Evaluation of the drying & size reduction processes for the production of Potato Flour

The following is the a project report by Massey University Bachelor of Food Technology Honours student Yvette Coyle

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This project involved investigating the drying of waste potatoes for the production of potato flour in New Zealand. No constant rate drying period was observed during the drying  of  fresh  or  waste  potatoes.  Because  of  this  the  drying  of  both  these  potato  types can be approximated as a single kinetic equation.

Drying  results  overall  showed  that  an  increase  in  temperature  and/or  air  speed  resulted  in  a  reduced  drying  time.  Increases  in  temperature  typically  had  a  larger impact than increases in air speed, however a large amount of variation was seen in the  results.  A  salt  water  blanch  of  the  potato  slices  prior  to  drying  resulted  in  a  reduced  drying  time  compared  to  equivalent  drying  of  potatoes  with  no    pre-­‐treatment.

It was also found that the loading density of the tray had an impact on the drying time, although  this  relationship  was  not  proportional.  The  length  of  the  chip  had  little  influence on the temperature change at the centre of the chip, and thus it is assumed the length of the chip has little influence on its time to dry. The humidity of the air in the  drying  chamber  determined  the  equilibrium  moisture  content  that  the  potatoes  reached.

The  project  also  involved  analysing  the  physical  properties  of  the  potato  flour  produced, and comparing these to wheat and pea flours. It was found that potato flour has  a  different  colour  than  both  pea  and  wheat  flour,  and  is  more  different  to  pea  flour. A pasting profile was generated for all three flours, which showed that potato flour follows an extremely similar pasting profile to wheat flour, but has significantly higher viscosity’s upon gelatinisation.

Different size reduction processes were analysed for the production of potato flour. It was concluded that a number of different mills would be appropriate for use.

It  is  recommended  that  the  following  actions  be  taken  for  the  continuation  of  this  project:

  1. Construct a moisture desorption isotherm with the potatoes to be dried so that the relationship between the humidity of the air in the drying chamber, water activity and the equilibrium moisture content can be determined.
  2. Conduct further trials to optimise the loading density of the potatoes and the time to dry to maximise throughput.
  3. Conduct further trials to assess the significance of a salt water blanch on the drying time of potatoes.
  4. Consult  with  the  customer  to  determine  desired  characteristics,  e.g.  particle size and moisture content of the final product.
  5. Assess the nutritional properties of the potato flour after the final product has been defined.