Influence of successive oxygen saturations of a grape juice, supplemented or not with laccase, on its color and hydroxycinnamic acids concentration

Abstract

Aim: This work studies how successive O2 saturations affects the color and hydroxycinnamic
acids concentration in the absence and presence of laccase from B. cinerea with the aim of better understanding the browning processes.

Materials and methods: Grapes of Muscat of Alexandria were harvested and pressed with a vertical press to extract 60% of their juice. Aliquots of 30 mL of this must were placed in 60 mL flasks equipped with a pill (PreSens Precision Sensing GmbH) for measuring oxygen by luminescence (Nomasense TM O2 Trace Oxygen Analyzer). These flasks were added or not with SO2 (50 mg/L) and with 2 UA/mL of laccase from B. cinerea (Giménez et al., 2022). All operations were carried out with a continuous nitrogen stream to protect the grape juice from air oxygen. The grape juices were then saturated in O2. The flasks were kept at 20±2 °C and O2 was monitored (Diéval et al., 2011). Once O2 was completely consumed, this operation was repeated twice to reach a total of three O2 saturations. Absorbances at 420, 320 and 280 nm were determined in all the samples. Hydroxycinnamic acids and GRP were analyzed by RP-HPLC-DAD-ESI-MS (Lago-Vanzela et al., 2013).

Results and discussion: Samples without SO2 and laccase consumed O2 after the 2st saturation in around 1 hour with an initial O2 consumption rate (OCR) of 0.262±0.009 mg of O2/minute. Surprisingly, no significant differences were found in the OCR of the samples supplemented with laccase in the 1^st saturation (0.266±0.075). However, the OCR decreased significantly for the 2nd and 3rd saturations in the case of the samples without laccase (0.128±0.003 and 0.101±0.011 respectively) whereas no significant decrease was observed when laccase was present (0.268±0.013 and 0.238±0.049 respectively). The supplementation with SO2 almost completely inhibited OCR in both cases, without and with laccase (0.006±0.002 and 0.011±0.003 respectively). The A420 nm (yellow color) increased after each saturation and this augmentation was significant higher in the samples supplemented with laccase. In contrast, the A320 nm (hydroxycinnamic acids) and A280 nm (total phenolic compounds) do the opposite. Finally, caftaric and cutaric acids and in a minor extent fertaric acid concentrations decreased after each saturation and this decrease was very similar in the samples supplemented or not with laccase. In contrast, the samples supplemented with SO2 hardly showed changes in the different absorbances or in the hydroxycinnamic acids.

Conclusions:

These results confirm that SO2 is very effective to prevent browning even in the presence of laccase. This data also indicate that the presence of laccase provokes higher browning even consuming the same O2 than without its presence, probably because can use more substrates than natural grape tyrosinase

References

Diéval, J.B., Vidal, S., & Aagaard, O. (2011). Measurement of the oxygen transmission rate of co-extruded wine bottle closures using a luminescence-based technique. Packaging Technology and Science, 24, 375–385.
Giménez, P., Anguela, S., Just-Borras, A., Pons-Mercadé, P., Vignault, A., Canals, J.M., Teissedre, P.L., Zamora, F. (2022) Development of a synthetic model to measure browning caused by laccase activity from Botrytis cinerea. LWT – Food Science and Technology 154 (2022) 112871. 
Lago-Vanzela, E.S., Rebello, L.P.G., Ramos, A.M., Stringheta, P.C., Da-Silva, R., García-Romero, E., Gómez-Alonso, S. and Hermosín-Gutiérrez, I. (2013) Chromatic characteristics and color-related phenolic composition of Brazilian young red wines made from the hybrid grape cultivar BRS Violeta (‘BRS Rúbea’ × ‘IAC 1398-21’). Food Research International 54, 33–43.