Post Harvest Management
Post harvest deterioration losses
The sugar accumulated in the stem of sugarcane represents a balance between synthesis of sugar and its utilization. A well ripened
harvested crop may lose its sugar within a few days after harvest, which tends to increase further due to high ambient temperature,
pre-harvest burning, harvest and transportation injuries and microbial infestation. Sucrose losses after the harvest of sugarcane and during
the subsequent milling operation are one of the most serious problems in many sugar processing mills in India. Staling beyond 24 hours
results in considerable loss in cane weight due to moisture loss and reduction in juice sucrose content due to inversion.
Such juice also creates problems in processing. The reduction is cane weight range between 7.4 and 17.0 per cent and sugar recovery
by about 2.0 per cent at different places in India due to staling of cane for 96 hours. Thus post harvest cane deterioration affects both growers because of loss in weight and sugar industry due to reduced recovery.
stale canes reduce not only the recoverable sugar but also create losses by reducing mill and boiling house capacities. It also increases loss of sugar in molasses. Soon after the harvest of sugarcane, endogenous invertase enzyme gets activated and acts as a cause of deterioration. The other type of deterioration which is known as biodeterioration caused by microorganisms mainly Leuconostoc sp.(L.mesenteroidesand L.dextranium) also takes place. These organisms convert sucrose into polysaccharides, such as dextran. Besides, loss of sucrose, the presence of dextran even in very small amount creates problem of filteration, clarification, crystallization and alters the shape of sugar crystals thereby affecting the quality of sugar.
I. Reasons for Stale Cane Crush
In sugarcane growing countries any of the following constraints seem to operate at farmers and factory level:
- Absence of a proper varietal balance and scientific harvesting schedule based on cane maturity.
- Extension of milling period during summer months when ambient temperature is high (>40oC).
- Inordinate delay in transport of harvested cane from farmer’s field/cane centres to the mills and lack of and efficient communication net/work.
- Shut down and other unforeseen circumstances, such as labour scarcity and power interruption.
- Mechanical harvesting of sugarcane (burnt crop) without proper and timely supply arrangements.
II Nature and Magnitude of Post Harvest Losses
The sugar recovery depends upon several factors especially cane quality and the efficiency of the mill. It can be increased from 0.4 to 0.6 per cent with efficient operations of the mill and from 1.5 to 2.0 per cent with high cane quality. Studies on the rate of post-harvest deterioration have shown that maximum deterioration of the harvested cane occurs at 38-40oC at 15% moisture loss. The loss in cane weight depends upon the maturity status of the crop and the prevailing weather
Nature of changes taking place in the cane after harvest:
- Loss of moisture from the cane due to evaporation to the extent of 1.5 to 2% for every 24 hours depending upon weather conditions.
- Loss in sucrose per cent juice by 0.1 to 0.2 units for every 24 hours particularly after 48 hours of harvest due to inversion.
- Increase in juice acidity, formation of gums and dextran which will adversely affect the processing of the juice.
- Apparent increase in fibre content due to loss in moisture leading to problems in juice extraction.
- Increase in reducing sugars (RS) content due to inversion of sucrose into glucose and fructose.
III. Biochemical Basis of Post Harvest Sugar Losses
The deterioration of harvested cane is primarily a biochemical process followed by bacterial through the cut ends or damaged sites of stalk. The enzyme invertase (s) are most abundant in the immature tissue but they are also present in fully mature stalks. An abundance of immature cane rich in acid invertase may play havoc during milling due to its high inversion rate. Soon after the harvest of sugarcane, endogenous invertase enzyme gets activated and acts as a cause of deterioration.
The other type of deterioration which is known as bio-deterioration caused by microorganisms mainly Leuconostoc sp. (L.mesenteroides and L.dextranium) also takes place. The bacteria enter the cane through the cut ends and cane pass upto 20 cm into stem within one hour. These bacteria enter into sugarcane from the soil through the cut ends of damaged sites of stalks and multiply in the mill corners, gutters, pipe lines and the mixed juice tank. These organisms convert sucrose into polysaccharides, such as dextran.
Besides, loss of sucrose, the presence of dextran even in very small amount creates problems of filteration, clarification, crystallization and alters the shape of sugar crystals thereby affecting the quality of sugar.
IV. Role of Microorganisms in Stale Cane
a) Dextran formation and sucrose losses:
The dextrans, which are polymers of glucose containing 60 per cent (1,6) linkage, are produced directly from sucrose by the
bacteria Leuconostoc Mesenteroides or L.dextranicum. It has been noticed that canes from ratoon crop are more prone to dextran
formation as compared to canes from corresponding plant crop. Dextrans are known to create problems in processing. Therefore, staling of canes from a ratoon crop may entail more difficulties in processing vis-a-vis losses as compared to a plant crop. The sucrose losses as a result of dextran formation are approximately 1.9 times the dextran formed.
b) Dextran production and sugar processing:
The detrimental dextran formation on sugar processing and recovery are:
- Formation of more reducing sugars and increased molasses purity.
- Formation of soluble polysaccharides in milled juice.
- Lowered heat exchange rate with lower evaporator efficiency.
- Slow crystallization, poor clarification and slow mud-settling rate.
- Formation of elongated needle shaped crystals of sucrose which affects its marketability.
- Increase in organic acids leading to scaling problem, requiring more heating time during evaporation.
- Increase in gum content leading to high viscosity of syrups, massecuites.
V. Factors in Post Harvest Cane Deterioration
a) Cane Variety:
Sugarcane varieties play a crucial role in sugar recovery, depending upon the climate and management practices followed. Due to
genetic variability different genotypes behave differently to post-harvest deterioration. The genetic nature of the variety and the morphological features of the cane such as cane thickness, rind hardness, wax coating etc, decide the extent of post-harvest deterioration.
There are ample evidences to show that weather is of prime importance in determining the rate of deterioration. Deleterious effects
of high temperature (around 40oC) and low atmospheric humidity (25-35%) on juice quality have been reported by many workers. Numerous early
workers surmised temperature-moisture relationship to deterioration of cane and there was general view that canes stored in the shade or
covered with trash are less prone to deterioration than if stored in open place.
c) Crop maturity:
The rate of post harvest deterioration is also dependent upon the cane maturity. Immature or over mature canes deteriorate rapidly as compared to matured canes. This deterioration is relatively faster in hot weather.
d) Green vs burnt cane:
Burnt and un-burnt cane behaves differently during storage. Young (1963) reported that when a cane is burnt, the sugar loss was more when it was cut and left in the field as compared to burnt standing cane. Delaying the harvesting of burnt standing cane for more than 24 hours resulted in marked loss in the yield of sugar.
e) Methods of harvesting:
In India, cane is harvested manually which is mostly unburnt full green cane. There is no planned burning of crop; however, in south Gujarat, irrespective of measures taken by the factories, burning of cane is a routine practice and burnt cane up to 80 per cent is observed, especially near the end of crushing season. In some parts of north India, burnt cane is supplied at the end of crushing season, especially when cane is in plenty. It has been observed that appreciable amount of sugar is lost during the time lag between harvesting to milling, even in well managed mills. On an average, Indian sugar mills lose about 10 to 15 kg of sugar per tonne of cane crushed. These losses are further escalated when crushing is extended till May/June or even later.The introduction of mechanized harvesting and subsequent chopping of green cane has also resulted in serious problem, especially dextran formation. In mechanically harvested cane due to increased number of bits of cane resulting in more exposure of area, the deterioration is faster as compared to hand cut cane. The post-harvest losses in crop, harvested by chopped harvester in Queensland (Australia) represented 6 to 11 per cent of the original CCS% as compared to a loss of 1 to 2 per cent in the stored whole cane.
f) Cane transport and storage system:
The cane transport system is a major factor governing quality of harvested cane. The time factor during transport, storage conditions, degree of damage from loading equipment and size and shape of transport containers are important factors in governing cane quality. Transport of fresh cane in small storage containers is less prone to deterioration. The cleanliness and hygiene in the yard is therefore, an important factor and first cane in should be the first cane out.
VI. Methods to Minimize Stale Cane Losses
- Use of varieties resistant to post-harvest deterioration in areas where delay in transport is anticipated.
- Harvesting of immature and over mature canes should be avoided.
- Quicker transport of varieties identified to be susceptible to post-harvest deterioration.
- Keeping the harvested cane under shade during hot weather period.
- Covering of harvested cane with trash and sprinkling of water periodically to keep the cane moist.
- It has been observed that topped cane deteriorates faster than cane with the crown of leaves attached. In case of any anticipted delay in crushing, topping should be avoided.
- Dipping the cut ends of cane in certain biocides like polycide @ml/ lit or bactrinol-@ 100 ppm and spraying the same on the stored cane could arrest deterioration upto 120 hours.
- Pre-harvest spray of chemical ripeners like polaris, ethrel, sodium metasilicate ect. have been found effective in checking post harvest losses. Studies have shown that application of 2% sodium metasilicate (3 days prior to harvest) has been found to maintain juice quality of stored cane for 6 days.
- Pre-harvest spraying of mercuric chloride (100 mg/litre) or cobalt chloride has been found effective in suppressing invertase activity maintained juice quality upto 20 days of storage.
- Minimum time lag between harvesting to milling and use of effective biocides is important to minimize sucrose loss after harvest and milling operation.
- Desai et al.(1985)
noticed that spraying of harvested cane with benzonic acid (100 ppm) and formaldehyde (100 ppm) significantly retarded post harvest deterioration.