Louise Heller Stahnke

Aroma components from dried sausages fermented with Staphylococcus xylosus.

Sausages with and without Staphylococcus xylosus were manufactured with four replicates. Antibiotics and a fungicide to inhibit growth of naturally occuring microorganisms were added to the control sausages. The volatile compounds from the sausages were collected and identified by gas chromatography/mass spectrometry, the effluent evaluated by sniffing and the sausages assessed by a trained panel. The study showed that sausages fermented with Staphylococcus xylosus contained several fragrant esters that were not found in control sausages without microbial growth. Control sausages had an unpleasant, rancid odour compared to sausages with Staphylococcus xylosus, indicating that the esterase activity of Staphylococcus xylosus or other microorganisms is very important in order to obtain the proper fermented sausage aroma. Although sausages with Staphylococcus xylosus contained the highest amounts of free fatty acids, it seemed to be of no importance to the aroma development. It is therefore questionable whether lipolytic activity of starter cultures has any influence on sausage flavour.

Generation of flavour compounds in fermented sausages-the influence of curing ingredients, Staphylococcus starter culture and ripening time.

The volatile profiles of fermented sausages made with either Staphylococcus xylosus or Staphylococcus carnosus starter cultures were studied with regard to the influence of salt concentration, ripening time and three different combinations of curing ingredients-nitrate, nitrite or nitrite/ascorbate. Emphasis was laid on volatile compounds originating from degradation of branched-chain amino acids. Volatile compounds were collected using dynamic headspace sampling and were identified by gas chromatography/mass spectrometry (GC/MS). Development in water activity, water loss and pH was monitored throughout maturation. Curing salts had a pronounced effect on the level of volatile compounds. In particular, curing with nitrate instead of nitrite resulted in a striking difference. Generally, nitrate increased the level of volatile compounds compared to nitrite, whereas ascorbate had only a small influence. The concentration level of NaCl had a considerable effect on the amount of volatile compounds but the effect was highly related to the ripening stage. Most compounds, but not all, increased in concentration as ripening proceeded. Major differences in the development of volatile compounds were observed depending on whether S. xylosus or S. carnosus were used as starter culture. In particular the effects of nitrate was much more predominant in the sausages made with S. carnosus than S.xylosus.

Growth and aroma production by Staphylococcus xylosus, S. carnosus and S. equorum--a comparative study in model systems.

A laboratory medium inoculated with 20 different Staphylococcus strains was prepared in accordance with a full factorial experimental design investigating the effect of temperature, pH, NaCl and glucose on growth. The 12 strains most suited to growth in a fermented meat environment were inoculated in sausage minces together with Pediococcus pentosaceus, incubated at 25 degrees C for 1 week and the produced aroma compounds collected. The data were analysed by multiple linear regression and partial least squares regression analysis. The results showed that increasing pH and temperature from 4.6 to 6.0 and 10 to 26 degrees C, respectively, increased growth of all strains with strong synergy between temperature and pH. Increasing salt concentration from 5% to 15% w/v decreased growth of most strains, but the effect of pH and temperature was much stronger than the effect of salt. Strains of S. carnosus were more salt tolerant than strains of S. equorum and S. xylosus, especially at high pH and temperature. Addition of glucose up to 0.5% w/v had no significant influence on growth of any of the strains. With regard to aroma production, species characteristics were detected. S. carnosus and S. xylosus were quite different regarding the overall aroma profiles, whereas the profiles of S. equorum lied somewhere in-between. Contrary to S. carnosus, S. xylosus and S. equorum did not produce 2-methyl-1-butanol. On the other hand, in particular, S. xylosus produced more 3-methyl-1-butanol. Except for one of the strains of S. equorum, S. xylosus and S. equorum formed more diacetyl, 2-butanone and acetoin and also more of the methyl-branched ketones arising from degradation of leucine, isoleucine and valine. S. carnosus produced more methyl-branched aldehydes, acids and corresponding esters from leucine, isoleucine and valine compounds that have been correlated with fermented sausage maturity in former studies. S. equorum produced the least of the methyl-branched aldehydes.

Mould starter cultures for dry sausages—selection, application and effects

The use of moulds on sausage surfaces can lead to both desirable and undesirable effects. The pursued effects are mainly related to successful production or consumer appeal. The undesirable effects are usually connected to growth of undesirable moulds. Most importantly, moulds may produce highly toxic secondary metabolites and β-lactams. Inoculations of sausages with moulds were traditionally done with the indigenous flora of the processing plants, the so-called houseflora, which was mainly composed of penicillia and aspergilli. The gradual shift in sausage production from small local producers to large-scale factories and increasing awareness of the risks for consumer safety has paved the way for industrialised procution of mould starter cultures. The industrialized starter cultures are carefully selected among hundreds of candidates going through multi-stage concepts including several analytical and biochemical investigations. While the technological aspects of mould inoculations are fairly resolved, its influence on prodution of secondary metabolites is yet emerging. Moulds produce enzymes for the degredation of lipid- and protein-matter, but studies show that the proteolytic and lipolytic capabilities differs significantly both between strains and is highly dependent on media, pH and temperature. Only few studies have addressed the aroma impact of mould growth on sausages, but information from related areas like milk based systems or sausage models still gives a quite clear picture of which components are important and their possible routes of information. One example is that methyl ketones play significant roles in the flavour of Blue cheeses. Here the presence and production of methyl ketones is ascribed to the β-oxidation activities of moulds and therefore investigations in sausages flavour have successfully focused on confirming this relationship and its aroma influence. Sausage producers are interested in using the established knowledge on aroma formation in sausages for improving aroma and texture but also for shortening ripening periods or even expanding shelf life. Addition of concentrates of enzymes have yielded some positive results but it is clear that the use of enzymes as additives in sausages production is not straightforward. To ensure optimal consumer safety starter cultures should be applied to achieve maximal controll over the mould population. Starter strains should under no circumstances show pathogenic or toxigenic signs in neither chemical or biological test. Additionally they should not be able to produce antibiotics.

Colour formation in fermented sausages by meat-associated staphylococci with different nitrite- and nitrate-reductase activities.

Three Staphylococcus strains, S. carnosus, S. simulans and S. saprophyticus, selected due to their varying nitrite and/or nitrate-reductase activities, were used to initiate colour formation during sausage fermentation. During fermentation of sausages with either nitrite or nitrate added, colour was followed by L(∗)a(∗)b measurements and the content of nitrosylmyoglobin (MbFe(II)NO) quantified by electron spin resonance (ESR). MbFe(II)NO was rapidly formed in sausages with added nitrite independent of the presence of nitrite reducing bacteria, whereas the rate of MbFe(II)NO formation in sausages with added nitrate depended on the specific Staphylococcus strain. Strains with high nitrate-reductase activity showed a significantly faster rate of pigment formation, but other factors were of influence as well. Product stability for the sliced, packaged sausage was evaluated as surface colour and oxidation by autofluorescence and hexanal content, respectively. No significant direct effect of the Staphylococcus addition was observed, however, there was a clear correspondence between high initial amount of MbFe(II)NO in the different sausages and the colour stability during storage. Autofluorescence data correlated well with hexanal content, and may be used as predictive tools. Overall, nitrite- and nitrate-reductase activities of Staphylococcus strains in nitrite-cured sausages were of limited importance regarding colour development, while in nitrate-cured sausages strains with higher nitrate reductase activity were crucial for ensuring optimal colour formation during initial fermentation stages.

Dried sausages fermented with Staphylococcus xylosus at different temperatures and with different ingredient levels — Part I. Chemical and bacteriological data

Sausages with added Staphylococcus xylosus were fermented at different temperatures and with different added levels of salt, glucose, nitrite, nitrate and Pediococcus pentosaceus in accordance with a six factor fractional design. The numbers of surviving Staphylococcus xylosus, lactic acid bacteria, pH, free fatty acids and residual amounts of nitrite and nitrate were measured. The effects of temperature and different ingredients on the chemical and bacterial data were tested using multiple linear regression and analysis of variance. The study showed that numbers of surviving Staphylococcus xylosus were reduced by high fermentation temperature, especially when salt concentration was low and glucose concentration high. High levels of nitrite and addition of Pediococcus pentosaceus had adverse effects as well. pH was lowered by high fermentation temperature, low salt concentration and addition of glucose and Pediococcus pentosaceus. On the other hand p H was increased by addition of nitrate. The pH-lowering effect of glucose was small when temperature was low. The residual levels of nitrite and nitrate were increased by addition of nitrate, but then increased and decreased, respectively, by increasing temperature. Addition of glucose and Pedio coccus pentosaceus lowered the residual amount of nitrite. The level of free fatty acids was reduced by salt and increased by higher temperature. Of the individual acids, the amount of linoleic acid was also increased by addition of Pediococcus pentosaceus and decreased by nitrate.

The influence of Debaryomyces hansenii and Candida utilis on the aroma formation in garlic spiced fermented sausages and model minces

The influence of the yeast starter cultures Debaryomyces hansenii and Candida utilis on fermented meat aroma was studied in model minces and in commercial-type fermented sausages. Volatile compounds from model minces and sausages were collected using diffusive and dynamic headspace sampling respectively and were identified by gas chromatography/mass spectrometry (GC/MS). A triangle test was carried out on the sausages to detect whether the yeast influenced the sausage odour. C. utilis demonstrated high metabolic activity in the model minces, producing several volatile compounds, in particularly esters. C. utilis also seemed to ferment the amino acids valine, isoleucine and leucine into compounds important for the aroma of sausages. D. hansenii on the contrary, had very little effect on the production of volatile compounds in the model minces. In the sausage experiment both yeast cultures died out before the ripening process ended and the sensory analysis showed only a slight difference between the sausages. A fungistatic test of the garlic powder added to the sausages indicated that garlic inhibits the growth of the yeast starter cultures.

Dried sausages fermented with Staphylococcus xylosus at different temperatures and with different ingredient levels — Part III. Sensory evaluation

Sausages with added Staphylococcus xylosus were fermented at different temperatures and with different added levels of salt, glucose, nitrite, nitrate and Pediococcus pentosaceus in accordance with a six factor fractional design. The odour of the sausages was evaluated by a quantitative descriptive method with ten descriptors and by gas chromatography olfactometry. The sensory profile was correlated to the experimental design and the volatile compounds by partial least squares analysis. Also, the effects of temperature and different ingredients on the strength of the individual descriptors were tested using multiple linear regression and analysis of variance. The study showed that salami odour was more pronounced in sausages fermented at low temperature than in sausages fermented at high temperature and added nitrite, glucose and P. Pentosaceus. High temperature sausages had a more sour and cheesy aroma, but were less fatty and sourdough-like. Salami odour was correlated with the presence of ethyl esters and 2-alkanones as well as with high numbers of Staphylococcus xylosus. 2- and 3-methylbutanal seemed to be influential as well. The sourish note to salami odour was especially caused by acetic and perhaps butanoic acid, the cheesy note by 2-methylpropionic, butanoic and 3-methylbutanoic acid.

Volatile compounds released during ripening in Italian dried sausage

A commercial production was analysed at six stages during ripening. Water content, pH and bacterial counts were followed, and volatile compounds from sausages were extracted by dynamic headspace sampling and analysed by gas chromatography/mass spectrometry. Total concentrations of all classes increased during ripening. Pepper compound concentrations peaked in the middle of the ripening period. Lipid oxidation products increased especially towards the end of ripening, in particular, the compounds 2-heptanol, 1-octen-3-ol, 2-heptanone and 2-nonanone. Surface moulds probably caused 4-heptanone to appear late in the processing. Benzeneacetaldehyde was absent in fresh mince, but increased to become one of the most abundant volatiles. Compounds from carbohydrate catabolism disappeared during the processing.

Growth and production of volatiles by Staphylococcus carnosus in dry sausages: Influence of inoculation level and ripening time.

Three sausage batches inoculated with normal inoculation level of Pediococcus pentosaceus (5×10(6) CFU/g) and with low, intermediate, and high inoculation levels of Staphylococcus carnosus (10(5), 5×10(6), 5×10(7) CFU/g, respectively) were produced. Cell counts and formation of volatiles were followed throughout a ripening period of three weeks. The staphylococci exhibited the fastest growth in sausages with a low inoculation level, whereas growth was only moderate in sausages with a high initial level. Analysis of volatiles showed that methyl-branched aldehydes and acids, phenylacetaldehyde, 2-methyl-1-butanol, dimethyldisulphide and dimethyltrisulphide were produced in higher amounts in sausages with a high inoculation level of S. carnosus, whereas a low inoculation level correlated with high amounts of diacetyl, ethanol and ethyl esters. The levels of most compounds increased over time, but the amount of diacetyl was negatively correlated to ripening time. A negative interaction effect between inoculation level and ripening time was observed for the amounts of methyl-branched aldehydes.