Fruit development and oil content of olives grown in the South Island of New Zealand: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Horticultural Science with Honours at Lincoln University

Abstract

The focus of this experiment was to monitor fruit development of olives grown in the South Island of New Zealand. Optimum harvest time is an important consideration for the production of olive oil in New Zealand. Growers require a simple and reliable test that can be used in the field to estimate the time when oil content and quality are at a maximum. Dry matter percentage and fruit colour were investigated as two potential indicators of maturity. Fruit development and oil content of five olive cultivars ('Barnea', 'Frantoio', 'Koroneiki', 'Leccino', and 'Manzanillo') from three groves in Blenheim and three groves in North Canterbury, New Zealand were monitored between 2 April and 2 July 2002. Fresh weight per fruit ranged from 0.62 g to 2.38 g and dry weight per fruit ranged from 0.25 g to 0.85g for the five cultivars at the final harvest on 2 July. From these measurements dry matter percentage was calculated. Colour development was measured by the International Olive Oil Council colour index, and values increased from a score of one (when the epicarp was green) to four (when the epicarp was black) however, not all cultivars completed epicarp pigmentation during this experiment. Olive oil was extracted from the fruit using a soxhlett extraction system and expressed as a percentage of fresh and dry weight. The highest oil content (as a percentage of fresh weight) recorded was 21.0% for the cultivar 'Frantoio' when grown at Blenheim. To obtain fresh and dry weights for the dry matter percentage calculations, a microwave drying method was developed for olive fruit. This was based on the protocol developed for the avocado industry (U.C.A.N.R., 2002). Olive fruit were dehydrated by microwave heating for a period of 50 minutes at a low power setting. Dry matter percentage were correlated with oil content (as a percentage of fresh weight) to try and establish a parameter that could be used to estimate optimum harvest date of olives grown for oil extraction in New Zealand. Dry matter percentage could be used as a predictor of fruit oil content, only if calibrated for each cultivar. This was because that the relationship between these two variables varied among cultivars (R² =0.09 - 0.86). Fruit colour development could also be used to estimate fruit maturity for individual cultivars but did not give as accurate or reliable correlation as dry matter percentage.