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At present, the most common storage methods are low temperature storage and SO2 preservative storage. Low temperature is the most important way to store grapes (fruits). Low temperature (4 ℃) can inhibit the respiration and ethylene synthesis of fruits, so as to delay the arrival of respiration peak and achieve the purpose of preservation. In addition to the changes of grape fruit itself, Botrytis cinerea and a variety of bacteria (Acetobacter) will attack the grape during storage and transportation. SO2 preservative not only has a strong inhibitory effect on Botrytis cinerea and the activity of polyphenol oxidase, but also can reduce the respiratory intensity of fruits and fruit stalks, improve the storage resistance of fruits and prolong the shelf life of grapes. Therefore, using preservatives combined with low temperature can effectively inhibit the respiration of grape fruit and the growth and reproduction of miscellaneous bacteria, which is the main way to store fresh grapes.
Liu Jingfang, Zhang Boqin, Zhu benzhong, et al. From China Agricultural University and the Key Laboratory of grape and wine of the Ministry of agriculture and rural areas, in order to study the suitable storage conditions of wine grape, in this paper, Cabernet Sauvignon grape was used as raw material, and different concentrations of sulfur dioxide (SO2) preservative were added under low temperature conditions for storage for 14 weeks. The results showed that SO2 treatment could reduce the rate of fruit decay and falling within 3 weeks. The storage time has the greatest influence on the aroma quality of wine. Prolonging the storage time will lead to the decline of the aroma quality of wine. High concentration SO2 (4 g SO2 / kg grape) treatment will increase the content of esters and phenylethanol, but also make the content of ethyl acetate too high, which will bring bad smell to wine. After storage, the content of biogenic amines in each experimental group increased (compared with the control), while the content of biogenic amines in the low concentration SO2 experimental group was lower. To sum up, the addition of SO2 under low temperature can guarantee the brewing quality of Cabernet Sauvignon grape in a certain period of time, but the storage time should be shortened as much as possible, preferably within one week.
Curve of decay rate and fruit drop rate of grape treated with different doses of SO2
The decay rate and fruit dropping rate increased with the increase of storage time. The decay rate and fruit dropping rate of grape fruit without SO2 preservative were the fastest. In the first three weeks, there was no significant difference between the low concentration and the high concentration of SO2. The decay rate and the drop rate were about 2% - 5%. But in the fourth week, the decay rate and the drop rate of the grape fruit were significantly increased, and the decay rate of the high concentration of SO2 was 13.6 %) significantly higher than the low concentration SO2 test group (8.2%). The above results showed that the addition of SO2 preservative in the storage period can slow down the grape fruit corruption, reduce the grape fruit decay and drop rate, but the time should be controlled within 3 weeks.
Analysis of main metabolites of grape samples after ethanol fermentation treated with different doses of SO2
The fermentation process of all samples was completed successfully (the total amount of reducing sugar decreased to below 4 g / L). The content of glycerin in the control group (0-n) was 7.09 g / L. with the extension of storage time of grape fruit, the content of glycerin in wine decreased, making the round feeling of wine decreased. However, different storage methods have no significant effect on the ethanol yield of wine. Acetic acid is a by-product of wine alcohol fermentation. According to gb1037-2006, the content of volatile acid (acetic acid meter) in wine shall not exceed 1.2g/l. Some studies have shown that when the concentration of acetic acid is 0.2-0.7 g / L, it has a positive contribution to the aroma of wine. In this study, the content of acetic acid in all samples did not exceed & lt; 1.2 g / L, but the content of volatile acid began to rise with the prolongation of storage time. After 3 weeks, the concentration of acetic acid exceeded & gt; 0.7 g / L. The increase of volatile acid concentration may be caused by the bacteria and putrefactive bacteria infected by rotten fruit. The addition of low concentration SO2 can inhibit the decay of grape to some extent and reduce the production of volatile acid, but it should also be controlled within 2 weeks. Tartaric acid is an important source of wine acidity and participates in the balance of wine taste. From the second week (except 2-L), the tartaric acid content of wine in each experimental group decreased significantly compared with the control group. This may be due to the high content of SO2 in the mash of the treatment group, which combined with tartaric acid in the early stage of fermentation. There was no significant difference in the content of other organic acids in wine (P & gt; 0.05).
Analysis of aroma components of grape samples fermented with alcohol and apple milk treated with different doses of SO2
Classification and analysis of aroma substances
With the extension of storage time, higher alcohols decreased significantly, while most esters increased. Adding high concentration of sulfur dioxide preservative can improve the content of some important esters, such as isoamyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, etc., but it will lead to the content of ethyl acetate exceeding the threshold value, which will bring some negative effects on wine.
Principal component analysis of aroma substances
After ethanol fermentation, the control group (0-n) was located in the third quadrant, while the other treatment groups were located in the first, second and fourth quadrants, which showed that there were significant differences in the aroma profile between the different experimental groups and the control group. The control group was located in the negative half axis of PC1 and PC2, which was closely related to citronellol, isobutanol and phenol. However, the experimental group (except 4-h) treated with high concentration of sulfur dioxide has a strong correlation with most of the esters and fatty acids, which can provide the wine with pleasant aroma of banana, rose, apple, strawberry, etc., and increase the complexity of wine aroma. At the end of apple milk fermentation, 1-N and 1-L of control group (1-N) and test group were in the fourth quadrant, closely related to ethyl hexanoate, caproic acid and 1-hexanol. The other experimental groups (except 2-L and 2-N) had similar aroma profile, and had strong correlation with ethyl acetate, isoamyl acetate, methyl octanoate and other substances. The results showed that the aroma profile of wine changed with the storage time. When the storage time is more than three weeks, the difference between the experimental group and the control group is obvious, and the effect of storage for one week is the least.
Analysis of variance of two factors of aroma substances
SO2 concentration and storage time had significant synergistic effect on the changes of the following aroma substances (P < 0.01): isoamyl alcohol, ethyl acetate, isoamyl acetate, ethyl butyrate, isoamyl octanoate and decanal. The storage time had a significant effect on 13 aroma compounds. From the value of F, it can be seen that the effect of storage time on aroma substances is more significant than that of SO2 concentration. For example, the content of isoamyl acetate is significantly affected by SO2 concentration and storage time (P < 0.001), but the effect of storage time is more significant (F1 = 24.716, F2 = 47.024). The result of apple milk fermentation is similar to that of alcohol fermentation, so we will not discuss it too much here. The above results showed that SO2 concentration and storage time significantly affected the aroma quality of wine, especially storage time. Therefore, the storage time should be strictly controlled while optimizing the SO2 concentration.
Treatment of grape samples with different doses of SO2 for ethanol fermentation and biogenic amines content after apple milk fermentation
The content of histamine was the lowest (0.7 mg / L) in the experimental group whose storage time was within one week, but with the increase of storage time, the content of histamine in most experimental groups would increase in varying degrees (4.0? 5.7 mg / L). After ethanol fermentation, the total amount of biogenic amines in the control group (0-n) was 36.3 mg / L, while the content of biogenic amines in the test group stored for 1-4 weeks was higher than that in the control group, and the total amount of biogenic amines in the 4-h test group was the highest, which was 1.46 times of that in the control group. This indicates that the storage of wine grape may increase the content of biogenic amines in wine, which may lead to adverse effects on the safety of wine. Compared with the high concentration SO2 group, the addition of low concentration SO2 can control the increase of biogenic amines to a certain extent, which has a positive effect on the quality of wine after storage. The content of biogenic amines in the 4-h group was 4.1 times higher than that in the 5.4 mg / l group. The histamine content of the experimental group with storage time within one week was similar to that of the control group. Therefore, from the perspective of wine safety, grape storage time should be controlled within one week as much as possible, adding low concentration of SO2 can reduce the content of biogenic amines in wine to a certain extent, and the specific mechanism needs further study.
conclusion
In this study, healthy and mature Cabernet Sauvignon grapes were used as raw materials. At low temperature (4 ℃), different concentrations of SO2 preservatives were used to treat the grapes for different times, and then alcohol and apple milk fermentation were carried out according to the conventional process. The effects of SO2 preservative pretreatment on wine aroma and biogenic amine content were studied. The results showed that at low temperature, the addition of SO2 with low and high concentration could reduce the grape decay rate by about 4% (within 3 weeks). The storage time has the greatest influence on the aroma quality of wine, and prolonging the storage time will lead to the decline of the aroma quality of wine. In addition, the addition of high concentration of sulfur dioxide can also increase the content of phenylethanol, isoamyl acetate, ethyl hexanoate, ethyl octanoate and ethyl decanoate in wine to a certain extent, bring pleasant flower and fruit fragrance to wine, increase the complexity of wine aroma, but it will lead to the increase of ethyl acetate, which will bring negative effects on wine aroma quality. After fruit storage, the total amount of histamine and biogenic amine in each experimental group increased (compared with the control). The content of histamine and biogenic amine in the low concentration SO2 experimental group was the lowest, which could guarantee the safety and quality of wine to a certain extent. To sum up, we can draw the following conclusion: under low temperature (4 ℃), pretreatment with SO2 preservative can guarantee the brewing quality of grape in a certain period of time, but the storage time should be as short as possible (controlled within 1 week).
This paper "the effect of sulfur dioxide preservative pretreatment on the aroma and biogenic amine content of wine" comes from "China Brewing" 2020, Vol. 39, No. 4, page 32-39, author: Liu Jingfang, Zhang Boqin, Zhu benzhong, Duan Changqing, Yan Guoliang.
doi: 10.11882/j.issn.0254-5071.2020.04.007。
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