Effects of dry-salting and brine-pickling processes on the physicochemical properties, nonvolatile flavour profiles and bacterial community during the fermentation of Chinese salted radishes

The correlation between flavor formation and microbial community dynamics during the fermentation of zha cai

BACKGROUND

Zha cai, a pickled vegetable with unique flavors, is produced by fermenting fresh mustard tubers. In this study, the main physicochemical indices and volatile flavor compounds were determined in three fermentation periods. The bacterial and fungal communities in the three fermentation periods of zha cai were also monitored using high-throughput sequencing. Key microbial communities were identified based on significant correlations with flavor substances.

RESULTS

Firmicutes and Proteobacteria were the main bacterial phyla found within the three fermentation periods. Lactic acid bacteria, namely Lactobacillus, was the predominant bacteria found at the genus level. Ascomycetes and Stenotrophomonas were the major fungal phyla found in the three fermentation periods. Yeast, namely Debaryomyces, was the predominant fungus found at the genus level. A total of 42 bacterial genera were negatively correlated with volatile flavor substances of zha cai, and 37 bacterial genera were positively correlated. Meanwhile, a total of 47 genera of fungi were negatively correlated with the volatile flavor substances of zha cai, while 50 genera were positively correlated. Several microbial genera were significantly correlated with volatile flavor compounds, including Lactobacillus, Halomonas, Rhodococcus, and Debaryomyces.

CONCLUSION

This study identified the microbial classes that positively regulate the flavor of zha cai which could provide valuable help for flavor modulation in zha cai production. © 2024 Society of Chemical Industry.

A cooperative combination of non-targeted metabolomics and electronic tongue evaluation reveals the dynamic changes in metabolites and sensory quality of radish during pickling

Pickled radish is a traditional fermented food with a unique flavor after long-term preservation. This study analyzed the organoleptic and chemical characteristics of pickled radish from different years to investigate quality changes during pickling. The results showed that the sourness, saltiness, and aftertaste-bitterness increased after pickling, and bitterness and astringency decreased. The levels of free amino acids, soluble sugars, total phenols, and total flavonoids initially decreased during pickling but increased with prolonged pickling. The diversity of organic acids also increased over time. Through non-targeted metabolomics analysis, 349 differential metabolites causing metabolic changes were identified to affect the quality formation of pickled radish mainly through amino acid metabolism, phenylpropane biosynthesis and lipid metabolism. Correlation analysis showed that L*, soluble sugars, lactic acid, and acetic acid were strongly associated with taste quality. These findings provide a theoretical basis for standardizing and scaling up traditional pickled radish production.

Effects of different pickling methods on physicochemical properties and flavor profiles of Tongling white ginger: Dry-salting, brine-pickling, and inoculation-pickling

Tongling white ginger is a Chinese fermented vegetable with unique flavors. However, little is known about its physicochemical properties, flavor characteristics, and sensory evaluation. The study examined the physicochemical (pH, titratable acidity [TA], nitrite, soluble protein, and color) and flavor characteristics (organic acids, free amino acids, and volatiles) of white ginger during fermentation. The results showed that the pH value and soluble protein in the dry-salted, brine-pickled, and inoculation-pickled decreased significantly while the TA value increased significantly, inoculation-pickled can effectively reduce the content of nitrite. After fermentation, inoculation-pickled produced the highest content of organic acids, while dry-salted produced the highest total amount of free amino acids. A total of 70, 68, 70, and 69 volatile compounds were identified in fresh, dry-salted, brine-pickled, and inoculation-pickled white ginger. The total contents of terpenoids of Tongling white ginger by three fermentation methods decreased; the total contents of alcohols and aldehydes were the highest in brine-pickled, and esters and ketones were more abundant in inoculation-pickled. The results showed that inoculation-pickled could shorten the fermentation time of Tongling white ginger, produce a unique flavor, and have the highest sensory score.

Fermented Vegetables: Health Benefits, Defects, and Current Technological Solutions

This review summarizes current studies on fermented vegetables, analyzing the changes in nutritional components during pickling, the health benefits of fermented vegetables, and their safety concerns. Additionally, the review provides an overview of the applications of emergent non-thermal technologies for addressing these safety concerns during the production and processing of fermented vegetables. It was found that vitamin C would commonly be lost, the soluble protein would degrade into free amino acids, new nutrient compositions would be produced, and the flavor correlated with the chemical changes. These changes would be influenced by the variety/location of raw materials, the original bacterial population, starter cultures, fermentation conditions, seasoning additions, and post-fermentation processing. Consuming fermented vegetables benefits human health, including antibacterial effects, regulating intestinal bacterial populations, and promoting health (anti-cancer effects, anti-diabetes effects, and immune regulation). However, fermented vegetables have chemical and biological safety concerns, such as biogenic amines and the formation of nitrites, as well as the existence of pathogenic microorganisms. To reduce hazardous components and control the quality of fermented vegetables, unique starter cultures, high pressure, ultrasound, cold plasma, photodynamic, and other technologies can be used to solve these problems.

Potential role of cell wall pectin polysaccharides, water state, and cellular structure on twice "increase-decrease" texture changes during kohlrabi pickling process

Pickled kohlrabi is a traditional and favored vegetable product in China. During pickling, the hardness, springiness, and chewiness of kohlrabi all experienced a typical change with twice "increase-decrease" trend. However, little is known about its mechanism. In this study, in situ analysis including immunofluorescence, low field nuclear magnetic, and transmission electron microscopy were used to explore the effects of cell wall pectin, water state, and cellular structure on kohlrabi texture changes during pickling. Results revealed that at the early stage, due to the rapid loss of water after three times salting, the cells shrank and the interstitial space reduced, resulting in the first increase on kohlrabi texture. Subsequently, the dehydration-rehydration caused by the first brine processing resulted in the first decrease on kohlrabi texture. Then under the action of PME enzyme, more low-esterified pectin was produced, and chelate-soluble pectin with more branched structure was further formed, leading to another elevation of the sample texture. As the pickling continued, under the combined action of PG and PME, the molecular weight of pectin was decreased and the rigidity of the cell tissue was destroyed, caused kohlrabi texture continued to decline. These researches could provide important information and guidance for better maintaining the texture of pickled vegetables during processing.

Improvement of physicochemical characteristics, flavor profiles and functional properties in Chinese radishes via spontaneous fermentation after drying

Spontaneously dried-fermented radishes have been consumed in China for hundreds of years and are usually fermented for a long time to acquire high quality. In this study, the spontaneously dried-fermented radishes with short-term manufacturing periods were made from five different varieties of radishes that grew in the same environment. In addition, the physicochemical characteristics (i.e., moisture content, soluble solid, and pH value), flavor profiles (i.e., free amino acids, organic acids, and volatile compounds), and functional properties (i.e., total phenolics content, total flavonoids content, sulforaphane content, and γ-aminobutyric acid [GABA] content) of these five raw radishes and spontaneously dried-fermented radishes were analyzed and compared. In detail, the content of volatile and nonvolatile compounds increased, especially in oxalic acid, succinic acid, and umami free amino acids. Furthermore, functional components, such as sulforaphane and GABA, were also enriched via spontaneous fermentation after drying. In addition, the results of principal component analysis, hierarchical clustering analysis, and redundancy analysis showed that there were significant discrepancies appeared when raw radishes were processed via spontaneous fermentation or not. These results suggested that the process of spontaneous fermentation after drying may contribute to improving the quality of fresh radishes. Notably, radishes with red skin and flesh were regarded as exceptional varieties for processing, because of the preferable flavor profiles and affluent functional substances via spontaneous fermentation after drying. Therefore, these findings could deliver a systematical insight into developing processed radishes with high quality. PRACTICAL APPLICATION: The spontaneously dried-fermented radishes were manufactured through the process of spontaneous fermentation after drying, which acquired tasty and healthy characteristics by accumulating the volatile and nonvolatile compounds as well as the functional components, like total phenolics, total flavonoids, sulforaphane, and γ-aminobutyric acid. Importantly, because of the excellent processing properties, the radishes with red skin and flesh could be more appropriate to produce spontaneously dried-fermented radishes. Our findings may provide a practical strategy for developing vegetable relishes with superb flavor profiles and good functional properties in pickled vegetables.

The Impact of the Fermentation Method on the Pigment Content in Pickled Beetroot and Red Bell Pepper Juices and Freeze-Dried Powders

The beetroot and red bell pepper are vegetables rich in active ingredients, and their potential for health benefits are crucial. Both presented raw materials are rich in natural pigments, but are unstable and seasonal; thus, it was decided to take steps to extend their durability. Lactic fermentation has been recognized as a food preservation method, requiring minimal resources. The activities undertaken were also aimed at creating a new product with a coloring and probiotic potential. For this reason, the study aimed to evaluate the impact of the method of fermentation on the content of active compounds (pigments) in pickled juices and freeze-dried powders. The lactic acid fermentation guided in two ways. The second step of the research was to obtain powders in the freeze-drying process. For fermentation, Levilactobacillus brevis and Limosilactobacillus fermentum were used. In juices and powders, pigments, color, and dry matter were tested. In this research, no differences in fermented juice pigment contents were seen; however, the color coefficient differed in raw juices. The freeze-drying process resulted in lowering the pigment content, and increasing dry matter and good storage conditions (glass transition temperatures 48–66 °C). The selection of vegetable methods suggested the use of fermentation and mixing it with a marinade (higher pigments and lactic acid bacteria content). All powders were stable and can be used as a colorant source, whereas for probiotic properties, a higher number of bacteria is needed.