Study of the influence of berry-blanching on syneresis in blueberry purées

A wider range of fruit-based products, preserving high nutritional and sensory attributes, aid towards achieving a healthy diet. Pigmented fruit, specially blueberries, are a natural source of phenolic phytochemicals which could be exploited through proper technologies, limiting by-product loss and detrimental impact of processing on fruit bioactive compounds. The influence of the mild thermal pretreatment of steam blanching on the syneresis of frozen blueberry purées was studied. Syneresis kinetic parameters, colour and phenolic profile of the serum from syneresis were analyzed, highlighting the relationship between quality data and pigment localization in the berry by a correlative microscopy study. Blanching induced a marked anthocyanin diffusion from the vacuoles of pigmented epidermal cells down to the core of berries. Monomeric anthocyanin pigments (MAP) decreased in blanched (BL) berries (−17.6%), but no further decrease was observed in BL purées, while puréeing of not blanched (NB) berries caused a significant loss in MAP (−28.0%) and total phenolic compounds (TPC) (−35.8%) and an increase in percent polymeric color. As a result BL purées had higher MAP and TPC compared to NB ones. A different syneresis behaviour was evidenced between BL and NB purées and a model fitting data was proposed; the retention of syneresis serum was higher in BL purée during the first 180 min after thawing, then it was higher in NB ones till 340 min, and thereafter was similar. BL serum samples showed higher TPC (+69%), MAP (+215%), lightness (L*) and red colour component (a*) compared to NB ones. The introduction of a berry-blanching step improves physical and chemical stability of ready-to-eat frozen blueberry purées. Correlative microscopy provides a useful integrated approach to fulfil quality requirements.