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Browning reactions during storage of low‐moisture Australian sultanas: Further evidence for arginine‐mediated Maillard reactions during storage, and some effects of vine‐shading and harvest date
Author(s) -
FRANK DAMIAN,
GOULD IAN,
MILLIKAN MARY
Publication year - 2004
Publication title -
australian journal of grape and wine research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 77
eISSN - 1755-0238
pISSN - 1322-7130
DOI - 10.1111/j.1755-0238.2004.tb00021.x
Subject(s) - browning , maillard reaction , chemistry , shading , horticulture , moisture , canopy , botany , food science , biology , organic chemistry , art , visual arts
Sultana grapevines ( Vitis Vinifera L. cv. Sultana syn. Thompson Seedless ) were subjected to four shading regimes: 50% shading (1), 25% shading (2), fully exposed‐top of canopy (3) and beneath canopy (4) and harvested early (21 February) and late (13 March) in the 1996/1997 sultana season. Grapes from each of the eight field‐treatment combinations represented a range of maturities (14.4 to 23.50 o Brix). Grape samples from each of the treatments were dipped and dried to 18% moisture, with half of each of the sultana samples further reduced in moisture by sunfinishing on plastic sheets in direct sun. These field treatments resulted in sixteen unique dried sultana bulk samples with a range of initial chemico‐physical properties; a w (0.481–0.691), skin‐polyphenoloxidase (PPO) activity (4.40–9.05 μmol O 2 /g.minute) free arginine in skin tissues (1.0–5.10 mg/g) and protein (16.40–27.18 mg/g). Sultanas were stored at 10 o C and 30 o C in either the presence or absence of oxygen for 10 months, and changes in CIE L*a*b* tristimulus values, hue‐angle ( h ab *) and chroma ( C ab *) were monitored. Significant changes in sultana colour occurred in samples stored at 30 o C, especially in higher a w non‐sunfinished sultanas. Although browning was more intense in the presence of oxygen, significant browning also occurred in the absence of oxygen. Lower concentrations of 5‐hydroxy methylfurfural, a key marker of Maillard browning in samples stored at 30 o C in the presence of oxygen, indicated that the non‐enzymatic reactions were sensitive to oxygen. Changes in the concentration of trans ‐caftaric acid, the main substrate of grape PPO, were also measured during sultana drying. Storage browning (changes in L*, b*, h ab *, C ab *)in dried sultanas could be predicted by regression models using pre‐storage a w , free‐skin arginine or Kjeldahl protein after 10 months' storage between 10 o C and 30 o C. Non‐enzymatic and Maillard‐type reactions (sensitive to both oxygen and a w ), made an important contribution to sultana storage browning. We provide only weak evidence that either shaded (immature) or green fruit was more susceptible to storage browning.