Note on sugars (based on Wikipedia "Fructose" article):

Fructose is an isomer of glucose. It has a 5-ring form and a 6-ring form - normally occurring as 70% 5-ring and 30% 6-ring.
The 5-ring form is 70% sweeter than sucrose, and the 6-ring form is about as sweet as sucrose.
Warming the 5-ring form converts it to the 6-ring form, so we can assume that fructose in cooked food is about as sweet as sucrose.
Glucose is about 75% as sweet as sucrose.

Sucrose is digested in the small intestine to produce equal quantities of glucose and fructose.
Most of the fructose is absorbed and then processed by the liver to produce glycogen. This processing may interfere with the liver performing other tasks.

Unabsorbed fructose enters the large intestine where it "can provide nutrients for the existing gut flora, which produce gas. It may also cause water retention in the intestine. These effects may lead to bloating, excessive flatulence, loose stools, and even diarrhea depending on the amounts eaten and other factors."

Glucose can be used directly by all cells of the body.

I get the impression that consuming high levels of fructose is not a good thing, but equal quantities of fructose and glucose is probably OK.

Maltose is about 32% as sweet as sucrose.

Maltose is digested by maltase to form glucose (2 glucose molecules per maltose molecule).

Table from Wikipedia:

Table 1 – Sugar content of selected common plant foods (g/100g)

Food Item Total

Carbohydrate

 Total

Sugars

 Free

Fructose

 Free

Glucose

 Sucrose Fructose /

Glucose

Ratio

 Sucrose

as a % of

Total Sugars
Fruit
Apple 13.8 10.4 5.9 2.4 2.1 2.5 19.9
Apricot 11.1 9.2 0.9 2.4 5.9 0.7 63.5
Banana 22.8 12.2 4.9 5.0 2.4 1.0 20.0
Grapes 18.1 15.5 8.1 7.2 0.2 1.1 1.0
Peach 9.5 8.4 1.5 2.0 4.8 0.9 56.7
Pear 15.5 9.8 6.2 2.8 0.8 2.1 8.0
Vegetables
Beet, Red 9.6 6.8 0.1 0.1 6.5 1.0 96.2
Carrot 9.6 4.7 0.6 0.6 3.6 1.0 70.0
Corn, Sweet 19.0 3.2 0.5 0.5 2.1 1.0 64.0
Red Pepper, Sweet 6.0 4.2 2.3 1.9 0.0 1.2 0.0
Onion, Sweet 7.6 5.0 2.0 2.3 0.7 0.9 14.3
Sweet Potato 20.1 4.2 0.7 1.0 2.5 0.9 60.3
Yam 27.9 0.5 tr tr tr na tr
Sugar Cane 13 - 18 0.2 – 1.0 0.2 – 1.0 11 - 16 1.0 100
Sugar Beet 17 - 18 0.1 – 0.5 0.1 – 0.5 16 - 17 1.0 100

Table from http://www.brewery.org/brewery/library/SugAcid.html:

Fruit   Sugar Content       Acid Content
        %of fresh weight    %of fresh weight
 
Lime             1%             5.0%
Avocado          1              0.2
Lemon            2              5.0
Tomato           3              0.5
Cranberry        4              3.0
Red Currant      6              1.8
Grapefruit       6              2.0
Guava            7              0.4
Cantaloupe       7              0.2
Strawberry       7              1.6
Raspberry        7              1.6
Blackberry       8              1.5
Papaya           8              0.1
Apricot          9              1.7
Watermelon       9              0.2
Peach            9              0.4
Black Currant   10              3.2
Pear            10              0.1
Honeydew        10              0.2
Orange          11              1.2
Plum            11              0.6
Blueberry       11              0.3
Gooseberry      11              1.8
Passion Fruit   11              3.0
Prickly Pear    11              0.1
Mango           11              0.5
Pineapple       13              1.1
Pomegranate     13              1.2
Apple           13              0.8
Cherry          14              0.5
Kiwi            14              3.0
Persimmon       14              0.2
Fig             15              0.4
Grape           16              0.2
Banana          17              0.3
Litchi          17              0.3



Sugar food sources Sugar content (g/100 gram food)
Dates, deglet noor  63.35
Apples, dried, sulfured, uncooked  57.19
Peaches, dried, sulfured, uncooked  41.74
Plums, dried (prunes), uncooked  38.12
Plums, dried (prunes), stewed, without added sugar  24.98
Strawberries, frozen, sweetened, sliced  24.01
Plums, canned, purple, heavy syrup pack, solids and liquids  22.31
Plums, canned, purple, heavy syrup pack, solids and liquids  22.30
Peaches, frozen, sliced, sweetened  22.18
Blueberry, frozen, sweetened 19.72
Peaches, canned, heavy syrup pack, solids and liquids  18.64
Grapes, red or green (european type varieties, such as, Thompson seedless raw)   15.48
Mangos, raw  14.80
Plums, canned, purple, juice pack, solids and liquids  14.22
Bananas, raw  12.23
Apple juice, canned or bottled, unsweetened, without added ascorbic acid  10.90
Apples, raw, with skin  10.39
Peaches, canned, juice pack, solids and liquids  10.27
Apples, raw, without skin  10.10
Blueberry, raw 9.96
Apricots, raw  9.23
Plums, raw  9.92
Kiwi fruit, (chinese gooseberries), fresh, raw  8.99
Peaches, raw  8.39
Melons, honeydew, raw  8.12
Melons, cantaloupe, raw  7.86
Papayas, raw  5.90
Strawberries, raw  4.67
Corn, sweet, white, cooked, boiled, drained, without salt  4.06
Corn, sweet, yellow, frozen, kernels on cob, cooked, boiled, drained, without salt  3.59
Corn, sweet, yellow, canned, vacuum pack, regular pack  3.56
Corn, sweet, yellow, canned, cream style, regular pack  3.23
Corn, sweet, yellow, cooked, boiled, drained, without salt  3.17
Corn, sweet, yellow, frozen, kernels cut off cob, boiled, drained, without salt  3.07
Lemon juice, raw  2.40


Table from http://www.thefruitpages.com/contents.shtml:


Food
energy
water
fiber
fat
protein
sugar
vit.A
vit.C
vit.B1
vit.B2
vit.B6
vit.E
 substance = 100 g.
kJ/Kcal
 %
g
g
g
g
ug
mg
mg
mg
mg
mg
Apple
207/49 
84
2.3
0
0.4
11.8
2
15
0.02
0.01
0.05
0.5
Apricot
153/36 
87
2.1
0
1.0
8.0
420
5
0.06
0.05
0.06
0.5
Avocado
523/126 
81
0.2
10
2.0
7.0
20
17
0.06
0.12
0.36
3.2
Blueberry
204/48 
80
8.4
0
1.0
11.0
0
10
0.02
0.03
0.05
1.9
Blackberry
170/40 
85
8.7
0
2.0
8.0
30
150
0.08
0.04
0.07
1.0
Banana
375/88 
76
2.7
0
1.2
20.4
3
10
0.04
0.03
0.36
0.3
Carrots
48 /11 
92
3.3
0
0.6
2.2
312
2
0.03
0.04
0.08
0.2
Cranberry
68 /16 
89
4.2
0
0.0
4.0
0
15
0.00
0.01
0.07
0
Cherry
221/52 
86
1.2
0
0.0
13.0
40
10
0.02
0.02
0.04
0.1
Date
1275/300
20
7.5
0
2.0
73.0
0
0
0.05
0.10
0.10
0.7
Fig
340/80 
80
2.0
0
1.0
19.0
10
3
0.06
0.05
0.11
-
Grapefruit, Red
128/30 
90
1.4
0
0.9
6.6
0
40
0.07
0.02
0.03
0.5
Grapes
274/64 
83
2.2
0
0.6
15.5
0
3
0.03
0.01
0.08
0.6
Guava
 306/72 
81
5.3
 0
1.0 
17.0 
30
218 
0.04 
0.04 
0.14 
- 
Gooseberry
170/40 
88
3.2
0
1.0
9.0
0
30
0.02
0.01
0.08
0.4
Food
energy
water
fiber
fat
protein
sugar
vit.A
vit.C
vit.B1
vit.B2
vit.B6
vit.E
 substance = 100 g.
kJ/Kcal
 %
g
g
g
g
ug
mg
mg
mg
mg
mg
Kiwi Fruit
168/40 
84
2.1
0
1.1
8.8
5
70
0.01
0.02
0.12
1.9
Kumquat
289/68 
82
1.5
0
1.0
16.0
160
55
0.14
0.06
-
-
Lemon
51/12 
96
1.8
0
0.0
3.0
0
40
0.06
0.02
0.04
0.8
Lime
 156/37 
91 
0.3
0 
0.0
7.0
0
40
0.03
0.02
0.08
-
Lychee
323/76 
82
1.5
0
1.0
18.0
0
39
0.05
0.05
-
-
Mandarin / Tangerine
177/42 
88
1.9
0
0.9
9.5
12
30
0.08
0.03
0.084
0.4
Mango
255/60 
84
1.0
0
0.0
15.0
210
53
0.05
0.06
0.13
1.0
Melon, Red Water
153/36 
93
0.6
0
1.0
8.0
30
6
0.04
0.05
0.07
-
Melon, cantaloupe
122/29 
89
0.6
0
0.9
6.3
7
32
0.05
0.02
0.10
0.2
Olive
586/142
75
4.4
14
1.0
3.0
50
0
0.03
0.08
0.00
2.0
Orange
198/47 
87
1.8
0
1.0
10.6
2
49
0.07
0.03
0.06
0.1
Papaya
136/32 
91
0.6
0
0.0
8.0
40
46
0.03
0.04
0.04
-
Passion Fruit
158/37 
88
3.3
0.4
2.6
5.8
125
23
0.03
0.12
-
0.5
Peach
151/36 
89
1.4
0
1.0
7.9
15
7
0.01
0.02
0.02
0.0
Pear
201/47 
86
2.1
0
0.3
11.5
0.0
4
0.01
0.01
0.02
0.1
Red Bell Pepper
119/28 
91
2.2
0
1.0
6.0
172
80
0.04
0.14
0.43
6.4
Persimmon
325/76
81
0.5
0
0.5
18.6
260
16
0.02
0.03
-
-
Pineapple
211/50 
84
1.2
0
0.4
12.0
20
25
0.07
0.02
0.09
0.1
Pomegranate
343/81 
82
3.4
0
1.0
17.0
10
7
0.05
0.02
0.31
-
Plum
177/42 
84
2.2
0
0.8
9.6
18
5
0.02
0.03
0.10
0.7
Strawberry
99/23
91
2.2
0
0.7
5.1
10
60
0.02
0.03
0.06
0.4
Tomato
48/11 
97
1.4
0
0.9
1.9
140
15
0.05
0.02
0.08
0.7
Food
enrgy
water
fiber
fat
protein
sugar
vit.A
vit.C
vit.B1
vit.B2
vit.B6
vit.E
 substance = 100 g.
kJ/Kcal
 %
g
g
g
g
ug
mg
mg
mg
mg
mg


Implications for cake recipe:

Current cake recipe includes:
    Banana    150gm
    Dates         75gm
    Milk          120gm
    Water         60gm    (for date paste - estimated)

Using the last table above, we get:
    Water content = 150*0.76 + 75*0.2 + 120 + 60 = 309gm
    Sugar content = 150*.204 + 75*0.73 = 85gm

If we were to get all the sugar from apples,  we would need:
    85 / 0.118 = 720gm of apples
This would provide:
    720*0.84 = 605gm of water (i.e. double what I currently use).

Cake: getting the right balance of ingredients

From http://www.nzbakels.co.nz/services/customer.cfm?content_id=362:

"examination of the balance of a formula enables recognition of limits for each ingredient. To study this, convert the quantity of each ingredient to a percentage of the flour of any formula. In a good normal cake, the following recipe is used: If the sugar content of a recipe is higher than 60% of flour weight, the total liquid must be increased to above 85% and/or the baking powder lowered. On the other hand, if the liquid content is above 85% then the sugar content will need to be above 60% to produce a good cake. The same result would be attained by increasing the baking powder."

My current cake recipe has:
    Flour:                  150gm
    Fat:                       75gm
    Dates:                   75gm
    Eggs:                       3 large (3 * 68 = 204gm)
    Cocoa:                   15gm
    Bananas:              150gm
    Baking powder:       2tspns (about 15gm?)
    Water:                  60gm
    Milk:                    120gm

This equates to:
    Sugar:                (150*.204 + 75*0.73) * 100 / 150 = 57%
    Total liquid:        (204 + 150*0.76 + 75*0.2 + 120 + 60) * 100 / 150 = 342%
    Fat:                    75 * 100 / 150 = 50%
    Baking powder:  15 * 100 / 150 = 10%