Effect of storage periods on quality characteristics and sugar yield of pre-harvest burnt and unburnt cane of sugarcane varieties (Saccharum spp. hybrid) at Finchaa Sugar Factory, Oromia, Ethiopia

Abstract

The study aimed to determine the effects of cane storage periods on pre-harvested burnt and unburnt green harvested canes on quality characteristics and sugar yield of sugarcane varieties at Finchaa Sugar Factory, Ethiopia. Experiments were conducted on a split–split plot design with two varieties, N 14 and N Co 334 as main plots, types of canes burnt and unburnt green harvested canes as sub-plots, and eight cane storage periods (0, 24, 48, 72, 96, 120, 144, and 168 h) as sub–subplots with three replications. All quality parameters were investigated using the standard procedure. The results showed that the loss in cane weight increased and pol %, purity % juice, estimated recoverable sugar, and sugar yield decreased significantly with increasing periods of storage. The results also indicated that losses were more in burnt harvested canes than the unburnt canes over the storage period. Brix and reducing sugar in juice increased with the storage periods and these were more in burnt canes than unburnt harvested canes. The loss in cane weight, pol, juice purity, recoverable sugar, and sugar yield was high in NCo334 variety at each storage period. The pol and purity % juice, recoverable sugar % cane, and sugar yield were more in burnt and unburnt harvested canes in both varieties at storage periods. The findings suggested that the N 14 cane variety of burnt harvested canes and green canes should be crushed within 24 and 48 h to obtain better sugar quality than N Co 334 variety.

Keywords:

• sugarcane
• storage periods
• green harvested cane
• burnt cane
• Ethiopia

1. Introduction

Sugarcane (Saccharum officinarum L.), is the world’s largest commercial crop, which is cultivated in more than 120 countries on about 26.27 million hectares, with a worldwide harvest of 1.90 billion tones (FAO, 2021). Cultivation of sugarcane is of great economic importance for the sugar and energy industry, for which purposes, ethanol production stands out, while for animal use, sugarcane silage is employed. As for human consumption, there is a greater range of products with an emphasis on the production of sugar, sugarcane liquor, raw brown sugar (rapadura), cane molasses, and brown sugar (Santos et al., 2020).

Developing countries particularly Ethiopia have 700,000 ha of land suitable for sugarcane cultivation, which shows the capacity to produce over one billion liters of bio-ethanol (Tiruye et al., 2021). Currently, there were eight large-scale sugar factories including Finchaa Sugar Estate. Sugar Corporation (2018) reported that the present level of national production from the eight-sugar estates was about 305,956.7 tons of white sugar per annum. This shows the high sugarcane production potential of the environment but was not efficiently utilized and the annual demand was not yet satisfied.

Cane deterioration occurs during pre-harvest burning, which increases with a delay between burning and harvesting cane (Misra et al., 2022). Sereno et al. (2020) reported that cane burning had a significant effect on dextran production. Besides this, delaying the harvesting of burned cane or supply of burned harvested cane could lead to a marked loss in the yield of sugar (Solomon, 2009).

Pre-harvest burning of sugarcane in partially dry storage conditions suppressed the growth of microorganisms particularly during long storage time. However, the degree of deterioration of burnt cane equaled or exceeded that of the unburnt cane due to the increasing activity of microorganisms and pre-harvest burning can lose sucrose (Peng et al., 2021). The pre-harvest burning is still a relatively common practice in smaller-scale plantations, and in other Brazilian states (Valente & Laurini, 2021).

Green cane harvesting has presented obvious environmental benefits, and it is the trend of the cane harvesting process due to the fewer greenhouse gasses (GHG) emissions (Kabeyi & Olanrewaju, 2022). The transition from burnt cane harvesting to green cane harvesting makes tops and leaves separated from stalks to form a surface trash blanket. The green cane trash blanketing (GCTB) not only increases soil nutrient content but also it has resulted in better moisture retention and weed control (Gonçalves et al., 2022). According to Wiedenfeld (2009), green sugarcane harvesting has some minor effects on soil properties which affect crop growth and yield. Any differences due to changes in nutrient availability, soil moisture-holding capacity, or soil temperature are probably not large enough or not long lasting. Sugarcane, like many agronomic crops in a subtropical environment, can compensate for these effects as soil differences disappear over time during the long growing season. The biggest challenge is to figure out how to handle and manage large amounts of residue efficiently and economically.

Several factors can contribute to the delay in crushing of pre-harvest burnt canes in sugar estates. There could be a problem with logistics, pre-harvest burning of sugarcane fields yielding an excess amount of canes than the daily crushing capacity of canes, the prevalence of unfavorable environmental conditions such as high temperature, the occurrence of rains blocking the movement of machinery in the field and breakdown of machinery in sugar mills and stoppage of sugarcane crushing and processing, etc. (Alemayehu & Lantinga, 2018).

Besides quality losses, sugarcane burning emission has an impact on the respiratory system of human health (Le Blond et al., 2018). Furthermore, gaseous and particulate matter emitted during biomass burning of sugarcane impacts the air quality and climate (Capaz et al., 2013). Therefore, harvesting green mature sugarcane is promoted the world over due to the pollution problem. Greencane harvesting potentially increases soil organic matter

Green cane harvesting potentially increases soil organic matter in the soil suitable for sugarcane production (Arbex et al., 2000). In many countries, green cane harvesting is being done for doing away with smoke air pollution contributing to maintaining climate and conceding to the global concern for climate change. However, the delay in crushing after harvesting green cane can also occur if the logistics are not properly managed (Datir, 2015).

Despite this, there was limited information on the effect of storage periods on quality characteristics and sugar yield of pre-harvest burnt and unburnt cane of sugarcane varieties at Finchaa Sugar Factory, Ethiopia. Therefore, this study aimed to determine the effect of storage periods on loss in cane weight, juice quality characteristics, sugar recovery, and sugar yield in burnt and unburnt harvested canes in sugarcane varieties at Finchaa sugar mills.

2. Materials and methods

2.1. Description of the study area

The experiment was conducted at Finchaa Sugar Factory, Oromia, Ethiopia. The area is located at 9^° 30^’to 10^° 00’ North latitude and 37^° 30^’ East longitudes and attitude about 1350–1600 m above sea level about 340 km northwest of Addis Ababa. The valley is surrounded by an almost parallel and near-vertical escarpment, which is raised approximately 700–850 m above the valley floor in the east–west and north–south directions. The floor project area is gently undulating with a general slope of 1–8% extending from south to north. The Finchaa river divides the farm area into western (Horro) and eastern (Guduru) banks. The area has an average maximum and minimum daily temperatures are 30.6°C and 14.5°C, with the highest monthly temperatures in March (34.1°C) and lowest in December (11.53°C), respectively. The average rainfall in the study area is 1316 mm which is characterized by unimodal rainfall pattern. About 80% of the annual rainfalls between May and September. The average annual relative humidity is about 84%. The maximum rainfall in the area is obtained in July while minimum rainfall is on January. Furthermore, the rainy season in the area is summer, while winter is the driest season. The map of the study area is indicated in Figure 1.

Figure 1. Map of the study area.

2.2. Experimental materials

Materials for the investigation comprised pre-harvest burnt and unburnt canes of two sugarcane varieties, N Co 334 and N 14. The following items required for carrying out the study were arranged at Finchaa sugar mill. About 1250 each burnt and unburnt canes of two varieties were harvested during storage periods to determine the effect of different storage periods on cane weight and quality characteristics.

2.3. Experimental design

The experiments were conducted in split–split design with two treatments of varieties, V1: NCo334 and V2: N14 as main plots, two types of harvested canes, C1: pre-harvest burnt and C2: unburnt canes as subplots, and eight cane storage periods after harvest of canes as a subplot, P1: 0 h, P2: 24 h, P3: 48, P4: 72, P5: 96, P6: 120, P7: 144 and P8 168 h with three replications. The treatment combination was 32 (2 × 2 × 8 = 32) multiplied by three replicates total to 96 (32 × 3 = 96) combinations.

2.4. Sample preparation

About 1250 pre-harvest burnt and unburnt harvested canes (Figure 2a,b) were collected for each of two varieties from the same field of variety. From the two types of canes pre-harvest burnt and unburnt harvested canes, 24 samples of 10 canes each were prepared. Twenty-four samples of 10 canes each from the pre-harvest burnt harvested and 24 samples of 10 canes from unburnt harvested canes were immediately crushed in Jeffco grinder/crusher/and taken to sugar laboratory for juice quality analysis: brix%, pol%, purity%, reducing sugars, estimated recoverable sugar and sugar yield.

Figure 2. (a) Unburned sugarcane at Finchaa sugarcane plantation site. (b) Burned sugarcane at Finchaa sugarcane plantation site.

These were given running numbers, from 1 to 24 for pre-harvest burnt cane for variety, NCo334 and other 24 samples of canes from the unburnt harvested with running numbers from 25 to 48. Similarly, 24 samples of 10 canes each from the pre-harvest burnt harvested canes were numbered from 49 to 72 for variety N14 in other 24 cane samples of 10 canes each were numbered from 73 to 96. Similarly, at intervals of 24 h of storage, three replications from burnt and unburnt green harvested canes were taken for weighing the weight of canes and crushing in a crusher for juice quality analysis in a sugar laboratory up to the 168-h storage periods. Then, the shredded cane samples were collected in a plastic bag and mixed well. The sample was further ground in a Jeffco grinder and collected in a plastic bag. After being homogenized the sample was weighted to 1000 g, and water was weighted to 5000 g and mixed. The mixture was transferred into a wet disintegrator. The disintegrator was closed and digested for 20 min for juice extraction. The extracted juice was sieved out through a 400 mm mesh screen into a 500 mL beaker. The sieved juice was put into the sample container, closed, and delivered to a laboratory for analysis

2.5. Data collection

2.5.1. Cane weight loss % at storage periods

Cane weight losses (%) for each sample were calculated by subtracting the weight of a sample after storage from the fresh weight and multiplying by 100 as the following equation.

[(Fresh weight of sample − weight at specified storage period of the sample)/Fresh weight of sample] x100 (Urgesa et al., 2021).

2.5.2. Brix% juice

Brix % juice for all samples of treatment combinations was determined by using brix hydrometer standard methods. The juice solution was transferred into a cylinder, and degree brix and temperature were determined. The brix of extracted juice was corrected from the temperature correction table. The reading by refractometer brix reading recorded = corrected brix. The reading by hydrometer brix % was corrected to Brix% juice as follows (Hundito et al., 2009).

Brix% juice (B) = b (6–0.0125F), where B = brix % juice, b = corrected brix, F = fiber %

2.5.3. Pol % juice

Pol percent juice was determined using Polari meter (Hundito et al., 2009). About 100 mL juice of each sample was taken and clarified by 0.5 g of basic lead acetate for flocculation of non-sugar. The sample was shaken and allowed to stand until flocculation was completed. The sample was filtered by using filter paper 90. The first 25 mL of filtrate was discarded, and the rest clear filtrate was collected in a beaker. The clear filtered juice was put into a 200 mm pol tube and polarized with a polarimeter. The pol% extracted was taken from the conversion table, and brix extracted was taken from the pol reading. Then, pol% of the juice was calculated according to the following:

Pol % juice = p (6–0.0125F), Fiber % cane = $\frac{D-6b}{1-0.0125b}$, Dry substance % cane = 100 gm − weight loss in gm, where; D = dry substance % cane, b = corrected brix, P= corrected pol, F = Fiber % cane (Jones, 2001).

2.5.4. Purity percentage

The juice purity percentage was calculated according to the following formula described by Satisha et al. (1996).

$\mathrm{P}\mathrm{u}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{y}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}=\frac{pol\mathrm{\%}juice}{Brix\mathrm{\%}juice}X100$

2.5.5. Reducing sugar percentage

Reducing sugar content in juice for each of the samples was determined by using the Lane and Eynon volumetric methods as outlined by ICUMSA (1994). After every crushing, one tablespoon of lead acetate was mixed in 100 mL of juice sample of cane varieties and filtered through Whatman No. 90 filter paper, and the filtrate was collected. Then, 25 mL of Na₂HPO₄ solution was added to precipitate the excess lead and again filtered through Whatman No. 90 filter paper, and the filtrate was again collected. Then. burette was filled with clarified filtrate of sugarcane juice. About 2.5 mL of each Fehling “A” and Fehling “B” was pipetted out into a conical flask using separate pipettes. The contents in the conical flask were diluted by adding 10 mL of distilled water and then heated on a burner and kept slowly boiling. The juice from the burette was slowly added till the color turns to red. At this stage, three to four drops of methylene blue indicator were added, so the solution again became intense blue. The addition of juice from burette was continued drop by drop till blue color was completely discharged, and brick red color of Cu₂O was produced. Then, reducing sugar was calculated by the following formula.

$\mathrm{R}\mathrm{e}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{i}\mathrm{n}\mathrm{s}\mathrm{u}\mathrm{g}\mathrm{a}\mathrm{r}\left(\mathrm{R}\mathrm{S}\mathrm{\%}\right)=\frac{\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{\%}\mathrm{d}\mathrm{i}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{f}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}-\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{\%}\mathrm{u}\mathrm{n}\mathrm{d}\mathrm{i}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{e}\mathrm{d}}{\mathrm{d}\mathrm{i}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{f}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}/100}$

2.5.6. Estimated recoverable sugar (ERS %)

Sugar recovery is the amount of sugar recovered from a fixed amount of sugarcane during the crushing process. It was calculated as follows (Hundito et al., 2009).

ERS %= {pol% juice − (Brix % juice − pol % juice) NSF} * CF

where

NSF is a non-sugar factor with a constant value of 0.70

CF is a cane factor with a constant value of 0.57

2.5.7. Estimated sugar yield

Sugar yield was recorded by multiplying sugar recovery percent with sample cane after specified storage periods (Jones, 2004).

Sugar yield (%) = weight of cane *Sugar Recovery (%).

2.6. Statistical analysis

The data obtained were subjected to an analysis of variance (ANOVA) adapted for Split- split-plot design using SAS 9.3. The difference between the mean was separated using the LSD procedure at 5% of significance for the selected characteristics to determine the relationship between the parameters.

3. Results and discussion

3.1. Effect of sugarcane varieties on cane weight loss and juice qualities

The results of the cane weight loss and cane juice qualities (brix%, pol%, purity%, reducing sugar, recoverable sugar, and sugar yield) on sugarcane varieties (N14 and NCo 334) are presented in Table 1. There was a significant (p < 0.05) variation in the cane weight loss and cane juice qualities (pol% and sugar yield) contents between the two sugar cane varieties. The obtained significant variation between the varieties was due to a large number of factors such as ambient temperature, humidity, nature of variety, period of storage, activities of soluble invertases in cane, and maturity status (Verret, 2013). However, there was no significant (p > 0.05) difference in brix, purity, reducing sugar, and recoverable sugar between the varieties.

Table 1. Effect of sugarcane varieties (N14 and NCo334) on cane weight loss at Finchaa, March 2020

Varieties	CWL%	Brix% juice	Pol% juice	Purity% juice	RS% juice	Recoverable sugar	Sugar yield
N14	14.26^b	19.82^ab	14.24^a	72.62^ab	1.40^ab	5.50^a	0.419^a
NCo334	14.62^a	20.28^a	13.53^b	73.61^a	1.60^a	5.46^ab	0.240^b
Mean	13.94	19.4	13.45	73.15	1.5	5.09	0.380
SE+	0.074	0.203	.242	.151	1.500	0.754	0.030
CV%	4.491	6.924	7.353	7.60	4.666	4.109	11.63

SE = Standard error, CV: coefficient of variation; Means with the same letters in superscript are not significantly different at a 5% level of significance (p>0.05). Means with the different letters in superscript are significantly different at a 5% level of significance (p< 0.05). CWL= Cane weight loss, RS= reducing sugar.

3.2. Effect of burnt cane and unburnt cane on cane weight loss and juice quality

The burnt cane was reported to deteriorate faster than unburnt canes (Gomez et al., 2006; Kent et al., 2003). The brix (%) in juice and reducing sugar of burnt harvested cane was significantly (p < 0.05) higher than in unburnt green harvested cane (Table 2). This could be due to more loss of moisture in burnt cane than the green harvested cane (Davies, 1998; Eggleston et al., 2008). Besides this, purity% juice in green cane was significantly (p < 0.05) higher than in burnt cane. This might be due to burnt cut cane dries out more quickly than does green cut cane (Davies, 1998). This finding depicted that harvesting green cane is beneficial in terms of reducing the rate of moisture loss and thus increasing the efficiency of processing, even if the cane may delay before milling.

Table 2. Effect of burnt cane and unburnt cane on cane weight loss at Finchaa, March 2020

Types	CWL%	Brix% juice	Pol% juice	Purity% juice	RS% juice	Recoverable sugar	Sugar yield
Burnt Cane	14.26^a	19.82^a	13.53^b	72.62^b	1.40^a	5.35^b	0.401^a
Green Cane	14.14^ab	18.42^b	13.77^ab	73.59^a	1.02^b	5.59^a	0.413^a
Mean	13.4	18.71	13.80	73.1	1.21	5.47	0.602
SE+	0.08	0.257	.051	.120	1.185	0.377	0.375
CV%	4.87	6.824	8.55	7.123	6.987	4.361	12.123

SE = Standard error, CV: coefficient of variation; Means with the same letters in superscript are not significantly different at a 5% level of significance (p>0.05). Means with the different letters in superscript are significantly different at a 5% level of significance (p< 0.05). CWL= cane weight loss, RS= reducing sugar.

3.3. Effect of storage periods on cane weight loss and juice quality

3.3.1. Effect of storage periods on cane weight loss and brix juice in sugarcane varieties

The average cane weight loss over 7 days of storage periods in two selected sugar cane varieties are indicated in Table 3. The interaction effects of varieties with storage periods were significant (p < 0.05) variation in the cane weight loss. Cane weight is an important aspect for considering the assessment of cane storage periods. Reports have shown that the cane starts to lose its sucrose as it is being cut leading to a loss in its weight. The percentage of loss in cane weight differs extensively. This variability is due to variations in temperature, humidity, speed of the wind of places along with varietal differences and storage methods (Solomon, 2009). The found result was similar to the findings reported by Kent et al. (2003) and Eggleston et al. (2008). The loss of cane weight for N14 varieties during 7 days of storage periods in this study was from 6.3 to 17.07 and 3.81% to 14.66% for burnt cane and unburnt cane, respectively, whereas NCo334 burnt had 8.5–17.33% and unburnt cane 5.59–15.66%, respectively.

Table 3. Effect of storage periods on cane weight loss and brix juice in burnt and unburnt sugarcane varieties at Finchaa Sugar Factory during March 2020

Storage periods	Cane weight loss % cane				Brix % juice
	N 14		NCo 334		N 14		NCo334
	BC	UBC	BC	UBC	BC	UBC	BC	UBC
0h	0.00^g	0.00^g	0.00^f	0.00^e	16.65^f	16.47^e	17.89^f	17.46^e
24h	6.83^f	3.81^f	8.50^e	5.66^de	17.49^e	17.35^de	17.51^ef	17.74^de
48h	8.96^e	5.41^de	11.14^de	9.33^d	18.70^de	18.60^d	18.77^e	18.74^de
72h	13.00^d	11.00^cd	13.66^c	12.33^cd	19.33^d	18.76^c	19.37^d	18.81^cd
96h	14.00^bc	12.18^c	14.33^bc	13.00^c	20.25^cd	18.80^bc	20.27^c	18.87^bcd
120h	13.16^b	13.33^bc	13.00^b	11.90^bc	20.70^bc	19.29^b	20.99^bc	19.96^abc
144h	16.30^ab	13.85^b	16.18^ab	14.70^ab	21.29^b	20.15^ab	21.91^b	20.44^ab
168h	17.07^a	14.66^a	17.33^a	15.59^a	22.00^a	20.65^a	22.18^a	21.81^a
Mean SE± CV%	10.53 1.046 17.042				19.21 0.063 2.052

Where, BC = Burnt cane, UBC = Unburnt cane; Means with the same letters in superscript are not significantly different at a 5% level of significance. SE= Standard error, CV: coefficient of Variation. Means with the same superscript letter in a parameter category are not different (p > 0.05) or similar text, while means with the different superscript letter in a parameter category are different (p < 0.05) or different text.

Brix percentage in juice represents total dissolved solids including sugars and non-sugars. Average brix % juice over 7 days of storage periods of sugarcane varieties during March is presented in Table 3. Brix percentage in juice on storage periods (24, 48, 72, 96, and 168 h) was significantly (p < 0.05) higher than the control sample. The results highlighted that the brix percent in juice increases with storage time. The rise in brix during the storage period was due to the loss of moisture from the cane stalks. The result was similar to the findings reported by Solomon (2009) (20.11–22.19%).

3.3.2. Effect of storage periods on pol and purity juice in sugarcane varieties

Average pol % juice over 7 days of storage periods in burnt and unburnt canes of varieties in March is presented in Table 4. The result showed that pol% juice of burnt harvested cane was significantly (p < 0.05) lower than in the unburnt green harvested cane. The results highlighted that there was significantly more loss in pol% in burnt cane than green harvested cane over cane storage periods. The value obtained in this study was similar with the findings of Misra et al. (2022). Furthermore, pol % juice over storage periods was more in N 14 than N Co334 variety. This might be due to genetic differences between varieties (Rípoli et al., 2000). Per harvest burning of sugarcane partially dry storage conditions suppressed the growth of microorganisms after a sufficiently long storage period. However, the degree of deterioration of burnt cane equaled or exceeded that of the unburnt cane due to the increasing activity of microorganisms and pre-harvest burning can lose sucrose about 2.7−5% of the potential yield (Gomez et al., 2006; Hiranyavasit, 2016).

Table 4. Effect of storage periods on pol and purity juice in burnt cane sugarcane varieties at Finchaa Sugar Factory during March 2020

Storage periods	Pol % juice				Purity % juice
	N 14		NCo 334		N 14		NCo334
	BC	UBC	BC	UBC	BC	UBC	BC	UBC
0hr	15.82^a	15.82^a	15.15^a	15.31^a	89.95^a	90.67^a	89.60^a	90.55^a
24hr	15.66^ab	15.75^ab	14.63^ab	14.77^b	83.57^b	83.87^ab	83.76^b	84.77^ab
48hr	14.81^b	14.84^b	14.50^bc	14.76^b	81.61^c	81.75^b	78.19^c	78.85^b
72hr	14.47^bc	14.37^bc	13.96^c	14.11^c	76.79^d	78.72^bc	74.88^d	75.01^c
96hr	13.94^c	13.89^c	13.66^d	13.65^d	71.44^e	72.97^c	68.89^e	70.60^d
120hr	13.40^d	13.45^cd	13.10^e	13.11^e	65.56^f	69.13^d	64.77^ef	66.31^e
144hr	13.19^e	13.26^d	12.56^ef	12.87^f	63.56^g	66.11^e	61.96^f	62.71^f
168hr	12.86^f	12.98^e	12.19^f	12.36^g	58.34^h	61.77^f	58.51^g	59.9^g
Mean SE± LSD CV%	14.04 0.051 0.145 1.244				73.80 0.148 1.219 1.986

Where, BC = Burnt cane, UBC Unburnt cane; Means with the same letters in superscript are not significantly different at a 5% level of significance. SE= Standard error, CV: coefficient of Variation; Means with the same superscript letter in a parameter category are not different (p > 0.05) or similar text while means with the different superscript letter in a parameter category are different (p < 0.05) or different text.

Purity % juice represents the ratio of pol over brix in percent and is an important quality characteristics from the point of sugar recovery. The purity% juice over seven storage periods in burnt and unburnt harvested canes in sugarcane varieties, N 14 and N Co 334 at Finchaa sugar mill is presented in Table 4. The result showed that the mean purity% of juice over storage periods and varieties was less in burnt canes than in unburnt green canes during March. This indicated that juice purity declined more in burnt cane than the unburnt canes. The findings also revealed that there was a significant loss in juice purity in burnt cane within 24–120 h. The burnt cane was reported to deteriorate faster than unburnt canes (Gomez et al., 2006; Kent et al., 2003). Allen et al. (2004) also confirmed that green harvested canes showed much slower deterioration than burnt canes in Brazil.

3.3.3. Effect of storage periods on reducing sugar % juice, estimated recoverable sugar, and sugar yield in sugarcane varieties at Finchaa Factory during March 2020

Average reducing sugar % juice over 7 days of storage periods in burnt and unburnt canes of varieties during March is presented in Table 5. Reducing sugars in juice refers to monosaccharides, glucose, and fructose which are generally flushed out into molasses. The increase of reducing sugars is an indication of deterioration of juice quality or the inversion of sucrose in the juice over cane storage periods. The reducing sugars in the juice of burnt harvested cane were significantly (p < 0.05) higher than in unburnt green harvested cane. This indicated that the quality of burnt canes deteriorated more than the green harvested canes over storage periods.

Table 5. Effect of storage periods on reducing sugar % juice, estimated recoverable sugar and sugar yield in sugarcane varieties at Finchaa Sugar Factory during March 2020

Storage periods	Reducing sugar % juice				Estimated recoverable sugar % juice				Estimated Sugar yield % juice
	N 14		NCo334		N 14		NCo334		N14		NCo334
	BC	UBC	BC	UBC	BC	UBC	BC	UBC	BC	UBC	BC	UBC
0hr	0.87^e	0.53^d	0.90^e	0.55^e	7.38^a	7.57^a	6.84^a	6.86^a	0.68^a	0.72^a	0.61^a	0.65^a
24hr	0.89^e	0.52^d	0.92^e	0.69^de	6.96^b	6.97^b	6.38^b	6.40^ab	0.62^ab	0.66^ab	0.52^b	0.60^ab
48hr	0.90^de	0.72^cd	0.98^de	0.81^d	6.59^c	6.69^c	6.23^bc	6.28^b	0.52^c	0.55^b	0.48^c	0.50^b
72hr	1.21^d	0.81^c	1.39^d	0.89^cd	5.85^d	5.92^d	5.66^c	5.73^c	0.42^d	0.50^c	0.34^d	0.40^bc
96hr	1.52^c	1.12^bc	1.77^c	0.98^c	5.47^e	5.58^e	5.38^d	5.53^c	0.34^e	0.44^d	0.30^e	0.33^c
120hr	1.60^bc	1.27^b	1.87^bc	1.32^c	4.82^ef	4.88^f	4.72^e	4.86^d	0.30^ef	0.33^e	0.27^e	0.31^d
144hr	1.87^b	1.52^ab	2.32^b	1.52^b	4.78^f	4.88^f	4.66^fg	4.79^e	0.25^f	0.30^f	0.23^f	0.28^e
168hr	2.77^a	1.53^a	2.82^a	1.92^a	3.83^g	4.55^g	3.11^g	4.01^f	0.22^g	0.27^g	0.20^f	0.25^e
Mean SE± CV%	1.28 0.11 7.98				6.59 0.06 8.01				0.54 0.05 7.56

Where, BC = Burnt cane, UBC = Unburnt cane; Means with the same letters in superscript are not significantly different at a 5% level of significance. SE= Standard error, CV: coefficient of variation; Means with the same letters in superscript are not significantly different at a 5% level of significance (p>0.05). Means with the different letters in superscript are significantly different at a 5% level of significance (p< 0.05).

The reducing sugars over storage periods in the juice of the NCo334 variety were significantly (p < 0.05) higher than in N14 variety. This could be due to more age of the sugarcane crop and unfavorable environmental factors (Zhao & Li, 2015). Reducing sugars at every cane storage period was more in burnt canes than the green harvested canes. It clearly showed that the juice quality of burnt cane deteriorated (increased reducing sugars) more than that in the green harvested canes. The results are in agreement with the findings of Nicolella and Belluzzo (2015), who reported that burnt deteriorated faster than the green cane after harvesting of sugarcane.

Average estimated recoverable sugar% cane over seven storage periods in burnt and unburnt harvested canes in sugarcane varieties, N14 and NCo334 at Finchaa sugar mill are presented in Table 5. The recoverable sugar % cane over storage periods in burnt cane was significantly (p < 0.05) lower than in unburnt green harvested cane. This indicated that there was significantly more loss in recoverable% cane in burnt cane than green harvested cane over cane storage periods. The green harvested sugarcane varieties recorded in this study had a much higher recoverable percentage of cane than burnt harvested during cane storage periods. Recoverable sugar % cane over storage periods had non-significant (p > 0.05) differences between N14 and N co334 variety. Cane burning can reduce the quantity of sugar recovered from the cane by as much as 5%. Estimates of recoverable sugar % cane were obtained from pol and brix percent juice, cane factor, and the milling efficiency.

Estimates of recoverable sugar percent cane at different cane storage periods are presented in Table 5. There was a significant (p < 0.05) differences in recoverable % cane among storage periods in both varieties. The recoverable % cane decreased significantly with the storage periods in burnt and unburnt canes at 48 h of cane storage. The findings of Hiranyavasit (2016) highlight that cane burning can reduce the quantity of sugar recovered from the cane by 5%. The measured net weight is automatically deducted to determine the true net weight of burned canes compared to a standard deduction of 2% for unburned canes. Sugar loss from burned cane harvests was mainly due to the burning process, while losses in green cane harvests were due to trash and in-field losses through the primary extractor (Gomez et al., 2006).

Estimates of sugar yield at different cane storage periods are presented in Table 5. There was a significant (p < 0.05) variation in the sugar yield among storage periods in both sugar cane varieties. The sugar yield decreased significantly with the storage periods in burnt and unburnt cane. The result also showed that sugar yield declined significantly at 48 h. The findings depicted that sugar yields were significantly reduced in the storage of burnt and unburnt canes but the extent of loss in sugar yield was generally more in burnt canes than in unburnt canes, or in other words, the percent sugar yields of the fresh sugar yield at every storage period were higher in green harvested canes than that of burnt canes. The results reported by Eggleston et al. (2001) and Gomez et al. (2006) indicate that burnt chopped cane deteriorates faster as compared to green chopped cane. The above mentioned authors also confirmed that delaying the harvesting of burned standing cane or supply of burned harvested cane could lead to a marked loss in the yield of sugar

4. Conclusions

In this study effect of storage periods (0, 24, 48, 72, 96, 120, 144 and 168 h) on quality characteristics and sugar yield of pre-harvest burnt and unburnt cane of sugarcane varieties (N 14 and NCo334) at Finchaa Sugar Factory, Oromia, Ethiopia, was investigated. The findings showed that there was a significantly (p < 0.05) increase in the cane weight loss and a decrease in the pol (%), purity (%), estimated recoverable sugar (%), and sugar yield with increasing storage periods. The findings also indicated that the losses in the cane weight and decreased quality of sugar were more in burnt canes than unburnt harvested canes over cane storage periods. Furthermore, N 14 cane variety had better juice quality, recoverable sugar, and sugar yield than N Co 334 variety over storage periods. Therefore, the findings suggested that pre-harvested burned canes should be crushed in the sugar mills within 24 h of harvesting, whereas green harvested canes should crush in the mills before 48 h of harvesting to generate maximum sugar recovery percent and the sugar yield.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Ebisa Olika Keyata

Ebisa Olika Keyata received BSc in Food Science and Bioprocess Technology from Wollega University in 2011, MSc and PhD in Food Science and Technology from Haramaya (2014) and Jimma University (2021), respectively. He has mentored postgraduate students in the areas of food technology, postharvest technology, Human nutrition, sugar technology, and Horticulture. He is involved in different research activities in areas of food processing technology, underutilized edible plants, grain science and technology, complementary and therapeutic food, postharvest handling and value addition of agricultural products. He has published different research articles in reputable journals.