Document details

Altas pressões hidrostáticas na conservação de sumo de maçã 100%

Author(s): Roldão, Maria Margarida Gomes

Date: 2014

Persistent ID: http://hdl.handle.net/10400.5/7091

Origin: Repositório da UTL

Subject(s): apple juice 100%; high hydrostatic pressure; polyphenoloxidase; pectinmethylesterase; microwaves; 5-hidroxymethylfurfural


Description

The aim of this study was to assess the causes of instability in 100% apple juice treated by high hydrostatic pressure (500 MPa, 120 s, 18 °C, 0.1% ascorbic acid) and seek solutions to maintain the its original quality. Enzymatic browning of the juice and the appearance of a precipitate in the bottom of containers is due to the fact that the treatment is able to only inactivate 66% of polyphenoloxidase and 84.9% of pectinmethylesterase enzymes. The addiction of ascorbic acid was essential to maintenance the colour of juice, at 4 °C during 35 days. By varying the applied pressure (450 to 600 MPa) it was concluded that the inactivation of polyphenoloxidase was directly proportional to pressure, however an effective inactivation was not reached even at higher pressures. Futhermore, for pressures higher than 578 MPa a complete (100%) inactivation of pectinmethylesterase was achieved. Microwave treatment (T = 87 at 105 °C, ramp time = 76 to 300 s, holding time = 0 to 180 s) was completely effective (100%) in the inactivation of the pectinmethylesterase across the studied range of radiation. The microwave treatment was equally effective in the inactivation of polyphenoloxidase only for temperatures above 87 °C and ramp time above 280 seconds and/or temperature above 101°C and ramp time above 80 seconds. However, it was found that this treatment promotes the formation of 5-hydroxymethylfurfural with concentration values above 150 μg.L-1.

Mestrado em Engenharia Alimentar - Instituto Superior de Agronomia

Document Type Master thesis
Language Portuguese
Advisor(s) Martins, Margarida Moldão; Pinheiro, Maria Joaquina da Cunha
Contributor(s) Roldão, Maria Margarida Gomes
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