Oliver Schlüter

Nutritional composition and safety aspects of edible insects

Insects, a traditional food in many parts of the world, are highly nutritious and especially rich in proteins and thus represent a potential food and protein source. A compilation of 236 nutrient compositions in addition to amino acid spectra and fatty acid compositions as well as mineral and vitamin contents of various edible insects as derived from literature is given and the risks and benefits of entomophagy are discussed. Although the data were subject to a large variation, it could be concluded that many edible insects provide satisfactorily with energy and protein, meet amino acid requirements for humans, are high in MUFA and/or PUFA, and rich in several micronutrients such as copper, iron, magnesium, manganese, phosphorous, selenium, and zinc as well as riboflavin, pantothenic acid, biotin, and in some cases folic acid. Liabilities of entomophagy include the possible content of allergenic and toxic substances as well as antinutrients and the presence of pathogens. More data are required for a thorough assessment of the nutritional potential of edible insects and proper processing and decontamination methods have to be developed to ensure food safety.

Interactions of Non-Thermal Atmospheric Pressure Plasma with Solid and Liquid Food Systems: A Review

Non-equilibrium atmospheric pressure plasma processes combine several advantages such as non-thermal operation and high antimicrobial activity and are thus proposed to be a prospective alternative to traditional food preservation methods, which suffer from undesired alterations of food quality and a lack of acceptance by the consumer. This review summarizes the latest research work in the field of food science and technology dealing with the application of plasma processes on solid and liquid foodstuff. Starting with the historical background of plasma, the basic principles of plasma generation and of the complex plasma chemistry are highlighted and insights into plasma–surface and plasma–liquid interactions are given. Important research results in terms of plasma application on foods are presented with emphasis on the impact of the food matrix on microbial inactivation. Furthermore, the results of recent studies about the behavior of food quality-related components and attributes during plasma exposure are presented.

Impact of cold plasma on Citrobacter freundii in apple juice: Inactivation kinetics and mechanisms

Various studies have shown that cold plasma is capable of inactivating microorganisms located on a variety of food surfaces, food packaging materials and process equipment under atmospheric pressure conditions; however, less attention has been paid to the impact of cold plasma on microorganisms in liquid foodstuffs. The present study investigates cold plasmas ability to inactivate Citrobacter freundii in apple juice. Optical emission spectroscopy (OES) and temperature measurements were performed to characterise the plasma source. The plasma-related impact on microbial loads was evaluated by traditional plate count methods, while morphological changes were determined using scanning electron microscopy (SEM). Physiological property changes were obtained through flow cytometric measurements (membrane integrity, esterase activity and membrane potential). In addition, mathematical modelling was performed in order to achieve a reliable prediction of microbial inactivation and to establish the basis for possible industrial implementation. C. freundii loads in apple juice were reduced by about 5 log cycles after a plasma exposure of 480s using argon and 0.1% oxygen plus a subsequent storage time of 24h. The results indicate that a direct contact between bacterial cells and plasma is not necessary for achieving successful inactivation. The plasma-generated compounds in the liquid, such as H2O2 and most likely hydroperoxy radicals, are particularly responsible for microbial inactivation.

Occurrence and genetic diversity of Arcobacter spp. in a spinach-processing plant and evaluation of two Arcobacter-specific quantitative PCR assays

Some species of the genus Arcobacter are considered to be emerging food pathogens. With respect to recent vegetable-borne outbreaks, the aim of this work was to investigate the occurrence and diversity of Arcobacter within the production chain of a spinach-processing plant by a combination of cultivation and molecular methods. Samples including spinach, water, and surface biofilm were taken over a period of three years from the entire processing line. Ten 16S rRNA (rrs) gene clone libraries were constructed and analysed using amplified rRNA gene restriction analysis (ARDRA). Approximately 1200 clones were studied that resulted in 44 operational taxonomic units (OTUs). Sequences with high similarities to Arcobacter cryaerophilus (13% of clones, 3 OTUs), A. ellisii (4%, 6 OTUs), A. suis (15%, 3 OTUs), and the type strain of A. nitrofigilis (1%, 7 OTUs) were identified. This represents the first report of the detection of the recently described species A. ellisii, A. suis and, in addition, A. venerupis from alternative habitats. A total of 67% of the clones (22 OTUs) could not be assigned to a genus, which indicated the presence of uncharacterised Arcobacter species. For the cultivation-independent detection of Arcobacter, two genus-specific quantitative PCR (qPCR) assays were developed and tested on 15 Arcobacter species. When these assays were applied to samples from the spinach-processing plant, they showed positive results for up to 35% of the samples and supported the conclusion that there is a considerable risk for the transfer of pathogenic Arcobacter species on vegetables, which was also verified by a cultivation approach.

Fluorimetric detection of protoporphyrins as an indicator for quality monitoring of fresh intact pork meat

In fresh meat production fast and non-destructive quality monitoring along the distribution chain is a key aspect to guaranteeing high quality and safe products for consumption. The applicability of fluorescence spectroscopy using protoporphyrins as indicators for meat ageing was investigated. Porcine musculus longissimus dorsi (MLD) was stored in slices over 20 days at 5 and 12°C and measured every day with an excitation of 420nm and an emission range of 550-750nm. Additionally, pH, drip loss and colour were examined to assess possible correlations. The obtained spectra of the MLD showed an increase in three peaks at 592, 638 and 705nm which could be reconstructed using the spectra of standard solutions of protoporphyrin IX (PP) and zinc protoporphyrin IX (ZnPP) or magnesium protoporphyrin (MgPP), respectively. Using principal component analysis (PCA) on the fluorescence spectral data, the meat slices stored at 5°C showed differences in the fluorescence signal after the 10th day and 5th day when stored at 12°C. An interrelationship between the additional analyses and the fluorescence intensities on these relevant days could not be established. In conclusion, the increase of ZnPP fluorescence due to temperature related changes of physiological meat properties is capable of serving as a quality indicator with regards to inadequate conditioning (e.g. during transportation and/or storage) of pork meat.

Recovery and techno-functionality of flours and proteins from two edible insect species: Meal worm (Tenebrio molitor) and black soldier fly (Hermetia illucens) larvae

Depending on the species, edible insects are highly nutritious and thus represent a noteworthy alternative food and feed source. The current work investigates the protein extractability and techno-functionality of insect flour fractions recovered from Tenebrio molitor and Hermetia illucens. T. molitor and H. illucens flours contained about 20% crude fat and 60% and 36 % crude protein, respectively. Defatting reduced the crude fat content to 2.8% (T. molitor) and 8.8% (H. illucens) and increased the crude protein content to 68% and 47%, respectively. To isolate proteins from the flours, protein solubility was optimized by varying the pH, the ionic strength, and the extraction temperature of the solvent. All products and by-products accumulated in the protein production process were characterized by composition, selected techno-functional properties, protein solubility, composition and structure as well as their microbial load.

Safety aspects of the production of foods and food ingredients from insects

At present, insects are rarely used by the European food industry, but they are a subject of growing interest as an alternative source of raw materials. The risks associated with the use of insects in the production of foods and food ingredients have not been sufficiently investigated. There is a lack of scientifically based knowledge of insect processing to ensure food safety, especially when these processes are carried out on an industrial scale. This review focuses on the safety aspects that need to be considered regarding the fractionation of insects for the production of foods and food ingredients.

Characterization of the cultivable microbial community in a spinach-processing plant using MALDI-TOF MS.

A better and regular control of the production chain of fresh fruits and vegetables is necessary, because a contamination of the product by human- and phyto-pathogenic microorganisms may result in high losses during storage and poses a threat to human health. Therefore, detailed knowledge about the occurrence and the diversity of microorganisms within single processing steps is required to allow target-oriented produce safety control. Recently, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was successfully used to identify bacterial colonies. Bacteria can be identified with high accuracy by comparing them with generated spectra of a reference database. In this study, spinach and wash water samples were taken of the complete process line of a spinach-washing plant. Bacteria in the samples were grown on plate-count, Arcobacter selective, marine and blood agar. In total, 451 colonies were evaluated by MALDI-TOF MS, 16S rRNA gene sequence and phylogenetic analysis. 50% of the detected species belonged to the class of Gammaproteobacteria. Firmicutes were present with 22%. Mostly, the detected species showed 16S rRNA gene sequence dissimilarities larger than 1% to known reference species and, hence, could not be assigned to a distinct species. However, many isolated species belonged to genera which contain pathogenic or opportunistic pathogenic bacteria. In addition, the bacterial diversity on the spinach surface increased after the first washing step indicating a process-borne contamination of the spinach.

Impact of the metastable state of water on the design of high pressure supported freezing and thawing processes

Increased hydrostatic pressure influences the phase transition of water by way of depressing the freezing/melting point as well as reducing the latent heat of fusion. This results in shortened freezing/thawing times of food materials. Furthermore different solid polymorphs of pure water with a higher density than the fluid exist under hydrostatic pressure above 209 MPa. Taking advantage of the phase diagram of water various pathways of changing the physical state of food can be followed using external manipulations of temperature or pressure. Recent studies on pressure supported phase transition processes focus mainly on the triple point of water/ice I/ice III at 209 MPa and -22 °C where the lowest onset temperature for pressure shift freezing and the highest temperature difference (sample - pressure transmitting medium) by decreasing the melting point of a food sample due to pressurization is expected. Generally, an analogous slope of the melting curve of food compared to that of pure water was assumed, but extensive data sets which show the liquid-solid phase boundary of food systems (especially at a pressure above 209 MPa) have been missing. Selected experimental techniques are appropriate for in situ detection of the transient temperature field of food samples inside the high pressure vessel. Temperature and pressure profiles detected clearly identify the pressure dependent melting curves of plant tissue (potato) in a pressure range up to 450 MPa. The curves derived from the experimental investigation can be defined by fitting the coefficients of the international equations for pressure along the melting curve of ordinary water (provided by IAPWS). Further the experimental data indicate a high degree of supercooling before the nucleation of water to a higher solid form than ice I takes place. When considering the experimental nucleation points a region of metastable water can be described in a range where ice III is thermodynamically stable. This behavior results in possible improvements for designing pressure supported freezing and thawing processes.

Effects of different storage conditions on quality related porphyrin fluorescence signatures of pork slices

This study evaluated the potential of fluorescence as an indicator of pork quality by determining the effects of various conditions on fluorescence signatures (excitation at 420 nm, emission at 550-750 nm). Storage of porcine musculus longissimus dorsi in PE bags led to a clear increase in porphyrin fluorescence intensity after approx. 10 d post mortem. Modified gas atmosphere (70% O(2), 30% CO(2)) inhibited the fluorescence emission of zinc protoporphyrin and protoporphyrin IX due to quenching by oxygen. Bleaching processes caused similar effects by halogen light exposure during meat storage. However, already formed signals could not be manipulated by oxygen or halogen light. Storage under vacuum reduced the quenching effects and resulted in increased fluorescence intensities. Freezing and thawing of meat samples delayed and reduced the increase in fluorescence intensity. Only minor effects could be detected at long-term frozen storage for two months. Consequently porphyrin fluorescence analysis is a potential means to indicate changes of pork quality and remaining shelf life.