Chemistry and instrumental analysis

Teaching

The Chemical Laboratory of the Department of Bioprocess Engineering is responsible for analytical training (lectures and practical courses) in the subjects of

  • General chemistry
  • Special chemistry
  • Instrumental analysis
  • Selected and special instrumental analysis
  • Molecular biological methods
  • Quality management
  • Sensors
  • Nutritional physiology

for all degree courses at the Ahlem campus.

In the chemical laboratory, a basic practical course is completed in the 1st semester (ML and TNR). In the 2nd semester, various foods and other products are examined for their ingredients (protein, fat, dry matter, etc.). In the advanced study programme, in the 6th semester, students who later want to work in the laboratory area have the option of deepening their analytical knowledge in the subject "Instrumental Analysis". In the Master's degree course in Dairy and Packaging Industry, a laboratory exercise is held on the subject of molecular biological methods (PCR) and microarray. In addition, chemical analyses are also carried out here for research purposes.

Impressions

The team

Research

Since 1994, various research projects have been carried out with well-known milk-processing companies and other firms in the field of instrumental-analytical monitoring of cheese ripening and assistance with a wide range of questions in order to be able to predict the quality of the final cheese product at the earliest possible stage. Instrumental-analytical data, sensory and technological characteristics were evaluated in combination by means of multivariate statistical methods:

AGIP project 1994-1995 “Chemical maturity marks in cheese" in cooperation with Nordmilch eG (DMK)

AGIP project 1996 – 1998 “Influence of whey cream on proteolytic cheese ripening" in cooperation with Nordmilch eG (DMK)

AGIP project 1998 – 2000 “Evaluation of proteolytic activity in cheese (bitterness and yield)" in cooperation with Chr. Hansen GmbH Nienburg and Horsholm (DK)

AGIP project 2001 – 2002 “Optimisation of cheese ripening using novel direct starter cultures (DVS cultures)" in cooperation with Chr. Hansen GmbH

AGIP project 2003 – 2005 “Optimisation of hole formation and sensory properties in industrial large hole cheese production" in cooperation with Kraft Foods Deutschland GmbH

AGIP project 2005 – 2008“Isolation and purification of proteinogenic maturation markers in industrial cheese production for BioChip development" in cooperation with Kraft Foods Deutschland GmbH, Fraunhofer IBMT Department of Molecular Bioanalytics Potsdam

EFRE project 2007 – 2009 “Further development and validation of a BioChip for the assessment of the ripening state in industrial cheese production" in cooperation with Chr. Hansen GmbH, Fraunhofer IBMT Department of Molecular Bioanalytics Potsdam, Kraft Foods Deutschland GmbH

EFRE project 2010 - 2012 “Influence of the addition of caseins and caseinates on the quality and ripening of cheese" in cooperation with DMK Deutsches Milchkontor GmbH and Chr. Hansen GmbH.

In addition to this research area, questions in the field of mycotoxin analysis, automatic nitrogen analysis and the cleaning performance of automatic cleaning machines in clinical and food industry practice were worked on in cooperation with industrial companies.

Furthermore, the Chemical Laboratory currently participates regularly in interlaboratory tests for the development and validation of reference analytical test methods at § 64 LFGB, DIN, CEN, ISO, IDF and VDLUFA and advises dairy and food technology companies on analytical and ingredient-related issues.

At present, the chemistry laboratory supports ongoing research projects and work within the framework of bachelor's and master's theses with the chemical analyses of samples (e.g. ash content, protein content determination, etc.).

Interesting techniques

Animal species differentiation by means of microarray

The microarray technique is a new analytical method in which molecules that can capture the analytes (e.g. complementary DNA strands, antigen-antibody reaction or the shape of the molecule as aptamers) are spotted onto a glass slide. The slide is immersed in the sample solution and the analyte bound to the spot is detected with a fluorescent dye in the microarray scanner. This enables rapid detection of many analytes in the smallest space of the slide in one step.

In an internship experiment, a commercially available microarray ("biochip") for animal species differentiation in food products with meat is carried out with the students. Simultaneous detection of the 8 animal species donkey, horse, cow, pig, chicken, turkey, sheep and goat on a biochip with a low detection limit (0.5 - 1%) allows the identification of the smallest animal components in food.

As a measuring principle, the fragment of the cytochrome b gene, which is specific for the corresponding animal species, is amplified on the DNA extracted from the samples by means of PCR (polymerase chain reaction) and fluorescently labelled with primers. After binding (hybridisation) of the amplified, labelled PCR products to the complementary DNA spots on the biochip, positively glowing spots can be assigned to a specific animal species by scanning at two wavelengths 532 (Cy3) and 635 nm (Cy 5).

Microwave-supported fast method for fat extraction

The ETHOS.lab microwave system from MWS Vertriebs GmbH (= MLS GmbH) available in the chemistry laboratory is used, among other things, for the semi-automatic digestion and determination of fat from e.g. quark, cheese, yoghurt and other complicated matrices for which the established reference fat extraction methods according to Weibull-Stoldt and Schmid-Bondzynski-Ratzlaff or the reference method according to Röse-Gottlieb would otherwise be used for the determination of the fat content of milk. The simultaneous acid digestion and fat extraction into the solvent phase in one step under the influence of microwaves and strong stirring, as well as the evaporation of the solvent, ensure a high time saving and increase in work safety compared to the complex reference methods.

N/C determination according to Dumas (protein content)

The Dumas combustion method is a traditional, safe, environmentally friendly and officially recognised routine method for determining the total nitrogen content of a wide variety of sample matrices (in our case mainly foodstuffs, animal feed and other natural substances) and the protein content of the sample to be calculated from this (multiplication by a specific factor).

The sample is completely burnt in a crucible at high temperatures (900 °C to 1200 °C) under oxygen supply and the combustion gases are freed from disturbing components (e.g. moisture, foreign elements) by various reduction and drying steps. The molecular nitrogen present at the end is quantitatively recorded with the help of a thermal conductivity detector, the nitrogen content is calculated in relation to the initial weight and output on the PC directly after the analysis. The protein content of the sample is calculated from the result by multiplication with a specific factor as in the reference method according to Kjeldahl.

Compared to the classical, wet-chemical and time-consuming reference method for nitrogen determination according to Kjeldahl, in which the sample is digested by boiling in high-percentage sulphuric acid, among other things, the Dumas method is characterised by a considerably lower workload, higher automation, time savings and, in particular, higher work safety (no aggressive chemicals or special laboratory equipment required).

 

Equipment

Dry mass determination
2 drying ovens T6060, T6120 by Heraeus Instruments GmbH
Infrared dry mass determination device Mettler LP 16 (drying device), Mettler PM 100 (balance) and printer GA 42 Printer by Mettler - Toledo GmbH

Ashing
Microwave ash furnace PYRO.start by MLS GmbH
Muffle furnace by Heraeus Instruments GmbH

Protein determination according to Kjeldahl
3 Kjeldahl digestion blocks 425 digesters and 430 digesters of Büchi Labortechnik GmbH
3 Kjeldahl distillation units KjelFlex K-360, distillation units 323 and
Distillation units 324 of Büchi Labortechnik GmbH
Scrubber (gas scrubber) B-414 of Büchi Labortechnik GmbH

N/C determination according to Dumas
Dumas device rapid MAX N exceed by Elementar Analysensysteme GmbH (new 10_2019)
Dumas device VarioMAX CN by Elementar Analysensysteme GmbH

Fat extraction
Ex-protected safety centrifuge with control unit Super Vario N of Funke - Dr. N. Gerber Labortechnik GmbH
Water bath ETC of Dinkelberg Analytics GmbH
Microwave fat extraction ETHOS.lab of MLS GmbH
Cooling water bath for fat extraction FLP250 from JULABO GmbH

UV/VIS photometry/enzymatics
2 High-resolution recording spectrophotometers Uvikon 931, 933 of Kontron Instruments

Cryoscopy
Freezing point meters Cryostar I of Funke - Dr. N. Gerber Labortechnik GmbH

Polarimetry
Digital circular polarimeter MCP 200 of Anton Paar GmbH

High performance liquid chromatography
2 HPLC preparative systems and analytical system La Chrom Elite of Merck Hitachi with different detection units

Gas chromatography
Gas chromatograph Varian 3900 of Agilent Technologies Inc

Electrophoresis (IEF/SDS-PAGE)
Power Supply EPS 3500 of Pharmacia
Power Supply Blue Power 3000 of Serva Elektrophoresis GmbH
Gel shaker Kick II of Serva Elektrophoresis GmbH
Cooling water bath WKL 230 of Lauda
Video densitometer BioDocAnalyze of Biometra GmbH (Analytik Jena AG)
Capillary electrophoresis P/ACE™ MDQ capillary electrophoresis system of Beckmann Coulter Inc.

Karl-Fischer titration
Karl-Fischer titrator DL 38 of Mettler - Toledo GmbH

PCR
Thermocycler Biometra of Analytik Jena AG

ELISA
Microplate reader VERSA max of MDS Analytics Technologics GmbH

Microarray (Biochip)
Mikroarray Scanner Genepix personal 4100 A of Molecular Devices GmbH

Heat indicators in dairy products
Fluorescence Photometer FLM 200 "Fluorophos Method" + Thermoblock of Advanced Instruments Inc. USA

Atomic absorption spectroscopy
AAS 1100B of Perkin Elmer Inc.

Miscellaneous
Lactostar of Funke - Dr. N. Gerber Labortechnik GmbH
Whipped cream tester Standard A-Lift of JANZ- Präzisionstechnik GmbH