Biochemical Variation of Tannins and Total Reducing Sugars during Three Ripening Stages of Naseberry (Manilkara zapota cv. Alano).

The mature unripe naseberry fruit is very astringent up until mid-ripe, and becomes very sweet when ripe. This study aimed to determine the internal colour and the concentration of total reducing sugars, and tannins within the pulp and skin of naseberry (Manilkara zapota cv. Alano) during three different ripening stages. Internal colour was assessed using a Chroma Meter CR-400 (Konica Minolta) where the L* value measures lightness and Chroma (C) measures colour intensity.   The biochemical content of the sample extracts, viz. reducing sugars and tannins were quantitatively assessed colorimetrically and via titration, respectively.  Results showed that the L* values and hue angle (hº) of the pulp were significantly different (p< 0.05) as the pulp darkened, while colour intensity (35.80 -34.76) showed no significant difference across all stages. Reducing sugars concentration increased (89.45 to 113.98 mg/g) throughout ripening, with ripening stage 1 being statically significant. The percentage of tannins content in pulp and skin were significantly different at stage1 (3.05% and 1.88%, respectively) and decreased during ripening. Additionally, a strong correlation existed between reducing sugars, tannin content, and hue angle, while  a very strong correlation was found between tannin content in the pulp and skin, and the hue angle (p<0.01). These parameters are good indicators for assessing the palatability and quality of the fruit in understanding the changes that occur in its biochemical content during ripening.

Key words: tannin, reducing sugars, Chroma, hue angle, Manilkara zapota.