Impact of tops and green leaves on sugarcane processing: laboratory testing

In Réunion, changes in harvesting practices have led to increased amounts of sugarcane tops and leaves delivered to factories. To anticipate the changes in sugar recovery processing, laboratory trials were undertaken. Samples with known quantities of tops or green leaves were prepared and cane processing was simulated at laboratory scale: juice extraction, clarification and evaporation with operating parameters similar to those in the factory. Juice and syrup were collected and analyzed for sugar quality parameters, as well as parameters that impact sugar recovery or processing quality: ash and reducing sugars contents were monitored to estimate the sucrose loss to molasses, while calcium, phosphate and oxalate contents were monitored to evaluate the risk of fouling in evaporator. Results highlight a degradation of juice composition with increasing quantities of tops and leaves, an increase in lime consumption, and color. An increase in residual calcium in syrup was observed thus increasing the risk of evaporator fouling. The mixed juice, clear juice and syrup qualities declined in the same proportion and the composition of the juice did not get worse with juice treatment.

Integrative transcriptomics reveals genotypic impact on sugar beet storability

Key message An integrative comparative transcriptomic approach on six sugar beet varieties showing different amount of sucrose loss during storage revealed genotype-specific main driver genes and pathways characterizing storability. Abstract Sugar beet is next to sugar cane one of the most important sugar crops accounting for about 15% of the sucrose produced worldwide. Since its processing is increasingly centralized, storage of beet roots over an extended time has become necessary. Sucrose loss during storage is a major concern for the sugar industry because the accumulation of invert sugar and byproducts severely affect sucrose manufacturing. This loss is mainly due to ongoing respiration, but changes in cell wall composition and pathogen infestation also contribute. While some varieties can cope better during storage, the underlying molecular mechanisms are currently undiscovered. We applied integrative transcriptomics on six varieties exhibiting different levels of sucrose loss during storage. Already prior to storage, well storable varieties were characterized by a higher number of parenchyma cells, a smaller cell area, and a thinner periderm. Supporting these findings, transcriptomics identified changes in genes involved in cell wall modifications. After 13 weeks of storage, over 900 differentially expressed genes were detected between well and badly storable varieties, mainly in the category of defense response but also in carbohydrate metabolism and the phenylpropanoid pathway. These findings were confirmed by gene co-expression network analysis where hub genes were identified as main drivers of invert sugar accumulation and sucrose loss. Our data provide insight into transcriptional changes in sugar beet roots during storage resulting in the characterization of key pathways and hub genes that might be further used as markers to improve pathogen resistance and storage properties.

Benchmarking and improving sugar recovery from final molasses

The sucrose loss in final molasses in raw sugar manufacture is the largest loss. One factor that typically limits the extent of sucrose recovery from final molasses is that cooling crystallizers are high capital and maintenance cost items. The target purity of the final molasses is the commonly used benchmark to assess the effectiveness of exhaustion of final molasses. However, this benchmark does not relate to an actual loss of sucrose. A benchmark that calculates the Target Sucrose Loss (TSL) in molasses for the factory is proposed. Factories would aim to maintain the sucrose loss in final molasses to within 1 unit of the TSL. A close approach to the target purity is still required as part of the drive to achieve this result. An advantage of the TSL is that it considers the influence of the quantity of soluble impurities in the cane supply on the actual sucrose loss in molasses. Data from Australian factories are presented to demonstrate the application of the TSL. Several factors affecting the exhaustion of final molasses are discussed, including the effects of Cmassecuite purity, crystallizer station performance and shear rate on the massecuite within the crystallizers. Some Australian factories have recently refurbished horizontal, rotating coil crystallizers with designs incorporating fixed cooling elements and rotating paddles to provide high shear rate conditions and overcome maintenance issues associated with the coil design. Experience shows that the fixed-element design is an economical way to provide strong exhaustion performance.

Influence of Beet necrotic yellow vein virus and Freezing Temperatures on Sugar Beet Roots in Storage

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is a yield-limiting sugar beet disease that was observed to influence root resistance to freezing in storage. Thus, studies were conducted to gain a better understanding of the influence of BNYVV and freezing on sugar beet roots to improve pile management decisions. Roots from five commercial sugar beet cultivars (one susceptible and four resistant to BNYVV) were produced in fields under high and trace levels of rhizomania pressure and subjected to storage using five temperature regimes ranging from 0 to −4.4°C for 24 h. After cold treatment, eight-root samples were stored in a commercial indoor storage building (set point 1.1°C) for 50 days in 2014 and 57 days in 2015. Internal root temperature, frozen and discolored tissue, and moisture and sucrose loss were evaluated. The air temperature at 0, −1.1, and −2.2°C matched internal root temperature but internal root remained near −2.2°C when air temperature was dropped to −3.3 and −4.4°C. In a susceptible cultivar produced under high rhizomania pressure, the percentage of frozen tissue increased (P < 0.0001) from an average of 0 to 7% at 0, −1.1, and −2.2°C up to 16 to 63% at −3.3°C and 63 to 90% at −4.4°C, depending on year. Roots from the susceptible cultivar produced under low rhizomania pressure and those from the resistant cultivars from both fields only had elevated (P ≤ 0.05) frozen tissue at −4.4°C in 15 of 18 cultivar–year combinations. Frozen tissue was related to discolored tissue (r2 = 0.91), weight loss (r2 = 0.12 to 0.28), and sucrose reduction (r2 = 0.69 to 0.74). Consequently, BNYVV will not only lead to yield and sucrose loss in susceptible sugar beet cultivars but also to more frozen root tissue as temperatures drop below −2.2°C. Based on these observations, the air used to cool roots in nonfrozen sugar beet piles throughout the winter should not drop below −2.2°C to maximize sucrose retention.

Influence of Harvest Timing, Fungicides, and Beet necrotic yellow vein virus on Sugar Beet Storage

Root rots in sugar beet storage can lead to multimillion dollar losses because of reduced sucrose recovery. Thus, studies were conducted to establish additional fungicide treatments for sugar beet storage and a greater understanding of the fungi involved in the sugar beet storage rot complex in Idaho. A water control treatment and three fungicides (Mertect [product at 0.065 ml/kg of roots; 42.3% thiabendazole {vol/vol}], Propulse [product at 0.049 ml/kg of roots; 17.4% fluopyram and 17.4% prothioconazole {vol/vol}], and Stadium [product at 0.13 ml/kg of roots; 12.51% azoxystrobin, 12.51% fludioxonil, and 9.76% difenoconozole {vol/vol}]) were investigated for the ability to control fungal rots of sugar beet roots held up to 148 days in storage during the 2012 and 2013 storage seasons. At the end of September into October, roots were harvested weekly for 5 weeks from each of two sugar beet fields in Idaho, treated with the appropriate fungicide, and placed on top of a commercial indoor sugar beet storage pile until early February. Differences (P < 0.0001 to 0.0150) among fungicide treatments were evident. Propulse- and Stadium-treated roots had 84 to 100% less fungal growth versus the control roots, whereas fungal growth on Mertect-treated roots was not different from the control roots in 7 of 12 comparisons for roots harvested each of the first 3 weeks in both years of this study. The Propulse- and Stadium-treated roots also reduced (P < 0.0001 to 0.0146; based on weeks 1, 3, and 4 in 2012 and weeks 1, 3, 4, and 5 in 2013) sucrose loss by 14 to 46% versus the control roots, whereas roots treated with Mertect did not change sucrose loss compared with the control roots in 7 of 10 evaluations. The predominant fungi isolated from symptomatic roots were an Athelia-like sp., Botrytis cinerea, Penicillium spp., and Phoma betae. If Propulse and Stadium are labeled for use on sugar beet in storage, these fungicides should be considered for root rot control in commercial sugar beet storage and on roots held for vernalization for seed production of this biennial plant species.

Effect of incorporating alum in cane juice clarification efficiency and sucrose losses

The effect of incorporating alum in the clarification stage of raw juice in sugarcane processing on the juice quality and sucrose loss was investigated. Alum was incorporated in both intermediate and hot liming clarification processes of cane juicing. One portion of the cane juice was used for With Pre-treatment Treatment (WPT) while the other portion constituted No Pre-treatment (NPT) juice. Alum at levels of 0 mg L-1, 50 mg L-1, 100 mg L-1 and 150 mg L-1 was incorporated in both intermediate and hot liming clarification processes in each of the two cane juice portions. Sugar concentration (sucrose, glucose and fructose), oBrix, pH, colour, settling performance (initial settling rates (ISR), final mud volume (MV∞), and turbidity) and residual aluminium ion concentration were evaluated. Any significant variations (p < 0.05) in these parameters were assessed. The study found significantly lower (p < 0.05) sucrose losses in clarified juice from intermediate liming of WPT after alum treatment than in the rest of the clarified juices. Colour and turbidity in the pre-treated cane juice of intermediate liming was reduced by 36.9% and 98.1%, respectively at 150 mg L-1 alum level. An initial settling rate of 260 mL min-1 in WPT cane juice of intermediate liming at 150 mg L-1 alum level resulted in the most compact final mud volume of 10.3%. The residual aluminium concentration (0.025 to 0.048 mg L-1) in alum treated clarified juices was lower than the natural aluminium concentration (0.088 mg L-1) in untreated cane juice. This study showed the potential for the use of alum in cane juice clarification to improve on clarification efficiency and lower sucrose loss.