Post harvest treatment for toxin-free wine
Crop production is always at risk from the presence of pathogens. Not only do they inflict physical damage from growth and reproduction but some produce harmful toxins. These may not be physically evident in the food or drink and therefore pose a hidden threat to health. One of these persistent toxins, ochratoxin A is produced by Aspergillus species in grapes and could therefore present itself to unsuspecting wine drinkers. Ochratoxin A (OTA) is a potential carcinogen and toxic to the kidneys. The fungi that produce this chemical are natural pathogens of the grape and inoculum is usually present in vineyards. Sound agricultural practice can help to avoid contamination but inevitably some of the fungus can be present in the grapes. Scientists at the Volcani Centre in Israel studied post-harvest treatments as a means of reducing OTA content in wine. Two types of trials were designed and executed. The first simulated storage of grapes during various conditions and treatments. Samples were then inspected for isolate number and OTA concentration. The second involved plating grape samples on agar after storage and counting the number of Aspergillus isolates after sterilisation treatment was applied on the plates. Sulphur dioxide (SO2) is an antioxidant and helps prevent microbial spoilage. It is used in the wine bottling process and initial sterilisation of the equipment. Different concentrations of SO2 generating pads and ethanol dips as a means of sterilising were applied. Time and temperature were also varied in the storage experiments. At all storage temperatures, control and grapes with ethanol dips contained Aspergillus niger and A. carbonarius with OTA content at a later stage. Interestingly, no isolates were recovered from SO2 treated grapes. In the plate tests, sulphur dioxide at the relatively low level of 0.5 parts per million (ppm) lowered the number of isolates by up to half. At 5 ppm, no isolates at all were recovered. Wine producers are keen to maintain the safety and quality of their product. On the basis of this research, post harvest treatments can help the wine industry to achieve this goal.