Using Commercial Tannin-Degrading Bacteria, or Isolated from the Rumen of some Ruminants to Improve the Nutritional Value of Pomegranate Peel

 Pomegranate has many secondary metabolites such as tannins and phenolic compounds, which have various properties such as antimicrobial, antioxidant, anti-inflammatory, and immune system stimulating effects. The amount of tannin in pomegranate skin has been reported up to 20.6%. The limiting effects of tannins can be related to reducing the use of nutrients, especially protein, reducing growth and performance, reducing palatability and feed consumption, and reducing the activity of digestive enzymes. In addition to the anti-nutritional effects in high concentration, the positive impact of dense tannins in optimal concentration includes improving live weight gain, preventing flatulence, increasing milk production, reducing intestinal nematodes, and reducing the production of NH3-N and methane in the rumen. Therefore, the present experiment was carried out to improve the nutritional value of pomegranate peel as a tannin-containing edible material by treating it with some tannase-producing bacteria for ruminants.

 Pomegranate peel was treated with tannin-degrading bacteria including Klebsiella pneumoniae and Acinetobacter (isolated from deer rumen), Lactobacillus fermentum (isolated from Najdi goat rumen), and commercial Lactobacillus fermentum, and its nutritional value including chemical composition, digestibility, and fermentation ability alone (first experiment) or as a combination in a standard fattening lamb diet (second experiment), with two-stage digestion method and gas production test were studied. In the first experiment, five experimental treatments included 1- Pomegranate peel without treatment (control treatment), treatment 2 to 5- Pomegranate peel treated with each of the four tannin-degrading bacteria. The five treatments of the second experiment included 1- Diets containing pomegranate peel without treatment (control treatment), 2-5- Diets containing pomegranate peel treated with each of the four tannin-degrading bacteria.

Results and discussion:

 Applying tannin-degrading bacteria reduced the tannin in pomegranate peel (P<0.05), which is caused by the tannin-degrading bacteria. In an experiment of ensiling and adding polyethylene glycol and urea to pistachio hull for tannin removal, total tannin decreased. The concentration of total tannin with the potential and rate of gas production, truly decomposed organic matter, microbial biomass production, and microbial biomass production efficiency improved in pomegranate peel treated with tannin-degrading bacteria compared to the control (P<0.05). Perhaps the reason for the decrease in gas production potential in the control treatments compared to the treatments treated with bacteria is their higher amount of tannins, because tannins and phenolic substances by forming bonds and complexes with nutrients such as carbohydrates, proteins, reduce the availability of microorganisms. Ruminants to them and as a result reduce their decomposition. Similar to the results of the present experiment, other studies have also shown the positive effect of tannin removal on the improvement of gas production parameters. NH3 concentration and population of protozoa of pomegranate peel treated alone and in the diet increased compared to the control (P<0.05). The reason for the increase in NH3 concentration and protozoa population after degrading the tannins with bacteria can be the presence of tannins and polyphenolic compounds in this edible material. By binding to protein and reducing the rate of protein decomposition, tannins reduce the concentration of NH3, on the other hand, these structures lead to the rupture of the protozoa cell membrane, the inactivation of enzymes, and the reduction of the substrate needed for cell metabolism. The percentage of digestibility of dry matter, NDF, and ADF of pomegranate peel processed alone and in the diet with tannin-degrading bacteria increased compared to the control (P<0.05). Due to the reduction of the tannin level by the isolates, the activity of proteolytic enzymes has probably increased, and releasing nutrients from the binding of tannin, has improved the digestibility of the materials. An increase in cell wall digestibility has been reported as a result of treatment with tannin-degrading bacteria in laboratory conditions. Gas production potential and rate, separation coefficient, microbial viable mass production, and microbial viable mass production efficiency were improved in diets containing processed pomegranate peel compared to the control (P<0.05).

Conclusion:

 The use of tannin-degrading bacteria in the processing of pomegranate peel by reducing the tannins concentration led to an increase in the digestion and fermentation potential of pomegranate peel and diets containing pomegranate peel processed with tannins-degrading bacteria compared to the control. Therefore, considering the positive effects of processing pomegranate peel with tannins-degrading bacteria, it can be said that processing it by reducing tannins is a suitable solution to improve its nutritional value.