Glasnik Zaštite Bilja, Vol. 33 No. 5, 2010.
Izvorni znanstveni članak
Shear rate influence ob rheological properties of apple puree at low temperatures
Andrija Pozderović
; Prehrambeno-tehnološki fakultet Osijek
Anita Pichler
; Prehrambeno-tehnološki fakultet Osijek
Tihomir Moslavac
; Prehrambeno-tehnološki fakultet Osijek
Sažetak
The knowledge of rheological properties is very important either for achieving specific food properties, or for designing production procedure. The texture is one of the significant factors, which specifies the quality of foodstuffs, including those, which are kept by freezing in order to preserve their stability for a longer period. The aim of this work was to investigate an influence of shear rate and continuous cooling on rheological properties of apple puree at low temperatures before freezing and during the process of freezing. Investigation was carried out with apple puree of Idared sort. Measurements of the rheological properties were made by a rotary viscosimeter Rheotest 3 with the refrigerating unit. The rheological properties of purees were measured and shown by graphic representation showing relation between shear stress and shear rate at the temperature of 10°C and by calculating the consistency coefficient and flow behaviour index.
The relation between shear stress, temperature and cooling rate was also measured at the constant shear rate. The temperature was measured at which shear stress increases and the temperature (Tk) falls. The lowest temperature of cooling at which the shear (Tm) is still present was also measured. The examinations showed that at low temperatures the rheological properties of apple puree depended of shear rate. If the apple purees were cooled at a freezing temperature, their temperature (Tm) depended of the shear rate. There were some significant changes of rheological properties of apple puree while being cooled due to ice crystals formation and growth. They were formed as solid particles and observed at temperatures ranging from – 5.55 to – 10.50°C depending on the shear rate.
Ključne riječi
apple puree; rheological properties; shear rate; low temperatures
Hrčak ID:
163338
URI
Datum izdavanja:
5.11.2010.
Posjeta: 989 *