Colour improvement in ripe olive processing by manganese cations: industrial performance Concepci  on Romero * , Pedro Garc  õa, Manuel Brenes, Antonio Garrido Food Biotechnology Department, Instituto de la Grasa (CSIC), Padre Garc  õa Tejero 4, 41012 Sevilla, Spain Received 1 April 2000; accepted 4 September 2000 Abstract The use of Mn to improve the darkening process of ripe olives was studied with Manzanilla, Hojiblanca, Carrasque~ na and Cacere~ na cultivars on both pilot and industrial scales during the ``desalting'' and storage steps. Results showed a general im- provement of colour when Mn was used, although it was limited in the case of the Cacere~ na cv. Its addition to the storage brine for a period of at least 1 month yielded the best darkened olives and gave rise to low residues of Mn (around 10 mg/kg) in the ®nal product, these conditions of processing being the most recommendable. This work has scaled up to use Mn during the oxidation process of ripe olives from pilot to industrial scale. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Ripe olives; Darkening; Manganese; Iron; Processing 1. Introduction The industrial production of ripe olives involves the storage of fruits in brine for a period up to 18 months (Garrido, Garc  õa, Monta~ no, Brenes, & Duran, 1993), the darkening step and then canning. Before darkening, storage brines are discharged and fruits are oxidised by successive treatments with NaOH solutions (lye). Dur- ing the intervals between lye treatments, olives are sus- pended in water bubbled with air (Garc  õa, Brenes, & Garrido, 1991). Throughout this operation, olives darken progressively due to the oxidation of o-diphe- nols, hydroxytyrosol (3,4-dihydroxyphenyl ethanol) and caeic acid (Brenes, Garc  õa, & Garrido, 1992). Then, a ferrous salt (gluconate or lactate) is added to ®x the colour formed (Brenes, Romero, Garc  õa, & Garrido, 1995a). Finally, fruits are canned and sterilised (Ro- mero, Garc  õa, Brenes, & Garrido, 1995). The whole process lasts for 5±7 days, generates a large volume of wastewater and does not always result in a shiny dark colour. Manganese cations are recognised as safe in the USA (Anonymous, 1996) and it has been reported that manganese salts catalyse the chemical oxidation of olive o-diphenols in model systems (Garc  õa, Romero, Brenes, & Garrido, 1996) and the darkening reaction involved in ripe olive processing (Brenes, Romero, Garc  õa, & Garrido, 1995b). The use of Mn salts in the dierent steps of ripe olive processing of Manzanilla cultivar (Olea europaea L.) markedly improved the colour. Manganese salts can be added to the storage brine or during the ``desalting'', an optional step applied previously to the oxidation in some industries (Romero, Garc  õa, Brenes, & Garrido, 1998). However, cultivars other than Hojiblanca, Carras- que~ na and Cacere~ na are also employed for the elabo- ration of ripe olives. Furthermore, it is not known what in¯uence the addition of Mn has when the fresh fruits are oxidised, neither what occurs during the preserva- tion time in brine. Nothing is also known about the eect of the manganese addition on the sensory char- acteristics of ripe olives. The aim of this work was to study, at laboratory level, the use of Mn ions in the ripe olive processing of dierent cultivars during the preservation time in brine and the desalting step. Results were also checked at industrial scale. 2. Materials and methods 2.1. Olives Experiments at laboratory scale were carried out on fresh fruits of the Hojiblanca, Manzanilla and Cacere~ na Journal of Food Engineering 48 (2001) 75±81 www.elsevier.com/locate/jfoodeng * Corresponding author. Fax: +34-954691262. E-mail address: crb@cica.es (C. Romero). 0260-8774/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 1 5 1 - 5