The effect of sample storage and homogenisation techniques on the chemical composition and near infrared spectra of white grapes

The effect of sample freezing, speed of homogenisation, time of homogenisation and homogeniser type on the chemical composition and near infrared (NIR) spectra of white grape berry samples has been examined. Samples of Chardonnay and Riesling sourced from South Australia were homogenised fresh and after different period of frozen storage (overnight, or 1, 2, 3 and 10 weeks) using a Retsch homogeniser or Waring blender. Two speeds (high and low) and two time intervals (20 and 60 s) were applied for samples homogenised with the Waring blender. All samples were analysed immediately after homogenisation by chemical and NIR analysis. The results showed that neither short time freezing nor prolonged frozen storage had any influence on TSS concentration and pH. However a significant increase in concentration of total phenolics was observed in samples after freezing and frozen storage. With the Waring blender, speed and time influenced total phenolics measurement. There was also an effect observed on the NIR spectra of the samples due to different speed and time of homogenisation.

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