Orange oil

A single 10-min training session was performed on PND 6 rat pups in temperature controlled (28°C) behavior rooms. After the drug infusion, pups were placed on peppermint-scented bedding (specifically, in those experiments where preference memory in presence of peppermint were compared with control groups) or orange-scented bedding (one experiment, see Fig. 5) for 10 min and stroked with a paint brush for 30 sec every other 30 sec. Pups in the nonlearning condition were placed on the peppermint-scented bedding for 10 min without stroking. Peppermint-scented bedding was prepared by adding 0.3 mL of peppermint extract (GE Barbour Inc.) to 500 mL of regular unscented woodchip bedding and covered for 10 min. Orange-scented bedding was prepared in a similar way by adding 0.3 mL of orange oil (natural, cold compressed, California origin, Sigma-Aldrich) to 500 mL of regular unscented woodchip bedding. Peppermint- or orange-scented bedding was then left uncovered in a fume hood for 10 min allowing any solvent to evaporate. Pups were returned to the dam immediately after training until sacrifice or further testing.

Unstandardised low-methoxyl (LM, GENU type ML-12 CG-Z), high-methoxyl (HM, GENU type B rapid set-Z) and sugar beet pectin (SBP, GENU BETA) were purchased from CPKelco (Lille Skensved, Denmark). Chloride salts used in emulsion preparation (CaCl₂, MgCl₂, ZnCl₂, AlCl₃, CrCl₃ and FeCl₃) were purchased from Sigma-Aldrich (Gillingham, UK). Medium chain triglyceride oil (MCT) was obtained from IOI Oleochemical (Witten, Germany), whereas orange oil and hexadecane were obtained from Sigma-Aldrich (Gillingham, UK). De-ionised water was used in all experiments. Molecular characteristics of pectins used in the present work are presented in Table S2.