Use of chemical method for preparing of protein hydrolysate from Silver carp (Hypophthalmichthys moltirix) viscera and its application as culture media for Listeria monocytogenes

The aim of this study is to chemically hydrolyze of silver carp (Hypophthalmichthys moltirix) viscera and the effect of obtained peptones as a nitrogen source for culture of Listeria monocytogenes. Silver carp viscera were provided by a local market in Sari, Northern Iran. After freeze-thawing of Viscera at 4°C was used for hydrolysis. Acidic and alkaline hydrolysis was done at two pH 3.3 and 12, and two temperatures of 70 and 85°C. At the end of hydrolysis DH% (hydrolysis degree) and protein content were measured. Then obtained peptones from these 4 treatments (three replicates for each treatment) used as Listeria monocytogenes culture media at 48 hours and compared with BHI culture media. Results showed that maximum and minimum protein concentration were related to alkaline hydrolysis at 85 °C and acidic hydrolysis at 70 °C, respectively (p<0.05). The highest DH% was related to alkaline hydrolysis at 85 °C and the lowest of  it was related to alkaline hydrolysis at 70 °C (p<0.05). Growth of Listeria monocytogenes in acidic and alkaline produced treatments at            70 °C had no significant differences compared to control (BHI) except at 36 and 48h. But at 85 °C had differences at all hours significantly (p<0.05). This study showed that alkaline hydrolysis in higher temperature is better than acidic hydrolysis and growth of bacteria in fish peptone could be done as well as commercial cultured media. Due to usage of fish viscera and alkaline method with low processing cost, it‘s economically suitable.