Investigating the usability of black locust (Robinia pseudoacacia L.) cultivars for feed purposes in Hungary

Abstract The increasing demand for protein in animal husbandry necessitates the identification of alternative feed sources to partially replace soybean meal. Black locust ( Robinia pseudoacacia L.), one of the most widespread tree species in Hungary, represents a promising candidate due to its high biomass production and potential nutritional value. The aim of this study was to evaluate the compositional characteristics and fermentation potential of leaves and pods from selected black locust varieties, in comparison with alfalfa as a reference feed. The chemical composition (dry matter, crude protein, fat, ash), total polyphenol content (Folin-method), polyphenol profile (HPLC), amino acid profile (HPLC), lipid profile (GC), antioxidant capacity (TEAC method), and the presence of antinutritional proteins were determined (PAGE). In addition, the lactic fermentation potential of the plant materials was assessed. Comparing the nutritional data of black locust to alfalfa (Blume et al. 2021), we found that the dry matter and protein content of the two feeds are similar (92%; 17%), while the fat content (2.8%—alfalfa; 4.27%—black locust) of black locust is higher and the ash content (14.6%—alfalfa; 6.1%—black locust) is lower. It should be emphasized that the total polyphenol content (30,000 mg GAE/kg—black locust; 6171 mg GAE/kg—alfalfa) and antioxidant capacity (225.71 mM Tr/kg—black locust; 9.6 mg mM Tr/kg—alfalfa) of black locust foliage are also significantly higher than that of alfalfa. Our experimental results showed that black locust leaves are lacto-fermentable, which may increase the digestibility and nutritional value of feeds. Antinutritional proteins such as Kunitz-type trypsin inhibitors or Bowman–Birk-type trypsin and chymotrypsin inhibitors could only be detected in the pod samples, not in the foliage, so they do not affect digestibility of foliage. These results indicate that black locust foliage and to a lesser extent the pods may serve as a valuable complementary protein source in animal feeding.