctionality, Physicochemical functionality Structure, Conformation 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 Physiological properties Nutritional properties 6

8 Selected parameter and their influence on solubility Concentration of soluble protein versus 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 Protein solubility of an OPC suspension (4% w/v) before and after homogenization (300 bar, 2 cycles) A homogenization step improves the protein solublility A heat-treatment improves the protein solubility at neutral ph 7

9 Continuous Phase Food with interfaces Dispersed Phase 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) 8

10 Interfacial properties of proteins Air or oil Most proteins are surface-active Interface Protein unfolds at interface and decreases interfacial tension 1 1 Diffusion 2 Adsorption 3 conformational changes 4 network formation Water 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). Proteins at interfaces schematic presentation of the behavior

11 Interfacial properties of oat protein 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 10

12 Emulsification OPC 5 % Extraction (1 h in 10 mm ph 4 or ph 6 buffer) Centrifugation ( g, 10 min) Protein extract (supernatant) Pre-Emulsification with ultra turrax (72 g extracts, 10 % oil) Emulsification 300 bar, 1 cycle Schematic presentation of the homogenizer valve c/homogenizer_valve_assembly.png/270px- Homogenizer_valve_assembly.png OPC 11

13 Emulsification 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 12

14 Foaming 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 13

15 Brightness distribution: median and width BD m is a measure for transmitted light Foam coarseness increases timedependent OPC samples at ph 7 are coarser BD w is a measure for foam inhomogeneity No major differences detected BD m after 100 and 1800 s Problem: low solubility of the OPC especially under acidic conditions BD w after 100 and 1800 s 14

16 Foaming of OPC is comparable to milk protein 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) At ph 4: OPC not foamable At ph 7: foaming properties comparable to WPI 15

17 Cultured fermented dairy products Milk yoghurt fortified with Cold-set after heat treatment Acidificaion (yoghurt) 16

18 Mechanism of structure development Heat treatment of 15% (w/v) OPC suspension at neutral ph Gelatinization of starch and increase in protein solubility Addition of starter culture Production of lactic acid and reduction of ph Acid-induced aggregation of the protein due to decreased solubility and charge neutralization Formation of a protein network through hydrophobic and electrostatic interactions Set-style oat yoghurt Course of storage modulus G, loss modulus Set-style milk yoghurt fortified with G`` and ph during fermentation of Lactobacillus delbrückii ssp. Bulgaricus and Streptococcus thermophilus at 45 C 19

19 Modification OPC (1:6 in destilled water) Extraction ph 9.2 Protein extract (supernatant) OPI suspensions ph adjustment ph 8.0 Tempering (45 C) Hydrolysis ph stat (alcalase or trypsin) Enzyme inactivation (78 C, 30 min) Cooling to room temperature Freeze-drying Freeze-drying OPI 83 % protein Hydrolyzed OPI 20

20 Modification: enzymatic hydrolysis 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 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 SDS polyacrylamide gel electrophoresis of 0.14% OPI-, OPA- and OPT- solutions at ph 7 (DH3) Protein solubility of OPI, OPA and OPT at different ph 22

21 Modification: tailored functionality Trypsin hydrolized oat protein has improved foam stability at ph 4 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) 23 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)

22 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 24

23 Acknowledgments & Contact 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: 25