A Basic Method for the Analysis of Starch in Clear Juice

The analysis of starch in factory streams and products is tedious and time consuming. It is not surprising, therefore, that only one South African sugar mill laboratory currently analyses the factory streams for seasonal starch levels and trends. This essentially means that high starch levels are picked up only in the final raw sugar, causing an uncomfortable delay between detection and application of starch hydrolysing enzymes to rectify the situation. Various attempts have been made world-wide to simplify the analysis. It appears that most of these attempts have been based on the ‘SASTA method’ or the ‘SASTA Simplified method’. The latter was further simplified by the Sugar Processing Research Institute (SPRI) in the United States of America, who developed the ‘Rapid Starch Test’. Further modifications made at the Sugar Milling Research Institute, as well as the application of this method to clear juice to eliminate the centrifugation step, resulted in the ‘Basic Starch Test’, which is the subject of this poster. To render this method even more straightforward, a predetermined calibration graph was set up and distributed for use in a ring test between several South African sugar laboratories. Feedback on the method was positive, and results indicated that the method could be used with confidence, albeit using a much higher tolerance. Introduction The starch content of raw sugars is one of the most important parameters when evaluating sugar for export purposes. It is also an important quality factor in raw sugar production and sugar refining. Starch arises in the actively growing part of the sugarcane plant and from immature cane – hence it is delivered to the factory together with the cane itself (Meade and Chen, 1977). Cane varieties differ widely in the amount of starch in juice, ranging from 200 ppm on Brix to around 1200 ppm (Godshall et al., 1996). Growing conditions and the immediate environment also influence starch content (Meade and Chen, 1977). However, high or low levels of starch in certain regions are still unexplained (Boyes, 1958). Starch in the process streams at the mill increases viscosity, hampers crystallisation, causes molasses sucrose content to increase and is partially passed into the raw sugar (Meade and Chen, 1977). Starch levels of around 400 ppm on Brix in cane juice will generally result in starch levels of above 150 ppm on Brix in raw sugar (Schoonees, 2003). Values of about 150 ppm and above in raw sugar adversely affect refining, especially in the carbonatation process (Meade and Chen, 1977). Starch may also cause a haze in sugar solutions and has been associated with the appearance of acid beverage floc (Edye, 2001). Clearly, high starch levels result in a lower quality product with a lower market value that may attract severe penalties (SASMAL Sugar Quality Committee, 2003).