Effect of blanching, freezing and thawing on olive fruits quality

Abstract

Freezing of olives includes an initial blanching step, followed by freezing itself and thawing. Fresh olive fruits (Olea europaea L. vars. Manzanilla and Hojiblanca), collected at the appropriated ripening stage, were immersed in a water bath at 95 °C for 2.5 min, subjected to calcium treatment, frozen by forced convection with air at -30 °C, packed under slight vacuum, stored at -24 °C (48 h) and thawed in sodium hydroxide (NaOH) solution at 1%. Olive firmness was determined through a texture analyzer equipped with a 2-mm diameter cylinder probe. Blanching operation had the most negative effect on alterations in drupe consistency. Compared to fresh samples, significant decreases in the cuticle hardness and pulp consistency were observed varying from 8.98 to 5.55 N and 9.66 to 6.19 Nmm, respectively in Manzanilla fruit and from 12.6 to 7.53 N and 11.3 to 6.48 Nmm, respectively in Hojiblanca one. However, subsequent freezing and thawing only cause an additional loss of cuticle hardness and pulp consistency, with respect to mechanical properties of fresh fruits, of 6.9 and 9.2% in Manzanilla and 8.0 and 12.8%, in Hojiblanca olives, respectively. Total chlorophylls content (TCC) and total carotenoids (TC) were determined by a spectrophotometric assay. TCC was similar in both fresh fruits (49.0±5.57 and 55.6±5.29 µg/g fw in Manzanilla and Hojiblanca, respectively). Blanching did not significantly change the TCC in Hojiblanca olive, but significantly increased (23%) in Manzanilla. TC was significantly higher in Hojiblanca than in Manzanilla (90.5±6.68 and 68.4±4.34 µg/g fw, respectively), and blanching increased (p < 0.05) TC by 68% and 14% in both cultivars, respectively. Complete processing maintained the TCC of both fresh drupes, but increased by 70% their initial TC. Results were dependent on cultivar and can help in designing blanching and freezing operations which can be applied in olive industry.