J.H. Houben

Biogenic amine formation and degradation by potential fish silage starter microorganisms

Abstract Fish waste can be advantageously upgraded into animal feed by fermentation with lactic acid bacteria (LAB). This procedure is safe, economically advantageous and environment friendly. The pH value of the fish pastes decreases to below 4.5 during ensilage. This pH decrease is partly responsible for preservation. Decreased pH values and relatively low oxygen concentrations within the silage facilitate decarboxylase activity. Biogenic amines may constitute a potential risk in this kind of product since their precursor amino acids are present in fish silage. It is of great importance to ensure that the LAB strains chosen for starters do not produce biogenic amines. Some bacteria, among which some LAB species, are able to degrade these metabolites by means of amino oxidases. This could be of interest for fish silage production, to control biogenic amine build-up in this product. Seventy-seven LAB cultures isolated from fish pastes submitted to natural fermentation at two temperatures (15 and 22°C) and selected combinations of these isolates were examined for histamine, tyramine, cadaverine and putrescine production. Of the isolates tested, 17% were found to produce one or more of these biogenic amines. The behaviour of diamine oxidase was tested under the conditions present in fish silage. Addition of 12% sucrose or 2% NaCl did not affect histamine degradation. Addition of 0.05% cysteine decreased histamine degradation. Degradation occurred at all temperatures tested (15, 22 and 30°C), but not at pH 4.5. Forty-eight potential fish silage starters were tested for histamine degradation in MRS broth containing 0.005 g l−1 histamine and incubated at 30°C. Indications were found that five of these isolates could degrade as much as 20–56% of the histamine added to the medium within 30 h, when used as pure cultures. No histamine degradation was observed with combinations of cultures. Histamine degradation (50–54%) by two of these isolates was also observed in ensiled fish slurry.

Lipid oxidation in n − 3 fatty acid enriched Dutch style fermented sausages

Dutch style fermented sausages were manufactured with a substitution of 10%, 15% and 20% of pork backfat by flaxseed oil and canola oil, pre-emulsified with soy protein isolate. The 15% and 20% substitution were also reached by adding encapsulated flaxseed oil and encapsulated fish oil and by adding flaxseed oil, pre-emulsified with sodium caseinate, respectively. The products were sliced, packaged in an oxygen-enriched atmosphere and stored in the dark for 12 weeks at 7°C. No differences were detected in moisture, protein and fat content between control and modified sausages, with the exception of the formulation with sodium caseinate. The PUFA/SFA ratio increased from 0.30 in the control to 0.42-0.48 in the sausages with canola oil and to 0.49-0.71 in the sausages with flaxseed oil. The n-6/n-3 ratio decreased from 11.20 in the control to 6.94-5.12 in the sausages with canola oil and to 1.93-1.05 in the sausages with flaxseed oil. The addition of canola oil and encapsulated flaxseed oil resulted in a comparable shelf life as the control in terms of lipid oxidation. In the samples with addition of pre-emulsified flaxseed oil, especially with sodium caseinate, lipid oxidation clearly increased during storage. Physical and sensory analysis showed that the sausages with encapsulated fish oil and flaxseed oil resembled the control most.

Effect of dietary vitamin E supplementation, fat level and packaging on colour stability and lipid oxidation in minced beef.

The effect of addition of vitamin E (2025 IU animal(-1) day(-1)) to the diet of beef bulls on the colour stability and lipid oxidation of minced beef was studied. Control and enriched diets were provided for the last 136 days before slaughter. Batches of freshly minced meat were prepared containing approximately 1.3 and 22.2 wt% fat, respectively. Half of the samples of minced meat from control (CON) and supplemented (SUP) beef were packaged on trays with oxygen-permeable over wraps and half in modified atmosphere (MA) packs (initial gas mixture: O(2)/CO(2)/N(2)=65/25/10). The minced beef was stored for 10 days at 7°C in an illuminated environment. The SUP meat at both fat levels was consistently more resistant to lipid oxidation than was the CON meat. The additional vitamin E had a greater anti-oxidant effect for the lean meat product. MA packaging in comparison to the oxygen-permeable foil over-wrap did increase lipid oxidation, the effect being most pronounced for the CON meat. A sensory panel considered the colour of the lean SUP meat during display as more attractive than that of lean CON meat, irrespective of packaging. A similar effect was observed occasionally for the relatively fat minced meat. These subjective findings were confirmed by objective assessment of colour. The stability of the colour of the MA packed meat was better than that of the oxygen-permeable foil-wrapped meat. Microbial growth patterns of enriched and control meat were similar. MA packaging retards the multiplication of mesophilic aerobic spoilage micro-organisms and Enterobacteriaceae.

Characterization and frequency distribution of species of lactic acid bacteria involved in the processing of mawè, a fermented maize dough from Benin.

Lactic acid bacteria involved in the natural fermentation of both home-produced and commercial mawè were investigated during a 72 h fermentation period. Lactobacillus spp. constitute the majority (94%) of the strains of the lactic acid bacteria isolated, among which 89% represent the Betabacterium group. They include L. fermentum (biotype cellobiosus) (41%), L. fermentum or L. reuteri (19%), L. brevis (26%), L. confusus (less than 2%), L. curvatus (less than 1%) and L. buchneri (less than 1%). Other isolated lactic acid bacteria were L. salivarius, Lactococcus lactis, Pediococcus pentosaceus, Pediococcus acidilactici and Leuconostoc mesenteroides. Several species were detected at the early stage of fermentation, but the final stage was dominated by L. fermentum (biotype cellobiosus) and L. fermentum or L. reuteri totalling 90% of the isolated strains. The trend was the same for both home-produced and commercial mawè. No strains of L. plantarum, generally reported as dominating lactic acid bacteria at the final stage of fermentation of most plant foods, were isolated.

Radio-Frequency Pasteurization of Sausage Emulsions as a Continuous Process

From different available methods, dielectric heating was chosen as the most promising technique for a continuous and flexible pasteurization process of sausage emulsions.Based on the dielectric properties of sausage emulsions and the required penetration depths, radio frequency heating was then selected.The results of stationary heating tests (27 MHz) and of tests in a specially designed continuous heating line (inner diameter 50 mm) are described. An approximately linear relationship was observed for the temperature increase as a function of the electrode voltage. Temperature increases up to 40°Clmin were realized. Overall energy efficiency was around 30% and probably can be improved.Sausage products heated in the continuous line hada good appearance smooth surface and did not show moisture or fat release.

Effect of dietary vitamin E supplementation on pork quality.

The purpose of this experiment was to examine the effect of dietary vitamin E supplementation on pork quality, and in particular on colour stability. Crossbred pigs (n = 72) at a mean weight of 44 kg were assigned to one of two treatments. One group received, during a period of 84 days prior to slaughter, a tapioca based diet, which contained 8 mg vitamin E per kg feed. The other group received during this period the same diet, except it was supplemented with 200 mg vitamin E per kg feed. Muscle samples of longissimus thoracis and lumborum (LL) and psoas (PM) were collected at 24 hr post mortem and meat quality was assessed: pH, drip and cooking loss, shear force and intramuscular fat content. Colour stability was evaluated in fresh muscle (LL and PM) and after freezing (LL only) by measuring redness (a(∗)-values) during 6 days of storage at 7 °C. TBA-values and microbiological counts were also determined during storage. Results showed that extra dietary vitamin E had no effect on pig performance (daily gain, feed efficiency, lean meat percentage) nor on meat quality traits. The vitamin E levels were five times higher in the muscles of the treated group than the control group. In comparison with fresh LL muscle, colour stability was lower in PM and after freezing. In both muscles, the vitamin E treatment reduced TBA-values, in particular after frozen storage. No effect was found on microbiological counts. Colour stability was improved in LL after 6 days of storage, but not in PM. The effect in LL is too late to be of practical significance, since pork is usually sold well before that time in The Netherlands. It is suggested that variation in feedstuff composition of the diet may possibly explain part of the variable results reported in literature for the effect of vitamin E supplementation on colour stability of pork.

Effect of dietary vitamin E supplementation on beef colour stability

The effect of dietary vitamin E upon colour, waterholding capacity, bacterial growth and lipid oxidation of beef longissimus thoracis (LT) and psoas major (PM) muscle were examined during aerobic display of fresh muscle and after aging in vacuum for 26 days. Forty crossbred beef bulls received a whole crop corn silage, supplemented with concentrate. Twenty bulls were each supplemented with 2025 mg vit E per day (added to the concentrate) for 136 day prior to slaughter and compared with non-supplemented control animals (n=20). In fresh LT muscle drip loss did not differ between treatment groups, while in PM muscle drip loss was significantly higher for the supplemented group. The treatment did not affect bacterial growth in fresh and aged muscles. Lipid oxidation during 12 day storage of fresh muscle was significantly lower for the supplemented group, as indicated by the lower TBA-values. No effect of the vitamin E treatment was observed on a (∗)-values of both fresh and aged LT muscle during display for 8 and 5 days, respectively. In PM muscle, supplemented beef had lower a (∗)-values in fresh (at day 1) and aged (at days 1 and 2) muscle, due to a lower oxygenation. The reason for this lower oxygenation is unclear. After aging, colour stability was decreased and more variable than in fresh muscle. Similar results were obtained when the difference in reflection values at 630 and 580 nm (R630-580), instead of the a (∗) value, was used as a parameter for colour stability. The absence of an effect of vit. E on the rate of discoloration, might possibly be explained from the observation that α-tocopherol levels in control muscle were relatively high (LT: 2.1 and PM: 3.2 μg/g muscle), compared with data from literature. Analysis of the feed for vit. E suggests that this was due to a relatively high natural vit. E uptake from the feed, which was calculated to be approx. 330 mg vit. E per animal per day for the control group.

Effect of the dietary supplementation with vitamin E on colour stability and lipid oxidation in packaged, minced pork

The effect of supplementation of vitamin E (200 W kg(-1) feed) in the diet of pigs on colour stability and lipid oxidation in minced pork was studied. Control and enriched diets were provided for the last 12 weeks before slaughter. Half of the samples of minced shoulder meat from control and supplemented pigs were packaged on trays with oxygen-permeable overwraps and half in modified atmosphere packs (initial gas mixture: O(2)/CO(2)/N(2) = 66/ 27/7). Meats were stored for 10 days at 7 °C in an illuminated retail display cabinet. The meat from vitamin E-supplemented pigs was more resistant to lipid oxidation than was the control meat. Gas packaging appeared to increase lipid oxidation in control meat, whereas lipid oxidation was stable in meat from vitamin E-supplemented pigs. Colour stability for gaspacked meat was comparable for both dietary groups. However, oxygen-permeable overwraps had a negative effect on colour stability in vitamin E-enriched meat. The reason for this is not known. The shelf-life of enriched and control meat was similar. Thus supplementation of pig feeds with vitamin E is recommended if an improved stability against lipid oxidation of (minced) pork is required.

Lipid and protein changes during the ensilage of blue whiting (Micromesistius poutassou Risso) by acid and biological methods

Fish waste is a potential source of protein for animal nutrition. Ensilage could provide an advantageous means of upgrading these residues. Careful control of the degree of proteolysis and lipid oxidation is required to produce silages of high nutritional value. This paper studies the changes in lipids and protein during storage (15 days) of acid silages (with 0, 0.25 and 0.43%, w/w, of formaldehyde) and biological silages (with 10 and 20% molasses or dehydrated whey) prepared from blue whiting. A remarkable reduction in protein solubilisation values was achieved by adding formaldehyde. However, formaldehyde addition led to an increase in the peroxide value of the oil extracted from the silages. Ensiling by biological methods seems promising. It yielded both a considerable reduction in protein solubilisation and in basic volatile nitrogen when compared with acid ensilage. In addition, the oil from biological silages had lower peroxide values than the oil from acid silages with added formaldehyde.

The effect of dietary vitamin E supplementation on drip loss of bovine Longissimus lumborum, psoas major and Semitendinosus muscles

The effect of dietary vitamin E supplementation (2150 IU/head/day) on drip loss and related quality traits of bovine M. longissimus lumborum M. psoas major and M. semitendinosus was examined. The effect of vitamin E supplementation on drip loss seemed to depend on muscle studied. Drip loss of longissimus muscles was not significantly influenced, whereas supplemented semitendinosus muscles lost significantly less (p < 0.05) and supplemented psoas major muscles significantly more (p < 0.05) drip than did control counterparts. In both supplemented and control samples, sarcolemma failure occurred. No ultimate pH differences were detected between control and supplemented samples regardless of the muscle considered. In supplemented semitendinosus muscles, the decrease in drip loss was accompanied by an increase of sarcoplasmic protein solubility and sarcomere length. It is discussed that both these variables may be related to the stability of mitochondria and sarcoplasmic reticulum, as affected by dietary supplementation of vitamin E. However, this view deserves further investigation and more evidence is needed to establish the mechanism by which vitamin E influences drip loss.