Effects of polyphenol oxidase on lipolysis and proteolysis of red clover silage with and without a silage inoculant (Lactobacillus plantarum L54)

Polyphenol oxidase (PPO) has been shown to reduce proteolysis and lipolysis in red clover through deactivation of proteolytic and lipolytic enzymes and/or through formation of protein–phenol–lipid complexes. This experiment investigated the time course of both lipolysis and proteolysis in two red clover lines with different PPO activities with and without addition of a silage inoculant to help understand the action of PPO in the silo, and its potential effects on protein and glycerol-based lipid conservation, and to determine effects of a more rapid pH reduction with inoculation on PPO activity. Four silages were prepared from high or low PPO precision chopped red clover in 60 test-tube-silos, each containing 120 g fresh weight: (a) high PPO red clover without inoculation (H−), (b) low PPO red clover without inoculation (L−), (c) high PPO red clover with inoculation (H+), and (d) low PPO red clover with inoculation (L+). Each treatment had three replicates for each time point of 1, 2, 4, 8 and 90 days. The inoculant used was Lactobacillus plantarum strain L54 applied at a rate of 10⁶ CFU/g fresh weight. Silage pH was reduced (P < 0.001) by inoculation with no effect of PPO. Inoculation had no effect on either lipolysis or free amino acid release, although more (P < 0.01) soluble protein and less (P < 0.01) ammonia-N was in inoculated silages. H silages had a lower level of both proteolysis (release of free amino acids, P < 0.05) and lipolysis (loss of membrane lipid, P < 0.01) than L red clover silages. Results indicate that PPO reduced proteolysis and lipolysis in the silo and that inoculation had no adverse effects on PPO activity.