The effect of low temperature fermentation on the type and content of wine aroma composition.

Proper cryogenic stress causes the metabolism of yeast to be regulated by different mechanisms and react accordingly, producing different content of metabolites, which in turn affects the quality of wineLow-temperature fermentation is conducive to improving the aroma and sensory properties of wine, mainly due to the increase of acetate and ethyl esters, and the reduction of advanced alcohol and volatile acid contentFrom the angle of wine aroma composition, related metabolism and gene expression, this paper analyzes the effect of low temperature on wine quality, and combines non-wine yeast suitable for low temperature fermentation, which provides a theoretical basis for low temperature fermented winearoma is one of the important characteristics of judging the quality of wineThe aroma of wine can be divided into three categories: variety aroma or primary aroma, determined by grape variety, fermented aroma or secondary aroma, produced by yeast and bacteria during the fermentation of alcohol and lactic acid, aging aroma or three-level aroma, derived from the transition between aromas during the aging processHundreds of compounds produced by the metabolism of microorganisms (mainly yeasts) in the process of alcohol fermentation play a leading role in the aroma composition of winethe chemical composition and fermentation conditions of grape juice are the two most important factors affecting yeast metabolismIt is generally believed that low temperature spent on wine fermentation can increase and retain more volatile aroma scents, and a simple explanation may be that low-temperature fermentation retains higher primary and secondary flavor substances than normal temperature fermentationAs a result, the improvement in the aroma and taste of low-temperature fermented wines can be attributed to more retention of steroids, increased production of volatile esters and C6-C10 medium-chain fatty acidests, and lower levels of advanced alcohols and volatile acidsHowever, temperature also affects the growth rate and fermentation rate of yeast, the lower the temperature, the longer the fermentation timeChanges in fermentation rates can also alter the ecology of yeast and bacteria, ethanol sensitivity and yeast metabolismAlthough fermentation temperature significantly affects the growth rate of yeast and its central metabolism, the effect of fermentation temperature on the biosynthesis pathway of yeast fragrance compounds is still unclearlow-temperature fermentation of wine increases the probability of slow or stagnant fermentation, which can be reduced by selecting wine yeasts suitable for low-temperature fermentation while maintaining good wine qualitySome non-brewery yeasts (Non-Saccharomyces, NSC) are better able to adapt to low temperatures than saccharomyces cerevisiaeThe secondary metabolites produced by NSC in the wine fermentation process play an important role in the formation of wine flavor substances, especially the early fermentation of NSC metabolism will produce esters, advanced alcohols, glycerin, aldehydes and succinic acid and other important components that affect the sensory characteristics of wine make wine have a more complex taste and aromaThis paper summarizes the effects of low temperature on the type and content of wine aroma composition, the metabolic pathways of low temperature on aroma composition, the effect of key enzymes and their gene expression, and the non-wine yeast suitable for low temperature fermentation, which aims to provide a theoretical basis for better studying the fermentation mechanism at low temperature and improving the quality of wine1 Low temperature seisquil effects on wine aroma compositionvolatile compounds synthesized from wine yeast include premium alcohols (heterool, almonds and flowers), medium chain and long chain volatile acids (fat, cheese and sweat), acetate and ethyl esters (fruit and flower), aldehydes (aromas of creams, fruits and nuts), and more1.1 alcoholsadvanced alcohols can be synthesized by anabolic by the sugar metabolism intermediate, or by the multi-step metabolic reaction - the Ehrlich pathway, by the branch chain amino acidsPropylene alcohol and isobutanol at a very low concentration of 0 -5 degrees C, the highest detection of the mass concentration of 48 mg/L; Low temperatures often lead to lower concentrations of advanced alcohols, which are thought to have a positive impact on product quality1.2 esterslow-temperature fermented wines, yeast produces an increase in floral aromas (fatty acid ethyls) and fruit (acetate) and maintains a high level of variety aroma (ferns)This is due to increased stability of volatile compounds, reduced evaporation loss, and metabolic differences in yeast, i.echanges in fatty acid synthesis to alter the composition of cell membranesAcetate is made of advanced alcohol and acetyl coenzyme AThis reaction is catalyzed by acetylmetase encoded by the genes ATF1 and ATF2, and the Esterases encoded by IAH1 and TIP1 also have an important effect on the final concentration of acetate in wineEthyl esters, such as ethyl acetate, buterate, ethyl hexate, ethyl acetate, ethyl acetate and ethyl lactate, give the wine the ideal fruit and flower aromaThey are produced by the combination of ethanol and acetylase A, which are catalyzed by an acetyyl transferase, which is encoded by the genes EHT1, EEB1, and YMR210WThe final concentration of ethyl esters in the same wine is also closely related to esterases encoded by IAH1 and TIP1The largest difference between the15 degrees C and 28 degrees C is the yield of ethyl esters, which is very high at 15 degrees C, which is consistent with other studies of wine volatile compoundsThe concentrations of 4 volatile compounds with positive sensory effects were significantly higher at 28 degrees C than 15 degrees C, namely, acetate-2-methylbutyleste, 2-methyl butylet (the fruit of bananas and pineapples), 2-phenethanol and 2-phenyl ethanol acetate (flower scent) THE RESULTS OF THE EXPERIMENTS OF GAMERO ET AL HAVE SHOWN THAT THE YIELD OF ACETATE INCREASES AT 28 DEGREES C, EVEN IF THE CORRESPONDING ALCOHOL YIELD IS HIGH AT 12 DEGREES C, WHICH MAY INDICATE AN INCREASE IN THE ACTIVITY OF ACETYL TRANSFERASE (ATF) AT HIGHER TEMPERATURES In addition to ethyl acetate, fermentation at low temperatures is significantly more conducive to the production of ethyl esters 1.3 acids volatile fatty acids also contribute to the aroma of wine Fatty acids are important components of cell membranes and precursors of more complex molecules, such as phospholipids They are re-condensed by acetyl coenzyme A and catalyzed by fatty acid synthase complex levels of malic acid, ethanol, and some advanced alcohols (isobutanol and isoprene) increase with temperature The concentration of acetic acid is reduced at low temperatures The concentration of succinic acid is also high at 21 degrees Celsius When the main component analysis of organic acids was carried out, no significant grouping was observed; Temperature has a greater effect on naturally fermented wines, which may be due to the interaction between temperature and other factors, such as the natural presence of yeast populations on the grape skin Fermentation is suitable for 18 degrees C, as the content of advanced alcohols and organic acids is appropriate Regardless of the yeast used, a temperature slightly below 20 degrees C is the most suitable temperature for wine fermentation One strategy yeast cells to adapt to low-temperature conditions is to increase the percentage of medium-chain fatty acids (MCFA) If the increase in MCFA is the most significant change in the strain of low-temperature growth, then the presence of citric acid (C8) is the most important characteristic of cold-resistant yeast Saccharomyces kudriavzevii compared to S cerevisiae cytoplasmic membrane fatty acid analysis showed that dry yeast had similar levels of unsaturation, between 70% and 80%, no medium chain fatty acids (MCFA), and long-chain saturated fatty acids (SFA) were the most frequent membrane fatty acids in the entire fermentation Lipid composition varies with the temperature of growth The S.cerevisiae strain regulates optimal membrane fluidity at low temperatures through changes in fatty acid unsaturation However, no change in the percentage of unsaturated fatty acids (UFA) at different growth temperatures was observed, but the concentration of MCFA was higher at low temperatures 1.4 Other aroma components in general, the reduction of acetaldehyde and acetic acid is one of the main advantages of low temperature fermentation The content of acetaldehyde and acetic acid produced by pre-adaptation vaccination was lower than that of a fermentation initiation agent only in some "simple" or "non-aromatic" grape varieties, such as the sashimi grapes, in the process of alcohol fermentation synthesis of characteristic varieties of aromas, proved to be volatile thiol Three major volatile aromatic thiols - 4-pyridine-4-methyl isopyl butylketone (4MMP), 3-pyridine-1-hexanol (3MH) and 3-pyrithyl hexyl ester (3MHA) - were identified as the characteristics of the "yellow poplar", "grapefruit" and "thyscoopyfruit" that make up this wine These compounds are also found in wines made by Joan, Riesling, Pigeon Cage White, Little Manson, Cabernet Sauvignon and Merlot Grapes Two sulfur compounds (4MMP and 3MH) are present in grape juice in the non-volatile form of sulfur-cysteine conjugate Volatile thiol is released by yeast from the corresponding sulfur-cysteine conjugate during alcohol fermentation Recent studies using genetic screening techniques identified four genes of the experimental strain that affect the release of volatile thiol 4MMP However, the mechanism by which yeast cysteine-related precursors are converted into aromas is not clear the final concentration of 4MMP and 3MH in the wine is higher than 13 degrees C when the alcohol is fermented at 20 degrees C Prior to HOWELL et al in synthetic medium, the effects of fermentation temperature (18 and 28 degrees C) on the release of 4MMP of different yeast strains were studied, and found that high temperatures (28 degrees C) had a positive effect on the 4MMP levels of 2 yeasts These comparisons of fermentation temperatures of 28 degrees C and 18 degrees C are consistent with those of 20 degrees C and 13 degrees C in maSNEUF and other studies, the concentration of 3MHA was higher in high-temperature fermentation samples The level of 3MHA is also closely related to the number of 3MH Therefore, for 3MHA, the temperature does not appear to affect yeast metabolism, but indirectly affects the level of 3MHA through the concentration of 3MH 2 the effects of low temperatures on yeast metabolism and related gene expression EUGENIA, etc., analyzed proteomics associated with saccharomyces bayanus var.uvarum winemaking properties The protein classification of molecular functions shows that there are 24 different categories at 13 degrees C, 8 of which are unique to 13 degrees C, and 16 different categories are identified at 25 degrees C, but none of them are unique These unique groups of 13 degrees C are (1) antioxidant activity; (2) amino acid binding; (3) heteroenzyme activity; (4) heteroenzyme activity; (5) protein markers; (6) peptide binding; (7) ribbrion complex binding; (8) metal cluster binding; 10% of the total Of particular interest is the antioxidant active group, which removes free radicals from cells to reduce molecular damage As mentioned earlier, wine is a mixture of natural compounds such as flavonoids and polyphenols, which have important antioxidant activity Their data support the hypothesis that the enzyme system that produces these compounds is raised during low-temperature fermentation the classification of the genetic ontological body of biological processes found 70 categories: 27 are unique to 13 degrees C and 17 are unique to 25 degrees C The number of categories described is high, indicating changes in the activity of different proteins during wine fermentation By further examining the categories at 13 degrees C, there are many metabolic processes involving wine aromas, such as (1) cell aldehyde metabolism processes; Most unique categories constitute the main way to contribute to the accumulation of metabolites such as wine aromas, which are directly related to the quality of the wine the specific categories described are: (1) fermentation; (2) cell growth; (3) polysaccharide metabolism process, (4) energy reserve/metabolic process, and (5) ethanol metabolism process, all of which involve different steps in the fermentation process, from cell growth to ethanol synthesis cold-resistant yeast S.bayanus var.uvarum in 13 degrees C expression of the increased protein is acetone acid de-serotonin, glycerin-1-phosphate hydrolytic enzyme 2, acetaldehyde dehydrogenase (Ald6p, Ald3p), thiamine synthase (Thi13p), oxyoxymethyl transferase and methonenine synth metabolism, including aromatic compounds These enzyme activities promote the anabolic metabolism of glycerin, isofrol and 2-phenyl ethanol acetate, consistent with the unique sensory characteristics of S.bayanus var uvarum in wines fermented at 13 degrees C 2.1 sugar metabolism the main sugars in grape juice, glucose and fructose fermented into ethanol and CO2 to provide energy and carbon compounds for yeast growth The winemaking process is mainly the conversion of sugars from grape juice into ethanol The sugar metabolism of yeast is the main metabolic process that determines the final ethanol content and, to a large extent, determines the sensory characteristics of wine In the process of yeast ethanol fermentation, due to the simultaneous presence of fermentation and other metabolic activities, yeast in addition to fermenting 92% - 95% of the sugar in grape juice into ethanol, CO2 and heat, yeast can also use another 5%-8% of the sugar to produce a series of other compounds, namely ethanol fermentation by-products The most important by-products are glycerin and acetic acid, followed by esters-based aromas glycerin is one of the main metabolites produced in the fermentation process of wine, which brings sweet, soft and plump taste to the quality of wine and reduces the astringent taste of the wine Glycerin is involved in the osmotic regulation of yeast and the adaptation to low temperature growth The production of glycerin balances the ratio of NADH/NAD in the cell, and glycerin, like algal sugar, acts as an antifreeze The synthesis of S.cerevisiae glycerin is produced by catalyzing the reduction of dihydroxypropylene phosphate (DHAP) by 3-phosphate glysphosphatase (GPP gene coding) by NAD-dependent 3-phosphate glycediadase (GPD gene coding), and then by catalytic 3-phosphate dephosphate Experiments have shown that the synthesis of glycerin in low-temperature-induced cells is activated immediately, and that the yield is higher than that of 12 degrees C </p