Process Biochemistry 40 (2005) 3714–3722 www.elsevier.com/locate/procbio
Hydrolysates from Atlantic cod (Gadus morhua L.) viscera as components of microbial growth media Stein Ivar Aspmo a,b,*, Svein Jarle Horn a, Vincent G.H. Eijsink a a
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 A˚s, Norway b Maritex AS, Havnegt. 17, N-8400 Sortland, Norway Received 28 February 2005; received in revised form 11 April 2005; accepted 4 May 2005
Abstract Three hydrolysates made from cod viscera by different enzymatic hydrolysis procedures were tested as a combined source for nitrogen, amino acids and vitamins in microbial growth media. Using a panel of five different microbes: Escherichia coli, Bacillus subtilis, Lactobacillus sakei, Saccharomyces cerevisiae and Aspergillus niger, the performance of these viscera hydrolysates was compared to the performance of common commercial peptones in an automated growth analyzer (Bioscreen C). The results show that the fish hydrolysates in general are promising alternatives to currently available commercial nitrogen sources of other origins. In the case of the food-grade and nutritionally fastidious L. sakei, two of the fish hydrolysates were clearly superior to all tested commercial peptones. For several microbes, the choice of the proteolytic enzymes used to produce the fish hydrolysate had considerable impact on performance of the resulting hydrolysate, both in terms of maximum growth rate and biomass production. In terms of hydrolysate performance, the generally best enzyme for production of a fish peptone from cod viscera was found to be Alcalase. # 2005 Elsevier Ltd. All rights reserved. Keywords: Fish hydrolysate; Viscera; Microbial growth; Growth media; Peptone
1. Introduction The biotechnological fermentation industry shows an increasing demand for microbial growth media. Usually, the most expensive component of microbial growth media is the nitrogen source, often termed peptone if made from non-heat coagulable water-soluble proteins/peptides [1]. Some microbes, such as lactic acid bacteria, are nutritionally fastidious and can only grow in media containing a varied selection of amino acids, vitamins and other growth factors [2]. Many microbes may in principle utilize cheap inorganic nitrogen sources, such as ammonium and even nitrate salts [3]. Even microbes capable of synthesizing all their primary metabolites de novo can be stimulated to grow faster and to higher cell densities in a rich complex medium due to the presence of more easily convertible nitrogen and favorable growth factors [4]. When defined media are formulated to * Corresponding author. Tel.: +47 64965908; fax: +47 64965901. E-mail address:
[email protected] (S.I. Aspmo). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.05.004
include all the necessary compounds for optimal growth, they frequently become quite expensive, limiting their use in commercial processes [5]. Peptones are primarily derived from products of bovine or porcine origin, such as meat, internal organs, gelatin, and milk, but also from plants and yeasts [6]. Because of recent outbreaks of bovine spongiform encephalopathy (BSE) [7] and a growing demand for raw materials that are kosher approved and certified free of swine flu, peptones of a nonmeat origin are becoming increasingly important. The use of fish materials as a source of nutrients for microbes was reported as early as 1949 [8]. Since then, several attempts to explore the use of fish peptones as a component of microbial growth substrates have been reported [1,9–15]. Fish peptones are usually produced either through hydrolysis with endogenous enzymes at a low pH favoring pepsin activity [16,17] by hydrolysis with exogenous enzymes [18– 20] or by a combination of these two methods. The acid hydrolysis is a lengthy process either performed with inorganic acids at very low pH (
