Changes in fruit quality and volatile flavor compounds during on-tree maturation of longkong

Abstract

© All Rights Reserved. Longkong (Aglaia dookkoo Griff.) is a non-climacteric fruit, juicy with typically aromatic smell and sweet but slightly sour taste. The optimal harvest period was started from 13 to 15 weeks after anthesis. The physical and chemical qualities of longkong at different stages of on-tree maturation were evaluated as follows: ripe (13 weeks after anthesis); medium ripe (14 weeks after anthesis); and full ripe (15 weeks after anthesis). It was found that longkong became light to bright yellow with the stages of maturation (p < 0.05). This can be indicated by the highest lightness (L* = 64.21) and yellowness (b* = 34.37) values shown in longkong at the full ripe stage. Moreover, the texture changed and softened with maturation (p < 0.05). The fruit size and weight increased with the stage of maturity but there was no significant difference (p < 0.05). The fruit were in the range of 3.17-3.30 cm in diameter and 19.94-21.36 g in weight. The moisture content was slightly increased with the stage of maturity (p < 0.05). During on-tree maturation, from the ripe to full ripe stages, acidity and organic acids (citric, maleic and malic acids) decreased while pH, TSS and total sugar content increased. The main sugars found in longkong were sucrose, glucose and fructose, respectively. From the ripe to medium ripe stages of longkong maturation, the sucrose content slowly increased from 9.88% to 11.44%. However, during the full ripe stage the sucrose content was 7.03% (p < 0.05). The glucose content significantly decreased from 1.98% to 1.46% during the ripe to medium ripe stages of the maturing longkong and then it increased again to 2.92% at the full ripe stage (p < 0.05). Similarly to fructose content, it also decreased from 2.76% to 2.20% during the ripe to medium ripe stages of the maturing longkong. After that it increased again to 3.39% at the full ripe stage (p < 0.05). The green aroma of 1-hexanol was the only volatile compound which was found in ripe longkong. From the ripe to full ripe stages, the longkong had more fruity and sweet characteristics. There were many terpenes and their derivatives. The key volatile flavor compounds were d-germacrene and 3-hydroxy-2-butanone. They had herbaceous and sweet attributes.