Impact of apple cultivar, ripening stage, fermentation type and yeast strain on phenolic composition of apple ciders
Introduction
Apples are known for their health benefits. The adage “an apple a day keeps the doctor away” is well known among the consumers and results of scientific research support it by showing presence of various bioactive molecules, such as various phenolic compounds. Health benefits associated with polyphenols in apples are cancer risk reduction, high antioxidative power, anti-inflammatory and anti-tumor properties and inhibition of carcinogenesis in skin, mammary, and colon etc. (Biedrzycka and Amarowicz, 2008, Francini, 2013).
Cider is generally regarded as a beverage made from apples. In North-America, the term “cider” generally refers to cloudy unpasteurized apple juice, and the term “hard cider” is used for a fermented product. In Europe, however, the term “cider” refers to the fermented product, an alcoholic beverage with alcohol content between 1.2 and 8.5% v/v (Lea & Piggott, 2003). In this study, the term “cider” refers to a fermented alcoholic beverage. Apple cider production starts with pressed apple juice. During the fruit crushing, pressing and juice extraction only a fraction of phenolic compounds is extracted (Van der Sluis, Dekker, & van Boekel, 2005). This is mainly due to the discard of the peel and seeds which are rich in different phenolic compounds (Francini, 2013, Wolfe et al., 2003). The polyphenolic content of apple juice depends on preparation method, such as possible utilisation of pectinolytic enzymes in order to release phenolic compounds from polysaccharide structures, and following treatments, such as pasteurisation, or fermentation parameters in cider production (Ye, Yue, & Yuan, 2014). Endogenous enzymes, such as polyphenol oxidase, oxidise phenolic compounds in the apple juice and affect the sensory quality of the product (Renard et al., 2011). Each apple cultivar has its own polyphenolic profile that is also dependent on harvest year, climatic variables, cultivation and storage conditions (Mattila et al., 2006, Mikulic-Petkovsek et al., 2010, Thompson-Witrick et al., 2014, Wolfe et al., 2003, Łata and Tomala, 2007). Therefore, in order to compare different cultivars, apples used in the current study shall come from the same orchard and are grown under the same conditions.
The phenolic contents and profile have important effects on the sensory properties of apple ciders, mainly on colour, bitterness, and astringency (Ye et al., 2014). High molecular weight procyanidins in ciders are known to contribute to astringency, whereas the smaller compounds contribute to bitter taste (Lea and Arnold, 1978, Symoneaux, Baron et al., 2014, Symoneaux, Chollet et al., 2014). Simultaneously, they influence the sweetness and sourness, thus further highlighting their importance in the overall flavour development (Symoneaux, Baron et al., 2014). In addition to the non-volatile phenolic compounds, the volatile phenolics mainly formed by enzymatic decarboxylation during fermentation contribute to aroma (Vanbeneden, Van Roey, Willems, Delvaux, & Delvaux, 2008).
The selection of yeast and fermentation conditions is an important factor influencing the development of sensory properties in ciders. The availability of different yeast strains is numerous; therefore, monitoring their influence on apple cider content and profile of phenolics is in the interest of both yeast manufacturers and apple cider producers. Malolactic fermentation (conversion of l-malic acid to l-lactic acid and carbon dioxide) used in cider-making process mainly to reduce the sourness of the product. The aim of the study was to investigate phenolic profiles of apple juices with those of ciders after the yeast fermentation as well as malolactic fermentation by using multivariate statistical models. Moreover, we compared the contributions of apple cultivar, with an emphasis on Estonian cultivars, and ripening stage to the phenolic composition of ciders and juices. Special focus was also on the impact of various commercial yeast strains on the compositional profiles of the fermented ciders.
Section snippets
Preparation of ciders
Four autumn or winter apple cultivars, ‘Antei’, ‘Kulikovskoye’, ‘Melba’, and ‘Orlovski sinap’ grown in South Estonia, at a private orchard in Valgjärve (58°8′ N, 26°66′ E) were used in the study. Samples were subsequently taken at three different stages of ripening: unripe, ripe, and overripe. Ripening time and thus the harvesting time varies in each season due to varying weather conditions. Therefore the estimation of ripening stage was based on the assessment of the experienced farmer and
Identification of the phenolic compounds
Identification of the analytes extracted from ciders and juices were based on the HPLC retention behaviour, UV–vis spectra, ESI-MS(-MS2) spectra, reference compounds, and literature comparisons (Chagné et al., 2012, Clifford et al., 2003, Diñeiro García et al., 2009, Malec et al., 2014, Marks et al., 2007, Picinelli Lobo et al., 2009, Ramirez-Ambrosi et al., 2013, Sanoner et al., 1999, Thompson-Witrick et al., 2014, Verdu et al., 2013, Verdu et al., 2014, Çam and Aaby, 2010). Representative
Conclusions
The impact of four different factors, fermentation type, apple cultivar, apple ripening stage and yeast strain, on the phenolic composition was studied using multivariate statistical models. The major difference was between ciders inoculated with additional malolactic bacteria in comparison to juices or ciders produced only with yeast fermentation. Malolactic fermentation which is typically used to “soften” the sour taste of wines and ciders by converting malic acid to lactic acid was shown in
Conflict of interest
The authors declare no conflicts of interest.
Acknowledgements
This research was supported by the Enterprise Estonia project EU48667. Authors would also like to thank OÜ Siidrikoda for providing the apples and Lallemand Inc. for providing the yeast cultures and malolactic strain. Additionally, Jukka-Pekka Suomela, Heta Haikonen and Matilda Lintunen are thanked for their contributions to the LC-DAD and LC-MS analyses.
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