Texture and structure of pressure-shift-frozen agar gel with high visco-elasticity |
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| Affiliation: | 1. Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand;2. School of Chemical Sciences, University of Auckland, Auckland 1142, New Zealand;3. Riddet Institute, Palmerston North, New Zealand;1. Pós Graduação em Engenharia Mecânica (PGMEC), Universidade Federal Fluminense (UFF), Av. dos Trabalhadores, 420, 27255-125, Volta Redonda, RJ, Brazil;2. Universidade Federal da Grande Dourados, Faculdade de Engenharia, Pós-graduação em Ciência e Tecnologia de Alimentos, P.O. Box 533, 79804-70, Dourados, Brazil;3. Laboratório de Engenharia e Tecnologia Agroindustrial (LETA), Universidade Federal Fluminense (UFF), Av. dos Trabalhadores, 420, Volta Redonda, RJ, 27255-125, Brazil;1. Department of Mechanical Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Taoyuan 333, Taiwan;2. Center for Biomedical Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Taoyuan 333, Taiwan;3. Institute of Biochemical and Biomedical Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Taoyuan 333, Taiwan;4. Medical Physics Research Center, Institute for Radiological Research, Chang Gung University and Chang Gung Memorial Hospital, Taoyuan 333, Taiwan |
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| Abstract: | To determine the effects of sucrose and high-pressure-freezing, two kinds of agar gel were compared; A gel with high visco-elasticity and B gel, an ordinary dessert gel. Both agar gels with 0, 5, 10 or 20% sucrose were frozen at 0.1–686 MPa and −20 °C. They were frozen during pressurization, and exothermic peaks were detected at 0.1, 100, 600 and 686 MPa and −20 °C (freezing). However, at 200 MPa, they did not freeze but froze with released pressure (pressure-shift-freezing). Thus, the amount of syneresis from gel pressure-shift-frozen at 200 MPa was smaller than that from gel frozen at other pressures. Also, amount of syneresis from A was smaller than B. In addition, compared to control gels, the appearance of 0% sucrose–agar gels frozen at 0.1, 100, 600 and 686 MPa differed greatly due to syneresis and a volumetric shrinkage of the gel. It was apparent that the rupture stress of the gels decreased, strain and size of ice crystals increased and quality declined. Conversely, due to quick freezing, the texture and structure of both A and B pressure-shift-frozen at 200 MPa were better than the other pressure-treated gels and gels frozen in freezers (−20, −30 or −80 °C) at atmospheric pressure. Consequently, pressure-shift-freezing was more effective. However, texture, structure and syneresis of A were somewhat better than that of B. It was found that the addition of sucrose to the gel was effective in improving the quality of frozen agar gels. |
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