1. Probiotic Potential of Lb. plantarum and Foods Fermented with It
belongs to the genus Lactobacillus
, which is widely considered to be a probiotic, and may have probiotic potential from species analysis. However, a prerequisite for probiotics to function in the host’s gastrointestinal tract is a good tolerance to unfavorable factors such as gastric acid, bile salts, and degrading enzymes, as well as the ability to complete colonization in the gastrointestinal tract 
. Therefore, Lb. plantarum
must have a high gastrointestinal survival rate to meet the basic requirements for development as a probiotic. Kriti Ghatani and Buddhiman Tamang 
isolated a strain of Lb. plantarum
from fermented yak milk products, and then added cholesterol and bile salts to MRS broth to determine the tolerance of the selected strain. Combined with acid resistance, bile salt hydrolase activity and cell surface hydrophobicity, they confirmed that this strain of Lb. plantarum
was tolerant to the corrosive and toxic effects of gastric acid and bile in humans, and can adhere to host cells to complete colonization. Wang, G.Q. and Chen, Y. et al. 
recorded the images of mouse intestines at different times after oral administration of Lb. plantarum
, confirming that Lb. plantarum AR17-1
can colonize and play a role in the intestinal tract, implying that Lb. plantarum
has probiotic potential.
As a carrier for Lb. plantarum
to enter the human body, Lb. plantarum
-fermented foods with high live counts have the potential to be developed into probiotic foods that can play a healthy role in the human body. However, the ability of these fermented foods to function as probiotic foods also depends on the gastrointestinal survival of the probiotic bacteria in the food. Different food matrices also have significant impacts on the gastrointestinal survival rate of Lb. plantarum
. The most widely used matrices are dairy products including yogurt, cheese, etc. The higher fat and whey protein content in dairy products result in their better buffering capacity against gastric acid, which can improve the gastrointestinal survival rate of probiotics 
. In addition, other fermented foods, such as fruit and vegetable juices, oats and cereals, and meat products are also commonly used as food matrices to create fermented foods that bring probiotics into the human gastrointestinal tract. The fat in meat products protects probiotics from low pH and bile salts 
, the higher sugar content in cereals allows probiotics to better tolerate intestinal conditions 
, and the relatively short digestion time of fruit and vegetable juices can greatly reduce the adverse effects of the gastric environment on probiotics 
. Current Lb. plantarum
-fermented foods that may have probiotic potential include dairy products, meat products, soy products, fruits and vegetables, and cereals, where the gastrointestinal survival of Lb. plantarum.
is high. However, studies on the effect of food matrices on the gastrointestinal survival rate of probiotics are still relatively few, and it is hoped that more research will focus on this in the future.
2. Recent Developments in Lb. plantarum-Fermented Food
As mentioned above, Lb. plantarum has the potential to be developed as a probiotic because of its excellent anti-cardiovascular properties, as well as its good tolerance in the gastrointestinal tract, which is important for human health. In addition, some studies have demonstrated that foods fermented with it have better health benefits than before fermentation, and may have the ability to be developed into probiotic functional foods. The applications of Lb. plantarum in different types of foods, and the corresponding effects of its fermented foods, are shown in Figure 1 and Table 1.
Figure 1. The application of Lactiplantibacillus plantarum in several different types of food. Lactiplantibacillus plantarum has been widely used as a fermenting strain in the production of a wide range of fermented foods. (Created with Biorender.com).
Table 1. The effects of Lb. plantarum fermented foods in the prevention of different diseases.
2.1. Fermented Food with Antioxidant Function
Fruits and vegetables are rich in phenolic substances, carotenoids, flavonoids, and vitamin C, which have good antioxidant effects. Therefore, scientists hope to develop functional beverages based on fruit and vegetable juices and improve their antioxidant capacity through fermentation. In earlier research, some fermented juices with antioxidant functions, such as apple, orange, jujube, and coconut juices have been produced and proven to have a better ability to scavenge free radicals. In recent years, there have also been many reports on the antioxidant functional juice fermented by Lb. plantarum
. Wu, Li, et al. 
compared the antioxidant activity of blueberry and blackberry juices before and after fermentation based on ABTS methods, and they found that the ABTS radical scavenging activity of blackberry and blueberry juices fermented with Lactobacillus plantarum increased by 53.3% and 64.0%, respectively, compared to the juice before fermentation. The same results were also reported in fermented vegetable juice. Zhang, Duan, et al. 
also found that the DPPH radical scavenging rate and ABTS free radical scavenging rate of carrot juice after 72 h of fermentation by Lb. plantarum WZ-01
were increased to some extent compared to their pre-fermentation state. These results suggest that fermentation by Lb. plantarum
can effectively enhance the free radical scavenging activity of juices, and fermented fruit and vegetable juices can be developed as a good antioxidant functional beverage.
In addition to fruit and vegetable juice, there are also reports on the application of Lb. plantarum
in the fermentation of other types of foods, including dairy products 
, soybean products 
, fermented sausages 
. All these types of fermented foods show better antioxidant capacity in vitro compared with prior to fermentation.
2.2. Fermented Food with Cholesterol-Lowering Function
The development of Lb. plantarum
-fermented foods with cholesterol-lowering effects have achieved some results, including dairy products, soybean products, fruits and vegetables, aquatic products. As early as 2015, Jeon, Lee, et al. 
isolated a strain of lactic acid bacteria from kimchi that could lower cholesterol in vitro, named Lb. plantarum EM
. Four years later, they utilized Lb. plantarum EM
as a fermenting strain in cabbage-apple juice to investigate the health-promoting effects of fermented juice on high-cholesterol diet rats. It was found that the serum levels of TG, TC, and LDL-C were greatly reduced, and HDL-C levels were increased in rats fed with fermented juice compared to unfermented juice. Many scientists have obtained similar results with different types of fermented foods. Cao, Wu, et al. 
pointed out that soy extract fermented by Lb. plantarum
could regulate lipid metabolism through signaling pathways and thus lower cholesterol. Li, Wu, et al. 
analyzed the microbial diversity of rat feces and found that skim milk fermented with Lb. plantarum WW
could regulate intestinal flora and lower cholesterol levels. Hu, Zheng, et al. 
found that Lb. plantarum FZU3013
-fermented Laminaria japonica could affect the expression of genes involved in lipid metabolism and bile acid homeostasis in rats.
2.3. Fermented Food with Blood Pressure Lowering Function
There are few reports on the hypotensive effects of Lb. plantarum
-fermented foods, and most of those reports focused on fermented foods that can inhibit ACE activity and are mainly fermented dairy products. In addition to dairy products, the same findings have been reported for other fermented foods, such as soy milk 
, fermented sausages 
, and fruits like guava 
. However, due to the lack of relevant studies, it cannot be ascertained whether fermented foods are effective in in vivo experiments.
2.4. Fermented Food with Hypoglycemic Function
Several studies have confirmed the hypoglycemic effect of Lb. plantarum
-fermented foods. Zhong, Abdullah, et al. 
used blueberry as a fermentation substrate. Blueberries are widely considered to have a good antidiabetic ability and the potential to treat early-stage diabetes. In their research, they found that, compared with the non-fermented blueberry juice, the fumarate contents in blueberry juice fermented by Lb. plantarum
were significantly increased, which could maintain glucose homeostasis. In addition, fermentation altered the concentrations of phenolic compounds in blueberry juice, which promoted glucose consumption. They employed HepG2 cell lines as a model to confirm that fermented juice significantly enhanced cellular glucose consumption 
. In addition to this, Lb. plantarum
fermentation also increases α-Amylase and α-glucosidase inhibitory activity, thus reducing carbohydrate hydrolysis for the effective control of diabetes 
2.5. Other Applications of Lb. plantarum
In conclusion, it can be seen that Lb. plantarum
-fermented foods show good effects in in vitro experiments, and have the potential to be developed into probiotic products. Moreover, in addition to conferring additional functional characteristics to the foods, Lb. plantarum
fermentation may improve the properties of traditional fermented foods. Compared with unfermented food, fermented food can produce bacteriocins with good antimicrobial properties and extended storage time 
; it may also have better stability 
, and its flavor will be improved to meet consumers’ demands 
. At present, there are various kinds of functional fermented foods reported covering the basic diet, such as dairy products, fruits, vegetables, meat products, soybeans, and cereals. These factors comprehensively show that developing Lb. plantarum
-fermented foods and supplementing these foods in daily life may be of great significance to human health.