Chemical Composition of Special Glutinous Rice and Its Effect on the Quality of Brewed Wine

Jiayong XIANG, Yuanyuan PENG, Liye LU, LU XIE, Qinxin XIE, Guiyuan MENG, Rong XIAO

College of Agriculture and Biotechnology, Hunan University of Humanities, Science and Technology, Loudi 417000, China

Abstract The chemical composition of 8 different special glutinous rice varieties was analyzed, and its effects on the physical and chemical properties of the wines brewed were investigated. The correlations between major chemical constituents and quality of glutinous rice were analyzed. The results show that the contents of the major chemical constituents in the special glutinous rice varieties were not much different, and they all ranked as starch’s > protein’s > fat’s. After 4-8 weeks of fermentation, the total acidity decreased with time (excepting Heixiangnuo), the total residual sugar reduced significantly, and the alcohol content increased significantly. The correlations between starch content of glutinous rice and physical and chemical indices and sensory quality of its brewed wine were not significant. There are positive correlations between protein content and various indices, and the correlation with total acidity reached the significant level. Fat content was negatively correlated with alcohol content, and positively correlated with sensory quality.

Key words Glutinous rice, Wine, Chemical composition, Quality, Correlation

1 Introduction

Rice wine is a collective name for beverage wines that are fermented by saccharifying agents such as koji taking rice and others as raw materials, with higher nutrition and health value[1-2]. In addition to the quality of koji and fermentation conditions, the raw material of glutinous rice is one of the important factors affecting the quality of rice wine[3]. There are differences in the chemical and nutritional components of different types of glutinous rice[4-7]. Too much protein residue in wine will affect the stability of wine quality[8]. Domestic and foreign research on rice wine mainly focus on the optimization of fermentation process and conditions and analysis of major constituents[9-11], but there are few reports on the effects of chemical components of special glutinous rice on fermentation process and quality of rice wine. Xinhua Watered Wine is a popular name for fermented glutinous rice wine brewed locally by Xinhua people. The quality of Xinhua Watered Wine is directly related to the koji, the brewing process and the variety and quality of glutinous rice. In this study, the differences in the major chemical constituents of different special glutinous rice varieties were analyzed, and the correlations between the major chemical constituents of special glutinous rice and the quality of wine brewed were explored, thereby providing an important theoretical basis for the selection of glutinous rice for brewing wine and quality improvement of the wine.

2 Materials and methods

2.1 Brewing technique of glutinous rice wine by fermentationDifferent varieties of glutinous rice were used as raw materials. The koji used was special smartweed (Polygonum hydropiper) wine. The brewing was carried out in Jiuda Village, Zhenshang Town, Xinhua County, Hunan Province according to the following procedure: soaking glutinous rice to saturation → washing and draining → cooking thoroughly under normal pressure steaming → spreading out for cooling → mixing with smartweed wine → transferring to jar (rice∶water=160∶100)→ fermenting at constant temperature for 20 d (primary fermentation)→ harrowing regularly → adding winter water (rice∶water=160∶160)→ fermenting for 40 d (subsequent fermentation)→ pressure filtration → membrane filtration → sterilization → canning → fished product.

2.2 Analysis on chemical composition of glutinous riceMoisture content was determined with direct drying method (GB 5009.3-2010); starch content was determined with enzymatic hydrolysis method (GB/T 5009.9-2008); protein content was determined with Kjeldahl method (GB 5009.5-2010); fat content was determined using Soxhlet extraction method (GB/T 5009.6-2003); and ash content was determined with burning method (GB 5009.4-2010).

2.3 Detection of physical and chemical indices of glutinous rice winesFrom the beginning of fermentation, wine mash was sampled once every week for determination of total sugar content and total acidity using sodium hydroxide standard alkali titration method and potassium ferricyanide titration method (GB/T 13662-2008). The collected samples were immediately pro-processed; and those cannot be pro-processed immediately must be stored in a 4℃ refrigerator, and the storage time cannot exceed 3 d. At the end of each of the primary fermentation period and subsequent fermentation period, the wine mash was sampled once for determination of alcohol content (GB/T 13662-2008).

2.4 Sensory evaluation of glutinous rice winesAt the end of each of the primary fermentation period and subsequent fermentation period, the wine mash was sampled for sensory quality evaluation. The fished product was also subjected to sensory quality evaluation. For each batch of sample, three replicates were arranged. According to GB13662-2008, the sensory quality of the samples was evaluated from aspects of color, aroma, taste and style[4]by 10 teachers and students of food science major. The wine mash samples were evaluated based on the actual situation and the characteristics of Xinhua Watered Wine.

3 Results and analysis

3.1 Differences in chemical composition of different special glutinous rice varietiesThe chemical composition of the special glutinous rice varieties is shown in Table 1. As shown in Table 1, in various glutinous rice varieties, the content of starch was the highest, followed by moisture and protein, and the contents of fat and ash were very little. There were some differences in the contents of major chemical constituents of different glutinous rice varieties. The contents of starch, protein, fat and ash in the special glutinous rice varieties ranged from 73.7%-78.3%, 7.4%-10.2%, 0.76%-1.30% and 0.21%-0.28%, respectively. The content of starch was highest in Haibainuo No.1 and lowest in Hongnuo. The content of protein was highest in Bancangnuo and lowest in Haibainuo. The content of fat was highest in Hongnuo and lowest in Jiahua No.1. The differences in the contents of major chemical constituents of the glutinous rice varieties would affect the stability and flavor of the wines brewed.

3.2 Effects of different special glutinous rice varieties on main physical and chemical properties of wine brewed

3.2.1Total acidity. The dynamics in total acidities of the wine mashes during 8 weeks of fermentation are shown in Table 2. The total acidities of the wine mashes from different glutinous rice varieties all decreased with time excepting that from Heixiangnuo. At week 4, the total acidities of the wine mashes ranged between 6.2-10.9 g/L, and at week 8, the total acidities ranged between 5.0-8.1 g/L, with an average decrease of 28.60%. The total activities of Bancangnuo and Nuo S687 were higher, and those of Haibainuo No.1, Jingnuo No.6, Hongnuo, Jiahua No.1, Zhongshannuo were lower. After 8 weeks of fermentation, the total acidities were all lower than 6.5 g/L. It indicates that in terms of only total acidity, Bancangnuo and Nuo S687 will affect the flavor of rice wine and have a certain effect on quality.

Table 2 Effects of different glutinous rice varieties on main physical and chemical properties of wine

3.2.2Total residual sugar. Table 2 shows the changes in total residual sugar content in the wine mashes of different glutinous rice varieties. At week 4, the total residual sugar content was higher, with a range of 67.8-100.0 g/L. By the 8th week, the total residual sugar content decreased significantly, with a range of 1.0-62.4 g/L. In the same period, the total residual sugar content of Jiahua No.1 was highest, followed by those of Bancangnuo and Heixiangnuo, and the total residual sugar contents of Zhongshannuo and Jingnuo No.6 were lower. In terms of only total residual sugar, Jingnuo No.6, Zhongshannuo, Haibainuo No.1 and Hongnuo have little effect on the quality of rice wine.

3.2.3Alcohol content. As shown in Table 2, during the 8 weeks of fermentation, the alcohol contents of the wine mashes of different glutinous rice varieties increased with time. At week 4, the alcohol contents of the wine mashes ranged from 15.6% to 18.4; and at week 8, the alcohol contents ranged from 18.6% to 21.6%, an average increase of 15.13% over the previous period. In the same period, the alcohol content of Jingnuo No.6 and Zhongshannuo were higher, and those of Hongnuo and Haibainuo No.1 were lower. There were no significant differences in alcohol content among the glutinous rice varieties, and if only considering alcohol content, the variety of glutinous rice has little effect on the quality of wine.

3.3 Sensory quality evaluation of wines from different special glutinous rice varietiesThe sensory evaluation results of the wine mashes of different glutinous rice varieties are shown in Table 3. As shown in Table 3, the wine mashes of Bancangnuo, Zhongshannuo, Hongnuo and Heixiangnuo were clear in the late fermentation; the red color of red glutinous rice had faded during soaking; the wine mash of Heixiangnuo was pink; the wine and rice flavors of the wine mashes of the four varieties were rich; and their rice grains were intact. Therefore, the four glutinous rice varieties are worthy of being developed into wine. Although the total residual sugar content and alcohol content of Jiahua No.1 were higher, its rice grains became minced just after the fermentation begun, thus the yield of wine mash obtained after pressure filtration would be affected. If the milky white solid of Jiahua No.1 can be stabilized in the wine mash system to develop into wine juice, the utilization of its nutritional resource will be maximized. According to the overall evaluation of grain morphology, color, aroma and flavor during the brewing process, the sensory evaluation scores of Hongnuo, Bancangnuo, Haibainuo No.1 and Jiahua No.1 were higher, indicating that the wines from these glutinous rice varieties have better quality in terms of sensory evaluation.

Table 3 Sensory evaluation of wines from different glutinous rice varieties

3.4 Correlation analysis between chemical composition of glutinous rice and quality of wine brewedThe correlations between the main chemical constituents of glutinous rice and the quality of wine are shown in Table 4. The starch content of glutinous rice was negatively correlated with the total acidity, alcohol content and sensory quality and positively correlated with the total residual sugar of wine brewed (P>0.05); and there were positive correlations between protein content of glutinous rice and various indices of wine (total acidity,P<0.05; others,P>0.05). It indicates that the higher the protein content in glutinous rice, the higher the total acidity, which is not conducive to the flavor and stability of rice wine; and the fat content of glutinous rice has a significant negative correlation with alcohol content, and a significant positive correlation with sensory quality of rice wine.

Table 4 Correlation analysis between main chemical constituents of glutinous rice and quality of wine

4 Conclusions

The main chemical constituents of 8 special glutinous rice varieties, and the main physical and chemical properties and sensory quality of the wines from these glutinous rice varieties were studied, and the correlations between the main chemical constituents of glutinous rice and the quality of wine were analyzed. There were little differences in the contents of main chemical constituents among the special glutinous rice varieties. In the glutinous rice, starch had the highest content, followed by protein, and the content of fat was extremely low. From week 4 to week 8, the total acidity decreased with time, with an average decrease of 28.60%; the total residual sugar significantly reduced, with an average reduction of 67.33%; and the alcohol content increased significantly, by an average of 15.13%. The correlations between starch content of glutinous rice and physical and chemical indices and sensory quality of wine were small; the protein content of glutinous rice was positively correlated with the physical and chemical indices and sensory quality of wine (total acidity,P<0.05); and the fat content of glutinous rice was significantly negatively correlated with alcohol content, and significantly positively correlated with sensory quality of wine.