Preservation of raspberry fruits by freezing: physical, physico-chemical and sensory aspects

Physical, physico-chemical, and sensory analysis were performed during freezing and long-term frozen storage (12 months) at –24 °C of four Spanish raspberry cultivars (Rubus idaeus), Heritage, Autumn Bliss (early cultivars), Zeva and Rubi (late cultivars). The purpose was to study the effect of the genetic origin and seasonal period of harvesting on the quality of the processed fruit with the aim of selecting the most suitable cultivar for frozen storage. Samples were evaluated by panellists through a 1-year period of storage at –24 °C in terms of three sensory attributes: firmness, colour, and taste/flavour. These sensory aspects were compared to the experimental physical and physico-chemical measurements of colour (L*, a*, b*, h, C and ΔE) and taste components (soluble solids content, titratable acidity, and quality index: °Brix/acidity). The freezing process itself did not produce significant changes in the more commonly assessed sensory quality parameters of firmness, colour, and taste/flavour. However, during storage at –24 °C, changes in sensory characteristics occurred and became more evident as storage continued (>6 months), especially in the late cultivars Zeva and Rubi. This evidence supports the notion that the early cultivars, Heritage and Autumn Bliss, could be more suitable for long-term frozen storage in terms of sensory aspects.