Mass transfer and aroma compounds Flavour release from food products Violaine ATHES, Cristian TRELEA october 2012 Erasmus Mundus Master Course FIPDes Food Innovation & Product Design

Small volatile molecules (MM<300g/mol), which partial pressure at atmospheric pressure is sufficient to induce a stimulus on olfactive sensors. Aroma compounds Aroma compounds « Key» compounds of organoleptic quality of foods

Aroma compounds properties Volatile molecules: odorous Low MM Low concentrations in food products Complex medium = Interactions between aroma compounds and other constituents of the food matrix How to formulate food products (aromatisation) for a perception meeting consumers expectations?

Product developpement Formulation/Process Storage in packaging Consumption Unit operations - mixing - cooking - Drying - separation - … Food Matrix Headspace Packaging Food Matrix Oral cavity, Pharynx, Nasal cavity Aroma compounds transfer in processes and products From process engineering to product engineering…

Sensorial analysis Consumers studies Food & Aroma Formulation / Process Reverse engineering Physico-chemical properties of aroma compounds

Sensorial analysis “Flavour Release” in air “unit operation” Mass transfer coupled to heat and momentum transfer Food & Aroma Formulation / Process

“Flavour Release” in mouth “unit operation in mouth” Mass transfer coupled to heat and momentum transfer

Flavour release during food consumption Nasal cavity Oral cavity Pharynx Œsophagus Tracheus => Difference in behaviours of flavour release 8 Flavour release Velo-pharynx opening Olfactive receptors Step 1: in mouth

Nasal cavity Oral cavity Pharynx Œsophagus Tracheus 9 Step 1: in mouth Step 2: Pharynx Flavour release Olfactive receptors Flavour release during food consumption => Difference in behaviours of flavour release => Layer on pharynx mucosa

Atmospheric Pressure Chemical Ionisation Mass Spectrometry Air sampling Heating (100°C) Ionisation Detection (mass spectrometry) Quantification (Real time evolution of known volatile compounds concentration) IN VITRO ANALYSIS

IN VIVO ANALYSIS

EXPERIMENTAL in vitro DEVICE GAZ Food sample Flow air Flow air + aroma API- MS Atmospheric pressure ionisation - mass spectrometer Calibration C gas time (min) Each volatile compound Constant temperature t = 0 “Headspace” IN VITRO

GAS LIQUID Interface Concentration Dg=0 C(t=0) C ’(t=0) x Partition EQUILIBRIUM : initial condition in the case of a closed packaging

Homogeneous LIQUID Convection (kl) Convection (kg) C(t) C’(x,t) Concentration Partition+Transfer Interface GAS Dg Dg+C(t)Dg DYNAMIC DILUTION of GAS PHASE Opening of packaging « convective» model : liquid product

I. Thermodynamic properties Equilibrium PARTITION COEFFICIENT

GAS LIQUID Interface Concentration Dg=0 C(t=0) C ’(t=0) x Partition EQUILIBRIUM at interface

THERMODYNAMIC PROPERTIES Vapour – Liquid equilibrium Binary mixture : solvent (j: water ) + aroma (i) 1. Vapour phase «Ideal» : Dalton law à T : 2. Liquid phase 2.1 «Ideal» solution : Raoult law 2.2 «non ideal» solution : activity coefficient a) diluted solution : Henry law ( ) b) concentration dependance ( ) Vapour Liquid P

Equilibrium Partition coefficient between gas and liquid Henry Constant Vapour+Gas Liquid P T à T : THERMODYNAMIC PROPERTIES LIQUID – GAS (AIR) EQUILIBRIUM

THERMODYNAMIC PROPERTIES PARTITION COEFFICIENT Activity coefficient (non ideality in solution) volatility = partition coefficient Vapour Pressure (pure compounds) T xixi 01 1

Partition coefficients of some aroma compounds in water  Volatility variation (K) from to depending on aroma (*) Theoretical K 

II. Kinetic properties Mass transfer DIFFUSION CONVECTION

LIQUID homogeneous Convection (kl) Convection (kg) C(t) C’(x,t) Concentration Partition+Transfer Interface GAS Dg Dg+C(t)Dg Convective model

TRANSFER GAS-LIQUID INTERFACE CLCL CGCG GASLIQUID (A) kLkL kGkG

(Resistances in serie) 2.2. Mass transfer at interface liquid/air: Cg(t))( KglCl(t) ko J(t) -= Kgl1 klkg += ko Mass balance in liquid J(t).A dt (t)dCl Vl. -= 2.1. Mass balance in air Dg.Cg(t)J(t).A dt dCg(t) Vg. -= Interface liquid / air : Condition initiale : Cg(t=0) = Kgl. Cl(t=0) = 0 Kgl = Cg*/Cl* Numerical solution (Matlab) Cg(t) & Cl(t) Convective model for a flavour release from a liquid in mouth ( in vitro )

Quantification of interactions between aroma compounds and non- volatile compounds (water, fat) ReferencesComplex food matrix Partition coefficient air / water Partition coefficient fat* / water Partition coefficient in emulsions * Data often available for organic solvent (octanol) rather than fat (LogP)

diacetyl  - décalactone water oil + air Guyot et al., 1996 Buttery et al., 1973 Fat content % m/m Example of result Partition coefficient prediction of aroma compounds in an emulsion : k air/emulsion

ANALYSE IN VIVO