Changes in guava (Psidium guajava L. var. Paluma) nectar volatile compounds concentration due to thermal processing and storage

Abstract

Guava nectars were formulated for approximately 10, 12, or 14 ºBrix, with 40% guava pulp. Sodium benzoate, 500 mg.kg-1 was used as preservative. The Brix value was adjusted with saturated sucrose syrup. The guava nectar was pasteurized (85 ºC/42 seconds) in tubular heat exchanger and then hot filled in 500 mL white glass bottles. The products were stored either at room temperature (25 ± 5 ºC) or refrigerated (5 ± 2 ºC) under fluorescent light exposure and analyzed on the day after processing (time zero) and also 40, 80, and 120 days of storage. Eight compounds were identified and quantified by Gas Chromatography (GC) -Mass Spectrometry (MS): hexanal, (E)-hex-2-enal, 1-hexenol, (Z)-hex-3-enol, (Z)-hex-3-enyl acetate, phenyl-3-propyl acetate, cinnamyl acetate, and acetic acid. There was no significant effect of thermal treatment on the volatile compound concentrations, except for a significant decrease (p = 0.0001) in hexanal and (Z)-hex-3-enyl acetate (p = 0.0029). As for the storage time, there was a much greater decrease in the esters contents, such as (Z)-hex-3-enyl and phenyl-3-propyl acetates. Cinnamyl acetate had the greatest decrease over storage time. Refrigeration was better than room temperature for guava nectar volatile compounds stability over storage time, mainly for esters compounds, which are important for the product aroma and flavor.

Néctares de goiaba foram formulados para 10, 12 ou 14 ºBrix. Benzoato de sódio, 500 mg.kg-1, foi usado como conservante. O Brix foi ajustado usando xarope saturado de sacarose. O néctar foi pasteurizado a 85 ºC/42 segundos, em trocador de calor tubular e envasado, a quente, em garrafas de vidro branco de 500 mL. Os produtos foram estocados à temperatura ambiente (25 ± 5 ºC) e sob refrigeração (5 ± 2 ºC), expostos à luz fluorescente e analisados um dia após processamento (tempo zero) e aos 40, 80 e 120 dias de estocagem. Oito compostos foram identificados e quantificados por Cromatografia Gasosa (CG) - Espectrometria de Massa (EM): hexanal, (E)-hex-2-enal, 1-hexenol, (Z)-hex-3-enol, acetato de (Z)-hex-3-enila, acetato de 3-fenilpropila, acetato de cinamila e ácido acético. O efeito do processamento térmico na concentração de compostos voláteis não foi significativo, exceto um decréscimo na concentração de hexanal (p = 0,0001) e acetato de (Z)-hex-3-enila (p = 0,0029). Observou-se maior decréscimo no teor dos ésteres (Z)-hex-3-enila e acetato de 3-fenilpropila durante a estocagem. O acetato de cinamila apresentou maior decréscimo de concentração após a estocagem. A refrigeração apresentou melhor efeito na estabilidade dos teores de voláteis, principalmente os ésteres.