Factors influencing mass transfer during immersion cold storage of apples in NaCl/sucrose solutions

Immersion chilling and freezing (ICF) consists of dipping a food material i n an aqueous freezant (AF). During ICF, mass transfer (solute, water) arise at the solid/liquid interface before and after thermal equilibrium (denote d respectively the primary and secondary stages). The aim of this work was to assess the evolution of mass transfer against time during the secondary stage. Apple cylinders (height 3 cm, diameter 2cm, initial temperature 5 de grees C) were soaked in four different AF: a binary monophasic NaCl-water l iquid (m(1) = 4.55 mol.kg(-1)), a biphasic mixture (m(1) = 4.25 mol.kg(-1)) obtained from a binary NaCl-water solution, and two ternary NaCl-sucrose-w ater liquids (m(1) = 4.55 mol.kg(-1) m(1) = 0.5 or 2 mol.kg(-1)). The effec t of temperature (-178 -17.4, -5 degrees C), composition and physical state (monophasic/biphasic) of the freezant, and of time duration (6h, 21 d) on mass transfer during the secondary stage were assessed. Results showed that mass transfer was lower over the whole process (stages I and II) when the AF temperature was lower for example, after 6 h WL and SG were less than 2% of initial material (i.m.) at T-AF = -17.8 degrees C, against more than 7% im. at T-AF = -5 degrees C. The addition of sucrose in the AF led to a sub sequent increase in WL (which could be as high as 29% i.m. after 21 d), but did not affect significantly SG levers over 21 d storage. Only the use of a biphasic mixture could limit mass transfer (less than 3.5% i.m, after 21 d).