The effect of calcium treatments on aspects of cell wall metabolism in apple cv. 'Braeburn'

'Braeburn' apple is appreciated because of its 'crispy' texture and acid taste but it is very susceptible to several storage disorders, mealiness included, because of its low calcium content. Many attempts are in progress to improve calcium flesh concentration and thus its keeping quality. Aim of the present work is to study the capability of both field and posthavest treatments in keeping fruit quality during cold storage. 'Braeburn' apples field or postharvest treated with diverse calcium formulae and additives, were examined for quality (total soluble solids, titratable acidity, flesh firmness and starch content), calcium content and cell wall composition (cellulose, total, soluble and insoluble pectins and neutral sugars) at harvest and after seven months of controlled atmosphere cold storage (ULO). Field and postharvest calcium treatments did not affect quality traits both at harvest and after storage, nevertheless they influenced calcium contents in fruit flesh and they modified cell wall composition. All field treatments increased fruit calcium content up to 10-60% and the effects lasted until the end of storage. Postharvest treatments increased cation level (8-60%) at the end of storage. Cellulose content increased for both treatments and the effect lasted during storage. Field supplies seemed to stimulate pectin biosynthesis also after harvest for long time, while postharvest treatments did not increase pectin biosynthesis but were very effective in preventing pectin solubilization. Field treatments reduced rhamnose content in stored fruits, thus reducing the side chain number of polygalacturonic acid with the consequent increase of the pectic matrix cohesion to which ascribe the flesh crispness of this apple cultivar. Galactose, a basic component of pectin chains, was positively affected by field supplies and its high level was maintained through the storage period. Postharvest calcium treatments did not increase galactose content, but were very active in keeping its level. This results confirmed the influence of calcium on cell wall metabolism.