Study on the changes in the content of functional compounds in fermented small lentils

Due to the high protein, vitamin, mineral, carbohydrate content and low fat content of lentils, they are increasingly attracting the attention of nutritionists. Additionally, a study indicates that lentil extracts can promote the growth of bifidobacteria, suggesting that lentils have great potential in developing fermented foods that protect the intestinal barrier and improve health.

Fermentation is an ancient technique traditionally used to enhance the shelf life, nutrition, and sensory quality of food. It can be divided into single-strain fermentation and multi-strain co-fermentation based on the type of strains used, and into solid-state fermentation (SSF) and liquid-state fermentation (LSF) based on the fermentation substrate. In the production process, due to the difficulties in operating solid-state fermentation on an industrial scale (controlling temperature, dissolved oxygen, pH, etc.), solid-state fermentation has been replaced by liquid-state fermentation. Solid-state fermentation also has advantages such as high productivity, good product stability, low production costs, and environmental friendliness, which largely indicates that it is an intensive application of biotechnology, beneficial for certain industrial productions with similar yields.

This study uses Lactobacillus plantarum TK9, Bacillus subtilis natto, and Lactococcus lactis TK1501 to evaluate the changes in the content of functional compounds in lentils under different fermentation modes, aiming to produce products with potential health benefits.

1. Total colony count of lentils after SSF/LSF under anaerobic/aerobic conditions.

Intestinal probiotics can promote health and longevity. In this study, we evaluated the final total colony count of lentils obtained during single or mixed fermentation processes.

The results indicate that anaerobic solid-state fermentation is more favorable for the co-cultivation of lactic acid bacteria and Bacillus subtilis natto, and an appropriate amount of Bacillus subtilis natto can increase the density of lactic acid bacteria. Therefore, we believe that Bacillus subtilis natto can consume oxygen to maintain an anaerobic environment, thereby increasing the number of lactic acid bacteria during the fermentation process. Lactic acid bacteria, in turn, can enrich beneficial intestinal flora. Thus, consuming foods fermented with both lactic acid bacteria and Bacillus subtilis natto may help maintain a stable intestinal microbiota and promote recovery of the gut after environmental disturbances.

2 Content of functional compounds in fermented lentils

The purpose of this study is to investigate the beneficial components produced during the fermentation of lentils to enhance the content of functional compounds in the fermented products. To determine the distribution of functional compounds, we measured the total phenols, free amino acids, and soybean isoflavones in the fermented foods.

2.1 Changes in total phenol content

Under aerobic conditions, solid-state fermentation with Bacillus subtilis natto and Lactococcus lactis TK1501, as well as liquid-state fermentation with Bacillus subtilis natto and Lactobacillus plantarum TK9 (Table 2). Under the same conditions, the total phenols of the mixed fermentation products were superior to those of the single probiotic fermentation products. The increase in total phenols may be related to the enzyme-induced non-enzymatic release of bound phenolic compounds, while the carbohydrates, glucosidases, and esterases produced by lactic acid bacteria, as well as the proteases produced by Bacillus subtilis natto, are related to the degradation of bound phenolic compounds. Therefore, co-fermentation can increase the total phenol content of lentils.

2.2 Changes in soybean isoflavone content

Most soybean isoflavones are glycosides, such as genistin, daidzin, and soy isoflavone. However, we only detected daidzin. Kohn et al. reported that the isoflavone profiles of unfermented green lentil samples from three different origins were different, indicating significant differences between the isoflavone components of lentils and those of soybeans. Similar to total phenols, daidzin significantly increased after fermentation. In mixed solid-state fermentation, anaerobic conditions were superior to aerobic conditions, while single probiotic solid-state fermentation was the opposite (Table 2).

2.3 Changes in free amino acid content

For free amino acids, there was an increasing trend in free amino acids under aerobic conditions in solid-state mixed fermentation (Table 2), with an increase of 294% compared to the pre-fermentation content. From Tables 1-2, it can be seen that Bacillus subtilis natto increased the free amino acids in the mixed culture. This is consistent with earlier reports that Bacillus subtilis natto produces proteases that hydrolyze proteins to increase ammonia nitrogen concentration. In single probiotic fermentation, the free amino acid content under anaerobic conditions was higher than that under aerobic conditions (Table 2). This result indicates that lactic acid bacteria can also degrade proteins into amino acids, but their proteolytic ability is lower compared to Bacillus subtilis natto.

3. Conclusion

Overall, the concentration of beneficial compounds obtained through solid-state fermentation is higher than that obtained through liquid-state fermentation. The quantity of beneficial substances produced by different fermentation processes in the experiment varies, but anaerobic solid-state fermentation yields better results. At the same time, the products obtained from co-fermentation have higher potential than those from single fermentation. The changes in total phenols, daidzin, and FAA in anaerobic solid-state co-fermentation are significant. Considering the processing costs before and after liquid-state fermentation, anaerobic solid-state fermentation may be more suitable for commercial production. Therefore, using lactic acid bacteria and Bacillus subtilis natto for anaerobic solid-state co-fermentation may be a useful method for producing fermented foods with higher functional compound content.

References: Co-fermentation of lentils using lactic acid bacteria and Bacillus subtilis natto increases functional and antioxidant components[J]. Journal of Food Science, 2020.

Note: This article is for informational purposes only and is not intended as medical guidance.