Influence of processing on the pectin structure–function relationship in broccoli purée

The structure–function relationship of pectin in broccoli purée as influenced by different types of (pre)processing was investigated. In particular, the effect of various broccoli pretreatments, including low-temperature and high-temperature blanching, two tissue disruption techniques, blending and high-pressure homogenisation, and a subsequent cooking step on the consistency and syneresis of broccoli purée was explored. The influence of these different purée preparation steps on pectin was examined via physicochemical analysis of fractionated cell walls and isolated polymers, and via anti-pectin antibodies. Purée prepared by blending non-pretreated or low-temperature blanched broccoli showed a rather high consistency and pronounced syneresis. High-temperature blanching, high-pressure homogenisation and cooking were all able to limit the degree of syneresis to a large extent. High-pressure homogenisation and cooking however resulted in an opposite effect on purée consistency: the former lowers the consistency of broccoli purée, presumably due to a reduction in broccoli tissue particle size, whereas the latter increases it. Cooking of broccoli purée led to a dramatic increase in pectin solubility which was attributed to the thermosolubilisation and β-eliminative depolymerisation of pectin at the high temperatures reached during this treatment. Moreover, it appeared that during the cooking step especially highly methyl-esterified homogalacturonan-rich components were leached out into the serum phase of the purée.Industrial relevanceThe deliberate application of particular thermal and mechanical processes on raw plant material makes it possible to design naturally structured/textured food products without the addition of texture-controlling agents such as starches, gums and stabilizers. In this study, research towards the role of in situ pectin on the consistency and degree of syneresis of differently (pre)processed broccoli purées is provided.

► Process–structure–function relationship of pectin in broccoli purée.
► High-temperature blanching, high-pressure homogenisation and cooking limit syneresis phenomena.
► High-pressure homogenisation decreases purée consistency while cooking increases it.
► High-esterified, homogalacturonan-rich pectin leaches out in serum during cooking.