Thermal softening kinetics of African black olive fruit: Influence of temperature and water absorption on the thermal maceration dynamics and thermophysical properties

Abstract

Softening of the pulp of African black olive fruit (Canarium schweinfurthii) is one of the unit operations in the maceration and de-pulping process of the pulp for consumption or to produce masticatories or oil. The softening process is temperature-sensitive, and hot water treatments are applied arbitrarily by local processors that might result in the hardening instead of maceration or softening of the fruits. This study, therefore, investigates the effect of hot water treatment on the softening and maceration kinetics of the fruits at different temperatures. To achieve this, two varieties of the fruits were selected and immersed in a water bath at temperatures of 30–60°C. Some of the parameters determined were the moisture absorption rate, hardness ratio, dimensional changes, thermal properties, and softening kinetics. The results showed that the softening curves and kinetics were directly affected by the temperature of the hot water. Hardening of the pulp occurred at a hot water temperature of 60°C for the long variety. In contrast, softening did not take place at 30°C for both varieties. Maceration occurred at 40–50°C for the long variety and 40–60°C for the short variety. The maximum maceration rate was at 50°C with an average softening rate of 0.161 N/hr for long variety and the least rate was 0.0565 N/hr for 40°C short variety. The activation energy was 47.46 kJ/mol for the short variety and 48.06 kJ/mol for the long variety. All the properties were presented as a function of the temperature or moisture content with good results. The obtained data will be helpful in the scaling up of the de-pulping process of the fruit by developing processing equipment for large-scale industrial processing and also prevents hardening that can result in losses for small-scale processors who soften and sell the fruits as snacks. Novelty impact statement Several studies abound on African black olive (Elemi) but none is available on the processing dynamics of softening the pulp for de-pulping the fruits to produce masticatories or oil. A good number of these research focused on physical properties, biochemical contents, proximate composition, and other in vivo assessments. Therefore, the present study highlights the softening kinetics of the fruit during the maceration process. It showed that (1) hardening of the pulp occurs at 60°C while 30°C cannot cause maceration; (2) The maceration rate follows a three-period pseudo first-order kinetics; (3) Quicker maceration can be achieved at 50°C soaking water temperature.