Heui-Dong Park

Effects of protectant and rehydration conditions on the survival rate and malolactic fermentation efficiency of freeze-dried Lactobacillus plantarum JH287.

In this study, Lactobacillus plantarum JH287 was used as a malolactic fermentation starter in Campbell Early wine production. L. plantarum JH287 was first lyophilized, and the malolactic fermentation potential of freeze-dried L. plantarum JH287 was investigated. Different protective media and rehydration conditions were tested to improve the survival rate of freeze-dried L. plantarum JH287. Optimal protective medium contained 10xa0% sorbitol and 10xa0% skim milk. The optimal rehydration condition was a 1-h rehydration time conducted in the same protective media, and the combination of these two methods produced a survival rate of 86.37xa0%. In addition, a 77.71xa0% survival rate was achieved using freeze-dried samples that were stored at 4xa0°C for 2xa0months. Freeze-dried L. plantarum JH287 and Saccharomyces cerevisiae Fermivin were used to inoculate the Campbell Early grape must to decrease its malic acid content. Using this mixed-fermentation method, wine showed a decrease in malic acid content after 9xa0days of fermentation. GC-MS analysis detected 15 volatile ester compounds in the wine. A sensory evaluation showed that the taste and aroma of mix-fermented wine were better than those of the control that had not been inoculated with L. plantarum JH287.

Effect of air-blast drying and the presence of protectants on the viability of yeast entrapped in calcium alginate beads with an aim to improve the survival rate

Five yeast strains, Saccharomyces cerevisiae D8, M12, and S13; Hanseniaspora uvarum S6; and Issatchenkia orientalis KMBL5774, isolated from Korean grapes, were entrapped in Ca-alginate beads, which are non-toxic, simple to use, and economical. Ca-alginate beads containing yeast cells were soaked in protective solutions, such as skim milk, saccharides, polyols, and nitrogen compounds, before air-blast drying to improve the yeast survival rate and storage ability. The results showed that both entrapment in Ca-alginate beads and soaking in protective agents favorably affected the survival of all strains. The microenvironment formed by the beads and protective agents can protect the yeast cells from harsh environmental conditions, such as low water (below 10xa0%). All the yeast strains entrapped in Ca-alginate beads showed greater than 80xa0% survival and less than 11xa0% water content after air-blast drying at 37xa0°C for 5xa0h. In addition, air-blast dried cells of S. cerevisiae D8, M12, S13; H. uvarum S6; and I. orientalis KMBL5774 entrapped in 2xa0% Ca-alginate beads and soaked in protective agents (10xa0% skim milk containing 10xa0% sucrose, 10xa0% raffinose, 10xa0% trehalose, 10xa0% trehalose, and 10xa0% glucose, respectively) after air-blast drying at 37xa0°C for 5xa0h showed 90, 87, 92, 90, and 87xa0% viability, respectively. All dried entrapped yeast cells showed survival rates of at least 51xa0% after storage at 4xa0°C for 3xa0months.

Optimization of air-blast drying process for manufacturing Saccharomyces cerevisiae and non-Saccharomyces yeast as industrial wine starters

Wine yeast (Saccharomyces cerevisiae D8) and non-Saccharomyces wine yeasts (Hanseniaspora uvarum S6 and Issatchenkia orientalis KMBL5774) were studied using air-blast drying instead of the conventional drying methods (such as freeze and spray drying). Skim milk—a widely used protective agent—was used and in all strains, the highest viabilities following air-blast drying were obtained using 10% skim milk. Four excipients (wheat flour, nuruk, artichoke powder, and lactomil) were evaluated as protective agents for yeast strains during air-blast drying. Our results showed that 7xa0g lactomil was the best excipient in terms of drying time, powder form, and the survival rate of the yeast in the final product. Finally, 7 types of sugars were investigated to improve the survival rate of air-blast dried yeast cells: 10% trehalose, 10% sucrose, and 10% glucose had the highest survival rate of 97.54, 92.59, and 79.49% for S. cerevisiae D8, H. uvarum S6, and I. orientalis KMBL5774, respectively. After 3xa0months of storage, S. cerevisiae D8 and H. uvarum S6 demonstrated good survival rates (making them suitable for use as starters), whereas the survival rate of I. orientalis KMBL5774 decreased considerably compared to the other strains. Air-blast dried S. cerevisiae D8 and H. uvarum S6 showed metabolic activities similar to those of non-dried yeast cells, regardless of the storage period. Air-blast dried I. orientalis KMBL5774 showed a noticeable decrease in its ability to decompose malic acid after 3xa0months of storage at 4xa0°C.

Overexpressed acetohydroxyacid reductoisomerase ( ILV5 ) gene in Saccharomyces cerevisiae reduces diacetyl contents in Korean Campbell Early and Muscat Bailey a grape wines

An ILV5 (acetohydroxyacid reductoisomerase) gene expression vector (designated pILV5) was constructed by cloning the yeast ILV5 gene into a yeast expression vector (pLG669Z) containing yeast CYC1 promoter. S. cerevisiae cells harboring the pILV5 plasmid showed ∼3.7-fold higher level of the diacetyl reductase activity compared with the control yeast cells. When they were applied to wine fermentation using Campbell Early and Muscat Baily A grapes, the diacetyl content level was reduced to ∼35.0–39.0% of those obtained with the control yeasts.

FERMENTATION CHARACTERISTICS OF CAMPBELL EARLY GRAPE WINE INOCULATED WITH INDIGENOUS KOREAN WINE YEASTS ENCAPSULATED IN CA-ALGINATE BEADS AFTER AIR-BLAST DRYING

The aim of this study was to test the possibility of using yeast cells encapsulated in calcium alginate (Ca-alginate) beads as a starter for wine fermentation. Characteristics of Korean Campbell Early wines fermented by five free yeast cell types and those encapsulated in 2% Ca-alginate beads were compared using physicochemical analyses and sensory evaluation tests. The encapsulated yeast cells were shown to ferment Korean Campbell Early grapes with a similar efficiency as that exhibited by the five free yeast celltypes. After fermentation, the characteristics of free cells and encapsulated cells did not show significant differences in terms of content of reducing sugars, soluble solids, total acids, organic acids, and free sugars, as well as in terms of viable cell numbers and other physicochemical properties. The encapsulated cells did, however, produce more alcohol than the free cells. Encapsulation in 2% Ca-alginate beads was furthermore found to decrease the production of negative volatile compounds. The sensory evaluation of wines fermented by free cells compared with those fermented by Ca-alginate bead-encapsulated cells yielded similar scores for the following properties: color, taste, flavor, and overall preference. Overall, no significant differences were observed between the two grape wines, and yeast cells encapsulated in 2% Ca-alginate beads therefore showed high stability and served as an effective yeast starter for wine fermentation.

Occurrence of Issatchenkia orientalis Exhibiting Inhibitory Effects against Soybean Lipoxygenase in Korean nuruk

Three yeast strains (designated SHA, SHC, and SHD) exhibiting strong inhibitory effects against soybean lipoxygenase were isolated from Korean nuruk and identified as Issatchenkia orientalis. Total 80 yeast isolates from two major Korean nuruk samples were analyzed by polymerase chain reaction-restriction fragment length polymorphism and phylogenetic analysis. The most abundant yeast was identified as Pichia anomala, comprising 47 out of 80 strains, followed by 15 strains of I. orientalis. All 15 I. orientalis strains showed significant inhibitory effects against soybean lipoxygenase, higher than that of Saccahromyces boulardii used as a positive control.