The insoluble form of starch contributes to lower sugar exhaustion from molasses during the manufacture of raw sugar

Gillian Eggleston, Stephania Imbachi Ordonez, Alexa Triplett and Lawrence Messina

Audubon Sugar Institute, LSU AgCenter, St. Gabriel, LA 70776, USA; geggleston@agcenter.lsu.edu

The greatest loss of sucrose in a raw sugar factory is in the final molasses. A 2-year (2020 and 2021 Louisiana processing seasons) study of weekly final molasses from three sugarcane factories revealed new information on the effect of starch on molasses exhaustion. The target purity difference (TPD) of final molasses is an important metric for factory performance to estimate final molasses exhaustion; generally, a lower TPD indicates greater recovery of sugar. During the 2021 season, LA factories experienced markedly higher target purity differences (TPDs), and thus lower exhaustion compared to the 2020 season (normal year). Differences in molasses exhaustion among the factories could not all be explained by conventional reducing sugar/ash (RS/ash) ratios, particularly in 2021. With the advent of new methods for the sugar industry to measure the amounts of soluble and insoluble starch as well as total starch, these three forms of starch were analyzed in weekly composite C-molasses from the three LA factories in both seasons. For the first time, the starch form was shown to impact molasses exhaustion. The greater the amount of insoluble starch in the molasses the higher the TPD value (R²=0.886). This is most likely because the insoluble swollen starch increases the viscosity of the molasses which, in turn, impedes sucrose exhaustion. The factory that added high-temperature (HT) stable amylase to the clarification settling tank consistently had the lowest TPD values in both years. The risk of carry-over amylase activity in raw sugar, however, increases with the addition of HT amylase, but this problem could be solved at the refinery with the use of activated carbon.