The pace of civilizational advancement and the ensuing increase in lifestyle diseases turns the spotlight on the importance of proper nutrition, including a diet rich in vegetables. Onions are well known to many for their health-promoting qualities. However, their limited shelf life as well as their specific taste and aroma may deter people from eating them. Therefore, it seems reasonable to seek natural ways to increase the share of onions in our daily diets by expanding their shelf life and also improving their taste. It may also be tempting to try and modify the health-promoting properties of onion to make the vegetable even healthier.
The study will be based on the onion varieties commonly available on the European market, but also on new varieties which are at the marketing stage and hold great promise as regards their bioactive content, resistance to pathogens and yield.
Onion dehydration
One way of modifying the properties of emerging cultivars of onion is osmoconcentration. Another one is lactic acid fermentation. The former involves dehydration in aqueous concentrated solutions of polyols (alternatives to sucrose and fructose), saccharides, and sodium chloride (a hydrophilic compound). The research is expected to allow us better understand the mechanism at play in these processes, as well as what the effect of the combined process on the properties of the fermented new varieties of onion. As you will know, fermented foods are rich in beneficial bacteria.
Lactic fermentation
The literature provides limited data on the changes in the health-promoting components of onions resulting from fermentation and no data on the changes brought about by osmoconcentration.
Preservation of the content of polyphenols (antioxidant compounds) as well as identification of the metabolic factors responsible for the antioxidant properties of the metabolites are critical. Taking into account that different polyphenolic substances can have synergistic effects it is also important to determine the effect of individual compounds on health-promoting properties. That is why one of the research objectives is to establish the course of lactic fermentation and the properties of the post-fermentation media in model solutions.
Lactic fermentation will be carried out with isolated new lactic bacteria cultures and a bacterial strain with documented probiotic activity, L. brevis ŁOCK 0944.
Bioactivity
Another important aspect of the research is to investigate the biological activity of dehydrated and fermented onion extracts in comparison to pure bioactive substances; it is more cost-effective to work on extracts rather than pure fractions of substances with health-promoting properties. Important for us are the following bioactive functions of compounds: antioxidant activity (limiting, e.g. carcinogenesis), antagonistic effect on food-borne pathogens (reducing the risk of food poisoning), limiting biofilm formation by these pathogens and genotoxicity of extracts (reducing mutations at the level of genetic material).
Effect of osmoconcentration on lactic fermentation
This effect will be determined based on the growth of lactic bacteria, changes in bioactive compounds, and the profile of bacterial metabolites. Furthermore, analysis of the stability and variability of bioactive compounds in fermented onions in refrigerated storage is also to be conducted.
The lactic acid present in many foods (e.g., dairy products, fermented foodstuffs) has two optical isomers (forms): L-form and D-form. Preliminary studies have shown that osmoconcentration performed prior to lactic fermentation can have a favorable effect increasing the proportion of the L-form, which exhibits biological activity, and decreasing the proportion of the D-form which interferes with the metabolism of animal organisms.
The part of the research that will be conducted at the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences in Olsztyn, is aimed to verify in in-vivo studies on rats the hypothesis that the metabolic effect of bioactive compounds after lactic fermentation of onions strongly depends on the physiological functions of different diets that include bioactive compounds from onions after osmoconcentration and lactic fermentation.
The findings will enhance current knowledge in the field of nutrition and food sciencse, as well as improve our understanding of the effects of osmoconcentration and lactic fermentation on the quality of plant products and their impact on the metabolism of animal organisms.
Photo by Filip Podgórski