Elsevier

Phytochemistry

Volume 55, Issue 1, September 2000, Pages 77-85
Phytochemistry

Changes in grape seed polyphenols during fruit ripening

https://doi.org/10.1016/S0031-9422(00)00196-5Get rights and content

Abstract

The quantity and characterization of extracted flavan-3-ol monomers and procyanidins was determined in seeds from Vitis vinifera cv. Cabernet Sauvignon berries, over the course of ripening and at different levels of vine water status. The per berry extractive yield of all polyphenols decreased with maturity, and followed second-order kinetics. The flavan-3-ol monomers decreased most rapidly, followed by the procyanidin extension units and finally, the terminal units. The relative proportion of procyanidin extension units did not vary with maturity. During fruit ripening, the mean degree of polymerization of extracted procyanidins is unchanged when analyzed intact by HPLC, but decreases by thiolytic degradation. The proportion of extracted procyanidins resistant to acid catalyzed thiolysis increased with maturity. Changes in vine water status affected polyphenol amounts, indicating that cultural practices can be used to influence composition. Oxidation of the seed polyphenols during fruit ripening, could explain these observations.

Introduction

The growth of the grape berry is characterized by two successive sigmoid curves, with a plateau in-between corresponding to three stages of development (Coombe, 1973) (Fig. 1). During stage I, characterized by the first period of berry growth, the pericarp and seed cell number increases. During this stage, the seed approaches its full size. During stage II, characterized by little change in berry size, the seed embryo develops with a concomitant hardening of the seed coat (Coombe, 1960). Stage III, characterized by the second period of berry growth, is the ripening stage when sugars rapidly accumulate. The inception of stage III (termed véraison) is characterized by berry softening and anthocyanin accumulation (red varieties). By véraison, much of the seed is fully developed.

The seed plays an important role during the making of red wine, contributing flavan-3-ol monomers and procyanidins (collectively called seed tannins by winemakers) to the final product. These compounds are important sensory components, providing red wine with bitterness and astringency (Robichaud and Noble, 1990).

Fruit maturity is important to the overall quality of red wine, yet it is unclear to what extent the seed tannins change during this period. There is evidence that extractable flavan-3-ol monomers (Mr: 290–442) and low molecular weight seed tannins (Mr: <900) decrease during fruit ripening (Czochanska et al., 1979, Romeyer et al., 1986). However, the molecular weight of grape seed tannins can exceed 3000 (Foo and Porter, 1981, Prieur et al., 1994), and no information on molecular weight and compositional changes during this period exists. Some evidences, based on seed weight gain during fruit ripening, indicate that the seed continues to develop during this time (Staudt et al., 1986), and this development could affect seed tannins.

Research on other plant species indicates that significant changes in procyanidin composition occur with respect to maturity and cultural practice, and can also influence the ability of procyanidins to act as astringents (Bate-Smith, 1973, Mole et al., 1986, Koupai-Abyazani et al., 1993). To investigate the effect of fruit maturity on grape seed polyphenols, changes in polyphenol amount, composition and molecular weight were determined during fruit ripening.

In addition to fruit maturity, environmental conditions (such as vine water status) have been associated with differences in grape polyphenols. It is clear that vine water status affects fruit growth (Matthews et al., 1987), the concentration of total phenolics (Matthews and Anderson, 1988), and wine sensory attributes (Matthews et al., 1990). Yet, it has not been established whether changes in seed polyphenol composition result from changes in irrigation practice. Therefore, this investigation was also conducted to determine the changes that grape seed polyphenols undergo with respect to grapevine water status.

Section snippets

Berry development

Three treatments were established to investigate (in addition to maturity) the effect of vine water status on seed polyphenols. For the standard irrigation (SI) treatment, water was applied weekly (8 h × 4 l/h/vine) beginning 2 weeks before véraison, and continued until 1 October. For the double irrigation (DI) treatment, water was applied at twice the SI rate (8 h × 8 l/h/vine). For the minimally irrigated (MI) treatment, water was applied (8 h × 4 l/h/vine) when the midday leaf water

Conclusion

Grape seed polyphenols decrease dramatically during ripening with a 90% decrease in flavan-3-ol monomers and a 60% decrease in procyanidins. The results described above, specifically:

  • 1.

    changing seed coat color

  • 2.

    decreasing flavan-3-ol monomers and procyanidins

  • 3.

    decreasing flavan-3-ol monomers in the order eCG⪢C>eC

  • 4.

    inconsistency between the procyanidin mDP when analyzed intact and the procyanidin mDP when determined by thiolysis.

  • 5.

    decreasing thiolytic yield

  • 6.

    second-order decline in polyphenols

are

Grape cultivation

Treatments were imposed in a commercial, drip irrigated vineyard [Vitis vinifera cv. Cabernet Sauvignon (UC Davis, FPMS clone #8) grafted onto 110 Richter rootstock] planted in 1989 on the valley floor in the Napa Valley, near Oakville, California, USA (latitude: 38°27′ N; longitude: 122°25′ W; elevation: 65 m). Vines were planted 1 m within the rows and 1.8 m between rows, and trained to bilateral cordons with shoots trained vertically. Fertilization, pest control and other vineyard operations

Acknowledgements

The authors are thankful to Roger B. Boulton for helpful discussions and comments. We gratefully acknowledge the Robert Mondavi Winery for the use of their vineyards and extraordinary cooperation in this experiment. We are also grateful to the North Coast Viticultural Research Group and the American Vineyard Foundation for intellectual as well as financial support. Finally, J.A. Kennedy would like to acknowledge the generous contributions from the Wine Spectator, Knights of the Vine, Mario P.

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