Effects of pretreatment methods and leaching methods on jujube wine quality detected by electronic senses and HS-SPME–GC–MS

Highlights

• Effects of pretreatment methods and leaching methods on jujube wine were measured and compared.

• Taste and aroma were profiled detected by electronic senses and HS-SPME–GC–MS.

• Multivariate statistical analysis is effective for the analysis of wine flavor.

• Blended-into-pulp and leached-by-pectase are most beneficial to jujube wine flavor.

Abstract

Conventional analysis, electronic senses and HS-SPME–GC–MS were applied to evaluate the effects of pretreatment methods and leaching methods on jujube wine quality. Significant differences (p < 0.05) in the levels of alcohol content, color, taste and aroma were observed among all the jujube wine samples, in which the pulp and pectase fermented jujube wine was the best among all. Moreover, rather than taste, aroma is the most significantly (p < 0.05) affected. In regard to aroma, a total of 182 volatile compounds were identified by HS-SPME–GC–MS. It was found that the blended-into-pulp treatment and the leached-by-pectase treatment had notable positive effects on jujube wine. The pulp and pectase fermented jujube wines exhibited the highest concentration of total volatile compounds as well as alcohols, esters, acids and aldehydes. Thus, the optimal pretreatment method and leaching method for jujube wine fermentation are blended-into-pulp and leached-by-pectase respectively.

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.