Development of a new strategy for studying the aroma potential of winemaking grapes through the accelerated hydrolysis of phenolic and aromatic fractions (PAFs)

Abstract

Current methods for assessing grape aroma potential are based on the fast hydrolysis of precursor fractions but provide hydrolyzates of poor aromatic quality. A new strategy based on the accelerated hydrolysis of reconstituted phenolic and aromatic fractions (PAFs) extracted from grapes is herein developed. PAFs are obtained by solid phase extraction on 10g-C18 sorbents of partially dealcoholized "mistelle", obtained from grapes treated with ethanol. Under optimal conditions, PAFs contain all aroma precursors but the most polar ones, such as those of DMS, more than 85% of the total phenolics and just traces of metal cations and of amino acids. PAFs reconstituted in model wine, aged in strict anoxia 7 weeks at 45ºC or 24h at 75ºC, develop strong aromas. At least 30 different odorants including lipid derivatives, volatile phenols, vanillins, norisoprenoids, terpenes, bencenoids and 3-mercaptohexanol were identified by GC-Olfactometry and GC-MS. Methodological aspects of the extraction, hydrolysis and analysis are optimized and discussed.

The Actual and Potential Aroma of Winemaking Grapes

“…formed very soon, sharp decrease [15,66] Geraniol Always found; up to 10% of total terpenes in Shiraz, 14% in Muscat [144] No [138]; 3-30% of levels found in enzymatic [12] Maxima in fermentation, sharp decrease in aging [14,143]; formed very soon, sharp decrease [15,66] (Z)-Rose oxide 11-29 ppb in Muscat, depending on maturity [145]; unrelated to free form in raisins [23] 0.04 ppb in Muscat, 0.01 ppb in Grenache; not found in Verdejo, Tempranillo, Chardonnay, Cabernet Sauvignon, or Merlot [12] Geranic acid Up to 2-3 ppm [146,147]; also found in raisins [23]; <4 ppb [145]; up to 7.5% total terpenes in Shiraz, 18% in Muscat [144] Not found [138]; 0.5-50% of levels found in enzymatic [12] 1.5 ppb in Chardonnay juices [148] Piperitone Derived from limonene, unknown accumulation pattern [149]; limonene accumulates in the first periods of aging, then slight decrease [66] n.d.: Not detected. Table 7.…”

“…formed soon and stable, maxima 17 ppb [15]; idem, with maxima 7 ppb [66] β-Ionone Not found; yes in frozen grapes [136]; not in wines [137]; <0.11 ppb in frozen grapes [12] Generally yes; not found in [12] Maxima (1.9 ppb) after short aging, stable with time [14]; formed soon, stable for a while, maxima 7.7 ppb [15] TDN Not found; yes in frozen grapes [136]; not in wines [137]; 1-6 ppb (5-30% of levels found in harsh acid hydrolysis) in frozen grapes [12] 8 ppb [138]; detected by GCO [12] 3 ppb [138]; 2-23 ppb depending varieties [12] Continuously formed, maxima 9 ppb [66] Terpenes Linalool Generally present; not found in Portuguese reds [140]; not found in Melon B [141]; not found in Shiraz [144]; found at low levels (less than 7% geraniol 1% total terpenes) [144] 3% levels found in enzymatic [138]; 10-50% of levels found in enzymatic [12] Found only in mild acid hydrolysis [141]; maxima after fermentation, sharp decrease in aging [14]; in Grenache, maxima after short aging [143];…”

“…Both components, γ-nonalactone and massoia lactone, have been found at higher levels in wines made from partially dehydrated (raisinized) Shiraz grapes [65]. Massoia lactone has been also identified in the hydrolysates of phenolic and aromatic fractions (PAFs) extracted from grapes [15].…”

“…Its precursor, ethyl cyclohexanoic acid, found in unfermented mistellas [153] Ethyl 4-methylpentanoate Its precursor, ethyl 4-methylpentanoic acid, found in unfermented mistellas [153] γ-Decalactone No [125] Identified [8] Detected by GCO [15,142] Massoia lactone Detected by GCO [15] Furaneol Aglianico up to 2 ppm in pulp and 0.6 in skin, Uva di Troia 1,2 ppm in pulp, 90 ppb in skin [125]; 15-51 ppm in muscadine [46] Detected by GCO [139] Detected by GCO [15] DMS Only found in grape or grape mistellas not in precursor fractions [15] Polyfunctional Mercaptans…”

“…A recently presented strategy tries to sort out these limitations by using a most powerful extraction strategy, carrying out the hydrolysis in strict anoxia and in the presence of grape polyphenols [15]. Grape polyphenols and most specific aroma precursors, except those of dimethyl sulfide (DMS), are coextracted from dearomatized "mistellas" and reconstituted in synthetic wine.…”