Texture evolution during brine storage in sweet cherries
Résumé
Sweet cherries (Prunus avium L. cv. Napoléon) produced in Vaucluse are mainly intended for processing to glacé cherries. They must be harvested within a short time (3-4 weeks) and are then stored in brine for processing all along the year. Texture is a primary quality attribute of brined sweet cherries and control or modification of this texture is a major objective in modern food technology. Different harvest itineraries were applied: harvest at two different maturity stage, manually or mechanically, with or without peduncle. The cherries were immersed in brine and examined over a 12-months period for firmness, calcium and total soluble solids diffusion and cytological remodeling. Firmness was quantified with a texture analyser consisting to a compression test such as routinely applied to other fruit species. Calcium concentration in the brine was measured by Atomic absorption spectroscopy equipped with an acetylene/nitrous oxide burner. The total soluble solids (TSS) were measured in the brine with a Digital Refractometer. Cytohistological analyses were performed as also described. Mechanical harvesting, late maturity stage and storage with peduncle decreased firmness instead of their respectively comparison. However only presence or absence of peduncle influenced salt and total soluble solids diffusion, whit peduncle absence facilitating the osmotic exchange in the first weeks of brine storage. Brine storage allowed a texture gain in the first two months in most cases compared to fresh cherries confirmed by a beneficial reshuffle of tissues and allows using cherries for candying over the whole duration between two harvest seasons. In addition to peduncle, treatment temperature could increase residual endogenous PME activity in order to release significant free carboxyl group amount from pectic acid polymers for interacting with calcium salt to form secondary cross-bridges which influence cell wall strength, leading to a higher quality final product.