Research Report: Ciku maturity

(ps. if you ask me why I put it here, it's for reference/backup purposes)

 So, a lot of people have been asking me how do I chose my ciku for research purposes. My initial answer, as I've said in the Proposal subject, is according to the ripeness index taught to me by a fellow lab technician. The reason is that there are no "Sapota Official Maturity Index"as there are for other fruits, say Carambola (Belimbing) or Papaya. The closest one for Sapota is the East African Standard, but is still in draft and not intended for official purposes.

So another way to specify the maturity level of the fruits that I chosen is by physico-chemical standards commonly employed in fruit grading. They are:

1) Color
2) Texture
3) Brix
4) pH
5) Moisture Content

Sampling method:
Sample is taken from the fruits dealer. Took as much similarly-ripened Ciku as I can (usually around 1.5kg). The ripeness is gauged by its firmness to the touch. Then after ripened overnight (I usually buy it slightly underripe) it was taken to the lab where ten of the fruit was selected for testing. They have relatively uniform size and shape.

1) Color
Color is measured using the Chroma Meter, Minolta Brand.

Ten samples is measured twice at different places and the results are recorded in L, a and b format, where L is for lightness, a is red-green and b is bluish-yellow. The sample is placed on the measuring head while making sure it completely covers the light source. Data taken are collected and averaged.




As seen here, the average is L: 61.041, a: 8.113 and b: 31.781. When put into the RGB calculator, this color is shown:

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which almost accurately represents the color of a ripe ciku.

2) Texture
Texture analysis can help gauge the maturity of fruit. Especially when it comes to firmness, which is directly correlated to maturity (the firmer the fruit the less mature it is).The instument is Ta-xT plus texture analyzer. Since there are no methods available to assess Ciku, The method for peach firmness (PCH1/BS) is used since peach are the most similar with ciku in size and shape. These are the parameters:

Probe: Blade set HDP/BS 5 kg load cell.

Mode: Measure force in compression
Option: Repeat until count
Count:10
Pretest speed: NA
Test speed: 5.0mm/s
Post test speed: 10mm/s
Distance: 38mm
Trigger: button
Tare: auto
Data aquisition rate: 200pps

Method:
i) parameters are loaded in the Exponent software.
ii) blade is calibrated using calibrate function.
iii) each ciku fruit is cut into wedges, of similar sizes and thickness.
iv) test is started. Ciku wedge is placed perpendicular to the blade, cut into half.
v) Ciku wedges are placed one after another, while making sure not to get fingers stuck in it.
vi) after 10 counts the experiment stops and measurement are taken.

Thus, from the result, the measurements average is 649.315g. Here we can see that the flesh is quite firm.

3) Brix
Brix is a measurement of sugar content in fruit. As the fruit goes ripe, the sugar content increases and brix also increased. The equipment used is a refractometer.

Source here

Procedure:
i) All ten sample pieces are mashed into pulp.
ii) A drop of the juice is put on the glass slide.
iii)The measurement is read by looking into the eyepiece.

The measurement for the Brix of ciku juice is 21.

4) pH
pH, similarly to Brix, increases as fruit ripens. From the 10 sample-pulp juice, the pH obtained is around 5.48. pH slowly increases the longer we leave the juice idling, thus the result may not be 100% representative of true pH value. Still, it is a good result.

5) Moisture Content
Moisture content determination is just an additional measurement parameter I added, that might be useful to relate it to Brix (as water content is correlated to Brix as well). The equipment used is the infrared moisture content analyzer FD-610.

A sample around 3-7 grams is put on the drier, and preset to 100C drying at 10 min. Four measurements are obtained, 49.1%, 10.0%, 19.5% and 29.1%. The average moisture content is 26.93%. I used the method of cabinet drying, which gives a similar average is 26.9996%.

The limitation of this method compared to conventional drier-oven method is that it does not dry completely. Although I did not exceed the 7g-limit and the fruit is in small pieces, the fruit is still moist. 

Conclusion
Even without a proper standard, we can classify a fruit's maturity using its physico-chemical properties. It can help identify what samples that are used and justify its behavior in subsequent testing.
Therefore, my ciku samples' specification is as follows:

Ciku type:Subang

Origin: Ipoh

Maturity level:-

Color: L: 61.041, a: 8.113 and b: 31.781 (|                   |)

Firmness: 649.315g

Brix: 21

pH: 5.48

Moisture content: 26.9%