Physical-chemical and Microbiological Stability During Refrigerated Storage of Microwave-pasteurized Guava Nectar

Abstract

Microwave technology for the pasteurization of fruit juices offers advantages over conventional processing methods due to volumetric heating and fast rates that result in shorter processing times. In this study, guava nectar was pasteurized by microwave heating (2450 MHz) to 90°C using 500 or 950 W. For comparison, nectar pasteurization at 90oC was performed using a plate heat exchanger (PHE) at 400 or 200 mL/min for holding times 3.1 and 12.5 s respectively. After thermal treatments, nectars were stored at 4°C and analyzed over a storage period of 12 days. Results showed a significant pectinmethylesterase inactivation. 94% of vitamin C was retained in microwave pasteurized nectar at 12th day storage for samples treated at 500 W. Rheological properties for nectar remained without significant variations during storage. Color was better preserved after microwave treatments (ΔE*= 0.69-0.75) as compared to samples processed by PHE (ΔE*= 1.84-2.75). Microbial counts remained below detectable levels throughout storage.