Characterization of Rhamnosidases from Lactobacillus plantarum and Lactobacillus acidophilus

Lactobacilli are known to use plant materials as a food source. Many such materials are rich in rhamnose-containing polyphenols, and thus it can be anticipated that lactobacilli will contain rhamnosidases. Therefore, genome sequences of food-grade lactobacilli were screened for putative rhamnosidases. In the genome of Lactobacillus plantarum, two putative rhamnosidase genes (ram1(Lp) and ram2(Lp)) were identified, while in Lactobacillus acidophilus, one rhamnosidase gene was found (ramA(La)). Gene products from all three genes were produced after introduction into Escherichia coli and were then tested for their enzymatic properties. Ram1(Lp), Ram2(Lp), and RamA(La) were able to efficiently hydrolyze rutin and other rutinosides, while RamA(La) was, in addition, able to cleave naringin, a neohesperidoside. Subsequently, the potential application of Lactobacillus rhamnosidases in food processing was investigated using a single matrix, tomato pulp. Recombinant Ram1(Lp) and RamA(La) enzymes were shown to remove the rhamnose from rutinosides in this material, but efficient conversion required adjustment of the tomato pulp to pH 6. The potential of Ram1(Lp) for fermentation of plant flavonoids was further investigated by expression in the food-grade bacterium Lactococcus lactis. This system was used for fermentation of tomato pulp, with the aim of improving the bioavailability of flavonoids in processed tomato products. While import of flavonoids into L. lactis appeared to be a limiting factor, rhamnose removal was confirmed, indicating that rhamnosidase-producing bacteria may find commercial application, depending on the technological properties of the strains and enzymes.