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Browsing by Person "Weiss, Jochen"

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Characterization and modulation of technofunctional properties of pea proteins
(2023) Moll, Pascal Bernd; Weiss, Jochen
Plant-derived ingredients for food formulation have gained increasing interest in recent years as animal products pose a higher burden on the environment. Among plant proteins, those from pea (Pisum sativum L.) are of particular interest because of their low allergenicity, low cost, high availability, and good reputation among consumers. However, the technofunctionality of pea proteins is often inferior to animal-derived proteins limiting a more widespread use in food products. These technofunctional properties include - among others - foaming, gelling, and binding of other ingredients and it depends on the food product, which functionality food scientists must utilize and optimize. Cost effective approaches to improve the technofunctionality of pea proteins are therefore desirable and would allow the industry to further implement the use of sustainable ingredients in foods. In line with these overall goals, the aim of the first section of this thesis was to characterize a commercial pea protein isolate and to modulate the physicochemical and technofunctional properties through homogenization for foaming application. The main goal of the second section was to mix pea proteins with pectin to obtain a suitable binder with desired properties for the application in meat alternatives. The mixing approach was based on previous research data that had shown that interacting protein-polysaccharide systems display a synergistic behaviour in terms of their functional properties. First section: Foams are two phase systems consisting of gas bubbles that are stabilized by surface-active ingredients such as proteins in the discontinuous, aqueous phase. The physico-chemical properties of proteins such as their solubility determines foaming performance. In Chapter I, a commercial pea protein isolate was fractionated into a water-soluble and a water-insoluble fraction for characterization. Although the two fractions were similar in protein composition, they showed distinct differences in physicochemical properties. For instance, the particle size of soluble pea proteins was around 40-50 µm at acidic pH (3-5), while no measurable particles were detected at neutral The insoluble pea proteins were large at pH 3 and 7 (> 80 µm) and ca. 40-50 µm close to their isoelectric point at pH 5. The results suggest that commercial pea protein isolates consisted of several fractions with differences in their physico-chemical properties. The yield of the water-insoluble fraction was higher and therefore used in Chapter II, where experimental results illustrated that dispersions of insoluble pea protein aggregates (5% w/w, pH 7) could be disrupted from 180 ± 40 µm (control) to 0.2 ± 0.0 µmm upon homogenization at pressures ≥ 125 MPa. This was attributed to a cleavage of intermolecular interactions such as disulphide bonds, hydrogen bonds, and hydrophobic interactions. The decrease in insoluble pea protein aggregate size was accompanied by an increase in solubility from 23 ± 1% to ≥ 80% that may be beneficial for its technofunctionality. Consequently, homogenization was applied to the same material at pH 3 and 5 with the aim of investigating its foaming performance in Chapter III. In general, unhomogenized dispersions of pea protein aggregates (5% w/w, pH 3 or 5) did not foam at both tested pH values due to large pea protein aggregates with low solubility and surface activity. At pH 3, the dissociation of pea protein aggregates into smaller, more soluble, and more surface-active proteins was responsible for a high foam capacity (FC = 360-520%) with medium foam stability as measured by drainage (FS = 19-30 min). Only a limited particle size reduction upon homogenization was observed at pH 5, which was close to the isoelectric point of the pea proteins. Nevertheless, the still large aggregates consisted of re-aggregated smaller protein particles that were able to form a smaller amount of rather stable foams with thick interfacial films (FC = 213-246%, FS = 32-42 min). Overall, homogenization of insoluble pea protein aggregates was shown to change its physicochemical properties thereby benefitting technofunctional properties such as foaming. Second section: Another technofunctionality of interest is binding of different structural elements in e.g., meat alternatives. For this, the binder must be i.) sticky to glue heterogeneous components together and ii.) able to readily solidify upon further processing thereby ensuring a coherent bulk matrix. In Chapter IV, the influence of pH (3.50, 4.75, 6.00) and biopolymer concentration (17.5-50.0% w/w) on the stickiness of a pea protein isolate – apple pectin mixture (mixing ratio r = 6:1) was investigated. It was found that biopolymer concentrations of 17.5-20.0% w/w led to low stickiness due to a lack of cohesive forces (WoA = 0.29-0.51 mJ). At high biopolymer concentrations of 40-50% w/w, the biopolymer mixtures were also not sticky because of adhesion being limited (WoA = 0.02-0.05 mJ). There was a good balance of adhesion and cohesion that facilitated a high stickiness (WoA = 0.48-0.65 mJ) at intermediate concentrations of 25-30% w/w, which was also indicated by a viscoelastic behavior (G’ ≈ G’’). At those concentrations, the mixtures at pH 6 were stickier due to increased swelling of the pea proteins. The importance of viscoelasticity for stickiness of biopolymer mixtures was confirmed in Chapter V, where pea protein isolate and apple pectin (25% w/w, pH 6) were mixed in different ratios r. Mixtures of pea protein and apple pectin and particularly the sample with r = 2:1 possessed high stickiness due to the development of a multiphase morphology that allowed for a good balance of adhesion and cohesion with distinct frequency dependency. Pea protein alone (r = 1:0, c = 25% w/w) had an elastic but soft texture with low stickiness due to limited viscous properties, whereas a sample solely consisting of apple pectin (r = 0:1, c = 25% w/w) was also not sticky because of its high cohesion and stiffness. The results of Chapter VI revealed that pea protein homogenization prior to mixing with apple pectin led to smaller protein particles in the blend that contributed to a higher cohesive strength. Interestingly, vacuum-dried pea proteins resulted in a higher network strength as this drying method prevented reaggregation of small protein particles to a higher extent as compared to freeze-drying. Overall, the mixture with homogenized and vacuum-dried pea proteins was nearly twice as sticky as the mixture with untreated pea proteins. In Chapter VII, sticky mixtures of different pea protein preparations (soluble, homogenized and unhomogenized pea proteins) and pectin (25% w/w, pH 6, r = 2:1) were tested for their ability to solidify upon different treatments, namely heating as well as the addition of transglutaminase, laccase, calcium, and combinations thereof. Calcium was found to facilitate crosslinking of pectin chains and thus induced solidification of the mixtures. For instance, the consistency coefficient K’ increased from 2800 ± 1000 Pasn for pea protein isolate – apple pectin mixtures to around 19000 Pasn when calcium was added. Heat treatment and transglutaminase did not lead to solidification indicating that pectin made up the continuous phase. Furthermore, laccase led to the highest degree of solidification when sugar beet pectin was used (K’ > 30000 Pasn) due to ferulic acid and pea protein tyrosine crosslinking. Consequently, the sticky mixture of pea protein and sugar beet pectin (25% w/w, pH 6, r = 2:1) with the addition of laccase for solidification was identified as the most suitable binder for a bacon type meat analogue, which was the object of the study carried out in Chapter VIII. This binder had the highest binding strength (W = 2.0-4.3 mJ) between textured protein, fat mimic, and both layers at 25 °C due to the introduction of covalent bonds by laccase within the binder and between the binder and the adherends. A control sample without laccase addition had lower binding properties (W = 0.7-1.0 mJ) and the binding strength of a methylcellulose hydrogel (6% w/w) serving as benchmark was only higher between two fat mimics at 70 °C (W = 1.8 ± 1.1 mJ) due to increased hydrophobic forces. Finally, the pea protein – sugar beet pectin binder (22.5% w/w, pH 6, r = 2:1) was tested in burger patty type meat analogues to glue textured vegetable protein and fat particles together (Chapter IX). The binder system did not influence the hardness of the burger patties suggesting that this property was governed by the structural elements and not the binder. However, the cohesiveness as determined by sensory analysis was found to be superior when the pea protein – sugar beet pectin binder was used (-0.7 ± 0.2) as compared to the methylcellulose benchmark (-2.9 ± 0.3). This was attributed to the sticky character of the biopolymer mixture that enabled improved binding of the different structural elements. Overall, this novel binder based on plant-derived ingredients was shown to be applicable in different meat alternatives. Last, Chapter X reviewed the functionality and binding mechanism of currently used binders in foods and showed that stickiness, hardening/solidification, and water holding capacity are of great importance. In many food products, the binder transitions from a sticky food glue to a solid matrix triggered by different process operations that depend on the characteristics of the applied binder. From the presented results, it can be concluded that pea proteins are useful functional ingredients in various application scenarios. The desired technofunctionality can be improved through different process operations such as fractionation, homogenization, or mixing with other plant-derived ingredients. For this, knowledge regarding structure-function relationship and other influential factors is needed. In some cases – such as in binders – process operations must be well orchestrated to induce structural transitions and therefore changes in functionality at the desired time during manufacturing. Overall, the results of this thesis contributed to a better understanding for a more widespread use of pea proteins to promote a more sustainable food system. The appended graphical abstract summarizes the key steps undertaken in this thesis to come to this conclusion.
Characterization of the aroma profile of food smoke at controllable pyrolysis temperatures
(2023) Rigling, Marina; Höckmeier, Laura; Leible, Malte; Herrmann, Kurt; Gibis, Monika; Weiss, Jochen; Zhang, Yanyan
Smoking is used to give food its typical aroma and to obtain the desired techno-functional properties of the product. To gain a deeper knowledge of the whole process of food smoking, a controllable smoking process was developed, and the influence of wood pyrolysis temperature (150–900 °C) on the volatile compounds in the smoking chamber atmosphere was investigated. The aroma profile of smoke was decoded by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Subsequently, the correlations in the most important substance classes, as well as in individual target components, were investigated by the Pearson test. Phenols and lactones showed an increase over the entire applied temperature range (rT = 0.94 and rT = 0.90), whereas furans and carbonyls showed no strict temperature dependence (rT < 0.6). Investigations on single aroma compounds showed that not all compounds of one substance class showed the same behavior, e.g., guaiacol showed no significant increase over the applied pyrolysis temperature, whereas syringol and hydoxyacetone showed a plateau after 450 °C, and phenol and cyclotene increased linear over the applied temperature range. These findings will help to better understand the production of aroma-active compounds during smoke generation in order to meet consumers preferences.
Effect of frozen to fresh meat ratio in minced pork on its quality
(2023) Tomasevic, Igor; Witte, Franziska; Kühling, Rike Elisabeth; Berger, Lisa M.; Gibis, Monika; Weiss, Jochen; Röser, Anja; Upmann, Matthias; Joeres, Eike; Juadjur, Andreas; Bindrich, Ute; Heinz, Volker; Terjung, Nino
The meat industry is typically using a mixture of fresh and frozen meat batters for minced meat production. Our goal was to find the exact threshold for fresh to frozen meat ratio capable of controlling the meat temperature during processing, but without having an adverse effect on the sensory quality of minced pork. To achieve this, the percentage of frozen meat used for the minced pork production was increased from 0% (control) to 50% (maximum) in 10% increments. To keep the minced meat temperature in control and make the processing resistant to fat smearing, the addition of 30% of frozen meat to the meat batter is sufficient. The soluble protein content, instrumental cutting force, and the sensory perceived firmness, juiciness, and inner cohesion were not affected by the addition of frozen meat. However, it has contributed to a significant increase of the drip loss and the amount of non-intact cells (ANIC). With the addition of frozen meat into the minced pork, the compliance to ANIC regulation by the German regulatory authorities is technologically (practically) almost impossible.
Effect of storage temperature on volatile marker compounds in cured loins fermented with Staphylococcus carnosus by brine injection
(2020) Bosse, Ramona; Wirth, Melanie; Weiss, Jochen; Gibis, Monika
In this study, the influence of low (5 °C), intermediate (15 °C) and high (25 °C) storage temperatures on the profile of volatile compounds of North European cured loins fermented with Staphylococcus carnosus strains was investigated. In this context, proteolytic activity, bacterial growth, key volatile compounds and sensory attributes were studied. In conclusion, storage temperature significantly affected the volatile marker compounds. A multiple regression indicated significant effects of seven volatile compounds (acetophenone, benzaldehyde, butanone, 3-methylbutanal, 1-octen-3-ol, nonanal and pentanone) on the overall odor (R2 = 95.9%) and overall flavor (R2 = 81.1%). The sum of the marker volatiles aldehydes, ketones and alcohol increased with rising temperatures and the highest amounts of the odor active 3-methylbutanal up to 155 and 166 ng/g meat were detected in high temperature-stored loins. Moreover, the addition of S. carnosus strain LTH 3838 showed maximum effect at 5 °C-storage temperature in comparison to the control.
Effects of fingerroot (Boesenbergia pandurata) oil on microflora as an antimicrobial agent and on the formation of heterocyclic amines in fried meatballs
(2024) Soikam, Panida; Rachtanapun, Chitsiri; Suriyarak, Sarisa; Weiss, Jochen; Gibis, Monika
This study aimed to determine the antibacterial activity of the essential oil of fingerroot (Boesenbergia pandurata) (EOF) as a natural preservative in ground meat and its effect on the formation of heterocyclic amines (HAs) in pan-fried meatballs. EOF was applied either by adding it to ground pork or marinating pork in it before grinding. In addition, the antibacterial activity of EOF was tested. Aerobic mesophilic total viable count (TVC), lactic acid bacteria (LAB), and Enterobacteriaceae bacteria were monitored. The results show that EOF exhibited strong antibacterial activity when added at concentrations of 1.0 and 2.5 wt%. Antimicrobial activity against TVC, LAB, and especially Enterobacteriaceae bacteria was observed at all EOF concentrations (0.25, 0.5, 1.0, and 2.5 wt%). A 2.5% concentration of EOF applied by marinating trimmings can extend the shelf-life of ground pork to 18 days, while 2.5% EOF applied via addition can extend the shelf-life to 15 days, compared with 3 days for the control sample. After frying the meatballs, the inhibitory effect on the formation of heterocyclic amines was only significant for MeIQx with the highest addition of EOF (2.5 wt%). Significant increases in the concentrations of all other HAs were determined by adding EOF (2.5 wt%).
High molecular weight λ-carrageenan improves the color stability of phycocyanin by associative interactions
(2022) Buecker, Stephan; Grossmann, Lutz; Loeffler, Myriam; Leeb, Elena; Weiss, Jochen
Phycocyanin is a protein-chromophore structure present in Arthrospira platensis commonly used as a blue-colorant in food. Color losses of phycocyanin can be reduced by electrostatic complexation with λ-carrageenan. The aim of this study was to investigate the effect of molecular weight (MW) of λ-carrageenan on the color stabilization of electrostatic complexes formed with phycocyanin and λ-carrageenan. Samples were heated to 70 or 90°C at pH 3.0 and stored at 25°C for 14 days. The MW of λ-carrageenan was reduced by ultrasound treatments for 15, 30, 60, and 90 min. Prolonged ultrasonication had a pronounced effect on the Mw, which decreased from 2,341 to 228 kDa (0–90 min). Complexes prepared with low MW λ-carrageenan showed greater color changes compared to complexes prepared with high MW λ-carrageenan. The MW had no visible effect on color stability on day 0, but green/yellow shifts were observed during storage and after heating to 70°C. Medium MW showed less color stabilization effects compared to low MW when heated to 70°C. Moreover, for solutions prepared with ultrasonicated λ-carrageenan, significant hue shifts toward green/yellow, and precipitation were observed after a heat treatment at 90°C. In addition, the sizes of the complexes were significantly reduced (646–102 nm) by using ultrasonicated λ-carrageenan, except for the lowest MW λ-carrageenan when heated to 90°C. Overall, these findings demonstrated that decreasing the MW of λC had adverse effects on the color stability of PC:λC complexes heated to 70 and 90°C.
Homogenization improves foaming properties of insoluble pea proteins
(2022) Moll, Pascal; Salminen, Hanna; Griesshaber, Elena; Schmitt, Christophe; Weiss, Jochen
Foams are essential in many food applications and require surface-active ingredients such as proteins for formation and stabilization. We investigated the influence of high-pressure homogenization on foaming properties of insoluble pea protein dispersions (5% w/w) at pH 3 and 5. Unhomogenized insoluble pea protein dispersions did not foam at either pH 3 or 5, as they consisted of large insoluble pea protein aggregates with limited surface activity. At pH 3, the homogenized pea protein dispersions generated foams due to higher protein solubility and surface activity through disruption of large protein aggregates into smaller particles. The foam stability decreased with increasing homogenization pressure and number of cycles due to a reduction in continuous phase viscosity. At pH 5, the insoluble pea proteins foamed when the homogenization resulted in formation of aggregates made of smaller protein entities, which was the case for homogenization ≥ 100 MPa and three cycles. In general, the foam capacity (amount of formed foam) was higher at pH 3 due to improved protein solubility and surface activity that facilitated incorporation of air, while the foam stability (resistance against foam collapse) was better at pH 5 because of the presence of larger protein aggregates that formed thicker and more viscous films around the air bubbles benefitting retention of gas bubbles. Overall, homogenization improved the foaming properties of insoluble pea proteins at pH 3 and 5.
HybridMeat - products from animal and plant sources
(2022) Ebert, Sandra Gabriele; Weiss, Jochen
Consumer diversification and concerns about insufficient protein supply and global malnutrition demand for an exploitation of alternative protein sources such as plant proteins. While manufacturers have made substantial progress in industrially scaled extraction processes and structuring of plant proteins e.g. by extrusion, there is still a lack of information on their fundamental functional and organoleptic properties and interactions with other ingredients in traditional formulations. As a result, food product developers are facing a lot of challenges and are often forced to base their work on trial-and-error rather than mechanistically guided approaches. This is in particular the case for foods where complex raw material requirements and production processes make the manufacture of products with high acceptance and shelf stability not trivial. This includes the design of hybrid meat products that are composed of mixtures of meat and plant proteins. There, traditional meat products are often set as a benchmark, making the performance of such mixed products mostly unsatisfactory. Establishing composition material property functionality relationships may be a first step to overcome these obstacles. Therefore, a variety of plant proteins was assessed for their composition, physicochemical properties, and techno functionalities to gain an understanding of their suitability for the formulation of hybrid meat products. This included their dispersibility, the miscibility of select plant protein fractions with solubilized meat proteins at varying pH and mixing ratios, and the characterization of their odor-active compounds. The latter included powdered as well as extruded plant proteins due to their increasing relevance in the manufacture of hybrid meat and analogue products. Following this, plant proteins were screened in terms of their performance in hybrid meat formulations and during traditional manufacture with a special focus on dry cured products in order to define feasible protein sources and application thresholds. The first part of this thesis showed that aqueous solubility, native pH, and appearance of a variety of 26 plant protein powders from carbohydrate and vegetable oil production correlated with purity and the extraction process. Solubility ranged from as low as 4 % to as high as 100 % based on the protein concentration and prevalence of select protein fractions. For example, large amounts of prolamins (wheat) or glutelins (rice, pumpkin) resulted in low values, while high shares of albumins and globulins promoted moderate to high solubility in sunflower, pea, and potato proteins. A highly soluble (100 %) small molecular weight fraction (< 24 kDa) of the latter was subsequently screened for its particle size and electrostatic and hydrophobic properties as compared to solubilized water and salt soluble meat proteins and the miscibility of both proteins was assessed at pH 3.0 to 7.0 and at select mixing ratios. Phase behavior of mixtures started to change below the isoelectric point (pI) of salt soluble meat proteins (pH ~ 5.5), which was identified as a defining boundary value. Here, one-phase/co-soluble systems (pH > pI) transitioned to two-phased/aggregated ones mediated by interactions (pH ≤ pI) in between individual meat and meat and potato proteins. This resulted in dense, irregularly shaped meat-potato heteroprotein particles, that deviated from the characteristic assembly of pure meat proteins into regular, anisotropic aggregates. A perturbing effect of potato proteins on the structural, organized association of meat proteins below their pI was found. Protein-protein interactions were based on both electrostatics and hydrophobics as shown by variations in surface charge, hydrophobicity, and particle size if sole potato/meat and mixtures were compared. For example, particle size of solubilized meat proteins increased from 18.0 ± 2.9 µm (pH 3.0) to 26.8 ± 9.0 µm (pH 3.0) in 50:50 mixtures. FTIR results confirmed alterations as a function of mixing ratio and pH. Image analysis of microstructures revealed a shift from elongated regular networks towards more disorder and irregularity along with a lower degree of branching. Besides solubility, organoleptic properties influence the suitability of plant proteins as food ingredients. Therefore, odor active compounds of two pea isolates were analyzed by gas chromatography mass spectrometry-olfactometry (GC MS O) after direct immersion stir bar sorptive extraction (DI SBSE), and results were compared to those of their respective extrudates to define changes during dry and wet extrusion. Twenty-four odor-active compounds were found, whereof nine represented major (off-) flavor contributors in peas: hexanal, nonanal, 2 undecanone, (E)-2-octenal, (E, Z)-3,5-octadiene-2-one, (E, E) 2,4 decadienal, 2 pentyl furan, 2-pentyl-pyridine, and γ-nonalactone. The quantity of these nine volatiles was affected distinctively by extrusion. Hexanal was reduced from 3.29 ± 1.05 % (Isolate I) to 0.52 ± 0.02 % (Wet Extrudate I) and (E,Z)-3,5-Octadiene-2-one and (E,E)-2,4-decadienal decreased by 1.5- and 1.8-fold when powdered and dry texturized pea proteins were compared. As a result of the perturbing effect of soluble potato proteins and the higher amount of off flavors in pea isolates compared to their extrudates, use of plant powders as additives was rejected in favor of extruded ones for all subsequent studies. As the focus of this work was the development of dry cured hybrid meat products, the effect of various amounts of extrudates on the traditional formulation and manufacture of this product class was assessed. This included the susceptibility of extrudates towards acid-induced pH changes as compared to pork meat, as well as their behavior in a traditional acidification and drying processes. To that purpose, pork meat and six wet extrudates from peas, pumpkin, or sunflower seeds were analyzed in their proximate composition and subjected to titration starting from the same pH value and using the same acid concentrations. It was shown that wet texturized pumpkin and sunflower proteins had the highest buffering capacity (BC), especially between pH 7.0 and pH 4.5, while pea protein extrudates and pork meat were more prone to acidification and similar in buffering capacity with an average of 881 ± 5 mmol H+/(kg*ΔpH). The obtained data was then used to relate BC with the compositional elements of extrudates such as minerals, proteins, select amino acid, and non–protein nitrogen. These findings on varying susceptibility towards acids were extended by studies on a minced meat model systems containing pork meat, curing salt, and various amounts (0 to 100 wt%) of wet extrudates and the chemical acidifier Glucono delta-lactone (GDL). It was shown, that increasing concentrations of plant extrudates resulted in a linear increase of the initial (pH0h), intermediate (pH6h), and final (pH48h) pH of minced meat model systems. A sufficient acidification to common target pH values in dry cured meat products (pH ~ 5.0) could be achieved with acidifier amounts of 1.0 wt% up at no more than 15 wt% of extrudates. A mathematical model was proposed to correlate pH, time, acidifier, extrudate concentration, and plant protein origin to aid in the adjustments of formulations at higher extrudate contents, and to describe thresholds of feasible extrudate and acidifier concentrations. The calculated concentrations were then implemented to manufacture dry cured hybrid sausages where meat was partially replaced by 12.5, 25, 37.5, and 50 % of pumpkin seed extrudates. All recipes reached the target pH value with an accuracy of pH 5.0 ± 0.06 thereby validating the proposed mathematical correlations. Hybrid recipes with up to 25 % of extrudates were comparable to the traditional all-meat formulation in both the drying behavior and the distribution of moisture and free water. However, higher meat replacement levels promoted distinct changes in drying behavior and product texture where chewiness, hardness, and cohesiveness decreased by up to 70 %. In conclusion, plant protein functionality differs profoundly from the one of meat proteins, and this functionality also depends on the respective protein source as well as the applied extraction process. Their structuring by extrusion provides beneficial organoleptic changes and eases their incorporation in hybrid formulations. The fundamental characterization of plant proteins in terms of their proximate composition and (physico)chemical properties may be used to establish mathematical correlations to estimate the effect of these novel ingredients in hybrid meat products. Thus, the obtained results offer a valuable basis that manufacturers can draw upon not only to create new foods within this product class but also to broaden and facilitate the application of plant proteins on a large scale.
Improving the colloidal stability of pectin–phycocyanin complexes by increasing the mixing ratio
(2024) Buecker, Stephan; Gibis, Monika; Bartmann, Laura; Bussler, Sara; Weiss, Jochen
In the food industry, the phycobiliprotein phycocyanin acts as a color pigment or the functional part of the superfood “Spirulina.” It is industrially extracted from Arthrospira platensis. Current scientific research is focusing on finding complex partners with the potential to stabilize phycocyanin against its sensitivity toward heating and pH changes. Less attention is paid to the factors that influence complexation. This study focuses on the mixing ratio of phycocyanin with pectin. Phycocyanin concentration was fixed, and the mixing ratios ranged from 0.67 to 2.50 (pectin:phycocyanin). All samples were analyzed for their color, size, microscopic structure, zeta potential, and sedimentation stability before and after heating at 85°C. It was found that increasing the pectin content fostered the initial interactions with the protein and chromophore, resulting in a color shift from blue to turquoise. The size of the complexes decreased from several micrometers to nanometers with increasing pectin concentration. Those smaller complexes that were formed at a mixing ratio of 2.5 showed a higher colloidal stability over a period of ∼2 days. It is suggested that at a low mixing ratio (0.67), phycocyanin cannot be completely entrapped within the complexes and attaches to the complex surface as well. This results in aggregation and precipitation of the complexes upon heating. With increasing aggregation and consequently size as well as density of the complexes, sedimentation was accelerated.
Influence of finely chopped meat addition on quality parameters of minced meat
(2022) Witte, Franziska; Sawas, Erik; Berger, Lisa M.; Gibis, Monika; Weiss, Jochen; Röser, Anja; Upmann, Matthias; Joeres, Eike; Juadjur, Andreas; Bindrich, Ute; Heinz, Volker; Terjung, Nino
Larger processing equipment to produce minced meat could affect its structure due to intensive processing and a high energy intake in the meat mass. To assess if this would result in alterations in the minced meat quality, finely chopped meat (FCM) was added in different concentrations (15, 30, 45, 60, 75, 90, and 100%) to minced meat and quality parameters were analyzed. FCM was used to simulate different intensity of an unintended destruction of meat cells due to various processes. The amount of non-intact cells (ANIC) was determined histologically and furthermore, soluble protein content, water holding capacity, mechanical and sensory texture, and scanning electron and confocal laser scanning microscopy was applied to analyze the meat structure and quality. ANIC indicated that even adding 15% FCM was statistically (p < 0.05) distinguishable from 100% minced meat and 30% FCM had already 50 Vol.-% ANIC. In contrast, the addition of 15% or 30% FCM did not result in significant differences in drip loss of raw and cooked meat as well as mechanical and sensory texture analysis. This study showed that intensive processing might be detectable via ANIC, but that the minced meat quality was not affected.
Influence of processing steps on structural, functional, and quality properties of beef hamburgers
(2022) Berger, Lisa M.; Witte, Franziska; Terjung, Nino; Weiss, Jochen; Gibis, Monika
In hamburger manufacturing, meat is subjected to four main processing steps (pre-grinding, mixing, grinding, and forming), whereby muscle fibers are disintegrated. In this study, the influence of these process steps was characterized by structural (amount of non-intact cells (ANIC), CLS-Microscopy), functional (drip loss) and qualitative (soluble protein content, lactate dehydrogenase (LDH) activity, myoglobin content (Mb)) parameters of the meat. Therefore, meat samples were analyzed after each process step. Histological analyses revealed an increased ANIC with progressive processing. Thereby, the first and second grinding steps caused the strongest increases (factors 2.43 and 2.69). Comparable results were found in the relative LDH activity (factor 2.20 and 1.62) and the Mb concentration (factor 2.24 and 1.33) of the extracted meat solution. The findings suggest that the disintegration of the meat structure increases with progressive processing, causing more vulnerable structures which result in increased leakage of intramuscular substances. Further, the type of stress acting on the meat determines the extent of the changes. The presented findings enable manufacturers to precisely adjust their process towards more gentle production parameters and thus, to meet the legal regulations.
Meat color and iridescence: Origin, analysis, and approaches to modulation
(2023) Ruedt, Chiara; Gibis, Monika; Weiss, Jochen
Meat color is an important aspect for the meat industry since it strongly determines the consumers’ perception of product quality and thereby significantly influences the purchase decision. Emergence of new vegan meat analogs has renewed interest in the fundamental aspects of meat color in order to replicate it. The appearance of meat is based on a complex interplay between the pigment‐based meat color from myoglobin and its chemical forms and light scattering from the muscle's microstructure. While myoglobin biochemistry and pigment‐based meat color have been extensively studied, research on the physicochemical contribution of light scattering to meat color and the special case of structural colors causing meat iridescence has received only little attention. Former review articles focused mostly on the biochemical or physical mechanisms rather than the interplay between them, in particular the role that structural colors play. While from an economic point of view, meat iridescence might be considered negligible, an enhanced understanding of the underlying mechanisms and the interactions of light with meat microstructures can improve our overall understanding of meat color. Therefore, this review discusses both biochemical and physicochemical aspects of meat color including the origin of structural colors, highlights new color measurement methodologies suitable to investigate color phenomena such as meat iridescence, and finally presents approaches to modulate meat color in terms of base composition, additives, and processing.
New approaches in salami manufacture with in-situ exopolysaccharide-forming starter cultures
(2021) Velasco Cucaita, Lina Maria; Weiss, Jochen
Lactic acid bacteria have always been of great importance in the production of fermented sausages such as salami, as they contribute not only to microbial stability but also to acidity and flavor profiles of such products. Recently, exopolysaccharide (EPS)-forming starter cultures have attracted the interest of the food industry. EPS have water-binding, gelling, viscosity-increasing, as well as emulsifying properties and, due to these technofunctionalities, can contribute to the improvement of existing products as well as to new product developments. However, compared to hydrocolloids, which have similar functionalities, in-situ formed EPS do not have to be legally declared as ingredients on a package. Initial studies looking at the use of such cultures in spreadable, short-ripened raw sausages showed that the use of EPS-forming starter cultures can lead to a significant improvement in the spreadability of fat-reduced tea sausage and deeper acidified onion mettwurst (pH 5.1 instead of 5.6). However, no study to date has comprehensively addressed the use of in-situ EPS-forming starter cultures in sliceable, raw fermented sausage products such as salami, which differ significantly from spreadable raw sausage products in terms of product matrix. Since growth kinetics and acidification depend on the microorganism and the food matrix used, the growth and acidification behavior of selected homo- and heteropolysaccharide (HePS)-forming lactic acid bacteria as a function of different sugar concentrations (2.5 - 10 g/kg) was initially investigated. This was done to obtain an indication of the sugar concentration required in the raw sausage mass to achieve a target pH of 4.8-5.3 in the final product. Subsequently, the performance of two HePS-producing strains L. plantarum TMW 1.1478, and 1.25; and the two homopolysaccharide-producing lactic acid bacteria L. curvatus TMW 1.624 and L. sakei TMW 1.411 was investigated in a raw sausage model system (inoculation concentration 106 CFU/g), which, in addition to 25% pork back fat, 75% lean pork meat, also contained ascorbic acid (0.5 g/kg), nitrite curing salt (28 g/kg), and dextrose or sucrose (5 g/kg). Thereby, the strains to be used were specifically analyzed with regard to their suitability for EPS-formation under typical fermentation conditions prior to use in salami production. The latter was done qualitatively by confocal laser microscopy (CLSM), followed by semi-quantitative data interpretation using MATLAB. The results showed that all selected strains were able to produce EPS in the raw sausage model matrix. There, EPS were located on the surfaces of the proteins. Since presence of HePS, which are more complex in terms of chemical structure and are often charged, can lead to changes in the organization of protein matrices even when used in very small amounts due to e.g. electrostatic interactions, sausages were subsequently prepared with a HePS-forming (L. plantarum 1.1478) and a non-EPS-forming starter culture (L. sakei 1.2037; control). Moreover, the influence of different inoculation concentrations (107 and 109 CFU/g) on fermentation and associated HePS-formation, as well as their effect on quality parameters of the final products, were investigated. The selection of inoculation concentrations was governed by the hypothesis that higher inoculation concentrations could lead to a higher in-situ formed HePS amount in the raw sausage matrix and therefore to enhanced structural and thus organoleptic relevant effects. For this purpose, pork meat and fat-based raw sausages were prepared by adding and mixing spices, 0.5 g/kg Na-ascorbate, 5 g/kg sugar, the appropriate starter culture (107-109 CFU/g), and in the end 28 g/kg nitrite curing salt. Afterwards, the mass was filled, fermented (24 °C), smoked, and dried to a weight loss of 31%. In addition to pH and bacterial plate counts, the formed EPS were detected by CLSM and the influence of the formed HePS on the texture of the raw sausages was analyzed by texture profile analysis (at 16, 23, 27, and 31% weight loss) and further evaluated in a sensory evaluation for the attributes of consistency and taste. Although no significant differences were found with respect to the detected HePS and the inoculation concentration used, dependencies emerged with respect to product quality. Raw sausages produced with the HePS-producing starter culture L. plantarum 1.1478 were significantly (p < 0.05) softer than the corresponding control samples. This effect was more pronounced the higher the inoculation concentrations, which was also reflected in the sensory evaluation of samples. Semi-quantitative data interpretation of the CLSM images revealed that the HePS were predominantly formed during the first 72 h of fermentation at 24 °C, until the final pH of 4.95 ± 0.05 was reached. Although there was no clear preference in the sensory analysis performed, raw sausages with a firmer consistency are generally preferred in Germany. Accordingly, the use of an EPS-forming culture could, depending on the market, also have a negative impact on product properties. To gain a better understanding of the observed results and the influence of process conditions on in-situ HePS-formation and its effects on the quality of sliceable raw fermented sausages, the temperatures of the fermentation phase were varied in a further study. In addition to the 24 °C already examined, an additional incubation temperature of 16 °C, commonly used in the production of raw sausages, and a low temperature incubation of 10 °C were chosen, since increased stress conditions are often associated with increased EPS formation. Raw sausages inoculated with L. plantarum 1.1478 or L. sakei 1.2037 (108 CFU/mL) were fermented at 10, 16, or 24 °C within the first 7 days and then dried under the same conditions (14 °C, controlled relative humidity) until a weight loss of 31% was reached. Microbial growth, pH, and weight loss development were monitored, EPS detected with CLSM, and products further characterized by texture profile analysis and a sensory test. Here, texture profile analysis was performed not only from the final product, but also after 21% and 26% weight loss to better understand the influence of the in-situ produced HePS. Differences were found depending on the starter culture used as well as on the fermentation temperature. Products manufactured with the non-EPS-forming strain L. sakei 1.2037 reached the target weight loss of 31% slightly faster than products manufactured with the HePS-former L. plantarum 1.1478. In both products, the final weight loss of 31% was reached faster at an initial fermentation temperature of 24 °C than at the lower fermentation temperatures. A correlation of temperatures with the amount of HePS formed could not be conclusively proven using semi-quantitative data analysis of CLSM images because matrix effects complicated the determination. However, texture profile analysis results showed a difference between products fermented at 24 °C and those fermented at cooler temperatures. In addition, significant (p < 0.05) differences were again observed between products with (softer) and without (harder) HePS-forming starter cultures at weight losses at or above 21%. These results were confirmed in the final sensory evaluation of the products (pH 4.89 - 5.01; 31% weight loss). In summary, the results of this thesis show that the use of a HePS-forming starter culture in sliceable raw fermented sausage can induce specific structural and textural changes. HePS-formation and associated quality attributes may be modulated via the inoculation concentration and control of processing parameters such as fermentation temperature. The texture softening observed in the present work, can be positively or negatively associated with the product depending on the target country and market. Taken together, results of this work underline the importance of a suitable starter culture selection for the production of fermented sausages.
Oral processing, rheology, and mechanical response: Relations in a two‐phase food model with anisotropic compounds
(2023) Oppen, Dominic; Weiss, Jochen
Food‐material poses a challenging matrix for objective material scientific description that matches the consumers' perception. With eyes on the emerging structured food materials from alternative protein sources, objectively describing perceived texture characteristics became a topic of interest to the food industry. This work made use of the well‐known methodologies of jaw tracking and electromyography from the field of “food oral processing" and compared outcomes with mechanical responses to the deformation of model food systems to meat alternatives. To enable transferability to meat alternative products, an anisotropic structuring ingredient for alternative products, high‐moisture texturized vegetable protein (HM‐TVP), was embedded in an isotropic hydrocolloid gel. Data of the jaw movement and muscle activities exerted during mastication were modeled in a linear mixed model and set in relation to characteristic values obtained from small‐ and large‐strain deformation. For improvement of the model fit, this work makes use of two new data‐processing strategies in the field of oral processing: (i) Muscle activity data were set in relation to true forces and (ii) measured data were standardized and subjected to dimensional reduction. Based on that, model terms showed decreased p‐values on various oral processing features. As a key outcome, it could be shown that an anisotropic structured phase induces more lateral jaw movement than isotropic samples, as was shown in meat model systems.
Plant protein gels as binders in meat product analogues
(2023) Herz, Eva Maria; Weiss, Jochen
In response to concerns about the environmental, ethical, and health impacts of meat consumption, plant-based meat analogues have become an important development in the food industry. To obtain prodcts with similar texture and nutritional properties, three major components of meat products (fibrous meat particles, adipose tissue, and myofibrillar meat proteins) need to be replicated. Furthermore, different binding mechanisms, such as heat, acid, and enzyme induction, and drying, are used to create coherent matrices for plant-based meat analogues. In Chapter 2, the study focuses on the use of soy protein gels as binders, with a particular emphasis on a combination of transglutaminase (TG) induced gels. The results indicate that TG-induced soy protein gels offer promising binding strength for meat analogues. Chapter 3 explores a combination of TG and slowly acidifying glucono-delta-lactone (GDL) as a binder, showing that this approach results in acidic gels with enhanced textural properties, making it suitable for acidic meat analogue products like fermented sausages. Chapter 4 applies previously studied soy protein gels as binders for sausage analogues. The research indicates that the choice of binder content influences the cohesiveness and hardness of the sausage analogues, with drying having a significant impact on hardness. In Chapter 5, hydrated gluten is used as a binder, leading to increased cohesiveness and springiness with rising binder content. It emphasizes the importance of adhesive properties between the binder and other particles in achieving desirable meat analogue texture. Overall, the thesis underscores that plant protein suspensions can serve as effective binders for meat analogue products, provided they exhibit both sufficient hardening through network formation and adhesive properties to ensure cohesiveness. It also discusses various formulation and process-based approaches to modulate the texture of meat analogue products.
Process, structure and function relationship in ground meat
(2023) Berger, Lisa Marie; Weiss, Jochen
Ground beef has enjoyed high popularity with consumers because it is convenient to use and facilitates a rapid preparation of a large variety of different meals. In the production of ground meat, the particle size of the meat is systematically reduced, and the cell structures are partially disintegrated. Ideally, the original cellular meat or fat structure is preserved as much as possible so that important quality attributes are optimized. However, the effect of varying conditions and parameters in modern processes on the quality of ground meat has not yet been investigated in detail. According to the current German “Leitsätze für Fleisch und Fleischerzeugnisse”, hamburgers must not contain more than 20 Vol.% of non-intact cell structures to be sold without further declaration. Therefore, this work aimed to identify process, structure, and function relationships in ground meat production to facilitate a gentler processing of in particular hamburgers. To investigate these effects systematically, a standardized production method for hamburgers was developed and a pilot plant scale meat grinder was set up with the possibility to record process-relevant data. The relationship between the structure and functionality of ground meat was investigated using a model system with increasing amounts of added meat batter to simulate changes in meat structure due to cell disintegration. A new term, i.e., the amount of non-intact cells (ANIC), was introduced to quantify the amount of disintegrated meat cells during processing. It was shown that changes in the structure due to a higher or lower ANIC resulted in altered physicochemical and functional properties of the ground meat system. The effect of frozen meat content and temperature on the structure and function of hamburgers was investigated to verify the above-obtained correlation to an application-relevant setting. As the specific cutting resistance is significantly higher in frozen than in chilled meat, it was assumed, that the impact on the ground meat’s structure and function differed accordingly. Indeed, this could be verified. In hamburger manufacturing, it is common practice to re-fed imperfectly molded patties, e.g., in a frozen, coarsely crushed state. In contrast to those findings, the use of up to 20 % re-fed material in hamburger manufacturing did not result in any noticeable differences as neither the specific mechanical energy input (SME) nor the ANIC was significantly changed. It was thus demonstrated, that some raw material variations can have an impact on both structure and function of hamburgers. Especially, temperature effects and associated changes in the cutting resistance of the raw material had the strongest influence on structure and function of ground meat. However, if structural differences were found, they were not sufficient to manifest in differences in sensory evaluation. This means that the consumer perception and thus the quality of the hamburger was not influenced. The process parameters and their impact on the structure and function of hamburgers were studied by investigating the impact of the four main processing steps pre-grinding, mixing, grinding, and forming. An increased ANIC was determined with progressive processing, whereby the grinding steps accounted for the strongest increase. Mixing and forming were of minor importance for structural and functional changes. By varying the cutting set parameters, the influence of the cutting set compositions on the structure and function of hamburgers was assessed. The SME and the ANIC increased if more cutting levels were used due to higher shear stress applied to the meat. However, the hole plate properties did cause no or only negligible changes in the ANIC and SME. Although an impact of the cutting set composition on the structure could be found, no or only marginal effects on the function and the sensory and optical quality of the hamburgers were found. It can therefore be concluded that the shear forces acting on the meat during grinding have the strongest influence on the structure and function of beef. By reducing the acting shear forces, the grinding can be designed to be gentler resulting in lower ANIC. Despite the influence on the process-control (SME, pressure, torque) and the structural parameters (ANIC), it needs to be emphasized that the influence on the function and quality of the hamburgers is small in application-relevant ranges. In application-relevant ranges this relationship is only slightly pronounced. Comparable results were found, as raw material variations only partially caused structural, functional, and quality effects in the hamburgers. This in turn means that changes in structure cannot always be linked to a shift in perceived quality. In order to carry out an integrated evaluation of the product, structural parameters and quality parameters must be defined, assessed separately, and merged into a combined overall sample assessment.
Solidification of concentrated pea protein–pectin mixtures as potential binder
(2023) Moll, Pascal; Salminen, Hanna; Stadtmüller, Lucie; Schmitt, Christophe; Weiss, Jochen
BACKGROUND: Binders in plant-based meat analogues allow different components, such as extrudate and fat particles, to stick together. Typically, binders then are solidiﬁed to transform the mass into a non-sticky, solid product. As an option for a clean- label binder possessing such properties, the solidiﬁcation behavior of pea protein–pectin mixtures (250 g kg−1 , r = 2:1, pH 6) was investigated upon heating, and upon addition of calcium, transglutaminase, and laccase, or by combinations thereof. RESULTS: Mixtures of (homogenized) pea protein and apple pectin had higher elastic moduli and consistency coefﬁcients and lower frequency dependencies upon calcium addition. This indicated that calcium physically cross-linked pectin chains that formed the continuous phase in the biopolymer matrix. The highest degree of solidiﬁcation was obtained with a mixture of pea protein and sugar beet pectin upon addition of laccase that covalently cross-linked both biopolymers involved. All solidi- ﬁed mixtures lost their stickiness. A mixture of soluble pea protein and apple pectin solidiﬁed only slightly through calcium and transglutaminase, probably due to differences in the microstructural arrangement of the biopolymers.

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