Effect of enzymatic cross-linking of milk proteins on functional properties of set-style yoghurt

1. Effect of enzymatic cross-linking of milk proteins on functional properties of set-style yoghurt Ko bong kuk

2. KEFIR in the Northern part YOGHURT in the southern part INTRODUCTION Legend The legend tells that yogurt and kefir were born on the slopes of Mount Elbrus in the Caucasus range by a miracle of Nature. Micro-organisms of various kinds happened to land in a pitcher of milk at the same time and at the right temperature, and found that they could live in symbiosis. On the southern slope of Mt. Elbrus, micro-organisms preferring relatively high temperatures, 40 – 45°C, came together in a milk pitcher that probably belonged to a Turkish nomad, and the result was what the Turks called “Yogurut”. Some sources say that this name was introduced in the 8th century and that it was changed in the 11th century to its present form, yogurt. Mount Elbrus in the Caucasus mountain range is the birthplace of Kefir and Yoghurt.

3. Yogurt In a fermented dairy product, resulting from the growth of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus bacteria in warm milk, characterized by a smooth, viscous gel with delicate walnutty flavor. Types Set type: Incubated and cooled in the package. Stirred type: Incubated in tanks and cooled before packing. Drinking type: Similar to stirred type, but the coagulum is “broken down” to a liquid before being packed. Frozen type: Incubated in tanks and frozen like ice cream.

4. Pre-treated milk Culture Stabilizer, sugar, fruit Flavouring Incubation Incubation Packing Cooling Mixing Flavouring Incubation Packing Cooling Pasteurization UHT treatment Homogenization Cooling Homogenization Aseptic packing Packing Aseptic packing Ambient storage Cold store Production steps Set Type Stirred Type Drink Type

5. Transglutaminase Protein-glutamin:amine -glutamyltransferase EC 2.3.2.13, TG Intermolecular Cross-linking between milk proteins Maximum sizes of 106~107g/mol Modify functional properties(Solubility, hydration ability) Rheological, emulsifying properties Heat stability

6. Acyl donor -carboxyamide groups of peptide-bound glutaminyl residues • Acyl acceptor The primary amino groups in variety of amine compounds Peptide-bound -amino groups of lysly residues

7. Acyl donor -carboxyamidegroups of peptide-bound glutaminyl residues • Acyl acceptor The primary amino groups in variety of amine compounds Peptide-bound -amino groups of lysly residues

8. Acyl donor -carboxyamide groups of peptide-bound glutaminyl residues • Acyl acceptor The primary amino groups in variety of amine compounds Peptide-bound -amino groups of lysly residues

9. Gel strength Gel stiffness Permeability Viscosity of protein solution Water-holding properties Replacement of fat and protein Breaking strength Dry, smooth and white shining surface Whey syneresis Milder taste The effects of transglutaminase action on the properties of yoghrut Gel strength Gel stiffness Permeability Viscosity of protein solution Water-holding properties Replacement of fat and protein Breaking strength Whey syneresis Dry, smooth and white shining surface Milder taste

10. Purpose of this articles On the properties of set-style yoghurt products With Without Inactivation of the enzyme The Effectof enzymatic cross-linking of milk proteins

11. MATERIALS AND METHODS Preparation of yoghurt with & without transglutaminase treatment Characterization of functional and sensory properties Scanning electron microscopy

12. MATERIALS AND METHODS Preparation of yoghurt with & without transglutaminase treatment The experimental station of the Federal Dairy Research Centre Raw milk Skimmed milk Separation of raw milk with a disk centrifuge Yoghurt milks with different fat contents Mixing skimmed milk and cream Protein and dry matter contents Addition of sodium caseinate and skim milk powder

13. Enzyme treatment Enzyme/substrate ratio 1/2000 Yoghurt samples Control 5 ℃ pH 4.68 Preparation of yoghurt with & without transglutaminase treatment Enzyme treatment Preheating Milk samples Enzyme/substrate ratio 1/2000 92 ℃ for 5 min incubating 40 ℃ for 2 h Heat treatment 80 ℃ for 1 min Starter culture Distribution Fermentation 150 ml plastic cups 43  1 ℃ 3% v/v

14. Transglutaminase 4 L pasteurized skim-milk Enzyme/substrate ratio : 1/4000 20 ml Skim-Milk Yoghurt samples Control Starter culture 3% v/v Distribution 150 ml plastic cups 5 ℃ Starter culture Fermentation 3% v/v 43  1 ℃ pH 4.68 Preparation of yoghurt with & without transglutaminase treatment

15. Characterization of functional and sensory properties Penetration measurement at 6 ℃ Gel strength Triplicate and expressed as N/cm2 Put 30 g of set-style yoghurt(4~6 ℃) on an analysis sieve Syneresis The weight of whey drained during a storage of 2 h at 6 ℃ Triplicate and expressed in percent

16. Characterization of functional and sensory properties Soxhlet-Henkel Titration acidity ºSH=ml 0.25 mol/1 NaOH/100 ml milk Panel of 16 assessors Sensory properties After 14 days storage at 4~6 ℃ Served at 10 ℃ 17 odour, 20 taste and 7 consistency Structured scale : (1) ~ (5) Attributes detected by at least 50% of the assessors

17. Instrument Yoghurt samples Scanning electron microscopy DSM 940 scanning electron microscope Cutting small pieces from the surface Fixation with 2% glutaraldehyde in 0.1 M sodiumphosphate buffer(pH 7) Transfer samples into microporous specimen capsules Dehydration, critical point drying with liquid carbon dioxide Coating with gold in a sputter coater

18. RESULTS AND DISCUSSION Transglutaminase treatment of milk prior to fermentation with inactivation of the enzyme Prolong fermentation time (20~40 min) Prolong fermentation time (20~40 min) The concomitant use of the starter culture & of the transglutaminase preparation without inactivation of the enzyme Did not result in a decrease of Did not result in a decrease of the acidification activity the acidification activity

19. Lower Acidification Titratable acidity Enzyme treatment

20. Gel strength Increase Gel strength TG treatment

21. Scanning electron micrographs of skim-milk yoghurt gels Untreated milk Transglutaminase-treated (2 h at 40 ℃)

22. Syneresis Syneresis smaller TG treatment

23. Gel strength & whey Syneresis (storage time : 14 days at 4~6 ℃, TG incubation : 2 h at 40 ℃) * (A) untreated milk, ** (B) TG-treated milk

24. Sensory properties Taste Odour Yoghurt Yoghurt + TG Consistency

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