Page 148 - The Manga Guide to Biochemistry

Oh...so sucrose-phosphate synthase is what makes sucrose by combining

glucose and fructose .

sucrose j Invertase

(low activity)

k sucrose-

phosphate
synthase

Glucose

fructose fructose 6-phosphate
UDP-glucose

So does that mean that a fruit gets sweeter as more sucrose is produced?

Well, glucose, fructose, and sucrose are all sweet. Of the three, fructose is the
sweetest, followed by sucrose, and then glucose.

Fructose Sucrose Glucose Degrees of
2 1.4 1 sweetness, when

the sweetness
of glucose

is considered
to be 1.

Wow!

So as fructose or sucrose increases, the fruit gets sweeter and becomes ripe. For
example, citrus fruits are best picked in winter, after their sucrose content increases
and they’re at their most sweet and delicious. For Japanese pears, on the other
hand, the difference in the amounts of these sugars is more striking; as the fruit
ripens, the fructose and sucrose both increase suddenly, as polysaccharides are
broken down.

Similar to citrus fruits, the sweetness of melons depends mostly on sucrose
content, and they’ll be most delicious when sucrose levels are highest.

When you look at the graphs on the previous page, you can see that the fructose or
sucrose increases, so the fruit gets really sweet in the harvesting season.

134 Chapter 3