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

Abstract

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 T P. Statistically significant differences were observed in the concentration of total anthocyanins in samples after 3 months of frozen storage.

Effect of Saccharomyces cerevisiae and Candida zemplinina on quercetin, vitisin A and hydroxytyrosol contents in Sangiovese wines

“…The clusters were transferred to the laboratory at low temperature and here stored at -20°C. The storage period at -20°C did not exceed 1 month, in order to avoid any chemical difference among grape musts, possibly caused by different times of storage (Cynkar et al 2004). While still frozen, the clusters were hand plucked one day before their use, placed in a plastic bag and well mixed in order to create a homogeneous lot from which aliquots of weighted frozen berries were obtained.…”

Effect of microwave heating on the near infrared spectra and on the prediction accuracy of chemical parameters in red grape homogenates

“…The total anthocyanins concentration was reported as the average of the duplicates and expressed as mg of malvidin-3-glucoside per g berry fresh weight, hereafter termed fresh weight. The conversion of A520 into malvidin-3-glucoside concentration was based on a generic extinction coefficient of malvidin-3-glucoside [3,17]. Samples of homogenate (c 1 g) were centrifuged (Hettich Universal 32R centrifuge, Tuttlingen, Germany, 4,000 g, 5 min) and TSS (°Brix) was measured on the supernatant using a digital portable refractometer (PR-101, Atago Co., Ltd., Japan).…”

“…Total soluble solids (TSS)°Brix, is a wellestablished parameter used for fruit quality assessment in the vineyard. Although sampling is always an issue, measuring TSS by refractometry is fast and accurate, making it useful for pre-harvest, field testing and testing at the point of delivery [3][4][5][6][7]. However, although fruit must achieve target ripeness to maximise quality sugars maturity alone does not guarantee quality.…”

“…However, both processing of the sample (e.g. grinding, drying) and presentation of the sample to the instrument are important factors in the robustness and accuracy of NIR as an analytical technique [1][2][3][4].…”

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

“…NIR spectroscopy should be considered a good option as it offers a possibility of multiple analyses in one measurement, and has been already used in assessment of red grape quality. Similarly to red grapes, when analysing white grape homogenates by spectroscopic methods it has to be taken into account that spectral analyses can be matrix dependant, e.g., due to particle size that can affect light dispersion, and might be influenced by the homogenisation techniques, as well as sample state (fresh versus overnight freezing) and storage (fresh versus frozen), (Cozzolino, Cynkar, Dambergs, Janik, & Gishen, 2005;Cynkar, Cozzolino, Dambergs, Janik, & Gishen, 2004).…”