The effects of homogenisation method and freezing on the determination of quality parameters in red grape berries of Vitis vinifera

The effect of sample processing with three different blenders, sample freezing and storage time on the determination of berry quality parameters - total anthocyanins, total soluble solids (TSS), total phenolics (TP) and pH - in homogenates of red grape berries has been examined. Samples of Cabernet Sauvignon, Merlot and Shiraz from four regions of South Australia were homogenised using Ultra-Turrax, Waring or Retsch commercial blenders applied to fresh samples, and to samples held in frozen storage overnight or for 1, 3, 6 and 12 months. All samples were analysed immediately after homogenisation. The results showed that neither homogeniser type nor freezing had any significant effect on total anthocyanins or TSS. However, freezing had an effect on total anthocyanins concentrations in samples with higher colour. The homogeniser type had a significant effect on TP and pH for all varieties analysed together. Freezing had no significant effect on TP, but significant effect on pH, the value being greater in samples at the lower end of the pH range. Frozen storage time of up to 3 months had no significant effect on total anthocyanins, TSS or TP. Statistically significant differences were observed in the concentration of total anthocyanins in samples after 3 months of frozen storage.