In this article we will discuss about the ripening of sugarcane.
The ultimate economic product of sugarcane is not the seed but the sugar, which is stored in the stalk and cannot be seen by naked eye. Sugarcane maturity, therefore, cannot be judged by the considerations applicable to grain crops.
Accumulation of sugar in the stalk begins soon after completion of elongation phase when glucose produced during photosynthesis is not utilised mainly for further growth but stored largely in the stalk as sucrose.
When concentration of this sucrose exceeds 16 per cent and juice purity increase over 85 per cent, the cane is said to be mature. These parameters, however, cannot be judged by physical appearance of the crop and so is the maturity.
Several methods are available to determine the quality parameters of cane juice but the estimation of pol per cent juice and pole per cent bagasse are important. The sum of the two, after converting them on cane basis, gives the pol per cent cane. Procedure for estimating quality of cane has been discussed by Gupta (1977).
Analysis Procedure of Ripening Sugarcane:
A minimum of two whole clumps or ten canes of all sizes, randomly selected, should be taken as a sample. The sample is cut into pieces of 45-50 cm, weighted and juice extracted by crushing in laboratory crusher twice which is collected in a weighed bucket containing 0.5 g mercuric chloride (preservative). Extracted juice is weighed and percentage of extraction calculated.
Juice Brix:
Suspended particles in juice are removed bypassing the juice through 150 mesh sieve. Fill up 1000 ml cylinder with the cane juice and allow it to settle for 15 minutes. Gradually lower the standard brix spindle and allow it to float. When the brix spindle becomes stationary, take the brix reading at the line with the plain surface of the juice and note the temperature of the juice and correct the brix at 20°C from the chart.
Juice Pol Per cent:
Transfer 100 ml juice sample into a 250 ml measuring flask with stopper and add minimum quantity of Horne’s lead subacetate for good clarification. Shake well and filter. Polarise the filtrate in 200 mm calibrated pol tube at room temperature and not the pol reading. Find out the pol per cent juice from the Schmitz’s table from corrected pol reading and corrected brix.
Moisture Per cent Bagasse:
Take 100 g of well composited bagasse in a weighed tray perforated all sides. Heat the sample in air oven at 110°C for 4-6 hrs to constant weight and calculate moisture per cent in bagasse.
Pol Per cent Bagasse:
Deerr Bagasse digester of 1000 g capacity is filled up with water till it over flows from upper stop-cock.
The quantity of bagasse sample to be taken for analysis is determined as indicated below:
where,
W = the water capacity of the vessel (ml)
a = moisture per cent of bagasse
x = quantity of bagasse.
The digester is filled with water containing about 1.0 g sodium carbonate up to the level of the upper stopper and required quantity of bagasse sample is taken in digester basket and immersed in the digester. Lid of the digester along with reflux condenser is placed in position and the whole apparatus is put on a 1500-Watt heater or stove.
It is heated to boiling and the boiling continued for at least an hr. Digester with its contents is removed and allowed to cool. The lid and condenser are removed and the contents well mixed by moving the basket up and down by the handle. Required quantity of the extract is drawn through lower stopcock into a flask and allowed to cool to room temperature.
Treat 200 ml of this extract with Home’s or ICUMSA standard lead subacetate, shake well, filter and polarise the clear solution in a 400 mm pol tube. The reading directly gives pol per cent bagasse.
Calculation:
Assessment of Ripening:
As the crop advances in maturity, its water content decreases (77-88%), sucrose content increases (8-22%) and reducing sugars decrease (0.3-3.0%). Both organic (0.5-1.0%) and inorganic (0.3-0.8%) non-sugars also decrease. At peak maturity, sugar content will be at its maximum, reducing sugars and non-sugars (or interfering substances in gur and sugar manufacture) at their optimum level.
When the cane stalk is cut across with a sharp knife, a little higher than its middle and the cut end exposed to reflect sunshine, if the end looks watery, the cane is unripe, if it sparkles slightly, it can be taken to be getting ripe. Trial boiling of juice to judge the maturity is common among farmers. If the gur set well in the boiling, gur making would be taken up. If not, the can will be tested again after a few days.
The top-bottom ratio is also used to judge ripening. When cane starts ripening, its top portion accumulates sugar rapidly than bottom portion. If the ratio of the sugar content of the top one-third cane to bottom one-third is much less than one, the cane is unripe. When the ratio is one, nearly one or more than one, the cane can be considered as ripe.
The content of invert sugar in juice could also be considered for assessing cane ripeness. When invert sugar reaches a level of 0.1 per cent or less in juice, the cane is said to be ripe and its juice fit for boiling. The test can be made more precise by taking only the penultimate top portion. A low invert sugar content of 3 per cent or less in this portion is an indication of peak maturity.
Specific gravity of juice gives fair idea of cane maturity because the concentration of juice in cane is mostly because of sugar accumulation. Apart from a cane crusher, only a brix sugar hydrometer and a jar are required for this method. Cane juice having 17 brix or more can be considered ripe.
In all the above assessments, actual determination requires less than a liter of juice. However, for a representative sample, at least 20-25 canes have to be harvested and crushed for each sample. The best way of sampling is to choose 4 to 5 places in the field at random and from each place cut and collect all the canes growing in a 60 cm length of row. The juice extracted has to be thoroughly mixed for analysis.
Where maturity of a standing crop is desired, a hand refractometer can be used. Its principle advantages are that it takes very little time and needs neither heavy equipment nor elaborate processing. There is no need for harvesting the stalks. Each determination requires only 3-4 drops of juice, which can be extracted from standing canes by a cane punching needle designed for the purpose.
The drops are placed on the glass stage of hand refractometer and the concentration of juice is read on the graduated scale, which can be seen through eyepiece.
An estimation of sucrose content can also be made using the refractometer brix reading with the following equation:
where, RB is the refractometer brix value.
Artificial Ripening:
Ripening occurs between rapid growth and ultimate death of cane. As the cane is ripened, sheath moisture should drop down from about 85 to 72 per cent and the nitrogen index from 2 to 1.25 per cent. In unripe cane, the activity of acid invertage is high. In humid and high temperature regions, conditions for natural ripening are limited. Hence, sugarcane ripeners are used. In India, northeastern and southeaster regions need artificial ripeners.
Promising sugarcane ripeners are given below:
1. Polaris (NI, N-bis phosphomethyl glycine) at 1.0 to 1.5 kg ha-1). Best response can be obtained from November application (9 months old cane) between 4 and 8 weeks after treatment.
2. Ethrel (2-chloro ethyl phosphoric acid) at 1.0 to 1.5 kg ha-1 applied at the beginning of the milling season.
3. Cycocel or CCC (2-chloroethyl trimethyl ammonium chloride) at 4 kg ha-1, nearly 50 to 70 days after treatment can produce maximum difference in pol per cent juice.
More recently, compounds of Glyphosate namely Polado and Round up (0.67 and 1.0 kg ha-1 respectively) are promising. They improve sucrose content of mature stalks and are called sucrose loaders. Their average response is around 3 t sucrose ha-1.
A new product Fusillade Super at 300 to 400 ml ha-1 appears to be more consistent than Polado and Etheral.
A large number of chemicals have been patented for amelioration of ripening.
These include:
1. N-Organo-phosphonomethylglycine-N-oxides
2. Substituted urea
3. S-triazines
4. 2,6-Dichlorobenzaldehyde tetrahydro-2-furoyl hydrazone
5. Ammonium isobutilyrate
6. Vanillin monosubstituted benzoic acids
7. Alkylarsinic acid
8. Aminopenicillanic acid
9. Penicillamine
10. Tetrahydrofuroic hydrazide
11. Polycyclic thiophene
12. Ethoxylated compounds.