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Effects of pressure‐shift freezing and conventional freezing on model food gels
Author(s) -
KalichevskyDong Monica T.,
Ablett Steve,
Lillford Peter J.,
Knorr Dietrich
Publication year - 2000
Publication title -
international journal of food science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.831
H-Index - 96
eISSN - 1365-2621
pISSN - 0950-5423
DOI - 10.1046/j.1365-2621.2000.00288.x
Subject(s) - gelatin , ice crystals , starch , agar , agar gel , retrogradation (starch) , chemistry , microstructure , ovalbumin , materials science , chromatography , chemical engineering , food science , crystallography , biochemistry , microbiology and biotechnology , amylose , physics , immune system , biology , bacteria , optics , immunology , genetics , engineering
Summary Gels of agar, starch, ovalbumin, gelatin and an industrial β‐lactoglobulin protein isolate, were frozen conventionally in a −30 °C freezer and by pressure‐shift freezing at 200 MPa at −15 °C. Thawing was carried out conventionally at 20 °C and by the application of a pressure of 200 MPa. The microscopic structure and mechanical properties of the thawed gels were compared with those of the initial gels. Microscopic examination showed that pressure‐shift freezing produces smaller and more uniform ice crystal damage than conventional freezing at −30 °C. The results also suggest that the freeze‐thaw behaviour of food gels can be categorized into two general types: (1) gels which have a reduced gel strength as a result of mechanical damage to the gel microstructure caused by ice crystal formation, and (2) gels which have an enhanced gel strength, as a result of molecular structural changes that take place in the frozen state. Agar and gelatin were found to be typical of type (1) gels, whereas starch, β‐lactoglobulin protein isolate and ovalbumin were found to be typical of type (2) gels. In the case of starch, retrogradation during thawing was found to be the most important factor.