Microwave-assisted maceration and stems addition in Bonarda grapes: effects on wine chemical composition and sensory properties over two vintages

Martín Fanzone^1,2, Ignacio Coronado^1,3, Santiago Sari¹,Anibal Catania¹, Mariona Gil i Cortiella⁴, Cristina Ubeda^5,6, Mariela Assof^1,2, Viviana Jofré^1,2,Vilma Morata de Ambrosini^3,7, Alvaro Peña Neira⁸
1 Estación Experimental Mendoza, Instituto Nacional de Tecnología Agropecuaria, Luján de Cuyo, Mendoza, Argentina
2 Universidad Juan Agustín Maza, Av., Mendoza, Argentina
3 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
4 Instituto de Ciencias Químicas Aplicadas, Universidad Autónoma de Chile, Santiago 8910060, Chile
5 Departamento de Nutrición y Bromatología, Toxicología y Medicina Legal, Facultad de Farmacia, Universidad de Sevilla, Sevilla, Spain
6 Instituto de Ciencias Biomédicas, Facultad de Ciencias, Universidad Autónoma de Chile, Santiago, Chile
7 Facultad de Ciencias Aplicadas a la Industria, Universidad Nacional de Cuyo, Bernardo de Irigoyen 375, 5600, Mendoza, Argentina.
8 Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile.

Email contact: fanzone.martin[@]inta.gob.ar

AIM: Bonarda, the second red grape variety in Argentina, produces high yields per hectare generating, in several cases, wines with low levels of quality compounds. Microwave-assisted extraction (MW) is a novel extraction technique for winemaking, widely applied in other foods. Stems addition (S) during vinification can be a sustainable technology for phenolic and aroma contribution without additional cost. Therefore, this study aimed to evaluate the combined effect of MW application with stem additions in different conditions, before fermentation, on the chemical composition and sensory properties of Bonarda wines.

METHODS: During two consecutive vintages (2018-2019), 450 kg of grapes were harvested (≈24°Brix) from a commercial vineyard (Mendoza, Argentina), and made into wine in 25 L following a standard protocol. The experimental design consisted of ten treatments (two factors) by triplicate. Two maceration strategies were applied [control (C), and microwaved-assisted extraction after grape crushing (MW; 2450 MHz, 7600 W, 45-50°C)], combined with five stem-contact conditions [control without stems (WS), 50% stems addition (S50), 50% stems addition + MW of the stems (S50MW; 2450 MHz, 7600 W, 60°C), 100% stems addition (S100), 100% stems addition + MW (S100MW)]. Wines were analyzed for basic chemistry (1), phenolic composition and color parameters (2-5), polysaccharides (6), and aroma profiles (7). Additionally, a descriptive sensory analysis (QDA) was performed with 19 panelists in 8 sessions, and 22 attributes were established.

RESULTS: In both seasons, the application of microwaves significantly reduced microbial flora in musts (fungi, yeasts, and acetic acid bacteria), in addition to inhibiting enzymatic activity (cellulase and pectinase). Due to the significant difference of the vintage and its interaction with some of the studied factors, the chemical and sensory characterization of wines were evaluated separately for each season. The 2018 wines showed higher pH with stem additions and MW application in both matrices. Stem additions increased tannin content by 63% (S100) and by >35% for the other treatments; while MW consistently improved phenolic extraction (mainly, anthocyanins and derivatives), and polymeric pigments formation. Likewise, combined strategies increased polysaccharides extraction (FI, 165 kDa; FII, 45 kDa; FIII, 12 kDa), enhanced wine color (greater saturation), and intensified violet hue. Finally, the PCA including sensory variables described the MWS50 wines with higher color intensity and chocolate aroma, and 100% stems addition treatments with more astringency and violet hue. The behavior observed in 2019 was similar, with a more marked effect of MW on wine color (C*_ab and polymeric pigments).

CONCLUSIONS: The reported results are promising and are considered the first advance in the knowledge of the impact of the proposed technological strategies on the chemical and sensory quality of red wines.

References:

1. OIV (2012). Compendium of international methods of analysis of wines and musts, vol. 1, Paris.
2. Harbertson, J.F. et al. (2003). American Journal of Enology and Viticulture, 54(4), 301–306.
3. Blanco-Vega, D. et al. (2011). Journal of Agricultural and Food Chemistry, 59(17), 9523–9531.
4. Lago-Vanzela, E.S. et al. (2013). Food Research International, 54(1), 33–43.
5. Gordillo, B. et al. (2012). Journal of Agricultural and Food Chemistry, 60(11), 2896-905.
6. Fanzone, M. et al. (2012). Food Research International, 45, 402–414.

Úbeda, C. et al. (2017). American Journal of Enology and Viticulture, 68(3), 390–399.