Non-destructive and destructive physical measurements as indicators of sugar and organic acid contents in strawberry fruit during ripening

Abstract

Strawberry fruit is appreciated by consumers for its characteristic taste, which can be attributed to the balance between sugars and organic acids content, but strawberries are also a rich source of vitamin C (ascorbic acid). This study focuses on the suitability of different physical parameters, such as ripening index (IAD), firmness and total soluble solids content, as indicators of the content of sugars and organic acids during ripening. Five ripening stages were defined - green, white, ripe red, fully ripe dark red and overripe stage at five different cultivars. As the fruit ripened, the content of ascorbic acid, sugars and sugar/acid ratio increased and the organic acids content decreased, but the changes varied among cultivars. The ripening index (IAD) strongly correlated with the total sugar content (r = -0.72), total organic acids content (r = 0.70) and sugar/acid ratio (r = -0.82). Additionally, firmness correlated well with the content of sugars and organic acids. On the other hand, TSS showed a weaker correlation with the total sugar content (r = 0.38). Although, both the ripening index (IAD) and firmness showed strong correlations with sugars and organic acids content and can help distinguish unripe fruit from ripe fruit, the use of these parameters for distinguishing between different of ripe fruit (from early ripe to overripe) can be limited only to certain cultivars.