Browning reactions during storage of low-moisture Australian sultanas: effects of vine nitrogen nutrition on subsequent arginine-mediated Maillard reactions during storage of dried fruit

• Autores: Ian Gould, Mary Millikan, Damian Frank
• Localización: Australian journal of grape and wine research, ISSN 1322-7130, Vol. 11, Nº 1, 2005, págs. 15-23
• Idioma: inglés
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• Resumen

  • Ten-year old Vitis Vinífera L. cv. Sultana (Thompson Seedless) grape vines were transferred into large cement pots in low nitrate soil and supplemented with four levels of nitrogen application in the form of ammonium nitrate as follows: O g (N0(, 8.5 g (N1(, 17.0 g (N2( and 25.0 g (N3(. Grapes were harvested from each nitrogen treatment, dipped and dried to low moisture (~1l.4%) and subsequently stored for 10 months at 10ºC and at 30ºC in either the presence or absence of oxygen. The pre-storage concentration of free arginine, free-proline and total protein in the dried sultanas increased with soil nitrogen application. Skin-pufyphenuluxidase (PPO( activity was higher in sultanas with added soil nitrogen (N1, N2, N3), however pre-storage differences in total phenolics, and the PPO substrate, truos-caftaric acid, were not significantly different. After 10 months storage al 300C significant browning was observed in both the presence and absence of oxygen. Greater browning corresponded to higher soil-nitrogen application rates. The concentration of skin irans-caftaric acid did not decrease in N0, N1 or N2 after 10 months at 30~C, in either the presence of absence of oxygen, although some decreases were measured in the highest nitrogen sultanas (N3(. While PPO oxidation of the phenolic substrate trans-caftaric acid was not the primary route to browning, a number of Maillard reaction product (MRP) were present in both sultanas and arginine-glucuse model systems. Those products were separated via reverse phase HPLC and partially characterised by UV-diode array spectroscopy. The lack of oxidation of trans-caftaric acid observed in the nitrogen storage trial was confirmed in an accelerated browning experiment in low-moisture sultanas, where despite browning at 50ºC after 12 days. no decreases in this primary substrate by PPO-mediated oxidation were measured.