Effects of heat processing on product quality of sous-vide broccoli packs

Abstract

To establish the optimum pasteurisation procedure, the effects of sous-vide heat processing on the pH, ascorbic acid and sensory aspects of broccoli (Brassica oleracea var. Italica) were studied. Broccoli florets were blanched using steam and ammonia(NH3)-steam, chilled to <2°C in ice water at O°C, and vacuum packaged. Sous-vide processing proceeded immediately at pasteurisation temperatures 73°, 76°, 79°, 82° and 85°C to a p~ = 100. Directly afterwards, the pH of the processed sous-vide broccoli was measured and percentage L-ascorbic acid loss calculated, by comparing sous-vide broccoli with unprocessed controls from the same broccoli head. Objective colour measurements were made using CIELAB L*, a* and b* co-ordinates. Consumer acceptance was tested using paired preference analysis. The same analyses were repeated after storage at 2° - 4°C for 21 days. Suitable statistical analyses showed significantly higher (P<0.05) pH-values in the case of NHrsteam-blanched broccoli, with the result that the ascorbic acid retention of NH3-steam broccoli was significantly lower (P<0.05) than that of steam blanched broccoli. Higher pasteurisation temperatures, and resulting shorter heat processing times, ii showed a significant reduction (P<O.05) in ascorbic acid losses. NHa-steam blanched broccoli was significantly (P<O.05) greener after pasteurisation than steam-blanched broccoli. Steam blanched broccoli deteriorated further significantly (P<O.05) towards a more yellow colour during a 21 day storage period at 2° - 4°C. Sensory analysis showed a significant consumer preference (P<O.05) for the greener NHa-steam- blanched broccoli but showed a significant preference (P<O.05) for the texture of steam blanched broccoli. No significant (P>O.05) taste preference was detected for broccoli from either blanching method.