Immobilized α-amylase from Bacillus licheniformis: a potential enzymic time—temperature integrator for thermal processing

Biphasic and nth-order models were tested as to their usefulness to fit experimental inactivation data of Bacillus licheniformis α-amylase, immobilized on glass beads, and were discussed with respect to their suitability to characterize the considered enzymic system as a time—temperature integrator (TTI) to evaluate heat processes. Both isothermal and non-isothermal inactivation experiments were carried out. Model (kinetic) parameters (rate constant k, activation energy E_A and reaction order n) were estimated using a non-linear regression procedure. The results obtained, especially the activation energy of about 293 kJ mole^–1, indicated a potential use of this system as a TTI for heating processes in the temperature range of 96–108°C.     

BIOGENIC AMINES IN FINNISH DRY SAUSAGES

A study was conducted to determine the biogenic amine levels of Finnish dry sausages and to compare the results with those of other surveys of different types of fermented sausages. Sausages with high amine concentration were analyzed microbiologically in order to identify amine-producing microorganisms. Tyramine was the most common amine: the mean of 68 samples was 82 mg/kg and the mode 110 mg/kg. Other vasoactive amines found were histamine (<1–200 mg/kg), phenylethylamine (<1–48 mg/kg) and tryptamine (<10–91 mg/kg). Increased amounts of the spoilage indicator amines putrescine and cadaverine were found from most of the samples containing vasoactive amines. The formation of amines can be linked with problem(s) in hygienic conditions of raw materials and manufacturing practices and it is thus proposed that the sum of tyramine, histamine, putrescine and cadaverine could serve as an indicator of quality in fermented meat products.     

Formation of Biogenic Amines during Ripening of Dry Sausages as Affected by Starter Culture and Thawing Time of Raw Materials

Raw materials affect formation of biogenic amines in dry sausages. Effects of thawing time of raw materials and amine-negative starter culture on amine formation were studied on a pilot scale. The levels of biogenic amines, precursor amino acids, pH, water activity, and microbial counts were measured. Use of starter culture significantly decreased levels of histamine, tyramine and cadaverine formed. The effect of thawing time on formation of biogenic amines was dependent on the use of starter culture.     

Biogenic Amines in Dry Sausages as Affected by Starter Culture and Contaminant Amine-Positive Lactobacillus

The effect of an amine-negative starter culture, containing Pediococcus pentosaceus and Staphylococcus carnosus, on the growth and amine formation of an amine-positive contaminant lactic acid bacterium (G 106) was studied in dry sausages. Levels of biogenic amines, precursor amino acids, pH, water activity and microbial counts were measured. Levels of phenylethylamine and tyramine increased in the sausages inoculated with the amine-positive strain. The starter culture did not prevent growth of G 106 or its amine formation capability. However, levels of histamine remained low although G 106 could produce histamine in vitro.