Effects of pretreatment methods and leaching methods on jujube wine quality detected by electronic senses and HS-SPME–GC–MS
Introduction
Jujube (Zizyphus jujuba Mill.) is a traditional culinary and medical fruit with a rich content of nutrients including fiber, minerals, vitamins, organic acids, phenolic compounds, flavonoids, carotenoids and cerebrosides, which has been cultivated since 4,000 years ago (Cai et al., 2019). China is the largest producing and consuming country of jujube in the world, with an annual production of > 7,000,000 tons (Cai et al., 2018). Xinjiang Uygur Autonomous Region is the main jujube producer in China, where jujube wine, a deeply processed product, has gained great popularity among the consumers.
Jujube wine is featured with yellowish and translucent color, pure and aromatic smell, sweet and refreshing taste (Lee, Yun, Lee, & Kim, 2018). During the past decade, there has been ever-increasing interests in jujube wine, and much research work has been done. Liu and Zhao (2011) assessed the effects of fermentation technics on jujube wine quality, through the research on initial sugar content, inoculation concentration of yeast, fermentation temperature and pH. W. Zhang, Zhang, and Xu (2016) evaluated the chemical and volatile compounds of jujube wine during fermentation, and found that leaching and pulp contact could significantly strengthen the intensity and complexity of aroma. Zhao, Liu, Wu, Xue, and Hou (2017) discovered that the pesticide residue levels of triadimefon and triadimenol in jujube wine and vinegar were affected by many factors including physicochemical properties, sensibility of fermentation organisms and fermentation environment. Lee et al. (2018) revealed that the physicochemical and sensory properties of jujube wine depended more on the drying process rather than the cultivar or the presence of seeds, furthermore, the flavor of jujube wine fermented by dried fruit is better than that fermented by fresh fruit, especially, aroma and sweetness. Guo et al. (2018) used High Performance Liquid Chromatography along with Head Space Solid Phase Microextraction Gas Chromatography and Mass Spectrometry (HS-SPME–GC–MS) to prove that enzymatic hydrolysis significantly improved the growth of yeast, the contents of total saponins and nitrogen sources, as well as the production of aroma. G. Li, Yuan, Wang, Meng, Li, Zhao, and Peng (2019) applied electronic nose (E-nose) technique with multiple linear regression to establish a forecast model to predict the alcohol content of jujube wine fermentation, and noticed that it is feasible to use E-nose to measure the alcohol content in real time during jujube wine fermentation. Xu et al. (2019) investigated the fermentation kinetics, compositions, volatile and sensory characteristics of pulsed electric fields preprocessed jujube wine, and found out that pulsed electric fields pretreatment can promote wine quality and sensory profile.
The process technology of jujube wine generally comprises steps including raw material pretreatment, leaching, fermentation and aging (Lee et al., 2018; Liu et al., 2011; Zhang et al., 2016, Zhao et al., 2017). However, jujube being a fleshy fruit, its fruit cell wall and middle lamella is pectin rich, which makes its various cellular contents difficult to be leached and fermented (Wang et al., 2012, Zhi et al., 2017). More than 75% of the pectins in jujube are water-soluble pectin, which is higher than other fruits (Wang et al., 2012). Thus, the raw material pretreatment and leaching process are two major steps in the processing of jujube wine that will be beneficial for the dissolution of sugar, the formation of flavor and the improvement of nutrition (Li et al., 2016).
At present, in the actual production of jujube wine, there are 3 pretreatment methods including blended-into-pulp, diced-into-pieces, filtered-into-juice, and there are also 3 leaching methods including leached-by-hot-water, leached-by-microwave, leached-by-pectase. Compared with our knowledge of jujube wine, little is known about the differences among pretreatment methods and leaching methods. Even less is known about how pretreatment methods and leaching methods are affecting the quality of jujube wine. Therefore, the purpose of this research is twofold. Firstly, it is attempted to detect alcohol content, color, taste and aroma of jujube wine processed with different pretreatment and leaching methods using electronic senses and HS-SPME–GC–MS combined with multivariate statistical analysis methods. Secondly, it is necessary to choose an appropriate pretreatment method as well as leaching method for jujube wine fermentation, which would provide reference for the subsequent processing and quality control of jujube wine.
Section snippets
Raw material
The fully ripened and undamaged jujube (Zizyphus jujuba cv. Junzao) was purchased (November 2019) from a local market from Aksu, Xinjiang, China.
Preparation
The jujube was washed thoroughly, stoned and processed with the combination of the following 3 different pretreatment methods (pulp, pieces, juice) and 3 different leaching treatment methods (hot-water, microwave, pectase), respectively to obtain fermentation broth:
- (1)
Pulp and hot-water (Pulp & H): the jujube was blended into pulp with the addition of
Conventional analysis
The alcohol content and the color attributes of jujube wines fermented by different pretreatment methods are presented in Fig. 1. These jujube wines exhibited similar levels of the alcohol content (10.54–13.84%), as a result of the initial sugar content adjustment to the same level (22 °Brix) before fermentation. However, the alcohol content of Pieces & P fermented jujube wines was the highest, while that of Juice & M fermented jujube wines was the lowest. Furthermore, the jujube wines leached
CRediT authorship contribution statement
Wenchao Cai: Software, Formal analysis, Writing - original draft, Writing - review & editing, Visualization. Fengxian Tang: Methodology, Project administration. Zhuang Guo: Investigation, Resources. Xin Guo: Data curation. Qin Zhang: Validation. Xinxin Zhao: Validation. Ming Ning: Validation. Chunhui Shan: Conceptualization, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by Xinjiang Production and Construction Corps Innovation Team Building Project in Key Areas (2017CB012) and Projects of Innovation and Development Pillar Program for Key Industries in Southern Xinjiang of Xinjiang Production and Construction Corps (2018DB002). The rigorous and responsible editors as well as anonymous reviewers have also contributed considerably to the improvement and publication of this paper.
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