Production of cysteine and methionine by selected proteolytic bacteria from chicken slurry

Abstract

The continuous growth of poultry industry in Malaysia has resulted in a significant increase o f waste by products generation that could be potentially used as renewable resource for the production of value added products. However, these wastes were not efficiently utilized due to the lack o f innovation and scientific research. Thus, this research focused on utilizing the indigenous proteolytic bacteria isolated from chicken viscera slurry to produce cysteine and methionine as supplements in cat food production. Twenty-nine pure bacteria strains were isolated where only three potential proteolytic strains coded as H1, L4 and L6 were selected for further investigation based on their halo zone formation and protease activities. Seven different microbial co-cultures (H1, L4, L6, H1L4, H1L6, L4L6 and H1L4L6) were tested at three different temperatures (37 °C, 45 °C and 56 °C). The initial pH and total fermentation time remained constant in order to optimize protein production. The highest protein concentration was observed in product incorporated with co-culture H1L6 (12.025 mg/mL). Amino acid analysis was carried out to determine whether those with the highest protein concentration also produced the highest amount of cysteine and methionine which served as the essential precursors of the chicken flavour. Product from co-cultures H1L6 produced significant amount of methionine at 56 °C which is 29.130 mg/mL whereby the highest production of cysteine (1.760 mg/mL) is seen in the product incorporated with L6 alone at 56 °C as well. In conclusion, the best incorporated co-cultures to yield the highest amount of cysteine and methionine are culture L6 and co-cultures H1L6 respectively and the optimum temperature is at 56 °C. The end products containing both cysteine and methionine can later be added in pet food particularly for cats to further test their palatability. With thorough optimization, this research will highly be beneficial to the rapidly-growing pet food industry in Malaysia.