Browsing by Subject "Milchprodukt"

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Entwicklung und Validierung schneller und selektiver Verfahren zum Nachweis von Salmonella enterica, Cronobacter spp. und Bacillus cereus in Milcherzeugnissen
(2014) Zimmermann, Jennifer; Schmidt, Herbert
The presence of pathogens is a serious problem in the food industry and contaminations of food with Bacillus cereus, Cronobacter spp. and Salmonella enterica are responsible for a large number of diseases worldwide. Milk products like milk, whey or cream powder are widely used in industry as an ingredient in other foods. Therefore it requires a fast and reliable identification of pathogenic microorganisms. The official methods according to § 64 LFGB or ISO/TS 22964 apply a common scheme of pre-enrichment, selective enrichment, detection and confirmation and take between three and six days. The aim of this work was the development and validation of a real-time PCR based method, which identifies the existence of the three pathogens in dairy products within 24 hours. The identification of B. cereus, Cronobacter spp. and S. enterica with the developed TaqMan real-time PCR was performed using specific genetic characteristics and an internal amplification control to eliminate false negative results. For B. cereus, the groEL gene, which codes for a heat shock protein, was selected as target. For the detection of Cronobacter spp. the ompA gene and for S. enterica the invA gene was chosen. Both genes are responsible for the invasion of the pathogens in the human epithelial cells. The adaptation of the method to the food matrix and an optimization of the enrichment time were affected by an artificial contamination of various dry dairy products. It was possible to detect 105 cfu/g C. sakazakii and S. Enteritidis cells with an initial concentration of 100 cfu/g in reconstituted powdered infant formula after enrichment of six hours. To simulate a natural contamination, powdered infant formula was contaminated with desiccated C. sakazakii cells in various concentrations and analyzed with the developed real-time PCR method. It was possible to detect an inoculum concentration of 0.01 CFU/g dry stressed C. sakazakii cells at low aw values (0.22). The new TaqMan real-time PCR is fast, reliable and specific for the clearly detection of the three major pathogenic microorganisms in milk products and was carried out within 24 hours.
Sensory and consumer-oriented studies on the effect of fat in different food matrices : a comparison between yoghurt, vanilla custard, Lyon-style and liver sausages
(2013) Tomaschunas, Maja; Busch-Stockfisch, Mechthild
The number of overweight and obese people all over the world increases and overweight and obesity promote the risk for a number of diseases. From the viewpoint of the consumer, it is important to change eating habits and to enhance the extent of physical activity in today’s sedentary lifestyles. From the viewpoint of the industry, the amount of fat in foods may be reduced. However, the degree of liking for a food is often related to its fat content because of the various effects of fat on sensory properties. The effect of fat depends on the food matrix and furthermore, consumers expect the presence of different properties as well as different intensities of certain properties depending on the food. Consequently, a detailed sensory approach is needed to successfully develop foods reduced in fat. Selection of samples for this study based on popularity, on differences in the food matrix as well as on the fact of belonging to the category of meat or rather dairy products, because current data showed that an increased fat intake amongst others arises from an increased consumption of meat and dairy products. Selection resulted in plain stirred yoghurt (0.1 to 12.0% fat) and starch-based vanilla custard (0.1 to 15.8% fat) as well as Lyon-style sausages (3.0 to 25.0% fat) and liver sausages (3.0 to 30.0% fat). Technologies to reduce or rather to substitute fat were adapted to each food matrix, applying innovative approaches. For each food matrix, samples with varying fat content were produced and were evaluated in terms of sensory properties using descriptive analysis, and consumers’ acceptability using hedonic tests. Afterwards, descriptive and hedonic data were statistically correlated. Therefore, the present work on the one hand aimed to apply adapted innovative technologies to reduce or rather to substitute fat in different food matrices and to survey their acceptability. On the other hand, the effects of fat and fat reduction on sensory properties and liking as well as the various drivers of liking and disliking were aimed to be examined and contrasted. Concerning yoghurt, the results showed an increasing effect of fat on attributes creamy (flavor and texture), viscous (appearance and texture) as well as fatty mouth feel. Consumers preferred yoghurts with medium fat (3.5 to 6.0%) and also high fat (12.0%) contents. Liking was driven by attributes sour, aromatic, astringent and partially by descriptors creamy, viscous and fatty mouth feel. Contrariwise, graininess and yellowness as well as too high intensities in attributes creamy, viscous and fatty mouth feel led to rejection. Substituting fat by means of adding whey protein did not enhance liking, but increasing protein did. Finally, the results showed that medium protein contents (4.5%) and high casein-to-whey protein ratios (80/20) could lead to accepted low-fat yoghurts. Regarding vanilla custard, fat increased intensities in attributes thick (appearance and texture), creamy (flavor and texture), sticky and fatty, whereas yellowness, surface shine, jelly, cooked and vanilla flavor, as well as harmonious were decreased by fat. Low to medium fat custards (1.5 to 8.6%) showed best liking scores and attributes vanilla and cooked flavor, harmonious, vegetable fat flavor, sticky, fatty and creamy texture were found to drive liking. On the opposite, custards high in jelly texture and partially too high in thickness, whiteness and creamy flavor were disliked. The addition of a vegetable fat cream led to well accepted medium fat (2.9%) vanilla custards. In Lyon-style sausages, fat exerted an increasing effect on attributes meat flavor, aftertaste meat flavor, greasy and juicy, and a decreasing effect on red color intensity, spicy, spicy aftertaste, raspy throat, coarse and firm. Regarding liver sausages, fat increased scores in attributes greasy, creamy texture, lumpy (appearance and texture), foamy, off-flavor and sweet. Contrariwise, it decreased red color intensity, odor attributes spicy, liver and metallic as well as flavor descriptors spicy, liver, aftertaste, peppery, bitter and metallic and also texture properties firm and furred tongue. For both types of sausage, preferences were mainly found for medium fat contents (10.0 and 17.0%), but consumers partially also liked sausages high in fat (25.0 or rather 30.0%) and low in fat (3.0%). No clear drivers of liking could be detected for the sausages. The results showed that the addition of inulin, citrus fiber and partially rice starch led to a successful imitation of fat or rather to acceptable fat-reduced sausages which are furthermore fiber enriched. The current study gives an interesting overview of the various effects of fat depending on the food matrix. It furthermore gives evidence for the successful development of an assortment of popular fat reduced meat and dairy products.