title: Yoghurt with candied chestnut: freeze drying, physical, and rheological behaviour.
abstract: As a novel product, yoghurt powder was produced by freeze drying and with added candied chestnut puree at ratios of 5, 10, and 20 % by weight. During the freeze drying process, mass loss, water activity, and the moisture content of the samples were determined and the colour (Hunter L, a, b) of the yoghurt powder products was measured. Results showed that increasing the percentage of candied chestnut puree resulted in an increase in water activity, moisture content, and colour change values of the end product. The drying behaviour, drying rate versus free moisture content, was also investigated. It was observed that yoghurt with or without added candied chestnut puree could be satisfactorily freeze-dried. Moreover, the performance of the dried product was observed in a ready-to-use, reconstituted form. For this purpose, the obtained powders were reconstituted to their original moisture contents. Shear stress and apparent viscosity against shear rate in a range of 1-1,000 (1/sec) was then measured by a Haake-Mars rotary viscometer. According to the results, the apparent viscosities of reconstituted products, as plain yoghurt and the one with an added 5 % chestnut puree were lower than that of fresh yoghurt. However, reconstituted yoghurts containing 10 % and 20 % chestnut puree had apparent viscosities higher than fresh yoghurt. Power Law explained well the rheological behaviour of reconstituted yoghurt samples for the applied shear rate range. Based on rheological data and sensory analysis, it was concluded that the freeze dried yoghurt containing 10 % (w/w) candied chestnut puree was an acceptable novel product.
authors.affiliation: Faculty of Engineering, Department of Food Engineering, Ege University, 35100 Bornova, Izmir Turkey.
authors.forename: Melike
authors.initials: M
authors.lastname: Sakin-Yilmazer
authors.affiliation: Faculty of Engineering, Department of Food Engineering, Ege University, 35100 Bornova, Izmir Turkey.
authors.forename: S Nur
authors.initials: SN
authors.lastname: Dirim
authors.affiliation: Faculty of Engineering, Department of Food Engineering, Ege University, 35100 Bornova, Izmir Turkey.
authors.forename: Davide
authors.initials: D
authors.lastname: Di Pinto
authors.affiliation: Faculty of Engineering, Department of Food Engineering, Ege University, 35100 Bornova, Izmir Turkey.
authors.forename: Figen
authors.initials: F
authors.lastname: Kaymak-Ertekin
keywords: Candied chestnut; Freeze-drying behaviour; Reconstitution; Rheology; Yoghurt