The investigation of the effects of infrared drying process conditions on the physicochemical properties of coconut (cocos nucifera L.) fruit and optimization of process

In this study, coconut was dried using infrared drying, one of the innovative drying methods. Different drying process parameters were applied, including lamp power (150, 200, and 250 W), drying time (30, 135, and 240 min), lamp distance (15, 20, and 25 cm), and sample thickness (10, 15, and 20 mm). Accordingly, the experimental study was conducted according to the central composite design of the response surface methodology. Moisture content (%), water activity (aw), pH, free acidity (%), total phenolic content (mg GAE/g), colour (L*, a*, b*) and FT-IR spectral analyses were performed on the coconut samples. Additionally, the total oil content and fatty acid composition of fresh coconut were determined using gas chromatography (GC). Three-dimensional graphs were drawn using the obtained results, analysis of variance (ANOVA) was performed at a 95% confidence interval and appropriate mathematical models were developed by using R2 values. In the drying experiments, the lowest moisture content (1.80%) and water activity (0.283) values were obtained with drying at 250 W lamp power, 240 min drying time, 15 cm lamp distance, and 10 mm sample thickness. The pH, free acidity, and total phenolic contents of the dried samples were determined in the ranges of 5.77–6.47, 0.56–1.35%, and 140.71–209.34 mg GAE/g, respectively. In coconuts dried at higher lamp power and longer drying times, the L* value (brightness), an important quality criterion, decreased, while the b* and a* values increased, and it was observed that the colour values were negatively affected by the increase in lamp power and drying time. The total oil content of the fresh sample was calculated as an average of 45.16%. Regarding the fatty acid composition, it was determined that medium-chain fatty acids were predominant in fresh coconut oil, with lauric acid (C12:0) being the dominant fatty acid at 49.78%. Based on the findings of this study, the effectiveness of infrared drying, the effects of drying conditions on coconut, and the applicability of the mathematical approach were demonstrated.