54F-24

J. Santiago, Universidad de las Americas Puebla, Departamento Ing. Quimica y Alimentos, Ex-Hacienda Santa Catarina Martir S/N, Cholula, Puebla, 72820, Mexico, F. SAN MARTIN, Ingenieria Quimica y Alimentos, Univ. de las Americas Puebla, Cholula, 72820, Mexico, J. Welti-Chanes, Ingenieria Quimica y Alimentos, Univ. de las Americas-Puebla, Cholula, Puebla, 72820, Mexico, and H. S. Garcia, UNIDA, Instituto Tecnologico de Veracruz, M.A. de Quevedo #2779, Col. Formando Hogar, Veracruz, Ver, 91897, Mexico.

Enzyme activity shortens the shelf-life of many products including fruit juices. Traditional thermal treatment can potentially affect the flavor of fruit juices. Studies on High Pressure Homogenization (HPH) for inactivation of pectinesterase are not available. Pectinesterase activity in orange juice causes cloud loss and decreases juice acceptability. The objective of this work was to evaluate the effect of HPH on pectinesterase activity and on native microflora of fresh orange juice. Fresh orange juice was treated at 62.5 and 100MPa in a continuous homogenizer (Duty Master,AC)(1-4 times) for residence times of 7.5, 15, 22.5 and 30s. Pectinesterase activity was determined by measuring the volume of NaOH 0.02N required to maintain a pH value of 7.5 for 10min. Total plate count and yeasts and molds were determined by pour plate method in nutrient and acidified potato dextrose agar. Pectinesterase thermal-inactivation kinetics were evaluated by treating juice samples at 40, 60 and 80^o C to determine whether inactivation was due to pressure or thermal effect. Results show that pectinesterase activity was reduced by HPH. Residual activity after treatment at 100MPa for 30s was 18%, enough to maintain acceptable cloud after storage for 2weeks at 5^o C. Thermal inactivation kinetics showed the presence of two well-defined regions in the inactivation curve. Each region was modeled as first-order kinetics. Decimal reduction times were 27.4, 19.5 and 7.6min at 40, 60 and 80^o C for the labile fraction, and 323, 213 and 10min for the heat-resistant fraction respectively. Microbial inactivation increased with increasing pressure. Aerobic mesophilic population decreased 2 log-cycles after treatment at 62.5MPa an 30s, whereas 5.7 log-reduction was observed after 100 MPa and 30s. High pressure homogenization is effective in reducing pectinesterase activity and microbial population of orange juice and could find application in processing tropical fruit juices where pasteurization would compromise flavor.

Session 54F, Nonthermal Processing: General I
2:00 PM - 5:30 PM, Monday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana