This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

When you think of sweet‐corn, you don't necessarily think of macular degeneration. Macular degeneration  was  the  leading  cause  of  blindness  in  Australia,  and the  rest  of  the  developed  world. The total cost of vision loss associated with macular degeneration in Australia was estimated at $5 billion dollars in 2010. The science was increasingly stacking up that the yellow pigments, zeaxanthin and lutein, in the macula protected the eye against the progress of macular degeneration, and that people with low levels of these pigments were more likely to suffer. As the human body cannot synthesize these pigments, they have to be obtained through our diet or supplements. While lutein can be sourced readily from green leafy vegetables, zeaxanthin was much  rarer  in  the  diet.  Sweet‐corn  was  one  of  the  best  sources  of  zeaxanthin,  but  the  levels  present in a normal cob of corn would require you to consume somewhere between 4‐11 cobs per  day  to  achieve  a  zeaxanthin‐intake  equivalent  to  that  used  in  clinical  studies  with supplements. Consequently, the aim of this project was to develop a sweet‐corn which could supply a supplemental dose of zeaxanthin (2 mg/person) as part of a normal meal (100 g kernels, or a small cob of corn), potentially minimising the need for an artificial supplement.

Inspiration  for  this  research  originally  came  from  the knowledge  that  zeaxanthin  had  been  linked to a lower incidence of macular degeneration, and that zeaxanthin was one of the main pigments in sweet‐corn. We also had access to the DAF sweet‐corn breeding program, and a wide  range  of  sub‐tropical  germplasm to  work  with.   As  Australian  consumers  wanted  a  natural (non‐GMO) product, we used a combination of selection, colour and carotenoid analysis, and cross‐breeding to develop a range of high‐zeaxanthin sweet‐corns. This process was gradual, and required us to select for lines producing a lot of carotenoids (zeaxanthin is a carotenoid) and lines that favoured the synthesis of zeaxanthin over lutein, which competed with the building blocks for zeaxanthin. We then combined these attributes together, to give  us  sweet‐corn  lines  with  a  zeaxanthin‐concentration  approximately  10  times  higher  (1000%) than standard sweet‐corn. To complicate matters further, we then had to develop hybrids (matching 2 parents together) that produced commercially‐sized cobs from vigorous, healthy plants. We now had the first cobettes of sweet‐corn in the world that supplied as much zeaxanthin  as  a  supplement,  with  our  hybrids  producing  7‐10  times  the  concentration  of  zeaxanthin concentration of a regular yellow sweet‐corn.

An additional benefit of increasing the zeaxanthin concentration was that it gave the sweet‐corn a  deeper  golden  colour,  so  it  can  be  easily  differentiated  in  the  marketplace  from  regular  sweet‐corn. This was seen as a major advantage, as the compound that changed the colour of the corn was also the active compound for ameliorating the effects of macular degeneration (what  you  see  is  what  you  get). Consumer  assessment  was  carried  out  to  determine  how  orange was too orange, and a working colour‐range for hybrids was established, to which we fitted our hybrids. Equally important, flavour and texture was found to be as good as, if not better  than,  regular  yellow  sweet‐corn.  Other  factors  were  also  investigated,  including  the  effect of seasonality on zeaxanthin concentration, refrigerated storage on zeaxanthin stability, cooking on changing colour intensity, the transient effect of freezing on kernel colour (if you were  to  freeze  your  corn),  as  well  as  whether  an  increase  in  zeaxanthin  caused  a  change  in flavour, through carotenoid‐derived volatile compounds.