Malolactic Conversion Research Articles

Changes in nutritional composition, volatile organic compounds and antioxidant activity of peach pulp fermented by lactobacillus

Fermentation with lactobacillus offers a natural means to modify nutritional and flavor properties of foods, and strains have crucial effects on it. In this study, peach pulp was fermented by five commercial probiotics (L. plantarum 21802, L. brevis 6239, L. pentosus 21798, L. alimentarius 21852 and L. pentosus 21832) to screen out a strain with higher adaptability ability and polyphenol bio-transformation capacity. Then, dynamics changes in microbial properties, nutritional composition, volatile organic compounds and DPPH radical-scavenging activity of peach pulp fermented by selected strain were studied and compared with the control sample. HPLC, LC-ESI-MS/MS and GC-MS were used for identification and quantification of phytochemistry. Results showed that the most efficient strain was L. plantaurm 21802 caused a significant (P < 0.05) increase in microbial population and total phenol content of peach pulp, which leads to an obvious decrease in fructose and glucose and a great increase in lactic acid content after 60 h fermentation. The malolactic conversion was completed within 12 h. Moreover, it caused an increase in β-carotene (14.82%), as well as chlorogenic acid (154.00%), vanillic acid (95.44%), epicatechin (27.99%), quercetin-3-O-glucoside (124.19%) and isorhamnetin (438.29%). Furthermore, lactobacillus fermentation resulting in the improvements of alcohols and aldehydes production, and the contents of four key aroma compounds (OVA>1), namely linalool, benzaldehyde, damascenone and eugenol, increased significantly (P < 0.05). These findings evidenced the potential use of L.plantarum 21802 in peach pulp fermentation for improving the nutritional and functional properties, and proved a possibility of peach fruit as a novel material for functional plant-based fermentation beverages.

Dynamics of changes in organic acids, sugars and phenolic compounds and antioxidant activity of sea buckthorn and sea buckthorn-apple juices during malolactic fermentation.

Sea buckthorn (Hippophaë rhamnoides L.) berries have high biological value as a rich source of phenolic compounds, fatty acids and vitamins A, C, E. Due to the high organic acid content and sour taste, the fruits are rarely used in juice production. Therefore, the study aimed to determine the metabolic activity of Lactobacillus plantarum, Lactobacillus plantarum subsp. argentoratensis and Oenococcus oeni strains along with the dynamics of changes in organic acids, sugars, phenolic compounds, and antioxidant activity during 72-h fermentation of 100% sea buckthorn and mixed with apple (1:1) juices. The strongest malolactic conversion was in mixed juices (to 75.0%). The most efficient strains were L. plantarum DSM 10492, 20174 and 6872. L. plantarum strains caused an increase in flavonols and antioxidant activity of sea buckthorn-apple juices. The results can be used to select conditions and strains in industrial-scale fermentation, to produce novel sea buckthorn products and increase their consumption.

Effects of lactic acid fermentation-based biotransformation on phenolic profiles, antioxidant capacity and flavor volatiles of apple juice

Apple juice (AJ) was fermented by six select lactic acid bacteria (LAB), namely Lactobacillus plantarum 90 (Lp90), Lactobacillus helveticus 76 (Lh76), Lactobacillus casei 37 (Lc37), Lactobacillus paracasei 01 (Lpc01), Lactobacillus acidophilus 85 (La85) and Bifidobacterium lactis 80 (Bla80). The effects of LAB fermentation on sugars and organic acids contents, phenolic profiles, antioxidant capacity and flavor volatiles of fermented AJ (FAJ) were investigated. Results showed that AJ was an excellent food matrix for LAB strains. Lh76 and Lp90 showed the highest viable counts of 12.7 log CFU/mL at the end of fermentation. Lp90, La85 and Bla80 exhibited strong malolactic conversion capacity and finally produced lactic acid more than 6.5 mg/mL. In addtion, LAB fermentation significantly (p < 0.05) decreased the total phenols and flavonoids levels. However, antioxidant activities based on DPPH and FRAP methods were enhanced during fermentation, especially for La85 which exhibited dramatical DPPH radical scavenging activity (90.05%) and FRAP (0.96 mmol Trolox/L). The improvement of antioxidant activities was suggested to be related to the increase in caffeic acid and phlorizin contents. The analysis of flavor volatiles showed that LAB fermentation resulted in formation of seven new alcohols and six new esters, and improvement of ketones and aldehydes production.

Evaluation of autochthonous Saccharomyces bayanus strains under stress conditions for making ice ciders

The product diversification policy being carried out by the Asturian cider industry includes the development of beverages similar to so-called ice ciders. During apple juice fermentations, yeast cells are affected by several stress conditions. In this study, 74 Saccharomyces bayanus strains isolated from Asturian cider, have been analyzed in synthetic media for their growth ability, sugar fermentation capacity and acetic acid production under the stress conditions that occurr during the production of ice cider. According to the data obtained 23 strains high proliferation capabilities, sugar fermentation capacity and low acetic acid production have been differentiated. Ten strains were chosen to produce ice ciders from apple juice (31.8 ºBrix) at 12 °C. The products obtained were characterized by not having developed the malolactic conversion and their low contents of acetic acid, methanol and ethyl acetate. Significant differences among ciders were detected for alcoholic degree, total acidity, and contents of glycerol, pyruvic, fumaric and shikimic acids due to the yeast strain used. A Multiple Correspondence Analysis showed four strains associated with sensory quality variables. Our results open up the possibility of using autochthonous S. bayanus strains as starters in the making of Asturian ice ciders.

Apple juice as a medium for fermentation by the probiotic Lactobacillus plantarum PCS 26 strain

Studies on the development of non-dairy probiotic foods and beverages are continuously emerging. Fruit and vegetable juices have proved to be promising carriers or growth media for probiotics. In this study, apple juice was explored as a growth medium for cultivation of the probiotic Lactobacillus plantarum PCS 26 strain. Fermentation was performed with free and Ca-alginate–embedded bacteria at different initial pH values, as well as with whey supplementation as a growth enhancer. During the fermentation, growth kinetics, pH, sugars consumption and lactic acid production were measured, along with culture survival during storage. The best results were achieved by fermentation at an initial pH of 4.2, reaching maximal cell density of 2.5 x 109 CFU/mL and a final pH of 4.7 after 24 h. Malolactic conversion was commenced by the strain as energy yielding mechanism, thereby lowering the consumption of sugars below the limit of determination by the analytical method used. Apple juice supplementation with 5 % v/v whey accelerated fermentation kinetics and resulted in a higher viable bacterial count. In contrast, entrapment of cells into Ca-alginate caused significantly slower growth, yielding a lower bacterial count at the end of fermentation (3.2 x 106 CFU/mL). However, stability during storage of the fermented product at 4–7 °C improved, and the survival of immobilized bacteria, estimated by Weibullian model, increased to 32.1 ± 5.2 days compared to 22.0 ± 0.68 days in the free-cell fermentation. In conclusion, apple juice was found to be an appropriate medium for fermentation by probiotic Lactobacillus plantarum PCS 26, resulting in a functional drink with potentially good sensory acceptance and shelf life.

Mutation and selection of Oenococcus oeni for controlling wine malolactic fermentation

Malolactic fermentation (MLF), mainly carried out by lactic acid bacterium, is of immense importance in winemaking allowing for improvement of microbiological stability and organoleptic characteristics of wine. However, it is difficult to address the problems of decoloration and loss of taste along with MLF induced by traditional starter culture. To further the aim at realizing a controlled and efficient MLF process, mutant of Oenococcus oeni strains after ultraviolet irradiation was selected to enhance quality of MLF. The treated strains with a lethality rate of 80–90 % were preliminarily screened, and then were secondly screened by evaluating their sensory and fermentation properties, by which O. oeni C10-1 were successfully screened. The malolactic conversion rate of O. oeni C10-1 is up to 38.81 %, which is remarkably increased when compared to original strains. Pivotally, wine fermented by O. oeni C10-1 demonstrated the highest color density of 9.240 and got the score of 5.95 in softness index, suggesting a remission of decoloration phenomenon and improved mouth feeling of wine. In all, these make it highly valuable for industrial application.

Characterisation of malolactic conversion by Oenococcus oeni to reduce the acidity of apple juice

SummaryThe high concentration of malic acid is responsible for the acidity and sourness in apple juice. Bio‐conversion of malic acid to lactic acid through malolactic conversion (MC) in apple juice using Oenococcus oeni was investigated. When apple juice was inoculated with O. oeni (1 × 106 CFU mL−1), over 90% of malic acid was converted into lactic acid within 96 h at room temperature. When pH of apple juice was adjusted to 4.1 prior to inoculation, MC was completed within 60 h. MC was enhanced at a higher temperature (30°C) when compared with room temperature. The rate of MC was directly proportional to the number of bacteria added and MC was completed within 24 h at 1 × 109 CFU mL−1 initial cell density. MC occurred equally under aerobic and anaerobic conditions. The sensory analysis of partial MC‐applied juice when compared against control revealed potential for use of MC for manufacture of low‐acid apple juice.

Ensilage and Bioconversion of Grape Pomace into Fuel Ethanol

Two types of grape pomace were ensiled with eight strains of lactic acid bacteria (LAB). Both fresh grape pomace (FrGP) and fermented grape pomace (FeGP) were preserved through alcoholic fermentation but not malolactic conversion. Water leaching prior to storage was used to reduce water-soluble carbohydrates and ethanol from FrGP and FeGP, respectively, to increase malolactic conversion. Leached FeGP had spoilage after 28 days of ensilage, whereas FrGP was preserved. Dilute acid pretreatment was examined for increasing the conversion of pomace to ethanol via Escherichia coli KO11 fermentation. Dilute acid pretreatment doubled the ethanol yield from FeGP, but it did not improve the ethanol yield from FrGP. The ethanol yields from raw pomace were nearly double the yields from the ensiled pomace. For this reason, the recovery of ethanol produced during winemaking from FeGP and ethanol produced during storage of FrGP is critical for the economical conversion of grape pomace to biofuel.

Genomic diversity of Oenococcus oeni from different winemaking regions of Portugal.

Oenococcus oeni is an alcohol-tolerant, acidophilic lactic acid bacterium that plays an important role in the elaboration of wine. It is often added as a starter culture to carry out malolactic conversion. Given the economic importance of this reaction, the taxonomic structure of this species has been studied in detail. In the present work, phenotypic and molecular approaches were used to identify 121 lactic acid bacteria strains isolated from the wines of three winemaking regions of Portugal. The strains were differentiated at the genomic level by M13-PCR fingerprinting. Twenty-seven genomic clusters represented by two or more isolates and 21 single-member clusters, based on an 85% similarity level, were recognized by hierarchic numerical analysis. M13-PCR fingerprinting patterns revealed a high level of intraspecific genomic diversity in O. oeni. Moreover, this diversity could be partitioned according to the geographical origin of the isolates. Thus, M13-PCR fingerprint analysis may be an appropriate methodology to study the O. oeni ecology of wine during malolactic fermentation as well as to trace new malolactic starter cultures and evaluate their dominance over the native microbiota.

Kinetics of sugars, organic acids and acetaldehyde during simultaneous yeast-bacterial fermentations of white wine at different pH values

Successfully inducing malolactic fermentation in the production of grape wines can be challenging, especially in wines with multiple inhibitors such as low pH values and high ethanol concentrations. In the present study, the kinetics of several chemicals of enological relevance was studied in Chardonnay vinified by traditional, consecutive alcoholic (AF) and malolactic fermentations (MLF), and simultaneous AF/MLF, where bacteria were co-inoculated with yeast. The Chardonnay must was adjusted to four pH values (3.2, 3.35, 3.5 or 3.65), and the concentrations of sugars, organic acids as well as acetaldehyde were followed throughout the fermentations. The degradation of glucose and fructose was slower at the lowest must pH value (3.2) but independent from the time point of bacterial inoculation. In all cases, malolactic conversion was faster after yeast-bacterial co-inoculation and was completed in simultaneous treatments at pH values of 3.35–3.65, and consecutive treatments at pH 3.5 and 3.65. No statistically significant difference was observed among the final acetic acid concentrations among all inoculation and pH treatments, but there was a trend towards higher acetic acid residues in wines produced by co-inoculation, especially at high pH values. Overall, simultaneous AF/MLF allowed for greatly reduced fermentation times, but the must pH remained a strong factor for fermentation success and determined the final concentration of various wine components. The time point of inoculation influenced formation and degradation kinetics of organic acids and acetaldehyde considerably, and these are of relevance for vinification decisions.

Degradation of free and sulfur-dioxide-bound acetaldehyde by malolactic lactic acid bacteria in white wine

Acetaldehyde is the major carbonyl compound formed during winemaking and has implications for sensory and colour qualities of wines as well as for the use of the wine preservative SO(2). The current work investigated the degradation of acetaldehyde and SO(2)-bound acetaldehyde by two commercial Oenococcus oeni starters in white wine. Wines were produced by alcoholic fermentation with commercial yeast and adjusted to pH 3.3 and 3.6. While acetaldehyde was degraded rapidly and concurrently with malic acid at both pH values, SO(2)-bound acetaldehyde caused sluggish bacterial growth. Strain differences were small. Efficient degradation of acetaldehyde can be achieved by commercial starters of O. oeni. According to the results, the degradation of acetaldehyde could not be separated from malolactic conversion by oenococci. While this may be desirable in white winemaking, it may be necessary to delay malolactic fermentation (MLF) in order to allow for colour development in red wines. SO(2)-bound acetaldehyde itself maybe responsible for the sluggish or stuck MLF, and thus bound SO(2) should be considered next to free SO(2) in order to evaluate malolactic fermentability. The current study provides new results regarding the metabolism of acetaldehyde and SO(2)-bound acetaldehyde during the MLF in white wine. The information is of significance to the wine industry and may contribute to reducing the concentration of wine preservative SO(2).

Evolution of malolactic bacteria and biogenic amines during spontaneous malolactic fermentations in a Greek winery

To study the population dynamics of indigenous malolactic bacteria in a Greek winery and to examine their potential to produce detrimental levels of biogenic amines (BA) under winemaking conditions. Although the wines studied were of different vintage, grape variety and enological characteristics, molecular typing of malolactic bacteria revealed only a low number of strains within the single-species populations of Oenococcus oeni that developed during spontaneous fermentations. Strain MF1, originating primarily from the vineyards surrounding the winery invariably predominated in almost all samples. HPLC analysis showed a slight increase in the BA, putrescine, tyramine and phenylethylamine after malolactic conversion, while histamine, methylamine and ethylamine remained unaffected. No correlation could be established between the BA profiles and the bacterial compositions or the amino acid concentrations in wine samples studied. A certain regional bacterial flora is established in the winery that prevails in spontaneous malolactic fermentations (MLF) irrespective of the wine characteristics. In all cases, the BA content of the wines after malolactic conversion was within enologically acceptable levels. This is the first report on the malolactic bacteria occurring naturally in spontaneous MLF in Greek red wines and a preliminary assessment of their impact on wine safety in relation to BA.

Fatty acid composition of cider obtained either by traditional or controlled fermentation

A pilot-scale model for controlled fermentation in cider-making is described. This technology is compared with the conventional induction of alcoholic fermentation and spontaneous malolactic conversion on the basis of the cider’s fatty acid profile. Controlled cider fermentations were carried out by means of sequential inoculation of Saccharomyces cerevisiae and Leuconostoc oenos. It was observed that there are significant differences in fatty acid composition depending on the fermentation process employed. The contents in fatty acids of ciders elaborated by a conventional process were higher than those of ciders obtained by controlled fermentation. The use of principal component analysis (PCA), linear discriminant analysis (LDA), soft independent modeling of class analogy (SIMCA) and partial least squares (PLS) in conjunction with the fatty acid composition allowed the authors to typify fermented apple products on the basis of the fermented technology. The most relevant variables for classification purposes were lauric and palmitic acids.

Glycerol metabolism in Lactobacillus collinoides: production of 3-hydroxypropionaldehyde, a precursor of acrolein

Lactobacillus collinoides is a lactic acid bacterium commonly found in fermenting apple juice. Although this bacterium is not particularly involved in malolactic conversion, the presence of L. collinoides in cider may have serious consequences on the product. L. collinoides is indeed considered to be responsible for the transformation of glycerol to 3-hydroxypropionaldehyde (3-HPA), a precursor of acrolein that spoils the product quality by generating bitter tastes. The purpose of our work was to evaluate the influence of environmental and culture conditions on the conversion of glycerol to 3-HPA in L. collinoides, and to obtain a DNA probe of the gene coding for glycerol dehydratase, the enzyme responsible for this conversion.

Microbial and chemical changes during the spontaneous ensilage of grape pomace

Pilot scale fermentations with grape pomace from two different wineries were investigated during the 24 weeks of the ensiling period, along with laboratory scale experiments in which the environmental temperatures were held constant at 20, 25, 30 and 35 °C. During this period, yeast and lactic acid bacteria (LAB) counts were made, after which the identity of both groups of organisms was studied, as were the major microbial metabolites present. Major microbial and chemical alterations occurred during the first 3 weeks of ensilage, leaving a more stable product differing significantly from the initial substrate. The results obtained indicated that after initial growth, yeast and LAB populations undergo progressive inactivation at environmental temperatures above 20 °C, although LAB seem to adjust better to this specific, post-fermentation environment. Homofermentative species of Lactobacillus were the dominant LAB. The initial yeast flora of non-Saccharomyces species was replaced by a typical wine yeast flora, i.e. predominantly Saccharomyces cerevisiae. At the chemical level, major alterations were due to an alcoholic fermentation and a malolactic conversion within the first 3 weeks.

INCIDENCE OF INDIGENOUS MICROBIAL FLORA FROM UTENSILS AND SURROUNDING AIR IN TRADITIONAL FRENCH CIDER MAKING

Lactic acid bacteria and yeasts were numerated, isolated and identified from two ciders obtained from similar raw materials used under different conditions. One cider was produced in a cellar of a traditional producer while the second one was produced under laboratory conditions. In both ciders alcoholic fermentation was achieved mainly by Saccharomyces cerevisiae. In the traditional cider, among the lactic acid bacteria (LAB) the species Leuconostoc oenos was predominant and malolactic conversion was observed. By contrast no development of LAB occurred in the second cider and therefore malolactic conversion was not achieved.

Use of Lysozyme to Inhibit Malolactic Fermentation and to Stabilize Wine After Malolactic Fermentation

Lysozyme was evaluated for its ability to reduce the lactic bacteria flora in musts and in wines after completion of the malolactic conversion. An addition of 500 mg lysozyme per liter of grape must inhibited malolactic fermentation, while the addition of 250 mg/L to red wines, after malolactic fermentation, promoted microbiological stabilization. Control lots (without lysozyme) had higher bacterial populations. In the wines to which lysozyme was added, there was no increase in the content of acetic acid and biogenic amines during a period of six months at 18°C. Control lots after fermentation and processing had volatile acidity levels 20% higher and a cumulative value for histamine, tyramine, and putrescine four times higher.

Cell-recycle membrane bioreactor for conducting continuous malolactic fermentation

A cell-recycle membrane bioreactor system has been evaluated for conducting rapid, continuous malolactic conversion in wine. A reactor (300 mL) containing 1010 cfu/mL of Leuconostoc oenos and operating at a flow rate of 6 mL/min for periods up to 56 h gave greater than 95% degradation of L-malic acid in a range of red and white wines. Stability of malic acid degrading activity and long term performance of the reactor varied with strain of Leuc. oenos, wine being processed and temperature. Increasing operating temperature from 20°C to 30°C caused rapid loss of activity. When grape juice was processed, reactor performance (>95% degradation of malic acid) was stable for at least 125 h. Addition of 10% ethanol to the juice caused a loss in reactor activity. Some off-flavours were acquired by the wine during processing in the reactors, but this problem was minimised by using reactors containing a mixture of cells of Leuc. oenos and Saccharomyces cerevisiae.

Influence of Cider-Making Technology on Cider Taste

Some major cider taste components (organic acids, sugars, alcohols and pectin substances) together with the microorganisms responsible for fermentations were determined in 12 ciders obtained by different technological methods in order to evaluate the quality of cider obtained. An analysis of variance revealed that the speed of pressing and the clarification system were the main factors influencing the efficiency of alcoholic fermentation, the speed of malolactic conversion and the microbiological stabilization of the cider.

A pre-spoilage marker for bacterial activity in fortified wine, conversion of L-malic acid to L-lactic acid

Sixty‐one different fortified wines, from the Douro valley, inoculated with Lactobacillus hilgardii previously isolated from a spoiled fortified wine, were sampled progressively for 280 d. Samples were analysed for volatile acidity (acetic acid) and frozen for subsequent analysis where appropriate. After 280 d, 7/61 wines showed increases in volatile acidity of >0.5 g l‐1 and were considered spoiled. Retrospective analysis of frozen samples of spoilage‐positive wines showed that all had apparently undergone a malolactic conversion before the onset of heterolactic activity (acetate production). It is suggested that the monitoring of L‐lactic acid might be a method of detecting activity of spoilage lactobacilli before the onset of spoilage.