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UGent campus Kortrijk, laboratorium voor voedingsmicrobiologie en biotechnologie

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Abstract bachelorproef 1 2016-2017Impact of trans-cinnamaldehyde on the enzymatic browning of iceberg lettuce

The focus of this bachelor thesis was to determine the influence of natural compounds (trans-cinnamaldehyde and chlorogenic acid) on the enzymatic browning of minimal processed fresh-cut iceberg lettuce in order to prolong the shelf life. Besides appearance and loss of desirable texture, browning is one of the fundamental factors affecting the quality loss in minimally processed iceberg lettuce and leads to an economic disadvantage. The key enzymes in this enzymatic browning process are phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD). A treatment of iceberg lettuce with a natural component to increase the shelf life, is a healthy alternative and might reduce the use of chemical additives in the food industry.

Iceberg lettuce was bought in a local grocery store and processed in order to obtain a homogeneous batch of midrib tissue. Lettuce samples were treated with a solution of chlorogenic acid and trans-cinnamaldehyde. Using spectrophotometrical methods, several parameters (BP and activity of PAL, PPO & POD) were monitored during 14 days of refrigerated storage in plastic bags.

Trans-cinnamaldehyde treatment was studied more in detail by microbial analysis and differentiating treatment times. Results of these experiments can be used for further optimization of the trans-cinnamaldehyde treatment in order to inhibit enzymatic browning in iceberg lettuce.

Abstract bachelorproef 2 2016-2017Impact of mineral enhancers on the bioaccessibility of iron and zinc in fermented cereal porridges

In developing countries (like Zimbabwe), there is a low bioaccessibility of trace minerals (iron and zinc) in fermented cereal porridges, which can lead to nutrient deficiency. This low bioaccessibility is caused by the presence of mineral inhibitors (phytic acid, phenolic compounds and condensed tannins), which are naturally present in cereals. By the addition of mineral enhancers (ascorbic acid, meat factor) or by adding enzymes (phytase, laccase, tannase), the bioaccessibility of iron and zinc could be increased.

Different mineral enhancers were added to the fermented porridges in a ratio 1:3. Different spectrophotometrically methods were used to determine the amount of the mineral inhibitors. An in vitro digestion was performed to have an estimation of the mineral bioaccessibility.

The fermented slurries with mineral enhancers still have an amount of mineral inhibitors, a decrease of the phytic acid and an increase of the phenolic compounds was observed. The amount of iron and zinc was increased in the fermented slurries when mopane worm powder was added, but only a small fraction was available for uptake in the body. Adding baobab to the fermented slurries had a positive influence on the bioavailability of iron and zinc. In the cereals treated with the enzymes, phytase was the only enzyme having a positive effect in the decrease of phytic acids.

This experiment has shown that baobab and mopane worm powder were not able to increase the bioavailability of minerals in these fermented porridges. In future studies, the influence of enzymes (specially phytase) is interested to study more in detail.

Abstract bachelorproef 1 2015-2016Antimicrobial activity of components of essential oils 
Wegens confidentialiteit kan de samenvatting niet gepubliceerd worden.
 
Abstract bachelorproef 2 2015-2016Prelimary research on the influence of cultivar variation and heat shock on browning of iceberg lettuce 
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Samenvatting eindwerk 1 2014-2015: The use of essential oils in marinades to extend the microbiological shelf life of meat matrices
In recent years, there has been an increased interest in essential oils as natural antimicrobials because most consumers have a negative view on synthetic preservatives. Now there is questioned if these EO’s can be used in a hydrophilic marinade to form a stable emulsion and if this antimicrobial activity can preserve meat for a longer period of time. 
In vitro studies have demonstrated antibacterial activity of cinnamon (Cinnamomum zeylanicum), oregano (Origanum compactum) and red thyme (Thymus zygis) essential oil against some micro-organisms in Nutrient Broth.
This study primarily focused on spoilage by the Gram-negative coliforms, yeasts and molds and the Gram-positive lactic acid bacteria on pork mignonettes and bacon. The microbiological growth was monitored for the coliforms on ChromoCult ® Coliform agar, lactobacilli on de Man, Rogosa and Sharpe agar and for fungi on Rose-Bengal Chloramphenicol agar.
The meat was incubated for two minutes in four different liquids: marinade (10% NaCl and 2% lactic acid) and three water-in-oil emulsions of 1% EO (oregano, red thyme and cinnamon) in marinade. Each treatment was performed in triplicate.
The micro-organisms were examined at the day of the sample preparation and after one, six, ten and sixteen days of storage. The samples were stored in an aerobic atmosphere at approximately four degrees. There still doesn’t exist a stable emulsion. Unsteady marination, non-homogeneous distribution of micro-organisms on biological matrices and the use of less samples caused a large dispersion of the results. This can be solved by making homogeneous emulsions and by inspecting a larger amount of samples for each treatment.
An inoculation has to prove if the treatments on both matrices have possible inhibitory effects on Escherichia coli. The following ranking of treatments, in order of decreasing antibacterial activity, could be made for the total coliforms on pork bacon: cinnamon > red thyme > oregano > marinade. The treatment of total coliforms on pork mignonette should be examined more in further studies.
The treatments which slowed down the growth of fungi on both matrices, in order of decreasing antibacterial activity, were: cinnamon > oregano/red thyme > marinade. Cinnamon oil had stronger antifungal activity and better solubility in the marinade than carvacrol and thymol. It could extent shelf life by causing a longer lag phase.
 
Samenvatting eindwerk 2 2014-2015: Using essential oils as an antimicrobial agent to extend the shelf-life of fish
Companies want to know if the use of essential oils can extend the shelf life of seafood products. The major cause of spoilage of most seafood products is microbial growth. When the growth of these micro-organisms can be inhibited with the use of essential oils, the shelf-life will increase. It’s known that the use of essential oils, more specifically cinnamon, oregano and thyme, inhibit the micro-organisms in a culture medium. Now is the question if the essential oils also have the same antimicrobial effects on food matrices.
To realize this, the seafood product, more specifically salmon and scampi, were coated with a marinade which contains the essential oils. This was done by incubating the seafood product for two minutes in the marinade. After this, the treated samples were retained for six days in the refrigerator at 4°C. On specific days of preservation, microbial analyses were performed. Yeast and molds, lactic acid bacteria and total plate count were the organisms that were analyzed.
The companies also want to know whether the seafood product will still be accepted by the consumer after treatment with the marinade. To check this, sensory tests were performed using test persons. Triangle tests were used to decide if consumers can recognize the different sample from the two identical samples. The decision was based on the smell and not on the general view. This was because there was no difference after 24 hours between the treated matrices.
Crustaceans are normally more susceptible than fish to spoilage organisms. In this case, it’s not like that. Possibly because the scampi were preheated. However, microbial analyses show that the bacterial activity on salmon can be inhibited by the use of cinnamon. Especially on the total plate count and yeast and molds. The inhibiting activity on yeast and molds is based on the antifungal activity of the component cinnamaldehyde, which is present in cinnamon. Cinnamon has probably got an effect on one or more groups of micro-organisms that make up a large part of the total plate count because the total plate count was inhibited by cinnamon. The only downside is that cinnamon just works for three days in the current storage conditions.
Thyme and oregano can, in their turn, be used against the micro-organisms in scampi. In particular against lactic acid bacteria and the total plate count. Preference is given to thyme because it had an antimicrobial activity for six days in the current storage conditions. It may be plausible that the growth of microorganisms on salmon can be reduced by the use of cinnamon, but only on the condition that it’s combined with another grow limited method. For scampi, thyme can be used to reduce the bacterial activity during the six days of preservation.
The sensory tests were only performed on raw and baked salmon. After the evaluation of the results, it was stated that all three of the essential oils have the same assessment. Therefore, companies can use all three the essential oils. Generally, the participants accepted the scent of essential oils better when the salmon was baked. Consequently, one percent essential oil can be used to reduce the microbial growth. By raw salmon, the essential oils were assessed worse. It may be decided that the general acceptability in terms of scent decreases as the concentration of essential oil increases.
 
Samenvatting eindwerk 2013-2014: Disinfection of wash water from food matrices with peracetic acid
In Belgium, most of the lettuce is cultivated outside, which leads to the fact that the lettuce is exposed to different kinds of pollution on a daily basis. These pollutions can be soil, sand, dirt, pesticides and vermin, but also micro-organisms (MO), such as spoilers and pathogens.
To remove these micro-organisms, each lettuce crop is washed after cutting and then packed. This washing step usually contains one or more washing baths. Nowadays, the washing water is reused to narrow the demand of fresh groundwater.
During the washing step, micro-organisms enter the water. In function of time, the number of MO accumulate in the water and the water itself becomes a vehicle for contamination.  To counter this potential cross-contamination, disinfection techniques can be used.
Traditional methods of reducing microbial populations involve disinfection treatment with chlorine. But chlorine form chlorine gas, which is harmful for the workers and the use of chlorine may lead to the formation of toxic and carcinogenic by-products. In addition, the concentration of chlorine decreases very fast (within one minute), as it reacts with organic matter in the water. All this has led to a search for alternative agents.
During this bachelor thesis, peracetic acid (PAA), an acid that is formed by the reaction between acetic acid and hydrogen peroxide, was evaluated as potential disinfectant for the fresh-cut industry as an alternative to chlorine disinfection. It reacts with the micro-organisms present in the water and breaks the disulfide bridges in proteins, enzymes and other metabolites. PAA can degenerate spontaneously with metal ions as catalyst. This can be solved by reducing the metal ions in the water by using chitosan. That is a polymer makes the organic matter precipitate.
In a second part of this bachelor thesis, the effectiveness of PAA in the wash water of a second food matrix, pangasius filet, was investigated. The experiment was similar to the experiment of the lettuce wash water, but without pretreatment with chitosan.
Peracetic acid seems a better disinfectant than chlorine. First, the concentration of peracetic acid is not decreasing fast, what makes it a more stable product to use than chlorine. However, there is a need for a higher concentration to disinfect compared to chlorine, but there is no need to constantly add peracetic acid, in contrast to chlorine. A disadvantage of the use of peracetic acid is that it can lead to a decrease in the sensory quality of the product when high concentrations of peracetic acid are used.
 
Samenvatting eindwerk 2012-2013: Invloed op de groei van Listeria monocytogenes op vismatrices door gebruik van essentiële oliën
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Address

Graaf Karel de Goedelaan 5
8500 Kortrijk
056241211
Belgium

Contacts

Traineeship supervisor
Katleen Raes
056241255
katleen.raes@howest.be
Traineeship supervisor
Imca Sampers
Traineeship supervisor
Celine Vanden Abeele
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