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.

Thermal Treatments for Fruit and Vegetable Juices and Beverages: A Literature Overview

“…New thermal technologies have been studied as alternative methods to heat treatment (Mercali and others ). MWH is a promising way for some benefits, like the reduced processing time, high energy efficiency, a good process control, and space savings (Salazar‐González and others ). An overview of the effects of MWH on fruit and vegetable beverages is shown in Table .…”

“…As a result, the optimization of heat treatments is a key tool to maintain an equilibrium between safety and nutritional quality of the raw material (Traffano‐Schiffo and others ). Apart from the conventional thermal processing, there are some other nonconventional thermal approaches (ohmic and microwave heating (MHW)), characterized by some benefits, such as a better energy efficiency, a lower capital cost, and shorter treatment time (Salazar‐González and others ; Lee and others ).…”

Dielectric Properties of Beverages (Tamarind and Green) Relevant to Microwave‐Assisted Pasteurization

“…The physicochemical properties of the tamarind beverage are similar to the reported for a Nigerian tamarind beverage, with 10.8°Bx, pH of 3.4, and total acidity of 0.7% (Adeola & Aworh, 2010). The green drink had similar values to those reported for guava nectar, with pH of 3.81 and 0.14% of titratable acidity (Salazar-González et al, 2014). The pH of the green drink was similar to the reported for nopal juice (pH 3.5; Saenz et al, 2006).…”

“…. (Cinquanta, Albanese, Cuccurullo, & Di Matteo, 2010), grapefruit juice (Igual, García-Martínez, Camacho, & Martínez-Navarrete, 2010), and guava nectar (Salazar-González, San Martín-González, Vergara-Balderas, López-Malo, & Sosa-Morales, 2014). A continuous microwave system was proposed for apple cider by Gentry and Roberts (2005).…”

“…Microwave applications for liquid foods have been widely researched, for example, batch treatments were reported for apple juice (Cañumir, Celis, de Bruijn, & Vidal, ), coconut water (Matsui, Gut, De Oliveira, & Tadini, ), orange juice (Cinquanta, Albanese, Cuccurullo, & Di Matteo, ), grapefruit juice (Igual, García‐Martínez, Camacho, & Martínez‐Navarrete, ), and guava nectar (Salazar‐González, San Martín‐González, Vergara‐Balderas, López‐Malo, & Sosa‐Morales, ). A continuous microwave system was proposed for apple cider by Gentry and Roberts ().…”