High-pressure homogenisation combined with blanching to turn lettuce waste into a physically stable juice

Lettuce waste was blanched, ground, pre-homogenised at 40 MPa and subjected to high pressure homogenisation (HPH) at 80 (1 pass) and 150 MPa (1, 10 passes) to obtain an ingredient intended for blended juice formulation. When lettuce was subjected to HPH without previous blanching, physically unstable juices were obtained. By contrast, the combination of HPH with a blanching pre-treatment allowed obtaining juices showing no physical separation and characterised by a bright green colour. This high stability was attributed to the modification of lettuce fibrous structure and to a 90% and 60% inactivation of polyphenoloxidase and pectin methylesterase, respectively. Juices presented a phenolic content of 3.5 ± 1.3 mg GAE/100 g and a microbial count at least 1 Log lower than that of corresponding not-blanched samples and below limits usually indicated for juice quality (4.7 Log CFU/g). During storage (4 °C), no phase separation was observed but microbial counts rapidly increased, suggesting the need for a further stabilization step. Industrial application Solid waste generated by fresh-cut processing of lettuce could be valorised by the application of blanching and HPH, leading to an innovative ingredient potentially exploitable in the formulation of healthy blended juices, smoothies and comminuted food. This effort is worth making considering that HPH is being increasingly introduced as processing operation in various industrial contexts, showing good feasibility and cost effectiveness, and could allow valorisation of different leaf discards.